Impacts of Low Levels of Residual Oils on Toxicity Assessment of Oil Spills using the Target Lipid Model

 


Joy McGrath and Dominic Di Toro

Abstract
A method is presented for developing scientifically defensible numeric guidelines for oil-related constituents, specifically monocyclic aromatic hydrocarbons (MAH) and polycyclic aromatic hydrocarbons (PAHs), in the water column and sediment. The guidelines are equivalent to a HC5, a hazard concentration value that protects 95 percent of the test species. The model of toxicity used in this evaluation is the target lipid model (TLM) that was developed for assessing the toxicity of Type I narcotic chemicals (Di Toro et al. 2000). Structurally the aromatic components of oil should exert an acute narcotic mode of action. This research focused on validating the TLM for its appropriateness in assessing the toxicity of these oil components, both on an acute and chronic basis. The methodology was determined to be effective at predicting the toxicity of MAHs and PAHs. The resulting HC5 guidelines were found to be protective of sub-lethal effects commonly associated with blue sac disease resulting from early life stage exposure to PAHs. The use of toxic units (TUs) as the metric for expressing the toxicity of mixtures of oil-related components, or mixtures of hydrocarbons in general, is demonstrated to be an effective means of normalizing toxicity data across different sources and different species. The toxicity of the mixture depends on which hydrocarbons are present because the toxicity of the individual components in the mixture varies. A concentration of 1 TU from the components in the mixture implies toxicity. A concentration of 1 µg/L of total measured compounds in a mixture may or may not be toxic and depends on which components are present, the concentration of those components and the species exposed. The use of TUs eliminates this confusion and normalizes the data across sources. The methodology presented can be used by the oil spill community, which includes the regulators and the regulated industries, to compare residual concentrations of MAHs and PAHs against defensible numeric guidelines to assess potential ecological impacts.

Keywords: Polycyclic Aromatic Hydrocarbons, Target Lipid Model, Model Validation, Oil Toxicity, Guidelines

Acknowledgements
Funding for this project was provided by the NOAA/UNH Coastal Response Research Center (Grant number NA170Z2607). John Sondey at HydroQual, Inc. was responsible for producing final graphical displays.

List of Acronyms

MAH

Monocyclic aromatic hydrocarbon

PAH

Polycyclic aromatic hydrocarbon

TPAH

Total Polycyclic aromatic hydrocarbon

TLM

Target Lipid Model

HC5

Hazard concentration value that protects 5% of test species

TU

Toxic unit

LC50

Lethal concentration to 50% of test species

EqP

Equilibrium partitioning

BTEX

Benzene, toluene, ethylbenzene, xylenes

K OW

Octanol-water partitioning coefficient

K OC

Organic-carbon partitioning coefficient

WSF

Water soluble fraction

TPH

Total petroleum hydrocarbon

CTLBB

Critical target lipid body burden

SPARC

SPARC Performs automated reasoning in chemistry

ACR

Acute to chronic ratio

TU PAH13

Toxic units from 13 key PAHs

TU PAH34

Toxic units from 34 PAHs

TU PAHTOT

Toxic units from Total PAHs

EVCO

Exxon Valdez Crude Oil

TMC

Total measured compound

TCDD

2,3,7,8-tetrachlorodibenzo-para-dioxin

LOEC

Lowest observed effect concentration

OEC

Observed effect concentration

NOEC

No observed effect concentration

BSD

Blue sac disease

TOC

Total organic carbon

IC25

Inhibition concentration- concentration causing 25% reduction of measured endpoint in relation to control

QSAR

Quantitative structure activity relationship



Table of Contents

1.0
Introduction 1
2.0 Objectives 1
3.0 Methods 4
3.1 Aqueous Acute Toxicity Prediction - Target Lipid Model 4
3.2 Aqueous Chronic Toxicity Prediction 9
3.3 Sediment Toxicity Prediction 9
3.4 Uncertainty in Toxicity Predictions 9
3.5 Application to Mixtures 11
3.6 Computing Total PAH Toxic Units in Sediment 13
3.7 Literature Review 14
3.8 Physical Chemical Properties 15
4.0 Results 15
4.1 Literature Review 15
4.2 TLM Validation - Water Column 16
4.3 TLM Validation - Sediment 27
5.0 Discussion and Importance to Oil Spill Response/Restoration 34
6.0 Technology Transfer 37
7.0 Achievement and Dissemination 37
References   38



List of Figures and Tables
Figure 1 Schematic Diagram of log(LC50) versus log(KOW). At log(KOW) equal to 0, the KOW is equal to 1 meaning that chemical concentration in the water is equal to the chemical concentration in octanol. (Adopted from Di Toro et al. 2000) 7
Figure 2. Log(LC50) Versus log(KOW) for the Indicated Species. (Redrawn from Di Toro et al., 2000). 8
Figure 3. Diagram of how acute toxicity data from aqueous and sediment tests using mixtures of chemicals will be displayed. Percent effect as a function of predicted total TUs. Dashed lines represent HC5 and HC95 values 13
Figure 4. Acute Exposures- Single Compounds - TLM predicted acute aqueous LC50 versus observed LC50 for MAHs and PAHs. Solid line represents 1:1 relationship. Dashed lines represent 90% confidence interval 17
Figure 5. Acute Exposures - Mixtures - Percent mortality as a function of total measured concentration (mg/L) (top panels) and predicted aqueous TUs (bottom panels). Data on the right is for Pimephales promelas exposure to WSFs prepared from neat and weathered Exxon Valdez crude oil (ENSR, 2000). Data on the left is for Oithona davisae exposure to WSF prepared from a mixture of 9 PAHs (Barata et al. 2005). Solid lines represent 50% mortality (horizontal) and 1 TU (vertical). Dashed vertical lines represent HC5 and HC95 for each species 19
Figure 6. Chronic Effects – Single Compounds - Distribution of acute to chronic ratios (ACRs) for aliphatic hydrocarbons (A), PAHs (B), BTEX (C) and the combined data set (D). 21
Figure 7 Chronic Effects – Mixtures – Observed mortality as a function of total measured concentration in WSF (mg/L) (left panel) and predicted aqueous TUs (right panel). Data are for Cyprinodon variegates embryos exposed to WSF prepared from No. 2 fuel oil (Anderson et al. 1977). Dashed vertical lines represent 5th and 95th percentiles based on variations in CTLBB and ACR. 22
Figure 8 Sub-lethal effects – Single Compounds – Comparison of OEC/LOEC/NOEC observed from early life stage fish exposures to single compounds to TLM chronic effect concentrations. The effects are those associated with sub-lethal endpoints such as abnormal larvae development and blue sac disease-like symptoms. The symbols represent the TLM chronic endpoint. The lines associated with the TLM chronic endpoints represent the 5th and 95th percentiles based on variations in CTLBB and ACR. The number located above the reported effect concentration is the assigned ranking number. See Table 4 for references. 25
Figure 9 Sub-lethal effects – Mixtures – Comparison of 18-d NOEC and LOEC from early life stage toxicity tests exposing Oryzias latipes to three prepared mixtures of PAHs to TLM chronic endpoints. The circles represent the TLM effect concentration. The bars represent the 5th and 95th percentiles based on variations in CTLBB and ACR. Data are from Rhodes et al. 2005. 26
Figure 10 Acute Sediment Exposures – Single Compound - Comparison of observed and TLM predicted sediment effect concentrations (see Table 5 for data). Solid line is 1:1 relationship. The dashed lines are 90% confidence intervals 28
Figure 11 Acute Sediment Exposures – Mixtures – Percent mortality of R. abronius as a function of PAH concentraton (mg/kg) (top panel) and normalized to total PAH sediment toxic units (bottom panel). All data are 10-d exposures. Solid lines at a toxic unit of 1.0 and 50 % mortality are shown for guidance. Dashed lines represent 5th and 95th percentiles based on variation in CTLBB. (• Swartz et al. 1997; Boese et al. 1999; Tay et al. 1992; Techratech, 1982; Swartz et al. unpublished; Swartz et al. 1989; • Ozetich et al. 2000; Page et al. 2000) 30
Figure 12 Acute Sediment Exposures – Mixtures – Percent mortality as a function of PAH concentraton (mg/kg) (top panel) and normalized to total PAH sediment TUs (bottom panel). See Table 6 for exposure information. Solid vertical and horizontal lines at a TU of 1.0 and 50 % mortality, respectively, are shown for guidance. 31
Figure 13 Chronic Sediment Exposures – Single Compounds - Comparison of reported OEC/LOEC/NOEC and TLM effect concentrations from long-term exposures of fluoranthene and phenanthrene to the marine copepods Coullana sp. and Schizopera knabeni. See Table 8 for references. 33
Figure 14 Chronic HC5 concentration for PAHs versus log (KOW). The HC5 concentration is based on the 5th percentile CTLBB for all species in the database. The observed NOECs for PAHs are denoted with a 0 (Table 10). 36
   
Table 1 Chemicals and their properties (at 25C) measured in various data sets.  
Table 2 Observed water-only acute LC50/EC50 values for PAHs and TLM predictions  
Table 3 Acute and chronic values used in the development of ACRs. Chronic endpoints are those effecting growth, reproduction or mortality of an organism.  
Table 4 Comparison of target lipid model chronic endpoints to NOECs, LOECs, OECs (sub-lethal effects) from early life stage tests for single PAH exposures.  
Table 5 Observed sediment acute LC50 values for PAHs and TLM predictions.  
Table 6 Summary of sediment data sets for acute toxicity from PAH mixtures.  
Table 7 Example demonstrating benefit of using adjustment factor to convert TU from 13PAH to Total PAH TU. Data are from Swartz et al. unpublished (Table D5).  
Table 8 Chronic effects from single PAH sediment exposures.  
Table 9 Summary of CTLBBs for different chemical classes.  
Table 10 Chronic HC5 values for MAHs and PAHs for aqueous and sediment toxicity.  
Table 11 PAH NOEC toxicity data for various species (measured data considered only).  



1.0 Introduction
This research project is directed at evaluating the impacts of low levels of residual oils based on assessment of the toxicity of oil-related constituents and their exposure risks. The primary compounds of interest in this research are the monocyclic aromatic and polycyclic aromatic hydrocarbons (MAHs and PAHs). Structurally, these compounds are Type I narcotic chemicals and their acute toxic mode of action is narcosis. The toxicity of such compounds is additive and therefore a methodology is needed that accounts for exposure to a mixture of hydrocarbons. The target lipid model (TLM) and the concept of toxic units (TUs) are used to assess the toxicity of oil-related chemicals. The TLM is a method of computing water criteria for Type I narcotic chemicals (Di Toro et al. 2000). Equivalent sediment criteria were derived using the equilibrium partitioning (EqP) model (Di Toro and McGrath, 2000). Aqueous and sediment criteria were derived using methodology based on narcotic chemicals in general, rather than MAHs and PAHs specifically. The United States Environmental Protection Agency (U.S. EPA) developed sediment benchmarks (water-only benchmarks were not presented) for PAH mixtures based on the TLM (U.S. EPA, 2003). These benchmarks were derived with the objective of protecting sediment organisms from long-term effects of mortality, growth and reproduction. Recent literature suggests that exposure to PAHs during an organism’s early life stage results in various sub-lethal effects similar to those of blue-sac disease (Carls et. 1999; Heintz et al. 1999; Incardona et al. 2004). These sub-lethal effects were not addressed in the EPA’s sediment benchmarks for PAH mixtures and therefore they may not be protective of these types of effects.

For this research, the appropriateness of the TLM for predicting the toxicity of MAHs and PAHs as single chemical exposures and in mixtures is investigated. The TLM is validated for predicting the toxicity of these chemicals in water-column and sediment exposures, both on an acute and chronic basis. Additionally, the TLM is evaluated to determine if computed endpoints are protective of sub-lethal endpoints such as yolk sac edema, hemorrhaging and larvae abnormalities. Once it has been demonstrated that the TLM methodology can be used to assess whether effects are expected at a certain concentration of a chemical or from a mixture of chemicals, the methodology is used to derive defensible chemical-specific guidelines. HC5 values, the ecological hazard concentrations that protect 95% of species, are presented on an aqueous basis and a sediment basis as a function of log octanol-water partitioning coefficient, KOW.

The beneficiaries of this research include regulators and the regulated communities because they will have an innovative scientifically defensible method to estimate toxicity of oil components in water and sediment.
Moving a research oriented model like CDOG into operational use requires more than adding a Graphical User Interface (GUI). Particularly for emergency response, the user has a task to accomplish as part of the response. That “task” is not running the model, though the task may involve running the model. For example, NOAA/HAZMAT provides trajectory analysis during a spill response. The GNOME model may be run, but the GNOME output is post-processed to add additional information from the trajectory forecaster to the Federal On Scene Coordinator (FOSC).


2.0 Objectives
The overall objective of this project is to evaluate the impacts of low levels of residual oils based on the toxicity assessment of oil-related constituents and their exposure risks. Generally, the short-term toxicity of petroleum is attributed to the water-soluble MAHs (i.e., benzene, toluene, ethylbenzene and xylene, commonly referred to as BTEX) and PAHs. BTEX are not expected to persist in the environment because they are volatile compounds and evaporate quickly and are fairly biodegradable. PAHs are less volatile and the heavier PAHs (those with 4 or 5 rings) are known to persist and they can potentially have a long-term impact on the aquatic environment. Specific objectives and how they were met include:

• Identify key components of residual oil that contribute to toxicity – The literature was reviewed for toxicity data resulting from exposure to single chemicals and mixtures of chemicals expected to be present in oils (i.e., MAHs and PAHs) both in the water column and in sediment. Toxicity endpoints reflected both short-term (acute) and long-term (chronic) effects.
• Provide a synthesized and reviewed effects database to use as a screening tool to evaluate risk to aquatic resources from petrogenic sources of MAHs and PAHs.
• Validate that the TLM of toxicity can predict the aqueous toxicity of oil related compounds – Toxicity predictions based on the TLM methodology were performed on the data sets identified in the literature review. Predictions were made for single chemical exposures for both acute and chronic effects. The predicted toxicity was compared to the observed toxicity.
• Establish that the TU can be used as a universal endpoint for expressing the toxicity from mixtures of compounds such as those resulting from different oil sources – The toxicity of different mixtures of compounds that result from various oil sources were normalized to TU and compared to mass based (i.e., mg/L) endpoints.
• Demonstrate that EqP theory is appropriate for converting the TLM-predicted aqueous effect concentrations for oil-related compounds to equivalent sediment effect concentrations – Sediment toxicity predictions based on the TLM and EqP methodologies were performed on the data sets identified in the literature. Predictions were made for single chemical exposures and mixtures of chemicals for both acute and chronic effects. Sediment toxicity predictions were compared to observed effects data.
• The TLM in conjunction with EqP theory was used to derive guidelines for oil-related compounds that may be protective of aquatic and benthic species from long-term sub-lethal effects.

These project objectives are directly related to the work of the oil spill community. A scientifically defensible methodology is presented for computing guidelines to judge what levels of oil-related compounds should not have an adverse impact on the aquatic community. The methodology is simple to use, only the log octanol-water partitioning efficients (KOW) of the chemicals in the mixture are needed. The method is versatile in that it allows the user to compute protective guidelines for a particular species or guidelines that protect 95% of all species considered in the method development (see Section 3.0 Methods).

In addition, the use of the TU as the toxicity metric for mixtures normalizes differences in toxicity among chemicals. This is of critical importance to the oil spill community because it allows data from one location/test to be directly comparable to data for another location/test. Historically, the measured concentrations of chemicals in the water phase have been summed to assess the aqueous toxicity of crude oils. Water-soluble fractions (WSFs) are prepared from different sources of oil and although the compositions of the WSFs vary and different compounds are measured, the interpretation of the toxicity is based on summed concentrations. The effects are often expressed as total petroleum hydrocarbons on a mass per volume basis (i.e., mg TPH/L) (Anderson et al. 1974; Rossi and Anderson, 1976; Moles et al. 1979; Brodersen, 1987) or total PAH concentrations (i.e., mg TPAH/L) (Anderson, 1977; Neff and Stubblefield, 1995; Carls et al.1999; Heintz et al. 1999). The fundamental problem with reporting toxicities of hydrocarbon mixtures on a total concentration basis is that it assumes all of the compounds have equal toxicities. The toxicity of hydrocarbons varies widely and has been related to the log KOW (Konemann, 1981; Veith et al. 1983). The toxicities of individual chemicals in a mixture are normalized by expressing the toxicity of each chemical in terms of a TU (Hermens, 1989; Peterson, 1994). Once the toxicities are normalized, comparisons of different oils can be made.

This research effort for determining impacts of low levels of residual oil components focused on meeting the objectives described above. It is impractical and probably impossible to develop guidelines that address every situation that may occur in the environment. The following is a listing of conditions and assumptions of the TLM that can impact the toxicity of oil-related components, which were NOT addressed in this research, but are important to consider when determining the effects from oil.

• The TLM assumes that octanol is a good surrogate for organism lipid and that the KOW describes the partitioning of the chemical between the water and the organism lipid – Other solvents or physical-chemical properties may be better descriptors for the partitioning.
• Some data suggest that a toxicity cut-off exists for compounds with log KOW greater than approximately 5.5 (i.e., compounds with log KOW values of 5.5 or greater have similar toxicity). The TLM ignores a cut-off and relies on the KOW to be the descriptor for the toxicity. The KMW, membrane-water partition coefficient, has been shown to be a better surrogate than KOW for describing the partitioning of a chemical into the organism lipid membrane. (Gobas et al. 1988; Vaes et al 1998; Verbruggern 2004). The log(KMW)-log(KOW) relationship is linear until a log KOW of approximately 5.5 where the log KMW no longer increases linearly with log KOW (Verbruggern 2004). However, the KOW is used in the TLM because a cut-off point for PAHs has not been confirmed or identified and toxicity from PAHs with log KOW values greater than 5.5 has been observed. The TLM would not have correctly predicted the toxicity if a cut-off or the KMW was used in the analysis.
• The TLM assumes that metabolites have the same mode of action as the parent compound – Recent literature suggests that some metabolites may be more toxic than parent compounds.
• Effects of photoactivation of PAHs – Some PAHs exert photoenhanced toxicity after accumulation in the tissues of organisms and exposure to ultraviolet radiation. Photoinduced toxicity can be orders of magnitude greater than baseline toxicity (i.e., narcosis) (Ankley et al. 1994; Spehar et al. 1999; Lyons et al. 2002).
• Other water-soluble components of oil – This research focused on MAHs and PAHs, the most commonly measured oil components, as being the causative agents of oil toxicity. There may be other water-soluble components that exert toxicity. Note that this methodology can be applied to any chemical, but the toxicity computed will be the chemical’s “baseline” or minimum toxicity.
• Time-variable concentrations – This methodology assumes that the exposure concentrations are constant with time or that equilibrium conditions have been achieved, particularly for sediment exposures. Time-variable concentrations are not addressed and it is difficult to assign observed effects to a concentration if the concentration is varying with time.
• Non-standard conditions – The physicochemical properties used in this research were determined at 25 ° C. These parameters vary with temperature. For example, organic compounds are usually less soluble in colder temperatures. Therefore, the computed guidelines would be conservative for temperature conditions less than 25 ° C.
• Other sediment partitioning phases – Equilibrium partitioning theory assumes organic carbon is the only partitioning phase, described by KOC, for non-polar organic contaminants. Some field data sets indicate that other partitioning phases may be present and include soot carbon or coal. PAHs seem to have a higher affinity for these other carbon phases than for organic carbon as described by KOC. Therefore, the PAHs will be less bioavailable than predicted using KOC as the sole partitioning coefficient. Ignoring other possible partitioning phases is conservative since the maximum toxicity will be predicted.



3.0 Methods
3.1 Aqueous Acute Toxicity Prediction - Target Lipid Model

Based on chemical structure, the MAHs and PAHs should exhibit a narcotic mode of action (Verhaar et al. 1992). The TLM (Di Toro et al. 2000) will be used to assess the toxicity of MAHs and PAHs resulting from exposure to low levels of oil in the water column. The TLM is for Type I narcotic chemicals, which are non-ionic organic chemicals with a similar mode of toxic action, namely narcosis. Narcosis is a reversible state of arrested activity. The toxic mode of action is non-specific and is caused by a variety of chemicals, such as gases, aliphatic and aromatic hydrocarbons, alcohols, chlorinated compounds, ethers and ketones (Veith et al. 1983; Verhaar et al. 1992). With narcosis, it is assumed that an equilibrium exists between the chemical concentration in the organism and the chemical concentration in the external media phase, such as the water phase.

The TLM model is based on the inverse relationship between toxicity in water-only exposures, as defined by the LC50, and the KOW. Numerous quantitative-structure activity relationships (QSARs) of log(LC50) versus log(KOW) have been developed for narcotic chemicals (Konemann 1981; Veith et al., 1983; Van Leeuwen et al., 1992). The TLM is an extension of these models. It is based on a single universal slope for the log (LC50)-log (KOW) relationship, independent of species. It includes corrections for chemical classes that are slightly more potent than baseline narcotics in particular MAHs and PAHs. And it interprets the y-intercepts as the species-specific critical body burdens for a particular endpoint. A complete presentation of the narcosis TLM is available (Di Toro et al. 2000). A brief description is provided below.

The derivation of the TLM begins with the observation by McCarty et al., 1991 that whole organism critical concentration can be computed from the bioconcentration factor (BCF) (L/kg wet wt.) and the LC50 (mmol/L)
   
  C*org = (BCF) (LC50)
(1)
   
where C*org is the critical body burden (CBB in the organism (mmo1/kg wet wt.). Both the BCF and LC50 have been shown to be related linearly to log(KOW) and the following relationships have been approximated
   
  log(LC50)= -log(Kow)+1.7
(2)
   
  log(BCF) = log(Kow)-1.3
(3)
   
  Substituting equations 2 and 3 into equation 1, the CBB corresponding to the LC50 for narcosis mortality can be computed as
   
  logC*org =log (BCF)+log(LC50)
(4)
   
  logC*org =log (Kow)-1.3 - log(Kow)+1.7
(5)
   
  C*org =2.5mmol/Kg wet wgt.
(6)
   
Therefore, McCarty et al. (1991) rationalized that the CBB for a narcotic chemical corresponding to narcosis mortality is constant at approximately 2.5 mmol/Kg wt wgt.
     
The log(BCF)-log(KOW) relationship used in the above derivation was for fish species. If different species are tested, then individual BCF expressions would be required to convert each LC50 concentration to a body burden. A more direct approach is to relate the lethality to a chemical concentration in the target tissue, rather than the whole body. The TLM extends the CBB hypothesis by assuming that lipid is the target tissue in the organism. The target lipid-water partition coefficient (KLW) is used in Equation 1 to estimate the CBB on a lipid basis. The KLW (L/kg lipid) is defined as the ratio of the chemical concentration in target lipid, CL (mmol/kg lipid) to the aqueous chemical concentration, CW (mmol/L).
   
  KLW=CL/CW
(7)
   
If the narcosis hypothesis is true – that 50% mortality occurs when the chemical concentration in the organism reaches a critical level – then C L becomes the critical concentration when the water concentration is the LC50
   
  C*L=(KLW)(LC50)
(8)
   
or
log(LC50)=log (C*L)-log(KLW)
(9)
   

It is assumed that KLW can be related to KOW using a linear free energy relationship of the form

   
log(KLW)=a0+a1-a1log(KOW)
(10)
   
Equations 9 and 10 are combined to produce a single linear relationship between log(LC50) and log(KOW)
   
  log(LC50)=log (C*L)-a0-a1 log(KOW)
(11)
   
or
log(LC50)=m log(KOW)+B
(12)
   
where m and b are the slope and intercept of the regression. The slope m = -a1, is the slope of the linear free energy relationship between the target lipid and octanol (equation 8). Assuming the target lipid has the same chemical partitioning property in all organisms, the slope should be the same for all species and the slope is a universal slope. The intercept b = -a0 + log(C*L) involves a parameter a0from the linear free energy relationship between target lipid and octanol (equation 8), and the critical target lipid concentration. The intercept b is therefore a function of both the chemical and the species and should vary across species depending on the sensitivity of the test species. In the TLM it is assumed that a0=0 and the intercept is the critical target lipid body burden, CTLBB.
     


This result can be understood by examining Figure 1. For a chemical with a log(KOW) equal to zero or KOW equal to 1.0, the y-intercept is the LC50. At a KOW equal to one, the chemical concentration in the water is equal to the chemical concentration in the octanol. Assuming octanol is a good surrogate for lipid, then the chemical concentration in the water is equal to the chemical concentration in the lipid (target tissue) of the organism. Therefore, the y-intercept is equal to the target lipid concentration producing an effect (i.e., 50% mortality, LC50) for that organism. In the TLM, the y-intercept is the CTLBB and has units of µmol/g octanol = µmol/g lipid). The CTLBB varies for each species. The slope of the line is a chemical property of the lipid and should be the same regardless of the species tested. The slope of line is referred to as the universal narcosis slope. Figure 2 shows the relationship of log(LC50)-log(KOW) for several species in the database. The symbols represent many chemicals from different chemical classes. The line drawn through the data is the universal narcosis slope (i.e., it is the same for all species).

Figure 1. Schematic Diagram of log(LC50) versus log(Kow) equal to 0, the (Kow) is equal to 1 meaning that chemical concentration in the water is equal to the chemical concentration in octanol. (adopted from Di Toro et al. 2000).


The TLM has been extensively validated using a large database to predict the aquatic toxicity of classic Type I narcotic chemicals. CTLBBs for 33 aquatic species (Di Toro et al. 2000) and 5 algae (McGrath et al. 2004) were computed with the TLM using the KOW values determined from a 1997 version of SPARC, a U.S. EPA sponsored computer program that estimates numerous physicochemical properties for chemicals based on chemical structure (Karickoff et al. 1991). Since 1997, SPARC has undergone enhancements in its programming. Therefore, KOW values computed using the 1997 version may be different than those values computed using the enhanced on-line version. To take advantage of the enhancements to SPARC, new KOW values were determined for all chemicals in the narcosis toxicity database and revised coefficients for the TLM were computed (see Appendix A for coefficients)

Figure 2 Log (LC50) Versus log (kow) for the Indicated Species. (Redrawn from Di Toro et al., 2000).

  The TLM equation that predicts the critical aqueous concentration is
   
  log(c*W)=m log(KOW)+log(C*L)+Ac
(13)
   
where C*W is the critical aqueous concentration (mmol/L) (i.e., LC50 for a mortality endpoint) and C*L is the CTLBB (µmol/g octanol). The CTLBBs range from 24.5 to 500 µmol/g octanol. The universal slope m was determined to be –0.936. There is also a correction for chemical classes (e.g., -0.109 for MAHs and –0.352 for PAHs) that exhibit additional toxicity when compared to baseline narcotics (e.g., alkanes and alcohols).
     

For the current CRRC-funded project, CTLBBs for nine additional species, not included in the model development, were computed if acute toxicity data were available. A total of 47 CTLBBs are available and provided in Appendix A. If the acute toxicity data for a particular species included more than four data points, corresponding standard errors were computed. If less than two data points were available, the associated standard errors could not be calculated. Also, for the two species that had three data points, Hyalella azteca and Chironomus tentans, standard errors were not computed because the three data points were all for the same compound.

3.2 Aqueous Chronic Toxicity Prediction
The critical aqueous concentrations computed from Equation 13 are acute concentrations that produce an effect in a short-term test (i.e., 96-h LC50). To convert the acute critical concentration to a chronic effect concentration, the TLM adopts the acute-to-chronic ratio (ACR) methodology used by the U.S. EPA in deriving water quality criteria (Stephan et al. 1985). The ACR is computed from paired acute and chronic toxicity data for a particular chemical to a specific organism as follows
     
 
ACR = Acute Effect Concentration /Chronic Effect Concentration
(14)
     
where the concentrations are in the same units. The chronic effect concentrations are those that cause an adverse effect on the organism’s ability to survive, grow or reproduce on a long-term basis as appropriate for the species.

The ACR is a means of comparing the acute and chronic toxicities. It does not assume that the toxic mode of action is the same for acute and chronic toxicity. For the application of the TLM, the mechanism for acute effects is assumed to be narcosis. For chronic effects, the mechanism is unknown. In the TLM development ACRs were provided for 34 paired acute and chronic data sets from 6 different species and several Type I narcotic chemicals (Di Toro et al. 2000). The ACRs ranged from 1.2 to 23 with a geometric mean value of 5.09. Since the ACRs were similar for narcotic chemicals, an average ACR was appropriate. For the current CRRC-funded project, a similar approach was taken using ACRs computed from toxicity data for MAHs and PAHs.


3.3 Acute and Chronic Sediment Toxicity Prediction
The EqP model (Di Toro et al. 1991) is used to convert the critical aqueous concentration computed from Equation 13 to the equivalent critical sediment concentration. EqP theory is based on two concepts: (1) non-ionic chemicals in sediments will partition between sediment organic carbon, pore water and benthic organisms; and (2) sediment toxicity can be predicted by comparing the pore water concentration to the critical concentration determined in a water-only exposure as shown by Adams et al. (1985). EqP rationalizes that for both of these concepts to be true, the pore water and the organic carbon phase of the sediment must be in equilibrium. At equilibrium, if the concentration in any one phase is known, then the concentrations in the other phases can be predicted. Assuming that the critical aqueous concentration computed using the TLM (Equation 13) is equivalent to the critical pore water concentration, the equivalent critical sediment concentrations producing the same effect on the same organism is
 
C*S=KOCC*W
(15)
where C*S is the organic carbon normalized critical sediment concentration (΅mol/g OC) and KOC is the organic carbon partitioning coefficient (L/kg OC) . The KOC was shown to be essentially equal to KOW and can be estimated using (Di Toro et al. 1991)
     
 
log(KOC)=0.00028+0.983log(KOW)
(16)
     
  Equations 13, 15 and 16 can be combined to yield  
     
  log(C*S)=0.00028+0.047 log(KOW)+log(C*L)+Ac-log(ACR) (17a)
     
  which is the equation to predict the critical sediment concentration for acute effects based on the TLM.  
     
  The equivalent equation to predict the critical sediment concentration for chronic effects is (17b)  
     
  log(C*S)=0.00028+0.047 log (KOW)+log(C*L)+Ac-log(ACR) (17b)
     

3.4 Uncertainty in Toxicity Predictions
Using the TLM The species-specific acute critical water effect concentrations computed from Equation 13 are dependent on the regression coefficients, the universal narcosis slope and the . Each of these coefficients has an uncertainty associated with it and therefore, there is inherent uncertainty in the predicted effect concentrations. McGrath et al. (2004) presented statistical extrapolation methodology to compute the fifth percentile concentration (HC5, mmol/L) that considers the variance in the universal narcosis slope and C*L. The resulting concentration is the acute HC5, which is the hazard concentration affecting 5% of the test population on an acute basis. When the ACR and its uncertainty are considered, the resulting effect concentration is the chronic HC5. The final equation is:

  equation (18)
     
where the E and V terms represent the mean and variance, respectively, of the slope,C*L , and ACR; and kZ is the 95% confidence sample size-dependent extrapolation factor. By using the fifth percentile C*L , Equation 18 computes the aqueous concentration that protects 95% of the species from chronic effects (McGrath et al. 2004). This idea of using the methodology to derive protective guidelines is addressed in Section 5.0. However, if a species-specific C*L and the variance associated with it are used, Equation 18 computes the predicted critical aqueous concentration that affects 5% of a particular species. Note that the kZvalue varies for each species due to sample size; these values are provided in Appendix A. To compute the 95 % concentration, HC95, the variance term in Equation 18 is added to yield
     
  equation
(19)
     

The HC5 and HC95 values represent the lower and upper confidence intervals, respectively, of the hazard concentration. The mean slope of the equation does not change, since it is universal across species and therefore, there is no variance associated with the slope. The ACR terms are only considered when computing chronic effect concentrations. (See Appendix E and F for example calculations).

3.5 Application to Mixtures
Type I narcotic chemicals are non-ionic organic chemicals that have a similar mode of action namely, narcosis (Bradbury et al. 1989; Verhaar et al. 1992). Hermens (1989) summarized the data that demonstrate that the toxicity of narcotic chemicals is additive if their concentrations are expressed as TUs (Sprague and Ramsay, 1965). Based on chemical structure, MAHs and PAHs are classified as Type I narcotic chemicals. PAHs are typically found as mixtures, rather than as single chemicals. PAHs also have a wide range in log KOW (e.g., log KOW for naphthalene is 3.26 and benzo(a)pyrene is 6.41) and therefore their LC50s also vary (see Section 3.1). Due to the varying aqueous toxicities, it is incorrect to report the toxicity from total PAH by summing up the individual PAH concentrations on a mass basis (i.e. mg/L total PAH). Since PAHs are present in the environment as mixtures and the toxicity of individual PAH varies, it is therefore appropriate to express the toxicity of mixtures of PAHs using TUs. (See Appendix E for example calculations).

The TLM incorporated the use of toxic units in assessing the toxicity of PAH mixtures in water, tissue and sediments (Di Toro and McGrath, 2000). The TLM and TU concept were validated for predicting the toxicity of gasoline, a complex mixture of hydrocarbons (McGrath et al. 2005). Swartz et al (1995) used the TU approach for assessing the toxicity of PAH mixtures in sediments. This discussion is limited to the water phase only, but applies to other phases such as sediments and tissue of an organism. In water, a TU is defined as:
(20) where CW,i is the measured concentration of chemical i in the water (mmol/L) and C*W,i is the critical effect concentration for chemical i computed from Equation 13. The molar concentrations are used in computing TUs to normalize molecular weight differences between compounds in the mixture. For each chemical in the mixture, the individual TUs are computed using Equation 20. The individual TUs are then summed to compute the toxicity of the mixture
     
  TUW,i=CW,i/C*W,i (20)
     

where CW,i is the measured concentration of chemical i in the water (mmol/L) and C*W,i is the critical effect concentration for chemical i computed from Equation 13. The molar concentrations are used in computing TUs to normalize molecular weight differences between compounds in the mixture. For each chemical in the mixture, the individual TUs are computed using Equation 20. The individual TUs are then summed to compute the toxicity of the mixture

     
  equation (21)

If the total TUs of the mixture are greater than or equal to 1, the mixture is predicted to be toxic. Using the LC50 as an example of an acute effect concentration, death would be predicted for 50% of the test organisms.

  TUW,i=CW,i/CLC50,i (22)
     

Toxicity data from aqueous or sediment tests using mixtures of chemicals, are presented graphically as percent observed effect (usually mortality) as a function of the predicted total TUs. The observed effects are graphed on an arithmetic scale and the predicted total TUs are graphed on a base ten logarithmic scale. An example of this type of graph for acute toxicity data is shown in Figure 3. Ideally 50% effects will be observed at a total toxic unit of 1.0 as computed from Equations 20 and 21. These indices will be shown as solid lines and are shown for illustrative purposes only. However, the indices of 50% effect and a total TU of 1.0 are not absolute. The HC5 and HC95 values represent the uncertain bounds for when effects are expected and are a function of the uncertainty associated with the species-specific CTLBB. These indices will be shown as dashed lines (Figure 3) and will vary for each species. Effects are expected to be low (less than 50%) for predicted total TUs to the left of the HC5 bound. Effects are expected to be high (greater than 50%) for predicted total TUs to the right of the HC95 bound. The area of uncertainty lies between the HC5 and HC95 bounds. Within this area of uncertainty effects may or may not occur. The larger the uncertainty associated with the CTLBB, the larger the area of uncertainty. For chronic toxicity data, the chronic prediction is assumed to the similar to an EC10. Therefore, the effects threshold is not 50%, but 10%. So with chronic predictions, the effects index would be 10% on the graph. However, it should be noted that control mortality is typically around 5 to 10% and can be as high as 24% (Berry et al. 1996). When comparing the percent of chronic effects observed, it is important to subtract out the percent of effects observed in the control mortality. For chronic toxicity, the area of uncertainty will be larger due to the additional uncertainty associated with the ACR.

To estimate the toxicity from exposure to MAH and PAH mixtures, such as those in WSFs prepared from oil or those that result from an oil spill, ideally measurements for all of the components in the mixture, whether in the water column or sediment, are needed. These measurements are then used in Equations 20 and 21 to estimate the total toxicity, expressed as TU, from the mixture. If measurements are not provided for all components, the total TU of the mixture can be underestimated. Even chemicals with high log (KOW) values will contribute TUs, with the maximum TU at their water solubility (Di Toro et al. 2007). Given the complex nature of oils, it is impractical to measure for the presence of every chemical that may be sufficiently water soluble to find its way into the environment. Since MAHs and PAHs are assumed to be the causative agents in oils, sufficient characterization of the MAHs and PAHs is desirable.




Figure 3. Diagram of how acute toxity data from aqueous and sediment tests using mixtures of chemicals will be displayed. Percent effect as a function of predicted total TU's. Dashed Lines represent HC5 and HC95 values.

A reasonable question to pose is: What characterization data are needed to compute a total TU? The U.S. EPA addresses this issue for sediments (see Section 3.6), but not for water column exposures. In this research, for water column exposures, at a minimum measurement for parent PAHs and some representation of the alkylated homologs of parent PAHs are required. Alkylated homologs are the parent PAHs substituted with carbon groups (e.g., methyl, ethyl, propyl, etc.). For example, C1-naphthalene represents parent naphthalene with one carbon (a methyl) substitution and C2-naphthalene represents parent naphthalene with two carbon (two methyls or one ethyl) substitutions. C1-naphthalene has two structural isomers, 1-methylnaphthalene and 2-methylnaphthalene. C2-naphthalene has twelve structural isomers. The number of structural isomers increases with the degree of alkylation. This pragmatic requirement for PAH measurements for water column exposures is necessary to capture some of the alkylated PAHs that are prevalent in petrogenic PAH sources and to eliminate data sets that have too few measurements where the toxicity can be severely underestimated.

3.6 Computing Total PAH TUs in Sediment
The U.S. EPA defined total PAHs in sediments to be the sum of the TUs from a minimum of 34 PAHs (18 parent PAHs and 16 alkylated PAHs) (U.S. EPA, 2003). These 34 PAHs were selected because they represented the maximum number of PAHs that were routinely measured in the U.S. EPA Environmental Monitoring and Assessment Program in estuaries of the Virginian Province (1990-1993) and Louisianan Province (1991-1993). The U.S. EPA recognized that different sediment monitoring programs require varying PAH characterization. Among the available sediment data sets, there were 13 and 23 common subsets of PAHs. Rather than requiring measurements for the 34 PAHs, adjustment factors were computed from the EMAP data sets to convert the commonly measured 13 or 23 to be equivalent to the 34 PAHs from a toxicity perspective. The mean adjustment factors for the 13 and 23 PAHs were 2.75 and 1.64, respectively. For sediments that had measurements for 13 PAH, the total (summed) TUPAH13 from the 13 PAHs would be computed and then multiplied by 2.75 to convert the TUPAH13 to TUPAH34 , which is equivalent to TUPAHTOT. A listing of the PAHs that comprise the 13 PAHs and 23 PAHs subsets, as well as the 34 PAHs, is provided in Table 1. The application of adjustment factors puts all of the sediment data on the same footing and reduces the uncertainty associated with the unmeasured PAHs. However, the U.S. EPA encourages the measurement of the 34 PAHs.


3.7 Literature Review
The literature was reviewed for water column and sediment effect data resulting from exposure to MAHs or PAHs, both as single compounds and as mixtures. The main search engine was Dialog, an on-line data retrieval system that services many fields including science and engineering. For data to be used in the TLM analysis, the following criteria had to be met:

• A CTLBB must be available for the test organism.

• For water column exposures, the concentration of the chemical(s) must be below its water solubility. If a chemical is tested at a concentration above its water solubility, then the chemical is present as a pure-phase which may exert a different toxic mode of action. For single chemical exposures, the solid solubility of the chemical is used. For mixtures of chemicals that are liquids, such as those in oils, the sub-cooled liquid solubility – the solubility of the component if it were a liquid at the temperature of interest – is used.

• For single chemical-spiked sediment exposures, the EqP-based chemical concentration in the pore water (computed using Equation 15 where the measured concentration normalized to organic carbon content is used instead of , the critical concentration) must be below the spiked chemical’s water solubility, again because pure phase may exert a different mode of toxic action. For single chemical exposures, the solid solubility of the chemical is used. For mixtures of individual spiked chemicals, the appropriate solubility is the sub-cooled liquid solubility.

• The exposure concentrations must be constant with time, particularly for long-term exposures where chronic effects are being observed. Laboratory studies that show diminishing or varying concentrations over time are difficult to interpret. One cannot assign a specific concentration to the observed effect.

• For exposures to mixtures of chemicals, such as water-soluble fractions prepared from oils or fuels or sediment contamination from an oil spill, the concentrations of the individual chemicals must be measured. Ideally, to determine the toxicity from a chemical mixture, the concentration of all components in the mixture should be measured because each component could potentially contribute toxicity. For sediments, the toxicity from unmeasured PAHs can be estimated from the concentration of select PAHs following guidelines established by the U.S. EPA (see Section 3.6). Using this methodology, the toxicity of total PAH can be estimated. A similar normalization to total PAH toxicity is not available for water column exposures. Therefore, for water exposures, the majority of expected water-soluble constituents should be measured. For a fresh petroleum source (i.e., non-weathered), the majority includes the BTEX, naphthalene, phenanthrene and some of their alkylated homologs. For a weathered petroleum source, the concentration of the heavier PAHs (i.e., chyrsene and fluoranthene homologs) must also be measured.

• For sediment exposures, the total organic carbon content in the exposure sediment must be reported.


3.8 Physicochemical Properties of Alkanes, MAHs and PAHs
A listing of chemicals that appeared in available data sets is provided in Table 1. Types of chemicals include: aliphatic alkanes, cyclic alkanes, MAHs and PAHs. In some data sets, concentrations of alkylated homologs were reported for MAHs and PAHs. These are represented with a ‘C#’ where the C represents a carbon and the number represents the number of carbon substitutions. For example, C3 represents three carbon substitutions (3 methyls, 1 methyl plus 1 ethyl, 1 propyl). [Section 3.6 contains a more detailed discussion.] The chemical properties include molecular weight, log (KOW), solid solubility and sub-cooled liquid solubility. SPARC was used to compute the molecular weight and log (KOW). Recommended solid solubility and sub-cooled solubility values were taken from MacKay et al. (1992a, 1992b, 1993 and 1995). Relationships between log (solubility) and log (KOW) were used to compute solid solubility and sub-cooled liquid solubility for chemicals that were not listed in MacKay et al. These relationships are provided in Table 1.



4.0 Results
4.1 Literature Review
The literature was reviewed for data sets where the effects on aquatic organisms exposed to oil-related chemicals were observed. For water column exposures, 141 references were reviewed of which 80 contained data that met the criteria specified in Section 3.7. For sediment exposures, 64 references were reviewed of which 21 contained data. In total, 205 references were reviewed of which 101 (approximately 49%) contained data deemed acceptable. A summary of the references reviewed and brief explanations for not accepting data are provided in Appendix B.

4.2 TLM Validation - Water Column
In this section, toxicity predictions using the TLM and TU methodologies are presented and compared to observed values. For large data sets, graphical summaries are presented. Data for these large data sets are provided in Appendix C.

4.2.1 Acute Effects (Lethality) - Single Compound Exposures
In this section, the TLM is applied to predict the acute lethal effects from exposure to single compounds. Acute toxicity data were considered if a CTLBB was available for the test organism. In addition to BTEX, other MAHs are included in the comparison. Most of these additional MAHs have a higher degree of alkylation (i.e., three methyl group substitutions) and include compounds such as trimethylbenzenes and propylbenzenes. Based on structure, the toxic mode of action for these compounds should be similar to BTEX. For MAHs, there are a total of 164 data points from 28 different species Appendix C (Table C1). For PAHs, there are a total of 139 data points from 20 different species. Toxicity data are summarized in Table 2, which also provides information relevant to the exposure condition (e.g.test type, organism life-stage). Note that Table 2 also contains data from eight tests where the observed LC50s were greater than the aqueous solubility of the test chemical. These data were not included in any analysis and are only shown for completeness. The predicted LC50 values for each exposure are also presented in Table 2. Example calculations are provided in Appendix E. The observed and predicted LC50s are compared in the top panel of Figure 4. The solid line represents the 1:1 relationship (i.e., where the observed and predicted LC50s are equal). The dashed line represents the 90% confidence interval. The confidence limits were computed as the 5th and 95th percentiles of the residuals where the residuals were the difference in the observed and predicted effect concentrations. The confidence limits are not symmetrical indicating that the distribution is not exactly log normal. The model tends to underestimate the toxicity. Based on this data analysis, with a 90% confidence, the TLM is able to predict acute toxicity to within a factor of approximately 7.

4.2.2 Acute Effects (lethality) – Mixtures
In this section, the TLM is applied to predict the acute effects, meaning lethality, from aqueous exposure to a mixture of oil-related compounds. Data sets were considered if the CTLBB of the test organism was available, the concentrations of individual components in the mixture were measured and the concentrations of the chemicals were relatively constant over time (See Section 3.7). Three data sets were available that met the selection criteria. Two data sets were laboratory investigations of the toxicity of WSFs prepared from oils. The other data set was a laboratory experiment using a prepared PAH mixture. All MAHs and PAHs measured in the mixture were included in the analysis.



Figure 4. Acute Exposures-Signle Compounds - TLM predicted acute aqueous LC50 versus LC50 for MAHs and PAHs (0). Solid line respresents 1:1 relationship. Dashed lines represent 90% confidence interval.

The toxicities of WSFs prepared from neat (unweathered) and naturally weathered Exxon Valdez Alaska North Slope crude oil (EVCO) were measured (ENSR, 2001). Neat oil was collected from the Exxon Valdez oil tanker seven days after the tanker ran aground in Prince William Sound, Alaska. Naturally weathered oil was collected approximately five months after the tanker grounded. WSFs were prepared from 10:1 (water:oil) solutions for the neat and weathered oils. Each WSF was analyzed for BTEX, biphenyl, 19 parent PAHs and 21 alkylated homologs of parent PAHs. These concentrations are provided in Appendix C (Table C2). Six dilutions of the WSFs were used in toxicity testing. The mortality to fathead minnows (Pimephales promelas) after a 48-h exposure in the various dilutions was recorded. The TLM total TU for the 100% WSF from neat and weathered oil were 0.62 and 0.28, respectively. The TLM computed toxic units associated with each chemical are provided in the Appendix C (Table C2). For the neat oil, BTEX contributes significantly to the TU (approximately 60% of the computed TU). This is not the case for weathered oil, where the BTEX account for less than 10% of the TUs. This analysis suggests that BTEX are important contributors to the toxicity of neat oil compared to their toxic contribution in weathered oil, as was demonstrated by Neff et al. (2000). For a discussion of the effect of weathering on the toxicity of oils, the reader is referred to Di Toro et al. (2007). The observed mortality as a function of the total measured concentration (mg TMC/L) in each treatment is shown in Figure 5A. The open and closed symbols represent the neat and weathered oil treatments, respectively. Greater than 50% mortality was only observed in the highest WSF exposure (100% WSF) using neat oil, indicating that the neat oil was more toxic than the weathered oil. All other dilutions resulted in less than 30% mortality. For each dilution, the observed mortality normalized to total TUs is presented in Figure 5B. Solid lines at a TU of 1.0 and 50% mortality are shown for guidance. The dashed lines represent the 5% and 95% uncertainties in the TLM predictions for P. promelas and are computed using Equations 18 and 19 without the terms for ACR. For this data set, the dose-response pattern was correctly predicted by the TLM. The one data point where greater than 50% mortality occurred falls within the uncertainty limits of the TLM. All of the other data points that have low observed mortality and corresponding low total TU fall to the left of the lower uncertainty bound where low mortality is expected.

States et al. (1982) also investigated the acute toxicity of PAH mixtures. In this study, WSFs were prepared from No. 6 fuel oil, No. 2 fuel oil and a solvent refined coal liquid. Acute toxicity to Daphnia magna (48 hour immobilization) was determined under static conditions. The major chemical constituents were provided for No. 2 fuel oil and the coal liquid only. No chemical analysis was provided for No. 6 fuel oil; therefore, the TU computation could not be performed and the TLM could not be applied to predict effects from the No. 6 fuel oil. Measurements were provided for aromatic hydrocarbons, which included, indan, tetralin, naphthalene and alklyated homologs of benzene and naphthalene. The chemical concentrations and computed TUs are provided in Appendix C (Table C3). The total computed TUs in the 100% WSF for No. 2 fuel oil were 0.36, suggesting that no toxic effects are expected. This result was in agreement with the reported no observed effects for the 100% WSF (States et al. 1982). The total TUs computed for the 100% WSF from the coal liquid were 8.4 indicating that the 100% WSF would be predicted to be toxic. Reported data indicated that 0.25% WSF from the coal liquid was toxic. The equivalent TU at this dilution is 0.021 and at this level no toxicity would be predicted fromthe aromatic hydrocarbons. In this case, the TLM predictions were not in agreement with the observed effects (low TU, high effect levels). However, States et al. (1982) attributed the toxicity of the coal liquid to phenolic compounds, which are not type I narcotic chemicals and are not included in the TLM analysis. The phenolic compounds were present at significantly higher levels on the coal liquid WSF (1360 mg/L) compared to the No. 2 fuel oil WSF (1.7 mg/L). If the phenolic compounds are the main contributors to the toxicity, it is not surprising that the TLM did not predict the effects correctly because they are not included in the TLM and TU calculation.

Barata et al. (2005) tested the acute toxicity of a mixture of 9 PAHs. The PAHs included naphthalene, 1-methylnaphtalene, 1,2-dimethylnaphthalene, phenanthrene, pyrene, fluorene, 1-methylphenanthrene, dibenzothiophene and fluoranthene. The mixture was tested at six dose levels (0.25x, 0.5x, 1x, 1.5x, 2x, 2.5x); however, chemical measurements were only provided for three exposures (0.5x, 1x, 1.5x). Mortality of the adult copepod, Oithona davisae, was measured after 48 h of exposure. The measured chemical concentrations and computed TU units are provided in Appendix C (Table 4C). The observed mortality as a function of the total measured concentration (mg TMC/L) and normalized to total TUs is shown in Figures 5C and 5D, respectively. The dashed lines are the 5 and 95 percent uncertainties for O. davisae based on variation in species-specific CTLBB. For O. davisae, the dose-response was correctly predicted by the TLM where 50% mortality occurs around 1.0 TU.



Acute Exposures - Mixtures - Percent mortality as a function of total measured concentration (mg/L) (top panels) and predicted aqueous TUs (bottom panels). Data on the right is for Pimephales promelas exposure to WSFs prepared from neat and weathered Exxon Valdez crude oil (ENSR, 2000). Data on the left is for Oithona davisae exposure to WSF prepared from a mixture of 9 PAHs (Barata et al. 2005). Solid lines represent 50% mortality (horizontal) and 1 TU (vertical). Dashed vertical lines represent HC5 and HC95 for each species.

The data analyses presented above demonstrated that the TLM and TU concept (i.e., theory of additivity) correctly predicted the acute effects from exposure to a mixture of oil-related compounds. The benefit of normalizing the concentration data to TU can also be realized through the data analysis. If the toxicity of the PAH mixture is expressed on a mass per unit volume of total measured concentration, then 50% observed mortality resulted from exposure of approximately 1 mgTMC/L of a mixture of 9 PAHs (Figure 5C) and 10 mgTMC /L of water soluble compounds in neat EVCO (Figure 5A). There is an order of magnitude difference in the concentration that resulted in similar effects. However, a comparison based on mass/volume concentration does not consider chemical differences in the mixtures or differences in organism sensitivity. Once normalized to TUs, 50% mortality occurs in the range of 0.6 to 1.0 TUs, within a factor of 2. Normalizing to TUs allows direct comparison among different studies. This illustrates that the total measured hydrocarbon concentration should NOT be used to assess toxicity, while TUs can be applied across different sources and organisms to express toxicity.

4.2.3 Chronic Effects (Growth, Reproduction and Mortality) - Single Compound Exposures
The analysis presented previously suggests that the TLM, which was developed for chemicals that have a narcotic mode of toxic action, can be used to predict the acute toxicity of BTEX (and other MAHs) and PAHs. To convert the acute TLM endpoint to a chronic endpoint, an acute-to-chronic ratio (ACR) is applied (Equation 14). Di Toro et al. (2000) demonstrated that the ACR is independent of chemical and species and can therefore be applied to any chemical and any species in their analysis. A mean ACR of 5.09 was computed from a database that included BTEX and PAHs as well as other chemicals, such as chlorinated alkanes and MAHs (i.e., 1,2-dichloroethane, 1,2,4-trichlorobenzene). More than half of the acute and chronic paired data sets were chlorinated compounds. Since petroleum products do not contained halogenated components, an analysis of the ACRs from non-halogenated compounds is more appropriate. In this section, the distribution of ACRs for aliphatic hydrocarbons, MAHs and PAHs were compared. A total of 29 paired data sets were available (Table 3), of which 17 were PAHs, 6 were MAHs and 6 were aliphatic hydrocarbons. The distributions for each chemical class are shown in Figures 6A-C. The distributions are similar, spanning an ACR range of approximately 1 to 11. Since the distributions were similar, the data sets were combined (Figure 6D). The geometric mean ACR from the combined data sets is 3.83. Although this research focuses on MAHs and PAHs, aliphatic hydrocarbons were included in the ACR computation because: (1) based on structure, aliphatic hydrocarbons are not expected to have a different mode of action; and (2) the ACRs for aliphatic hydrocarbons fell on the high end of the distribution and including them in the computation resulted in a higher average ACR and is therefore the more conservative approach for computing a chronic endpoint.

The use of an ACR to convert an acute endpoint to a chronic endpoint does not mean that the toxic mode of actions for acute toxicity and chronic toxicity are the same. Rather, an ACR is a means of relating the acute toxicity of a chemical to its chronic toxicity. In addition, the toxic modes of action are not necessarily the same for different chemical classes that have similar ACRs (i.e., PAHs, MAHs and aliphatic hydrocarbons). The fact that the distributions are similar supports the application of an average ACR. If the ACRs were orders of magnitude different, then perhaps the use of an average ACR would not be appropriate.



Figure 6. Chronic Effects – Single Compounds - Distribution of acute to chronic ratios (ACRs) for aliphatic hydrocarbons (A), PAHs (B), BTEX (C) and the combined data set (D)

4.2.4 Chronic Effects (Growth, Reproduction and Mortality)- Mixtures
One study that satisfied all of the criteria investigated the chronic effects from exposure to No. 2 fuel oil. Anderson et al. (1977) investigated the hatching success of three marine species: Cyprinodon variegates (Sheepshead minnow), Fundulus heteroclitus (Mummichog) and Fundulus similus (Longnose killifish). A CTLBB is only available for C. variegates and therefore only the effects on this organism can be evaluated. Embryos were exposed to various dilutions of a WSF prepared for No. 2 fuel oil. The WSF was renewed daily. Concentrations of 31 hydrocarbons (11 alkanes, 8 MAHs, 12 PAHs) in the WSF were provided in Anderson et al. (1974a). With the exception of the lowest dilution, 100% mortality was observed in all exposures. The observed mortality as a function of total concentration in the WSF (mg/L) (left panel) and predicted aqueous TUs (right panel) is shown in Figure 7. For this data set, the TLM correctly predicted the observed effects, 100% mortality occurred at greater than 1 TU and low effects occurring at less than 1 TU.



Figure 7. Chronic Effects – Mixtures – Observed mortality as a function of total measured concentration in WSF (mg/L) (left panel) and predicted aqueous TUs (right panel). Data are for Cyprinodon variegates embryos exposed to WSF prepared from No. 2 fuel oil (Anderson et al. 1977). Dashed vertical lines represent 5th and 95th percentiles based on variations in CTLBB and ACR.

Moles (1998) compared the sensitivity of 10 aquatic species to long-term exposure to crude oil. In this study, WSFs were prepared from Cook Inlet crude oil. Organisms were exposed to various dilutions of the WSFs for 4 and 28 days. Although the concentrations of individual components in the WSFs were not measured, the 4-d and 28-d LC50s were reported and used to compute ACRs. The computed ACRs ranged from 1 to 2.5 (data for which 4-d LC50 could not be computed were omitted from analysis). These ACRs for crude oil are similar to the ACRs computed for individual chemicals that comprise oil and further support the use of a mean ACR of 3.8 for oil-related components.

4.2.5 Sub-Lethal Effects
There is a significant amount of recent literature that suggests exposure to PAHs during a fish’s early life-stage can result in a variety of sub-lethal effects (e.g., yolk sac edema, pericardial edema, hemorrhaging, craniofacial and spinal deformities, lesions, defects in cardiac function and reduced growth) (Carls et al. 1999; Heintz et al. 1999; Brinkworth et al. 2003; Incardona et al. 2004; Rhodes et al. 2005). Many of these symptoms are similar to those of blue-sac disease, which is related to exposure to planar, halogenated aromatic compounds such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (Hornung et al. 1999). These sub-lethal effects were not included in the development of the ACRs and so, the ACRs may not be protective of these types of effects. However, since recent literature is focusing on these types of effects and exposure to PAHs causes these effects, it is appropriate to determine if the TLM is protective of these effects. This section presents the application of the TLM and ACR methodology to determine if it is protective of these types of effects (i.e., whether the methodology predicts chronic endpoints that are lower than concentrations observed to cause these effects).

4.2.5.1 Single Compound Exposures
The literature was reviewed to identify data sets where early life-stage organisms were exposed to single compounds (BTEX and PAHs) and sub-lethal effects were observed. These data sets were then screened to meet the four main criteria of (1) available CTLBB, (2) exposure concentrations below compound solubility constant exposure, (3) constant exposure concentrations (i.e., flow-through vs. static test conditions), and (4) measured concentrations. Fourteen data sets were identified for analysis; however; only 6 datasets satisfied all four criteria. In all data sets, the chemical exposure concentrations were below the chemical’s water solubility and species-specific CTLBBs were available for all test organisms. For some of the exposures, the reported test concentrations were nominal rather than measured values and the exposure conditions were static (i.e., not constant) rather than flow-through or static renewals (i.e., constant). In following the U.S. EPA water quality criteria guidelines (Stephan et al.1985) credence is given to measured data generated under flow-through or static renewal conditions. Due to the scarcity of data, all data were analyzed. To put some perspective on the conditions under which the data were generated, they were given a ranking number determined as follows:

1 = Nominal concentration
2 = Static test conditions, measured concentrations
3 = Static renewal conditions, measured concentrations
4 = Flow-through conditions, measured concentrations


Data that have a ranking number of 3 or 4 are more comparable for use in the TLM since the effect concentrations were based on measured concentrations and the test concentrations were relatively stable throughout the test duration. Six data sets were given a ranking number of at least 3 (see Table 4 for a summary of the data).

For each exposure, the organism, chemical, relevant test conditions, observed effects and reported effect concentration are listed. The TLM chronic endpoint and HC5 and HC95 values are also provided for comparison. The TLM chronic endpoint is computed from Equations 13 and 14 using the average ACR of 3.83. The HC5 and HC95 are the 5th and 95th percentiles and include variability in ACR and CTLBB. Example calculations are provided in Appendix E. Data were available for five fish species, Japanese medaka (Oryzias latipes), fathead minnow (Pimephales promelas), rainbow trout (Oncorhynchus mykiss), Inland silverside (Menidia beryllina) and zebra danio (Brachydanio rerio). The compounds tested included toluene, naphthalene, phenanthrene, dibenzothiophene, retene, benzo(a)pyrene, benzo(a)anthracene, 4,6-dimethyldibenzothiophene, 7,12-dimethylbenzo(a)anthracene and benzo(k)fluoranthene. The reported concentrations included lowest observed effect concentrations (LOEC), no observed effect concentrations (NOEC) and observed effect concentrations (OEC). Ideally, the TLM chronic endpoint should fall between the reported LOEC and NOEC. In two exposures, no effects were reported at concentrations tested below the chemical’s water solubility (Table 4 - benzo(a)anthracene and 4,6-dimethyldibenzothiophene exposure to Japanese medaka). Based on the TLM, effects should have been observed at the concentrations tested. The fact that no effects were observed at levels predicted by the TLM suggests that the TLM is overly protective and conservative. For eight data points, the average TLM chronic endpoint was above the LOEC. However, it is more appropriate to compare the HC5 value to the observed effect concentration when determining if a criterion is protective. For the majority (13 out of 15) of the early life stage exposures, the TLM methodology was protective of sub-lethal effects. There were two data points for which the TLM chronic endpoints were above the observed effect concentrations (i.e., not protective). In one test, the reported 27-d LC50 for mortality (grossly deformed larvae counted as dead) for rainbow trout exposed to naphthalene was 120 ?g/L (Black et al. 1983) compared to the TLM HC5 of 170 µg/L. The reported 36-d LOEC for abnormalities to rainbow trout exposed to phenanthrene was 0.21 ?g/L (Hannah et al 1982; Hose et al 1984) compared to the TLM HC5 of 0.36 ΅g/L. Both of these exposures had a ranking number of 3 or 4, indicating that the test conditions were optimum and that the data should be of high quality. A graphical presentation comparing the early life stage data to the TLM predictions is shown in Figure 8. The lower and upper bars around the TLM chronic endpoint represent the HC5 and HC95, respectively.

4.2.5.2 PAH Mixtures
Several laboratory studies demonstrated that long-term exposure to oil results in various sub-lethal effects in early life stage pink salmon (Oncorhynchus gorbuscha) and pacific herring (Clupea pallasi) (Marty et al. 1997; Carls et al. 1999; Heintz et al. 1999). Data from these studies could not be analyzed because the chemical exposure concentrations were not constant and drastically decreased (by orders of magnitude) during the exposure period. Due to the variable exposure concentrations, linking the observed effects to the exposure concentrations was not possible.

Rhodes et al. (2005) determined the effects of PAH mixtures on embryonic development. In this study, early-life stage O. latipes were exposed for 18 days to three different mixtures of PAHs. One mixture contained three parent PAHs (phenanthrene, dibenzothiophene and benzo(a)anthracene). Another mixture contained three dimethylated PAHs (3,6-dimethylphenanthrene, 4,6-dimethyldibenzothiophene and 7,12-dimethylbenzo(a)anthracene). The last mixture was an oil sands extract. The exposure system was static renewal and therefore the exposure concentrations were fairly constant. Nominal concentrations were reported for the two mixtures prepared from three PAHs. For the extract, the concentrations of 16 U.S. EPA priority pollutant PAHs and their alkylated homologs were measured. The endpoints evaluated were prevalence of BSD (blue sac disease) symptoms, % hatch, time to hatch and % normal larvae. For each mixture, the NOEC and LOEC values were reported when effects were observed. For the parent PAH mixture, the NOEC and LOEC values for % hatch and % normal larvae were 100 and 200 µg TPAH/L, respectively. The TLM chronic endpoint for the parent mixture was 80 µgTPAH/L. The only observed effect from the dimethylated PAH mixture was % hatch, where the NOEC and LOEC values were 25 and 50 µgTPAH/L, respectively. The TLM chronic endpoint for the dimethylated parent mixture was 15 µgTPAH/L. The oil sands extract was the only mixture that induced BSD symptoms. The NOEC and LOEC values for BSD and % normal larvae were 8.8 and 22 µgTPAH/L, respectively. Hatch length was affected at lower concentrations of the oil sands extract with NOEC and LOEC values of 0 and 2.2 ΅gTPAH/L, respectively. The TLM chronic endpoint for the oil sands mixture was 10 µg/L. A comparison of the observed and predicted effect concentrations for the three mixtures is shown in Figure 9. All data are provided in Appendix C (Tables C6 and C7). For the TLM predicted concentrations, the symbol represents the predicted concentration. The vertical bars represent the 5th and 95th percentiles and are based on variation in CTLBB for a species and variation in ACR. For all three mixtures, the TLM chronic endpoint was below the LOEC and in some cases below the reported NOEC, indicating that the method is protective. The one exception was for the oil sands extract where the LOEC for hatch length was 2.2 µg/L, which was below the average TLM endpoint of 10 µg/L. However, the HC5 of 0.2 µg/L, is below the LOEC. This is another dataset that supports the use of the HC5 as the criterion value. It should be noted that the large uncertainty in predictions for Japanese medaka (i.e., wide range in HC5 and HC95) is due to the large kz value of 4.47. The dataset used to compute the CTLBB only consisted of 5 data points. With such a high kz value, it is almost certain that the HC5 will be lower than the observed effect concentration. Medaka is a commonly used test organism and additional acute toxicity data are needed to better quantify the statistics of the CTLBB.




Figure 8. Sub-lethal effects – Single Compounds – Comparison of OEC/LOEC/NOEC observed from early life stage fish exposures to single compounds to TLM chronic effect concentrations. The effects are those associated with sub-lethal endpoints such as abnormal larvae development and blue sac disease-like symptoms. The symbols represent the TLM chronic endpoint. The lines associated with the TLM chronic endpoints represent the 5th and 95th percentiles based on variations in CTLBB and ACR. The number located above the reported effect concentration is the assigned ranking number. See Table 4 for references.



Figure 9. Sub-lethal effects – Mixtures – Comparison of 18-d NOEC and LOEC from early life stage toxicity tests exposing Oryzias latipes to three prepared mixtures of PAHs to TLM chronic endpoints. The circles represent the TLM effect concentration. The bars represent the 5th and 95th percentiles based on variations in CTLBB and ACR. Data are from Rhodes et al. 2005.

This section presented several comparisons of toxicity data resulting from laboratory experiments to toxicity predictions made by the TLM for water column exposures. For acute exposures, it was demonstrated that the TLM reliably predicts the toxicity, particularly for single chemical exposures. For chemical mixtures, the results were not as supportive due to a limitation of available and acceptable data. For data that were available the combination of the TLM and the TU concept produced results that were in agreement with the observed data. It was also shown that normalizing the toxicity data to a TU metric allowed for comparisons of toxicity between data sets, which was not possible when the toxicity data are presented on a mass basis. For evaluations of chronic toxicity, it was shown that the use of an average ACR was appropriate to convert acute toxicity values to chronic values. These chronic endpoints included growth, reproduction and mortality. Recent investigations have indicated that chronic exposure of low levels of PAHs to developing embryos causes sub-lethal effects, such as edemas, heart abnormalities and deformities, which were not included in the derivation of the ACR. The TLM methodology was evaluated to determine if it was protective of these types of endpoints, meaning that the TLM predicted toxicity value was lower than the observed endpoint. It was shown that within the uncertainty of the model (i.e., the variation associated with the parameters) the TLM was protective of these types of endpoints and in some cases it was over protective.


4.3 TLM Validation- Sediment
In this section, the TLM and equilibrium partitioning theory are coupled to predict the effects of organisms exposed to oil-related contaminants in sediments. The equations for computing the sediment effect concentrations were provided in Section 3.3 Graphical comparisons of the toxicity predictions and observed values are presented.

4.3.1 Acute Effects – Single Compound Exposures
For sediment toxicity, 40 data points were found for acute exposures to single PAH compounds. Interestingly, sediment toxicity data for BTEX were not available. Since BTEX are fairly volatile compounds, they are not expected to partition to the sediment. As a result, investigations of their sediment toxicity are not commonly done. Data were available for six different species: Rhepoxynius abronius, Eohaustorius estuaries, Leptocheirus plumulosus, Hyalella azteca, Schizopera knabeni and Coullana sp., and ten different PAHs. The measured data and the corresponding TLM acute predictions are presented in Table 5. The observed and TLM predicted LC50 values are compared in Figure 10. Dashed lines represent the 90% confidence intervals (see Section 4.2.1). The two data points that fall far to the right were considered outliers and not used in the computation of the 90% confidence limits. The majority of the data fall within a factor a three. Based on this analysis, the TLM methodology, coupled with EqP theory, can be used to predict the toxicity of sediment-associated PAHs.




Figure 10. Acute Sediment Exposures – Single Compound - Comparison of observed and TLM predicted sediment effect concentrations (see Table 5 for data). Solid line is 1:1 relationship. The dashed lines are 90% confidence intervals.

4.3.2 Acute Effects – PAH Mixtures
There were 12 data sets available that had acute toxicity for PAH mixtures (Table 6). Three data sets were for laboratory prepared exposures where the contaminants were spiked into the sediment. Two of the laboratory tests were various mixtures of PAHs. The other laboratory exposure involved spiking diesel fuel into sediment. Nine data sets involved a variety of field sediments where PAHs were expected to be the major contaminants of concern. Toxicity data were available for five sediment dwelling organisms, with the amphipod R. abronius being the most commonly used sediment bioassay organism. For each of these data sets, the concentrations of PAH in the mixtures and the corresponding TOC concentrations were provided. The field data sets were not consistent with respect to the number of PAHs measured. Some data sets measured only 13 PAHs (the U.S. EPA defined as priority pollutants) (see Table 1). Other data sets had measurements for all parent PAHs and their alkylated homologs (greater than 30 PAHs). For PAH contamination from petrogenic sources, the alkylated component is known to be large and if the toxicity from those alkylated PAHs is not considered, the toxicity from PAHs can be underestimated. For data sets that only have 13 PAHs measured, the TU from 13 PAH was normalized to total PAHs TU via adjustment factors provided in the U.S. EPA Equilibrium Partitioning Sediment Benchmarks for PAH mixtures (U.S. EPA, 2003) (see Section 3.6). The measured concentrations of PAHs, TOC, sample ID, effect data and TLM toxic units are provided in Appendix D, Tables D1 through D12.

The 10-d mortality data for R. abronius are presented in Figure 11. The top panel presents the percent mortality as a function of measured PAH (mg/kg dry weight basis). In the bottom panel, the sediment concentration data are normalized to total PAH toxic units. On a mg/kg basis, relatively low mortality occurs below a measured PAH concentration of 3 mg/kg and 100 % mortality occurs above 500 mg/kg. The area of uncertainty – the area where a mixture of low and high effects occurs at similar levels - is 3 to 500 mg/kg. At this concentration range, effects may or may not be observed. Normalizing to total PAH TU, slightly reduces that uncertainty. On a total PAH TU basis, low mortality occurs below a TU of 0.1 and 100% mortality occurs at a TU of greater than 5.0. This comparison indicates that dry weight normalization works almost as well as PAH TU. This is not unexpected for a particularly species. The TLM predicted species-specific sediment LC50s for PAHs are similar on an organic carbon basis. For R. abronius, the LC50s range from 19.7 µmol/goc for naphthalene to 27.8 µmol/goc for benzo(a)pyrene (see Table D4). Since the sediment effect concentrations are similar, a comparison of measured total PAH concentration on an organic carbon basis to the average sediment LC50 on an organic carbon basis is equivalent to the TU analysis (see Di Toro and McGrath, 2000 for equations). If the organic carbon concentration is similar for different sediments, then the dry weight normalization will work as well as the organic carbon normalization and the TU analysis. The advantages of the organic carbon normalization and TU approach are that sorption is considered, species sensitivity is considered and the data are normalized to a total PAH basis.

On a TU basis, the area of uncertainty ranges from 0.1 to 5, which is slightly lower than the uncertainty range determined on a mass concentration basis, suggesting that TUs are the better metric for relating concentration to effects. This uncertainty is slightly larger than the range bracketed by the HC5 and HC95 (0.23 to 4.3 TU) and could be attributed to the high degree of scatter commonly observed in field-collected data, compared to laboratory data. In addition, this analysis assumes that PAHs are the primary causative agent, which may not be the case for all field data sets. If other constituents are present in the sediments and contributing to the toxicity, higher than expected mortality would occur at low TUs.



Figure 11. Acute Sediment Exposures – Mixtures – Percent mortality of R. abronius as a function of PAH concentraton (mg/kg) (top panel) and normalized to total PAH sediment toxic units (bottom panel). All data are 10-d exposures. Solid lines at a toxic unit of 1.0 and 50 % mortality are shown for guidance. Dashed lines represent 5th and 95th percentiles based on variation in CTLBB. (• Swartz et al. 1997; Boese et al. 1999; Tay et al. 1992; Techratech, 1982; Swartz et al. unpublished; Swartz et al. 1989; • Ozetich et al. 2000; Page et al. 2000.

There are four data sets that have acute mortality data for species other than R. abronius. Comparisons of percent mortality as a function of measured PAH (mg/kg) and total PAH TU are shown in Figure 12. DeWitt et al. (1992b) determined the mortality to two species (E. estuaries and L. plumulosus). Since the CTLBB for these species are very similar (41.4 and 43.1 mmol/g octanol), the computed total PAH TUs are almost identical. Therefore, the observed range of mortality for the two species is shown as a function of the sediment concentration (Figure 12, panels E and F). Due to limited data available to compute CTLBB for sediment organisms, HC5 and HC95 values could not computed for E. estuaries, Chironomus riparius, Schizopera knabeni and Ampelisca abdita. For all four data sets, the dose-response is as expected with low total PAH TUs corresponding to low mortality and around 1 TU corresponding to about 50 % mortality.





Figure 12. Acute Sediment Exposures – Mixtures – Percent mortality as a function of PAH concentraton (mg/kg) (top panel) and normalized to total PAH sediment TUs (bottom panel). See Table 6 for exposure information. Solid vertical and horizontal lines at a TU of 1.0 and 50 % mortality, respectively, are shown for guidance.


It should be noted that the measured concentrations in the field datasets represent different numbers of PAHs measured ranging from 13 to 40. For example, a value of 10 mg/kg in a sediment sample contaminated from the Exxon Valdez oil spill (Page et al. 2002) that was computed as the sum of 40 PAHs is not necessarily equivalent to a value of 10 mg/kg in a sediment sample collected in Eagle Harbor, WA (Swartz et al. 1989) that was computed as the sum of 13 PAHs. In addition, the bioavailability of the sediment-associated PAHs is a function of the organic carbon concentration of the sediment (Di Toro et al. 1991). Two sediment samples that have 10 mg/kg of the same 40 PAHs, may have different toxicities if the organic carbon concentrations are different. Therefore, concentrations of measured PAHs in different sources should not be compared nor should effects be assigned based on mass based concentrations. Using the summed TU approach for sediments (i.e., converting individual sediment PAH concentrations to individual PAH TU, summing the individual PAH TU and then applying a factor to convert to total PAH TU) considers the toxicity from unmeasured PAHs and considers the difference in organic carbon concentration and therefore reduces the uncertainty associated with PAHs measurements across different sources and allows for comparisons to be made.

The importance of applying the adjustment factor to account for unmeasured PAHs is demonstrated using a San Diego Bay sediment dataset (Swartz et al. unpublished). In this dataset, 13 PAHs were measured in 54 sediment samples. The test organism was R. abronius and the endpoint was 10-d mortality. Table 7 presents a comparison of the TUs computed from the measured 13 PAH and from Total PAH as they relate to the observed mortality. A correction prediction was one where the observed mortality was greater than or equal to 50% and the computed TUs were greater than or equal to 0.4 (the uncertainty based on the ratio of the HC5 and the TLM endpoint for R. abronius) or where the observed mortality was less than 50% and the computed TUs were less than 0.4. When the TUs were computed from the 13 PAH only, there were 42 correct predictions. When the adjustment for unmeasured PAHs was considered the number of correct predictions increased to 45. In addition to the number of correct predictions, one can compare the number of times that the criterion was protective, meaning high mortality was observed and correctly predicted. The observed mortality was greater than or equal to 50% in 13 samples. Based on TUs from 13 PAHs, one sample would have been predicted to be toxic (station STA28 100% with TU of 0.608 from 13 PAH). In comparison, the TUs from Total PAHs were greater than 0.4 in eight of the samples with high mortality. This analysis demonstrates the importance of adjusting for the toxicity from unmeasured PAHs. The overall number of correct predictions (toxic and non-toxic) increased. Furthermore, the number of correct toxic predictions increased from 1 to 8 with the incorporation of the adjustment factor.

4.3.3 Chronic Effects – Single Compound Exposures
There are several data sets available that report chronic effects from exposure to sediment spiked with single PAHs. The chronic effects are growth and reproduction endpoints. The tests species are Coullana sp. and S. knabeni (Figure 13). The CTLBBs for these species were measured on a lipid basis (Lotufo, 1998). The effect of fluoranthene on grazing and reproduction for Coullana sp. was reported (Lotufo, 1998). The 10-d LOECs ranged from 3133 to 8800 mg/goc for grazing and reproduction, respectively. The 10-d NOECs ranged from 1200 to 3111 mg/goc. The TLM predicted chronic effect concentration of 1410 mg/goc was below the observed LOECs indicating that the TLM correctly predicted the effects. The chronic effects of phenanthrene and fluoranthene on grazing and reproduction of S. knabeni were determined (Lotufo, 1997; Fleeger and Lotufo, 1999). Phenanthrene had a reported 14-d IC25 (inhibition concentration - concentration causing 25% reduction of measured endpoint in relation to control) of 1730 µg/goc for reproduction effects. The reported 10-d NOEC and LOEC were 1470 and 3000 µg/goc, respectively, for hatching success. The TLM predicted chronic effect concentration of 3560 µg/goc was slightly higher than the reported OEC/LOEC. Fluoranthene had reported 10-d LOECs of 1200 and 3133 µg/goc for grazing and reproduction, respectively (Lotufo, 1998). The TLM predicted chronic effect concentration of 4130 µg/goc was slightly higher than the reported LOEC. These data are summarized in Table 8 and Figure 13.


The CTLBBs for S. knabeni and Coullana are measured values based on a single compound (fluoranthene) and the uncertainty associated with them could not be determined. In addition, Lotufo (1998) stated that the lipid content was based on an initial value, which could have changed during the exposure time. The variability in the reported CTLBB for these species is unknown. Therefore, these data are presented for informational purposes only and the results of the analysis should not be used to assess the performance of the TLM.




Figure 13. Chronic Sediment Exposures – Single Compounds - Comparison of reported OEC/LOEC/NOEC and TLM effect concentrations from long-term exposures of fluoranthene and phenanthrene to the marine copepods Coullana sp. and Schizopera knabeni. See Table 8 for references.


4.3.4 Chronic Effects – PAH Mixtures
Fleeger and Lotufo (1999) investigated the chronic effects on S. knabeni from exposure to a sediment spiked with diesel fuel. They measured the concentrations of 20 PAHs and TOC in the sediment. The sediment was spiked with the diesel fuel and dilutions were prepared for use in the bioassay. The resulting total PAH concentrations in the sediment were 19, 45, 93, 130, 185 and 370 mg/kg. The LOEC and NOEC for reproductive effects were 93 and 45 mg/kg, respectively. The equivalent TLM Total PAH TU for the LOEC and NOEC were 1.7 and 0.8, respectively (Table 10D). Based on these equivalent TUs, effects should have been have observed at 45 mg/kg. While the TLM was overprotective (i.e., effects were predicted at concentrations where no effects were observed), these data cannot be used to assess the performance of the TLM because of the uncertainty in the CTLBB (See Section 4.3.3).



5.0 Discussion and Importance to Oil Spill Response/Restoration
This research focused on developing a methodology that can be used to assess the toxicity of low levels of residual oil, focusing on the MAH and PAH components. The methodology has to be able to predict the toxicity of these components in the aqueous phase and in the sediment, on acute and chronic bases. The methodology had to include the derivation of a metric that enabled the toxicity from one location to be comparable to the toxicity at another.

It has been demonstrated that the TLM can be used to assess the acute and chronic toxicity of oil-related components on an acute basis in the water column and sediments. It has been shown that the use of an ACR to relate the acute toxicity to an equivalent chronic toxicity is appropriate without consideration of the toxicity mechanism. Within the uncertainty of the model, the TLM has been shown to be protective of sub-lethal effects that result from exposure to low levels of PAHs during an organism’s early life stages. The TLM coupled with the theory of additivity via the concept of TUs can be used to predict the toxicity of mixtures of chemicals present in oils. TUs are a means of normalizing the toxicity of different chemicals. A total TU of 1.0, implies toxicity. A total concentration of 1µg/L is not necessarily toxic. Rather, its effect is dependent on the specific chemical(s) to which the organism is exposed and the sensitivity of the organism. It should be noted, that the available toxicity data for mixtures that met the criteria for inclusion, both on an acute and chronic basis, are limited. There is research need to determine the toxicity of mixtures of chemical resulting from exposure to oil for species where a CTLBB is available. These data would further validate that the TLM and TU concept are appropriate for predicting the toxicity.

For sediment assessment, the TLM aqueous effect concentrations are converted to sediment effect concentrations via EqP methodology. In the sediment, the chemical concentration can be related to the bioavailability by normalizing the chemical concentration to the organic carbon concentration. The TU metric allows for the consideration of the toxicity from unmeasured PAHs by incorporating the U.S.EPA adjustment factors, which cannot be done on a mass basis (i.e., mg/kg). Organic carbon normalization and TU conversion allow for the generation of a toxicity metric that is applicable across a broad range of sediment types and representative of toxicity from Total PAH.

In addition to being used as a tool that can assess whether effects are expected at a certain concentration of a chemical or from a mixture of chemicals, the methodology can be used to derive defensible chemical-specific guideline values. When the statistics (geometric mean and variance) of the CTLBB of all test species are used in Equation 18, the computed HC5 is the aqueous concentration that protects 95% of the species. These HC5s can be used as decision-making values to determine the concentration of a particular chemical that will not likely have an adverse impact on the aquatic community. The geometric mean CTLBB of all tests species for baseline chemicals (i.e., aliphatic hydrocarbons, alcohols, see Appendix A) is 123 ΅mol/g octanol. The geometric mean CTLBB for specific chemical classes is computed as
  C*L(geometicmean, Chemicalclassi) = C*L(geometicmean,baseline)XdeltaCi (23)

whereC is the chemical class correction factor for chemical class i (see Appendix A). The CTLBBs for the various chemical classes are provided in Table 9.
The resulting equation to compute the chronic HC5 values for PAHs is:

     
  figure 24 (24)
     
  figure 25 (25)

The 95% confidence sample size-dependent extrapolation factor (kz = 2.3) was based on the number of ACRs (29) rather than the number of CTLBBs (47) to ensure that the calculations were conservative. A summary of chronic HC5 values for MAHs and PAHs is provided in Table 10. EqP theory was used to convert the aquatic HC5s to sediment HC5 values (Equation 15). The values are presented on a molar basis (i.e., µmol/L, mmol/KgOC) and a mass basis (i.e., µg/L, mg/KgOC). Details of the calculations are provided in Appendices E and F.

To assess the management implications of adopting chronic HC5s derived via the TLM for decision-making, a comparison was made of the aqueous HC5 values to NOECs values for PAHs. The NOECs values used in this analysis are presented in Table 11 and Figure 14. A total of 27 NOECs were compiled for 7 different PAHs. Two NOECs fell below the HC5 line. Both of these NOECs were for phenanthrene and ranged from 5 to 5.5 µg/L, which were considerably lower than NOECs for other compounds. The excursion of two data points below the HC5 is consistent with the 95% protection level goal (i.e., 92.6% (25/27)). The HC5 derived from the TLM is very close to the expected level of protection. Therefore, these values are appropriate for use as numeric chemical-specific benchmarks and can be used to assess the ecological risk of contaminated sediments and/or establish safe levels for cleanup activities. Of course, one needs to consider the assumptions of the TLM and the conditions that can impact the toxicity of MAHs and PAHs (refer to Section 2.0) to determine the appropriateness for applying these guidelines to a specific location.




Figure 14. Chronic HC5 concentration for PAHs versus log (KOW). The HC5 concentration is based on the 5th percentile CTLBB for all species in the database. The observed NOECs for PAHs are denoted with a 0 (Table 10).

6.0 Technology Transfer
The results of this research effort on the application of the TLM to predict acute and chronic effects on oil-related compounds and the derivation of HC5 will be submitted to Environmental Chemistry and Toxicology. An abstract focusing on the application of TLM to be protective of sub-lethal effects from exposure to PAHs has been submitted to the Society of Environmental Chemistry and Toxicology (SETAC) for presentation at the Fall 2006 North America meeting. Intermediate results of this research effort were presented at a March 2005 workshop entitled “Emerging Research in Oil Spill Response and Restoration”, at a September 2006 summit for the PAH Toxicology Working Group, at a September 2006 workshop entitled “Innovative Coastal Modeling: Integrating Physical, Biological and Toxicological Models”, all sponsored by CRRC, and at the 2005 SETAC North America meeting.


7.0 Achievement and Dissemination

Workshops and Conferences

Workshop on Emerging Research in Oil Spill Response and Restoration. 2005. “ Impacts of Low Levels of Residual Oil: Predicting the Acute and Chronic Toxicity of Residual Oil”. Office of Response and Restoration of NOAA. Silver Spring, Maryland. March 2005.

26th Annual SETAC North America Meeting. 2005. “Predicting the Acute and Chronic Effects of PAHs using the Target Lipid Model of Narcotic Toxicity: Is a New Paradigm Needed? Baltimore, Maryland. November 2005.

PAH Toxicology Working Group Summit. 2006. “ Impacts of Low Levels of Residual Oil: Predicting the Acute and Chronic Toxicity of MAHs and PAHs”. CRRC. Seattle, Washington. August 2006.

Workshop on Innovative Coastal Modeling: Integrating Physical, Biological and Toxicological Models. 2006. “ Impacts of Low Levels of Residual Oil: Predicting the Acute and Chronic Toxicity of MAHs and PAHs”. CRRC. Durham, New Hampshire. September 2006.

27th Annual SETAC North America Meeting. 2006. “Predicting the Chronic Effects of PAHs using the Target Lipid Model of Narcotic Toxicity”. Montreal, Canada. November 2005.
7.0 Achievement and Dissemination






Table 1. Chemicals and their properties (at 25 o C) measured in various data sets    
               
    Molecular Weight (g/mol)   Subcooled Liquid Solubility ( m g/L) b,d Key PAHs e    
  Log K ow a Solid Solubility ( m g/L) b    
               
ethane 1.730 30.00 1350000 1350000      
benzene 1.943 78.11 1780000 1780000      
propane 2.370 44.09 248000 248000      
toluene 2.438 92.14 515000 515000      
butane 2.868 58.12 61400 61400      
isobutane 2.869 58.12 48900 48900      
o-xylene 2.946 106.17 220000 220000      
cyclopentane 2.991 70.00 156000 156000      
ethylbenzene 3.006 106.17 152000 152000      
m-xylene 3.032 106.17 160000 160000      
p-xylene 3.051 106.17 215000 215000      
9,10-Anthracenedione 3.080 208.22 116000 130000      
naphthalene 3.256 128.19 31000 110000 A,B,C    
isopentane 3.335 72.15 13800 13800      
acenaphthylene 3.436 152.20 16100 75000 A,B,C    
C3-benzenes c 3.455 120.00 19700 19700      
pentane 3.471 72.15 38500 38500      
9-fluorenone 3.510 180.20 25000 48000      
methylcyclopentane 3.571 84.00 42000 42000      
1-methylnaphthalene 3.781 142.20 28000 28000 B    
C1-naphthalenes c 3.788 142.20 7900 22000 C    
2-methylnaphthalene 3.789 142.20 25000 31100 B    
acenaphthene 3.878 154.21 3800 19200 A,B,C    
fluorene 3.930 166.20 1900 15100 A,B,C    
biphenyl 3.936 154.21 7000 20000      
2-chloronaphthalene 3.940 162.64 5500 18000      
1-chloronaphthalene 3.950 162.64 5400 5400      
methylcyclohexane 3.963 98.19 14000 14000      
hexane 4.053 86.00 9500 9500      
C2-naphthalenes c 4.244 156.23 1970 9400 C    
1,3-dimethylnaphthalene 4.257 156.23 8000 8000      
1-methylfluorene 4.370 180.25 1090 4270      
C1-fluorenes c 4.370 180.25 1510 8400 C    
anthracene 4.546 178.20 45 3500 A,B,C    
2,3,5-trimethylnaphthalene 4.570 170.20 580 5200 B    
2,3,6-trimethylnaphthalene 4.570 170.20 740 5200      
phenanthrene 4.584 178.23 1100 6210 A,B,C    
n-heptane 4.584 100.20 2930 2930      
dimethylbiphenyl c 4.692 182.00 530 4400      
C3-naphthalenes c 4.730 170.25 440 3800 C    
C2-fluorenes c 4.819 194.27 380 3600 C    
C1-Dibenzothiophene c 4.859 198.30 340 3400      
9-methylanthracene 4.996 192.26 261 945      
1-methylphenanthrene 5.036 192.26 270 2520 B    
C1-phenanthrene/anthracene c 5.037 192.26 180 2300 C    
2-methylphenanthrene 5.040 192.26 180 2300      
pyrene 5.126 202.26 132 2610 A,B,C    
fluoranthene 5.190 202.26 260 1700 A,B,C    
C4-naphthalenes c 5.220 184.28 97 1500 C    
C1-fluoranthene/pyrene c 5.257 216.28 101 1600 C    
C3-fluorenes c 5.318 208.30 80 1400 C    
C2-Dibenzothiophene c 5.332 212.30 78 1400      
3,6-dimethylphenanthrene 5.340 206.29 73 1300      
4,6-dimethyldibenzothiophene 5.450 212.30 53 1100      
C2-phenanthrene/anthracene c 5.455 206.29 51 1000 C    
C2-fluoranthene/pyrene c 5.557 230.31 40 950      
Triphenylene 5.630 228.30 43 2260      
benzo(a)anthracene 5.744 228.29 11 240 A,B,C    
chyrsene 5.782 228.29 2.0 376 A,B,C    
C3-Dibenzothiophene c 5.810 226.30 17 560      
C4-phenanthrene/anthracene c 6.357 234.34 3.0 190 C    
benzo(b)fluoranthene 6.341 252.32 1.5 38.9 A,B,C    
C3-fluoranthene/pyrene c 6.384 244.34 2.9 190      
benzo(k)fluoranthene 6.400 252.32 0.80 63.6 A,B,C    
benzo(a)pyrene 6.409 252.31 3.8 116 A,B,C    
7,12-dimethylbenzo(a)anthracene 6.420 256.35 50.00 455      
Benzo(e)pyrene 6.447 252.30 4.0 130 B,C    
perylene 6.447 252.31 0.40 124 B,C    
C2-Chyrsenes/benzo(a)anthracene c 6.593 256.34 1.5 130 C    
C4-fluoranthene/pyrene c 6.687 258.35 1.1 110      
C5-phenanthrene/antracene c 6.700 248.37 1.1 99.5      
C1-benzofluoranthene c 6.743 266.11 1.0 97.6      
benzo(ghi)perylene 6.886 276.34 0.26 83.2 B,C    
C3-Chyrsenes/benzo(a)anthracene c 6.972 270.36 0.47 62 C    
dibenz(a,h)anthracene 7.129 278.35 0.60 148 B,C    
C2-benzofluoranthene c 7.200 280.13 0.23 40.5      
C4-Chyrsenes/benzo(a)anthracene c 7.421 284.38 0.12 26 C    
               
a Log K ow computed from SPARC  
b Solubility data from Mackay et al. 1992a, 1992b, 1993 and 1995 or computed from relationships below  
Solid solubility computed from Log S = (-1.4136)(LogK ow ) + 7.1022 where solubility has units of m mol/L
Sub-cooled solubility computed from Log S = (-0.8857)(LogK ow ) + 5.5367 where solubility has units of m mol/L
c Mixture of isomers  
d For compounds that are liquid at room temperature, the solid solubility and sub-cooled solubilitiy are equal.  
e A = PAH is one of key 13 EPA priority PAHs; B= PAH is one of key 23 PAHs; C = PAH is one of 34 PAHs  
               


Table 2. Observed water-only acute LC50/EC50 values for PAHs and TLM predictions.
             
Species PAH Life Stage Test Type b Observed LC50 ( m g/L) Predicted LC50 ( m g/L) Reference
             
Artemia salina naphthalene larvae S,U 10600 9000 Abernethy et al. 1986
  naphthalene larvae S,M 11070 9000 Maclean and Doe, 1989
  1-methylnaphthalene larvae S,U 2560 3500 Abernethy et al. 1986
  2-methylnaphthalene larvae S,U 4740 3500 Abernethy et al. 1986
  2-chloronaphthalene larvae S,U 2330 1300 Abernethy et al. 1986
  1-chloronaphthalene larvae S,U 1840 1300 Abernethy et al. 1986
  phenanthrene larvae S,U 680 790 Abernethy et al. 1986
Chlamydomonas angulosa naphthalene not applicable S,U 9600 16000 Hutchinson et al. 1980
  1-methylnaphthalene not applicable S,U 1700 6100 Hutchinson et al. 1980
  2-methylnaphthalene not applicable S,U 4480 6000 Hutchinson et al. 1980
  phenanthrene not applicable S,U 945 1400 Hutchinson et al. 1980
Chlorella vulgaris naphthalene not applicable S,U 19200 21000 Hutchinson et al. 1980
  1-methylnaphthalene not applicable S,U 5100 8200 Hutchinson et al. 1980
  2-methylnaphthalene not applicable S,U 8900 8000 Hutchinson et al. 1980
Cyprinodon variegatus naphthalene unknown M 2400 5300 Anderson et al. 1974 a
  1-methylnaphthalene unknown M 3400 2100 Anderson et al. 1974a
  2-methylnaphthalene unknown M 2000 2000 Anderson et al. 1974a
  acenaphthene juvenile S,U 2200 1800 Heitmuller et al. 1981
  acenaphthene adult FT,M 3100 1800 Ward et al. 1981
  1-chloronaphthalene juvenile S,U 2400 760 Heitmuller et al. 1981
  1-chloronaphthalene juvenile F,M 690 760 Ward et al. 1981
  phenanthrene juvenile FT,M 429.4 460 Battelle Ocean Sciences, 1987
  phenanthrene juvenile R 478 460 Moreau et al. 1999
Daphnia magna naphthalene juvenile S,U 4723 5400 Abernethy et al. 1986
  naphthalene unknown S,U 8600 5400 U.S. EPA, 1978
  naphthalene neonate S,M 11800 5400 Maclean and Doe, 1989
  naphthalene unknown S,U 3400 5400 Crider et al. 1982
  naphthalene unknown S,U 4100 5400 Crider et al. 1982
  naphthalene unknown S,U 22600 5400 Eastman et al. 1984
  naphthalene unknown S,M 2160 5400 Millemann et al. 1984
  1-methylnaphthalene juvenile S,U 1420 2100 Abernethy et al. 1986
  2-methylnaphthalene juvenile S,U 1491 2100 Abernethy et al. 1986
  acenaphthene unknown S,M 320 1900 EG&G Bionomics, 1982
  acenaphthene unknown S,M 1300 1900 EG&G Bionomics, 1982
  acenaphthene unknown FT,M 120 1900 EG&G Bionomics, 1982
  acenaphthene unknown S,U 3450 1900 Randall and Knopp, 198
  fluorene unknown S,U 430 1800 Finger et al. 1985
  2-chloronaphthalene juvenile S,U 1640 780 Abernethy et al. 1986
  1-chloronaphthalene unknown S,U 1600 770 LeBlanc, 1980
  phenanthrene juvenile S,U 207 470 Abernethy et al. 1986
  phenanthrene unknown S,U 843 470 Eastman et al. 1984
  phenanthrene neonate S,M 700 470 Millemann et al. 1984
  phenanthrene unknown FT,M 117 470 Call et al. 1986
  9-methylanthracene juvenile S,U 124.8 210 Abernethy et al. 1986
  pyrene juvenile S,U 90.9 170 Abernethy et al. 1986
  fluoranthene juvenile S,M 45 140 Oris et al. 1991
  fluoranthene unknown S,M 100 140 EG&G Bionomics, 1982
  fluoranthene unknown S,M 105.7 140 Suedel and Rogers, 1996
  benzo(a)pyrene unknown S 250 a 13 Atienzar et al. 1999
Daphnia pulex naphthalene unknown S,U 4663 4210 Smith et al. 1988
  fluorene unknown S,U 212 1400 Smith et al. 1988
  1,3-dimethylnaphthalene unknown S,U 767 650 Smith et al. 1988
  1,3-dimethylnaphthalene neonate S,U 1280 650 Passino and Smith, 1987
  2,6-dimethylnaphthalene unknown S,U 193 630 Smith et al. 1988
  phenanthrene neonate S,U 734 370 Passino and Smith, 1987
  phenanthrene unknown S,M 100 370 Trucco et al. 1983
  phenanthrene unknown S,U 350 370 Smith et al. 1988
Ictalurus punctatus acenaphthene juvenile FT,M 1720 1180 Holcombe et al. 1983
  fluoranthene juvenile S,M 37.4 91 Gendusa, 1990
Lepomis macrochirus acenaphthene juvenile S,U 1700 2100 Buccafusco et al. 1981
  fluorene unknown S,U 910 2000 Finger et al. 1985
  1-chloronaphthalene juvenile S,U 2300 870 Buccafusco et al. 1981
  phenanthrene juvenile FT,M 234 540 Call et al. 1986
  fluoranthene juvenile FT,M 44 160 Spehar et al. 1999
Leptochirus plumulosus acenaphthene adult FT,M 589.4 690 Swartz, 1991
  phenanthrene adult FT,M 198.4 180 Swartz, 1991
  pyrene juvenile FT,M 66.49 62 Champlin and Poucher, 1992
  fluoranthene unknown R,M 51 54 Boese et al. 1997
Menidia beryllina acenaphthene juvenile R,U 5564 a 4700 Thursby, 1991
  acenaphthene unknown S,U 2300 4700 Horne et al. 1983
  fluoranthene unknown R,U 616 a 360 Spehar et al. 1999
Mysidopsis bahia acenaphthene juvenile R,U 1190 550 Thursby et al. 1989a
  acenaphthene juvenile S,U 970 550 Ward et al. 1981
  acenaphthene juvenile FT,M 460 550 Thursby et al. 1989b
  acenaphthene juvenile S,M 160 550 EG&G Bionomics, 1982
  acenaphthene juvenile FT,M 190 550 EG&G Bionomics, 1982
  acenaphthene juvenile FT,M 466.1 550 Horne et al. 1983; Thursby, 1991
  acenaphthene juvenile FT,M 271.9 550 Horne et al. 1983; Thursby, 1991
  1-chloronaphthalene juvenile S,U 370 230 U.S. EPA, 1978
  phenanthrene juvenile FT,M 17.7 140 Battelle Ocean Sciences, 1987
  phenanthrene juvenile FT,M 27.1 140 Kuhn and Lussier, 1987
  fluoranthene juvenile S,U 40 43 U.S. EPA, 1978
  fluoranthene juvenile FT,M 87 43 EG&G Bionomics, 1982
Neanthes arenaceodentata naphthalene immature young adult S,U 3800 8500 Rossi and Neff, 1978
  acenaphthene unknown S,U 3600 2900 Horne et al. 1983
  phenanthrene immature young adult S,U 600 740 Rossi and Neff, 1978
  fluoranthene immature young adult S,U 500 a 230 Rossi and Neff, 1978
Oithona davisae naphthalene adult S,M 7195 6600 Barata et al. 2005
  1-methylnaphthalene adult S,M 2652 2600 Barata et al. 2005
  fluorene adult S,M 1800 2200 Barata et al. 2005
  1,2-dimethylnaphthalene adult S,M 617 990 Barata et al. 2005
  dibenzothiophene adult S,M 551 a 1010 Barata et al. 2005
  phenanthrene adult S,M 522 580 Barata et al. 2005
  1-methylphenanthrene adult S,M 931 a 230 Barata et al. 2005
  pyrene adult S,M 154 a 200 Barata et al. 2005
  fluoranthene adult S,M 196 180 Barata et al. 2005
Oncorhynchus mykiss naphthalene juvenile FT,M 1600 3100 DeGraeve et al. 1982
  naphthalene unknown FT,M 2300 3100 DeGraeve et al. 1980
  naphthalene pre SU S,U 1800 3100 Edsall, 1991
  naphthalene pre SU S,U 6100 3100 Edsall, 1991
  naphthalene pre SU S,U 2600 3100 Edsall, 1991
  naphthalene pre SU S,U 4400 3100 Edsall, 1991
  naphthalene pre SU S,U 5500 3100 Edsall, 1991
  2-methylnaphthalene unknown R 1456 1200 Kennedy, 1990
  acenaphthene juvenile FT,M 670 1100 Holcombe et al. 1983
  fluorene juvenile S,U 820 1020 Finger et al. 1985
  1,3-dimethylnaphthalene pre SU S,U 1700 480 Edsall, 1991
  phenanthrene juvenile FT,M 375 270 Call et al. 1986
  fluoranthene unknown S,M 187 82 Horne and Oblad, 1983
  fluoranthene juvenile FT,M 26 82 Spehar et al. 1999
Palaemonetes pugio naphthalene unknown S,M 2350 2700 Tatum et al. 1978
  naphthalene unknown M 2600 2700 Anderson et al. 1974 a
  2-methylnaphthalene unknown M 1700 1000 Anderson et al. 1974a
  acenaphthene larvae R,U 1697 920 Thursby et al. 1989a
  acenaphthene unknown S,U 676 920 Horne et al. 1983; Thursby, 1991
  dimethylnaphthalene unknown M 700 400 Anderson et al. 1974a
  phenanthrene adult R,U 201 230 Battelle Ocean Sciences, 1987
  phenanthrene adult FT,M 145.4 230 Battelle Ocean Sciences, 1987
  fluoranthene juvenile S,U 142 71 Spehar et al. 1999
Pimephales promelas naphthalene juvenile FT,M 6080 5700 Holcombe et al. 1984
  naphthalene juvenile FT,M 7900 5700 DeGraeve et al. 1982
  naphthalene unknown FT,M 4900 5700 DeGraeve et al. 1980
  naphthalene juvenile FT,M 8900 5700 DeGraeve et al. 1980
  naphthalene juvenile S,M 1990 5700 Millemann et al. 1984
  1-methylnaphthalene juvenile S,U 9000 2200 Mattson et al. 1976
  acenaphthene juvenile FT,M 1600 2000 Holcombe et al. 1983
  acenaphthene juvenile FT,M 608 2000 Cairns and Nebeker, 1982
  acenaphthene juvenile S,M 1500 2000 EG&G Bionomics, 1982
  acenaphthene adult R,U 3700 2000 Academy of Natural Sciences, 1981
  acenaphthene juvenile S,M 3100 2000 Marine Bioassay Lab, 1981
  acenaphthene juvenile FT,M 1730 2000 Geiger et al. 1985
  fluoranthene juvenile S,M 95 150 Horne and Oblad, 1983
  fluoranthene juvenile S,M 77.1 150 Gendusa, 1990
Tanytarsus dissimilis naphthalene larvae S,U 12600 8500 Darville and Wilhm, 1984
  naphthalene larvae S,U 20700 8500 Darville and Wilhm, 1984
Tetrahymena elliotti 1-methylnaphthalene not applicable S,M 9400 5000 Rogerson et al. 1983
Xenopus laevis naphthalene larvae FT,M 2100 7600 Edmisten and Bantle, 1982
  benzo(a)pyrene unknown R 13400 a 18 Propst et al. 1997
Rhepoxynius abronius 2,3,5-trimethylnaphthalene unknown unknown 156 100 Ozretich et al. 1997
  fluoranthene unknown unknown 24 39 Ozretich et al. 1997
  naphthalene unknown unknown 10346 1400 Ozretich et al. 1997
  2,6-dimethylnaphthalene unknown unknown 192 220 Ozretich et al. 1997
  1-methylfluorene unknown unknown 45 200 Ozretich et al. 1997
  2-methylphenanthrene unknown unknown 67 51 Ozretich et al. 1997
  9-methylanthracene unknown unknown 32 56 Ozretich et al. 1997
             
a Observed LC50 greater than solubility. These data were not used in the comparison.      
     
b S= static; R = renewal; FT= flow-through; U = unmeasured or nominal; M = measured      


Table 3. Acute and chronic values used in the development of ACRs. Chronic endpoints are those effecting growth, reproduction or mortality of an organism.  
Species Chemical Chemical Code Acute LC50/EC50 (µg/L) Chronic Endpoint Chronic (µg/L) ACR Source  
 
                 
Cyprinodon variegatus Acenaphthene PAH 3,100 survival 710 4.36 Ward et al. 1981  
Daphnia magna Fluoranthene PAH 117 growth 24.5 4.78 Spehar et al. 1999  
  Phenanthrene PAH 117 survival and reproduction 96.4 1.21 Call et al. 1986  
  Biphenyl MAH 362   322 1.12 Gersich et al. 1989  
  Methyltertbutylether ALI 472,000 not specified 42,000 11.2 Mancini et al. 2002  
Mysidopsis bahia Acenaphthene PAH 466 reproduction 286 1.63 Horne et al. 1983  
  Acenaphthene PAH 460 reproduction 64.0 7.19 Thursby et al. 1989b  
  Fluoranthene PAH 30.5 survival and reproduction 14.4 2.11 Spehar et al. 1999  
  Fluoranthene PAH 40.0 survival and reproduction 15.9 2.52 U.S. EPA, 1978  
  Phenanthrene PAH 27.1 survival 8.13 3.33 Kuhn and Lussier, 1987  
  Pyrene PAH 28.3 reproduction 4.53 6.24 Champlin and Poucher, 1992a and b  
  Methyltertbutylether ALI 187,000 not specified 36,000 5.2 Mancini et al. 2002  
Onchorhyncus mykiss Phenanthrene PAH 50.0 survival and growth 6.32 7.91 Call et al. 1986  
Paratanytarsus species Acenaphthene PAH 2,040 survival, growth and reproduction 411 4.96 Northwestern Aquatic Sciences, 1982  
  Acenaphthene PAH 2,040 survival and growth 227 8.97 Northwestern Aquatic Sciences, 1982; Thursby, 1991  
Pimephales promelas Acenaphthene PAH 608 growth 405 1.50 Cairns and Nebeker, 1982; Thursby 1991  
  Acenaphthene PAH 608 growth 419 1.45 Cairns and Nebeker, 1982  
  Naphthalene PAH 7,900 survival and growth 620 12.7 DeGraeve et al. 1982  
  Fluoranthene PAH 69.0 survival and growth 15.0 4.60 Spehar et al. 1999  
  Methyltertbutylether ALI 980,000 not specified 289,400 3.39 Mancini et al. 2002  
Brachionus calyciflorus Xylene MAH 248,500   40,300 6.17 Snell and Moffat, 1992  
Ceriodaphnia dubia Toluene MAH 3,750   2,780 1.35 Niederlehner et al. 1998  
  Ethylbenzene MAH 3,200   1,680 1.90 Niederlehner et al. 1998  
Selenastrum capricornutum Benzene MAH 100,000 biomass growth 8,300 12 Mayer et al. 2001  
  Cyclohexane ALI 9,317 biomass growth 952 9.8 Exxon Biomedical Sciences, 1998  
  Methyltertbutylether ALI 491,000 biomass growth 103,000 4.8 European Commission, 2000  
  Pentane ALI 10,700 biomass growth 2,040 5.2 Exxon Biomedical Sciences, 1997  
Skeletonema costatum Ethylbenzene MAH 7,700   4,500 1.7 Boeri, R. 1987  
Onchorhyncus gorbuscha Naphthalene PAH 1,200 growth 380 3.2 Moles and Rice, 1983  
                 
Geometric mean           3.8    
                 
MAH: Monoaromatic hydrocarbon              
PAH: Polycyclic aromatic hydrocarbon            
ALI: Aliphatic hydrocarbon              
                 


Please click here for Table 4

Please click here for Table 5

Table 6. Summary of sediment data sets for acute toxicity from PAH mixtures    
Contaminant Source PAH Measurement Number of Samples Species Endpoint Reference
           
           
Laboratory prepared mixtures 4 Parent 7 Rhepoxynius abronius 10 day mortality Swartz et al. 1997
           
PAH contaminated sediment (Halifax Harbor, Nova Scotia) 13 Parent PAHs 11 Rhepoxynius abronius 10 day mortality Tay et al. 1992
         
           
PAH contaminated sediment (Curtis Creek, Virginia) 13 Parent PAHs 6 Leptocheirus plumulosus 10 day mortality DeWitt et al. 1992
    Eohaustorius estuarius    
           
PAH contaminated sediment (Eagle Harbor, Washington) 13 Parent PAHs 10 Rhepoxynius abronius 10 day mortality Tetratech, 1986
         
           
PAH contaminated sediment
(San Diego Bay, California)
13 Parent PAHs 54 Rhepoxynius abronius 10 day mortality Swartz et al. unpublished data
         
           
PAH contaminated sediment (Eagle Harbor, Washington) 13 Parent PAHs 8 Rhepoxynius abronius 10 day mortality Swartz et al. 1989
         
           
PAH contaminated sediment (Elliott Bay, Washington) 40 PAHs (parent and alkylated) 30 Rhepoxynius abronius 10 day mortality Ozretich et al. 2000
    Leptocheirus plumulosus    
           
           
Laboratory prepared mixtures 2 to 6 PAHs 12 Rhepoxynius abronius 10 day mortality Boese et al. 1999
           
PAH contaminated sediment (Asphalt) (Estonia) 11 Parent PAHs 8 Chironomus riparius 10 day mortality and growth Huuskonen et al. 1998
         
           
Dilutions of Spiked Diesel fuel 20 PAHs (parent and alkylated) 4 Schizopera knabeni 4 day mortality Fleeger and Lotufo, 1999
           
           
PAH contaminated sediment
(Exxon Valdez Crude Oil Spill)
39 PAHs (parent and alkylated) 470 Rhepoxynius abronius 10 day mortality Page et al. 2002
         
           
PAH contaminated sediment
(North Cape Oil Spill)
33 PAHs (parent and alkylated) 12 Ampelisca abdita 4 day mortality Ho et al. 1999
         


Table 7. Example demonstrating benefit of using adjustment factor to convert TU from 13PAH to Total PAH TU. Data are from Swartz et al. unpublished (Table D5).
                   
    No Adjustment factor for unmeasured PAHs        
  Observed Mortality (%) 13 PAH TU Toxic based on 13 PAH TU Correct prediction? 1 Was Criterion Protective? 2 Total PAH TU Toxic based on Total PAH TU Correct prediction? 1 Was Criterion Protective? 2
STATIONS
                   
STA 15-1 15.0 0.058 no yes   0.159 no yes  
STA 15-2 25.0 0.060 no yes   0.164 no yes  
STA 15-3 15.0 0.074 no yes   0.202 no yes  
STA 15-4 5.0 0.050 no yes   0.137 no yes  
STA 27-1 40.0 0.159 no yes   0.437 yes no  
STA 27-2 85.0 0.203 no no no 0.559 yes yes yes
STA 27-3 80.0 0.201 no no no 0.553 yes yes yes
STA 27-4 35.0 0.250 no yes   0.689 yes no  
STA 27-5 50.0 0.179 no no no 0.491 yes yes yes
STA 28-1 100.0 0.103 no no no 0.283 no no no
STA 28-2 95.0 0.151 no no no 0.417 yes yes yes
STA 28-3 100.0 0.089 no no no 0.244 no no no
STA 28-4 100.0 0.123 no no no 0.337 no no no
STA 28-5 100.0 0.092 no no no 0.253 no no no
STA 28-6 90.0 0.150 no no no 0.414 yes yes yes
STA 28X-1 15.0 0.084 no yes   0.232 no yes  
STA 28X-2 20.0 0.083 no yes   0.227 no yes  
STA 28X-3 35.0 0.111 no yes   0.304 no yes  
STA 28X-4 25.0 0.099 no yes   0.273 no yes  
STA 28X-5 25.0 0.100 no yes   0.276 no yes  
STA 33-1 0.0 0.007 no yes   0.020 no yes  
STA 33-2 5.0 0.006 no yes   0.017 no yes  
STA 33-3 10.0 0.005 no yes   0.014 no yes  
STA 33-4 5.0 0.006 no yes   0.016 no yes  
STA 33-5 30.0 0.021 no yes   0.057 no yes  
STA 40-1 10.0 0.014 no yes   0.038 no yes  
STA 40-2 0.0 0.012 no yes   0.033 no yes  
STA 40-3 15.0 0.016 no yes   0.044 no yes  
STA 40-4 15.0 0.012 no yes   0.033 no yes  
STA 40-5 15.0 0.016 no yes   0.044 no yes  
STA 13-1 10.0 0.076 no yes   0.209 no yes  
STA 13-2 20.0 0.173 no yes   0.476 yes no  
STA 13-4 0.0 0.098 no yes   0.270 no yes  
STA 13-5 5.0 0.090 no yes   0.247 no yes  
STA 13-6 5.0 0.244 no yes   0.672 yes no  
STA 11-1 10.0 0.023 no yes   0.065 no yes  
STA 11-2 10.0 0.021 no yes   0.058 no yes  
STA 11-3 15.0 0.020 no yes   0.055 no yes  
STA 11-4 0.0 0.016 no yes   0.044 no yes  
STA 11-5 25.0 0.018 no yes   0.049 no yes  
STA 11-6 15.0 0.021 no yes   0.057 no yes  
STA 44-1 0.0 0.053 no yes   0.145 no yes  
STA 44-2 0.0 0.046 no yes   0.128 no yes  
STA 44-3 10.0 0.061 no yes   0.167 no yes  
STA 44-4 0.0 0.040 no yes   0.110 no yes  
STA 44-5 0.0 0.045 no yes   0.125 no yes  
STA 44-6 5.0 0.051 no yes   0.141 no yes  
YAQ BAY 0.0 0.001 no yes   0.004 no yes  
STA28 0% 14.0 0.031 no yes   0.086 no yes  
STA28 13% 32.0 0.070 no yes   0.194 no yes  
STA28 22% 61.0 0.101 no no no 0.279 no no no
STA28 36% 81.0 0.149 no no no 0.410 yes yes yes
STA28 60% 93.0 0.268 no no no 0.738 yes yes yes
STA28 100% 98.0 0.608 yes yes yes 1.672 yes yes yes
                   
Number of overall correction predictions: 42       45  
Number of incidences criterion was not protective 1       8
                   
1 A correction prediction is where the observed mortality was greater then 50% and the computed TU was greater than 0.4.
2 yes = greater than 50% mortality observed and greater than 0.4 TU computed          
no = greater than 50% mortality observed and less than 0.4 TU computed    



             
Table 8. Chronic effects from single PAH sediment exposures
      Effect   TLM Predicted chronic (mg/g oc )  
Species Chemical Method a Observed Effect
(mg/g oc )
Reference
             
Schizopera knabeni fluoranthene S,M 10-d LOEC (grazing) 1200 4310 Lotufo, 1998
      10-d NOEC (grazing) 330    
      10-d LOEC (offspring prod.) 3133    
      10-d NOEC (offspring prod.) 1200    
Schizopera knabeni fluoranthene S,M 14-d IC25 realized reproduction 1230   Fleeger and Lotufo, 1999;
Lotufo, 1997
  phenanthrene S,M 14-d IC25 realized reproduction 1730 3560  
  phenanthrene S,M 10-d LOEC (hatching success) 3000    
  phenanthrene S,M 10-d NOEC (hatching success) 1470    
             
Coullana sp. fluoranthene S,M 10-d LOEC (grazing) 3133 1410 Lotufo, 1998
      10-d NOEC (grazing) 1200    
      10-d LOEC (offspring prod.) 8800    
      10-d NOEC (offspring prod.) 3133    
a S = static; M = measured          


Table 9. Summary of CTLBBs for different chemical classes      
  Chemical class correction    
Class of Compounds   (C L * )
      ( m mol/g octanol )
       
Baseline 0   119
Halogenated -0.339 0.458 54.3
Monoaromatic hydrocarbon (MAH) -0.109 0.778 92.3
Halogenated MAH -0.448 0.356 42.3
Polycyclic aromatic hydrocarbon (PAH) -0.352 0.445 52.7
Halogenated PAH -0.701 0.199 23.6
       
       
a see Appendix A      
       


Table 10. Chronic HC5 values for MAHs and PAHs for aqueous and sediment toxicity
           
    Aqueous Sediment
    HC5 HC5 HC5 HC5
Chemical log K ow (mmol/L) (mg/L) (mmol/kg oc ) (mg/kg oc )
           
benzene 1.943 30.892 2413 2.51 196
toluene 2.438 10.600 977 2.64 244
o-xylene 2.946 3.534 375 2.78 295
ethylbenzene 3.006 3.104 330 2.80 297
m-xylene 3.032 2.935 312 2.81 298
p-xylene 3.051 2.816 299 2.81 299
naphthalene 3.256 1.033 132 1.64 210
acenaphthylene 3.436 0.700 107 1.67 254
C3-benzenes 3.455 1.175 141 2.93 351
1-methylnaphthalene 3.781 0.332 47.2 1.73 246
C1-naphthalenes 3.788 0.327 46.4 1.73 246
2-methylnaphthalene 3.789 0.326 46.3 1.73 246
acenaphthene 3.878 0.269 41.5 1.75 269
fluorene 3.93 0.240 39.9 1.75 292
biphenyl 3.936 0.415 64.0 3.07 474
2-chloronaphthalene 3.94 0.108 17.5 0.80 131
1-chloronaphthalene 3.95 0.105 17.1 0.81 131
C2-naphthalenes 4.244 0.122 19.0 1.81 283
1,3-dimethylnaphthalene 4.257 0.118 18.5 1.81 283
methylbiphenyl 4.259 0.206 34.7 3.17 533
2,6-dimethylnaphthalene 4.27 0.115 18.0 1.81 283
1,2-dimethylnaphthalene 4.27 0.115 18.0 1.81 283
dibenzothiophene 4.34 0.099 18.2 1.83 336
1-methylfluorene 4.37 0.093 16.7 1.83 330
C1-fluorenes 4.37 0.093 16.7 1.83 330
anthracene 4.546 0.063 11.3 1.86 332
2,3,5-trimethylnaphthalene 4.57 0.060 10.2 1.87 318
2,3,6-trimethylnaphthalene 4.57 0.060 10.2 1.87 318
phenanthrene 4.584 0.058 10.4 1.87 333
dimethylbiphenyl 4.692 0.081 14.7 3.31 602
C3-naphthalenes 4.73 0.042 7.23 1.90 323
C2-fluorenes 4.819 0.035 6.80 1.91 371
C1-Dibenzothiophene 4.859 0.032 6.37 1.92 381
9-methylanthracene 4.996 0.024 4.59 1.94 374
1-methylphenanthrene 5.036 0.022 4.21 1.95 375
C1-phenanthrene/anthracene 5.037 0.022 4.20 1.95 375
2-methylphenanthrene 5.04 0.022 4.17 1.95 376
pyrene 5.126 0.018 3.64 1.97 398
fluoranthene 5.19 0.016 3.17 1.98 401
C4-naphthalenes 5.22 0.015 2.70 1.99 366
C1-fluoranthene/pyrene 5.257 0.014 2.93 1.99 431
C3-fluorenes 5.318 0.012 2.47 2.01 418
C2-Dibenzothiophene 5.332 0.012 2.44 2.01 426
3,6-dimethylphenanthrene 5.34 0.011 2.33 2.01 415
4,6-dimethyldibenzothiophene 5.45 0.0089 1.89 2.03 431
C2-phenanthrene/anthracene 5.455 0.0088 1.82 2.03 419
C2-fluoranthene/pyrene 5.557 0.0071 1.63 2.05 472
Triphenylene 5.63 0.0060 1.38 2.07 472
benzo(a)anthracene 5.744 0.0047 1.08 2.09 477
chyrsene 5.782 0.0043 0.99 2.10 478
C3-Dibenzothiophene 5.81 0.0041 0.92 2.10 475
C3-phenanthrene/anthracene 5.907 0.0033 0.729 2.12 467
Retene 6.12 0.0021 0.488 2.16 507
indeno(1,2,3-cd)pyrene 6.158 0.0019 0.530 2.17 600
C1-Chyrsenes/benzo(a)anthracene 6.19 0.0018 0.434 2.18 527
C4-phenanthrene/anthracene 6.357 0.0012 0.292 2.21 518
benzo(b)fluoranthene 6.341 0.0013 0.325 2.21 557
C3-fluoranthene/pyrene 6.384 0.0012 0.287 2.22 541
benzo(k)fluoranthene 6.4 0.0011 0.286 2.22 560
benzo(a)pyrene 6.409 0.0011 0.281 2.22 560
7,12-dimethylbenzo(a)anthracene 6.42 0.0011 0.278 2.22 570
Benzo(e)pyrene 6.447 0.0010 0.258 2.23 562
perylene 6.447 0.0010 0.258 2.23 562
C2-Chyrsenes/benzo(a)anthracene 6.593 0.0007 0.191 2.26 579
C4-fluoranthene/pyrene 6.687 0.0006 0.157 2.28 589
C5-phenanthrene/antracene 6.7 0.0006 0.147 2.28 567
C1-benzofluoranthene 6.743 0.0005 0.143 2.29 609
benzo(ghi)perylene 6.886 0.0004 0.109 2.32 641
C3-Chyrsenes/benzo(a)anthracene 6.972 0.0003 0.089 2.34 632
dibenz(a,h)anthracene 7.129 0.0002 0.065 2.37 660
C2-benzofluoranthene 7.2 0.0002 0.056 2.39 669
C4-Chyrsenes/benzo(a)anthracene 7.421 0.0001 0.035 2.43 692



Table 11. PAH NOEC toxicity data for various species (measured data considered only)
Chemical Species Endpoint Endpoint (µg/L) Reference
Naphthalene Daphnia magna 21-d NOEC - Reproduction 600 European Commission, 2003
  Oncorhynchus kisutch 40-d NOEC - Larval growth 370 Moles et al. 1981
  Pimephales promelas 30-d NOEC - Larval growth 450 DeGraveve et al. 1982
Acenaphthene Paratanytarsus sp. 26-d NOEC - Survival/Growth/Repro 295 Northwestern Aquatic Sciences, 1982
  Paratanytarsus sp. 26-d NOEC - Survival/Growth/Repro 164 Northwestern Aquatic Sciences, 1982
  Pimephales promelas 32-d NOEC - Growth 109 Academy of Natural Sciences, 1981
  Pimephales promelas 32-d NOEC - Growth 50 Academy of Natural Sciences, 1981
  Pimephales promelas 32-35-d - Growth 332 Cairns and Nebeker, 1982
  Pimephales promelas 32-35-d - Growth 345 Cairns and Nebeker, 1982
  Pimephales promelas 32-d NOEC - Survival 64 ERCO, 1981
  Americamysis bahia 35-d NOEC Survival 240 Horne et al. 1983
  Americamysis bahia 25-d NOEC Survival/Reproduction 44.6 Thursby et al. 1989
  Cyprinodon variegatus 28-d NOEC Survival 520 Ward et al. 1981
Phenanthrene Daphnia magna 21-d NOEC - Reproduction 180 Hooftman and Evers-de Ruiter, 1992b, c
  Daphnia magna 21-d NOEC - Survival 56 Hooftman and Evers-de Ruiter, 1992b, c
  Daphnia magna 21-d NOEC - Growth 32 Hooftman and Evers-de Ruiter, 1992b, c
  Daphnia magna 21-d NOEC - Reproduction 57 Call et al. 1986
  Brachydanio rerio 42-d NOEC - Growth 56 Hooftman and Evers-de Ruiter, 1992b, c
  Oncornhynus mykiss 90-d NOEC - Survival/Growth 5 Call et al. 1986
  Americamysis bahia 32-d NOEC Survivial 5.5 Kuhn and Lussier, 1987
Fluoranthene Brachydanio rerio 41-d NOEC - Growth 22 Hooftman and Evers-de Ruiter, 1992d
  Daphnia magna 21-d NOEC - Growth 17 Spehar et al. 1999
  Pimephales promelas 32-d NOEC - Survival/Growth 10.4 Spehar et al. 1999
  Americamysis bahia 31-d NOEC - Survival/Reproduction 11.1 Spehar et al. 1999
Pyrene Americamysis bahia 28-d NOEC Reproduction 3.82 Champlin and Poucher, 1992b
Benzo(k)fluoranthene Brachydanio rerio 42-d NOEC - Growth 0.48 Hooftman and Evers-de Ruiter, 1992a
Benzo(a)pyrene Brachydanio rerio 42-d NOEC - Growth 6.3 Hooftman and Evers-de Ruiter, 1992c



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Table A1. Revised Regression Coefficients for the Target Lipid Model            
Species Scientific Name Common Name Environment Habitat N k z a log (C L * ) SE (log (C L * )) (C L * ) SE (C L * ) b
Oncorhynchus gorbuscha Pink Salmon Both Water column 18 2.57 1.389 0.029 24.5 1.6
Rhepoxyinus abronius Amphipod Saltwater Infauna 7 3.59 1.494 0.158 31.2 12.5
Hyalella azteca Amphipod Freshwater Epibenthic 3 - 1.512   32.5  
Mysidopsis bahia Mysid Saltwater Epibenthic 29 2.30 1.535 0.087 34.3 7.1
Chlamydomonas reinhardtii Green algae Many different Variety 9 3.19 1.536 0.141 34.4 12.1
Chironomus tentans Midge Freshwater Infauna 3 - 1.599   39.7  
Eohaustorius estuarius Amphipod Saltwater Infauna 2 - 1.617   41.4  
Leptocheirus plumulosus Amphipod Saltwater Epibenthic, Infauna 4 5.49 1.634 0.203 43.1 23.8
Selenastrum capricornutum Green algae Freshwater Variety 24 2.41 1.687 0.091 48.6 10.5
Portunus pelagicus Flower crab, sand crab Saltwater Epibenthic 4 5.49 1.727 0.203 53.3 29.4
Ampelisca abdita Amphipod Saltwater Infauna 1 - 1.731   53.8  
Palaemonetes pugio Grass shrimp Saltwater Epibenthic, Water column 10 3.06 1.758 0.127 57.3 17.9
Oncorhynchus mykiss Rainbow trout Freshwater Infauna 47 2.13 1.820 0.067 66.1 10.4
Jordanella floridae American flagfish Saltwater Water column 18 2.57 1.827 0.101 67.1 16.3
Ictalurus punctatus Channel catfish Freshwater Epibenthic 7 3.59 1.864 0.149 73.1 27.4
Daphnia pulex Cladoceran Freshwater Water column 26 2.36 1.957 0.089 90.6 19.2
Cyprinodon variegatus Sheepshead minnow Saltwater Epibenthic, Water column 24 2.41 2.055 0.094 114 25.5
Daphnia magna Cladoceran Freshwater Water column 117 1.93 2.062 0.050 115 13.4
Pimephales promelas Fathead minnow Freshwater Water column 185 1.87 2.087 0.044 122 12.5
Danio rerio Zebrafish Freshwater Water column 18 2.57 2.099 0.101 126 30.5
Rana catesbian American bullfrog Freshwater Water column 5 4.47 2.101 0.174 126 57.1
Oryzias latipes Japanese medaka Freshwater Water column 5 4.47 2.104 0.174 127 57.5
Lepomis macrochirus Bluegill Freshwater Water column 70 2.04 2.117 0.059 131 18.1
Orconectes immunis Crayfish Freshwater Epibenthic 6 3.93 2.137 0.160 137 56.0
Oithona davisae Copepod Saltwater Epibenthic 9 3.19 2.151 0.142 142 50.2
Carassius auratus Goldfish Freshwater Water column 43 2.16 2.180 0.067 151 23.8
Leucisus idus melanotus Golden orfe Freshwater Water column 27 2.34 2.183 0.078 152 28.1
Xenopus laevis South african clawed frog Freshwater Water column 6 3.93 2.214 0.160 164 66.9
Alburnus alburnus Bleak Freshwater   7 3.59 2.234 0.147 171 63.3
Nitocra spinipes Copepod Freshwater   6 3.93 2.256 0.158 180 72.6
Neanthes arenaceodentata Annelid worn Saltwater Infauna 4 5.49 2.260 0.202 182 99.8
Tanytarsus dissimilis Midge Freshwater Infauna 10 3.06 2.264 0.132 184 59.9
Artemia salina nauplii Brine shrimp Saltwater   33 2.25 2.288 0.079 194 36.2
Lymnaea stagnalis Snail Freshwater   5 4.47 2.288 0.174 194 87.9
Gambusia affinis Mosquito fish Freshwater   8 3.37 2.310 0.147 204 75.4
Hydra oligactis Brown hydra Freshwater   5 4.47 2.329 0.174 213 96.6
Culex pipiens House mosquito not applicable   5 4.47 2.333 0.174 215 97.5
Scenedesmus subspicatus Green algae Freshwater   24 2.41 2.345 0.086 221 45.2
Ambystoma mexicanum Mexican axolotl Freshwater   5 4.47 2.388 0.174 244 111
Daphnia cucullata Cladoceran Freshwater Water column 5 4.47 2.394 0.174 248 112
Poecilia reticulata Guppy Freshwater   14 2.74 2.402 0.108 252 65.8
Aedes aegypti Yellow fever mosquito not applicable   5 4.47 2.415 0.174 260 118
Tetrahymena elliottii Ciliate Freshwater   10 3.06 2.435 0.129 272 86.5
Menidia beryllina Inland silverside Saltwater Water column 8 3.37 2.465 0.143 292 104
Chlamydomonas angulosa Green algae Freshwater   29 2.30 2.524 0.083 334 65.7
Chlorella vulgaris Green algae Freshwater   34 2.22 2.650 0.078 447 82.3
Ankistrodesmus falcatus Green algae Freshwater   9 3.19 2.699 0.139 500 173
Table A1. Revised Regression Coefficients for the Target Lipid Model (Continued)            
Species Scientific Name Common Name Environment Habitat N k z a log (C L * ) SE (log (C L * )) (C L * ) SE (C L * ) b
                   
Chemical Class corrections                
Aliphatic correction           0.000      
Alcohol correction           0.000      
Ketone correction           0.000      
Ether correction           0.000      
halogenated chemical correction         -0.339 0.032 0.458 0.034
PAHs correction           -0.352 0.053 0.445 0.055
Monoaromatic hydrocarbon correction         -0.109 0.034 0.778 0.061
slope           -0.936 0.015    
                   
a extratropolation constants for use in HC5/HC95 calculations (Aldenberg and Slob, 1993)              
b Standard errors are based on assumption that the estimation errors are gaussian. See Di Toro et al. 2000 for formulas.            

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