Progress Report for the Period: October 15, 2008 to April 15, 2009

Principal Investigators: Dr. Dr. Rainer Lohmann

Accomplishments since Last Detailed Report:
Scheduled Tasks:
Our task within the wider ‘Oil-in-Ice: Transport, Fate, and Potential Exposure’ project is to detect compounds released from oil spills, with a focus on polycyclic aromatic hydrocarbons (PAHs). In more detail, we will compare and validate two different passive samplers, namely polyethylene (PE) sheets with solid-phase micro extraction (SPME) fibers. These passive samplers take up the analytes of interest by diffusion, thus only accumulating the biologically available fraction. Our tasks involve studying the equilibrium distributions of PAHs under a wide range of temperatures and salinities, as would be typically found in ice-infested regions.

Our general objectives for this project were to:
(i) Verify the equilibrium partitioning constants for a selection of the components listed in Table 1 of the proposal at cold temperatures and high salinities for PE and SPME samplers, and
(ii) Include performance reference compounds (PRCs) in SPME/PE matrix to enable the use of PE/SPME samplers in the kinetic uptake phase in the field.

The following tasks were scheduled for the time-frame October 2008 – April 2009:
a) Reproducibly load passive samplers with PRCs;
b) Establish loss rates for performance reference compounds (PRCs);
c) Equilibrium and kinetic validation of equilibrium constants in the field; and
d) Beginning of the cold water and salinity experiments.

Progress on These Tasks
Progress has been made on all objectives, specifically general objective (ii) of impregnating the SPMEs with PRCs, which is complete. For the remaining tasks included in this scheduled time frame, advances have been made. Once the passive samplers were reproducibly loaded with PRCs, other work could begin. The loss rates for the PRCs were obtained under laboratory conditions. Equilibrium and kinetic validation of equilibrium constants were investigated in the field and the deployment of the samplers is complete, however data analysis is still on going. The first of the cold water and salinity experiments is complete, and new experiments have begun.

Difficulties Encountered:
A minor difficulty was experienced with gaining reproducible concentrations of the PRCs in the passive samplers. Unfortunately, work could not progress until this task was accomplished. The problems were overcome with three modifications of our method. The SPMEs/PEs were exposed to the PRC solution for an extended period of time. During this time of approximately two weeks, the SPMEs/PEs were agitated on a shaker table or stir plate. Another step was included to obtain reproducible results for the SPMEs. A small rack was constructed to separate the SPMEs and expose maximum surface area to the PRC solution. This rack (Figure 1) was also used in other laboratory and field experiments.

The deployment of SPMEs in the field posed another challenge. Though SPMEs are excellent passive samplers for their quick equilibration time, they propose a unique problem to deploy in the marine environment without loss of the samplers. The rack constructed for the SPMEs was combined with a housing of copper pipe drilled out to allow sufficient water flow. The copper housing performed well (Figure 2), however the rack was not built with stainless steel wire and eroded over time in the marine environment. SPMEs were lost during recovery process, as only a few SPMEs had to be removed from each housing at different sampling periods and environmental conditions such as wind complicated this process. Other SPMEs were lost as the wire rack eroded over time. For the next deployment of the SPMEs in the field, one copper housing will be used for each deployment period or replicate, so that the entire housing can be recovered and SPMEs removed from the housing in the laboratory. Also, the wire rack will be constructed of stainless steel wire, so as not to erode in the marine environment.

Preliminary Data, Discussion:
1.) Establish loss rates for performance reference compounds (PRCs)

Once the passive samplers could be reliably and reproducibly loaded with PRCs, other work could commence. The first task accomplished was investigating the loss rate of the PRCs. PRCs are compounds not found in the environment, therefore there is only a loss of these compounds from the passive sampler. The selected PRCs are chemically and structurally similar to the compounds of interest, hence their loss rate is assumed to be similar to the uptake of the compounds of interest. Thus, PRCs can be employed to infer the extent of equilibrium of the compounds of interest reached after a given deployment duration. The loss rate (k_e) tends to decline with increasing molecular weight and increasing passive sampler-water partitioning coefficients (log K_passive-w) and can be calculated through assessing the concentrations of the PRCs at time zero (prior to deployment, C_SPME⁰) and after exposure time t (hours, C_SPME^t)) as follows:

(1)
Based on a correlation between log K_spme-w and k_e, we can predict the times necessary for other PAHs to reach 95% equilibrium in the field under turbulent conditions, or more specifically the percent of equilibrium reached. This time period was found to range from a less than an hour for naphthalene-d8 to few days (60 hours) for PAHs up to benzo(a)pyrene-d12 (Figure 3), but longer times are needed for PAHs with molecular weights greater than 264.


Figure 3: Percent lost of PRCs over a deployment period of 108 hours.

Experiments to investigate loss rates under static conditions have been completed; however they are still undergoing data analysis.  Knowing the loss rates in both turbulent and static environments will allow us to predict the deployment time necessary for compounds from oil spills to equilibrate with passive samplers in the field with varying flow conditions.

2.) Equilibrium and kinetic validation of equilibrium constants in the field
Beginning March 26, 2009, SPMEs and PEs were deployed in Narragansett, RI and recovered after various periods of time.  Samples were collected after 1, 2, 4, 7, and 14 days.  Water samples were collected on days 7 and 14 to provide a comparison of the dissolved concentrations of PAHs in the water column.  Data was to be collected after 28 days deployed, however as discussed previously, some SPMEs were lost during recovery.  Data is currently being analyzed.

3.) Beginning of the cold water and salinity experiments
The first cold water and salinity experiment conducted was at -4°C and a salinity of 100 psu.  Water was prepared with Instant Ocean® to desired salinity.  Rough salinity measurements were performed with a calibrated refractometer and more precise measurements were achieved with chlorinity titrations.  Prepared water ranged from 98.60 to 100.54 psu.  Temperature in chamber remained constant at -4°C, with the exception of a brief thaw period during each day where temperatures would increase to approximately 0°C.  To minimize equilibration times, experiments were constantly agitated; SPME samples were placed on a shaker table, while the PE samples were on stir plates.  One blank was prepared for each sampler with six replicates for each passive sampler.  After three, four and five weeks, two samples of each sampler were removed from the chamber and extracted to evaluate percent equilibrium reached.

Equilibrium partioning coefficients (K_passive-w) were calculated using a dissolved water concentration assuming no losses occurred.  For the three different sampling time periods, the log K_passive-w were not significantly different from each other for either the SPMEs or the PEs (Figures 4& 5).  The K_passive-w values are plotted against the log of the octanol-water partitioning coefficients (Kow), which is a good proxy for apolar organic compounds, such as PAHs.  In Figure 4, SPME-1-C-3wk sample was discarded, as it was proven to be an outlier for the majority of the PAHs of interest.

The full range of PAHs were included in Figures 4 and 5, from phenols to benzo(g,h,i)perylene.  The lower molecular weight phenols were removed from the trend line of K_passive-w versus K_ows as SPMEs are apolar, but octanol is not. A more appropriate fit for the phenol compounds would be to graph the K_passive-w against a hexadecane-water partitioning coefficient, and then a trend line with a slope of one could be achieved.  The higher molecular weight compounds such as benzo(g,h,i)perylene tended to be below the expected line, causing an overall decrease in the slope.  This occurs because the higher molecular weight compounds have a higher affinity to absorb to dissolved organic carbon (DOC). Correcting for the binding of the PAHs to DOC will increase the derived Kpassive-w, and increasing the overall slope of the trend line accordingly. As of yet, the DOC content of the water has not been assessed, but will be in the near future to address this problem.

When (log K_passive-w) are plotted for PAHs with log K_ow < 5.5 (without the phenols), the data points fit a trend line with a slope ~ 1, similar to previous studies (Figure 6). Our derived log Kpassive-w are higher than previously reported values for PAHs at higher temperatures and no salinities, supporting our premise that we need to take both into account when using passive samplers in cold and hypersaline environments.


Figure 4: Measured log K_spme-w of PAHs versus their log K_ow

Figure 5: Measured log K_pe-w of PAHs versus their log K_ow




Figure 6: Measured log K_spme-w of PAHs versus their log K_ow (3-5.4)

Discussion and Importance to Oil Spill Response/Restoration
The study directly addresses the need for exposure and injury assessment tools for oil spills in cold climates. The use of passive samplers is a fast and cheap method to detect PAHs, one of the most toxic groups of compounds present in oil. In this project, we characterize two different passive samplers under varying temperatures and salinities as tools to detect PAHs from oil spills in ice. They will be used by project collaborators to detect the transport and fate of oil-derived PAHs in ice cores.

Manuscripts, Reports, Presentations
An introductory seminar, “Verification of Equilibrium Partition Coefficients of Solid Phase Micro-Extraction (SPMEs) Fibers in Hyper-saline, Arctic Conditions”, was given by Pamela Luey to the URI-GSO community on March 23, 2009.

Personnel
The following personnel has worked on the project during this reporting period:
1) Dr. Rainer Lohmann (PI, URI-GSO) – general oversight of the project, instruction of students in their work, ordering of standards/equipment, liaison with other project partners.
2) Pamela Luey (graduate student, URI-GSO) – spiking of PE samplers, preparation of standard solutions, PRC and instrument calibration curves.
3) Dave Adelman (laboratory technician, URI-GSO) – support of Pamela Luey in engineering and construction of field deployment devices.

Tasks for the Next Detailed Reporting Period:

Tasks and Activities for Next Reporting Period to Meet Project Objectives.
These tasks to be completed by the next reporting period are:          
a) Continue to perform cold water and salinity experiments;
b) Obtain dissolved organic carbon concentrations of the sample water;
c) Analyze field deployment data of SPMEs and PEs in Narragansett Bay, RI.

Concerns or Difficulties Anticipated:
The problems encountered in gaining reproducible PRC concentrations within the passive samplers as well as delay in use of the chamber has caused a delay in the overall anticipated start time of the cold water and salinity experiments. Initial plan included a four week equilibration period of the samplers at each temperature. With the conclusion of the first experiment, it seems that three weeks is an optimal amount of time to reach equilibrium and hopefully will bring us back onto the projected schedule.

Schedule:
The original timeline for URI’s project part was as follows:
The current schedule means that we are slightly behind the original timeline. Our projected tasks bring us back into the projected timeline.