CICEET Progress Report for the period 3/16/06 Through 9/15/06

Project Title: An in situ sediment porewater sampler for organic micropollutants based on solid phase microextraction (SPME) technology
Principal Investigator(s): Keith A. Maruya, Eddy Y. Zeng and Steven M. Bay
Project Start Date: 9/1/05 (anticipated); 11/14/05 (actual)

Figures

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5a

Figure 5b

Tables

Table 1

Table 2

Table 3

Tasks to meet objectives
(1) Procure native and radiolabled HOCs, prepare spiking solutions, obtain and process field-collected sediments, spike with target HOCs, and equilibrate for a minimum of 60 d
(2) Design and perform spiked sediment experiments to determine the time to equilibrium for SPME prototype sampler under dynamic and static conditions
(3) Design and perform experiments to examine the relationship between spiked sediment and porewater concentrations under static conditions
(4) Carry out equilibrium calibration experiments to compare K_f values for different SPME PDMS coating thicknesses (7, 30 and 100µm)

Progress on Tasks
Tasks 1, 2a/b and 3 were completed and results presented herein.

Have the results/data gathered during this reporting period changed the project objectives when compared to your original proposal?
The results/data gathered during this reporting period have not changed the project objectives stated in the original proposal.

Dissemination activities during this reporting period
Project-related presentations:
(1) Invited seminar “Passive in situ samplers for dissolved and sediment-associated organic contaminants”, Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA, September 8, 2006. (~25 participants)

Manuscripts:
(1) Yang, ZY, Zeng EY, Xia H, Wang JZ, Mai BX, Maruya KA. 2006. Application of a static solid-phase microextraction procedure combined with liquid-liquid extraction to determine poly(dimethyl)siloxane-water partition coefficients for selected polychlorinated biphenyls. J Chromatogr A 1116:240-247.

(2) Yang ZY, Zeng EY, Maruya KA, Mai BX, Ran Y. Predicting organic contaminant concentrations in sediment porewater using solid phase microextraction. Accepted by Chemosphere

Outreach Activities:
(1) Attended/participated in workshop titled Evaluating Approaches and Technologies for Monitoring Organic Contaminant Loading, Alliance for Coastal Technologies Workshop, University of Michigan, Ann Arbor, MI, June 11-13, 2006.

Contact with End Users:
This project is incorporated into the 2006-07 SCCWRP Draft Research Plan, and was presented to SCCWRP’s Technical Advisory Group at their quarterly meeting on 8/9/06. Group members represent large POTWs, regulatory agencies and other primary stakeholders involved with the regulation and management of organic pollutants in contaminated sediments. (~30 participants).

Student activity:
This project is partially supporting the dissertation of Ph.D. candidate Z. Yang of the Guangzhou Institute of Geochemistry/Chinese Academy of Sciences (GIGCAS).

Difficulties
None.

Data Generated to date
Preparation of spiked test sediments. Intertidal sediments from the Newport Bay (NB) (California, USA) and Pearl River (PR) estuaries (Guangdong Province, China) were collected, sieved, homogenized and analyzed for several parameters (TOC, DOC, native HOC concentrations and black carbon content). For the PR sediment, sediment-seawater slurries (6:4 w:w) spiked with native HOCs (Table 1) at 50 to 100 ng/g (each compound) were prepared in a large glass desiccator (15 L) using a mechanical shaker. Slurries preserved with sodium azide (to minimize biotransformation) were aged for six months in the dark at 10°C and stirred weekly. For NB sediment, 5L aliquots were spiked at nominal concentrations of 50, 100, 500 and 1000 ng/g (each analyte) in sealed glass bottles that were homogenized daily on a roller table for two months. After equilibration, spiked sediments were kept in the dark at 4°C until use.

Determination of time to equilibrium. In order to determine the characteristic time to equilibrium for target HOCs in sediment-water systems, we exposed 100 _m PDMS-coated SPME fibers to spiked PR slurries in replicated glass containers. Exposures were performed with and without agitation (“dynamic” and “static”, respectively) for 20, 30 and 60 days. Results under dynamic conditions (Figure 1) indicate that equilibrium concentrations were reached after 20 days for 7 of 13 project analytes. Concentrations of three of the six remaining compounds -- PCB153, 180 and benzo[a]pyrene ­ stabilized after 30 days. This is in contrast to previous results in our lab that suggested K_f values stabilized after 16 days. One possible reason for this difference is that the dynamic extraction process employed herein temporarily depleted the HOC available for partitioning onto the SPME fiber. This would occur if the chemical uptake rate by the fiber was more rapid than the desorption rate from the sediment matrix, resulting in a longer time for a given HOC to reach equilibrium with the PDMS coating. Concentrations of o,p’- and p,p’-DDT decreased and/or were not detected at longer extraction times. Because these compounds did not suffer significant losses in sediment over time (% recovery was 69.6% and 66.8%, respectively at 60 d), it is plausible that transformation in sediment porewater was more rapid than their respective rates of desorption from sediment, a theory supported by the observed increase of p,p’-DDE in fibers with increasing extraction time (Figure 1). It is well known that DDT degrades to DDE under aerobic conditions, likely to have been induced by the agitation provided in the slurries and the imperfect sealing of slurry containers. Because of this apparent transformation, however, we cannot ascertain the extent of SPME sorption for p,p’-DDE.

A comparison of SPME-derived water concentrations in slurries maintained under dynamic or static conditions for 20 days indicated that extraction kinetics in the static experiment was much slower (Figure 2) for the majority of target analytes. This suggests that a 20-day static extraction is insufficient to reach equilibrium for the more hydrophobic analytes, and that a different approach, e.g. a longer time series experiment, is needed to determine the appropriate time to equilibrium for all analytes of concern.

Relationship between sediment and SPME-measured porewater concentrations. To determine if our prototype sampler design (Figure 3) would in practice sense a gradient of porewater concentrations, we exposed two different sizes of our samplers to spiked, aged NB sediments. Duplicate 0.8 cm dia x 15 cm L (V = 7.5 cm³; “small’) and a single 1.3 cm dia x 15 cm L (V=20 cm³; “large”) samplers were placed in 500mL spiked sediment in 1L glass graduated cylinders and removed for analysis after a 60d exposure period. Porewater concentrations measured by SPME (C_w,spme) were compared with those measured by liquid-liquid extraction (C_w,LLE) of the centrifugate isolated at the end of the experiment. The difference between C_w,spme for the small and large samplers was negligible, and more importantly increased with increasing spiked (nominal) sediment concentrations (C_spiked) for all target analytes (Figure 4). C_w,spme also appeared to be correlated with C_w,LLE (Figure 5a and Figure 5b), although the magnitudes were clearly different for lower concentrations in sediment (lower panel). In each case, however, C_w,spme -- proposed as the dissolved or “bioavailable” fraction in porewater -- is less than the corresponding C_w,LLE, which would include HOCs bound to dissolved organic matter (DOM) as well as the truly dissolved fraction and thus can be thought of as the “total” porewater concentration.

Effect of SPME coating thickness on PDMS-water distribution coefficients (K_f). K_f values for the target HOCs were determined for SPME fibers coated with 7, 30 and 100µm PDMS using (water only) batch equilibrium experiments (Table 2). Except for p,p’-DDD, K_f values for the 7 mm thickness were universally greater than those for 100 mm. For PAHs, there appears to be a decreasing trend in K_f with increasing coating thickness. For all other analytes, however, the 30mm values were highest. It is also clear that the variability in these determinations is greater (roughly 2-fold) for the thinnest (7 mm) coating. As our previous data suggested little or no coating thickness dependence on K_f, and that accurate estimation of this parameter is key to high quality aqueous phase measurements using SPME, we plan to investigate this matter further using radiolabled analogs (see also Project Objectives for Next Reporting Period).

Project Objectives for Next Reporting Period

Objectives
(1) Finalize and validate fiber calibration parameters (K_f, t_eq) for different PDMS coating thicknesses (7, 30 and 100 mm)
(2) Explore strategies to minimize sampler exposure times in situ
(3) Create a uniformly aged test sediment spiked with target hydrophobic organic compounds (HOCs) for Year 2 bioaccumulation/bioavailability experiments
(4) Document findings in peer-reviewed literature

Work plan to Meet Objectives
(1) Design and initiate experiments to establish K_f and t_eq under static conditions with different SPME fiber PDMS coating thicknesses, using native target HOCs and radiolabled analogs
(2) Determine forward and reverse SPME sorption kinetic parameters in time series experiments using “pre-loaded” fibers
(3) Initiate preparation of spiked sediments for Year 2 bioaccumulation studies
(4) Draft outline for manuscript(s) summarizing Year 1 findings

Dissemination Objectives for next reporting period
(1) Presentation of project results at Fourth International Conference on Remediation of Contaminated Sediments (Jan 22-25, 2007)
(2) Submission of manuscript(s) documenting fiber/sampler calibration results
(3) Continued contact with multiple end users through SCCWRP’s Technical Advisory Group
(4) Participation in Annual CICEET PI Workshop

Overall Project Timeline Update
See Table 3.

Expenditures
A total of $130,492 has been encumbered by SCCWRP since project inception (11/14/05) to 08/31/06 (Expenditures for the period 08/31/06 to 09/15/06 were not available at time of press). A total of $57,000 was transferred to co-PI Dr. E. Zeng at the Guangzhou Institute of Geochemistry, including $12,000 to cover the stipend of Dr. Zeng’s Ph.D. student (Ms. Z. Yang) who is working on the project as a visiting scholar. Because of the nearly 3-month delay in the original project start date, the expenditures to date are in the range anticipated for the work accomplished in this reporting period. We anticipate an increased rate of encumbrance over the next reporting period in support of the multiple tasks planned.

End User Advisor Feedback
End User Advisor: Chris Beegan
Organization: State Water Resources Control Board, California
Location: Sacramento, CA
Phone number: 916 341 5577
E-mail: cbeegan@waterboards.ca.gov

1) At this stage, what are the potential applications for this research? Please discuss how you and others could potentially use the technology. A SPME porewater sampler would provide a direct measure of the potential bioavailability of sediment-associated organic pollutants. This measure could be incorporated into guidelines for sediment quality objectives currently under development for the State of California, as well as for assisting in the interpretation and promulgation of guidelines for other regulatory/remedial actions associated with contaminated sediments (e.g. dredging). Project results to date are promising, and suggest that this technology could become a valuable tool for sediment quality assessment and stressor identification.

2) What, if anything, has changed about this project's potential applicability since the last reporting period (not applicable to the first Progress Report)? Demonstration that the SPME-based sampler prototype can sense increasing levels of organics in porewater in real (albeit spiked) sediments and correspondence with alternate porewater measurements (i.e. LLE) indicates that the overall concept and design is sound. While the State Water Board is moving forward with a sediment quality control plan for bays and estuaries, sediment managers are still hampered by the lack of tools that provide an accurate measure of bioavailability. These results suggest that SPME may significantly improve our ability to determine which chemicals could potentially harm aquatic life. Staff at the State Water Board believes that developing sound and reproducible measures of bioavailability is critical to the long-term success of sediment quality management and restoration.

3) Do you see any key challenges that the researchers may want to address or keep in mind? The recent finding that pre-calibration may be coating thickness dependent will possibly diminish the simplicity and ultimately the cost-effectiveness of SPME for sediment quality studies. Also, the required deployment/response time in situ (Year 3) will prove to be a critical factor in the overall utility of this technology.

4) Does this report offer you enough information to adequately address the above questions? Yes

5) Other feedback? These preliminary findings are very encouraging.