The Sediment Bioavailability Initiative was a technology transfer project on the use and application of passive samplers to manage contaminated sediments. Several types of passive sampling methods have been developed under other SERDP and ESTCP projects that reliably measure concentrations of freely dissolved/bioavailable contaminants in sediments. These methods included solid phase microextraction (SPME) with polydimethylsiloxane (PDMS), low density polyethylene (LDPE), polyoxymethylene (POM) for hydrophobic organic contaminants (ER-1491; ER-200835), and diffusion gradient in thin films (DGT) for metals. While a considerable amount of support for passive sampling measures began to appear in the scientific literature, there was no single reference methods available for Department of Defense (DoD) and agency Remedial Project Managers (RPMs).
The objectives of this project were to: (1) produce a joint EPA, SERDP, and ESTCP Practices Manual that summarized the current state-of-the-practice for passive sampler methods and standard operating procedures for field and laboratory applications; (2) develop an Integrated Assessment and Management Framework that would provide potential users with a clear picture of how information obtained from passive samplers could be used to assess and manage contaminated sediment sites; and (3) provide outreach and scientific support for incorporation of reliable measures of bioavailability into remedial management decisions.
Management decisions for contaminated sediments at DoD sites are routinely based upon risks posed by bioaccumulation of contaminants from sediments into sediment-dwelling organisms. Once in the food chain, the contaminants can be transferred up through the food chain to fish, wildlife, and potentially human exposure through fish and shellfish consumption. Direct measures of contaminants that can be bioaccumulated from sediments lead to improved exposure assessments, decreased uncertainty associated with the risk characterizations, and increased confidence in remedial management decisions. Direct measures of bioavailable contaminants thus support the design, implementation, and long-term monitoring of contaminated sediments.
Passive samplers are devices that provide these direct measures. When placed into sediments or soils to extract chemicals, the sampling material “passively” extracts contaminants from the water phase within the sediment matrix (“porewater”). The passive sampler approach is based on the premise that the chemical activity of a hydrophobic organic contaminant (HOC) in sediment is directly proportional to its freely dissolved concentration in pore water (i.e., not associated with particulates or dissolved organic carbon). More importantly, the freely dissolved concentration is proportional to the bioavailable concentration. Thus the amount of chemical accumulated by the sampler can be used to calculate the amount that is freely dissolved in the porewater, and may be directly correlated to the exposure of biota.
The “technology” products for this work are two documents:
The User’s Manual is a joint ESTCP and EPA document written by the leading scientists in the field. The User’s Manual provides chapters covering use of POM, PDMS, and LDPE for hydrophobic organic compounds, DGTs for metals, field deployment and retrieval methods, selection and use of performance reference compounds, quality assurance and quality control procedures, and methods for laboratory analysis. Case studies, and examples of Standard Operating Procedures and Quality Assurance Project Plans are included.
The Remedial Project Managers Guide provides RPMs guidance on how to integrate passive sampling into management of contaminated sediment sites. Written as a companion document to the User’s Manual, the author team conducted extensive interviews with DoD and EPA RPMs, scientists, analytical laboratories, and practitioners. From that input, the Guide focuses principally on passive sampling of hydrophobic organic compounds (e.g., PCBs, dioxin/furans, PAHs) using POM, PDMS or LDPE. Topics covered include what do passive samplers measure, how can they be used in remedial investigations feasibility studies (RI/FS) or remediation, examples of use in the RI/FS and remediation process, a list of commercial laboratories that can do this work, and how to use the results in the decision-making process.
Sediment contamination remains a significant liability for the DoD, with overall liabilities estimated to approach $2 billion. Contaminants at DoD sites include a wide variety of compounds; PCBs, PAHs, various metals and metalloids, and military-unique compounds such as munitions constituents. With the publication of the User’s Manual and the Remedial Project Managers Guide, DoD site managers as well as federal and state regulators now have a referenced set of standard-operating-procedures to implement passive sampling at contaminated sediment sites. Passive sampling can now reliably and reproducibly be applied to remedial investigations, risk assessments, feasibility studies, and long-term monitoring of selected remedies.
Explicit consideration and acceptance of bioavailability for exposure assessment and management will make it possible for the DoD to use more cost-effective remedial methods that are based on reducing exposure by reducing bioavailability (treatment and reactive caps). Actual measures of exposure that incorporate bioavailability also generally lead to more focused remedial approaches (i.e., smaller areas or volumes requiring remediation). Preliminary estimates show that remedial costs for contaminated sediments can be reduced by orders of magnitude when these two aspects are combined. In addition, because explicit consideration of bioavailability can reduce the footprint of remediation and the potential harm of remediation (by using more passive treatment methods), DoD-impacted waterways may benefit from reduced disruption to natural resources.