Contaminated Sediment Screening Levels for Superfund Sites

Objective/Intended Use

The purpose of this research project is develop a methodology for deriving screening levels of sediment contaminants that would be applicable to Superfund sites. These screening levels would be used to screen sites from further data collection/risk assessment activities based on the levels of contaminants present in sediments. This project involves a synthesis of data and models on the bioaccumulation of sediment contaminants and associated exposure and effects to ecological receptors. This work supports the research objectives identified by OERR for improving risk assessments involving contaminated sediments.

Abstract

Sediments serve as the dominant sink for many chemical pollutants, in particular those which are highly hydrophobic and have a greater tendency to bioaccumulate in aquatic food webs. A variety of toxicological benchmarks and laboratory bioassays have been developed for assessing the direct toxicity of sediments to aquatic biota (e.g., OW draft Equilibrium Sediment Guidelines, NOAA's ERLs & ERMs values, sediment toxicity tests, etc.). However, these approaches focus on benthic organisms and/or exposure via pore water. As a result, they do not consider indirect toxicity to predatory ecological receptors that can result from dietary exposure of contaminants (i.e., food web transfer). For poorly metabolized, highly hydrophobic chemicals (e.g., PCBs), food web transfer can be a critical exposure pathway for higher trophic level receptors including aquatic- dependent wildlife. This concern is common to many of the Nation's Superfund sites. The proposed research activity would support the development of Contaminated Sediment Screening Levels (CSSLs) which are analogous to the draft soil Eco-SSLs developed by OERR, ORD, and others. The intent of the CSSLs would be to provide a tractable method for determining whether potential ecological risks from contaminated sediments in a given locale warrant additional concern (i.e., additional data gathering and assessment). Not unlike other screening values, the CSSLs would be conservative in their assumptions and treatment of variability and uncertainty. Thus, a CSSL would not be equated with a sediment criterion nor would it be used to determine clean up levels/remedies. Rather, it would represent a value (or an algorithm) that could be used to screen sites from further (and costly) information gathering. For highly bioaccumulative contaminants, the approach would build on mechanistic bioaccumulation models that have been developed and previously applied for the purposes of setting human health and wildlife water quality criteria in the Office of Water. These models inherently include chemical partitioning to sediments in their structure. The effort would initially focus on nonionic organic chemicals, where such models have been developed and more widely evaluated. This effort involves partnerships between staff from NCEA, NHEERL, OERR and OW. The benefits of such CSSLs includes standardizing how potential risks of contaminated sediments are initially assessed at Superfund sites and the basis for deciding whether additional data gathering and assessment are needed. Currently, no standardized method exists for screening risks of contaminated sediments via bioaccumulation in aquatic food webs. Project was not supported by OSWER and work was stopped in the early stages.

Project Status

This project began in late FY2002. NCEA's responsibility involves producing a series if issue papers which critically examing the methods and data available for deriving CSSLs. The topics of these issue papers include: 1) identifying/prioritizing chemicals for CSSL derivation, 2) identifying and selecting target ecological receptors, 3) selecting and integrating bioaccumulation models, 4) feasibility of probabilistic-based CSSLs, and 5) evaluating options for setting the level of protection of CSSLs. These issue papers will serve to support an interAgency workgroup on the development of CSSLs. Issue papers are expected to be complete by early calendar year 2004.

Project Start Date

10/01/2002

Project Completion Date (Actual/Projected)

09/30/2004