Land: Contaminated Sites

Contaminated sediments research at the Division focuses on the ecological effects of sediment-associated contaminants, particularly as they are assessed and managed under the EPA's "Superfund" program. All but the most labile of environmental contaminants generally end up in association with sediment to some degree, making contaminated sediments an essential piece of the challenge for assessing risk. The interaction of chemicals with sediments can affect exposure and associated risk in several ways. Sediments can serve as a sink for some contaminants, sequestering them for eventual burial and removal from the biotic zone. Alternatively, contaminants can become a source of exposure to organisms directly exposed to sediment or to those indirectly exposed through the food chain, or both. Finally, sediments serve as a source of contamination to overlying water. Although the sediment environment may appear static at any given point in time, natural or anthropogenic disturbances can disrupt the sediment bed, changing both the spatial and temporal nature of exposure.

Persistence and hydrophobicity are two properties that increase the propensity of chemicals to accumulate in sediment; these same properties are those that tend to encourage bioaccumulation of chemicals in aquatic organisms. Risks from sediment-associated chemicals can be broken down into two basic types: direct effects on organisms in contact with sediment, and indirect effects via chemicals released into the water column or transferred through the food chain.

Contaminated sediments research within the Division focuses on developing tools to assess effects from bioaccumulative chemicals. Two of the most common assessment tools used for these types of chemicals are bioaccumulative factors (BAFs) and biota-sediment accumulation factors (BSAFs), which express the concentration of chemical in organism tissue relative to the concentration in water or sediment, respectively. While they are often measured empirically in specific systems being assessed, they can also serve as tools to predict bioaccumulation from measured concentration in water/sediment or predicted values from fate and transport modeling. BAF and BSAF approaches developed in the Division are now being used to measure and predict accumulation of chemicals in aquatic life and aquatic dependent wildlife, which are then used to calculate risks in humans. This work has been used by the Office of Water to develop both human health and ecological water quality criteria.

Though BAFs and BSAFs are often thought of as empirical indices determined from site-specific measurements, these techniques can be applied more broadly. The Division is pursuing these hybrid empirical/mechanistic approaches for assessing bioaccumulation, and also has been engaged in large scale modeling of persistent bioaccumulative chemicals in fish in the Great Lakes. An integrated fate/transport/bioaccumulation model developed by the Division has been used to identify the key sources of PCB exposure through time and to model many different remedial scenarios. From this analysis, one can select the alternative that provides the best balance of remedial costs and magnitude (or acceleration) of resulting environmental improvement.

Other research on contaminated sediments deals with developing tools to diagnose the cause of toxicity of field samples, which is captured in the Division's Water Quality research area.

Abstracts of Contaminated Sites Ongoing Research Projects

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