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8. Contaminated Sediments
The EPA National Sediment Quality Survey (EPA 823-D-96-002, July 1996) recently analyzed the existing data on sediment quality to identify the national extent and severity of sediment contamination. Based on existing data bases, 75 percent of sediments sampled have a probability of an adverse human health or aquatic life effect. The study reported that 26 percent of the 21,000 freshwater and estuarine sampling stations throughout the United States were characterized as having sediment chemistry and toxicology with potential aquatic life or human health effects, while another 49 percent was categorized with intermediate probability of adverse effects.
The question for researchers is, "What are the extent, severity, and human health and ecological consequences of contaminated sediments?" In its study on relative risk, EPA's Science Advisory Board cited the problem of input of toxics to surface waters, to which contaminated sediments would contribute, as a moderate source of risk. EPA's Contaminated Sediment Management Strategy (EPA 823-R-94-001, August 1994) highlights ecological impacts and human health concerns expressed through the 1200 fish consumption advisories that were issued in the last year by various state agencies, in which potential consumers are warned of unsafe levels of toxic chemicals in fish and shellfish.
A major issue is the reliability of the risk characterization of contaminated sediments which supports proposed management action decisions. If assessment endpoints have not been demonstrated to reflect ecosystem conditions, expenditures of large amounts of funds for remedial activities may not be justified. EPA seeks research applications for conducting field validations of sediment quality criteria, validations of test methods, and validation of models for determining and assessing ecological effects of contaminated sediments.
Field Validation of Sediment Quality Criteria
Sediment quality criteria based on equilibrium partitioning make specific predictions of concentrations in sediments below which no effects should be seen and above which effects may be seen. The two chemical classes for which sediment quality criteria have been proposed are non-ionic organic chemicals and the cationic metals, cadmium, copper, nickel, lead, and zinc. A mixture model has been proposed for PAHs and metals. Studies of criteria levels for chemical groups need to be conducted to determine the degree of protection provided. It should be possible to examine field sites and to address multiple chemicals to determine if methods to predict total toxicity can be related to aquatic system communities.
Measures of ecological effects which are needed include in situ sediment toxicity, disruption of benthic communities, and elevated body burdens in organisms. Chemical measurements in pore water may be a useful determination. For metals, seasonal variations may be important since acid volatile sulfide levels are known to vary seasonally. The concern is that sediments would exhibit toxicity during the period of low acid volatile sulfides. Also, flux to overlying water could violate water quality criteria. The comparison of ecological effects to calculated sediment quality criteria will require the collection of additional chemical and flux data to provide interpretive information.
Field Validation of Chronic Toxicity Tests
With most laboratory tests the question of lab-to-field extrapolation becomes a major issue. Toxicity assessment methods for contaminated sediments have been proposed by EPA for acute toxicity, and, within a short time, chronic test methods will be made available. Field studies should be done to obtain data sets from toxicity tests and population studies obtained on the same spatial and time scales. Studies are needed especially to relate chronic toxicity tests for benthos-associated organisms to populations in the marine and freshwater environments.
Approximately $2 million is expected to be available in FY 97 for awards in this program. Proposals in the $100,000 to $150,000/year range are encouraged. Duration of awards may be up to 3 years.