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GLERL AQUATIC CONTAMINANTS RESEARCH PROGRAM
General Background
Persistent contaminants introduced into the aquatic ecosystem bind to particles that either remain suspended in the water column (particle-associated contaminants) or settle into the sediment (sediment-associated contaminants). The particles slowly release contaminants into the water column, providing continued exposure. Aquatic bottom-dwelling organisms (benthos) in particular are exposed to these particle-associated contaminants through their contact with the sediment. Because the persistent contaminants are resistant to degradation and biotransformation, their introduction into the lower food chain acts as a point of entry for transfer up the aquatic food web, ultimately to fish, and threaten human health as well as the health of the ecosystem.
GLERL's Aquatic Contaminants research focuses on organic contaminants in the Great Lakes and coastal marine environments. Considerable progress has been made in the past 30 years reducing inputs of toxic contaminants to the aquatic environment through point-source control. This has resulted in detectable decreases in contaminant levels for both fish and deposited surface sediments, especially in the Great Lakes ecosystem. However, the success of point-source controls has elevated the relative importance of secondary contaminant sources such as atmospheric deposition, non-point-source runoff, and release from contaminated sediments. These are now the most prevalent sources of contaminants entering the aquatic food web. Toxic contaminants from secondary sources continue to be present in concentrations sufficient to cause environmental problems such as reproductive failure in lake trout and fish-eating birds and mammals, deformities in the offspring of fish-eating birds, and possible effects on human reproduction for heavy consumers of Great Lakes fish.
GLERL's past research focused primarily on the transport and fate of toxic organic contaminants in the ecosystem - the routes, pathways, and processes by which organisms are exposed to contaminants, and how they enter and move within the aquatic ecosystem. Our research in the early 1980s demonstrated the importance of sediments in the Great Lakes as long-term, capacitor-like sources of contaminants. We have shown that it can take in excess of 100 years for a particle-associated contaminant recently introduced into the Great Lakes to be buried to the point of removing it from the ecosystem. Because of the potential for long-term inputs from sediments, the factors that influence the bioavailability of sediment-associated contaminants to the lower food web have been a focus of GLERL's recent research. The lower food web is the major pathway for reintroduction of these contaminants into the aquatic community. Food web transport of contaminants in the Great Lakes has recently gained added significance because of the changes in ecosystem structure brought about by the invasion of nonindigenous species, especially the zebra mussel, in the late 1980s.
This research program has improved hazard assessment for contaminated sediments by revealing the limitations in existing methods for evaluating the hazard levels. Trying to assess the exposure of benthic organisms to contaminants in sediments using the standard approach, which is to measure the contaminant concentration in the external environment, is not satisfactory. The major issue continues to be the difficulty in evaluating the portion of the contaminant associated with sediment particles that is bioavailable to aquatic organisms. GLERL's research has shown that exposure to sediment-associated contaminants depends on the composition of the sediment, the characteristics of the toxicant, and the behavior and physiology of the organism. Benthic organisms exhibit a wide range of feeding behaviors, ranging from filtering the overlying water (most bivalves) to general sediment ingestion (oligochaete worms). As a result, not all benthos receive equivalent exposures. GLERL’s research continues to explore new methods for evaluating the bioavailability of sediment-associated contaminants. Because of the limited ability to interpret bioavailability and the need to determine the hazard associated with bioaccumulated residues in aquatic organisms, GLERL has begun a research program to evaluate the toxic response associated with the accumulated body residue. Using body residue as the measure of dose must be established not only for various chemical compounds but also for the duration of exposure, since increasing the length of exposure tends to reduce the total body residue required to produce a toxic response. This approach should provide direct information on the hazard of bioaccumulated residue, permit improved interpretation of the toxic action of mixtures of contaminants, and allow for improved risk assessment for persistent contaminants.
Last updated: 2004-03-25 mbl