HA5 Bioaccumulation and Biomagnifications
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() Challenges to conventional wisdom regarding biomagnification in aquatic food webs.

Durda, J.1, Williams, L.2, Preziosi, D.1, 1 Integral Consulting Inc., Annapolis, MD, USA2 Integal Consulting Inc., Seattle, WA, USA

ABSTRACT- Biomagnification is the process whereby chemical concentrations increase with increasing trophic level within a food web. In aquatic systems, the conventional assumption is that biomagnifying chemicals will be highest in predatory species located at the top of the food web, and lowest in herbivorous or detritivorous species located near the bottom. This relationship routinely holds in situations where contamination by biomagnifying compounds is spatially widespread, such as in the Great Lakes. In situations where contamination is more localized, however, such as often occurs at waste sites or in association with point source discharges, biomagnification may not be an important phenomenon. We recently examined biomagnification in a Texas bayou where historical releases of DDT resulted in localized contamination of aquatic sediments. DDT is an organochlorine compound known to biomagnify in aquatic food webs. We evaluated DDT accumulation in juvenile striped mullet (primarily a bottom-feeding detritivore), blue catfish (a bottom feeding invertivore/piscivore), and yellow bass and largemouth bass (pelagic piscivores), occupying trophic levels II, III, and IV, respectively in our bayou system. Total whole body residues of DDT and its metabolites DDE and DDD (collectively DDTr) were consistently highest in the mullet, with mean concentrations ten or more times greater than those measured in bass or catfish. We explain this accumulation pattern by considering the home range, feeding strategy, physiology and metabolism of mullet compared to bass or catfish. We suggest that these factors are more important than trophic position in determining bioaccumulation associated with spatially explicit contamination. This paper presents the support for our hypothesis and also discusses implications of our findings for monitoring program design and risk assessment.

Key words: DDT, biomagnification, mullet

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