M11 AM Using Stable Isotopes in Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 11:40 AM in 343-344

(STE-1117-835479) Trophic enrichment of trace elements in aquatic food webs: A paradigm shift from the organics world.

Stewart, A¹, Croteau, M-N¹, Luoma, S¹, ¹ U.S. Geological Survey, Menlo Park, CA, USA

ABSTRACT- Our understanding of contaminant enrichment in aquatic food webs has been greatly enhanced through the use of stable isotopes of carbon and nitrogen. Stable isotope techniques are extremely effective in explaining how concentrations of organic contaminants such as organic mercury biomagnify along food webs. Relationships between inorganic pollutants and trophic position have been less transparent, leading to erroneous conclusions that most metals are not enriched in food webs in nature. Here we measured Se, Hg and Cd concentrations in algae, invertebrates and fish from estuarine and freshwater food webs from the San Francisco Bay/Delta to illustrate how traditional application of stable isotopes in studies of organic contaminants or mercury may not be appropriate for trace elements. Analysis of these food webs show how trophic enrichment is a function of feeding guild, consumer physiology, habitat, prey type and trophic position rather than a single relationship with trophic position or percent lipid. By dividing food webs into discrete units based on these ecological and physiological relevant processes we are able to identify important trophic links that lead to enhanced exposure in predators. A shift in the way we perceive food webs is essential if we are to identify those individuals and species most at risk for trace element toxicity.

Key words: stable isotopes, metals and metalloids, trophic transfer, exposure pathways