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TA3 Metals in the Environment: Aquatic Biological Perspectives
() Cadmium shipping, receiving and handling: Comparative bio-dynamics in stream insects.
Buchwalter, D1, Cain, D1, Luoma, S1, 1 US Geological Survey, Menlo Park, CA, USA
ABSTRACT- Aquatic insects are commonly used indicators of environmental quality, including the assessment of heavy metal-contaminated streams. Numerous field-based studies have led to observations of species sensitivity differences to metals. However, the underlying physiological processes that determine species-specific metal tolerance differences remain poorly understood. For a metal to be toxic to an organism, it must accumulate at target sites at concentrations above those that the organism can effectively deal with the metal insult. Therefore, not only are the kinetics of metal uptake and loss fundamentally important, but the manner in which the metal is handled once taken up by the organism is also critical. In radiotracer experiments, we measured dissolved cadmium uptake and loss kinetics in several species of aquatic insects from the orders Ephemeroptera, Plecoptera and Trichoptera. We further investigated how cadmium was partitioned in sub-cellular fractions. These fractions can be divided into metal sensitive fractions (organelles, mircosomes, and non-metallothionein like proteins), detoxified/stored metals (metallothionein-like proteins, and biologically inert material), and cell debris. Wide variation was found in Cd uptake (Ku) and efflux (Ke) values. Predicted steady state concentrations based on kinetic parameters were found to range by 3 orders of magnitude among the 8 species tested. Furthermore, species exhibited large differences in their abilities to detoxify Cd via metallothionein-like proteins or other storage mechanisms. By linking kinetic parameters with Cd partitioning, it is possible to infer dissolved Cd sensitivity differences among aquatic insect species. However, diet also plays a major role in metal accumulation. Currently, we are examining the dietary Cd accumulation, loss, and fractionation in predatory stoneflies to address the following questions: Are dietary Cd burdens handled (partitioned) similarly to burdens accumulated via the dissolved route? Are Cd efflux rate constants (Ke) values similar for dietary and aqueous sources. Are assimilation efficiencies similar among closely related species?
Key words: cadmium, aquatic insects, biokinetics, detoxification
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