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TP3 Linking Aquatic Toxicology with Ecosystem Indicators
(271) Differences in metal bioconcentration among species of stream insects: Mechanistic explanations.
Buchwalter, D1, Luoma, S1, 1 USGS, Menlo Park, CA, USA
ABSTRACT- In metal contaminated streams, ecologists have observed profound sensitivity differences among aquatic insect species. However, the mechanistic bases for differences in species sensitivity to heavy metals remain unclear. Morphological and physiological factors that determine heavy metal accumulation differences among aquatic insect species were explored. Using radioisotopic tracers (65Zn and 109Cd) we compared the rates of dissolved cadmium and/or zinc accumulation among several aquatic insect species including, mayflies, caddisflies, a stonefly and a chironomid. Initially, the time course of uptake was followed in individual animals for 4 hours. Accumulation rates varied among taxa exposed to low metal concentrations (0.14nmol/l), and ranged from 0 - 7 pmol/g/hour. Species that accumulated Cd at higher rates also tended to accumulate Zn at higher rates. Metal accumulation was not related to gill size or water permeability. Accumulation rates appeared to be related to the densities of specialized osmoregulatory structures (chloride cells and epithelia), which exist on the insects' body surfaces, however. Chloride cells were identified qualitatively by silver precipitation and scanning electron microscopy. Kinetic uptake studies (uptake rates as a function of Cd concentration) were conducted to compare the relative number of metal transporters among 3 mayfly species, in relation to chloride cell densities (which are used by insects for ion exchange with the surrounding water). Vmax on the Michaelis Menton curves varied up to 170-fold among mayfly species with dramatically different uptake rates. Metal uptake rates from solution in insects can differ by orders of magnitude, thus affecting their exposures in metal-contaminated conditions. To the extent that dissolved uptake is a primary source of exposure these differences could be a cause of substantial differences in sensitivity to metals either in nature or in toxicity tests.
Key words: metals, aquatic insects, bioconcentration, indicators
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