Sublethal toxicity of metals to copepods

Toxicity tests used for water quality criteria only examine exposure to metals via the dissolved phase, express results relative to ambient concentrations only, and do not consider the mechanism of toxicity. These tests may not mimic environmental conditions closely enough to accurately predict the impact of anthropogenic contamination. My objectives were: (1) to compare the response of copepods to sublethal levels of metals (Ag, Hg, Cd, Zn, Mn and Se) accumulated from food and from water, (2) to relate any detected effects as a function of ambient concentration and to metal concentration within sensitive tissues of the organism, and (3) to characterize the mechanisms by which any toxic effects occur.; I conducted a series of experiments, in which copepods were exposed to sublethal concentrations of stable metals to determine toxicity via the dissolved phase, while another set was exposed to radiotracers of the same metals to determine metal body burden. In the next set of experiments, algal food was exposed to the same metal concentrations (either of radiotracers or of stable metals) and then fed to copepods. Toxic impact and body burdens were compared.; This toxic impact occurred at body burdens elevated roughly 4-fold for Ag, 6-fold for Hg and 2-fold for Cd. These body burdens were well within the range observed following dissolved phase exposure. I hypothesized that the difference in toxic effect arose because of a difference in metal deposition following different uptake routes. Metals accumulated from food were primarily deposited in internal tissues, where they appear to have interfered with the organisms' metabolic activity, whereas those accumulated from water were primarily deposited in the exoskeleton.; The mechanism of metal toxicity appears to be altered vitellogenesis, since the ovary did not develop and the protein content of eggs produced was reduced. Selenium acts through a different toxic mechanism. Se taken up from food depresses egg production of diapause (or resting) eggs only. Furthermore, the pattern of hatching rates suggest that the eggs that are produced under diapausing conditions are not diapause eggs, as they hatch immediately instead of being dormant until they receive a seasonal cue.; My findings simply that uptake from food should be included as an exposure route in standardized toxicity tests if these tests are to accurately predict environmental toxicity, and that rate of accumulation is also an important determinant of effect. (Abstract shortened by UMI.)...