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Avoidance of a blend of four metals (relative ratios: 1.00 copper, 0.54 chromium, 1.85 arsenic, and 0.38 selenium) by schools of fathead minnows (Pimephales promelas) was determined in a steep-gradient, laminar-flow laboratory chamber, an artificial stream supplied with raw river water, and a natural stream. Laboratory avoidance responses were determined seasonally during twelve months for unexposed (control) fish and for two groups of metals-acclimated fish. Field avoidance responses were determined for control fish in the artificial stream in spring and summer and in the natural stream in summer. Field avoidance responses of metals-acclimated fish were determined in the summer in the artificial stream and in the natural stream. The laboratory control fish avoided the metals blend at a concentration of 29 µg/L. The field control fish avoided 71.1 and 34.3 µg/L of total metals in the artificial stream in spring and summer, respectively, and 73.5 µg/L in the natural stream. Laboratory fish acclimated to a total metals concentration of 49 µg/L for three months did not respond to metals levels up to 245 µg/L. Laboratory fish exposed to 98 µg/L of total metals preferred elevated concentrations of 294 µg/L after three months of exposure, mildly avoided 490 µg/L after six months, and were not responsive to concentrations approaching 980 µg/L after nine months of exposure. Field-acclimated fish did not respond to metal blends as high as 1470 and 2940 µg/L in the artificial and natural streams, respectively. Water hardness, turbidity, and physical setting are implicated as possible causative factors in the differences in field avoidance levels among the control fish. The 96-h median lethal concentration (LC50) of the metals blend for acclimated fish was 1.25 and 1.41 times higher than that for control fish for the laboratory and field groups, respectively.
fish avoidance, field validation, metals acclimation, synergism, toxicity, hazard evaluation
Research associate, University of Maryland, Horn Point Environmental Laboratories, Cambridge, MD
Professor, Virginia Polytechnic Institute and State University, Blacksburg, VA
Director, University Center for Environmental Studies, Virginia Polytechnic Institute and State University, Blacksburg, VA