Acute toxicity of selenium dioxide to freshwater fishes

Acute toxicity tests of selenium dioxide were conducted for 96 to 336 hr in intermittent-flow bioassay systems using six species of freshwater fish. The decreasing order of species sensitivity was: fathead minnow, flagfish, brook trout, channel catfish, goldfish, and bluegill. Curves relating median lethal concentration to exposure time for each species exposed for more than 168 hr were sigmoid in shape and were characterized by a change in slope indicating a more rapid mortality rate after 96 to 168 hr toxicant exposure. The 96-hr LC50 estimates ranged from 2.9 mg/L SeO₂ for fathead minnow fry to 40.0 mg/L for bluegill juveniles.Effects of brief toxicant exposure (24 hr) on fathead minnow and flagfish juveniles included limited delayed mortality and no effects on growth over a 28-day period.Research supported by the U. S. Environmental Protection Agency National Water Quality Laboratory, Duluth, Minnesota. (Contract No. 68-01-0748).