Chronic toxicity of hexavalent chromium to the fathead minnow (Pimephales promelas).

The chronic effects of hexavalent chromium on the fathead minnow (Pimephales promelas) were investigated. Survival was affected only at the high test concentration of 3.95 mg Cr/L. All chromium concentrations, including 0.018 mg/L, the lowest tested, retarded the early growth of first-generation fish, but this effect was only temporary. Growth of second-generation fish was not affected at concentreations of 1.0 mg/L or lower. Reproduction and hatchability of eggs were not affected at any chromium concentration tested. The maximum acceptable toxicant concentration (MATC) for fathead minnows in hard water (209 mg/L as CaCO3 at pH 7.7) was based on survival and lies between 1.0 and 3.95 mg Cr/L, respectively. The application factor (MATC/96-hr LC50) is between 0.03 and 0.11.