Influence of water hardness on fluoride toxicity to rainbow trout

Static bioassays were conducted to determine effects of water hardness on toxicity of sodium fluoride to rainbow trout (Salmo gairdneri). Ninety-six hour LC50 values increased from 51 to 193 mg/L [F] as water hardness levels rose from 17 to 385 mg/L CaCO3. Tests of chronic toxicity at different water hardness levels are needed before fluoride standards for aquatic life, such as fish, can be set.