The influence of mineral salts on fecundity of the water flea (Daphnia magna) and the implications on toxicity testing of industrial wastewater

Abstract

The effects of mineral salts constituting water hardness on fecundity ofDaphnia magna were assessed. Of the salts tested, increased concentrations of NaHCO3 and MgSO4 had no effect on fecundity, CaSO4 significantly increased fecundity, and KCl significantly reduced fecundity. The number of offspring produced per daphnid was correlative to the CaSO4 concentration at CaSO4 concentrations between 91 and 2100 mg/l. The effects of CaSO4 on daphnid fecundity could influence the interpretive outcome of industrial wastewater toxicity tests using this species when the waste and dilution waters contain different concentrations of CaSO4. It is recommended that when performing these tests, dilution water be sampled at the intake site of the industry's water source, thus assuring initial comparability of the waste and dilution waters. The CaSO4 content of the water prior to and after industrial use should be determined to identify any alterations of CaSO4 concentration during use. Identification of CaSO4 concentration differences can aid in the interpretation of effects associated with the wastewater.