An evaluation of nickel toxicity to Ceriodaphnia dubia and Daphnia magna in a contaminated stream and in laboratory tests

Seven‐day tests with Ceriodaphnia dubia were used to document ambient toxicity in two industrially contaminated streams in southeastern Tennessee. Low survival of Ceriodaphnia dubia was linked to concentrations of Ni (74‐200 μg/L) below Environmental Protection Agency (EPA) water quality criteria. A toxicity identification evaluation consisting of Ceriodaphnia dubia, Daphnia magna, and Pimephales promelas (fathead minnow) toxicity tests with Ni, chemical analyses, and experiments with a Ni‐selective resin were used to show that Ni was the primary toxicant in one of the streams. Nickel nitrate and Ni chloride were both extremely toxic to Ceriodaphnia dubia but were not very toxic to Pimephales promelas: Ni at a concentration of 7.5 μg/L (water hardness, 40 mg/L as CaCO₃) was lethal to Ceriodaphnia dubia within 7 d, but 16 mg/L Ni did not reduce survival or growth of Pimephales promelas. When dilution water with a hardness of 177 mg/L was used, 15.0 μg/L killed all the Ceriodaphnia dubia in 7 d (no reduction in survival or fecundity occurred in 7.5 μg/L). Daphnia magna was less sensitive than Ceriodaphnia dubia to Ni: A concentration of 40 μg/L significantly reduced fecundity but not survival in 21 d. In stream water containing 49 μg/L Ni (hardness, 656 mg/L), 100% mortality of Ceriodaphnia dubia occurred in 7 d, but 70% of the Daphnia magna survived for 14 d. When the Ni in the stream water was reduced to 10 μg/L with the resin, 60% of the Ceriodaphnia dubia lived for 7 d and all the animals reproduced; survival and reproduction of Daphnia magna remained high for all 14 d. Thus, in both ambient water and pure chemical tests, Ceriodaphnia dubia was found to be much more sensitive to Ni than Daphnia magna. Experiments with ⁶³Ni showed that both species accumulated similar amounts of Ni, so the difference in toxicity was not a result of Ni uptake. The high sensitivity of Ceriodaphnia dubia to Ni and the lower than expected reduction in Ni toxicity to Ceriodaphnia dubia with increasing hardness have important implications for effluent and ambient testing and toxicity reduction efforts.