Influence of Ion Deficiency in Freshwater Short-Term Chronic and Acute Toxicity Tests with Ceriodaphnia dubia, Daphnia magna and Pimephales promelas - Abstract
While several studies have been focused on the toxicity of elevated concentrations of one or more of the major freshwater ions (e.g., Ca2+, Na+, Cl-), fewer data are available on the adverse impacts of ion deficiency. Short-term chronic (STC) toxicity tests, with Ceriodaphnia dubia, Daphnia magna, and the fathead minnow, Pimephales promelas, were conducted using laboratory-prepared test waters representing a range of water quality conditions. In addition, acute studies of an ion-deficient (reverse osmosis) effluent were conducted with C. dubia and P. promelas. Ceriodaphnia dubia was the most tolerant of the three species in STC tests, with 50% survival in deionized water, while there was 100% mortality of the other two species. Reproduction of C. dubia was unaffected in any of the other reconstituted waters, even at a hardness of only 10 mg/L as CaCO3. In treatments having surviving organisms, growth (biomass) of D. magna was significantly reduced in the softest water, while growth of P. promelas was significantly reduced in the two softest waters. In the acute studies, only P. promelas survival was significantly reduced in RO effluent. A modest increase in the hardness and alkalinity of the RO effluent eliminated the ion deficient effect, resulting in 100% survival. Based on these data, D. magna and P. promelas have similar sensitivities to ion deficiency. These studies demonstrate the importance of evaluating ion deficiency as well as excess when assessing wastewaters and receiving waters.