John Wiley & Sons, Ltd.

The interactive toxicity of cadmium, copper, and zinc to Ceriodaphnia dubia and rainbow trout (Oncorhynchus mykiss)

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Traditionally aquatic toxicity studies examine the toxicity of a single chemical to an organism, while organisms in nature may be exposed to multiple toxicants. Given this is a more realistic exposure scenario in situ, the authors were interested in understanding the interactive toxicity of multiple metals to aquatic organisms. We performed a series of studies using equitoxic mixtures of cadmium, copper, and zinc to 2 aquatic organisms, rainbow trout (Oncorhynchus mykiss; RBT) and the waterflea, Ceriodaphnia dubia. Single metal toxicity tests were conducted to determine acute LC50 values for RBT and short‐term chronic EC50 values for C. dubia. All 3 metals were then combined in equitoxic concentrations for subsequent mixture studies using a toxic unit (TU) approach (i.e., 1 TU = EC50 or LC50). For C. dubia, the mixture study showed greater‐than‐additive effects in hard water (TU based EC50 = 0.74 TU), but less‐than‐additive effects in soft water (TU based EC50 = 1.93 TU). The mixture effects for O. mykiss showed less than additive effects in both hard and soft waters, with TU based LC50 values of 2.33 and 2.22 total TU, respectively. These data are useful in helping to understand metal mixture toxicity in aquatic systems and indicate that although in most situations the assumption of additivity of metal mixture toxicity is valid, under certain conditions it may not be sufficiently protective. This article is protected by copyright. All rights reserved

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