Testing British Columbia's water quality guidelines as a mixture of four important contaminants, hardness, exposure time, and species effects

Abstract

Provincial water quality guidelines are established in order to prevent detrimental effects of a single toxicant from affecting the health of resident aquatic life. However, the elevation of pollutants in freshwater can occur from many sources simultaneously and interact to form mixtures. In this study, three common freshwater species, Daphnia magna, Hyalella azteca and Oncorhynchus mykiss, were exposed to cadmium, selenium, nitrates and sulphates as a mixture at concentrations the same as British Columbia’s provincial water quality guidelines (BC WQG) for the protection of aquatic life with hard (250 mg/L as CaCO3) and soft (50 mg/L as CaCO3) water conditions. For all three organisms, both acute (48 hour) and chronic (21 day) exposures were used to examine the four contaminants and their mixture at maximum and average BC WQG concentrations. In the short term exposures, the only treatment that was harmful was cadmium, which had a 43% (p = 0.115, n = 3) and 64% (p < 0.0001, n = 5) mortality for D. magna in soft and hard water respectively. The toxicity of the four part mixture (including cadmium) was reduced, due to the antagonistic effect of selenium on the toxicity of cadmium. During a chronic exposure, the mixture was more (to D. magna) or less hazardous (to H. azteca and O. mykiss) than single contaminants; leading to the conclusion that pollutants can have a different overall effect when simultaneously exposed for longer periods of time. Overall, the interactions between pollutants in a complex mixture should be considered when deriving water quality guidelines. To provide appropriate protection of the environment, these complex interactions should be further investigated with representative species in the BC ecosystem.