John Wiley & Sons, Ltd.

Realistic environmental mixtures of micropollutants in surface, drinking and recycled water: Herbicides dominate the mixture toxicity towards algae

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Mixture toxicity studies with herbicides have focused on a few priority components that are most likely to cause environmental impacts and experimental mixtures were often designed as equipotent mixtures; however, real world mixtures are made up of chemicals with different modes of toxic action at arbitrary concentration ratios. The toxicological significance of environmentally realistic mixtures has only been scarcely studied. Few studies have simultaneously compared the mixture effect of water samples with designed reference mixtures comprised of the ratios of analytically detected concentrations in toxicity tests. Here, we address the effect of herbicides and other chemicals on inhibition of photosynthesis and algal growth rate. We tested water samples including secondary treated wastewater effluent, recycled water, drinking water and stormwater in the combined algae assay. The detected chemicals were mixed in the concentration ratios detected and the biological effects of the water samples were compared to the designed mixtures of individual detected chemicals to quantify the fraction of effect caused by unknown chemicals. Our results showed that herbicides dominated the algal toxicity in these environmentally realistic mixtures and the contribution by the non‐herbicides was negligible. A two‐stage model, that used concentration addition within the groups of herbicides and non‐herbicides followed by the model of independent action to predict the mixture effect of the two groups could predict the experimental mixture toxicity effectively but the CA model for herbicides was robust and sufficient for complex mixtures. Therefore, we used the bioanalytical equivalency concept to derive effect‐based trigger values for algal toxicity for water quality monitoring of recycled and surface water. All water samples tested would be compliant with the proposed trigger values associated to the appropriate guidelines. Environ Toxicol Chem © 2014 SETAC

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