Toxicity of environmentally realistic concentrations of chlorpyrifos and terbuthylazine in indoor microcosms

- Environmentally realistic concentrations were assessed with higher-tier approaches.
- Food-web interactions (indirect effects, recovery of populations) were recorded.
- Terbuthylazine potentiated the effect of chlorpyrifos on feeding rates.
- Zooplankton food-web interactions with multiple chemical stressors need to be evaluated.

Few studies have been conducted into the evaluation of environmentally realistic pesticide mixtures using model ecosystems. In the present study, the effects of single and combined environmentally realistic concentrations of the herbicide terbuthylazine and the insecticide chlorpyrifos were evaluated using laboratory microcosms. Direct toxic effects of chlorpyrifos were noted on copepod nauplii and cladocerans and the recovery of the latter was likely related with the decrease observed in rotifer abundances. Terbuthylazine potentiated the effect of chlorpyrifos on feeding rates of Daphnia magna, presumably by triggering the transformation of chlorpyrifos to more toxic oxon-analogs. Possible food-web interactions resulting from multiple chemical (and other) stressors likely to be present in edge-of-field water bodies need to be further evaluated.