The ecotoxicity of binary mixtures of Imazamox and ionized ammonia on freshwater copepods: Implications for environmental risk assessment in groundwater bodies.

Groundwater bodies are impacted by substances such as pesticides and N-fertilizers, which usually occur in the environment as complex mixtures rather than isolated pollutants. The threat that these mixtures pose to groundwater-dwelling organisms is still poorly understood. The aims of the present study were to test the acute effect of a binary mixture of a herbicide (Imazamox) and NH on epigean (Eucyclops serrulatus) and hypogean (Diacyclops belgicus) freshwater copepod species. In addition, to evaluate if the effect of the mixture can be explained by referencing non-interaction models or by more complex interaction models; and the implications for groundwater risk assessment. Compared with the action of the compounds evaluated separately, the effects of Imazamox and NH in the binary mixture were more than additive or synergistic for both species. MixTox models evidenced a dose ratio and dose level deviations from concentration addition and independent action traditional models. The hypogean species was three times more sensitive to NH that the epigean species when assayed as a single chemical. However, D. belgicus was only 1.13 times more sensitive than E. serrulatus when NH was assayed in the mixture. The use of an integrated approach for substances that are known to interact in groundwater, should include copepods species as test organisms.