An efficient and pragmatic approach for regulatory aquatic mixture risk assessment of pesticides

The current regulatory approach to address aquatic mixture toxicity for pesticides in the EU (EFSA J 11:3290, 2013) is rather complex: in typical cases it requires conducting the entire mixture risk assessment scheme for every exposure scenario separately (e.g. 6–8 ecotoxicological endpoints, for each of the nine exposure scenarios for the European Central Zone with 24 common mitigation measure combinations result in over 1700 sub-scenarios to be assessed). This article discusses the available concepts for a mixture toxicity assessment, the key questions raised and the implementation of these questions in existing risk assessment approaches. Based on this, an alternative, more efficient assessment scheme for aquatic mixture risk assessment (AMiRA) is proposed with the aim of facilitating the practical conduct and interpretation of the assessment while addressing the key questions and preserving the level of protection. The scheme assesses product risk (including a check for non-additive effects), the presence of a risk driver and gains efficiency by the straightforward use of risk quotients (RQ) to calculate mixture risk quotients (RQ_mix) that are equivalent to the calculation of exposure toxicity ratios for a mixture (ETR_mix,CA = Exposure-Toxicity-Ratio for mixtures based on concentration addition) proposed by EFSA (EFSA J 11:3290, 2013). A case study is provided underlining the equivalence of the proposed approach to the EFSA (EFSA J 11:3290, 2013) decision tree.