Review and recommendations on criteria to evaluate the relevance of pesticide interaction data for ecological risk assessments.

Mixing pesticides with different modes of action can provide a wider spectrum of control with fewer applications compared to using single active ingredients and is essential for comprehensive management of pest resistance. Mixture studies with pesticides are performed to assess compatibility, combined efficacy, and potential for toxicological interactions that damage crops. The purpose of this paper is to review and recommend previously published scientific criteria for evaluating the quality, relevance and interpretability of data on toxicological interactions and to demonstrate a methodology for applying them objectively to mixtures studies used in ecological risk assessment. The recommended criteria reflect the consensus of the literature on interaction analysis from decades of research in pharmacology and toxicology and are broadly applicable to mixtures of drugs, pesticides, industrial chemicals and food additives. They are useful for researchers who design and analyze interaction studies, for risk assessors who use interaction data in risk assessments, and for those who make risk management decisions pertaining to pesticides. This paper describes our methodology for assessing data on the combined activity of pesticides and then discusses how to interpret such data in the context of an ecological risk assessment. Examples have been drawn primarily from studies with herbicides and nontarget plants, and several example analyses have been included that can inform whether mixture data are sufficiently reliable and relevant for use in regulatory decision making.