Effects of atrazine on fish, amphibians, and reptiles: update of the analysis based on quantitative weight of evidence

Quantitative weight of evidence (QWoE) provides a framework and process for evaluating different toxicological studies based on quality and relevance of the results. This framework allows for data from these studies to be combined in separate lines of evidence to address causality, and relevance to environmental risks. In 2014, such a QWoE that examined the body of available company reports and peer reviewed literature regarding the effects of the herbicide atrazine on fish, amphibians, and reptiles was published. Since that time, new studies have been conducted and/or published. One of the advantages of the QWoE framework is that additional information can be added as it becomes available. Thus, these new studies were evaluated in the same manner as previously and the new data incorporated into the existing QWoE. As before, the new updated QWoE was based on the same process of objective scoring of individual studies with respect to the quality of the methods and the relevance of individual responses to the apical endpoints of survival, growth, development, and reproduction. These new data did not identify new responses or indicate any relevant effects of atrazine. The new updated QWoE analysis concluded that atrazine does not adversely affect fish, amphibians, and reptiles, at environmentally relevant concentrations (<100 µg atrazine/L), which is consistent with the previous conclusions. These new studies and data are discussed in this paper and the accompanying supplement information provides detailed and transparent information to support these conclusions.