Predicting the aquatic toxicity of commercial pesticide mixtures

In more than 50% of cases, the predicted and observed mixture toxicity deviated by less than factor 2. An indication for a synergistic interaction was only detected with regard to algal growth inhibition for mixtures of fungicides that inhibit different enzymes of ergosterol biosynthesis. The greatest degree of compliance between prediction and observation was found for the acute toxicity of fungicidal products towards Daphnia and fish, while the greatest degree of underestimation of product toxicity occurred for the acute toxicity of herbicidal products towards Daphnia and fish. Using the lowest available toxicity measures within taxonomic groups as the most conservative approach resulted in a bias towards overestimation of product toxicity, but did not eliminate cases of considerable underestimation of product toxicity.The results suggest that the CA concept can be applied to predict the aquatic toxicity of commercial pesticide mixtures using the heterogeneous data typically available in a risk assessment context for a number of clearly identified combinations of test species and pesticide types with reasonably small uncertainty.The environmental risk assessment of plant protection products (PPP) in the European Union (EU) relates to the individual active substances [1]. Depending on the outcome of the EU risk assessment, an active substance (a.s.) may be included in the positive list (the Annex I of the directive 91/414/EEC). Only PPP containing a.s. included in this Annex I can be authorized at the level of the member states. This principle is retained in the new EU regulation 1107/2009 [2], which repeals directive 91/414/EEC and shall apply from June 2011. The new regulation applies not only to PPP and their a.s., but also to other substances contained in commercial PPP, namely safeners, synergists, co-formulants, and adjuvants [2]. The four last component groups are hereafter designated additives. PPP generally represent a mixture of at least one a.s. combined