Abstract
Previous studies reported on a large (> 80%) compliance between the observed toxicity of pesticide mixtures and their toxicity as predicted by the concept of concentration addition (CA). The present study extents these findings to commercially sold and frequently applied pesticide mixtures by investigating whether the aquatic toxicity of 66 herbicidal and 53 fungicidal combination products, i.e., authorized plant protection products that contain two or more active substances, can reliably be predicted by CA. 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.
Highlights
Previous studies reported on a large (> 80%) compliance between the observed toxicity of pesticide mixtures and their toxicity as predicted by the concept of concentration addition (CA)
By investigating 119 combination products, the present study aims to extend the assessment of compliance between mixture toxicity prediction and observation to a broader range of combinations of pesticides, and to those combinations that are present in commercially applied pesticide mixtures
Percentage model deviation ratio (MDR) is related to the number of herbicidal and fungicidal combination products for which data for the product and all active substances were available for the given endpoint
Summary
Previous studies reported on a large (> 80%) compliance between the observed toxicity of pesticide mixtures and their toxicity as predicted by the concept of concentration addition (CA). The present study extents these findings to commercially sold and frequently applied pesticide mixtures by investigating whether the aquatic toxicity of 66 herbicidal and 53 fungicidal combination products, i.e., authorized plant protection products that contain two or more active substances, can reliably be predicted by CA. 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. Because an experimental testing of all potentially relevant environmental mixtures of pesticides is not feasible due to the large number of a.s. and their respective combinations, so-called component-based (in silico) approaches can be considered as an alternative option for a predictive environmental risk assessment that takes joint effects of pesticide mixtures into account. A recent state-of-the-art report on mixture toxicity summarizes the scientific background of mixture toxicity concepts as well as the implications of existing approaches for a predictive mixture toxicity assessment in the regulation of chemicals [13]
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