In agricultural spray series the mixtures of pesticides from former and multiple applications are the rule. A model was developed to calculate soil concentrations of pesticides and the resulting time-dependent mixture risk for earthworms in such spray series (Sybertz et al. 2020a). The model is called MITAS (MIxture Toxicity of Application Spray series). It allows the simulation of the impact of an application series and the resulting maximum mixture risk for soil organisms for a period of up to three years. The calculation of the soil concentration is based on the assumptions of the German pesticide registration.

 

The model has been applied to a real spray series for apple orchards that contained 15 different active substances and 26 different application dates during the growing season (Sybertz et al. 2020b). The simulation of the real pesticide spray series showed the chronic mixture risk of the spray series to be temporarily about twice as high as the individual substance with the highest chronic risk. Further, the threshold value defined in the risk assessment is exceeded when several substances are considered for a long period of time.

 

 

Sybertz A., Roß-Nickoll M., Schäffer A., Scholz-Starke B., Daniels B., Ottermanns R. (2020a): MITAS: A model for assessing the time-dependent risk of sequential applications of pesticides for soil organisms by consideration of exposure, degradation and mixture toxicity. MethodsX, 7: 100763. https://doi.org/10.1016/j.mex.2019.12.004

 

Sybertz A., Ottermanns R., Schäffer A., Scholz-Starke B., Daniels B., Frische T., Bär S., Ullrich C.,  Roß-Nickoll M. (2020b): Simulating spray series of pesticides in agricultural practice reveals evidence for accumulation of environmental risk in soil. Science of the Total Environment, 710: 135004. https://doi.org/10.1016/j.scitotenv.2019.135004