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

Abstract In agricultural landscapes it is common practice to apply pesticides as a spray series. Within a vegetation period multiple applications result in a mixture of different pesticides in the soil and other environmental compartments. • A model named MITAS (MIxture Toxicity of Application Spray series) has been developed to calculate the soil concentration of pesticides and the resulting time-dependent mixture risk for earthworms. MITAS creates tables and graphs representing the mixture risk for an applied spray series time-dependently. • A simulation of the impact of application series for a period of up to three years is possible with MITAS. Calculation of the soil concentration is based on the assumptions of the German pesticide registration. Mixture risk for each day within the entire modelling period is calculated. • Mixtures of pesticides from former and multiple applications are the rule in agricultural soils as various studies have shown. Thus, considering the impact of pesticide mixtures is necessary to protect soil organisms. MITAS can assess not only the maximum mixture risk for soil organisms, but also how long a certain risk threshold may be exceeded, above which unacceptable effects on exposed organisms may occur.