Statistically based approach to select worst-case groundwater scenarios for environmental risk assessment of pesticides in Brazil

Exposure scenarios in combination with simulation models have been used in the procedure of Environmental Risk Assessment (ERA) of pesticides to estimate exposure concentrations in environmental compartments.The appropriate definition of exposure scenarios is primordial to guarantee ERA purpose to evaluate if a pesticide use in an intended area can be considered safe. This work had the aim to present and test a geoand statistically based approach to define worst-case groundwater exposure scenarios for Brazil. To do so, soil-climate data of Mato Grosso do Sul state consisting of 42 locations (3 soil classes and 14 meteorological stations) were used to generate populations of Predicted Environmental Concentrations (PEC) at 3 and 5-m depth for a simulation period of 24 years. A total of 3,780 graphs were generated of PEC populations for 15 “dummy” pesticides. After setting equal risks in both dimensions (spatial and temporal) equal to 20%, the overall risks exceedance of tested worst-case groundwater exposure scenarios were about 10% for both depths. Thus, this approach can be considered suitable to guarantee a pre-defined overall risk exceedance once defined by the regulatory authorities in Brazil.