Environmental risk assessment of atrazine in a tropical river basin using regulatory exposure modeling in Brazil

Abstract Mathematical modeling and predictive simulation have improved Environmental Risk Assessment (ERA) of pesticides, particularly in exposure characterization. This research applied the regulatory tool Pesticide in Water Calculator (PWC) to estimate environmental exposure to atrazine in surface waters of the Rio Preto Basin (Federal District, Brazil), a predominantly agricultural region within the Cerrado biome. Six conservative Tier 1 exposure scenarios for maize were developed to represent worst-case conditions under local edaphoclimatic and land-use conditions. Estimated Environmental Concentrations (EECs) were integrated with standard aquatic ecotoxicological endpoints to calculate Risk Quotients (RQs). Risk quotients (RQs) exceeded regulatory Levels of Concern (LOCs) for some exposure scenarios, particularly for algae, indicating greater sensitivity of primary producers among the evaluated taxa. A Tier 2 refinement incorporating conservation practices as mitigation measures reduced exposure estimates and associated risk. Refining exposure scenarios reduced atrazine EECs by more than 50%, rendering the risk acceptable under the analyzed conditions. The findings indicate that the development of exposure scenarios under tropical environmental conditions enhances the representativeness of risk estimates, strengthens the ERA process, and provides robust technical support for regulatory decision-making.