Evaluation of the Concentration-Addition Approach for Pesticide Mixture Risk Assessment in Agricultural Watersheds

The environment is a complex system composed of various creatures and pollutants caused by human activity. In this study, a mixture toxicity assessment based on the concentration-addition (CA) model was applied to 51 types of pesticides detected in the Saemangeum Watershed (the Mangyeong and Dongjin Rivers) for one year to evaluate pollution levels. A mixture toxicity assessment was conducted based on the measured environmental concentration (MEC) and the predictive values of basic ecotoxicity data (algae, daphnids, and fish). The risk and the trophic levels that showed the highest sensitivity varied depending on the sampling time and point for each mode of action (MoA) group of pesticides. In particular, the mixture risk for chloroacetamide and thiocarbamate pesticides was high (risk quotient > 1), and the potential risk was highest in autumn. In addition, the driving forces of seasonal changes were examined for samples that exhibited potential risks, and it was found that one to four substances contributed the most to the risk. The results of this study show that an initial risk assessment based on a mixture toxicity assessment can help in managing pesticide pollution in rivers.