Pesticides are beneficial in protecting crops from pests and improving agricultural productivity; however, concerns on pesticide pollution in water have increased due to their indiscriminate use and lack of adequate regulations. Many studies have focused on the risks of pesticides considering the limited number and types of pesticide residues in crops and soils, and duration, and very few have focused on surface water throughout the year. Therefore, this study comprehensively identified 308 pesticides in surface water samples collected monthly over one year in the Saemangeum Basin, Korea. Both targeted and non-targeted analyses were used to identify 171 and 24 pesticides, respectively. Results highlight the extensive extent of pesticide contamination. Among the quantified pesticides, bromobutide and pretilachlor consistently exhibited high concentrations and risk levels, as indicated by their elevated risk quotient (RQ) values. Seasonal variations in pesticide concentrations revealed distinct patterns with intensified herbicide use during summer and increased insecticide concentrations during autumn. This study highlights the presence, distribution, and associated ecological risks of pesticides in surface waters, emphasizing the necessity of comprehensive monitoring and regulatory measures to protect aquatic ecosystems. The high RQ values identified for specific pesticides underscore the urgent need to implement effective strategies to mitigate these environmental risks.

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.

Carbamazepine (CBZ) is a widely used pharmaceutical for various purposes, including as an anticonvulsant, antibiotic, and antiepileptic agent, and it undergoes diverse metabolic pathways in both the environment and the human body. Therefore, this study aimed to explore the distribution of CBZ, the presence of its transformation products (TPs), and the transformation pathways in the Mangyeong and Dongjin Rivers in the Saemangeum watershed of Korea using non-targeted screening. The concentration distribution results for CBZ and its TPs showed that the average concentrations in the Mangyeong and Dongjin Rivers were 128.8 ng/L and 89.0 ng/L, respectively. The Mangyeong River exhibited a higher CBZ concentration than the Dongjin River, which was similar to those of the reported CBZ concentrations in other major domestic and international rivers. The types and detection frequencies of the identified TPs exhibited similar trends. The detection frequencies of the TPs decreased in the following order: CBZ-EP > DiOH-CBZ > 10OH-CBZ > 2OH-CBZ > 9-carboxyacridine > 9-acridinecarboxaldehyde. The detection frequency of the main TPs was high, and some were believed to be generated during the water treatment process. The presence of additional TPs (CBZ-O-quinone, acridine, and iminostilbene) was confirmed by the generated molecular networks. This study presents the transformation pathway of the CBZ and provides foundational data for understanding the environmental behavior of TPs, improving wastewater treatment plants, managing water quality, and establishing water environmental policies.