Land Use Influencing the Distribution of Pesticides in Surface Water: The Case of the Ma River and Its Tributaries in Thanh Hoa Province, Vietnam

Pesticide residues are regularly found in surface water, which could be dangerous for freshwater ecosystems and biodiversity. Pesticides may enter waters through a variety of pathways, but runoff from irrigation or precipitation has the highest quantities. Previous studies analyzing the pesticides pollution or ecological risks of pesticides focused on few regions (e.g., European and United States), whereas analysis of pesticide pollution in Southeast Asia and especially in Vietnam is limited. This study presents an investigation of banned pesticides used across the range of land use in catchments of the Ma river and its tributaries in Thanh Hoa province, Vietnam. Applying principal component analysis (PCA), we investigated the relationship between specific pesticides and land use. Besides, cluster analysis (CA), the method of aggregating monitoring locations, was applied in this study to find spatial pattern of pesticides pollution. Due to their persistence and remobilization during floods and runoff, all ten banned pesticides—eight insecticides (aldrin/dieldrin, BHC, chlordane, endrin, heptachlor, lindane, malathion, and parathion) and two herbicides (paraquat, and 2,4D)—still remain in surface water and are not presumably influenced by the fraction of land use area in the catchments. Clustering results revealed that banned pesticides still occur in some areas. Site TH08 close to Le Mon industrial zone and TH18 in Thanh Hoa city have higher concentrations of banned pesticides than other sites due to their highly toxic and long-time existence in the environment. Overall, our study provides approach to investigate pesticides in surface water for a province in Vietnam that may be used for future ecotoxicological studies to enhance risk assessment for stream ecosystems.