Concentrations of Systemic Insecticides Including Neonicotinoids and Their Metabolites in Surface Water, Groundwater, and Tap Water in Japan

Since 1993, systemic insecticides such as neonicotinoids have been extensively applied in Japanese rice farming, leading to contamination of surface waters. These chemicals may infiltrate groundwater, which serves as a source of tap water, yet data on their occurrence in Japan remained unclear. This study investigated the contamination of neonicotinoids and their metabolites, sulfoxaflor, and triflumezopyrim in surface water and groundwater of Hii River and tap water in Izumo City, Shimane Prefecture, Japan. Monthly sampling over one year followed by the liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis showed that all water types contained at least three compounds. Mean concentration ratios across surface water, groundwater, deep groundwater, and tap water were approximately 10:8:4:1, indicating that deeper depth and water treatment may reduce concentrations. Dinotefuran showed a 100% detection with concentrations far exceeding other compounds, particularly in summer months during the rice-growing season, reaching 225 ng/L in surface water. Its two metabolites were also present throughout all environmental water compartments. The findings emphasize that systemic insecticides could persist in deep groundwater up to 20 meters, leading to their occurrence in tap water.