Monthly monitoring of neonicotinoid concentrations in tap water in Japan

Tap water is a major source of drinking water in Japan, raising concerns about potential contamination by neonicotinoid insecticides. To assess this risk, monthly sampling was conducted at twelve sites across the country from May 2022 to April 2023. The sites, located in rice-producing regions, represented different water sources (river water, soil-filtered water, and groundwater) and treatment processes, including systems with and without activated carbon. Seven neonicotinoids-acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam-were quantified using liquid chromatography-tandem mass spectrometry. Dinotefuran was detected consistently throughout the year at all sites, with peak concentrations in summer coinciding with aerial applications to rice paddies. Tap water treated with activated carbon generally contained neonicotinoid levels below the EU benchmark of 100 ng/L, while soil-filtered waters exhibited lower contamination than surface-derived waters. These results highlight how watershed characteristics, particularly rice paddy coverage, influence neonicotinoid contamination in tap water in Japan.