Neonicotinoid detection in rainwater in Japan

Since 1993, neonicotinoid insecticides have been used extensively in Japan, primarily for rice cultivation and pine forest protection. The spread of neonicotinoids to the natural environment is largely through runoff from agricultural lands; however, precipitation could also become a potential medium even though neonicotinoids have low vapor pressures. While previous studies have reported the dry deposition and particulates of neonicotinoids in the air, this study investigated the wet deposition of these insecticides. Rainwater samples from Tsukuba and Kashiwa, Japan, were collected and analyzed by liquid chromatography–tandem mass spectrometry in April, June, and September 2023, as well as in January, April, June, August, and September 2024. Results revealed that 91% of the samples contained neonicotinoids, with the highest total concentration of 1.72 ng/L detected in August 2024. Acetamiprid ranked first with a detection frequency of 82% and an average concentration of 0.36 ng/L, followed by thiacloprid (73%, 0.28 ng/L) and dinotefuran (45%, 0.52 ng/L). This research is the first report on neonicotinoid presence in precipitation, suggesting that neonicotinoids, as low volatile matter, can still be dispersed to the environment via precipitation.