National trends in pesticides in drinking water and water sources in Japan.

Although agricultural activities-especially paddy rice cultivation-are prominent in watersheds in Asian countries, few comprehensive studies have examined pesticide concentrations in water in these areas. Here, we report the concentrations of 162 pesticides in treated drinking water and source water (14,076 samples) in Japan, where rice cultivation is common, along with trends in sales of herbicides, fungicides, and insecticides from 1963 to 2016. Herbicides and fungicides-especially those used in rice farming were frequently detected in drinking water sources. The herbicide bromobutide, which is not listed in drinking water quality standards or guidelines except in Japan, as well as the widely used-and-detected bentazone, were frequently detected in source water (bromobutide and bentazone were detected at concentrations >0.1 μg/L in 31.1% and 33.8% of samples, respectively). Dymron and tefuryltrione were also detected in over 10% of samples at concentrations >0.1 μg/L. The highest observed concentration of bromobutide was 10 μg/L, and 7.5% of samples had concentrations >1 μg/L. High concentrations were also observed for halosulfuron methyl (7.9 μg/L), pyroquilon (7.0), molinate (6.8), and metominostrobin (4.6). Some of the pesticides frequently detected in source water were not detected at all in drinking water, but the main cause of the non-detection appeared to be degradation by chlorine. From the 1970s onward, sales of herbicides and fungicides with higher acceptable daily intakes (ADIs; i.e., with lower toxicity) have increased. However, the percentage of herbicides with very low ADIs (<10

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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.