Concentration Fluctuations of Pesticide Residues, Including Four Neonicotinoids, and Related Metabolites in a Small River Located Near Rice Paddy Fields

It is important to investigate contamination levels of neonicotinoide insecticides and the other pesticides that may cause adverse effects, not only to human health but also to the environmental ecosystems near rivers because of the large amounts of pesticides used for the paddy rice fields. Therefore, the runoff movements of commonly used 31 pesticides (12 fungicides, 4 neonicotinoid insecticides, 8 insecticides, and 7 related metabolites) in a small river basin, which branches from a major river, located near paddy rice fields in Japan were presented in this study. The concentration of the pesticide residues found in the present study fluctuated depending on the applied periods and amounts as well as the flow of the river water. No pesticides exceeded the standard levels in environmental and drinking water set by the government of Japan. The maximum loadings of total pesticides in the river were obtained in July for fungicides, August for neonicotinoids and May for the other insecticides. The monthly loading of total pesticides exhibited unique variations. The runoff ratios of neonicotinoids from paddy fields to the river ranged from 078% of imidacloprid to 10% for dinotefuran. Results obtained in this study are important for the evaluation of the actual behavior of the insecticides and fungicides in small rivers.