Occurrence of imidacloprid and its transformation product (imidacloprid-nitroguanidine) in rivers during an irrigating and soil puddling duration

Abstract

Liquid chromatography/triple quadrupole mass spectrometry is a promising technique to detect trace contaminants in water environments. This technique requires reference standard reagents to develop selected reaction monitoring (SRM) conditions, but emerging contaminants like pesticide transformation products are often commercially unavailable in markets. Thus in this study, high resolution mass spectrometry was coupled with sensitive triple quadrupole mass spectrometry to develop SRM conditions by using environmental samples instead of reference standard reagents. The SRM conditions for imidacloprid-nitroguanidine (1-((6-chloropyridin-3-yl)methyl)-2-nitroguanidine), an transformation product of a neonicotinoid, were successfully developed by using a concentrated paddy water sample. Prior to its synthesis, imidacloprid-nitroguanidine was verified to be present in actual river water samples. Without such verification, the synthesis of imidacloprid-nitroguanidine could be meaningless if its concentrations in samples were below detection limit. After that, it was eventually synthesized to acquire its calibration curve. In the sampling site, imidacloprid has been applied to nursery boxes of rice seedling. Rice seedlings raised in nursery boxes were transplanted to paddy fields along with the soil in boxes. Imidacloprid-nitroguanidine was detected in the soil and its penetration into river water may cause pollution. Obvious pollution was observed before the rice plantation began because of irrigating and soil puddling in paddy fields, which indicates that monitoring of transformation product in soil must be started before rice plantation begins.