Study on the dissipation pattern and risk assessment of metalaxyl-M in rice grains and paddy soil and water by liquid chromatography-tandem mass spectrometry.

Herein, field experiment trials were conducted at two different sites (Heilongjiang and Hubei Province) in China to determine the residual levels and dissipation kinetics of metalaxyl-M in rice grains, and paddy soil and water. A modified quick, easy, cheap, effective, rugged, and safe "QuEChES" method coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed for determination of metalaxyl-M residual levels in different matrices. The method showed an excellent linear response (R2 > 0.99) over the concentration range of 0.01-0.50 mg kg-1 with satisfactory recovery rates in between 76.00 and 111.36%. The limits of quantification (LOQ) were estimated to be 0.010 mg kg-1 for all matrices. Half-lives of 0.27 to 10.83 days in rice plant, paddy soil, and water indicate that the analyte is easily degraded in the environment within a relatively short time. The terminal residues of metalaxyl-M in rice husks and rice grains were less than 0.05 mg kg-1. Dietary risk assessment showed that harvested rice treated with metalaxyl-M would not pose unreasonable risk to humans or the environment.