Decrease of pirimiphos-methyl and deltamethrin residues in stored rice with post-harvest treatment.

A modified quick, easy, cheap, effective, rugged (QuEChERS) method with multi-walled carbon nanotubes (MWCNTs) as reversed-dispersive solid phase extraction (r-DSPE) material was applied to the analysis of pirimiphos-methyl and deltamethrin residues in stored rice. Two dustable powder (DP) formulations (2% pirimiphos-methyl and deltamethrin DP; 5% pirimiphos-methyl DP) were applied in simulated storehouse trials in the lab. The residues and dissipation of the two pesticides in stored rice were investigated. Slow dissipation of both pesticides was observed in stored rice. The half-lives of pirimiphos-methyl were 23.9-28.9 days, and those of deltamethrin were 23.9-24.8 days. Residues of pirimiphos-methyl from application rates of 4.5-6.75 a.i. mg/kg (active ingredient milligram per kilogram) and 10-15 a.i. mg/kg were 1.6-3.8 mg/kg and 3.0-4.5 mg/kg at 60 days Pre-harvest Interval (PHI). Residues of deltamethrin from an application rate of 0.5-0.75 a.i. mg/kg were 0.13-0.14 mg/kg at 60 days PHI. Both pesticides residues were below the Maximum Residue Limits (MRLs) established by the Codex Alimentarius Commission (CAC). Therefore, at the recommended dosages they are safe for use on stored rice.