Abstract
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.
Highlights
Pesticides benefit grain storage in controlling the losses caused by insect pests
The modified QuEChERS procedure was evaluated for analysis of pirimiphos-methyl and deltamethrin residues in rice
The linearity of each pesticide was studied in the range of 0.01–1 mg/L with five calibration points (0.01, 0.06, 0.1, 0.5 and 1 mg/L for pirimiphos-methyl; 0.06, 0.1, 0.5, 1 and 2 mg/L for deltamethrin) in rice matrix
Summary
Pesticides benefit grain storage in controlling the losses caused by insect pests. Some pesticides can be applied directly to the commodity and pesticide residues from these post-harvest treatments may be hazardous to human health [1]. The environment in the storehouse and the moisture content in stored grain will affect the dissipation of organophosphate and pyrethroid pesticides from grains [2], the behaviors of residues of pesticides applied to stored grain should be investigated. Pirimiphos-methyl (Figure 1) is widely used in the major grain-producing countries to protect against insect attack, and this organophosphate insecticide has long insecticidal activity persistence [4]. Deltamethrin (Figure 1), a pyrethroid insecticide, is considered to be of relatively low toxicity compared to other insecticides [5]. It is currently available for controlling insect pests in stored products [6]. Pirimiphos-methyl and deltamethrin are usually used in stored grains directly, making pesticide residues a problem. Maximum residue limits (MRLs) of pirimiphos-methyl and deltamethrin in rice have been set by the European Union (5 mg/kg and 2 mg/kg), USA (8 mg/kg and 1 mg/kg), China (0.5 mg/kg for deltamethrin) and the Codex Alimentarius Commission (CAC, 7 mg/kg and 2 mg/kg)
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