Occurrence of pesticides in fruits and vegetables from organic and conventional agriculture by QuEChERS extraction liquid chromatography tandem mass spectrometry

Human exposure to pesticides commands the implementation of food safety control, but few studies have provided a comparative assessment of conventional and organic products. This study set out to examine 22 pesticides in four distinct commodities (lettuce, apples, grapes, and tomatoes) from conventional and organic agriculture available to consumers. A multiresidue procedure based on QuEChERS extraction and ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) was first validated for its robustness. Suitable determination coefficients (R-2 > 0.99) and recoveries generally between 70 and 110% were obtained. Intraday and interday variations were < 20% and low matrix effects were noted with sample-to-sample variation. Method limits of detection (LOD) in the overall range of 0.05-2 mu g kg(-1) were obtained. The validated method was applied to 133 fruit and vegetable samples purchased in Canada, including conventional and organic culture samples. Overall, 47% of the 133 samples had levels above the LOD for at least one pesticide. Neonicotinoid insecticides were detected in all four product types. Imidacloprid (0.08-29 mu g kg(-1)), acetamiprid (0.11-108 mu g kg(-1)), and clothianidin (0.13-141 mu g kg(-1)) were the most recurrent. Atrazine was reported in approximately a third of the lettuce samples (0.25-7.5 mu g kg(-1)). For varieties with samples available from both organic and conventional agriculture, the proportion of insecticide levels > LOD was significantly higher (p < 0.05) for samples from conventional agriculture (9.7%) than from organic agriculture (2.0%). Measured levels were compliant to Canadian Maximum Residue Limits (MRLs), but a thorough human health risk assessment has yet to be conducted for many of these pesticides.