Assessment of Pesticide Residues in Soils Using a QuEChERS Extraction Procedure and LC-MS/MS

The concentration levels of some important pesticides were evaluated in soil samples from different areas of the North of Iran (Golestan province) and to indicate the possible sources and risks of contamination. A multiresidue analytical procedure using the QuEChERS approach was developed to extract and measure 12 pesticide residues from ten different classes in 145 soil samples including agricultural, garden, forestal, and residential areas. The analysis was performed using reversed-phase liquid chromatography equipped with an ESI mass spectrometry instrument by multiple reaction monitoring (MRM) in positive-ion modes. Retention times and occurrence of two conventional transitions were used as identification criteria. Three pesticide residues including malathion, propargite, and butachlor were observed in soil samples. Malathion residue was found in > 51% of soil samples, and its levels in approximately 35% of the cases were more than the residue limit (50 mu g kg(-1)). Propargite residue was observed in 49% of the samples and its levels in 11% of the cases were more than the residue limit. The most frequently observed levels of malathion and propargite were found in forestal and residential areas. The amount of butachlor residue in one of the residential soil samples was at least 10 times more than the residue limit. Some of the pesticides including imidacloprid, cyproconazole, diazinon, and chlorpyrifos displayed residue levels below 50 mu g kg(-1). The other pesticides, namely carbaryl, thiophanate-methyl, fenpropathrin, krezoxim-methyl, and pinoxaden, were not detected in any soil samples. These findings might be useful for implementing programs to monitor the presence of pesticides in soils and the related crops, to carry out more precise risk assessment studies.