Occurrence of multi-class pesticide residues in soils of selected farmlands and farmer’s household surroundings in the southwestern part of Oyo State, Nigeria

The indiscriminate use of pesticides for crop production in Nigeria has led to contamination of the environment. Specifically, soil contamination from pesticide residues, including banned compounds raises serious public and environmental health concerns. However, very little is known about the occurrence of pesticides in Nigerian soils. Therefore, this study investigated the occurrence and concentration of organochlorine, organophosphate, carbamate and pyrethroid pesticide residues in farm and farmers’ house compound soils at a depth of 0-20 cm. Soil pesticide residues were analyzed using gas chromatography-mass spectrometry (GC-MS). A total of 41 pesticides were detected including; 14 organochlorine, 15 organophosphate, 9 carbamates and 3 pyrethroids. In maize crop soil, heptachlor, chlorpyrifos, carbofuran and cypermethrin were found having the highest concentrations (0.257±0.006, 8.567±0.907, 5.100±1.127 and 0.173±0.021 µg/kg, respectively). In cassava crop soil, endosulfan, pirimiphos-methyl, carbofuran and permethrin had the highest concentrations (2.300±0.200, 3.567±0.569, 0.467±0.176 and 0.223±0.038 µg/kg, respectively). While in the farmers’ house compound soil, heptachlor, pirimiphos-methyl, carbofuran and cypermethrin were found having the highest concentrations (0.165±0.007, 0.742±0.931, 0.225±0.050 and 0.076±0.020 µg/kg, respectively). Overall, the cumulative concentrations of the pesticides showed organochlorine and pyrethroid were higher in cassava crop soil while organophosphate and carbamate were higher in maize crop soil. This study revealed the use of highly (e.g., carbofuran) and moderately (e.g. chlorpyrifos) hazardous pesticides, as well as detection of extremely hazardous (e.g., oxamyl) and banned (e.g., endosulfan) pesticide residues. The results pointed out the use of multiple pesticides by farmers in this area, of which, some are highly hazardous. Overall, these findings underscore the need to restrict the use of highly hazardous pesticides in food crop production. The use of safer pesticide alternatives as well as remediation of the already contaminated soil environment are recommended.