Organophosphorus pesticide residues in soils and drinking water sources from cocoa producing areas in Ghana

Abstract

Pests and diseases are recognised as major factors responsible for the decline in cocoa yield in Ghana. This has resulted in an increased use of pesticides to increase productivity. The regular application and indiscriminate use of chemicals have been associated with unintended environmental and human health consequence. The objective of this study was to determine levels of 13 organophosphorus pesticide residues in soils and drinking water sources in and around cocoa farms in Brong Ahafo region of Ghana. Organophosphorus pesticide residues were determined by the use of a high resolution Varian CP-3800 Gas Chromatograph equipped with pulse flame photometric detector (PFPD) in 32 soils and 64 drinking water samples from 16 cocoa farms in the Dormaa West District of Ghana. Four organophosphorus residues were detected in the soil and water samples at varying concentrations. The organophosphorus residues detected in soil samples were chlorpyrifos (0.01–0.04 mg/kg), profenofos (0.02–0.04 mg/kg) and pirimiphos-methyl (0.01–0.04 mg/kg) while the organophosphorus residues recorded in the water samples were chlorpyrifos (0.01–0.05 µg/L), diazinon (0.01–0.04 µg/L) and pirimiphos-methyl (0.01–0.03 µg/L). The concentrations of organophosphorus pesticide residues in the soil samples analysed from the various sites were generally below and within US MRLs for agricultural soils. However, mean concentrations of chlorpyrifos and pirimiphos-methyl recorded at Nkrankwanta (S1) were found to be above their respective US MRLs for agricultural soils. The trends of organophosphorus pesticide residues in the water samples analysed from the various distances to cocoa farms decreased with increase in distance to cocoa farm (ranking; 0–15 > 16–30 > above 30 m). All organophosphorus pesticide residues recorded in the water samples from the various sites within the various distances were below and within their respective WHO MRLs for drinking water except chlorpyrifos at Diabaa (S2) and Kwakuanya (S4) at distance 16–30 m and diazinon at Kwakuanya (S4) at a distance 0–15 m which exceeded their WHO MRLs. There were no significant (p > 0.05) sites differences in mean values of pesticide residues detected in soils and water samples. The presence of organophosphorus in the samples analysed was an indication of the use of the pesticides by cocoa farmers in the study area to control pest and diseases. The pesticide residues in the soil poses danger to soil organisms as well as contaminate surrounding water bodies through runoff and leaching. In addition, there is the likelihood of translocation of these residues from the soil into the cocoa beans and other crops (like vegetables that are commonly intercropped with cocoa) through the root system, thereby posing health risks to consumers. Chlorpyrifos and diazinon concentrations in drinking water exceeded their respective WHO MRLs at some sampled sites and may pose health hazard to farmers’ household and the communities.