Impact of pesticides use on heavy metals pollution in cocoa soils of Cross-River State, Nigeria

摘要

The high incidence of phytophthora pod rot and mirids resulting from high rainfall and relative humidity in cocoa producing areas of Nigeria necessitated the use of fungicides and other pesticides on cocoa. This is causing increased worldwide concern about heavy metal contamination of the soil environment and cocoa beans. Thus the objective of this study is to evaluate the status of some heavy metals in selected cocoa farms in Ikom, Etung and Boki local government areas of Cross River State - the highest cocoa producing state in eastern Nigeria, where farmers use a lot of pesticides to combat pests and diseases. The results indicated that the soil contents of the heavy metals were in the order (Cr > Pb > Co > Ni > Se > Cd > As) in the selected farms evaluated in the three local government areas. The values ranged between 0.88 and 1.33 mg/kg for chromium and between 0.59 and 0.86 mg/kg for lead. The soil contents of the heavy metals in the adjacent forest were similar to that obtained in the cocoa farms. The values of chromium ranged between 1.01 and 1.02 mg/kg soil while that of lead ranged between 0.5 and 0.74 mg/kg soil in adjacent forest. This suggests that heavy metal contents of the soils in the cocoa farms evaluated were not primarily due to chemicals being sprayed but probably naturally occurring. Their concentrations were also below the optimum limit allowed in the soil.