In Situ Remediation Activities of Rock Phosphate In Heavy-Metal Contaminated Cocoa Plantation Soil In Owena, South Western, Nigeria

The continuous use of copper-based fungicide over the years in the control of black pod disease has led to heavy-metal accumulation in cocoa soils due to its non biodegradable nature. Considering the limited, available forest, it is therefore, necessary for the existing heavy-metal contaminated cocoa soils to undergo soil remediation in order to reduce the bioavailability of metals for plant uptake and ultimately minimize the risk of heavy metal toxicological effects in consumers of cocoa products. Polypropylene pots were filled with 2.5kg heavy-metal contaminated soil collected from a cocoa plantation in Idanre, Ondo State, Nigeria. The soil samples were thoroughly mixed with Sokoto rock phosphate at the rate of 20, 40 and 60g phosphate per kg soil before sowing cocoa beans in the soils. The experiment was in a completely randomized block design (RCBD) replicated thrice. At six months after planting, the seedlings were removed and processed according to standard procedure. Seedlings’ leaves were analyzed for Cu and Pb using Atomic absorption spectrophotometer. Results showed that, bioavailable Cu in soil was reduced by 19, 35 and 42% due to application of 20, 40 and 60g phosphate per kg soil respectively while, Pb was reduced by 12, 23 and 25% respectively. The application of 20g, 40g and 60g rock phosphate reduced foliar Cu by 80, 69 and 85% while foliar Pb was reduced by 88, 89 and 77% respectively. The findings showed that, Sokoto rock phosphate which is readily available is a potential candidate for the remediation of heavy metal contaminated cocoa soils.