Global Journal of Environmental Research 6 (1): 30-35, 2012 ISSN 1990-925X © IDOSI Publications, 2012 DOI: 10.5829/idosi.gjer.2012.6.1.385 Corresponding Author: P.E. Aikpokpodion, Cocoa Research Institute of Nigeria, P.M.B. 5244, Ibadan, Nigeria. 30 Assessment of Heavy Metals Mobility in Selected Contaminated Cocoa Soils in Ondo State, Nigeria P.E. Aikpokpodion, L. Lajide and A.F. Aiyesanmi 1 2 2 Cocoa Research Institute of Nigeria, P.M.B. 5244, Ibadan, Nigeria 1 Federal University of Technology, Akure, Nigeria 2 Abstract: Phytophtora pod rot is currently the most important limiting factor in the Nigeria cocoa Industry with a total losses of 30-90% crop loss. To overcome this problem, Nigerian cocoa farmers solely use copper-based fungicides to control the disease. Copper being a metal is not biodegradable. Hence, it accumulates in the soil as a result of continual use. Heavy metals are potentially toxic to soil microbes and soil environment in general. Toxicity depends on chemical association in soil. For this reason, determining the chemical form of a metal in soils is important to evaluate its mobility and bioavailability. Sequential extraction was used to fractionate four heavy metals (Cu, Zn, Cd and Pb) in soils from ten contaminated cocoa plantations across Ondo State, Nigeria into six operationally defined pools: water soluble, extractable, carbonate, Fe-Mn oxide, organic and residual. The organic fraction was the most abundant pool for copper and zinc, extractable fraction for Lead and residual for cadmium. Mobility and bioavailability of these four metals in the studied soils were in the order : Pb>Zn>Cd>Cu. This indicates that lead had the highest chance of being accumulated in cocoa beans. Key words: Cocoa % Contamination % Heavy metals % Black pod % Ondo INTRODUCTION Pollution of the natural environment by heavy metals is a Nigeria is currently the fourth largest producer of most of them have toxic effects on living organisms [4]. cocoa in the world. Cocoa is a crop of economic Many studies have been conducted on heavy metal importance with more than 650,000 ha of land being contamination in soils from various anthropogenic cultivated in Nigeria [1]. It ranked first amongst sources such as industrial waste [5], automobile agricultural export crops in its contribution to foreign emissions [6] and agriculture practice [7]. Soils samples earnings [2]. Incidence of black pod disease caused by collected from cocoa plantations which had received Phytophtora sp. has being implicated in the dwindling application of copper-based fungicides over the years in production of cocoa in Nigeria. The main economic loss Ondo and Cross River States (both in Nigeria) were is from the infection of the pods which in turn affect the reported contaminated with copper [8]. Based on primary quality of the beans in the pods. In order to check the accumulation mechanisms in soil, heavy metal can be menace of Phytophtora sp. on Cocoa, Nigerian cocoa classified into six categories: (i) water soluble (ii) farmers solely use copper based fungicide which is known Extractable (iii) bound to carbonate phases (iv) bound to to be the most effective means of controlling black pod reducible phases (Fe and Mn oxides) (v) bound to organic disease. For farmers to get optimum yield of cocoa beans matter (vi) detrital or lattice metals (Residual) [9]. Heavy during harvest, they use fungicides on regular basis. metals present in these categories have different Leonila [3] reported that, when pesticides are applied to remobilization behaviors under changing environmental protect crops from the attack of pests and diseases, only conditions [10]. Geochemical forms of heavy metals in soil 15% of it hits the target while the remaining 85% is affect their solubility, which directly influence their distributed between soil and air. The soil is the main matrix bioavailability [11]. Therefore, determining total heavy for pesticide disposition and the bulk of pesticides are metals is insufficient to assess their environmental impact generally confined to the upper 5cm of the top soil. on soil and sediments. It therefore implies that, it is the global problem because of their indestructible nature and