DISTRIBUTION OF HEAVY METALS IN COCOA BEAN AND SOILS ALONG TOPOSEQUENCE OF COCOA PLANTATIONS

  • E.U. Eteng Department of Soil Science and Meteorology, Michael Okpara University of Agriculture, Umudike Nigeria
Keywords: Cocoa bean, coca-cola extractant, heavy metals, bioavailability, toposequence, soil, and leaf

Abstract

This study was conducted in April, 2018 to evaluate the relationships between Cu, Fe, Mn and Zn in cocoa bean
and in soils along a toposequence of cocoa-growing areas of Abia State, Nigeria. Twelve composite soil samples
and 10 plant tissues (leaves and cocoa pods) were randomly collected from twelve (12) different cocoa
plantations along a toposequence (crests, upper, middle, lower and bottom) for laboratory analyses. The
concentrations of Cu, Fe, Mn and Zn in both plant tissues and soils were determined. Results showed that the soils
were sandy clay loam, strongly acidic, low in organic matter and sufficient in the four heavy metals contents. The
content of coca-cola extractable Cu, Fe, Mn and Zn in soils, cocoa bean and leaf varied significantly along the soil
toposequence. The bioavailability of the metals in soils and in plant tissues were in the order: Cu>Zn>Fe>Mn,
while, the comparative abundance of the four metals followed the order: cocoa bean > leaves > soil. Significant
positive relationships were also established between the metals in cacao tissues and corresponding levels of
bioavailability in soils. This suggests that, the primary source of the heavy metals in cocoa beans could be linked
to its primary uptake from the soils and secondary from the leaf sprayed with metals containing pesticides. This
result can possibly be used as predictive parameter for evaluating Cu, Fe, Mn and Zn levels in cacao bean and
cocoa products.

Published
2020-04-30

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eISSN: 0300-368X