Metal contents of Cocoa (Theobroma cacao l.) Beans and Plantation Soils in Ondo State, Nigeria

Abstract

The use of pesticides to increase and stabilize cocoa production has become a global concern because portions applied to the foliage and pods end in the plantation litter and soils for uptake by the crop. The resultant heavy metal contamination of the soils has implications for product quality and food safety. This study assesses the heavy metal contents of surface layer (0-15 cm) and subsoil (15-30 cm) samples of soils in plantations and the parts of cocoa beans in Ondo State, Nigeria. The samples were collected from nine villages across three Local Government Areas and analyzed for the heavy metals using standard laboratory procedures. 90 copies of type 1 questionnaire were administered on 10 randomly selected farmers per village and 10 copies of type 2 questionnaire administered on 3 or 4 store keepers. Descriptive statistics of frequency counts, percentage, means and standard deviation were used to analyze the responses while data of heavy metals were subjected to analysis of variance. The average age, farm size and family size were 52±14 years, 9±13 acres and 6±2 persons, respectively. The farmers were males (87.8%) with formal education (91.5%), had used seeds harvested from plantations for planting (74.4%) and adopted 1111 seedlings ha-1 (90.3%). Only 47.6% used fertilizers and the main products were NPK 15-15-15 and NPK 20-10-10 mainly at 2 bags acre-1. The heavy metal contents of the soils were higher at 0-15 cm than 15-30 cm and the values significantly differed (p<0.05) among the locations. The order of abundance was Cu > Pb > Cd with Cu and Cd (detected in one location) above the permissible limits of 140 and 3 mg kg-1 respectively. The whole bean, testa and kernel were contaminated with Pb in all locations while Cu contamination of the whole bean and testa was in 3 and 2 locations respectively. The threat posed to market demand by quality and food safety concerns means that farmers should adhere to the recommended types and doses of pesticides to reduce heavy metal contamination while all stakeholders should monitor the cocoa from production through processing to packaging for the market.