Soil-to-Crop Transfer, Bioaccumulation, and Health Risk Assessment of Heavy Metals in Cassava Grown in Illicitly Mined Areas of Noyem and Nyafoman, Eastern Ghana

Abstract

Introduction: Illicit mining contaminates Ghana with heavy metals, risking soil fertility, food safety, and public health. Despite concern, data on metal transfer into staple crops like cassava remains limited. This study assessed heavy metal levels in soils from illicitly mined sites at Noyem and Nyafoman and examined their transfer into cassava tubers to evaluate ecological and health risks. Soil and cassava samples were collected from mined and control sites.

Method: Concentrations of Zn, Fe, Cu, Hg, and Cd were determined by Atomic Absorption Spectrophotometry (AAS). Soil–plant transfer factors and ecological risk indices were calculated, while dietary exposure was assessed using estimated daily intake (EDI) and risk index (RI) per FAO/WHO guidelines. Data were analyzed using SPSS v20.0 with descriptive statistics and correlation analysis.

Result: Higher concentrations of Zn, Fe, Hg, and Cd were found in mined site soils versus controls. Fe levels exceeded control limits, while Zn remained below permissible limits. Mercury was detected at notable levels, consistent with Ghanaian mining studies reporting 0.68-17.03 mg/kg. Cassava tubers from mined soils showed higher Cu and Hg accumulation, exceeding FAO/WHO limits. Associations between soil and cassava Cu concentrations indicated cassava's tendency to accumulate Cu, suggesting its use in monitoring metal transfer in mining-affected agroecosystems. Zn, Hg, and Cd showed weak soil-plant relationships, reflecting differences in metal bioavailability influenced by soil pH and organic matter. Dietary risk assessment revealed long-term Cu exposure concerns, while Zn intake exceeded safety thresholds for children (RI > 1), indicating increased susceptibility.

Conclusion: Illicit mining at Noyem and Nyafoman increases heavy metal levels in soils and cassava, affecting environmental quality and public health. The findings support the need for improved regulation of illicit mining, monitoring of soils and crops, and sustainable remediation strategies to protect food security in mining-affected regions of Ghana.