Mitigation of Potentially Toxic Elements in Corn (Zea Mays) Grown in Farmlands Near Cu-Ni Mine in Central Botswana

Abstract

Mismanagement of mine waste at Bamangwato Concessions Limited (BCL) Cu-Ni mine have led to serious environmental degradation, resulting in elevated levels of potentially toxic elements (PTEs) in agricultural soils. Field trials were conducted in three farmlands at varying distances to evaluate the effects of amendments (fly ash -FA, compost -COMP, and lignite -LIG; and FA+COMP+LIG) on soil chemical properties, growth, PTE uptake by corn, and its subsequent risk when consumed by humans. The amendments significantly reduced total and available PTEs in soil on all farms and the concentration of PTEs in corn tissues, especially FA+COMP+LIG, which resulted in Cr reduced by 11.65X, Ni by 2.37X, Cu by 1.79X, Zn by 2.41X, As by 13.07X, and Pb by 4.10X in corn kernels and subsequently the estimated daily intake (EDI) values. The estimated hazard quotient (HQ) and hazard index (HI) values from the consumption of corn kernels were significantly reduced by amendments, although the values were still greater than 1. Overall, the application of amendments in farmlands near the BCL Cu-Ni mine can reduce PTE availability in soil and corn tissues, particularly in edible parts and subsequently lower the health hazards. Additional verification and efficacy tests under long-term field conditions are recommended.