Soil amendments reduced potentially toxic elements (PTEs) in peanuts (Arachis hypogaea L.) grown in farmlands near Cu-Ni mine in Central Botswana.

Abstract

This study evaluated the effects of fly ash (FA), compost (COMP), lignite (LIG), and their combination (FA+COMP+LIG) on soil chemical properties, PTE total and available concentrations, PTE uptake by peanut (Arachis hypogaea L.) tissues, and associated human health risks in agricultural soils near BCL Cu-Ni mine. A field experiment was conducted in three farmlands located 2.6 km, 5 km, and 10 km from the BCL Cu-Ni mine in Selibe-Phikwe, Botswana. The experiment consisted of five treatments arranged in a randomized complete block design (RCBD) with three replications: unamended control, FA at 20 t ha^-1, COMP at 20 t ha^-1, LIG at 10 t ha^-1, and FA+COMP+LIG at 20 + 20 + 10 t ha^-1. Amendment application increased soil pH and reduced both total and available PTE concentrations in soils across all farms. Additionally, all amendments improved peanut dry matter yield compared to the control treatment. The combined treatment showed the greatest reduction in PTE accumulation in peanut tissues, particularly in kernels, where the reduction exceeded 30% relative to the control. Estimated daily intake (EDI), hazard quotient (HQ), and hazard index (HI) values for both children and adults were significantly reduced following amendment application, indicating lower dietary exposure to PTEs. However, despite the observed reductions, the HQ and HI values for some PTEs remained above the threshold value of 1, suggesting potential health hazards. Overall, the combined application of FA, COMP, and LIG showed the greatest potential for reducing PTE uptake by peanuts and decreasing associated human health risks in mine-affected agricultural soils. Further long-term field studies are recommended to evaluate the sustainability of these remediation effects.