Temporal Dynamics of Heavy Metal Uptake and Food Safety Risk in Cassava Grown on Rehabilitated Post-Tin Mining Soils

Post-tin mining soils are highly degraded environments that often contained elevated concentrations of potentially toxic elements, posing persistent risks to food safety when reused for agriculture. This four-year field experiment evaluates whether soil amendment strategies can promote soil regeneration while reducing heavy metal transfer to major staple crop, cassava (Manihot esculenta Crantz). Six treatments were established in an intercropped plot system with legume species: control (no amendment), dolomite, compost, charcoal, charcoal + compost, and charcoal + sawdust. Temporal changes in soil pH and soil organic carbon (SOC) were monitored as key indicators of soil recovery. Cassava yield was measured, and Pb, Cd, and As concentrations in cassava edible part were analysed to trace the temporal changes in heavy metal uptake. All amended treatments showed progressive increases in soil pH and SOC over the four-year period, indicating gradual recovery of soil chemical quality of post-tin mining soils. Cassava yield increased accordingly, with the charcoal + compost treatment consistently producing the highest yields. From a food safety perspective, Pb, Cd, and As concentrations in cassava tissues exhibited a clean declining trend all treatments through time, demonstrating a temporal reduction in metal bioavailability and plant uptake. The strongest decreases in tissue metal concentrations were associated with treatments that most effectively increased SOC and stabilized soil pH. This long-term case study demonstrates that targeted soil rehabilitation strategies can mitigate contamination risks while restoring agricultural function to post-mining soils. Tracing soil regeneration alongside temporal patterns of plant tissue contamination provides a robust framework for evaluating the food safety of mining-impacted lands and supports sustainable land management.