Field application of local soil amendments to post-tin mining soils – Effects on heavy metal(loid) concentration in crops and soils

Heavy metal(loid) (HM) contamination in post-mining areas poses serious risks to ecosystem integrity and food safety. This study evaluated the effectiveness of locally sourced soil amendments in reducing HM availability and plant uptake in post-tin mining soils on Bangka Island, Indonesia. A field experiment was conducted using five treatments: (1) dolomite, (2) compost, (3) charcoal, (4) charcoal + compost, and (5) charcoal + sawdust. Cassava (a staple food crop) and Centrosema (a legume forage crop) were intercropped, and HM concentrations in soil and plant tissues were measured. Cassava in the control treatment exhibited high cadmium (Cd) concentrations in leaves, with the highest bioaccumulation and transfer factor observed in the control treatment (BAF = 15.17; TF = 3.98). Charcoal + compost treatment significantly reduced Cd accumulation, lowering the BAF and TF to 5.05 and 1.73, respectively. Plant concentrations of lead (Pb) and arsenic (As) varied across treatments, showing no consistent trend. In soils, dolomite reduced oxalate-extractable Cd and Pb in soil by up to two-thirds, although As remained unchanged. The charcoal + compost treatment increased aqua regia-extractable iron (Fe), zinc (Zn), and copper (Cu) (640, 16, and 0.89 mg kg−1, respectively), indicating improved essential HM availability. These findings highlight charcoal + compost treatment can significantly reduce toxic HM uptake while enhancing soil health status. This approach offers an accessible solution for subsistence farmers, reducing reliance on imported inputs while fostering sustainable land use. By linking soil rehabilitation with improved agricultural productivity, the study provides a practical pathway for enhancing both environmental quality and rural livelihoods. © 2025