Phytotoxicity and Metals Mobility Assessment in Mining Wastes Amended with Various Biochars

Abstract

Mining activities often contaminate soils with heavy metals, generating environmental and health risks. This study investigates the ecotoxicity of muddy (Mw) and sandy (Sw) mining wastes on Phaseolus vulgaris and assesses the impact of five locally sourced biochar amendments on plant growth and soil pore water (SPW) properties. Most biochars improved water retention, except for argan nut shells (An) biochar, highlighting the importance of feedstock type. Sw supported better plant growth than Mw regardless of biochar addition, due to textural differences. Palm fronds (Pf) biochar significantly enhanced surface leaf area in Sw. SPW analysis revealed that biochar affected pH and electrical conductivity (EC) differently across soil types. Mw consistently increased pH, while Sw’s pH was biochar-dependent. A significant 5.1-fold EC increase was recorded in Sw amended with Pf. All biochars reduced Pb availability in Mw at planting, while Cu availability decreased in Sw at harvest. In Mw, Pb, Zn, and Cu, uptake and accumulation were unaffected by biochar, while a slight reduction was observed in Sw roots. A germination test with Lepidium sativum confirmed these findings, particularly the inhibition observed with An. This dual approach highlights the toxicity of mining soils and biochars’ potential as amendments for soil remediation programs.