A comprehensive insight into ecological risk assessment and remediation of metal contaminated coal mine soil: Towards a cleaner and sustainable environment

Abstract

The current study directs attention towards investigating the Mobility Factor, Risk Assessment Code and Potential Ecological Risk Index of non-carcinogenic heavy metals in coal mine waste contaminated soil and its remediation with organic waste amendment. Coal mining has adverse impact on the environment and leads to major degradation of soil quality. Degradation due to anthropogenic activities led to complete loss of vegetation in two inactive coal mining sites in Assam, India. An immediate restoration of the land and its natural habitat is of dire need and the current work aims to align with the sustainable development goal (SDG) 15. Mine waste soil (MWS) was collected from Ledo and Tikak sites and mesocosm study was conducted with vegetable waste compost (VWC) enrichment at different ratios. Soil physico-chemical properties, soil fertility, metal bioavailability, leachability and chemical speciation were observed up to a period of 120 days. 20% and 35% VWC (w/w) showed improved pH, electrical conductivity, organic carbon, cation exchange capacity, nitrogen, phosphorous and potassium levels as compared to 5% VWC addition. The sustainable approach of VWC enrichment to the soil matrix reduced metal bioavailability, leachability and speciation. Fe, Zn, Ni, Mn, and Cr concentration in the control (MWS) and amendments were checked. Cr showed a 100% reduction in water soluble, plant available and leachable fractions. Cr was found to be present in the residual fraction in the sequential extraction of metals. The response of one of the soil pollution indicator crop viz., Phaseolus vulgaris was studied in the control and compost enriched MWS. MWS enriched with 20% VWC (w/w) showed the best results for all the studied ratios and aspects thus, it can be used for ameliorating coal mine waste contaminated soil.