Ecological risk assessment of soil contamination by trace elements around coal mining area

Coal mining activities are inevitably connected with production of acidic drainage and airborne compounds such as fly ash and bottom ash with high metal content. Soil is a prominent sink for trace elements discharged from anthropogenic sources. Thus, understanding the occurrence, accessibility and ecological risk of trace elements around coal mining areas is of utmost importance in view of implications for environmental health. Seventy-five soil samples from 25 different sites were collected from Jharia coal field (India) and analyzed for pH, electrical conductivity, total organic carbon, and trace elements. For the background values of trace elements, black shale and sandstone were collected from the study area and analyzed for trace element concentrations. Sampled soils were evaluated for the level of soil contamination with respect to average shale concentrations of toxic trace elements in the region and assessed for their ecological risk in terms of enrichment factor, contamination factor, and pollution load index. Interactions among different trace elements and their spatial distribution were analyzed by the use of multivariate approaches. The study also quantifies the potential sources of contamination for each element and their relation with emission source. The average concentrations of Pb, Ni, Cu, Mn, Fe, Zn, and Cd in the soil exceeded the world averages, while Cu and Zn overstepped their respective critical limit in the soil. Enrichment factor values showed that soil near coal mine areas was loaded with Pb, Cd, Cu, Zn, and Ni. The pollution load index and contamination factor suggest that the soils were contaminated by all the investigated trace elements and areas near coal mines were the most polluted. The absolute principal component score technique, combined with multiple linear regression analysis revealed three major factors, coal mining activities/mine fires (40 %), windblown dust (23 %), and crustal (24 %), were responsible for soil trace element pollution in the area. Coal mining activities, mine fires, and windblown dust are the chief contributors of soil pollution in the area. Coal mining activities/mine fires are the main contributing sources to soil Ni, Cu, and Cr, while crustal input was mainly represented by Mn and Zn and windblown dust for Pb, Fe, and Cd. High concentrations of trace elements at any site depend on the feasibility and availability of respective pollution sources.