[Accumulation Characteristics, Pollution Risk, and Source Analysis of Soil Heavy Metals Around a Coal Mining Area in the Baiyin Section of the Upper Yellow River].

Abstract

To quantitatively assess and accurately ascertain the characteristics, sources, and ecological risks of soil heavy metal pollution in the arid and semi-arid coal mining areas of the upper Yellow River Basin, the Wangjiashan coal mining area in Pingchuan of the Baiyin City was selected for this study. Based on the concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the soils of the urban areas and agricultural lands around the coal mining region, the geo-accumulation index, enrichment factor, modified Nemerow comprehensive pollution index, and comprehensive ecological risk index were employed to systematically quantify the levels of soil heavy metal pollution and associated ecological risks. Furthermore, cluster analysis and the positive matrix factorization receptor model were jointly utilized to quantitatively explore the sources of soil heavy metals and their respective contribution rates. The results showed： ① The contents of the eight heavy metals in the urban soils around the study area were below the risk screening values for Type I construction land in the "Soil Environmental Quality Risk Control Standard for Soil Pollution of Construction Land （Trial）" （GB 36600-2018）. However, the contents of Pb, Hg, Cd, Zn, Cu, As, and Cr exceeded the soil background values of Gansu Province in 100%, 88.89%, 44.44%, 22.22%, 16.67%, 13.89%, and 2.78% of the samples, respectively. The contents of the eight heavy metals in the agricultural soils were below the screening values for soils with pH > 7.5 in the "Soil Environmental Quality Risk Control Standard for Soil Pollution of Agricultural Land （Trial）" （GB 15618-2018）. Yet, the concentrations of Pb, Hg, Cd, Cu, Zn, As, and Ni exceeded the soil background values of the Gansu Province in 100%, 89.74%, 38.46%, 25.64%, 23.09%, 23.08%, and 17.95% of the examined samples, respectively. ② The soil pollution in the surrounding areas was predominantly characterized by Hg and Pb, overall presenting a moderate level of contamination. However, the degree of comprehensive pollution in urban soils exceeded that of agricultural soils. The urban soils were in a state of relatively high ecological risk, whereas the agricultural soils exhibited a moderate ecological risk. Notably, Hg was the principal hazardous element contributing to the ecological risk of the soils around the study area. ③ In the surrounding soils, the presence of As was impacted by coal combustion-agricultural sources and natural sources, contributing 40.73% and 26.68%, respectively. Cd originated from industrial and transportation sources, with contribution rates of 37.07% and 26.17%, respectively. Cr was affected by natural sources at 35.37%. Cu and Zn were influenced by the combined effects of coal combustion-agricultural sources and transportation sources, with respective contribution rates of 29.94% and 41.19% for Cu and 31.41% and 40.32% for Zn. Hg was predominantly influenced by coal mining activities, accounting for 99.99% of its source.