Pollution Characteristics and Spatial Distribution of Heavy Metals in Coal-Bearing Sandstone Soil: A Case Study of Coal Mine Area in Southwest China

Abstract

Soil pollution in coal mining areas is a serious environmental problem in China and elsewhere. In this study, surface and vertical profile soil samples were collected from a coal mine area in Dazhu, Southwestern China. Microscopic observation, concentrations, chemical speciation, statistical analysis, spatial distribution, and risk assessment were used to assess heavy metal pollution. The results show that the weathering of coal-bearing sandstone and mining activities substantially contributed to soil pollution. The concentrations of Fe, Ni, Cu, Zn, Mn, Cd, Hg, and Pb exceeded their background values. Cd caused the most intense pollution and was associated with heavily–extremely contaminated soils. The residual fraction was dominant for most metals, except Cd and Mn, for which the reducible fraction was dominant (Cd: 55.17%; Mn: 81.16%). Zn, Ni, Cd, and Cu presented similar distribution patterns, and Hg and As also shared similar distribution characteristics. Factor 1 represented anthropogenic and lithologic sources, which were affected by mining activities; Factor 2 represented anthropogenic sources, e.g., fertilizers and traffic pollution; and Factor 3 represented the contribution of metals from soil-forming parent material. More than half of the study area had high pollution risk and was not suitable for vegetable cultivation.

Spatial Distribution and Migration of Heavy Metals in Dry and Windy Area Polluted by Their Production in the North China

“…This study showed that the concentrations of Cu, Zn, As and Pb in vertical distribution were negatively correlated to depth. This was consistent with the results of previous studies in North China [8,9], and contrary to the results of studies in the 0-20 cm range in South China [28]. This was due to differences in precipitation and soil pH between them.…”

“…The distribution of soil heavy metals shows a ring outward direction from the mining area in many previous studies [7][8][9][10]. And the concentration of heavy metals in soil decreases with increasing the distance from mining or production areas.…”

“…Compared with Cu, Zn and Pb, concentrations of As and Cr show a greater decline in soil by 1-2 folds when the distant from mining area increases from 20 m to 100 m [10]. And Zn can transport a longer distant than Pb and Cd by 2-6 times [8]. However, Gao et al (2017) [9] found distributions of Cu, Zn, Cr, Pb and Cd appear two peaks along distance from mining area within 0-3 km, and they reach the second peak at 2 km from mining area, then decline to the background value [9].…”

Heavy Metal Pollution and Source Contributions in Agricultural Soils Developed from Karst Landform in the Southwestern Region of China

“…Meanwhile, the regional chemical atlas of China and the 1:200,000 stream sediment survey results also show that heavy metals in soils have a naturally high background attribute in karst landform areas of the southwest regions of China, especially the Cd element [ 11 , 12 ]. Heavy metals pollution has become a major problem in the southwest regions of China [ 13 , 14 , 15 , 16 ].…”

“…With the research into heavy metals pollution becoming the focus of attention, many scholars have carried out some related research about the content status, distribution characteristics, pollution levels and enrichment factors of heavy metals in the southwest karst landforms of China in recent years [ 13 , 14 , 15 , 16 , 21 , 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. However, there are few studies on the sources of agricultural heavy metals, which affects the scientific judgment about soil heavy metals pollution.…”