RISK ASSESSMENT OF SOIL HEAVY METAL POLLUTION IN A TYPICAL COAL MINE AREA IN CENTRAL CHINA AND ITS EFFECTS ON ENZYME ACTIVITIES

In order to study heavy metal pollution in a coal mine area in Central China, and the effects of heavy metal pollution on soil enzyme activity, soil samples were collected at various distances from the mine entrance. The heavy metal content (Cr, Mn, Cu, Zn, Cd, Pb) in the collected soil samples was evaluated against the baseline value of Central China soil using four methods: single factor pollution index, comprehensive pollution index, geoaccumulation index, and potential ecological risk index. Results showed that the average content of Cr, Mn, Cu, Zn, Cd, and Pb in the uranium tailing area was 16.86, 141.95, 38.81, 100.06, 1.23, and 58.72 mg"kg-1, respectively, of which the highest Cd content was 4.12 times that of the baseline value. The geoaccumulation index for Zn and Pb ranged from 0 to 1, indicating light pollution. The geoaccumulation index for Cd was between 2 and 3, indicating moderate pollution. Evaluation using the potential ecological risk index shows that heavy metal pollution in the surrounding soil of the coal mine area is generally at a high ecological risk level, and that the pollutant with the highest potential ecological risk index is Cd. The results of principal component analysis show that the sources of Mn, Cu and Cd may be associated with the uranium mining process, reflecting the local uranium mining and smelting activities. Soil urease, sucrase, dehydrogenase, and catalase showed 38.34%, 50.53%, 55.06%, and 73.43% reduced activities levels, respectively. Multiple regression analysis showed that, in the presence of heavy metal soil pollution, the inhibitory effect of Cr, Mn, Cu, Zn, Cd, and Pb on the activity of four soil enzymes could be ranked as Cd > Cu > Mn > Zn > Pb > Cr.