Effects of heavy metal compound contamination of Cd, Zn, Cu andPb on soil biological activity

Soil microbial indicators and enzyme activity in Dongchuan copper mining wasteland of Yunnan Province were comparatively studied in laboratory with collected field samples. Incubation experiment was also conducted to investigate the influence of combined heavy metal pollution of cadmium, copper, zinc and lead on soil microbial indicators and soil enzyme activity. The results indicated that soil organic matter, available nitrogen (N), phosphorus (P) and potassium (K), and pH significantly decreased with decreasing distance of soil sampling points from the mines. Enzyme activity, microbial quantity, microbial biomass carbon (C) and N also decreased with decreasing distance of soil sampling points from the mines. Compared to the control (10 000 m from the mines), sucrase, urease, acid phosphatase, catalase and dehydrogenase activities along with amounts of bacteria, actinomyces and fungi in collected soil samples at 0~800 m from mine decreased by 25.5%~47.3%, 22.6%~74.2%, 30.9%~83.1%, 16.7%~69.1%, 34.6%~92.3%, 30.5%~80.1%, 8.1%~49.9% and 3.3%~8.3%, respectively. Whereas microbial biomass C and N decreased by 23.7%~66.2% and 31.8%~74.7%, respectively, while microbial biomass carbon to nitrogen ratio increased with decreasing distance from the mines. Soil Organic matter, available N, P and K significantly decreased probably due to significant reductions in soil enzymatic activity, microbial amount, microbial biomass C and N. Compared with other indicators, soil phosphatase and catalase activity along with soil bacteria population were more sensitive to the degree of heavy metal pollution. Under incubation experiment at 25 ℃, soil enzyme activity, microbial population, and microbial biomass C and N were enhanced by combined pollution of low Cd, Zn, Cu and Pb. This, however, obviously decreased under combined pollution of high Cd, Zn, Cu and Pb. There were synergistic and antagonistic effects among Cd, Zn, Cu and Pb. While synergistic effects between Pb and Cd, Zn or Cu were related to microbial biomass C and N, antagonistic effects between Pb and Cd, Zn or Cu were related to bacteria population. Synergistic effects coexisted with antagonistic effects between Pb and Cd, Zn, Cu in relation to fungi and actinomyces populations, respectively.