Effects of Heavy Metal Contamination on Microbial Biomass and Community Structure in Soils.

Zinc smelting near Magu Town, Hezhang County, Guizhou Province, resulted in vegetation destruction and the accumulation of heavy metals, to varying extent, in adjacent soils, where up to 162.2 - 877.9 mg · kg-1 Zn, 37.24 - 305.6 mg · kg-1 Pb, and 0.50 - 16.43 mg · kg-1 Cd, were detected. These values greatly exceed the background levels of these elements in soils. The concentrations of heavy metals (particularly Pb, Zn) were positively correlated with the contents of Fe2O3 and Al2O3 in the soils, showing that Fe and Al oxides play an important role in retaining heavy metals. Chemical fractionation indicates that Pb and Zn were associated mainly with Fe and Mn oxides and minerals, whereas Cd was dominated by exchangeable form. Microbial biomass in the soils was relatively low, in the range of 57.00 - 388.0 µg C · g-1, and was negatively correlated with heavy metal concentrations in the soils. The correlation coefficient of microbial biomass C to Zn concentrations in the soils was as high as -0.778 (p < 0.01), indicating that the heavy metal contamination has toxic effects on microorganisms in soil. The results of Biolog measurements demonstrated that there were no significant changes in microbial community structure in the heavy metal contaminated soils. Gene fragments were similar to one another after the DNA was extracted from soil microbes and experienced PCR (polymerase chain reaction) and DGGE (denaturing gradient gel electrophoresis) reactions. These results indicated that light heavy-metal pollution may not result in any change in soil microbial community structure. [ABSTRACT FROM AUTHOR]