Effects of heavy metals in soil on microbial processes and populations (a review)

The effects of Cd, Cu, Zn, and Pb on soil microorganisms and microbially mediated soil processes are reviewed. The emphasis is placed on temperate forest soils. The sensitivity of different measurements is discussed, and data compiled to compare relative toxicity of different metals. On the whole the relative toxicity of the metals (on a μg g^?1 soil basis) decreased in the order Cd > Cu > Zn > Pb, but differences between different investigations were found. The influence of abiotic factors on metal toxicity is briefly discussed and especially examplified by different soil organic matter content. Evidence of tolerance and adaptation in the soil environment and the time scale involved in the evolution of a metal-tolerant microbial community after metal exposure are also considered.