Effects of heavy metal contamination and remediation on soil microbial communities in the vicinity of a zinc smelter

Heavy metal contamination can impact soil ecosystems sufficiently to result in significant losses in soil quality, The negative impact of heavy metals results from their toxicity to biological processes, including processes catalyzed by soil microorganisms. Therefore, it is postulated that the soil microbial community could serve as an indicator of losses in soil quality due to heavy metal contamination and of changes in soil quality resulting from reclamation. In this study, the size, activity, and structure of microbial communities from remediated and unremediated soils in the vicinity of a Zn smelter were evaluated. Both total and soluble metal loadings in these soils increased with proximity to the smelter. Indicators of microbial activity (dehydrogenase activity) and viable population size (plate counts) were negatively affected by the elevated metal levels, Microbial community structure also varied with increasing contamination, as indicated by cluster analysis and principal component analysis of BIOLOG community metabolic profiles, Remediated soils at this site were treated by surface application of a mixture of sewage sludge and fly ash, Remediation resulted in a decrease in soluble metals and an increase in indicators of biological activity and viable population size. Remediated soils also showed metabolic profiles that were more similar to the least contaminated site, suggesting recovery of the microbial populations. These data suggest that the microbial community may be a useful indicator of changes in soil quality with management of these highly contaminated soils.