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 r esult in significant losses in soil quality, The negative impact of he avy metals results from their toxicity to biological processes, includ ing processes catalyzed by soil microorganisms. Therefore, it is postu lated that the soil microbial community could serve as an indicator of losses in soil quality due to heavy metal contamination and of change s 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. Bot h total and soluble metal loadings in these soils increased with proxi mity to the smelter. Indicators of microbial activity (dehydrogenase a ctivity) and viable population size (plate counts) were negatively aff ected by the elevated metal levels, Microbial community structure also varied with increasing contamination, as indicated by cluster analysi s and principal component analysis of BIOLOG community metabolic profi les, 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 met abolic 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 s oil quality with management of these highly contaminated soils.