Lead (Pb) contaminated soils represent severe environmental problems as well as a significant hazard to human health.  Prolonged exposure to high levels of toxic metals exerts considerable selective pressure on the soil microbial community and alters soil and ecosystem health.  The objective of this study is to understand how the total level of Pb contamination, as well as Pb speciation in these soils, has affected the soil microbial community structure in terms of fungal:bacterial ratios at an abandoned small-arms firing range in east Tennessee.

Ninety-two soil samples were collected in a spatially explicit sampling design across two basic ecosystem types, grassland and forested, surrounding the backstop at the abandoned firing range.  Soils were analyzed via qPCR for total fungi and bacteria and fungal:bacterial ratios were calculated.  Soil pH, total Pb, extractable Pb, total C and N, nitrate N, organic matter, phosphate, sulfate, and  water content were all determined across the site and site maps, or interpolations, were created using ArcGIS 10.1.

Soil Total Pb concentrations ranged from below detection limits to over 9,000 mg kg^-1 with the highest total lead concentrations geographically located along the slope of the earthen berm to the north of the firing backstop and the lowest lead was found in the grassland soils to the south and furthest from the backstop.  Soil microbial properties did not directly correlate with soil chemical properties but some areas of high fungal abundance overlapped with areas of high total and extractable soil Pb and soil sulfate. 

Many species of fungi are capable of transforming insoluble metal compounds into soluble derivatives, an environmentally important process when these fungi constitute a significant portion of the overall soil community.  Understanding how soil microbial community structure responds to soil lead content and the dynamic biogeochemical impacts the soil fungal community may exert on extant lead in soils will yield a greater understanding of lead bioavailability in soils and human risk assessment.