Effects of Pahs on Microbial Activity and Diversity in Freshly Contaminated and Weathered Soils

Polycyclic aromatic hydrocarbon (PAH)-contaminated soils are of concern to the Environmental Protection Agency (EPA) due to their mutagenic and carcinogenic nature. Bioremediation of PAHs is aimed at increasing the overall rate of natural degradation. Microbial bioremediation promotes processes by which microorganisms can take up and/or degrade organic molecules and their metabolites. Microorganisms can use organic molecules for energy or convert them into cell biomass, ultimately releasing carbon dioxide and water to the environment. Changes in microbial biomass and CO2 evolved are used as indices of degradation rates. In situ bioremediation utilizes indigenous microorganisms and/or involves addition of specific microorganisms with enzymatic capabilities (such as enhanced oxidative functions) to establish conditions favorable to microbial degradative activities. The overall goal of this study was to assess the biodegradation of the target PAHs, pyrene and phenanthrene, in rhizosphere soils. Comparisons of microbial diversity and activities due to PAH contamination between a weathered loam and a clean sandy loam were made. Carbon substrate utilization was the estimate of microbial functional diversity used in this study. Functional diversity was evaluated using the Biolog® assay system. Results from the study show significant differences in substrate utilization and microbial diversity between the two soil types and various treatments.