Biodegradation of simple chemical mixtures in soil

Exogenous microorganisms often are used to enhance bioremediation. This study compared the capabilities of two exogenous microbial cultures and an indigenous population to detoxify a Weswood silt loam soil amended with a simple chemical mixture. The first three treatments were unamended soils inoculated with either indigenous microorganisms, Pseudomonas aeruginosa, or Phanerochaete sordida. Three additional treatments consisted of soil amended with benzo[a]pyrene, pentachlorophenol, and 2,4,6-trinitrotoluene, which were inoculated with either indigenous microorganisms, P. aeruginosa, or P. sordida. Samples were collected from the soils at several time points from 0 through 540 or 720 d, sequentially extracted with methylene chloride and methanol, and analyzed for genotoxicity (using the Salmonella/microsome assay) and chemical degradation. Although the indigenous microorganisms were effective for removal of benzo[a]pyrene, the Pseudomonas bacteria exhibited slightly greater removal rates for 2,4,6,-trinitrotoluene. The fungal cultures were significantly more effective at degrading pentachlorophenol. The day 540 extracts from all model chemical-amended treatments were genotoxic. In most cases, the day 540 extracts were more genotoxic than the day 0 extracts. The results suggest that, under appropriate conditions, enriched cultures of microorganisms may have an increased capacity to degrade individual chemicals. However, the products of degradation in some cases might be more genotoxic than the parent compounds.