Factors affecting the biodegradation of polyaromatic compounds in soil.

摘要

The goal of this research was to determine the indigenous mineralization rates and extents of select polycyclic aromatic hydrocarbons (PAHs) and N-heterocyclic aromatic (NHAs) compounds in soils known to be contaminated with hydrocarbons. Bacteria were to be isolated from these soils and used for enhancing mineralization of certain compounds by reintroducing cultures into soils in the laboratory. Early results indicated that the mineralization of added compounds varied between soils, so further investigation focused on the effect of soil organic matter (SOM) on the mineralization of one compound by a degrading microorganism. The compound used was pyrene, and the microbe an isolated pyrene-degrading Mycobacterium sp. Soil organic matter was extracted from both impacted and non-impacted soils using a standardized method followed by isolation of fulvic acids (FAs) from each. Mineralization of pyrene by the Mycobacterium sp. was significantly greater in the presence of FAs from non-impacted soils than that of impacted soil FAs. There appeared to be no correlation between pyrene mineralization and the concentration of FA added. To determine the effects of the extracted FAs on the survival of the Mycobacterium sp., experiments were set up to allow for measurement of microbial activity by acetate incorporation into lipids and acetate mineralization, microbial biomass by lipid phosphate, and plate counts of the sand/FA slurries. The added mycobacteria were found to be affected by the presence of increasing amounts of added FAs in that there was a decrease in the measured levels of the survival assays with increasing FA concentration. Chemical characterization of the extracted FAs indicated the presence of high levels of inorganic material; these were found to be mostly NaCl. Survival studies in the presence of increasing NaCl concentration showed no mineralization or incorporation of added acetate above 5% NaCl, but plate counts showed that the organisms still survived after 3 days even at concentrations up to 20%. Many of the compounds under study were mineralized by the indigenous soil microbial populations. It appears that addressing the question of the effects of extracted SOM on the bioavailability and fate of these chemicals to known isolated degrading microbes can be complicated by the methods of extraction utilized.