BIODEGRADATION OF THREE MODEL CHEMICALS IN SOIL
|K.C. Donnelly, H.J. Huebner, L.D. Claxton, and L.Y. He, Department of Veterinary Anatomy and Public Health, Texas A&M University, College Station, TX 77843-4458 and National Health and Environmental Effects Research Laboratory, USEPA, North Carolina||
Exogenous cultures of microorganisms are often utilized to attack specific chemicals or classes of chemicals during the course of bioremediation. The purpose of this study was to compare the capability of three microbial cultures, Pseudomonas aeruginosa, Phanerochaete chrysosporium, and an indigenous population to detoxify soil amended with a simple mixture of three chemicals. A Weswood silt loam soil was amended with three model chemicals (benzo(a)pyrene (BAP), pentachlorophenol (PCP), and 2,4,6trinitrotoluene (TNT)).
Samples were collected from the soils at several time points from 0 through 720 days, sequentially extracted with methylene chloride and methanol, and analyzed for loss of the parent compound and genotoxicity (using S. typhimurium). The indigenous microorganisms reduced BAP concentrations to below detection limits within 540 days, while the PCP concentration was below detection limits within 180 days in soils inoculated with the fungal cultures. The concentration of TNT in soil collected after 540 days was lowest in soil inoculated with the Pseudomonas bacteria.
The maximum specific activity was observed in the extracts of soils collected on days 90 and 180. However, mutagens were detected in the extracts of all soils collected on day 540. The extracts of samples collected on day 180 induced the maximum weighted activities. The combined weighted activities of day 180 extracts were 4700 revertants per gram, 1510 revertants per gram, and 766 revertants per gram for soils inoculated with the indigenous organisms, bacteria, and fungi, respectively.
Although the weighted activity was reduced at days 540 and 720, mutagenic activity continued to persist. The results suggest that specific cultures of microorganisms may have an increased capacity of attacking individual chemicals. In addition, while chemical analysis suggested that contaminant concentrations were appreciably reduced after 540 days, a mutagenic response was detected in the extracts of soil.
Key words: biodegradation, mutagenicity, mixtures, benzo(a)pyrene, 2,4,6-trinitrotoluene
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