DEGRADATION AND DETOXIFICATION OF 2,4,6-TRINITROTOLUENE BY FOUR STRAINS OF WHITE-ROT FUNGUS
|J.C. Chen, H.J. Huebner, L.Y. He, and K.C. Donnelly, Department of Veterinary Anatomy and Public Health, Texas A&M University, College Station, TX 77843-4458||
Initial studies with four different strains of white-rot fungi demonstrated that the fungi were capable of metabolizing and detoxifying 2,4,6-trinitrotoluene (TNT) under aerobic conditions in non-ligninolytic liquid medium. Subsequent studies were conducted to examine the effect of growth substrates, pH, incubation temperature, and TNT concentration on the extent of TNT mineralization. Loss of TNT from the culture medium was determined using high performance liquid chromatography (HPLC), and 14Clabelled TNT.
Detoxification was measured using the Salmonella/microsome mutagenicity assay. The data indicate that (1) the addition of starch (1% w/w) to the liquid media was critical to fungal growth and TNT detoxification; (2) detoxification and degradation of TNT by Phanerochaete chrysosporium incubated at 37°C or 25°C were similar; (3) the fungi, P. chrysosporium and P. sordida, grew most rapidly and produced the highest degree of TNT detoxification at a pH of 4 and 5; and (4) the fungi were able to grow and detoxify TNT effectively at concentrations up to 92 mg/L.
Under nitrogen-limiting conditions (2.4 mM), 36 days of fungal treatments produced mineralization of TNT ranging from 3.2% by P. chrysosporium to 9.9% by Cyathus stercoreus. However, under higher nitrogen conditions (i.e., 12mM or 24 mM), TNT mineralization was found to be negligible. During incubation, a decrease in solvent soluble 14C (parent compound) and an increase in 14C (metabolites) was observed. Mass balance data show that after 36 days of treatment, approximately 40% to 60% of 14C was trapped in the fungal biomass, and less than 10% of 14C was mineralized.
These studies demonstrated that the selected white-rot fungi were capable of metabolizing and detoxifying TNT in liquid medium. The most extensive rates of degradation and detoxification occurred when an extra growth substrate was provided and the system was maintained at a pH of 4.0 to 5.0. TNT concentrations above 90 mg/L appeared to be inhibitory and the highest rates of mineralization occurred at low nitrogen concentrations.
Key words: degradation, 2,4,6-trinitrotoluene, mutagenicity, Phanerochaele chrysosporium
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