Metabolism of benzene, toluene, and xylene hydrocarbons in soil

Enrichment cultures obtained from soil exposed to benzene, toluene, and xyl ene (BTX) mineralized benzene and toluene but cometabolized only xylene iso mers, forming polymeric residues, This observation prompted us to investiga te the metabolism of C-14-labeled BTX hydrocarbons in sail, either individu ally or as mixtures. BTX-supplemented soil was incubated aerobically for up to 4 weeks in a sealed system that automatically replenished any O-2 consu med, The decrease in solvent vapors and the production of (CO2)-C-14 were m onitored. At the conclusion of each experiment, C-14 distribution in solven t-extractable polymers, biomass, and humic material was determined, obtaini ng C-14 mass balances of 85 to 98%, BTX compounds were extensively minerali zed in soil, regardless of whether they were presented singly or in combina tions. No evidence aas obtained for the formation of solvent-extractable po lymers from xylenes in soil, but C-14 distribution in biomass (5 to 10%) an d humus (12 to 32%) was unusual for all BTX compounds and especially for to luene and the xylenes, The results suggest that catechol intermediates of B TX degradation are preferentially polymerized into the soil humus and that the methyl substituents of the catechols derived from toluene and especiall y from xylenes enhance this incorporation. In contrast to inhibitory residu es formed from xylene cometabolism in culture, the humus-incorporated xylen e residues showed no significant toxicity in the Microtox assay.