Outgassing losses of toluene and m-xylene evaluated by C-14-based mass balances for laboratory bioventing simulations

Mixtures of toluene, ethylbenzene, and the,xylenes spiked with C-14-labeled toluene or m-xylene were added to bench-scale bioventing simulation column s filled with hydrocarbon-contaminated subsurface soils. After 2 to 4 weeks of incubation during which air was pumped through the column at rates of a t least 2 ml . min(-1) . kg(-1), Between 54 and 84% of the radiolabel was,r ecovered in traps as outgassed parent compound from four columns sterilized with gamma-irradiation. In contrast, seven nonsterilized but otherwise ide ntically treated (except for inorganic nitrogen addition) columns lost less than 0.4% (and one column lost 0.7%) of the radiolabel through outgassing of the parent compound. Nonsterilized columns lost 40 to 61% of the radiola bel as (CO2)-C-14, whereas gamma-irradiated columns usually lost only trace amounts of C-14 in this form. Biologically active columns also retained mu ch larger fractions than sterilized columns of the radiolabel in the subsoi l in forms, possibly microbial biomass, from which it could be recovered by wet oxidation. Addition of 10 or 40 mg/kg of mineral nitrogen had no consi stent effect on bioventing performance.