Modulation of metabolic activity prevents degradation of sorbed toluene

The factors affecting the ability of a bacterial species to degrade differe nt amounts of toluene (8.5 to 217 mg/g) sorbed to granular activated carbon (GAC), in an aqueous solution of mineral salts, were investigated. After 1 44 days the amounts of toluene remaining on one type of GAC ranged from 7.5 to 9.5 mg/g, and the aqueous concentrations of toluene ranged from 2 to 7 mu g/L. Neither bacterial death nor an inhibition by accumulating by-produc ts could explain why the remaining toluene had not been degraded. However, at these low concentrations of toluene, and probably because of cell starva tion, bacteria were observed to be more than 100-times less efficient to de grade toluene than at high concentrations. We propose that this low degrada tion ability is responsible for the presence of residual toluene on the GAG , and that this mechanism may contribute to the persistence of low concentr ations of sorbed pollutants in the environment. (C) 1999 Elsevier Science L td. All rights reserved.