Mineralization of desorption-resistant 1,4-dichlorobenzene in wetland soils

Abstract

Laboratory studies were conducted to investigate the biologically mediated, aerobic mineralization of both freshly added and artificially aged, desorption-resistant 1,4-dichlorobenzene (1,4-DCB). The adsorption and desorption of 1,4-DCB isotherms were established in three wetland soils using decant-refill batch techniques. Significant nonlinearity and hysteresis were observed in the isotherms with a hysteresis index ranging from 0.11 (relatively low hysteresis) in a marsh soil to 2.26 (relatively high hysteresis) in a bottomland hardwood soil from the Petro Processor (PPI) Superfund site. Mineralization of freshly added 1,4-DCB was observed in all three soils without lag after the addition of a 1,4-DCB degrading culture. Mineralization curves were plotted above theoretical lines predicted from a first-order model assuming instantaneous desorption, indicating that the microbial population had access to sorbed 1,4-DCB. In separate experiments, mineralization of artificially aged, desorption-resistant 1,4-DCB was also observed. Mineralization curves in these studies also indicated that the microbial population could directly access sorbed 1,4-DCB. The extent and rate of mineralization of desorption-resistant 1,4-DCB decreased significantly, including rate constants decreasing from approximately 0.01 d-1 in the freshly added treatments to approximately 0.002 d-1 in the desorption-resistant treatments. Although sorption/desorption partitioning helped explain mineralization patterns in the treatments with freshly added 1,4-DCB, no differences were observed in mineralization curves in the desorption-resistant treatments between soils with widely varying sorption/desorption properties.