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

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.