Desorption controlled mobility and intrinsic biodegradation of anthracene in unsaturated soil

Desorption, sorption and biodegradation control the fate of polycyclic arom atic hydrocarbons (PAH) in contaminated soils. The interaction of these pro cesses was studied in a two-layer column experiment with uncontaminated and spiked A-horizon material (C-13 anthracene) at unsaturated water flow cond itions. During constant irrigation (part I of the experiment) the developme nt of a stationary effluent composition mas observed. The onset of anthrace ne breakthrough was delayed by 350 pore volumes (pvs) indicating high affin ity sorption towards soil organic matter. The coincidence of anthracene bre akthrough with increasing dissolved organic carbon (DOC) concentrations poi nted to a carrier-mediated transport of the contaminant. Flow interruptions of varied duration (part II of the experiment) yielded a pronounced respon se of solution phase parameters. Effluent DOC increased linearly with time of flow interruption, indicating a zero-order rate-limited release. In cont rast, anthracene concentrations showed a sharp drop after the stopped-flow events. Thus, the effluent anthracene concentration observed in part I may have been controlled by rate-limited sorption in the uncontaminated layer. Biodegradation of anthracene was evident from C-13-labelled metabolites and the complete decline of effluent anthracene after 1400 pvs. Although PAH s eepage in soils is enhanced by rate-limited sorption it map be effectively counteracted by microbial activity. (C) 1999 Elsevier Science Ltd. All righ ts reserved.