Fate of anthracene in contaminated soil - Transport and biodegradation under unsaturated flow conditions

The interplay of release, transport, and biodegradative processes employing an unsaturated (aerated), column outflow experiment under steady state and transient flow conditions was studied to evaluate the fate of PAH. Degradation compounds identified were, e.g., 3-hydroxy-2-naphthoic acid and 2,3 dihydroxynaphthalene. The predominance of 3-hydroxy-2-naphthoic acid was consistent with its key role in the bacterial anthracene degradation pathway. The integrative approach showed that PAH mobility in layered contamination is controlled by non-equilibrium processes. Residence-time sensitivity of anthracene output indicated rate-limitations to both the sorption and release processes. Microbial activity might substantially lower PAH concentrations in seepage water. At the same time, incomplete metabolism under dynamic flow conditions could lead to the generation of highly mobile compounds and thereby promoted the export of contaminant-derived carbon into groundwater. With respect to the solid phase, the amount of anthracene removed by biodegradation was low, highlighting the persistence of PAH in soil environment. Limited bioavailability of the contaminant was related to the short residence time imposed by transport conditions. Thus, results obtained from static bioreactor studies might seriously overestimate the biodegradation potential at contaminated field sites.