Sediment Biobarriers for Chlorinated Aliphatic Hydrocarbons in Groundwater Reaching Surface Water

摘要

Polluted groundwater in urban and industrial areas often represents acontinuous source of diffuse contamination of surface waters. However, the fate of theinfiltrating groundwater pollutants might be influenced by the sediment in eutrophicwater bodies since they might possess characteristic biological and physico-chemicalproperties influencing pollutant degradation. In a part of the eutrophic river Zenne (Vilvoorde,Belgium), we studied the intrinsic capacity of river sediment microbial communitiesto degrade chlorinated aliphatic hydrocarbons (CAHs). The CAH concentrationsdetermined in groundwater, sediment, and porewater samples indicate that the Zennelocally drains groundwater polluted with vinyl chloride (VC) and cis-1,2-dichloroethene(cis-DCE). The groundwater discharge spatial distribution is highly heterogeneous,mostly depending on local sediment permeability in the riverbed. At some locations, fulldechlorination was observed, while VC and cis-DCE reach the surface water and dischargeinto the river at spots with a high-velocity groundwater influx. To monitor theCAH influx in function of time, Teflon porewater samplers were installed at differentlocations and depths in the riverbed and sampled monthly. Anaerobic batch degradationtests with sediment material from the Zenne showed a rapid microbial dehalogenation ofboth VC and cis-DCE to non-toxic ethene (1000 μg/L in 19 days). In congruence, chloroethenedegrading Dehalo-coccoides species were present in the sediment as shown bydetection of their 16S rRNA genes. Furthermore, the VC reductive dehalogenases vcrAand bvcA from respectively Dehalococcoides sp. strain VS and BAV1 were detected inthe river sediment by PCR analysis. Both Dehalococcoides species can grow on VC andcis-DCE as a sole energy source and are probably responsible for the observed degradationof these groundwater pollutants in the laboratory and in situ in the riverbed.