title: In situ measurements of volatile aromatic hydrocarbon biodegradation rates in groundwater.
abstract: Benzene and alkylbenzene biodegradation rates and patterns were measured using an in situ microcosm in a crude-oil contaminated aquifer near Bemidji, Minnesota. Benzene-D6, toluene, ethylbenzene, o-, m- and p-xylenes and four pairs of C(3)- and C(4)-benzenes were added to an in situ microcosm and studied over a 3-year period. The microcosm allowed for a mass-balance approach and quantification of hydrocarbon biodegradation rates within a well-defined iron-reducing zone of the anoxic plume. Among the BTEX compounds, the apparent order of persistence is ethylbenzene > benzene > m,p-xylenes > o-xylene >or= toluene. Threshold concentrations were observed for several compounds in the in situ microcosm, below which degradation was not observed, even after hundreds of days. In addition, long lag times were observed before the onset of degradation of benzene or ethylbenzene. The isomer-specific degradation patterns were compared to observations from a multi-year study conducted using data collected from monitoring wells along a flowpath in the contaminant plume. The data were fit with both first-order and Michaelis-Menten models. First-order kinetics provided a good fit for hydrocarbons with starting concentrations below 1mg/L and Michaelis-Menten kinetics were a better fit when starting concentrations were above 1mg/L, as was the case for benzene. The biodegradation rate data from this study were also compared to rates from other investigations reported in the literature.
authors.affiliation: U.S. Geological Survey, 431 National Center, 12201 Sunrise Valley Drive, Reston, VA 20192, USA. icozzare@usgs.gov
authors.forename: Isabelle M
authors.initials: IM
authors.lastname: Cozzarelli
authors.forename: Barbara A
authors.initials: BA
authors.lastname: Bekins
authors.forename: Robert P
authors.initials: RP
authors.lastname: Eganhouse
authors.forename: Ean
authors.initials: E
authors.lastname: Warren
authors.forename: Hedeff I
authors.initials: HI
authors.lastname: Essaid
mesh_terms: D001673:Biodegradation, Environmental; D004784:Environmental Monitoring / Q000379:methods*; D006841:Hydrocarbons, Aromatic / Q000737:chemistry / Q000378:metabolism*; D012989:Soil Pollutants / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000737:chemistry / Q000378:metabolism*
chemical_list: D006841:Hydrocarbons, Aromatic; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical