Evidence for in situ degradation of mono-and polyaromatic hydrocarbons in alluvial sediments based on microcosm experiments with 13C-labeled contaminants

Abstract

A method based on 13 C-labeled substrates was developed to determine the intrinsic biodegradation potential of aromatic pollutants under oxic and under anoxic conditions. AbstractA microcosm study was conducted to investigate the degradation of mono-and polyaromatic hydrocarbons under in situ-like conditions using alluvial sediments from the site of a former cokery. Benzene, naphthalene, or acenaphthene were added to the sediments as 13 C-labeled substrates. Based on the evolution of 13 C-CO 2 determined by gas chromatography isotope-ratio mass spectrometry (GC-IRMS) it was possible to prove mineralization of the compound of interest in the presence of other unknown organic substances of the sediment material. This new approach was suitable to give evidence for the intrinsic biodegradation of benzene, naphthalene, and acenaphthene under oxic and also under anoxic conditions, due to the high sensitivity and reproducibility of 13 C/ 12 C stable isotope analysis. This semi-quantitative method can be used to screen for biodegradation of any slowly degrading, strongly sorbing compound in long-term experiments.

Intrinsic biodegradation potential of aromatic hydrocarbons in an alluvial aquifer – Potentials and limits of signature metabolite analysis and two stable isotope-based techniques

“…was shown by adding 14 C-labeled naphthalene to aquifer material and to marine harbor sediments (Chapelle et al, 1996;Coates et al, 1996;Langenhoff et al, 1996). Recently, naphthalene was also used in 13 C-labeled form to confirm biodegradation in sedimentegroundwater microcosms (Morasch et al, 2007).…”

“…C at six positions (99% purity, Cambridge Isotope Laboratories) was dissolved in the anoxic groundwater that was added to the culture bottles (Morasch et al, 2007). The headspace either was air for sediments from the unsaturated zone or N 2 for microcosms with sediments from the saturated zone.…”

“…Compared to Morasch et al (2007), we applied an advanced, quantitative approach where first-order rate constants (l) of intrinsic contaminant degradation were determined based on an inorganic carbon mass balance (Eq. (8) (Table 2).…”

“…Sampling intervals were between three and seven days at the beginning of the incubation and three-monthly toward the end of the experiment (Table S2). Concentration measurements of CO 2 and stable carbon isotope measurements were performed connecting a headspace autosampler (Tekmar Dohrmann 7000) to the GC-IRMS using a previously described protocol (Morasch et al, 2007). CO 2 concentrations were quantified based on five-point calibration curves with an average correlation of r ¼ 0.98.…”

“…The aromatic compounds were extracted from the headspace of 2 mL vials filled with 0.5 mL of groundwater and 0.3 g of NaCl using polydimethylsiloxane fibers (100 mm film thickness, Supelco). Extraction and analysis were performed as described previously (Morasch et al, 2007).…”