TY - JOUR
T1 - Assessing chlorinated ethene degradation in a large scale contaminant plume by dual carbon-chlorine isotope analysis and quantitative PCR
AU - Hunkeler, Daniel
AU - Abe, Yumiko
AU - Broholm, Mette M.
AU - Jeannottat, Simon
AU - Westergaard, Claus
AU - Jacobsen, Carsten Suhr
AU - Aravena, Ramon
AU - Bjerg, Poul L.
N1 - Funding Information:
The authors gratefully acknowledge the site access, information and funding provided by the Region of Southern Denmark and The Danish Ministry of The Environment . The authors also thank the two anonymous reviewers and the editor for their helpful comments.
PY - 2011/1/25
Y1 - 2011/1/25
N2 - The fate of chlorinated ethenes in a large contaminant plume originating from a tetrachloroethene (PCE) source in a sandy aquifer in Denmark was investigated using novel methods including compound-specific carbon and chlorine isotope analysis and quantitative real-time polymerase chain reaction (qPCR) methods targeting Dehaloccocoides sp. and vcrA genes. Redox conditions were characterized as well based on concentrations of dissolved redox sensitive compounds and sulfur isotopes in SO42−.In the first 400 m downgradient of the source, the plume was confined to the upper 20 m of the aquifer. Further downgradient it widened in vertical direction due to diverging groundwater flow reaching a depth of up to 50 m. As the plume dipped downward and moved away from the source, O2 and NO3− decreased to below detection levels, while dissolved Fe2+ and SO42− increased above detectable concentrations, likely due to pyrite oxidation as confirmed by the depleted sulfur isotope signature of SO42−.
In the same zone, PCE and trichloroethene (TCE) disappeared and
cis-1,2-dichloroethene (cDCE) became the dominant chlorinated ethene.
PCE and TCE were likely transformed by reductive dechlorination rather than abiotic reduction by pyrite
as indicated by the formation of cDCE and stable carbon isotope data.
TCE and cDCE showed carbon isotope trends typical for reductive dechlorination with an initial depletion of 13C in the daughter products followed by an enrichment of 13C as degradation proceeded. At 1000 m downgradient of the source, cDCE was the dominant chlorinated ethene and had reached the source δ13C value confirming that cDCE was not affected by abiotic or biotic degradation.Further downgradient (up to 1900 m), cDCE became enriched in 13C by up to 8‰ demonstrating its further transformation while vinylchloride (VC) concentrations remained low (< 1 μg/L) and ethene was not observed. The correlated shift of carbon and chlorine isotope ratios of cDCE by 8 and 3.9‰, respectively, the detection of Dehaloccocides
sp genes, and strongly reducing conditions in this zone provide strong
evidence for reductive dechlorination of cDCE. The significant
enrichment of 13C in VC indicates that VC was transformed
further, although the mechanism could not be determined. The
transformation of cDCE was the rate limiting step as no accumulation of
VC occurred. In summary, the study demonstrates that carbon–chlorine
isotope analysis and qPCR combined with traditional approaches can be
used to gain detailed insight into the processes that control the fate
of chlorinated ethenes in large scale plumes.
AB - The fate of chlorinated ethenes in a large contaminant plume originating from a tetrachloroethene (PCE) source in a sandy aquifer in Denmark was investigated using novel methods including compound-specific carbon and chlorine isotope analysis and quantitative real-time polymerase chain reaction (qPCR) methods targeting Dehaloccocoides sp. and vcrA genes. Redox conditions were characterized as well based on concentrations of dissolved redox sensitive compounds and sulfur isotopes in SO42−.In the first 400 m downgradient of the source, the plume was confined to the upper 20 m of the aquifer. Further downgradient it widened in vertical direction due to diverging groundwater flow reaching a depth of up to 50 m. As the plume dipped downward and moved away from the source, O2 and NO3− decreased to below detection levels, while dissolved Fe2+ and SO42− increased above detectable concentrations, likely due to pyrite oxidation as confirmed by the depleted sulfur isotope signature of SO42−.
In the same zone, PCE and trichloroethene (TCE) disappeared and
cis-1,2-dichloroethene (cDCE) became the dominant chlorinated ethene.
PCE and TCE were likely transformed by reductive dechlorination rather than abiotic reduction by pyrite
as indicated by the formation of cDCE and stable carbon isotope data.
TCE and cDCE showed carbon isotope trends typical for reductive dechlorination with an initial depletion of 13C in the daughter products followed by an enrichment of 13C as degradation proceeded. At 1000 m downgradient of the source, cDCE was the dominant chlorinated ethene and had reached the source δ13C value confirming that cDCE was not affected by abiotic or biotic degradation.Further downgradient (up to 1900 m), cDCE became enriched in 13C by up to 8‰ demonstrating its further transformation while vinylchloride (VC) concentrations remained low (< 1 μg/L) and ethene was not observed. The correlated shift of carbon and chlorine isotope ratios of cDCE by 8 and 3.9‰, respectively, the detection of Dehaloccocides
sp genes, and strongly reducing conditions in this zone provide strong
evidence for reductive dechlorination of cDCE. The significant
enrichment of 13C in VC indicates that VC was transformed
further, although the mechanism could not be determined. The
transformation of cDCE was the rate limiting step as no accumulation of
VC occurred. In summary, the study demonstrates that carbon–chlorine
isotope analysis and qPCR combined with traditional approaches can be
used to gain detailed insight into the processes that control the fate
of chlorinated ethenes in large scale plumes.
KW - Biodegradation
KW - Chlorinated ethenes
KW - Groundwater
KW - qPCR
KW - Stable isotopes
UR - http://www.scopus.com/inward/record.url?scp=78650949546&partnerID=8YFLogxK
U2 - 10.1016/j.jconhyd.2010.09.009
DO - 10.1016/j.jconhyd.2010.09.009
M3 - Article
VL - 119
SP - 69
EP - 79
JO - Journal of Contaminant Hydrology
JF - Journal of Contaminant Hydrology
SN - 0169-7722
IS - 1-4
ER -