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Isotope effects in abiotic reduction reactions of chlorinated groundwater contaminants

English title Isotope effects in abiotic reduction reactions of chlorinated groundwater contaminants
Applicant Hofstetter Thomas
Number 104965
Funding scheme Fellowships for advanced researchers
Research institution Oceanographic Institution Dept. of Marine Chemistry and Geochemistry
Institution of higher education Institution abroad - IACH
Main discipline Hydrology, Limnology, Glaciology
Start/End 01.10.2004 - 30.09.2005
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Keywords (9)

stable isotopes; kinetic isotope effect; abiotic dechlorination; tetrachloroethene; reduction; iron; Fe(0); chlorinated ethenes; trichloroethene

Lay Summary (English)

Lay summary
Abiotic reduction of chlorinated aliphatic and olefinic hydrocarbons byreduced iron species is an important transformation pathway in pollutedgroundwaters. These reactions can be monitored in contaminatedenvironments by compound specific stable isotope analysis assuming thatstable isotope fractionations occurring in different reactions areindicative for a specific reduction pathway. In the proposed researchproject this hypothesis will be tested by investigating hydrogen, carbon,and chlorine isotope effects during the transformation of chlorinatedethenes with zero-valent iron species. These model reactions are suited tostudy isotope fractionations occurring in important environmentalreactions such as reductive ?-elimination, hydrogenolysis, ordehydrohalogenation. In addition, knowledge of transformation pathways ofdifferent chlorinated hydrocarbons is crucial for the design ofappropriate remediation techniques for the cleanup of contaminatedgroundwaters. Depending on the reaction pathway, reduction of contaminantssuch as tetrachloroethene (PCE) or trichloroethene (TRI) can result eitherin the formation of (bio)degradable compounds such as ethene and ethane orthe more recalcitrant and toxic vinylchloride.In a series of well-defined laboratory model systems, fractionations ofhydrogen, carbon, and chlorine isotopes will be measured and kineticisotope effects (KIE) will be determined for selected reduction reactions.In order to study chlorine isotope effects in reduction reactionsinvolving the formation of chlorinated intermediates, new analyticalprocedures will be tested for sample preparation and off-line measurementof compound specific chlorine isotope effects. Abiotic dechlorination ofchlorinated ethenes with Fe(0) was proposed to represent a surfacemediated process that involves the formation and breaking of metal-carbonbonds as well as the breaking of carbon-halogen bonds. Rates of reductionstrongly depend on the presence of chlorinated intermediates, whichcompete for reactive surface sites. Therefore, the influence of varyingrates of chlorinated ethene reduction on hydrogen, carbon, and chlorineisotope effects will be examined. A comparison of the derived KIEs willprovide first evidence whether isotope fractionations of abiotichydrocarbon reduction reactions are suitable measures to identify suchreduction pathways in contaminated environments. Furthermore, themechanistic information obtained from model systems with Fe(0) can providea basis for the investigation of similar reactions with naturallyoccurring Fe(II) reductants present at mineral surfaces. Reductionsinvolving Fe(II) species have been shown to be very relevant for naturalattenuation processes of organic groundwater contaminants such as avariety of pesticides and nitroaromatic explosives.
Direct link to Lay Summary Last update: 21.02.2013

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Associated projects

Number Title Start Funding scheme
139111 Expanding Compound-Specific Isotope Analysis Towards Polar Organic Micropollutants and Chlorine Isotopes 01.09.2012 R'EQUIP