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Demonstrating a natural origin of chloroform in groundwater using stable isotope analysis

English title Demonstrating a natural origin of chloroform in groundwater using stable isotope analysis
Applicant Hunkeler Daniel
Number 132740
Funding scheme Project funding (Div. I-III)
Research institution Centre d'hydrogéologie et de géothermie Université de Neuchâtel
Institution of higher education University of Neuchatel - NE
Main discipline Geochemistry
Start/End 01.10.2010 - 30.09.2012
Approved amount 201'540.00
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Keywords (6)

groundwater; organic contaminants; isotopes; stable isotopes; chloroform; Chlorinated hydrocarbons

Lay Summary (English)

Lead
Lay summary
Chlorinated hydrocarbons are among the most common groundwater contaminants. For example, in Switzerland, in nearly a quarter of the drinking water wells traces of chlorinated hydrocarbons are detected. It is generally believed that these compounds originate from anthropogenic activities such as metal processing industries or dry cleaners. However, recently, it was found that some chlorinated hydrocarbons, especially chloroform, can also be naturally produced during degradation of organic matter by fungi in forest soils. While, the natural production of these compounds has clearly been documented at some locations, it is not known yet how widespread this process is. For planning effective remediation measures and risk assessment, it is important to know the source of theses compounds. The main aim of the project is to develop a method to identify locations where chlorinated hydrocarbons are of natural origin, to apply the method to evaluate how widespread natural chlorinated hydrocarbon production is and to identify conditions under which these compounds can reach groundwater. The method to identify the origin of chlorinated hydrocarbons relies on stable isotope analysis. Preliminary studies have demonstrated the chloroform from natural sources contains more of the heavy carbon isotope, 13C, compared to the anthropogenic chloroform. The difference can be explained by the different origin of the carbon in the molecule. An analytical method will be developed to measure the carbon isotopic composition of chloroform at low concentrations. The method will then be applied to identify locations where chloroform is of natural origin. Finally, at some of these locations, detailed studies will be carried out to investigate how natural chlorinated hydrocarbons can reach groundwater.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Formation mechanisms of trichloromethyl-containing compounds in the terrestrial environment: A critical review
Breider F., Albers C. N. (2015), Formation mechanisms of trichloromethyl-containing compounds in the terrestrial environment: A critical review, in Chemosphere, 119, 145-154.
Investigating chloroperoxidase-catalyzed formation of chloroform from humic substances using stable chlorine isotope analysis
Breider F., Hunkeler D. (2014), Investigating chloroperoxidase-catalyzed formation of chloroform from humic substances using stable chlorine isotope analysis, in Environmental Science and Technology, 48(3), 1592-1600.
Mechanistic insights into the formation of chloroform from natural organic matter using stable carbon isotope analysis
Breider F., Hunkeler D. (2014), Mechanistic insights into the formation of chloroform from natural organic matter using stable carbon isotope analysis, in Environmental Science and Technology, 125, 85-95.
Demonstrating a Natural Origin of Chloroform in Groundwater Using Stable Carbon Isotopes
Hunkeler Daniel, Laier Troels, Breider Florian, Jacobsen Ole Stig (2012), Demonstrating a Natural Origin of Chloroform in Groundwater Using Stable Carbon Isotopes, in ENVIRONMENTAL SCIENCE & TECHNOLOGY, 46(11), 6096-6101.
Position-specific carbon isotope analysis of trichloroacetic acid by gas chromatography/isotope ratio mass spectrometry
Breider Florian, Hunkeler Daniel (2011), Position-specific carbon isotope analysis of trichloroacetic acid by gas chromatography/isotope ratio mass spectrometry, in Rapid Communications in Mass Spectrometry, 25, 1-7.
Assessing the role of trichloroacetyl-containing compounds in the natural formation of chloroform using stable carbon isotopes analysis
Breider Florian, Albers Christian Nyrop, Hunkeler Daniel, Assessing the role of trichloroacetyl-containing compounds in the natural formation of chloroform using stable carbon isotopes analysis, in Chemosphere.

Collaboration

Group / person Country
Types of collaboration
Geological Survey of Denmark and Greenland (GEUS) Denmark (Europe)
- in-depth/constructive exchanges on approaches, methods or results
University of Nantes, France France (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Gordon Research Conference - Isotopes in Biological & Chemical Sciences - Centennial Celebration of the Discovery of Stable Isotopes Talk given at a conference Carbon and chlorine isotope effects during degradation of chlorinated hydrocarbons: Mechanistic insights and environmental application 05.02.2012 Galveston, Texas, US, United States of America Hunkeler Daniel; Breider Florian;
EuChemMS International conference on Chemistry and the Environment Talk given at a conference NN 11.09.2011 Zurich, Switzerland Breider Florian;
International Isotope Conference Talk given at a conference NN 20.06.2011 Geraux-les-Bains, France, France Breider Florian;


Communication with the public

Communication Title Media Place Year
New media (web, blogs, podcasts, news feeds etc.) Isotopes help clear up concerns about chloroform in groundwater Chemical and Engineering News, American Chemical Society International 2012

Associated projects

Number Title Start Funding scheme
117860 Demonstrating a natural origin of chloroform in groundwater using stable isotope analysis 01.10.2008 Project funding (Div. I-III)

Abstract

In recent years, an increasing number of naturally produced organohalogens has been discovered. Environmental studies on organohalogens have frequently focused on chloromethane, a naturally produced ozone-killer, and its release to the atmosphere. However, there is increasing evidence that organohalogens produced in soils, especially chloroform, can also be transported to groundwater. The relatively frequent detection of chloroform in ambient groundwater suggests that natural chloroform production may be widespread. However, it is difficult to demonstrate a natural origin of chloroform in groundwater given its widespread use as an industrial solvent. For long-term evaluation of groundwater quality and because anthropogenic chloroform may frequently be associated with other contaminants, it is important to know to what extent chloroform in groundwater originates from natural sources.This project is a continuation of the project n°200020-117860, which corresponds to the first two years of a PhD thesis. In the previous project, soil gas measurements were carried out at several sites with natural chloroform production. Carbon isotope ratios between -25 and -30‰ were observed which are significantly more enriched in 13C compared to anthropogenic chloroform (-50 to -70‰). This clearly demonstrates the potential of using carbon isotope data to distinguish between natural and anthropogenic chloroform. At the study sites, a strong correlation between the chloroform concentration in soil gas and the quantity of base-hydrolysable trichloroacetyl-groups in soil samples was observed suggesting that the latter could be a precursor of naturally formed chloroform. Using base-hydrolysis, the site-specific isotope ratio of the trichloromethyl position was determined and values of -10 to -15‰ were obtained. If this position is the chloroform precursor, a substantial carbon isotope fractionation has to occur during their release. This is indeed the case as demonstrated in experiments with model compound and humic acids, and as was also shown in a study recently published by another research group. A carbon isotope enrichment factor of about -15‰ was found which explains the isotope ratio of soil gas chloroform very well. The fairly stable isotope ratio of soil gas chloroform implies a fairly stable isotope signature of the trichloromethyl-position despite fractionation during their release. A stable isotope ratio can be achieved if the precursor pool is large compared to the rate of chloroform production or if a steady state between formation and release of this position is established. Based on these considerations a simplified mathematical process model was developed incorporating different carbon pools leading to chloroform that reproduces the observed isotope values and temporal trends well. In the next project phase (year 3 and 4 of the PhD), we plan to explore these hypotheses of chloroform formation in more detail and to “validate” the mathematical process model with laboratory experiments. In addition, we plan to include chlorine isotopes as well for two reasons. On the one hand, by measuring chlorine isotope ratios, it will be possible to further confirm the conceptual model of chloroform production in soils. On the other hand, chlorine isotope ratios could also be used to distinguish between natural and anthropogenic sources of chloroform. Indeed, an adaptation of the simplified process model to chlorine suggests that chlorine isotope ratios in chloroform should substantially deviate from those of inorganic chlorine in soil. Since part of the soil-produced chloroform escapes to the atmosphere, its isotope ratio might be influenced by diffusion in addition to reactive processes. This possible effect will also be explored using column experiments and, in case of chlorine, diffusion isotope effects will be evaluated on an isotopologue basis. In the further project, the well-established collaboration with Geological Survey of Denmark and Greenland will be continued and some of the studies will be carried out at their well-characterized research field sites. Moreover, field sampling and measurement will be carried out in different Swiss sites selected on the basis of the data of the national groundwater monitoring network (NAQUA) to study the dynamics and isotope evolution of the trichloroactyl-pool and chloroform under field conditions.
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