Transformation of org. Pollutants in Groundwater

Compound-specific stable isotope analysis (CSIA) to assess in-situ and ex-situ transformation of organic pollutants in contaminated aquifers

The aim of our research is to develop CSIA in combination with groundwater dating as a tool in the assessment of contaminated field sites. CSIA is capable to

• distinguish on-going pollutant transformation from concentration decrease caused solely by dilution.
• identify transformation mechanism(s). e.g., aerobic/anaerobic, biotic/abiotic, reduction/oxidation.
• determine the extent of in-situ pollutant degradation caused by natural and stimulated attenuation.
• quantify transformation rates (CSIA in combination with groundwater dating techniques).
  
• allocate (or delineate) sources of contamination.

Isotopes of interest in CSIA: ¹H/²H, ¹²C/¹³C, ¹⁴N/¹⁵N, ¹⁶O/¹⁸O, ³⁵Cl/³⁷Cl

Assessment of Natural and Stimulated Attenuation

		Determination of isotopic enrichment to elucidate transformation mechanisms (ε, epsilon)
		Evaluation of toxicity threat to drinking water and the environment
		Determination of transformation rates (i.e., time scale of detoxification in aquifer)

Examples

Extent of in-situ PCE degradation and quantification of transformation rates at a contaminated site.

Panel A: Isotopic mass balance (δ¹³C Σ(CEs)) indicating degrees of PCE dechlorination to ethene.

Panel B: First order degradation rate constants k Σ(CEs) of complete dechlorination using B Σ(CEs).

Reference
Aeppli C., et al. 2009, submitted.

Characterization of in-situ degradation mechanisms of MTBE.

Plot of hydrogen versus carbon isotopic shifts for MTBE.
(• red) aerobic biodegradation in a batch experiment;
(• green) anaerobic biodegradation at different field sites;
(• blue) field data from contaminated aquifer.

Reference
Zwank L., et al. 2005. New Evaluation Scheme for Two-Dimensional Isotope Analysis to Decipher Biodegradation Processes: Application to Groundwater Contamination by MTBE. Environ. Sci. Technol. 39, 1018–1029.

C and N isotopic characterization of Nitrobenzene transformation mechanisms.

Changes of ¹³C and ¹⁵N signatures for the biodegradation of nitrobenzene by oxidative (•, red) and reductive (•, blue) pathways. Color-shaded areas indicate exclusive occurrence of either one of the two degradation  mechanisms. Solid lines represent the evolution of isotope signatures if both processes occur in the ratio of 3:1, 1:1, and 1:3. Dashed lines show the extent of nitrobenzene biodegradation.

Reference
Hofstetter T.B., et al. 2008. Identifying Competing Aerobic Nitrobenzene Biodegradation Pathways by Compound-Specific Isotope Analysis.
Environ. Sci. Technol. 42, 4764–4770.

H, C and N Isotope Fractionation of Atrazine

Panels a, b, and c, show the evolution of the δ¹³C, δ²H, and δ¹⁵N values vs the remaining fraction of atrazine (circles). Panels d, e, and f show the linearized isotope enrichment used to derive enrichment factors.

Reference
Hartenbach A.E., et al. 2008. Carbon, Hydrogen, and Nitrogen Isotope Fractionation During Light-Induced Transformations of Atrazine. Environ. Sci. Technol. 42, 7751–7756.

Identification of Fe minerals involved in CCl4 degradation.

Isotopic enrichment factors of CCl₄ versus log kobs. Pseudo first-order rate constants vs isotopic enrichment observed for Fe sulfides and polysulfide (open circles) and for iron(hydr)oxides (filled circles). The right-hand section shows isotopic enrichment values for reactions in homogeneous solution.

Reference
Zwank L., et al. 2005. Carbon Isotope Fractionation in the Reductive Dehalogenation of Carbon Tetrachloride at Iron (Hydr)Oxide and Iron Sulfide Minerals. Environ. Sci. Technol. 39, 5634–5641.

• contact: michael.berg@eawag.ch