|Characterization and quantification of in situ biodegradation of groundwater contaminants using stable isotope fractionation analysis: advantages and limitations
|Environmental and regional air pollution
|Thullner, M.; Richnow, H.-H.; Fischer, A.
|Gallo, D.; Mancini, R.
|Air, Water and Soil Pollution Science and Technology
|For many contaminated sites Natural Attenuation (NA) of groundwater contaminants has become a common remediation strategy. The main process contributing to the NA of organic contaminants is their degradation by microorganisms inhabiting a groundwater aquifer, a process referred to as in situ biodegradation. As a consequence, the assessment of in situ contaminant biodegradation has gained increasing importance in recent years. Compound-specific stable isotope analysis (CSIA) is one of the few methods allowing for an evaluation of in situ biodegradation and tills method is increasingly used for characterizing and quantifying microbial removal of groundwater contaminants. CSIA relies on the fractionation of stable isotopes during biodegradation, leading to all enrichment of heavier isotopes In the residual fraction of a contaminant. In many studies, the Rayleigh equation is used to obtain a quantification of contaminant biodegradation based on measured changes in isotope ratios. However, the standard Rayleigh equation considers only a single process affecting simultaneously the concentration and the isotope ratio of contaminants, a constraint often not fulfilled in the field. In many field cases, contaminant concentrations can also be affected by abiotic processes e.g. mixing, volatilization or sorption to the aquifer matrix. As the Rayleigh equation links changes in isotope ratios to concentration shifts, these abiotic processes need to be taken into account, even if they do not cause any isotope fractionation. The present study evaluates the applicability of the Rayleigh equation for the assessment of in situ biodegradation and shows the advantages and limitations of this concept. A review Of Studies in the literature addressing this issue is combined with the detailed discussion of a new modification of the Rayleigh equation. This modification allows considering abiotic concentrations changes in the quantification of in situ contaminant biodegradation based on stable isotope measurements. The applicability of this modification was tested against numerical modeling results using virtual flow path scenarios.
|Persistent UFZ Identifier
|Thullner, M., Richnow, H.-H., Fischer, A. (2009):
Characterization and quantification of in situ biodegradation of groundwater contaminants using stable isotope fractionation analysis: advantages and limitations
In: Gallo, D., Mancini, R. (eds.)
Environmental and regional air pollution
Air, Water and Soil Pollution Science and Technology
Nova Science Publishers, New York, p. 41 - 81