Sources of Uncertainty in Biotransformation Mechanistic Interpretations and Remediation Studies using CSIA.

Compound-specific isotope analysis (CSIA) is a powerful tool to understand the fate of organic contaminants. Using CSIA, the isotope ratios of multiple elements (δC, δH, δCl, δN) can be measured for a compound. A dual-isotope plot of the changes in isotope ratios between two elements produces a slope, lambda (Λ), which can be instrumental for practitioners to identify transformation mechanisms.

Isotopic evidence suggests different initial reaction mechanisms for anaerobic benzene biodegradation.

The initial metabolic reactions for anaerobic benzene biodegradation remain uncharacterized. Isotopic data for carbon and hydrogen fractionation from nitrate-reducing, sulfate-reducing, and methanogenic benzene-degrading enrichment cultures and phylogenic information were used to investigate the initial reaction step in anaerobic benzene biodegradation. Dual parameter plots of carbon and hydrogen isotopic data (deltadelta2H/ deltadelta13C) from each culture were linear, suggesting a consistent reaction mechanism as degradation proceeded.

Effects of trace element concentration on enzyme controlled stable isotope fractionation during aerobic biodegradation of toluene.

The effects of iron concentration on carbon and hydrogen isotopic fractionation during aerobic biodegradation of toluene by Pseudomonas putida mt-2 were investigated using a low iron medium and two different high iron media. Mean carbon enrichment factors (epsilonc) determined using a Rayleigh isotopic model were smaller in culture grown under high iron conditions (epsilonc = -1.7+/-0.

Pathway dependent isotopic fractionation during aerobic biodegradation of 1,2-dichloroethane.

1,2-Dichloroethane (1,2-OCA) is a widespread groundwater contaminant known to be biodegradable under aerobic conditions via enzymatic oxidation or hydrolytic dehalogenation reactions. Current literature reports that stable carbon isotope fractionation of 1,2-DCA during aerobic biodegradation is large and reproducible (-27 to -33/1000). In this study, a significant variation in the magnitude of stable carbon isotope fractionation during aerobic biodegradation was observed.

Carbon and hydrogen isotopic fractionation during anaerobic biodegradation of benzene.

Compound-specific isotope analysis has the potential to distinguish physical from biological attenuation processes in the subsurface. In this study, carbon and hydrogen isotopic fractionation effects during biodegradation of benzene under anaerobic conditions with different terminal-electron-accepting processes are reported for the first time. Different enrichment factors (epsilon ) for carbon (range of -1.

Hydrogen isotopic enrichment: an indicator of biodegradation at a petroleum hydrocarbon contaminated field site.

Compound-specific carbon and hydrogen isotope analysis was used to investigate biodegradation of benzene and ethylbenzene in contaminated groundwater at Dow Benelux BV industrial site. delta13C values for dissolved benzene and ethylbenzene in downgradient samples were enriched by up to 2+/-0.5 per thousand, in 13C, compared to the delta13C value of the source area samples.