Limitations in the use of compound-specific stable isotope analysis to understand the behaviour of a complex BTEX groundwater contamination near Brussels (Belgium)

Multi-element isotope fractionation concepts to characterize the biodegradation of hydrocarbons — from enzymes to the environment

“…Identification of reaction mechanism/biodegradation difficult or impossible [78] Mass transfer processes at larger scales: dispersive/ diffusive transverse contaminant transport; sorption and volatilization, isotope sensitive mass transfer Reduced magnitude of isotope fractionation; difficulties to identify reaction mechanism; changing L values also potential for detecting specific hydrocarbon biodegradation pathways in oil reservoirs focusing on the combined analysis of carbon and hydrogen isotopes [55]. Studies on isotope fractionation of low molecular mass alkanes or other volatile hydrocarbons might be very useful for studying degradation in deep geological sections and oil reservoirs [56,57], at natural gas seeps, leaking oil and gas well or for monitoring of fracking operations.…”

Combined Source Apportionment and Degradation Quantification of Organic Pollutants with CSIA: 1. Model Derivation

“…In fact, Moore and Semmens and Xue et al emphasized that isotope fractionation due to transformation processes impedes source identification and apportionment with CSIA. Correspondingly, CSIA of two elements did not allow for unambiguous identification of BTEX sources at a field site with two emission sources because both mixing of the two contaminant plumes and degradation-induced isotope fractionation presumably influenced CSIA values . Similarly, since isotope fractionation effects during denitrification had to be taken into account, Seiler could not clearly attribute nitrate contamination of groundwater wells to the potential sources fertilizer, wastewater, and natural nitrate, or a mixture of those.…”

“…Correspondingly, CSIA of two elements did not allow for unambiguous identification of BTEX sources at a field site with two emission sources because both mixing of the two contaminant plumes and degradation-induced isotope fractionation presumably influenced CSIA values. 35 Similarly, since isotope fractionation effects during denitrification had to be taken into account, Seiler 22 could not clearly attribute nitrate contamination of groundwater wells to the potential sources fertilizer, wastewater, and natural nitrate, or a mixture of those. For the same reason, Kellman and Hillaire-Marcel 39 questioned the use of nitrate isotope data in source identification, whereas Liu et al 40 disregarded isotope fractionation due to denitrification in order to facilitate CSIA-based source apportionment.…”

“…Various field sites are characterized by mixing of contaminant plumes from adjacent source areas ,, and contaminant transformation by more than one metabolic pathway. ,, However, combined SA and QED has not yet been described for the case of several sources and reaction pathways. In fact, Moore and Semmens and Xue et al emphasized that isotope fractionation due to transformation processes impedes source identification and apportionment with CSIA.…”

Evolution of carbon isotope signatures during reactive transport of hydrocarbons in heterogeneous aquifers

“…Thus, a reliable quantification of the accumulated extent of in situ contaminant degradation becomes challenging (e.g., Braeckevelt et al, 2012;Fischer et al, 2007;Thullner et al, 2012;Van Breukelen and Prommer, 2008). For instance, in complex field situations CSIAbased in situ biodegradation estimates for BTEX compounds can be accompanied by relatively high uncertainties for a variety of reasons and accordingly restrict its applicability to being only a qualitative indicator (e.g., Van Keer et al, 2012).…”