Multi-element (C, H, Cl, Br) stable isotope fractionation as a tool to investigate transformation processes for halogenated hydrocarbons

In groundwater and other environmental compartments, compound-specific stable isotope analysis (CSIA) has been used for the determination of specific degradation pathways by analyzing the stable isotopes of two elements. This &#8216;dual-isotope&#8217; or two-dimensional isotope&#8217; analysis also allows for an estimation of the contribution of two different pathways contributing both to the overall degradation and stable isotope fractionation. Heterogeneous groundwater flow patterns lead to some yet acceptable uncertainities in the results of this method. &#160;Recent CSIA approaches also allow for investigating the simultaneous stable isotope fractionation effects for three different elements. Such information on the stable isotope fractionation of three different elements of a degradable compound could be used for a quantitative analysis of the contribution of different degradation pathways in systems with three different pathways, but up to know there is no theoretical concepts providing such quantitative estimate.The aim of the present study is to overcome this shortage and to present such theoretical concept for the quantification of single pathway contribution to the overall biodegradation in groundwater and other systems with three parallel degradation pathways. For this purpose the approach of Centler et al. (2013) for the analysis of dual-isotope analysis has been expanded to consider the fractionation of three different elements affected by three different pathways. The obtained analytical expression allows for the quantification of each pathway to total degradation based stable isotope enrichment factors and measured stable isotope signatures. The applicability of the concept is demonstrated using data from Wijker et al. (2013).&#160;Centler, F., Hesse, F., and Thullner, M. (2013) Journal of Contaminant Hydrology, 152, 97-116.Wijker, R. S., Bolotin, J., Nishino, S. F., Spain, J. C., and Hofstetter, T. B. (2013) Environmental Science & Technology, 47, 6872-6883.&#160;

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Assessing Transformation Processes of Organic Compounds Using Stable Isotope Fractionation

Environmental Science & Technology ◽

10.1021/es801384j ◽

2008 ◽

Vol 42 (21) ◽

pp. 7737-7743 ◽

Cited By ~ 67

Author(s):

Thomas B. Hofstetter ◽

René P. Schwarzenbach ◽

Stefano M. Bernasconi

Keyword(s):

Stable Isotope ◽

Organic Compounds ◽

Isotope Fractionation ◽

Stable Isotope Fractionation ◽

Transformation Processes

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Unravelling the process of petroleum hydrocarbon biodegradation in different filter materials of constructed wetlands by stable isotope fractionation and labelling studies

Biodegradation ◽

10.1007/s10532-021-09942-1 ◽

2021 ◽

Author(s):

Andrea Watzinger ◽

Melanie Hager ◽

Thomas Reichenauer ◽

Gerhard Soja ◽

Paul Kinner

Keyword(s):

Stable Isotope ◽

Constructed Wetlands ◽

Hydrogen Isotope ◽

Petroleum Hydrocarbon ◽

Isotope Fractionation ◽

Isotope Effects ◽

Filter Material ◽

Hydrocarbon Biodegradation ◽

Stable Isotope Fractionation ◽

Filter Materials

AbstractMaintaining and supporting complete biodegradation during remediation of petroleum hydrocarbon contaminated groundwater in constructed wetlands is vital for the final destruction and removal of contaminants. We aimed to compare and gain insight into biodegradation and explore possible limitations in different filter materials (sand, sand amended with biochar, expanded clay). These filters were collected from constructed wetlands after two years of operation and batch experiments were conducted using two stable isotope techniques; (i) carbon isotope labelling of hexadecane and (ii) hydrogen isotope fractionation of decane. Both hydrocarbon compounds hexadecane and decane were biodegraded. The mineralization rate of hexadecane was higher in the sandy filter material (3.6 µg CO2 g−1 day−1) than in the expanded clay (1.0 µg CO2 g−1 day−1). The microbial community of the constructed wetland microcosms was dominated by Gram negative bacteria and fungi and was specific for the different filter materials while hexadecane was primarily anabolized by bacteria. Adsorption / desorption of petroleum hydrocarbons in expanded clay was observed, which might not hinder but delay biodegradation. Very few cases of hydrogen isotope fractionation were recorded in expanded clay and sand & biochar filters during decane biodegradation. In sand filters, decane was biodegraded more slowly and hydrogen isotope fractionation was visible. Still, the range of observed apparent kinetic hydrogen isotope effects (AKIEH = 1.072–1.500) and apparent decane biodegradation rates (k = − 0.017 to − 0.067 day−1) of the sand filter were low. To conclude, low biodegradation rates, small hydrogen isotope fractionation, zero order mineralization kinetics and lack of microbial biomass growth indicated that mass transfer controlled biodegradation.

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