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Isotope Techniques in Flood Analysis
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Samir Al-Gamal, Saeid Eslamian
The isotopic literature abounds with different approximations of the Rayleigh equations, including the three equations below. These equations are so named because the original equation was derived by Lord Rayleigh (pronounced “raylee”) for the case of fractional distillation of mixed liquids. This is an exponential relation that describes the partitioning of isotopes between two reservoirs as one reservoir decreases in size. The equations can be used to describe an isotope fractionation process if: (1) material is continuously removed from a mixed system containing molecules of two or more isotopic species (e.g., water with 18O and 16O, or sulfate with 34S and 32S), (2) the fractionation accompanying the removal process at any instance is described by the fractionation factor a, and (3) a does not change during the process. Under these conditions, the evolution of the isotopic composition in the residual (reactant) material isdescribed by: R/Rº=X1/X1ºa−1
Petroleum Hydrocarbon Environmental Forensics and Remedial Site Investigation
Published in Rong Yue, Fundamentals of Environmental Site Assessment and Remediation, 2018
During chemical reactions, the partitioning of isotopes between two substances with different isotope ratios is called isotope fractionation (Hoefs 1987). The phenomenon of isotope fractionation has found applications in many scientific fields. In environmental site characterization and remediation at organic contaminant sites, one of the key elements is to evaluate the biodegradation process. Because the degradation of organic contaminants often results in a change in the ratio of stable isotopes, stable isotopes, especially compound-spe cific isotope analysis (CSIA), can provide an in-depth understanding of biodegradation or abiotic transformation processes in contaminated aquifers (EPA 2008). This better understanding helps in monitoring the progress of natural attenuation and selecting appropriate remedies.
New advance in the application of compound-specific isotope analysis (CSIA) in identifying sources, transformation mechanisms and metabolism of brominated organic compounds
Published in Critical Reviews in Environmental Science and Technology, 2022
Jukun Xiong, Guiying Li, Taicheng An
In addition, CSIA can be applied to characterize transformation pathway and describe transformation mechanism of various organics (Horst et al., 2019; Hunkeler & Aravena, 2000; Keppler et al., 2000; Kuntze et al., 2016). (Bio)chemical reaction can change the relative abundance of stable isotopes within molecules. Heavier isotopes form stronger chemical bonds and are therefore less reactive than lighter ones, resulting in an enrichment of heavier isotopes in parent compounds and lighter isotopes in their products (Horst et al., 2019; Melander & Saunders, 1980). This change in stable isotopes of an element is called isotopic fractionation. Isotopic fractionation mainly originates from bonding changes, especially bond cleavage in the rate-limiting step. This fractionation leads to kinetic isotope effects (KIEs) for these reacting atoms. Their KIEs values provide important information for the (bio)chemical reaction. For example, isotopic fractionation measured in individual compounds during (bio)chemical reaction process can often be rationalized according to bonding change along with (bio)chemical reaction pathway. As such, they serve as a valuable proxy for characterizing reaction types and describing mechanistic pathway of reaction (Elsner et al., 2005; 2012; Kuntze et al., 2016; Ratti et al., 2015; Xiong et al., 2015; 2020). Previous studies have also shown the broad applications of CSIA in characterizing transformation reaction and describing transformation mechanism of organic compounds (Balaban et al., 2016; Elsner et al., 2005; Fischer et al., 2016; Kuntze et al., 2016; Nijenhuis & Richnow, 2016; Wang et al., 2015; Xiong et al., 2020).