Position-specific isotope modeling of organic micropollutants transformation through different reaction pathways

Abstract

The degradation of organic micropollutants occurs via different reaction pathways. Compound specific isotope analysis is a valuable tool to identify such degradation pathways in different environmental systems. We propose a mechanism-based modeling approach that provides a quantitative framework to simultaneously evaluate concentration as well as bulk and position-specific multi-element isotope evolution during the transformation of organic micropollutants. The model explicitly simulates position-specific isotopologues for those atoms that experience isotope effects and, thereby, provides a mechanistic description of isotope fractionation occurring at different molecular positions. To demonstrate specific features of the modeling approach, we simulated the degradation of three selected organic micropollutants: dichlorobenzamide (BAM), isoproturon (IPU) and diclofenac (DCF). The model accurately reproduces the multi-element isotope data observed in previous experimental studies. Furthermore, it precisely captures the dual element isotope trends characteristic of different reaction pathways as well as their range of variation consistent with observed bulk isotope fractionation. It was also possible to directly validate the model capability to predict the evolution of position-specific isotope ratios with available experimental data. Therefore, the approach is useful both for a mechanism-based evaluation of experimental results and as a tool to explore transformation pathways in scenarios for which position-specific isotope data are not yet available.

Experimental Determination of Isotope Enrichment Factors – Bias from Mass Removal by Repetitive Sampling

“…First-principle based numerical modeling is an important approach to describe the evolution of concentration and stable isotope ratios both in batch and flow-through systems. ,− The importance of model-based interpretation of biodegradation experiments has been increasingly recognized, and isotope modeling has been performed for a wide range of contaminants such as chlorinated solvents, ,, aromatic hydrocarbons, , and organic micropollutants . In this study, we adopt a numerical model to simulate concentration and isotope evolution during microbially mediated TCE dechlorination.…”

“…4,27−30 The importance of modelbased interpretation of biodegradation experiments has been increasingly recognized, and isotope modeling has been performed for a wide range of contaminants such as chlorinated solvents, 11,29,31 aromatic hydrocarbons, 32,33 and organic micropollutants. 34 In this study, we adopt a numerical model to simulate concentration and isotope evolution during microbially mediated TCE dechlorination. The model accounts for substrate degradation and interchange of volatile organic compounds (TCE and cis-DCE) between water-and gasphase, as well as the removal of solute mass and water volume at sampling events.…”

Photodegradation of pesticides using compound-specific isotope analysis (CSIA): a review

“…The difference in stable isotope fractionation between different degradation pathways is not only related to the reaction mechanism of different degradation pathways, but also to the specific degradation conditions. Jin and Rolle 116 proposed a mechanism-based modeling approach to simulate the degradation of IPU. Their model can be used to explore the phototransformation pathways in scenarios for which position-specific isotope data are unavailable.…”

Modeling position specific carbon isotopologue fractionation of thermogenic propane and precursors

“…[15][16][17] The reactive carbon atoms of propane isotopically fractionate while other carbon atoms inherit isotope compositions of precursors. 16,18 Moreover, even δ 13 C PSIA signals of thermogenic propane is dependent on source materials characteristics, how and on what extend these parameters of precursors will influence propane's carbon PSIA patterns still remains unclear. Thus, resolving the isotopomers' signature of thermogenic propane definitely require more sophisticated models [19][20][21][22] in order to understand position specific isotope fractionation of thermogenic propane.…”