Isotope Effects as New Proxies for Organic Pollutant Transformation.

Assessing the pathways and rates of organic pollutant transformation in the environment is a major challenge due to co-occurring transport and degradation processes. Measuring changes of stable isotope ratios (e.g.

Carbon and nitrogen isotope effects associated with the dioxygenation of aniline and diphenylamine.

Dioxygenation of aromatic rings is frequently the initial step of biodegradation of organic subsurface pollutants. This process can be tracked by compound-specific isotope analysis to assess the extent of contaminant transformation, but the corresponding isotope effects, especially for dioxygenation of N-substituted, aromatic contaminants, are not well understood. We investigated the C and N isotope fractionation associated with the biodegradation of aniline and diphenylamine using pure cultures of Burkholderia sp.

Carbon, hydrogen, and nitrogen isotope fractionation associated with oxidative transformation of substituted aromatic N-alkyl amines.

We investigated the mechanisms and isotope effects associated with the N-dealkylation and N-atom oxidation of substituted N-methyl- and N,N-dimethylanilines to identify isotope fractionation trends for the assessment of oxidations of aromatic N-alkyl moieties by compound-specific isotope analysis (CSIA). In laboratory batch model systems, we determined the C, H, and N isotope enrichment factors for the oxidation by MnO(2) and horseradish peroxidase (HRP), derived apparent (13)C-, (2)H-, and (15)N-kinetic isotope effects (AKIEs), and characterized reaction products. The N-atom oxidation pathway leading to radical coupling products typically exhibited inverse (15)N-AKIEs (up to 0.

Using nitrogen isotope fractionation to assess the oxidation of substituted anilines by manganese oxide.

We explored the N isotope fractionation associated with the oxidation of substituted primary aromatic amines, which are often the position of initial attack in transformation processes of environmental contaminants. Apparent (15)N-kinetic isotope effects, AKIE(N), were determined for the oxidation of various substituted anilines in suspensions of manganese oxide (MnO(2)) and compared to reference experiments in homogeneous solutions and at electrode surfaces, as well as to density functional theory calculations of intrinsic KIE(N)for electron and hydrogen atom transfer reactions. Owing to the partial aromatic imine formation after one-electron oxidation and corresponding increase in C-N bond strength, AKIE(N)-values were inverse, substituent-dependent, and confined to the range between 0.

pH-dependent equilibrium isotope fractionation associated with the compound specific nitrogen and carbon isotope analysis of substituted anilines by SPME-GC/IRMS.

Solid-phase microextraction (SPME) coupled to gas chromatography/isotope ratio mass spectrometry (GC/IRMS) was used to elucidate the effects of N-atom protonation on the analysis of N and C isotope signatures of selected aromatic amines. Precise and accurate isotope ratios were measured using polydimethylsiloxane/divinylbenzene (PDMS/DVB) as the SPME fiber material at solution pH-values that exceeded the pK(a) of the substituted aniline's conjugate acid by two pH-units. Deviations of δ(15)N and δ(13)C-values from reference measurements by elemental analyzer IRMS were small (<0.

Reduction of polychlorinated ethanes and carbon tetrachloride by structural Fe(II) in smectites.

Ferrous iron associated with clay minerals can be important for the reductive transformation of organic contaminants in anoxic soils and groundwaters. We investigated the reactivity of structural Fe(II) in ferruginous smectite for the reduction of a series of polychlorinated alkanes (hexa-, penta-, 1,1,1,2-and 1,1,2,2-tetrachloroethane, and carbon tetrachloride (CCl4)) in laboratory batch reactors. Evaluation of reaction kinetics, product distribution, and C-isotope fractionation suggest that polychlorinated ethanes containing three alpha-Cl atoms reacted via reductive beta-elimination to the corresponding ethenes while CCl4-reduction leads predominantly to the formation of chloroform.