posted on 2017-05-09, 00:00authored byClara Torrentó, Jordi Palau, Diana Rodríguez-Fernández, Benjamin Heckel, Armin Meyer, Cristina Domènech, Mònica Rosell, Albert Soler, Martin Elsner, Daniel Hunkeler
To
use compound-specific isotope analysis for confidently assessing
organic contaminant attenuation in the environment, isotope fractionation
patterns associated with different transformation mechanisms must
first be explored in laboratory experiments. To deliver this information
for the common groundwater contaminant chloroform (CF), this study
investigated for the first time both carbon and chlorine isotope fractionation
for three different engineered reactions: oxidative C–H bond
cleavage using heat-activated persulfate, transformation under alkaline
conditions (pH ∼ 12) and reductive C–Cl bond cleavage
by cast zerovalent iron, Fe(0). Carbon and chlorine isotope fractionation
values were −8 ± 1‰ and −0.44 ± 0.06‰
for oxidation, −57 ± 5‰ and −4.4 ±
0.4‰ for alkaline hydrolysis (pH 11.84 ± 0.03), and −33
± 11‰ and −3 ± 1‰ for dechlorination,
respectively. Carbon and chlorine apparent kinetic isotope effects
(AKIEs) were in general agreement with expected mechanisms (C–H
bond cleavage in oxidation by persulfate, C–Cl bond cleavage
in Fe(0)-mediated reductive dechlorination and E1CB elimination
mechanism during alkaline hydrolysis) where a secondary AKIECl (1.00045 ± 0.00004) was observed for oxidation. The different
dual carbon-chlorine (Δδ13C vs Δδ37Cl) isotope patterns for oxidation by thermally activated
persulfate and alkaline hydrolysis (17 ± 2 and 13.0 ± 0.8,
respectively) vs reductive dechlorination by Fe(0) (8 ± 2) establish
a base to identify and quantify these CF degradation mechanisms in
the field.