Effect of diffusive/dispersive processes on stable isotope ratios of organic contaminants in aquifer systems
Final Report Abstract
Diffusive/dispersive processes play a crucial role for contaminant transport in different aquatic environments, including groundwater systems. In complex environmental systems, these processes are typically coupled with biological and chemical transformation reactions. Compound-specific stable isotope analysis has developed as a powerful tool to shed light on contaminants’ fate and degradation mechanisms. For the most important organic pollutants in groundwater, however, the focus has been the study of stable isotope evolution during (bio)transformation processes. Physical processes, instead, have received considerably less attention. In particular, the effects of diffusive isotope fractionation of organic contaminants in aquatic systems have been largely unexplored. The main goal of this project was to experimentally investigate diffusive/dispersive stable isotope fractionation of the most important groundwater organic contaminants, including chlorinated hydrocarbons and BTEX compounds and to provide quantitative modeling tools to interpret isotopic evolution during transport and transformation processes. We developed, and extensively tested, different experimental setups allowing resolving diffusive isotope gradients of labeled/nonlabeled organic contaminants, as well as compounds at natural abundance. We performed both diffusion and flow-through experiments with different contaminants and considering different boundary conditions. A common outcome of the extensive experimental study was the significance of diffusive isotope fractionation for the investigated organic contaminants. However, the extent of fractionation was largely different between the different contaminants (e.g., between deuterium-labeled compounds and compounds at natural isotope abundance). The performed experiments also allowed documenting unexpected effects, such as the inverse diffusive isotope fractionation of deuterium-labeled benzene. We have also proposed modeling approaches to incorporate diffusive/dispersive isotope effects in reactive transport models of organic contaminants in groundwater, as well as novel methods to include mechanistic understanding of transformation pathways into numerical models of contaminant degradation. Despite diffusive isotope fractionation in condensed systems, such as aqueous solutions, remains a challenging process to investigate and to conceptualize in a solid theoretical framework, this project has made remarkable contributions to advance the knowledge in this field. Such knowledge is much needed in practical applications to improve our capability to understand and predict the fate and transport of organic contaminants in aquatic systems and we envision a development of this important, yet underexplored, environmental research field in the near future.
Publications
- (2017) Normal and Inverse Diffusive Isotope Fractionation of Deuterated Toluene and Benzene in Aqueous Systems. Environ. Sci. Technol. Lett. (Environmental Science & Technology Letters) 4 (7) 298–304
Rolle, Massimo; Jin, Biao
(See online at https://doi.org/10.1021/acs.estlett.7b00159) - Numerical simulation of isotope fractionation in steadystate bioreactive transport controlled by transverse mixing. J. Contam. Hydrol. 2012, 140–141, 95–106
Eckert, D.; Rolle, M.; Cirpka, O.
(See online at https://doi.org/10.1016/j.jconhyd.2012.08.010) - Transverse hydrodynamic dispersion effects on isotope signals in groundwater chlorinated solvents’ plumes. Environ. Sci. Technol. 2012, 46, 7700–7708
Van Breukelen, B; Rolle, M.
(See online at https://doi.org/10.1021/es301058z) - Integrated carbon and chlorine isotope modeling: Applications to chlorinated aliphatic hydrocarbons dechlorination. Environ. Sci. Technol. 2013, 47, 1443–1451
Jin, B.; Haderlein, S.B.; Rolle, M.
(See online at https://doi.org/10.1021/es304053h) - Diffusive fractionation of BTEX and chlorinated ethenes in aqueous solution: Quantification of spatial isotope gradients. Environ. Sci. Technol. 2014, 48, 6141–6150
Jin, B.; Rolle, M.; Li, T.; Haderlein, S.B.
(See online at https://doi.org/10.1021/es4046956) - Mechanistic approach to multi-element isotope modeling of organic contaminant degradation. Chemosphere 2014, 95, 131–139
Jin, B.; Rolle, M.
(See online at https://doi.org/10.1016/j.chemosphere.2013.08.050) - Joint interpretation of enantiomer and stable isotope fractionation for chiral pesticides degradation. Water Res. 2016, 105, 178–186
Jin, B.; Rolle, M.
(See online at https://doi.org/10.1016/j.watres.2016.08.057) - Position-specific isotope modeling of organic micropollutants transformation through different reaction pathways. Environ. Pollut. 2016, 210, 94–103
Jin, B.; Rolle, M.
(See online at https://doi.org/10.1016/j.envpol.2015.11.014) - Experimental determination of isotope enrichment factors – bias from mass removal by repetitive sampling. Environ. Sci. Technol. 2017, 51, 1527-1536
Buchner D., Jin B., Ebert K., Rolle M., Elsner M. and S.B. Haderlein
(See online at https://doi.org/10.1021/acs.est.6b03689)
