Two-stage chromium isotope fractionation during microbial Cr(VI) reduction

Guojun Chen; Juncheng Han; Yang Mu; Huimin Yu; Liping Qin

doi:10.1016/j.watres.2018.09.034

Two-stage chromium isotope fractionation during microbial Cr(VI) reduction

Water Res. 2019 Jan 1:148:10-18. doi: 10.1016/j.watres.2018.09.034. Epub 2018 Sep 29.

Authors

Guojun Chen¹, Juncheng Han², Yang Mu², Huimin Yu¹, Liping Qin³

Affiliations

¹ CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China.
² CAS Key Laboratory for Urban Pollutant Conversion, Department of Chemistry, University of Science & Technology of China, Hefei, 230026, China.
³ CAS Key Laboratory of Crust-Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, 230026, China; State Key Laboratory of Geological Processes and Mineral Resources, University of Geosciences, Beijing, China. Electronic address: lpqin@ustc.edu.cn.

PMID: 30343194
DOI: 10.1016/j.watres.2018.09.034

Abstract

Chromium isotope fractionation analysis is a promising approach for the assessment of microbial Cr(VI) reduction in groundwater. Understanding the mechanisms and other parameters that control Cr isotope fractionation factors (between the product Cr(III) and reactant Cr (VI)) in microbial Cr(VI) reduction is critical to this application. To date, such studies are very limited. Here, the influence of critical factors on observed Cr isotope fractionation during Cr(VI) reduction by Shewanella oneidensis MR-1 under various conditions was investigated. The Cr(VI) concentration and Cr isotope ratio measurements were conducted on unreacted Cr(VI) remaining in solution to determine Cr isotope fractionation factors. The changes in ambient environmental conditions (e.g., pH, temperature) have limited influence on Cr isotope fractionation factors. However, as a result of Cr(VI) consumption as the experiments proceed, the change in bioavailability of Cr(VI) has a significant impact on Cr isotope fractionation factors. For example, in temperature-controlled experiments, Cr isotope fractionation showed two-stage behavior: during Stage I, the values of ε were -2.81 ± 0.19‰ and -2.60 ± 0.14‰ at 18 °C and 34 °C, respectively; during Stage II, as Cr(VI) reduction progressed, Cr isotope fractionation was significantly masked, and the ε values decreased to -0.98 ± 0.49‰ and -1.01 ± 0.11‰ at 18 °C and 34 °C, respectively. Similar two-stage isotope fractionation behaviors were observed in pH-controlled experiments (pH = 6.0 and 7.2) and in experiments with and without the addition of a competing electron acceptor (nitrate). Masking of isotope fractionation in Stage II indicated restrictions on the bioavailability of Cr(VI) and mass-transfer limitations. This study provides an explanation for the variation in Cr isotope fractionation factors during microbial Cr(VI) reduction in the environment, furthering the viability of Cr isotope ratio analysis as an approach in understanding Cr biogeochemical cycling.

Keywords: Bioavailability; Chromium isotope fractionation; Mass-transfer limitations; Microbial Cr(VI) reduction; The values of ε.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Chemical Fractionation*
Chromium Isotopes
Chromium*
Oxidation-Reduction

Substances

Chromium Isotopes
Chromium
chromium hexavalent ion