Overview
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Key numbers
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- cations and remediation strategies such as chemical (Fig. 1, Table 1), where Cr(III) is present in minerals
- Table 1 Geogenic and anthropogenic sources and environmental occurrence of Cr(III) and Cr(VI)
- inorganic complexes (Krüger et al., 2017; Liang whereas Cr(VI) is stable under oxidizing, alkaline
- or sodium dithionite, reduce Cr(VI) to less mobile Natural groundwater typically contains < 10 µg/L
- Cr(III) compounds (Wu et al., 2022). Cr(VI) (Table S1), though levels up to 300 µg/L
- In California, 31% of sampled wells contained detect-
- In soils, chromium predominantly exists as Cr(III) able Cr(VI), with 4% exceeding the 10 µg/L MCL
- conditions. Cr(III) is stable in reducing environ- lower Cr(VI) levels (< 5 µg/L) due to dilution, unless
- contrast, Cr(VI) is stable under oxidizing and alka- tions, organic matter, Fe2⁺, and sulfides facilitate the
- (Fig. 2, Table 2). Although Cr(III) is less toxic and direct electron transfer at the solid-solution inter-
- more stable than its hexavalent equivalent, it can be face (Fig. 2), with the efficiency strongly dependent
- Table 2 Mechanisms of Cr(III) Oxidation to Cr(VI)
- jee, 2010), as shown in Eq. 6. H₂O₂ can also act indi- reactive than stable forms like chromite (Liang et al.,
- Table 3 Comparison of Cr(III) Oxidation Pathways under Laboratory and Environmental Conditions
- processes. microbial activity (Figure S1; Table S2) (Choppala
- Cr(VI) adsorption (%) = 704.5 + 65.7 × TOC (%) − 88.4 × pH 2023). Sulfate- and iron-reducing bacteria generate
- domonas) can reduce over 99% of dissolved Cr(VI)
- ability of electron donors (Table S3). redox-active minerals and creating reactive interme-
- char, can achieve 97–100% Cr(VI) immobilization
- Table 4 Summary of chromium remediation strategies, their advantages, and disadvantages
- Solidification/Stabi- Chemical Encapsulation or Stable, lowers leach- Alters soil; may (Komaei et al., 2025)
- Fe2⁺, sulfides, and organic matter, forming stable long-term remediation of chromium-contaminated
- Coetzee, J. J., Bansal, N., & Chirwa, E. M. N. (2020). Chro- redox equilibria and formation of metastable H2O2 under
- evidenced by Cr stable isotopes. Journal of Hazardous Sharma, P., Singh, S. P., Parakh, S. K., & Tong, Y. W. (2022).
Methods (brief)
- In California, 31% of sampled wells contained detect-
Implications
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