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Photo-oxidation of Cr(III)-citrate complexes forms harmful Cr(VI).
Environ Sci Technol. 2010 Sep 15; 44(18):6959-64.ES

Abstract

Photo-oxidation is a potential pathway for the transformation of Cr(III) to Cr(VI) in natural environments. In this study, the Cr(III)-citrate complex (Cr(III)-cit) was prepared and its speciation was determined by high performance liquid chromatography (HPLC). Results showed that Cr(III)-cit existed in [Cr(III)-H-cit](+) and [Cr(III)-cit] species in a pH range of 3-5, in [Cr(III)-cit] only from pH 6-8, in [Cr(III)-cit] and [Cr(III)-OH-cit](-) from pH 9-11, and only in [Cr(III)-OH-cit](-) at pH 12. Additional experiments were conducted in batch systems with pHs of 5 to 12 at 25 °C, where aqueous Cr(III) and Cr(III)-cit were fully exposed to light from medium pressure mercury lamps and a xenon lamp mimicking solar light irradiation. Results demonstrated that oxidation of Cr(III) in Cr(III)-cit was much faster than that in aqueous Cr(III). Rates of Cr(III) photo-oxidation were not sensitive to pH in the range from 7 to 9 but increased significantly with further increases in pH, which was consistent with the distribution of Cr(III) forms. It appeared that [Cr(III)-cit-OH](-) was the most photochemically active form and Cr(II), resulting from a ligand-to-metal charge-transfer (LMCT) pathway after light absorption, was a precursor of the oxidation of Cr(III) to Cr(VI). Both dissolved oxygen and the hydroxyl radical ((•)OH), an intermediate, served as oxidants and facilitated the oxidation of Cr(II) to Cr(VI) via a multiple step pathway. The photoproduction of (•)OH was detected by HPLC using benzene as a probe, supporting the proposed reaction mechanism.

Authors+Show Affiliations

College of Sciences, Nanjing Agricultural University, Nanjing 210095, PR China.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

Language

eng

PubMed ID

20715867

Citation

Dai, Runan, et al. "Photo-oxidation of Cr(III)-citrate Complexes Forms Harmful Cr(VI)." Environmental Science & Technology, vol. 44, no. 18, 2010, pp. 6959-64.
Dai R, Yu C, Liu J, et al. Photo-oxidation of Cr(III)-citrate complexes forms harmful Cr(VI). Environ Sci Technol. 2010;44(18):6959-64.
Dai, R., Yu, C., Liu, J., Lan, Y., & Deng, B. (2010). Photo-oxidation of Cr(III)-citrate complexes forms harmful Cr(VI). Environmental Science & Technology, 44(18), 6959-64. https://doi.org/10.1021/es100902y
Dai R, et al. Photo-oxidation of Cr(III)-citrate Complexes Forms Harmful Cr(VI). Environ Sci Technol. 2010 Sep 15;44(18):6959-64. PubMed PMID: 20715867.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Photo-oxidation of Cr(III)-citrate complexes forms harmful Cr(VI). AU - Dai,Runan, AU - Yu,Changyuan, AU - Liu,Jing, AU - Lan,Yeqing, AU - Deng,Baolin, PY - 2010/8/19/entrez PY - 2010/8/19/pubmed PY - 2010/12/24/medline SP - 6959 EP - 64 JF - Environmental science & technology JO - Environ Sci Technol VL - 44 IS - 18 N2 - Photo-oxidation is a potential pathway for the transformation of Cr(III) to Cr(VI) in natural environments. In this study, the Cr(III)-citrate complex (Cr(III)-cit) was prepared and its speciation was determined by high performance liquid chromatography (HPLC). Results showed that Cr(III)-cit existed in [Cr(III)-H-cit](+) and [Cr(III)-cit] species in a pH range of 3-5, in [Cr(III)-cit] only from pH 6-8, in [Cr(III)-cit] and [Cr(III)-OH-cit](-) from pH 9-11, and only in [Cr(III)-OH-cit](-) at pH 12. Additional experiments were conducted in batch systems with pHs of 5 to 12 at 25 °C, where aqueous Cr(III) and Cr(III)-cit were fully exposed to light from medium pressure mercury lamps and a xenon lamp mimicking solar light irradiation. Results demonstrated that oxidation of Cr(III) in Cr(III)-cit was much faster than that in aqueous Cr(III). Rates of Cr(III) photo-oxidation were not sensitive to pH in the range from 7 to 9 but increased significantly with further increases in pH, which was consistent with the distribution of Cr(III) forms. It appeared that [Cr(III)-cit-OH](-) was the most photochemically active form and Cr(II), resulting from a ligand-to-metal charge-transfer (LMCT) pathway after light absorption, was a precursor of the oxidation of Cr(III) to Cr(VI). Both dissolved oxygen and the hydroxyl radical ((•)OH), an intermediate, served as oxidants and facilitated the oxidation of Cr(II) to Cr(VI) via a multiple step pathway. The photoproduction of (•)OH was detected by HPLC using benzene as a probe, supporting the proposed reaction mechanism. SN - 1520-5851 UR - https://www.unboundmedicine.com/medline/citation/20715867/Photo_oxidation_of_Cr_III__citrate_complexes_forms_harmful_Cr_VI__ L2 - https://doi.org/10.1021/es100902y DB - PRIME DP - Unbound Medicine ER -