Bacterial Production of Organic Acids Enhances H2O2-Dependent Iodide Oxidation

• Published in: Environmental science & technology 2012-05, Vol.46 (9), p.4837-4844
• Main Authors: Li, Hsiu-Ping, Yeager, Chris M, Brinkmeyer, Robin, Zhang, Saijin, Ho, Yi-Fang, Xu, Chen, Jones, Whitney L, Schwehr, Kathleen A, Otosaka, Shigeyoshi, Roberts, Kimberly A, Kaplan, Daniel I, Santschi, Peter H
• Format: Article
• Language: English
• Subjects: Applied sciences; Bacteria - metabolism; Biological and physicochemical phenomena; Biological and physicochemical properties of pollutants. Interaction in the soil; Carboxylic Acids - chemistry; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Hydrogen Peroxide - chemistry; Iodides - chemistry; Iodine Radioisotopes - chemistry; Natural water pollution; Oxidation-Reduction; Pollution; Pollution, environment geology; Soil and sediments pollution; Soil Microbiology; Soil Pollutants, Radioactive - chemistry; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es203683v

To develop an understanding of the role that microorganisms play in the transport of 129I in soil–water systems, bacteria isolated from subsurface sediments were assessed for iodide oxidizing activity. Spent liquid medium from 27/84 bacterial cultures enhanced iodide oxidation 2–10 fold in the presence of H2O2. Organic acids secreted by the bacteria were found to enhance iodide oxidation by (1) lowering the pH of the spent medium, and (2) reacting with H2O2 to form peroxy carboxylic acids, which are extremely strong oxidizing agents. H2O2-dependent iodide oxidation increased exponentially from 8.4 to 825.9 μM with decreasing pH from 9 to 4. Organic acids with ≥2 carboxy groups enhanced H2O2-dependent iodide oxidation (1.5–15-fold) as a function of increasing pH above pH 6.0, but had no effect at pH ≤ 5.0. The results indicate that as pH decreases (≤5.0), increasing H2O2 hydrolysis is the driving force behind iodide oxidation. However, at pH ≥ 6.0, spontaneous decomposition of peroxy carboxylic acids, generated from H2O2 and organic acids, contributes significantly to iodide oxidation. The results reveal an indirect microbial mechanism, organic acid secretion coupled to H2O2 production, that could enhance iodide oxidation and organo-iodine formation in soils and sediments.