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Published March 1, 1998 | public
Journal Article

Rapid Oxidation of Geothermal Arsenic(III) in Streamwaters of the Eastern Sierra Nevada


Arsenic redox cycling was examined in source waters of the Los Angeles Aqueduct, specifically at Hot Creek, a tributary of the Owens River. Elevated arsenic concentrations in Hot Creek result from geothermal inputs. Total arsenic and As(III) concentrations were determined in the creek and in hot spring pools along its banks. Samples were processed in the field using anion-exchange columns to separate inorganic As(III) and As(V) species. Downstream of the geothermal inputs, decreasing contribu tions of As(III) to total arsenic concentrations indicated rapid in-stream oxidation of As(III) to As(V) with almost complete oxidation occurring within 1200 m. Based on assumed plug flow transport and a flow velocity of about 0.4 m/s, the pseudo-first-order half-life calculated for this reaction was approximately 0.3 h. Conservative transport of total dissolved arsenic was observed over the reach. Pseudo-first-order reaction rates determined for As(III) oxidation in batch studies conducted in the field with aquatic macrophytes and/or macrophyte surface matter were comparable to the in-stream oxidation rate observed along Hot Creek. In batch kinetic studies, oxidation was not observed after sterile filtration or after the addition of antibiotics, which indicates that bacteria attached to submerged macrophytes are mediating the rapid As(III) oxidation reaction.

Additional Information

© 1998 American Chemical Society. Received for review July 21, 1997. Revised manuscript received December 2, 1997. Accepted December 5, 1997. This work was supported by funding from the UC Water Resources Center (W-829) and the National Science Foundation (BES-9258431 and BES 9553208). The authors thank P. Kneebone (Caltech), V. Chiu (UCLA), and T. Salmassi (Caltech) for assistance with sampling and analytics; C. Farrar (USGS, Carnelian Bay, CA) for flow data; T. Heller (U.S. Forest Service, Mammoth Lakes, CA) for access to restricted areas of Hot Creek; D. Sedlak (UCB) and A. Bentley (UCB) for help with photochemical studies; D. Ball (DWP, Los Angeles, CA) for additional sample collection; D. Dawson for use of the UC Sierra Nevada Aquatic Research Laboratory; and M. Sorey (USGS, Menlo Park, CA) for discussions of this work.

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