Modeling Phosphate Influence on Arsenate Reduction Kinetics by a Freshwater Cyanobacterium |
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Authors: | Christopher T Markley Bruce E Herbert |
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Institution: | (1) US Nuclear Regulatory Commission, MS: EBB 2-BO2, Washington, DC 20555-0001, USA;(2) Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843-3115, USA |
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Abstract: | Arsenic speciation in natural surface-water systems can be highly impacted through biological processes that result in non-thermodynamically
predicted species to dominate the system. In laboratory experiments, arsenate reduction by a freshwater cyanobacterium exhibited
saturation kinetics increasingly inhibited by elevating solution phosphate concentrations. Approximately 100% arsenate reduction
occurred by days 4, 7, and 10 in the low (0.35 μm), middle (3.5 μm), and high (35 μm) phosphate treatments, respectively,
with maximum arsenate reduction rates ranged from 0.013 μmol As g C−1 day−1 in the high-phosphate treatment to 0.398 μmol As g C−1 day−1 in the low-phosphate treatment. Saturation kinetic models were utilized to evaluate the impact of cell growth and arsenate-phosphate
uptake competition on arsenate reduction rates by the cyanobacterium. Results showed reduced arsenicals dominate arsenic speciation
once growth reached steady state, indicating reduced arsenicals may dominate natural systems, even when considering conservatively
high, abiotic arsenic reoxidation. |
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