Redox transformations and transport of cesium and iodine (-1, 0, +5) in oxidizing and reducing zones of a sand and gravel aquifer

Patricia M. Fox; Douglas B. Kent; James A. Davis

doi:10.1021/es902865s

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Redox transformations and transport of cesium and iodine (-1, 0, +5) in oxidizing and reducing zones of a sand and gravel aquifer

Patricia M. Fox·Douglas B. Kent·James A. Davis

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Abstract

Tracer tests were performed in distinct biogeochemical zones of a sand and gravel aquifer in Cape Cod, MA, to study the redox chemistry (I) and transport (Cs, I) of cesium and iodine in a field setting. Injection of iodide (I - ) into an oxic zone of the aquifer resulted in oxidation of I - to molecular iodine (I 2 ) and iodate (IO 3 - ) over transport distances of several meters. Oxidation is attributed to Mn-oxides present in the sediment. Transport of injected IO 3 - and Cs + was retarded in the mildly acidic oxic zone, with retardation factors of 1.6-1.8 for IO 3 - and 2.3-4.4for Cs. Cs retardation was likely due to cation exchange reactions. Injection of IO 3 - into a Fe-reducing zone of the aquifer resulted in rapid and complete reduction to I - within 3 m of transport. The nonconservative behavior of Cs and I observed during the tracer tests underscores the necessity of taking the redox chemistry of I as well as sorption properties of I species and Cs into account when predicting transport of radionuclides (e.g., 129 I and 137 Cs) in the environment.

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Source-reported bounding extent: 41.509605687197975° to 42.10943017110108° latitude; -70.69427490234375° to -69.90463256835938° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Patricia M. Fox, Douglas B. Kent, James A. Davis. 2010-02-19. Redox transformations and transport of cesium and iodine (-1, 0, +5) in oxidizing and reducing zones of a sand and gravel aquifer. https://doi.org/10.1021/es902865s

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