Redox transformations and transport of cesium and iodine (-1, 0, +5) in oxidizing and reducing zones of a sand and gravel aquifer.
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 (10(3)(-)) over transport distances of several meters. Oxidation is attributed to Mn-oxides present in the sediment Transport of injected 10(3)(-) and Cs(+) was retarded in the mildly acidic oxic zone, with retardation factors of 1.6-1.8 for 10(3)(-) and 2.3-4.4 for Cs. Cs retardation was likely due to cation exchange reactions. Injection of 10(3)(-) into a Fe-reducing zone of the aquifer resulted in rapid and complete reduction to I(-) within 3 m of transport. Then on conservative 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.
Fox
Patricia M
PM
U.S. Geological Survey, 345 Middlefield Road, MS 496, Menlo Park, California 94025, USA. pfox@usgs.gov
Kent
Douglas B
DB
Davis
James A
JA
D000327:Adsorption; D002586:Cesium / Q000737:chemistry*; D052918:Environmental Restoration and Remediation; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D007454:Iodides / Q000737:chemistry*; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012822:Silicon Dioxide / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry*
D007454:Iodides; D014874:Water Pollutants, Chemical; D002586:Cesium; D012822:Silicon Dioxide