Extraction Efficiency and Chemical Speciation of Iodine in Soil (Technical Paper)
Waleed.H. Shetaya1,2*, Elizabeth. H. Bailey1, Scott D. Young1
1Air Pollution Department, Environmental Research Division, National Research Centre, 33 EL Bohouth St., Dokki, Giza, 12622, Egypt 2Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham,Sutton Bonington Campus, Loughborough, Leicestershire LE12 5RD, United Kingdom
The extraction efficiency of tetra-methyl ammonium hydroxide (TMAH) for soil iodine, and the effects of experimental procedures and conditions on the speciation of extracted iodine were tested. In addition, the possibility of extracting radioactive inorganic iodineforms (129I- and 129IO3-) sorbed on soil metal oxides by competition with PO43- was investigated. Results showed that changing TMAH concentration, extraction time, extraction temperature or soil particle size did not generally affect the concentrations of total iodine extracted. The ratio of iodide to total iodine in the TMAH extracts varied with the extraction conditions which led to the conclusion that part, or all, of the measured iodide is possibly produced by hydrolysis of organic iodine forms. This conclusion was confirmed by the detection of high concentrations of iodide in TMAH extracts of a humic acid. Only iodide was observedin the phosphate extracts of soil and it constituted up to 33% of the total iodine in the KH2PO4 extracts which indicates that most of the iodine mobilised by KH2PO4 is organically bound. When soil / KH2PO4 suspensions were spiked with 129I- and 129IO3-, at least 50% of 129I-and 15% of 129IO3-wasrecoverable after 72 hours of reaction. The lowest recoveries were observed atthe highest concentration of KH2PO4, which also mobilised the greatest concentrations of DOC, indicating that although KH2PO4 is capable of releasing soil-sorbed iodide and iodate, it may also promote iodide and iodate reaction with soil organic matter.