Abiotic reaction of iodate with sphagnum peat and other natural organic matter

Abstract

Previous studies have shown that iodine (including ¹²⁹I) can be strongly retained in organic-rich surface soils and sediment and that a large fraction of soluble iodine may be associated with dissolved humic material. Iodate (IO ⁻₃ ) reacts with natural organic matter (NOM) producing either hypoiodous acid (HIO) or I₂ as an intermediate. This intermediate is subsequently incorporated into the organic matter. Based on reactions of model compounds, we infer that iodine reacts with peat by aromatic substitution of hydrogen on phenolic constituents of the peat. Alternatively, the intermediate, HIO or I₂, may be reduced to iodide (I⁻). The pH (and temperature) dependence of the IO ⁻₃ reaction (reduction) has been explored with sphagnum peat, alkali lignin, and several model compounds. The incorporation of iodine into NOM has been verified by pyrolysis gas chromatography/mass spectrometry (GC/MS). Model compound studies indicate that reduction of IO ⁻₃ to HIO may result from reaction with hydroquinone (or semiquinone) moieties of the peat.