Chemical behaviour of iodine in organic and mineral soils

Abstract

Iodine is an essential nutrient for animals and humans, yet knowledge of the behaviour of I in soils is incomplete. The objective of this study was to investigate the behaviour of I in organic and mineral soils. Experiments included the loss of iodide from solution to soils, the desorption of aged I in soils, the speciation of the desorbed I, the extraction and analysis for I of specific mineral soil components, EDTA extraction to quantify the chelation potential of I and, finally, gross chemical fractionation, including humic/fulvic acid separation. Microbes may play an indirect role in the retention of I in soils, but their effect is very short term. It is clear that the loss of I from solution is a first-order reaction. Desorbed I is generally anionic, with some neutral or positively charged species also present. There is no firm evidence that retention in soils is due to any specific chemical reaction. Although I may be attracted to soil surfaces through a weak electrostatic action it is proposed that retention may be primarily through physical association with the surfaces and entrapment in the micropores and structural cavities of the intricate fabric of the organic matter.