BACKGROUND Identifying the occurrence form of iodine in soil and the law of iodine migration and transformation in soil is of great significance for evaluating the biogeochemical behavior of iodine and preventing human iodine deficiency diseases.

OBJECTIVES To review the source, content, speciation, transportation, and transformation of iodine in soils; and briefly summarize the transportation of iodine between soil and plants.

METHODS The source, content, speciation, transportation, and transformation characteristics of iodine in soils were reviewed. The influences of soil types, environmental factors, organic matter, microbial activity, pH, and Eh on iodine dynamics were summarized. Great emphasis was laid on the main factors affecting the sorption of iodine in soil, which is the key process regulating soil iodine mobility and bioavailability.

RESULTS The dry and wet deposition of the atmosphere, the weathering of the soil parent rock, and the absorption and release of plants are the main sources of iodine in soil. Iodine contents in soil typically range from 1 to 5mg/kg. Organic iodine is the dominant form of iodine in soil due to the close association of iodine with organic matter, which is the critical factor affecting soil iodine dynamics. Sorption is the key process regulating soil iodine mobility and bioavailability. Under acidic conditions, hydroxyl groups on soil mineral surface are protonated, and thus facilitating iodine sorption via electrostatic interaction.

CONCLUSIONS Due to the complex composition of soil, establishing a complete soil iodine database is the basis for exploring soil iodine related aspects. It is necessary to further seek better soil iodine analysis methods. Studying the adsorption mechanism of soil iodine and the effect of organic matter and microorganisms on iodine in soil are also an important direction for future research.