Iodine is a trace halide found in the environment. A majority of global iodine budget resides in ocean while lithosphere and pedosphere contain the rest limiting the bioavailability of iodine in terrestrial environment. Iodine cycles involve the multivalence state chemical speciation at the air-water-sediment interfaces. The mobility and reactivity of these inorganic and organic iodine species are impacted by changes in physicochemical factors (e.g., pH and ionic strength), and macro- and micro-biological activities. Although iodine aqueous biogeochemistry has been extensively investigated in marine systems in the past, the partitioning mechanisms of iodine at the geomedia-water interface remained poorly understood. This chapter covers environmental soil chemistry of iodine and the impact to human and ecological health.