Define about the Environmental deficiency of iodine?

The ultimate causative Factor is deficient intake of iodine. Iodine occurs in soil and sea as iodide, the ions of which arc oxidized by sunlight to elemental iodine (which is volatile). Iodine in the atmosphere returns to soil by rain. The return of iodine, however, is slow and small in amount compared with original loss. In hilly slopes, repeated flooding leaches out the iodine from soil or erodes topsoil causing iodine deficiency in the soil. All crops grown in this soil will, therefore, be iodine deficient. As a result, human and animal populations, which are totally dependent on food grown in such sail, become iodine deficient.