What do you mean by iodine deficiency? : a geochemical perspective

A medical perspective of iodine deficiency would rely on parameters such as urinary iodine or thyroid size. Geochemists would use the iodine concentrations of environmental materials such as soil, water, and crops to define the level of iodine in a region. While we could generalize and say a low iodine population may indicate a low iodine environmental, it is a mistake to assume this is always the case. Surface waters are probably the best index of an environment's status. Their iodine represents the mobile form of the element and waters are easier to determine for iodine than other media. Soil iodine levels are very variable and will be dependent on numerous soil characteristics. If we define an iodine deficient environment as one that is unable to supply sufficient iodine for the local population, then most land areas of the earth are iodine deficient; it is iodine sufficient areas that are the exception rather than the norm.