The role of volatility in the distribution of iodine in the secondary environment

Iodine in the secondary environment is derived from the oceans by way of the atmosphere and as a result near-coastal soils and surface waters are greatly enriched relative to central continental areas. However, it is likely that appreciable quantities of the I are re-cycled from soils and terrestrial waters by volatilisation. In acid soils and waters I is present as the I^- ion which can be oxidized to I₂ and volatilised. In alkaline conditions the I is more likely to be present as IO^-₃, which is not converted to I₂. Soils formed on limestone are enriched in I relative to soils formed over other rock types, and waters draining limestone areas are similarly enriched. Because plants, and possibly animals, are thought to derive much of their I by direct absorption from the atmosphere, the frequent association of I deficiency diseases with limestone areas could be due to the non-volatility of the element in the alkaline conditions.