Iodine in the environment and endemic goitre in Sri Lanka Geological Society, London, Special Publications

نویسندگان

  • C. B. Dissanayake
  • R. L. R. Chandrajith
چکیده

The prevalence of endemic goitre is extremely high in certain parts of Sri Lanka where rates as high as 44% have been observed. With nearly 10 million people at risk the aetiology of endemic goitre in Sri Lanka needs to be clearly ascertained. The endemic goitre belt of Sri Lanka coincides with the wet climatic zone, indicating an apparent relationship of iodine geochemistry with climatic factors. However, the fact that there is a correlation of only -0.64 between the iodine content and the prevalence of goitre suggests the existence of other factors such as humic substances in the soil, clay minerals and soil pH that exert an influence on the bioavailability of iodine. Iodization of salt used in food is the most convenient method of goitre prevention. It has been estimated that out of a population of 17 million in Sri Lanka, nearly 10 million people are at risk of goitre (Fernando et al. 1987). The association between iodine and goitre was one of the earliest demonstrated links between a trace dement in the environment and human health and nutrition. However, there is still very little information on the geochemistry of iodine and its effect on the prevalence of endemic goitre in Sri Lanka. The few studies carried out (Mahadeva & Shanmuganathan 1967; Weerasekera et al. 1985; Chandrajith 1987; Fernando et al. 1987, 1989; Balasuriya et al. 1992; Dissanayake & Chandraj i th 1993) have shown that the endemic goitre belt of Sri Lanka lies in the wet climatic zone and that the climate has a marked influence on the geochemical distribution of iodine in the environment. Geochemistry of iodine Iodine with a large univalent anion does not usually enter crystal lattices of minerals on account of its large size. Ionic substitution of iodine is therefore unlikely and its geochemistry is mainly governed by the surface chemistry of geological materials. Fuge & Johnson (1986) in a review of the geochemistry of iodine have noted that iodine is particularly concentrated in the biosphere with strong affinities for organic matter. The easy transfer of iodine to the atmosphere and the mechanical and chemical removal from soil by groundwater tend to deplete soil of iodine. The geochemical cycle of iodine in the soil is critically important in the geographical distribution of goitre. Levels o f iodine in soil and water in

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تاریخ انتشار 2007