Environmental controls in IDD: a case study in the Xinjiang Province of China. (CR/01/045N).
In many medically driven studies carried out to date, the iodine deficient state of the population has been superimposed on the local environment without examining the parameters that control the distribution and uptake of iodine into the food chain via the soil-cropanimal- water-human interface. In Xinjiang Province, north-west China a new approach based on adding iodine (iodine dripping) to irrigation water had been tested by previous investigators and the present study had the opportunity to examine environmental iodine and impacts on health in three contrasting areas:
Area 1 - AC148, low (3.5%) recent goitre prevalence (20% historic rate); no iodine irrigation; iodised salt available
Area 2 - Kuqa District, > 30% goitre prevalence rate, no iodine irrigation; iodised oil programme implemented
Area 3 - Wushi District, 40 - 60% goitre prevalence rate; iodine irrigation; iodised oil programme implemented
The results of this study confirm previous investigations and demonstrate that in subsistence populations consuming low-iodine foodstuffs, water can be an important dietary contributor if supplied from deep groundwater resources, which generally contain much higher concentrations of iodine than surface waters. Thus in some situations, the provision of deep groundwaters for drinking may prove another useful environmental intervention technique in IDD and may happen inadvertently as groundwater resources are often supplied in developing country situations to avoid bacterially contaminated surface waters.
During the present study, the iodine status of the population was determined. Results show that the thyroid volumes are low (0.1 - 7.09 mls) by all standards even taking into account the smaller size of the children studied compared to Western counterparts. The results reflect the adequate natural intake (mainly from water) and salt iodination programmes in AC148 and the recent iodination initiatives in Kuqa and Wushi demonstrating the success of these programmes.
Although the results of this study show that the iodination programmes carried out in northern Xinjiang Province have been successful and no incidents of goitre were evident, the population is still at risk from an iodine deficient environment and without the prospect of rapid economic and social development will remain so into the future requiring on-going supplementation. Whereas iodised oil, iodised salt and water-based iodine releasers address inadequacies directly in the human population, they do not impact upon the broader environmental deficiency. Consideration of the wider environmental issues is important because increases in the iodine content of soils and plants also improve crop and animal productivity and can therefore enhance the general economic and nutritional well being of communities contributing to sustainable development. Therefore, although the results of this study suggest that the iodine added in irrigation waters is only active for 1 or 2 years it is still a very cost effective method (1 Yuan per person per year) to increase environmental levels. In order to maximise the benefits of this technique, it is recommended that agricultural practices to enhance the retention of soil iodine should be considered and factors that will strongly fix the iodine in the soil and make it unavailable for uptake to crops should be restricted. In Xinjiang, such methods could include the addition of organic matter, for example, ploughing back straw and manure, to the soils to help retain the iodine. It is also recommended that the long-term fate of soil iodine added by the irrigation programmes be investigated more fully. Further investigations into the costs of iodine supplementation programmes are recommended. Such studies should take account of benefits other than monetary issues such as the effects of additional iodine on animal and crop productivity, the antibacterial effect of iodine when added to water or other environmental components and possible toxicity in the human and animal population.
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