Studies On The Vegetable And Environmental Iodine Contents Distribution Of Carbonate Rock Areas And The Soil Iodine Enrichment By Vegetables

Iodine is an essential element for human and mammals; the insufficient iodine intake will cause iodine deficiency disorders (IDD). China is one of the countries where IDD is the most widely distributed in the world. The geochemical mechanisms controlling the prevalence of IDD in carbonate rock areas are always the hotspot and difficulty concerned by global academies. The key problem of IDD origin is the phytoavailability of iodine in environment. Thus the studies on the soil iodine enrichment mechanisms by plants in carbonate rock areas are necessary.In the study, surface water, soils and vegetables from some carbonate and non-carbonate rock areas, coast and inner-land regions in China were sampled. The iodine contents in these samples were determined by hydrothermal pyrolysis-arsenic cerium catalysis spectroscopy method. Simulation experiments on leaf (Brassica campestris, Spinacia oleracea), stem (lettuce) and root (Raphanus) vegetables plantation were conducted in special devices using the soils collected from research areas. The iodine contents in various organs of different vegetables, iodine content of soils and the physiochemical properties of soils were determined.The results of field samples analysis indicate that the closer the sampling location is distant from the ocean, the higher content the surface water contains. The iodine contents in surface water and soils of carbonate rock areas are higher than those of other areas. The iodine contents in drinking water, rice and the edible parts of vegetables were very low which cannot satisfy the nutritional demand of human. Thus the ingestion of food with high contents iodine is still required; and the promotion of iodized salt in IDD epidemic regions is essential. The results of simulation experiments show that the type of parent rocks and the nature of soils rather than the distance from sea are the primary factors affecting the soil iodine contents. Different soil types resulted in different iodine contents in the same kind of vegetable, but the iodine contents in the vegetables in carbonate rock areas were not significantly lower than those in non-carbonate rock areas. The iodine enrichment ability of plants depends on soil properties, of which alumina oxide content, organic matter, pH and cation exchange capacity (CEC) serve as affecting factors in an order from primary to trivial and iron oxide exerts the least effect on iodine enrichment. Also the iodine contents in different parts of the same plant and the iodine enrichment factors of different vegetables were different. Regarding to the edible parts, spinach and Chinese cabbage have the largest and second largest iodine enrichment factors; radish and lettuce own relatively low iodine enrichment factors. Spinach can be selected as iodine enrichment vegetables in IDD areas. The iodine contents in the vegetables in simulation experiments were higher than those from field samples and those reported in related literature. It might result from the difference in the input from outside between simulation experiments and farmyard vegetable fields, i.e. only use the tap water in simulation experiments without manure fertilization,which makes the iodine sequestration abilities of the soils in simulation experiments less than those in farmyard vegetable fields.Overall, the illustration of the iodine enrichment mechanisms of vegetables in carbonate rock areas reveal the geochemical mechanism of soil iodine enrichment by plants and provide support for the iodine addition and IDD control in carbonate rock areas.