Accumulation Of Iodine In The Environment By The Plants And Its Geochemical Control Mechanism

Iodine is an essential element for humans and animals. It has been well established that a lack of I can cause a number of health problems known as iodine deficiency disorders (IDD). IDD is more specifically prevalent in the limestone regions than the adjacent non-limestone areas. 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 limestone areas are necessary.Ali from limestone region in Gui yang were selected as the studying areas, and the adjacent areas, Caoba from dolomite region were selected as their control areas. Qianshiyao from limestone region in Ju County was selected as the studying area, and the adjacent area, Guxi from granite region was selected as its control area. Shuiyanba and Shuiyi from limestone region in Zhijin County were selected as the studying areas, and the adjacent areas, Qingjiao from sandstone region and Shuitang from basalt region were selected as their control areas. Typical local plants and the soil around their roots were sampled in the studying areas and the control areas. Iodine content and its chemical speciation, major and trace elements, pH value were determined for these samples.The results show that the type of parent rocks rather than the distance from sea were the primary factors affecting the plant iodine contents. Generally the iodine contents of plant in limestone regions, compared with the other adjacent areas, were lower.The iodine content of fruits were significantly lower than its roots and leaves, the mean is that the fruits as a source of iodine to human contribution were still limited.The iodine content of roots and leaves was significantly positively correlated.The iodine contents in the stem was significantly lower than the lamina and root of the plant, which indicates that stem is the transport channel and its enrichment capacity of iodine is less than root and lamina.Different soil types resulted in different iodine contents in the soil, in general the iodine contents of soils in limestone regions were higher than that of adjacent non-limestone areas. The distance from sea are no significantly affecting the iodine contents of soil. The percentages of water-solube iodine in total iodine in soils are very low, its scope is0.81～6.18%, and the vast majority of the water soluble-iodine is organically bound iodine, inorganic iodine(IO3-, I-), less than15%. The type of parent rocks of soils are significantly affecting the percentages of water-solube organically bound iodine. In general the contents of water-solube organically bound iodine in limestone region was less than that of adjacent area. Most soil with lower contents of water-solube organically bound iodine has less the iodine contents of plant in limestone region, thus the phytoavail able iodine in soil has been reduced. I-is the dominant form in water-soluble soil iodine, more than85%, which is beneficial to the iodine enrichment by plants, because most plant accumulates more I-than IO3-in water-solution through root system. Soil pH and its water-soluble iodide was significantly negatively correlated. Improving the acidity of soil may be beneficial for plant to accumulate more iodine in limestone region.