Study On The Spatial Distribution Of Iodine In Terrestrial Soil And Sediment In The Typical Valley

Iodine is an essential trace element and having important physiological function in the human body.Iodine is one of the wide distribution elements in the earth,but its distribution is uneven.The concentration of iodine in the natrual environment is greatly affected by the different environmental factors,and its distribution and migration rules are complex.It is significant to study on the geochemistry characteristics of iodine distribution and the rule of iodine migration in natural media and environment for the study of iodine geochemistry.In this paper,the concentration of iodine in the sediments and soils come from majorriver basin and main coverage area were compared.The six major river basins in China including of Yangtze valley,Pearl River basin,Yellow River basin,Liaohe river basin,Heilongjiang river basin and Xinjiang endorheic system.The main coverage area of soil with different types including of the Songnen plain,the Liaohe plain,the North xinjiang,the North China plain,the Sichuan basin,the Yangtze river plains and the Pearl river delta.The effects of environmental factors such as monsoon,precipitation,climate,lithology of water system,vegetation cover and soil properties on the concentration of iodine in the soils and sediments were investigated.The spatial distribution of iodine in soil and sediments of major river basin and main coverage area in China was constructed.In addition,the characteristics of distribution and migration of iodine for rock-soil system were discussed in Jiaodong Peninsula with complicated geological background.The main research results are as follows:?1?The accurate determination method of trace iodine in geological samples by ICP-MS with dilute ammonia extraction and methane sensitization were established.High temperature and high-pressure digestion were used in sample treatment.And purified ammonia water was used as the extraction solution for extracting iodine in soil and sediment samples,which could inhibit the loss of volatile iodine and reduce the background signal of iodine.A small amount of methane is introduced into ICP torch as sensitizing gas,which increases the ionization of iodine and the signal intensities of iodine were increased two times.The detection limit?LOD,3D?is 0.006?g L^-1.The RSD of 53standard reference materials was less than 5%?n=3?.The analytical results are consistent with the recommended values.At the same time,the iodine concentration of five geological certified reference materials?GSD-1,GSD-3^GSD-6?without reference values were reported in this paper.?2?The spatial distribution characteristics of iodine in sediments of major river basins in China were investigated.The effects of environmental factors such as monsoon,rainfall,climate and lithology on the concentration and spatial distribution of iodine in sediment samples of major river basins in China were compared.The results indicated that the iodine concentration in sediments was decreased from south to north and or from humid to arid areas in China under the influence of monsoon precipitation and dry and wet climate.The iodine concentration in tropical and subtropical monsoon humid areas is more than 1?g/g,while the iodine concentration in other areas is lower than 1?g/g,especially in arid areas.The sediments with iodine concentration more than 2?g/g were mostly located in meiyu area.The iodine concentration in river sediments for quartzite sandstone drainage basin?0.2?g/g?,granite drainage basin?<0.7?g/g?and acidic volcanic rock drainage basin?about 1?g/g?was lower,while the iodine concentration for carbonate drainage basin?>1.5?g/g?was higher.?3?The distribution characteristics of iodine in different types of soil in China were explored.Influenced by monsoon,precipitation,climate,vegetation in China,the iodine concentration in the differential type soil were decreased from the south to the north or from the humid area to the arid area.However,the change trend of soil iodine concentration in some regions are affected by soil type,texture,weathering degree and the physicochemical properties,which are inconsistent locally.The iodine from the ocean and atmosphere can only affect the soil with a fraction of distance between the coast and inland,and the change trend of the iodine concentration in the soil is not completely consistent with the amount of rainfall.The results indicated that soil with high iodine concentration?>4?g/g?was mostly concentrated in tropical and subtropical monsoon humid areas,while other areas was generally less than 3?g/g.Different from the stream sediments,the soil iodine concentration in meiyu area?<4?g/g?is lower than in the tropical and subtropical monsoon humid areas.This phenomenon indicates that the soil iodine concentration will be reduced when precipitation is frequent in a certain period.Vegetation coverage has a positive effect on the iodine retention in soil.The soil with higher organic matter,and sticky is useful for retaining iodine.?4?The distribution and migration characteristics of iodine in the rock-soil system of Jiaodong peninsula were studied.The migration of iodine in soil profiles of different geological units is related to lithology of geological units.The migration of iodine in rock-soil system showed that the soil iodine concentration has a certain inheritance to the iodine concentration in rocks.The iodine migration trend in the soil profiles is from deep soils to shallow soils.The migration behavior of iodine in soil profiles from different lithologies is obviously different.In the soil profiles formed by igneous rock weathered,iodine mainly migrates from deep soil to shallow soil.While in the soil profiles formed by sedimentary rock weathered,the migration pathway of iodine is different.The migration behavior of iodine in the soil profile formed in the metamorphic rock weathered is close to the rock type before metamorphism.