Study On Selenium And Cadmium Sources And Land Safety Zoning In Typical Se-Enriched Areas

Selenium is one of the most important trace elements for human body.It has many biological functions and is closely related to the health of the human,animals and plants.Enshi City,Hubei Province,is known as the “Selenium Capital of the World”.In this area,the selenium contents is abundant both in the soil and crops,which are in line with the basic conditions for the development of selenium-enriched agricultural products.However,there are also some problems of excessive levels of heavy metals in the soil and crops.Through the investigation and analysis of the distribution characteristics,sources and bioavailability of selenium and other heavy elements in the soil and crops of Shadi Town,Enshi City,the model was established and the zoning of safe land utilization was carried out.The results were concluded as following:1.The variation of coefficient of Se and Cd in the soil of the study area is significant,and the degree of dispersion is conspicuous,which are mainly affected by the distribution of stratum.The Se,I,F and Cd in the soil were higher than the average contents of surface soil elements in Hubei Province and the whole country,indicating that the soil of the study area was rich in healthy elements,meanwhile,the Cd content was also at a high level.The results of land quality evaluation showed that the soil resources of health elements as Se and F in the study area were very rich,and Cd with serious pollution risks.2.Through the method of statistics,it is found that the Se has a high correlation with heavy metals such as Cd,which is mainly controlled by clay minerals and black rock series in the soil.The correlation between soil organic carbon and heavy metals such as Cd in the soil of the study area is not significant.3.There was serious Cd exceeding the national standard in corn,rice and pepper samples in the study area.The pepper was especially serious,and the over-standard rate was as high as 100%.There was also a certain degree of Pb exceeding the standard in the corn samples.As and Hg did not exceed the standard in the main crops in the study area.In addition,there are differences in the degree of absorption of elements by different types of crops.4.Combined with the research results of human dose effect in the study area,that is,the antagonism of Se on Cd,the safety threshold value of Cd in the main bulk crops of Shadi Town in Enshi City was obtained.Using this value for safety zoning,it is found that considering the antagonism of Se on Cd,the area of the structural adjustment zone increased by 17.1%,while the area of the strictly controlled zone decreased by 26.3%,which greatly improved the area of safe land use.Through the statistical content characteristics of Se and Cd in the main crops of the study area,combining with the results of safe zoning,it is suggested that the priority protection area and the safe use area can vigorously develop the Se-rich agricultural products.The structure adjustment area is recommended to plant corn or tea.