Selenium Speciation And Selenium-Cadmium Interaction In Staple Crops

Selenium(Se)plays an important role in antioxidation,regulating hormones and mineral elements metabolism.However,China is a typical Se-deficiency country with a Se-deficiency belt crossing from Northeast to Southwest.According to the recent studies,only 17% of the population in China have a dietary Se intake that meets the WHO/FAO appropriate intake criteria(55-400 ?g/day/adult);while 39-61% still have a low dietary Se intake,which is potentially affecting the nutritional health of Chinese populations.But according to the latest geochemical survey on soil,some hot-spot soils with Se-rich were discovered in Hubei,Guangxi,Shanxi,and Jiangxi,producing natural Se-rich agri-foods.However,the heavy metal Cd usually accompanied with Se in soils,which leads to excessive Cd accumulation in Se-rich agri-foods,greatly limiting the development and utilization of natural Se soil resources.Therefore,the need of reduction impact of Cd pollution while using the natural Se-rich soil resources to produce Se-rich crops is a realistic problem to be mitigate.(1)Till now,it is impossible to analyze the Se speciation in staple crops with Se contents lower than 1 mg/kg,limiting the exploration of the distribution of Se speciation in natural Se-rich crops and the further development of related standards.Thus,it is the priority to set up the Se speciation analysis method via HPLC-ICP-MS.Firstly,the optimal mobile phase configuration parameters are determined by testing the standard samples,and the instrument parameters were compared to ensure that the ICP-MS has no ion interference with Se.Secondly,the external standard method and the area normalization method were compared.Thirdly,optimization on drying,extraction,concentration and purification was conducted.The finalized method via HPLC-ICP-MS could be used to determine the Se speciation on natural Se-rich agri-products with Se content higher than 20?g/kg.(2)Based on the established HPLC-ICP-MS,Se speciation analysis was performed on staple crops from typical Se-rich areas.The results showed the proportions of Se(VI)in wheat and potato decreased first and then increased along increasing total Se contents.The proportions of SeMet in the crops were usually more than 50% when the total Se contents were lower than 1 mg/kg;but the proportions of MeSeCys were significantly increased when the total Se contents were higher than 1 mg/kg.Moreover,SeMet was predominant in grains,and SeCysCysSe was significantly higher in leaves as edible parts than those of other edible parts.MeSeCys could account for more than 10% in stems and roots as edible parts.The present study showed that the Se speciation in staple crops was not only controlled by the total Se contents,but also the edible parts.(3)When the soil bioavailable Se-Cd molar ratio was lower than 0.7,the Cd contents in the corn tissues increased with the increase of the ratio;however,when the soil bioavailable Se-Cd molar ratio was greater than 0.7,the Cd contents in the corns decreased with the increase of the ratio.Meanwhile,the transportation efficiency was high from soil to root,but low from root to aerial part with increasing Se contents of soils.Furthermore,SeCysCysSe played an important role in limiting the migration of Cd in the group with lower bioavailability of Se-Cd molar ratio(<0.7),but SeMet and Cd-bound compounds were present in corn leaves in the group with higher bioavailability of Se-Cd molar ratio(>0.7).There was no significant correlation between the Se-Cd binding patterns in maize roots and stems,but there was a significant positive correlation between Cd-SeCysCysSe,Se-Met and Cd-unknown ratios in stems and leaves,likely indicating that there is some interfacial effect between the root and stem tissues of the corn,and this interface causes the distribution characteristics of Se and Cd to change during the migration process.