Preparation And Improvement Of Selenium-enriched Reference Materials And Selenium Fractionation/Species Analysis And Their Applications

Selenium（Se）is a metalloid element,widely used in metallurgy,glass,semiconductor,printing,solar energy,medicine,forage and other fields.Selenium is an important trace element necessary for human and animal life activities,with a narrow range between beneficial and harmful intake for human bodies.As a component of the earth’s crust,selenium is ubiquitous in soil,rock,air,water,vegetation and food,and continuously circulates between different reservoirs.The human body mainly ingests Se through diet,in which plant Se acts the main source of human intake of Se,and the physical and chemical properties and geochemical characteristics of soil and their impact on Se bioavailability are the main factors determining the Se absorption by plants.Therefore,the study of the Se fractionation/species and its distribution in soil-crop system is very important for understanding the migration,transformation and bioavailability of Se in the environment and developing Se-enriched agriculture.However,there is still a lack of unified and effective analysis methods for Se fractionation/species in Se-enriched rocks/soils and crops,as well as reference materials certified with corresponding Se fractionation/species values.This study will establish and optimize the analysis method for Se fractionation/species of Se-enriched rock/soil and crops,and develop the reference materials for Se-enriched rock,soil and crop for components and Se fractionation/species analysis,and explore the distribution and influence mechanism of Se and its fractionation/species in soil-crop systems,and evaluate the health risk of residents in typical Se-enriched areas.This study will also provide technical basis and quality monitoring materials of analyzing components and Se fractionation/species for Se-enriched geological samples and crops,and provide technical support and scientific basis for the biogeochemical research of Se in soil-crop systems,as well as the development of Se-enriched agriculture and the evaluation of Se-enriched soil.Based on the environmental and biogeochemical characteristics of Se,this study established and optimized a five-step sequential extraction procedure for Se fractionation in Se-enriched rocks/soils and the analysis method for Se species in Se-enriched crops.This study also developed a series of candidate reference materials of Se-enriched rock,soil and crop for component and Se fractionation/species analysis,according to the established Se fractionation/species analysis method.Besides,the distribution mechanisms of Se and Se fractionation/species in soil-crop systems and health risks in Liujiang District,Guangxi,were also studied.The main results were achieved as follows:1.A five-step sequential extraction procedure for Se fractionation in Se-enriched rock/soil was established and optimized.The Se fractionation in rock/soil were divided into five forms,namely water soluble Se,exchangeable Se,organic bound Se,acid soluble Se and residual Se.After extracting with appropriate reagents and treatment,the solutions were tested by atomic fluorescence spectrometer（AFS）,and the method had been proved with good precision and accuracy.Compared with Tessier and BCR method,the extracted forms are more stable and characterize the Se distribution in each geochemical phase in a greater extent.The Se species in crops（rice and wheat）were extracted by protease XIV+lipase+Tris HCl（p H=7.5）with ultrasound+driselase,and tested by high performance liquid chromatography inductively coupled plasma mass spectrometry（HPLC-ICP-MS）.The precision and accuracy of this method were proved to be good.2.Four Se-enriched rock reference material candidates（YTB,BYP,GQ and HP）were developed,with certified values and expanded uncertainties of Se contents of 0.96±0.05 mg/g,1.03±0.05 mg/g,49±4 mg/kg and 38.5±1.9 mg/kg,respectively.Five Se-enriched soil reference material candidates（ES,ZY,HN,FC and ZHJ）were developed.The certified values and expanded uncertainties of Se contents were 19.5±2.1 mg/kg,9.4±1.4 mg/kg,2.7±0.4 mg/kg,0.91±0.10 mg/kg and 0.83±0.07 mg/kg,respectively.In addition,the information values of water soluble Se,exchangeable Se,organic bound Se,acid soluble Se and residual Se in sample ZY were 0.14 mg/kg,0.24 mg/kg,1.23mg/kg,5.84 mg/kg and 1.41 mg/kg.The information values of Se fractionations in sample HN are 0.029 mg/kg,0.47 mg/kg,1.53 mg/kg,0.064 mg/kg and 0.61 mg/kg,respectively.Four Se-enriched crop reference material candidates（DM1,DM2,DM3 and XM）were developed,with certified values and expanded uncertainties of Se contents of 0.48±0.09mg/kg,0.28±0.06 mg/kg,0.14±0.03 mg/kg and 0.57±0.12 mg/kg,respectively.Besides,the certified or information values and expanded uncertainties of Se Cys₂,Se Met and Se（VI）were 0.025 mg/kg,0.26±0.05 mg/kg and 0.0084±0.0021 mg/kg in sample DM1,and 0.027 mg/kg,0.27±0.05 mg/kg,0.0096 mg/kg in sample XM.3.The geochemical characteristics of soil Se and its Se fractionation distributions,the enrichment mechanisms and health risk assessment of Se and heavy metals in rice were studied in Liujiang District,Guangxi.The average Se contents of paddy soil and sugarcane planting soil in Liujiang District were 0.38 mg/kg and 0.68 mg/kg,respectively.The Se content of paddy soil was mainly affected by soil organic matter,and was higher in alkaline soil with higher calcium and magnesium contents.The Se content of sugarcane planting soil was mainly affected by soil organic matter and iron manganese nodules.Paddy soil in Liujiang District was mainly polluted by Cd,and was moderately polluted in general,while sugarcane planting soil was mainly polluted by Cd and Cr,and was slightly polluted in general.The average proportions of Se fractionations in paddy soil of Liujiang District were as follows:organic bound Se（36.0%）>residual Se（24.6%）>acid soluble Se（23.8%）>exchangeable Se（8.75%）>water soluble Se（6.85%）;The average proportions of Se fractionations in sugarcane planting soil were as follows:organic bound Se（53.9%）>acid soluble Se（16.6%）>residual Se（11.5%）>exchangeable Se（10.9%）>water soluble Se（7.07%）.Organic bound Se in paddy soil acted as the key source of Se uptake by rice,while exchangeable Se,organic bound Se and acid soluble Se in sugarcane planting soil were the key sources of Se absorption by sugarcane.The average Se contents of rice and sugarcane in Liujiang District were 0.063 mg/kg and 0.010 mg/kg respectively,with a certain proportion of Cd exceeded the safe standard both.The bioavailability of soil Se and heavy metals decreased with the increase of soil TFe₂O₃,TOC contents and p H values.Taking rice consumption into consideration,the Se intake of residents in Liujiang District was 28.5μg/d.The main Se species in rice were Se Met（83.3%）and SeCys₂（10.4%）.