| Selenium whose safety threshold is very narrow has a ambivalent.Selenium deficiency or excess can affect human health.Arsenic(As)and mercury(Hg)widespread in nature is high toxic heavy metals.Toxicological effects,ecological effects,metabolism,transformation of arsenic,selenium and mercury in environment depend on their forms and contents distribution.Therefore,arsenic,selenium and mercury analysis were listed as key monitoring indicators in food safety,toxicology,and environmental monitoring.Rice is the staple food of more than 60%population in China,which was one of the biggest rice consumer and producer.Rice is the important dietary source of trace elements for human.However,heavy metal pollution is more and more serious with the unreasonable treatment of pollutants and the use of pesticides,fertilizers containing heavy metals.Heavy metals such as arsenic and mercury enter into the soil,enhancing the arsenic and mercury contents in soil.Arsenic and mercury can invade rice through contamination soil contamination,making rice to be the main source of arsenic and mercury for human.When rice is ingested by human,the different species of arsenic,selenium and mercury in rice would go into human body.They might interact with protein,then influence or change the structure and function of protein.Therefore,it is important to analysis of arsenic,selenium and mercury species in rice,the risk evaluation on human health as well as the interaction of their species with protein.It is helpful to know the facts such as their exposure levels,ecological environment influence,risk assessment of rice,improvement of the whole process control from farm to meal,biological consequence of arsenic,selenium and mercury species.The aim of this thesis is to analyze 11 trace elements in 21 kinds of rice samples from 8 regions in China and one rice sample in Thailand by ICP-MS,develop a method of simultaneous analysis of arsenic and selenium species in 8 kinds of rice samples whose contents exceed national standards by HPLC-ICP-MS and evaluate the risk of arsenic,selenium and mercury in rice samples for human health.The circular dichrosim spectroscopy(CD)was used to investigate the interaction of As(?),As(?),Se(?),Se(?),CH3Hg+ and Hg2+ which are more toxic in arsenic,selenium and mercury species with the spectra and secondary structure of BSA.The research specifics and results are as follows:(1)Developed a microwave digestion-ICP-MS method for determination of trace elements such as Cr,Mn,Co,Ni,Cu,As,Se,Cd,Sn,Pb and Hg in 22 kinds of rice samples from 9 regions.The relative standard deviation(RSD)was in the range of 1.08%?2.86%.The recoveries of spiking rice samples and the detection limits were 80.0%?113.7%and 0.010?1.904 ng g-1,respectively.This method was used to analysis of trace elements in GBW10012-component analysis of biological reference materials-corn standard sample and the results were consistent with the standard value.The analytical method was simple,fast and accurate.(2)Study on As and Se species in rice and the interaction with BSA.? Developed a HPLC-ICP-DRC-MS method for simultaneous analysis As and Se species in 8 kind of rice samples which had higher contents of As and Se.Artificial gastric juice was used as extracting agent to extract As and Se species in rice samples.Above 70%of total As and Se was extracted by artificial gastric juice.The separation was achieved by using Hamilton PRP X-100 anion-exchange column with mobile phase containing 50 mmol L-1(NH4)2CO3(pH 9.5)at the flow rate of 1.5 ml min-1 by gradient elution.The ion 75As12CHH+ was determined to eliminate the interference of 75ArCl+ for 75As+ and the potentially interfering 40Ar40Ar+ for 80 Se+ was reduced by using CH4 as reactive gas of ICP-MS.Arsenobetaine(AsB),arsenite(As(III)),dimethylarsinic acid(DMA),methylarsonate(MMA),arsenate(As(V)),sodium selenite(Se(IV))and sodium selenate(Se(VI))were separated in less than 14 min.The detection limits for As and Se were in the range of 0.02?0.06 ng mL-1.The RSD of As and Se mixture ranged from 0.32%to 4.67%.In this study,the contents of inorganic As containing As(III)and As(V)were high and took up 70%of total As.The amount of daily intake of inorganic arsenic in rice samples was about 22800?38000 ng by calculating and was higher than a daily intake arsenic 20000 ng of the World Health Organization recommends.The contents of Se were low and just a small amount of Se(IV)was detected in Jiangsu-1 and,Zhejiang Hangzhou-2 rice samples.Total Se intake from rice samples was about 12660?21100 ng and was lower than the Se Recommended Dietary Allowance(RDA)in humans(70000 ng day-1).Because rice was the predominant diet in the China,higher As and lower Se in rice samples might lead to the As intoxication and Se deficiency of inhabitants in China.It might have a negative impact on human health.? The interactions of As(III),As(V),Se(IV)or Se(VI)with bovine serum albumin(BSA)were studied by CD at physiological pH 7.4 with the molar concentration ratio from 1:1 to 5:1.The experimental results showed that As(III),As(V),Se(IV)or Se(VI)caused the amplitude change of CD spectra,but no shift of the characteristic peaks of BSA.The secondary structure of BSA changed to different degrees.(3)Study on Hg species in rice and the interaction with BSA.? Developed a HPLC-ICP-MS method to analyze Hg species in Zhejiang Huzhou-2,Sichuan-2 and Sichuan-3 rice samples whose contents was higher than Hg limits in the national standard GB 2762-2005.Hg species in rice samples were extracted with ultrapure water,mobile phase and artificial gastric juice.Hg species were separated by C18 column with 60 mmol L-1 acetamide/0.4%2-mercapoethanol(pH 6.8),5%CH3OH as mobile phases and the detection limits for CH3Hg+ and Hg2+ were 0.006 ng mL-1.In this study,the mobile phase was propitious to Hg extraction in rice,but the effects of three extract solvents were not very good.CH3Hg+ and Hg2+ were not detected in three rice samples with ultrapure water as extract solvent.When mobile phase and artificial gastric juice were used as extractants,CH3Hg+ and Hg2+ were detected in Zhejiang Huzhou-2 and Sichuan-2 rice but only Hg2+ was detected in Sichuan-3 rice.? The interactions of CH3Hg+ or Hg2+ with bovine serum albumin(BSA)were studied by CD at physiological pH 7.4 with the molar concentration ratio from 1:1 to 5:1.The experimental results showed that CH3Hg+ or Hg2+ caused the amplitude change of CD spectra,but no shift of the characteristic peaks of BSA.The secondary structure of BSA changed to different degrees. |
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