| Microelement selenium is closely related to human health.The main source of selenium in human body is dietary intake,and plant food is the main body of diet,so plants play an important role in selenium supplement.Different selenium species have different toxic and biological effects on environment and human health.The behavioral effect of selenium is not only determined by the total amount of selenium,but also can play a role in the ecological environment,life system and organism only in a specific content range and species.Therefore,it is of great significance to establish an accurate and efficient method for speciation analysis of selenium in environmental samples and to carry out environmental geochemical research on selenium and human health based on the speciation analysis of selenium for scientific evaluation of the impact of selenium on the environment and biological system.In this paper,high performance liquid chromatography inductively coupled plasma mass spectrometry?HPLC-ICP-MS?was used to establish the analytical method of Seleno-Cysteine?SeCys2?,?Methyl?Seleno-Cysteine?MeSeCys?,Selenite?Se????,Selenomethionine?SeMet?and Selenate?Se????.At the same time,the analysis of selenium species in soil and plant samples was carried out.On this basis,rice,corn and soil in enshi area of hubei province was taked as research objects,and the distribution,main selenium species and the correlation between selenium in soils and plants were discussed.The main progress achieved is as follows:1.The analytical methods of total selenium and selenium species in soil and plant samples was established.In order to realize the effective analysis of total selenium in plant and soil,reduce the loss of selenium in sample processing and reduce the test cost,the sample pretreatment method was optimized.Finally,the method of graphite predigestion-closed digestion-inductively coupled plasma mass spectrometry was adopted.The methods of total selenium in soil and plant samples was accurate and reliable.The analytical method of five selenium species in plant samples was established.In order to achieve the effective separation of five selenium species?SeCys2,MeSeCys,Se???,SeMet,Se????,the effects of different detector,chromatographic column,mobile phase and pH on the speciation analysis of selenium species were investigated.Finally,five selenium species were completely separated on a Hamilton PRP-X100 anion exchange column using 20mmol·L-1 citric acid solution?pH 4.0?,20 mmol·L-1 citric acid solution?pH 6.0?and methanol as the mobile phase under gradient elution within 9 minutes.The correlation coefficient?R2?of the five selenium species was greater than 0.9991.2.The pretreatment conditions of selenium species analysis in plant and soil samples were optimized.In order to achieve the effective extraction of selenium species from plant samples,the effects of different extraction agents,enzyme dosage and extraction time on the extraction efficiency of selenium species were investigated.Finally,20 mg of XIV protease and 10 mg of Driselase were dissolved in 3 mL of 75 mmol·L-1 Tris HCl?pH 7.5?as extractant,and the selenium species of the sample was extracted by shaking at 37?for 3 h.The detection limits of SeCys2,MeSeCys,Se?IV?,SeMet and Se?VI?were 0.88?g·L-1,0.69?g·L-1,1.00?g·L-1,0.90?g·L-1 and 0.82?g·L-1,respectively.The recoveries of the spiked samples were between 73.2%and 107%.The established method for selenium species analysis in plant samples is accurate and reliable.By using the method of literature research,referring to the previous studies on the analytical method of selenium forms in soil,combined with the purpose of this study,the step-by-step extraction method of the occurrence state of selenium in soil was determined.The selenium species of available selenium in water-soluble and exchangeable forms were further analyzed by HPLC-ICP-MS.3.The occurrence state of selenium in plants and soils of Enshi was analyzed.The samples of rice,corn and soil were collected from 12 villages in Enshi,including 10 rice samples,6 corn samples and 16 soil samples.The total selenium and selenium species of the samples was determined by the established method.The results showed that the spatial distribution of total selenium content in soil was quite different and more than 58%of them was higher than the reference value(0.30?g·g-1)in the selenium excess area of China.The enrichment characteristics of selenium in rice were rice root>rice grain>rice leaf>rice stem,which indicates that selenium is easier to accumulate in the root.According to the limit of selenium-enriched rice in GB/T 22499-2008 and GB 2762-2012,the rice grain samples are all selenium-enriched rice.Therefore,the local residents need to eat selenium-enriched products reasonably according to the daily dietary selenium demand of human body.If they eat selenium-enriched products in area for a long time,the health risks brought by them can not be ignored.The proportion of available selenium in soils is only between 6.08%and 17.5%,indicating that only a small part can be absorbed and utilized by plants.The bioavailable selenium species in water-soluble and exchangeable forms of soils were analyzed by HPLC-ICP-MS.It was found that the main selenium species in water-soluble form was Se???,followed by Se???,while only Se???was detected in exchangeable form.There was no organic selenium species was detected in water-soluble and exchangeable forms of all soil samples.The results showed that the selenium in soil of Enshi sampling area mainly migrated to plants in inorganic species.Selenium forms in rice are mainly organic forms,mainly SeMet,which accounts for more than 50%of the total selenium content,and there are some differences in the composition and content of selenium forms in different parts of rice.The correlation between the content of SeMet in rice and the content of selenium species in water-soluble and exchangeable forms in soil was analyzed.The results showed that SeMet in rice had no significant correlation with Se???in water-soluble form of soil,but had significant positive correlation with Se???in water-soluble form at the level of P<0.01,and Se???in exchangeable form at the level of P<0.01.Through literature research,we can know the migration rule of selenium species in plants,and the distribution rule of selenium species in the samples in this study is consistent with the migration rule of selenium species in plants in the previous studies.In this paper,the analytical method of selenium content and species in soil and plant samples was established.The method is simple,fast and efficient.The distribution and existing species of selenium in soil and plant samples in Enshi selenium rich area were preliminarily explored by using the established method.Meanwhile,the correlation between selenium in different parts of rice and selenium in soil was discussed in order to provide technical support for quantitative evaluation of effective nutrients and human health risk evaluation. |
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