| 其他摘要 | Selenium(Se) is an essential trace element for human and animals, the excessive and deficient intake of Se would lead to different health effect. Recent studies have shown that the bioavailability of selenium was mainly controlled by chemical speciation of selenium rather than its total concentration in the environment. Different Se species affect the mobility, transformation, bioavailability and toxicity of selenium in the environment due to their obvious differences geochemical characteristics. Yutangba is the only site in China where a sudden incidence of human selenosis took place, the organic bound Se is more than 60% of Se inventory in the weathered Se-rich carbonaceous rocks and Se-rich soils in this area, and the further study on organic bound Se will be helpful to comprehensively understand the biological availability of Se and to elucidate the biogeochemical secondary enrichment process and cycle mechanism of Se during the weathering of Se-rich carbonaceous rocks. Based on an improved seven operationally defined chemical sequential extraction, optimized extraction procedure of organic bound Se, and Hydride Generation-Atomic Fluorescence Spectroscopy, we study the speciation distribution of Se associated with organic matter in Enshi. The major conclusions are drawn as follows:
1. The factors such as solution/solid ratio and extracted reagents were optimized based on seven steps sequential chemical extraction protocol, and other fractionations were also discussed The results show that suitable solution/solid ratio is from 20 to 50 during extraction procedure. 0.1～0.5M NaOH can effectively extract organic-bound selenium under heated water bath. 1M Na2SO3 is better reagent for elemental selenium extraction. NaOH＋H2O2 is suitable absorded liquid, 500～600mL/min airflow flux ensure that H2Se formed during sulfide/selenide selenium reduced by CrCl2+HCl mixture is fully adsorbed.
2. As for weathered Se-rich carbonaceous rocks and Se-rich soils, we use an optimized chemical sequential-extraction procedure to extract organic bound Se and separate the humic acid fraction and the fulvic acid fraction, then Se concentrations was determined by PEFE-HG-AFS. The results show that the recovery of the scheme is 84.4~104.2%, with an average of 96.1% . The linear correlation coefficient is 0.999 (n=14) and the slope is 1.0026. We use the self-made hydride generation and absorbed devices to isolate weakly bound Se (IV) and strongly bound Se from humic substance. The recovery rate of fulvic acid fraction is from 86.3% to 107. 6%(average value is 97.1%), while the recovery rate of humic acid fraction is from 85.5% to 105.9%(average value is 97.9%). All of these indicate that the experimental schemes used in this study is feasible.
3. The humic acid fraction in the weathered Se-rich carbonaceous rocks has a higher proportion from 36.3% to 75.8%, with an average value of 56.6%, but humic acid fraction is not the absolute advantage, it has vary distribution in samples. In Se-rich soils, fulvic acid fraction takes a proportion from 25.4% to 85.0% in total organic bound Se, most samples have proportion values between 70% and 80%. It shows that fulvic acid fraction is main for soil samples in Yutangba, and it may be converted to be absorbed by plants in the appropriate conditions (such as the environment changes in the pH-Eh). Besides, high humic acid fraction in rocks and high fulvic acid fraction in soils indicates the possible transport and transformation law during the weathering procedure of selenium.
4. The speciation analysis about fulvic acid fraction and humic acid fraction show that the distribution of Se is vary in different rock samples without regularity, which may be caused by weathering level of different rock samples. While the content of weakly bound Se(IV) is larger than the Se bound humic substance for soil samples, especially the Se(IV) in the fulvic acid fraction which takes a proportion value 83.2% and 95.4% at most. This weakly bound Se(IV) is easily be released than Se strongly bound to fulvic acid fraction, which also further confirm that fulvic acid fraction is easily converted to bio-available Se when the environment being changed(pH-Eh) or the exists of sesquioxide.
5. HA-Se and FA-Se are certain proportions of organic bound Se. The research we’ve done is limited to quantitative, but how this part of Se bound the humic substance is not clear. Therefore, it is necessary to study further in this area. |
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