摘要：
Selenium (Se) accumulation in rice (Oryza sativa L.) has become a major global concern. Se offers multiple health benefits in humans; however, its inadequate or excessive intake can be harmful. Therefore, determining the factors driving Se abundance and bioavailability in paddy soils is essential to ensure the safety of human Se intake. This study investigated the accumulation, bioavailability, and distribution of Se in 820 paddy soil and rice grain samples from Luxi County, China to assess how soil properties (soil organic matter [SOM], cation exchange capacity [CEC], and pH), geographical factors (parent materials, elevation, and mean annual precipitation [MAP] and temperature [MAT]), and essential micronutrients (copper [Cu], zinc [Zn], and manganese [Mn]) govern Se accumulation and bioavailability in paddy soils. Results showed that the average soil Se content was 0.36mgkg(-1), which was higher than that in China (0.29mgkg(-1)). Alternatively, the average rice grain Se content was 0.032mgkg(-1), which was lower than the minimum allowable content in Se-rich rice grains (0.04mgkg(-1)). Five studied parent materials all had a significant effect on soil Se content but had little effect on Se bioavailability (p<0.05). CEC, elevation, and SOM, as well as the soil contents of Cu, Zn, and Mn were positively correlated with soil Se content, but pH, MAP, and MAT were negatively correlated. Correspondingly, Se bioavailability was negatively correlated with SOM and soil Zn content, but positively correlated with MAP and grain contents of Cu, Zn, and Mn. Furthermore, partial least squares path analysis revealed the interactive impacts of the influencing factors on Se accumulation and bioavailability in soils. On this basis, prediction models were established to predict Se accumulation and bioavailability in paddy soils, thereby providing theoretical support for developing efficient control measures to meet Se challenges in agriculture.
摘要：
Phyllosilicate nanoparticles play an important role in regulating the biogeochemical processes of Fe(II) and As(III) in paddy soils due to their high mobility and activity. In the present work, two prepared muscovite nanoparticles with different sizes (LNPs and SNPs) were used to investigate the effect of the size of phyllosilicate nanoparticles on the coprecipitation of Fe(II) and As(III) during oxidation process. The results showed that muscovite nanoparticles could significantly promote the removal of Fe(II) and As(III) during coprecipitation process. The formation of crystalline iron oxide and oxidation of As(III) tended to be suppressed by the two muscovite nanoparticles, and the suppression increased as muscovite nanoparticle size decrease. The findings of this study provide a contribution to understanding the roles of the natural phyllosilicate nanoparticles in regulating the biogeochemical processes of Fe and As elements in polluted paddy soils.
关键词：
Ancient paddy soils;Fulvic acid;Humic acid;Solid-state 13C cross-polarization magic-angle-spinning nuclear magnetic resonance
摘要：
The study of organic matter in ancient paddy soils is helpful for understanding the influence of human activities on soil carbon sequestration and global climate change. However, little information on the spatial distribution and structural characteristics of the humic substances (HS) in ancient paddy soils is available. The spatial distributions of humic acids (HAs) and fulvic acids (FAs) in ancient paddy soils and modern cultivated paddy soils at the Shanlonggang site on the Liyang Plain were investigated, and the associated structures were characterized by using (13)C nuclear magnetic resonance (NMR). The (13)C NMR spectra revealed the following carbon types in HAs and FAs in both types of paddy soil in order of decreasing abundance: O-alkyl carbon (ranging from 39.7 to 51.8% and from 42.6 to 50.9%, respectively) >/= alkyl carbon (ranging from 16.8 to 23.5% and from 15.7 to 22.4%, respectively) approximately carboxyl carbon (ranging from 13.3 to 19.3% and from 16.9 to 22.0%, respectively) > aromatic carbon (ranging from 12.8 to 23.5% and from 10.0 to 17.2%, respectively). Moreover, the degree of aromaticity of HA was higher than that of FA in both soil samples. The humic constituents of the buried ancient paddy soils were less aromatic and oxidized than those of the modern cultivated paddy soils. The organic carbon in the ancient paddy soils was also less aromatic and oxidized than that in the modern cultivated paddy soils, suggesting that the structures of the HS in the ancient paddy soils were relatively simple. The results of this study provide new insights into the effect of secondary paddy soil formation on the spatial distribution, structural characteristics, and stability mechanisms of the HS in ancient paddy soils.
摘要：
The isomorphous substitution in the structure of phyllosilicate minerals plays an important role in regulating of surface chemical properties. In this work, iron muscovite nanoparticles with various Al species were successfully prepared to explore the structural Fe and Al species on the capture of Cd(II) from solutions. The synthesized nanocrystals have irregular shapes with diameters of 10-50 nm. The incorporation of Al(III) into the iron muscovite nanostructure has slight effect on the species of Fe and the crystal phase of the products. The degree of Al(III) substituting Si(IV) in the tetrahedral sheets of the minerals obviously increased with increasing of Al doping levels. For the samples with low Al doping levels (5% and 10%), the adsorption capacity of the iron muscovite nanoparticles for Cd(II) increased slightly. With increasing of Al doping ratio to 15%, the obtained iron muscovite nanoparticles exhibited a maximal uptake of 41.4 mg g(-1) for Cd(II), which is about two times that of the undoped samples (22.8 mg g(-1)). The solution pH had a slight effect on the Cd (II) capture at a wide pH range from 4 to 8. The adsorption of Cd(II) is very fast and reached a steady state within 5 min. Desorption results showed that the binding strength between Cd(II) and iron muscovite nanoparticles was obviously enhanced by incorporation of Al at a high level. The ion exchange and surface complexation are principal mechanisms in the Cd(II) capture by the iron muscovite nanomaterials with various structural Al species. (C) 2019 Elsevier Ltd. All rights reserved.
