Rhizosphere enrichment and crop utilization of selenium and metals in typical permian soils of Enshi.

Enshi, China, is renowned as "Selenium(Se) Capital" where widely distributed soils derived from Permian parent rocks are notably rich in Se, as well as metals, particularly cadmium(Cd). However, the soil enrichment and crop uptake of Se and metals in these high-Se and high-Cd areas are not well understood. To propose the optimal crop planting plan to ensure the safety of agricultural products, we investigated the soils and corresponding typical crops (rice, tea, and maize). The results showed significant soil enrichment of elements, with average contents (mg/kg) as follows: Cr (185), Zn (126), Cu (58.8), Pb (31.1), As (15.7), Se (6.85), Cd (5.41), and Hg (0.211). All soil Se contents were above 0.4 mg/kg, indicating Se-rich soils. Se primarily existed in an organic-bound form, accounting for an average proportion of 61.3%, while Cd was mainly exchangeable, with an average of 62.5%. Cd exhibited higher activity according to the Relative Index of Activity (RIA). Nemerow single-factor index analysis confirmed significant soil contamination, with Cd showing the highest level, followed by Cr and Cu, while Pb had the lowest level. Tea exhibited a high Se rich ratio (82.0%) without exceeding the Cd standard. In contrast, corn and rice had relatively lower Se-rich ratios (42.0% and 51.5% respectively) and high rates of Cd exceeding the standard, at 49.0% and 61.0% respectively. Canonical analysis revealed that rice was more influenced by soil factors related to Se and Cd compared to maize and tea crops. Therefore, tea cultivation in the Enshi Permian soil area is recommended for safe crop production. This study provides insights into the enrichment, fractionation, and bioavailability of soil Se, Cd, and other metals in the high-Se and high-Cd areas of permian stratas in Enshi, offering a scientific basis for selecting local food crops and producing safe Se-rich agricultural products in the region.

Geochemical relationship and profile distribution of Selenium and Cadmium in typical Selenium-enriched areas in Enshi.

Selenium (Se) is an essential nutrient element for humans, and Se-enriched products are gaining popularity due to their health benefits. However, Enshi, a region in China naturally rich in Se, a high background value of cadmium (Cd) is discovered, which severely impacts local Se-enriched agriculture. Therefore, it is crucial to explore the geochemical relationship between Se and Cd. In this study, we analyzed soil profiles and parent rocks of different geological ages from Enshi to investigate the accumulation and distribution of Se and Cd. The ratio of redox sensitive elements and the multivariate statistical analysis, along with XRD and XPS analysis, were utilized to investigate the correlated relationship between Se and Cd and the underlying geochemical mechanisms. The results showed that average Se and Cd contents in rocks were 1.67 and 0.32 mg/kg. Se and Cd levels reached highest at Permian in rocks of different geological ages, which may be related to the Permian Dongwu movement near the study area. The highest migration rate of Cd and Se from rock to soil was 12 and 1.5 times. The soil Se and Cd fractions were mostly in bound states, with the largest fraction of Se being organic-bound at an average of 45.9%. The reducible and the residue state accounted for the largest proportion in the Cd fractions, with an average of 40.6% and 25.6%. Redox-sensitive element ratios indicate a reducing forming environment of deep sediments in the Permian strata. Furthermore, the correlation and PCA analysis revealed highly significant positive correlations between Se, Cd, V and Cr, suggesting that the sources of Se and Cd were closely related to volcanic and biological activities. In conclusion, a strong geochemical relationship was observed between Se and Cd. And as a result, metal pollution must be closely monitored during the production of Se-enriched agriculture in Se-enriched regions.

Smartphone as a simple device for visual and on-site detection of fluoride in groundwater.

Developing a portable device for visual and on-site detection of fluoride in groundwater is highly anticipated. In this paper, 2-(tert-butyl-diphenylsilanyloxy)-5-nitro-1H-benzoimidazole (1) has been rationally designed via a silanization reaction for self-calibration detection of fluoride, and the detection limit was calculated as 0.11 µM. The contact of 1 with fluoride would induce the cleavage of Si-O bond and trigger the emergence of excited state intramolecular proton transfer (ESIPT) process, and then the enol-like emission at 437 nm decreased accompanying with the increase of keto-like tautomerism emission at 550 nm. More importantly, considering the demand of field detection for fluoride in groundwater and combining the function of smartphone to obtain the chroma of photos. The chroma value of the fluorescence color changes from blue to yellow could be conveniently determined through a color recognizer application installed in smartphone. The device can accurately reflect the concentration of fluoride by analyzing the chroma value. The test in actual water samples confirmed that the simple device based on smartphone could be used efficiently for visual, on-site and accurate detection of fluoride in groundwater.

Surface acidity and basicity of Mg/Al hydrotalcite for 2, 4-dichlorophenoxyacetic acid degradation with ozone: Mineralization, mechanism, and implications to practical water treatment.

The Mg/Al hydrotalcite (Mg/Al HT) was firstly used as a heterogeneous ozonation catalyst and 2,4-dichlorophenoxyacetic acid (2,4-D) was efficiently degraded by Mg3/Al HT with a COD removal of 68 %. It was higher than that of α-FeOOH with a COD removal of 50 %. The effects of Mg/Al atomic ratio, phosphate and pyrrole on the ozonation performance of Mg/Al HTs were also investigated. The X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption experiment and temperature programmed desorption of adsorbed CO2 or NH3 were used to characterize the surface properties of Mg/Al HT. The surface acidity and basity was proven to be responsible to the excellent ozonation activity of Mg/Al HT. The results of electron spin resonance (ESR) analysis and probe experiments confirmed that OH, O2- and 1O2 were involved in the 2,4-D degradation process and their contributions are as followed: OH > O2- > 1O2. The synergistic effect of surface acid (ozone adsorption center) and base sites (catalytic center) determines Mg/Al HT in the enhanced catalytic ozone decomposition into reactive species. More important, the transition metal free based Mg/Al HTs is steady, non-toxic, naturally abundant and environment friendly, which provided a promising alternative in practical water treatment by catalytic ozonation.