[Migration, Transformation Characteristics, and Ecological Risk Evaluation of Heavy Metal Fractions in Cultivated Soil Profiles in a Typical Carbonate-Covered Area].

In China, high heavy metal concentrations in cultivated soil are mainly distributed in carbonate-covered areas. The migration and transformation of heavy metals in such soils are influenced by interactions between natural processes and human activities. This study examined the profiles of nine paddy soils, derived from carbonate rocks in Guangxi. The Cd, As, Zn, Cr, Cu, Hg, Ni, and Pb contents we determined, and soil properties such as pH, Corg content, and fractions of Cd, As, Zn, and Cr were tested. Based on the above data, we assessed the vertical distribution of heavy metal fractions, as well as the ecological risks and factors affecting the migration ability of heavy metals, under the influence of human activities and natural soil formation. The results show that compared with the carbonate rocks in Guangxi, the soil profile of the study area is significantly enriched with all eight heavy metals. Among them, Cd, As, Zn, and Cr exceeded China's agricultural land (paddy field) pollution risk screening values, and Cd and As partially exceed the risk intervention values. All fractions of Cd in the soil profiles are widely distributed. The proportion of water-soluble and ion-exchange Cd fractions with high ecological risk decreased significantly from the surface to greater depths in the soil profile. As, Zn, and Cr in the soil profile were mainly in residual states, and the proportion of water-soluble and ion-exchange fractions did not change considerably with increasing depth. The evaluation results of RAC and RSP show that Cd pollution risk in the study area is relatively high, whereas As, Zn, and Cr are generally pollution-free or risk-free. In naturally developed soil in the study area, the clay mineral content and degree of soil development have significant effects on Cd migration, whereas in the cultivated layer affected by human activities, the soil pH and organic matter content are the main controlling factors. The migration ability of soil As is mainly related to soil organic matter, Fe2O3 content, and soil development degree, but organic matter has an obviously enhanced effect in the tillage layer. The main controlling factor of Zn and Cr migration in soil is pH, and the effects are more intense under the disturbance of human activities.

[Factors Affecting the Translocation and Accumulation of Cadmium in a Soil-Crop System in a Typical Karst Area of Guangxi Province, China].

To understand the main factors influencing the translocation and accumulation of cadmium (Cd) in soil-crop systems in typical karst areas, 68 sets of paddy soil and rice grain samples were collected in Guangxi Province. These were used to analyze Cd concentrations and soil properties (pH, organic matter (OM) content, oxide content, and texture). Spearman's correlation coefficients and principal component analysis (PCA) were used to examine the effects of soil properties on Cd concentrations and identify the main influencing factors. The studied soils were highly enriched in iron oxide (TFe2O3), aluminum oxide (Al2O3), and manganese oxide (MnO) compared to background levels, with average concentrations of 20.2%, 19.0%, and 0.2%, respectively. However, the soils are relatively depleted in silica (SiO2), with an average concentration of 41.0%. The soils are strongly weathered and leached in study area, giving rise to rich occurrences of Fe-Mn nodules. The concentrations of TFe2O3 and MnO in the study soils were significantly correlated with soil Cd, rice seed Cd, and the Cd bioconcentration factor (BCF). The PCA analysis further showed that TFe2O3 and MnO in soils were the main factors affecting the migration and enrichment of Cd while soil pH, OM, and Al2O3 had less of an influence. Furthermore, SiO2 and soil texture indirectly affected the migration and enrichment of Cd. It is suggested that the Fe-Mn nodules effectively adsorb and immobilize Cd in the study area soils, acting as a heavy metal scavenger that reduced the biological accessibility of Cd.

[Bioavailability, Translocation, and Accumulation Characteristic of Heavy Metals in a Soil-Crop System from a Typical Carbonate Rock Area in Guangxi, China].

This study uses 68 sets of paddy soil and rice grain samples collected from an area of carbonate rocks in Guangxi Province, China, to explore the ecological risks of heavy metals (As, Cd, Cr, Cu, Hg, Pb, Ni, and Zn) in soils from a high background area. We analyzed the concentrations of these heavy metals in soil and grain samples, and their chemical speciation in soil, and use these data to assess the associated ecological risks by means of statistics, a geo-accumulation index, bioconcentration factors (BCF), and correlation analysis. The arithmetic mean values of heavy metals concentrations in soil samples from the study area were (75.8±50.1), (1.91±1.02), (467.0±253.1), (48.5±9.8), (0.21±0.08), (76.2±28.1), (84.2±25.0), and (258.0±122.6) mg·kg-1 for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, respectively, which were remarkably higher than of those from other regions within Guangxi Province and China. In comparison to China's soil environmental quality standard risk screening values (GB 15618-2018), the over-standard rates of Cd, As, and Cr were 95.6%, 86.8%, and 69.1%, respectively. In comparison to risk intervention values, the over-standard rates of Cd, As, and Cr were 27.9%, 17.6%, and 5.9%, respectively. Speciation analysis on heavy metals indicated that As, Cr, Cu, Ni, Pb, and Zn were mainly found in a residual form, and accounted for>80% of the total concentrations, and had a low bioavailability. The bioactive components (F1+F2+F3) of Cd accounted for 21%, and the bioactivity of Cd was higher than other elements. The potential bioavailable components (F4+F5+F6) of Hg accounted for 44%, with low total concentrations, which are understood to have little potential ecological harm for crops. However, the over-standard rates of Pb, Cd, and Cr in rice grains were only 23.5%, 8.8%, and 2.9%, respectively. Correlation analysis showed that there was no significant correlation between the concentrations of heavy metals in soils and the corresponding rice grains. The mean BCFs of each heavy metal were <0.1, and the BCFs of Hg, Pb, As, Cr, and Ni were <0.05. Overall, we found relatively high concentrations, low activity, and low ecological risks for heavy metals in the study area. For high geological background materials such as carbonate rocks, factors such as metal speciation, biological activity, and crop over-standard rates should be taken into account along with the traditional use of the total amount of heavy metals in a soil as the evaluation standard when formulating pollution control policies.

Alkaloids from Sophora flavescens Aition.

Although the quinolizidine alkaloids and flavonoids, the main active components of the traditional Chinese medicine Sophora flavescens, have been largely investigated, a new matrine alkaloid derivative 9alpha-hydroxy-7,11-dehydromatrine (1) and a rare 1,4-diazaindan-type alkaloid flavascensine (17), together with 15 known alkaloids, were isolated from S. flavescens. The structures were established on the basis of spectroscopic techniques.

Limonoids from the root of Dictamnus radicis cortex.

Chemical investigation of the roots of Dictamnus radicis Cortex led to the isolation of a new limonoid isodictamdiol (1) and a known dictamdiol (2), the first 5S/9S-type degraded limonoids, together with other six known limonoids (3-8). The chemical structures were identified on the basis of modern spectroscopic methods, including IR, MS, NMR ((1)H-NMR, (13)C-NMR, (1)H-(1)H COSY, HMQC, HMBC, NOESY). Additionally, the absolute configurations of limonoid isodictamdiol (1) and dictamdiol (2) were separately elucidated by single crystal X-ray diffraction, as well as their circular dichroism spectra. Furthermore, all compounds were evaluated for antibacterial activity against three bacterial cultures.