The fate of Arsenic associated with the transformation of iron oxides in soils: The mineralogical evidence.

The influence of iron (oxyhydr)oxides on the transformation and migration of arsenic(As) has garnered significant attention. Previous work has largely focused on the transformation of iron oxides related to As fate at molecular and mechanistic levels. However, studies examining the interplay between As concentration and iron oxides transformation within complex soil system are sparse. This study investigates the transformation of iron oxides in soils with varying As concentration during microbial dissimilatory iron reduction (DIR), employing humic acid (HA) as electron shuttle and assesses the impact on As speciation transformation. Comparative analyses indicate that in soils with high As concentration (>1000 mg/kg), the secondary transformation of iron (oxyhydr)oxides to other forms, such as the conversion of ferrihydrite to goethite and lepidocrocite, or schwertmannite to goethite, is impeded. Consequently, the formation of goethite and lepidocrocite, which would typically re-stabilize As, is inhibited, leading to elevated release of As(III). On the other hand, an increase in magnetite formation in soils with low As concentration (<100 mg/kg) appears to re-stabilize As effectively. Furthermore, the formation of new secondary iron (oxyhydr)oxides in soils with As concentration <200 mg/kg enhances fraction F5, which subsequently contributes to the re-immobilization of As, sequestering it within the soil matrix. This process results in a lower release of As(III) from soils with As concentration below 200 mg/kg. These findings enhance the understanding of the interdependent relationship between the transformation of iron oxides and the fate of As in complex soil systems.

Changes in stoichiometric characteristics of ambient air pollutants pre-to post-COVID-19 in China.

To prevent the Corona Virus Disease 2019 (COVID-19) spreading, Chinese government takes a series of corresponding measures to restrict human mobility, including transportation lock-down and industries suspension, which significantly influenced the ambient air quality and provided vary rare time windows to assess the impacts of anthropological activities on air pollution. In this work, we divided the studied timeframe (2019/12/24-2020/2/24) into four periods and selected 88 cities from 31 representative urban agglomerations. The indicators of PM2.5/PM10 and NO2/SO2 were applied, for the first time, to analyze the changes in stoichiometric characteristics of ambient air pollutants pre-to post-COVID-19 in China. The results indicated that the ratios of NO2/SO2 presented a responding decline, especially in YRD (-5.01), YH (-3.87), and MYR (-3.84), with the sharp reduction of traffic in post-COVID-19 periods (P3-P4: 2.34 ± 0.94 m/m) comparing with pre-COVID-19 periods (P1-P2: 4.49 ± 2.03 m/m). Whereas the ratios of PM2.5/PM10 increased in P1-P3, then decreased in P4 with relatively higher levels (>0.5) in almost all urban agglomerations. Furthermore, NO2 presented a stronger association with PM2.5/PM10 variation than CO; and PM2.5 with NO2/SO2 variation than PM10. In summary, the economic structure, lockdown measures and meteorological conditions could explain the noteworthy variations in different urban agglomerations. These results would be in great help for improving air quality in the post-epidemic periods.

The expression and significance of NF-κB, MMP1, and MMP2 in rats with abdominal aortic aneurysm.

This study aimed to investigate the expression and significance of NF-κB, matrix metal protein1 (MMP1), and matrix metal protein2 (MMP2) in rats with abdominal aortic aneurysm (AAA). 48 Wistar rats were collected, then they were divided into an experiment group and a control group (n=24). The rats in the experiment group were used to carry out an abdominal aortic aneurysm modeling, while the rats in the control group were infused with a same dose of saline through catheters. qRT-PCR and ELISA were used to detect the expressions of EGF and VEGF-C in skin tissues and mRNA of NF-κB, MMP1, and MMP2 in their abdominal aorta. A vernier caliper was used to measure the diameter of their abdominal aorta. Western blot was used to detect the expressions of NF-κB, MMP1, and MMP2 in their abdominal aorta. In the experiment group, the abdominal aorta of the rats expanded to some extent after they were infused compared to that before they were infused (P< 0.05), and the abdominal aorta of them was significantly larger than that of the rats in the control group. On the 3rd week after modeling, the abdominal aorta of the rats expanded more obviously compared to that after they were infused for a while in the experiment group, and the expansion rate of the diameter was (57.19 ± 4.67)% (P< 0.05). Protein expression levels of NF-κB, MMP1, and MMP2 in the abdominal aorta of the rats increased significantly in the experiment group compared to those of the rats in the control group (P<0.05). The increase of NF-κB, MMP1, and MMP2 may be related to the pathogenesis of abdominal aortic aneurysm in abdominal aortic aneurysm models of rats.

The role of major functional groups: Multi-evidence from the binding experiments of heavy metals on natural fulvic acids extracted from lake sediments.

Fulvic acid (FA) plays a key role in governing the environmental geochemistry behavior of heavy metals. In this work, the roles of major functional groups were investigated based on binding experiments of heavy metals on natural FA extracted from lake sediments. The results showed that the adsorption capacities were ranked as Cu2+ > Pb2+ >Cd2+. The differences of peak area at 3412, 1713, 617and 2430 cm-1 pre- and post-binding reactions in FTIR spectra suggested that phenolic, carboxyl and nitrogen-containing groups were the major functional groups providing sites binding heavy metals. Moreover, the results of bi-Langmuir model and the ionic strength effects jointly indicated that electrostatic attraction was the key mechanism during the adsorption process. The fitted results of Ligand-binding model suggested that the major functional groups in FA were classified into two types binding sites: weak (i.e. phenolic and carboxyl groups) and strong binding sites (i.e. nitrogen-containing groups). Additionally, there might be p-benzoquinone-like formed in FA which were then reduced to hydroquinone during the adsorption process, corresponding to the changing of peak area at 1614 and 830 cm-1 in FTIR spectra, the occurrence of Peak C in Fluorescence excitation-emission matrix (EEM) spectra and the ratios of H/C (<1) and O/C (≈1). The organic matter in sediments from Lake Wuliangsuhai presented similar characteristics with terrestrial plants due to the lake characterized by Phragmites australis and Potamogeton pectinatus L. being the dominant species, which shared large proportions of woody tissues as well as waxy hydrocarbons resembling that of terrestrial plants. This work is useful to insight the environmental effects of FA on heavy metals in environment.

Responses of Organic Phosphorus Fractionation to Environmental Conditions and Lake Evolution.

Geochemical fractionation is used to assess the significance of environmental factors on organic phosphorus (OP) pools in sediments. Labile, moderately labile, and nonlabile OP pools in the sediments from Lake Hulun, Inner Mongolia, were fractionated, and their responses to environmental conditions and lake evolution were investigated based on the spatial and vertical distribution of OP fractionations. In light of the recalcitrant characteristics of organic matter (OM) in different environmental conditions, the pH presents significant negative effects on the amount of labile OP, while water depth shows an important role in regulating the distribution between the moderately labile and nonlabile OP pools. A latitudinal zonation in the distribution of OP pools in surface sediments from different lakes was apparent with this zonation likely linked to the gradient effects of climate and anthropogenic activities on OM decomposition and thereby on the sediments capacity to hold phosphorus. These results show that OM plays a role in governing the impacts of weather and environmental factors on OP fractionation in aquatic environments. This work suggests that OP pools in the sediment core could be used as an archive for environmental conditions and lake evolution.

Distribution characteristics and potential ecological risk assessment of heavy metals (Cu, Pb, Zn, Cd) in water and sediments from Lake Dalinouer, China.

The concentrations of Cu, Pb, Zn and Cd were measured in water and sediment to determine their distribution characteristics and potential ecological risks of the Lake Dalinouer. The results revealed that the dominate form of Cu, Pb, Cd and Zn in surface sediments respectively were organic sulfides, Fe-Mn oxides, carbonates and Fe-Mn oxides, with a mean content of 4.28mgkg(-1), 0.76mgkg(-1), 7.84µgkg(-1) and 1.77mgkg(-1), respectively; the concentrations of bio-available metals had an increase tendency from the northeast to the southwest part of this lake. Acid volatile sulfides (AVS) and simultaneously extracted metal (SEM) were used to predict the potential bioavailability of heavy metals. The horizontal distribution of AVS (0.15-2.4µmolg(-1), mean 0.53µmolg(-1)) in surface sediments shows an increasing trend from southwest to northeast of the lake, whereas SEM (0.02-0.99µmolg(-1), mean 0.37µmolg(-1)) had an opposite pattern. The relative high salt and pH which restrained the bioactivities of sulfate-reducing bacteria (SRB) were the main controlling factor in AVS concentrations. The vertical variation of AVS concentration in sediment core increased with depth and different from SEM. Potential ecological risk index (PERI) and geo-accumulation index (Igeo) were used to assess heavy metals accumulation. The results indicated that moderate contamination of most heavy metals was prevalent and presented a decreased trend from southern to northern of the lake, and element Cd emerged the greatest potential ecological risk. The pollution of heavy metal in the southern of the Lake Dalinouer should be taken into consideration seriously.