Distribution and soil threshold of selenium in the cropland of southwest mountainous areas in China.

To investigate the distribution characteristics of selenium (Se) in mountainous soil-crop systems and examine the threshold value of Se-rich soil, 275 soil samples and 153 associated crop samples (rice, maize, tea, nuts, konjac, mushrooms, buckwheat, and coffee) were collected in Ximeng County, a typical mountainous area in southwest China. The total Se, available Se, organic matter, pH, sampling point elevation, and crop Se content were analyzed to examine the distribution characteristics of soil Se and the ability of primary crops to enrich Se in Ximeng County. Random forest and multiple regression models were established to identify the factors influencing the available soil Se and the crop Se enrichment coefficient. Finally, the Se-rich soil threshold was examined based on the total Se, available Se, and Se content in primary crops (rice, maize, and tea). The results showed soil Se resource abundance in the study region, with high Se soil accounting for 64.72% of the entire area. The soil Se content displayed significant spatial autocorrelation. The average Se enrichment coefficient of the main cultivated crops included mushrooms > nuts > rice > coffee > tea > maize > buckwheat > konjac. The total Se content in the soil had the highest impact on the available Se content in the soil and the Se enrichment coefficient of crops. A Se-rich soil threshold of 0.3 mg·kg-1 was used for rice and maize, while that of tea was 0.4 mg·kg-1. This result provided a theoretical basis for developing and utilizing Se resources in mountainous soil in southwestern China and dividing the Se-rich soil threshold.

Analyzing the quality differences between healthy and moldy cigar tobacco leaves during the air-curing process through fungal communities and physicochemical components.

Introduction: The air-curing process of cigar tobacco, as a key step in enhancing the quality of cigars, is often susceptible to contamination by mold spores, which severely constrains the quality of cigar tobacco. Methods: This study employed high-throughput Illumina sequencing technology and a continuous flow analysis system to analyze the differences between the microbial communities and physicochemical components of moldy and healthy cigar tobacco leaves. Furthermore, correlation analysis was performed to reveal the impact of mold on the quality of cigar tobacco. Results: The differences between the microbial flora and physicochemical compositions of moldy (MC) and healthy (HC) tobacco leaves were analyzed, revealing significant disparities between the two groups. Aspergillus spp. represented the dominant mold in MC, with nine out of twelve isolated molds showing higher quantities on MC than on HC. Mold contamination notably decreased the total nitrogen (TN), total phosphorus (TP), total alkaloids (TA), starch, protein, and flavor constituents while increasing the total fatty acid esters (TFAA), which was accompanied by a shift towards weakly acidic pH in the leaves. Fungal community analysis indicated a significant reduction in the fungal operational taxonomic unit (OUT) numbers and diversity indices in MC, contrasting with the bacterial trends. Aspergillus exhibited significantly higher relative abundance in MC, with LEfSe analysis pinpointing it as the primary driver of differentiation. Furthermore, significant negative correlations were observed between Aspergillus and TP, starch, TA, and protein, while a significant positive association was evident with TFAA. Network analysis underscored the pivotal role of Aspergillus as the species influencing disparities between HC and MC, with its abundance serving as a critical determinant during the air-curing process. Discussion: This study elucidated substantial quality distinctions between MC and HC during air-curing, with Aspergillus emerging as the key species contributing to leaf mold.

Research status of soda residue in the field of environmental pollution control.

High-quality soda ash (Na2CO3) is mainly produced using the ammonia-alkaline method, generating a significant amount of industrial waste called soda residue. In China, the annual production of soda residue exceeds 10 million tons. The large-scale open-air storage of soda residue not only occupies land but also causes severe pollution to the surrounding environment. Soda residue displays characteristics such as strong alkalinity, high reactivity, and a well-developed pore structure, making it a valuable raw material for producing environmentally functional materials. This article provided an overview and summary of soda residue, including its sources and hazards, basic properties, applications in environmental management (wastewater treatment, flue gas desulfurization, and soil remediation), and associated risks. The limitations of using soda residue in "waste to waste" technologies were also analyzed. Based on this analysis, the article suggests focusing on simultaneous removal of heavy metal ions using soda residue, safely disposing of and acquiring resources from metal-laden sludge, efficiently dechlorinating soda residue, using soda residue for contaminated soil solidification, stabilization, and assisted remediation, controlling pollution via green and circular utilization approaches, and assessing long-term risk.

Removal of hydrogen sulfide in the gas phase by carbide slag modified bentonite.

Bentonite-based adsorbents for the removal of hydrogen sulfide (H2S) were prepared by a wet-mixing method using carbide slag as the active component. The effects of carbide slag content, calcination temperature, calcination time, and reaction temperature on the H2S adsorption capacity were investigated. The results showed that compared with the blank bentonite adsorbent, the carbide slag-modified bentonite-based adsorbent enhanced the chemisorption of H2S. The adsorption capacity of the carbide slag modified bentonite adsorbent (2.50 mg g-1) was more than 40 times higher than that of the blank bentonite-based adsorbent (0.06 mg g-1) under optimal conditions. The optimal conditions for H2S removal were 3 : 5 ratio of carbide slag-to-bentonite, calcination temperature of 450 °C for 2 h, and reaction temperature of 95 °C. H2S was mainly removed in the mesopores and macropores of the adsorbent and was finally transformed to CaS and sulfate on the adsorbent surface. The adsorption process of H2S followed the Freundlich adsorption isotherm equation and Bangham adsorption kinetic model.

Solidification/stabilization of soil heavy metals by alkaline industrial wastes: A critical review.

Solidification/stabilization technology is one of the most desirable technologies for the remediation of heavy metal contaminated soils due to its convenience and effectiveness. The annual production of alkaline industrial wastes in China is in the hundreds of millions of tons. Alkaline industrial wastes have the potential to replace conventional stabilizers because of their cost effectiveness and performance in stabilizing heavy metals in soils. This paper systematically summarizes the use of four alkaline industrial wastes (soda residue, steel slag, carbide slag, and red mud) for the solidification/stabilization of heavy metal contaminated soils and provides a comprehensive analysis of the three mechanisms of action (hydration, precipitation, and adsorption) and factors that influence the process. In addition, the environmental risks associated with the use of alkaline industrial wastes are highlighted. We found that soda residues, steel slag and carbide slag are appropriate for solidification/stabilization of Pb, Cd, Zn and Cu, while red mud is a potential passivation agent for the stabilization of As in soils. However, implementation of remediation methods using alkaline industrial wastes has been limited because the long-term effectiveness, synergistic effects, and usage in soils containing multiple heavy metals have not been thoroughly studied. This review provides the latest knowledge on the mechanisms, risks, and challenges of using alkaline industrial wastes for solidification/stabilization of heavy metal contaminated soils.

Gram-scale synthesis of ultra-fine Cu2O for highly efficient ozone decomposition.

Nowadays, it is necessary and challenging to prepare Cu2O in a large scale for various applications such as catalysis due to its excellent properties. Here, gram-scale Cu2O with nm size is successfully prepared using a simple liquid-phase reduction method at 25 °C. The amount of NaOH is found to be the key factor to determine the particle size of Cu2O by modifying the complexation and reduction reactions. The obtained ultra-fine Cu2O exhibits high performance of >95% efficiency for removing high-concentration (3000 ppm) ozone at 25 °C and even at a high relative humidity (RH) of 90% for more than 8 h. Furthermore, the Cu2O nanoparticles are coated onto an aluminium honeycomb substrate to form a monolithic catalyst, which shows high ozone removal efficiency of >99% in dry air and >97% in 90% RH for >10 h at a space velocity of 8000 h-1. The high performance could be attributed to the enhanced release of the ozone decomposition intermediate by the small size of Cu2O, as verified by O2 temperature-programmed desorption and X-ray photoelectron spectroscopy. All these results show the industrial promise of the large scale synthesis of ultrafine Cu2O applicable for high-performance ozone removal.

Proteomics reveals surface electrical property-dependent toxic mechanisms of silver nanoparticles in Chlorella vulgaris.

Silver nanoparticles (AgNPs) are known to exert adverse effects on both humans and aquatic organisms; however, the toxic mechanisms underlying these effects remain unclear. In this study, we investigated the toxic mechanisms of various AgNPs with different surface electrical properties in the freshwater algae Chlorella vulgaris using an advanced proteomics approach with Data-Independent Acquisition. Citrate-coated AgNPs (Cit-AgNPs) and polyethyleneimine-coated AgNPs (PEI-AgNPs) were selected as representatives of negatively and positively charged nanoparticles, respectively. Our results demonstrated that the AgNPs exhibited surface electrical property-dependent effects on the proteomic profile of C. vulgaris. In particular, the negatively charged Cit-AgNPs specifically regulated mitochondrial function-related proteins, resulting in the disruption of several associated metabolic pathways, such as those related to energy metabolism, oxidative phosphorylation, and amino acid synthesis. In contrast, the positively charged PEI-AgNPs primarily targeted ribosome function-related proteins and interrupted pathways of protein synthesis and DNA genetic information transmission. In addition, Ag+ ions released from the AgNPs had a significant influence on protein regulation and the induction of cellular stress. Collectively, our findings provide new insight into the surface electrical property-dependent proteomic effects of AgNPs on C. vulgaris and should improve our understanding of the toxic mechanisms of AgNPs in freshwater algae.

Surface charge-dependent bioaccumulation dynamics of silver nanoparticles in freshwater algae.

Silver nanoparticles (AgNPs) can gradually accumulate in algae to exert their toxicity; however, there is little knowledge about their bioaccumulation dynamics. For the first time, this study reports the effect of surface charge of AgNPs on their bioaccumulation dynamics in freshwater algae (Chlorella vulgaris) using biodynamic modeling. Polyethylene-coated AgNPs (PEI-AgNPs) and citrate-coated AgNPs (Cit-AgNPs) were selected as positively and negatively charged AgNPs, i.e., P-AgNPs and N-AgNPs, respectively. Their uptake and elimination dynamics were investigated at a concentration of 50% inhibition of growth rate values (EC50) and 10% inhibition of growth rate values (EC10). The one-component model can generally well simulate the algal uptake and elimination kinetics of N-AgNPs but not of P-AgNPs. At both concentrations, the uptake rate constants (ku) for P-AgNPs were ∼20 times higher than that for N-AgNPs. The parameters of biphasic elimination kinetics revealed that P-AgNPs were eliminated faster than N-AgNPs during depuration compared to in subsequent processes. Compared with N-AgNPs, extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and dark-field imaging revealed that P-AgNPs can be rapidly absorbed on the algal cell surface membrane owing to their remarkably lower energy barrier between algal cells, resulting in a faster adsorption/uptake process and aggregation of algal cells. Our results clearly demonstrate that the AgNPs exhibited surface charge-dependent bioaccumulation dynamics in algal cells. Thus, AgNP surface charge primarily influences the AgNP accumulation dynamics in algal cells.

Effect of silver nanoparticles on gill membranes of common carp: Modification of fatty acid profile, lipid peroxidation and membrane fluidity.

Although the toxicity of silver nanoparticles (AgNPs) in aquatic organisms has been extensively investigated, the mechanism by which AgNPs damage membranes remains unclear. This study investigated the toxic effects of a series of sub-lethal concentrations of AgNPs on the membranes of freshwater carp (Cyprinus carpio) gills, based on changes in membrane fatty acid (FA) profile, membrane fluidity, membrane lipid peroxidation, and histopathology. Most of the FAs in fish gill membrane was not significantly affected by exposure to multiple AgNPs concentrations, only few significant changes occurred in some specific FAs species at a high concentration of AgNPs exposure. In particular, high concentrations of AgNPs significantly decreased the proportions of two important long-chain n-3 series polyunsaturated FAs (C20: 5n3, and C22: 6n3), resulting in a decreased ratio of n-3 polyunsaturated FAs to n-6 polyunsaturated FAs (Σn-3UFA/Σn-6UFA). The AgNPs also caused a dose-dependent decrease in fish gill membrane fluidity, increased the level of lipid peroxidation, and inhibited Na+/K+-ATPase enzyme activity. Further histopathological examination revealed that exposure to AgNPs can cause toxic responses in the lamellae, including the thinning of the basement membrane, malformation, and inflammation. Together, the results suggest that the mechanism of AgNPs membrane toxicity involves the oxidization of long-chain omega-3 unsaturated FAs to saturated FAs via lipid peroxidation, resulting in, decreased membrane fluidity and ultimately the destruction of the normal physiological function of the fish gill membrane. The findings contribute significantly to our understanding of nanoparticle-induced membrane toxicity and potential risks in aquatic environments.