This research explores the stabilization of clay soil through the application of geopolymer binder derived from silicomanganese slag (SiMnS) and activated by sodium hydroxide (NaOH). This research aims to evaluate the effects of key parameters, including the percentage of slag, the activator-to-stabilizer ratio, and curing conditions (time and temperature), on the mechanical properties of the stabilized soil. Unconfined compressive strength (UCS) tests were conducted to assess improvements in soil strength, while scanning electron microscopy (SEM) was employed to analyze the microstructural changes and stabilization mechanisms. The results demonstrated that clay soil stabilized with SiMnS-based geopolymers exhibited significant strength enhancement. Specifically, the sample stabilized with 20% SiMnS and an activator-to-slag ratio of 1.6, cured at room temperature for 90 days, achieved a UCS of 27.03 kg & frasl;cm2. The uniaxial strength was found to be positively correlated with the SiMnS content, activator ratio, curing time, and temperature. Additionally, the strain at failure remained below 1.5% for all samples, indicating a marked improvement in soil stiffness. SEM analysis revealed that geopolymerization led to the formation of a dense matrix, enhancing soil particle bonding and overall durability. These results emphasize the potential of SiMnS-based geopolymers as a sustainable and effective soil stabilizer for geotechnical applications.

In recent years, excessive accumulations of iron (Fe), manganese (Mn), and nitrogen (N) have been observed in the groundwater of agricultural regions, particularly in flood irrigation areas. Nevertheless, the causes of this phenomenon and the associated hydrobiogeochemical processes remain elusive. This study demonstrated that redox fluctuations instigated by flood irrigation triggered a synergistic interaction between the N cycles and the activation of Fe and Mn oxides, thereby resulting in elevated concentrations of Fe, Mn, and N simultaneously. Static experiments revealed that the properties of the topsoil exerted a profound influence on the N induced release of Fe and Mn. The black soil (TFe: 1.5-2.3 times, Mn(II): 1.1-1.5 times, nitrate: 1.3-1.4 times) had greater release potential than meadow and dark brown soils due to higher electron donors/acceptors and substrates. Dynamic column experiments further elucidated that the wet-dry cycles induced by agricultural cultivation regulated the release process through the formation of zonal redox gradients and the structuring of microbial community. Organic nitrogen mineralization, chemolithotrophic nitrification, and Feammox/Mnammox were identified as the primary mechanisms responsible for the reductive dissolution of Fe-Mn oxides. On the other hand, autotrophic denitrification, with nitrate serving as the electron acceptor, constituted the main process for the reoxidation of Fe and Mn. Furthermore, the agricultural activities exerted a significant impact on the nitrate attenuation process, ultimately resulting in the recurrence of TFe (black soil: 1.5-6.3 times) and nitrate (black soil: 1.4-1.6 times) pollution during the phase after harvesting of rice (days 40-45) in saturated zone. The findings of this study not only deepened the understanding of the intricate interactions and coupled cycles between primary geochemical compositions and anthropogenic pollutants, but also provided a scientific foundation for the effective management and prevention of groundwater pollution stemming from agricultural cultivation processes.

A cutting-edge smart nano-hybrid technology, offering potential benefits for plants, has recently been developed to address the pervasive issue of heavy metal pollution. This study explored the potential of this technology in mitigating chromium (Cr) stress in rapeseed using a nano-based system that integrates 100 mu M hydrogen sulphide (H2S) and 50 mu M manganese nanoparticles (Mn-NPs). This strategy reveals Cr-stress tolerance mechanisms through physiological assessments and transcriptome data analysis. The results demonstrated that Cr stress substantially inhibited rapeseed growth while increasing oxidative damage markers (MDA and ROS levels). Conversely, Mn-NP and H2S co-treatment significantly mitigated these effects, as shown by: (1) restored growth metrics, (2) improved photosynthetic performance and membrane integrity, (3) optimized Mn/H2S homeostasis, and (4) reduced tissue Cr accumulation. The reduction in Cr content was attributed to enhanced Cr-detoxification mechanisms, driven by the upregulation of enzymatic antioxidant activities, like superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase. Transcriptomic profiling revealed marked upregulation of genes involved in core metabolic processes, including photosynthetic pathways, carbon assimilation, secondary metabolite biosynthesis, inositol/phosphatidylinositol signalling systems, and stress-response networks. Under Cr stress, Mn-NP and H2S co-treated rapeseed plants displayed enhanced tolerance, highlighting the crucial role of these signalling agents in activating Cr-defence mechanisms. Our findings demonstrate that the integration of nanotechnology and gasotransmitter signalling molecule H2S presents a novel strategy for enhancing heavy metal tolerance and plant productivity in contaminated soils.

Ferromanganese nodules (FMNs), simultaneously termed as manganese nodules, are metallic concretions typically found in the B horizon of iron and manganese-rich soils. These nodules are primarily formed through the biomineralization process driven by favorable redox reactions and microbial activity. The formation of FMNs in the soil is governed by complex geochemical interactions and influenced by both biotic and abiotic factors, such as temperature, pH, organic matter, redox potential (Eh), wet/dry cycles, and nucleation sites. FMNs typically vary in size, ranging from a few microns to several centimeters, and exhibit diverse shapes, from spherical to irregular. These nodules play a crucial role in nutrient cycling and the adsorption of heavy metals, including phosphorus, lead, copper, zinc, cobalt, and nickel, thereby improving soil quality and preventing metal leaching into aquatic environments. The ion exchange during redox reactions, complexation, occlusion, and adsorption are the key mechanisms through which heavy metals can become immobilized in soil FMNs. The formation of FMNs involves Mn-oxidizing bacteria, such as Bacillus, Pedomicrobium, Erythrobacter, Pseudomonas putida, Geobacter, and Leptothrix discophora, which use specific functional genes such as mnxG, moxA, mopA, CumA, ombB, omaB, OmcB, and mofA to facilitate manganese oxidation. This process reacts with geological material, resulting in the precipitation of metal leachates and the development of metal oxide coatings that serve as nucleation sites for FMNs. Such microbial activities are not only essential for FMNs formation but also for trapping heavy metals in soil, highlighting their importance in soil biogeochemical cycling and ecological functions. However, further research is needed to unravel the complex biogeochemical interactions that influence FMNs growth and composition, as well as to understand the stabilization and release dynamics of nutrients and heavy metals, and the roles of microbial communities and functional genes involved in these processes, particularly in relation to soil fertility and plant nutrition.

Plastic pollution is a common concern of global environmental pollution. Polystyrene (PS) and polyethylene (PE) account for almost one-third of global plastic production. However, so far, there have been few reports on microbial strains capable of simultaneously degrading PS and PE. In this study, Microbacterium esteraromaticum SW3, a non-pathogenic microorganism that can use PS or PE as the only carbon source in the mineral salt medium (MM), was isolated from plastics-contaminated soil and identified. The optimal growth conditions for SW3 in MM were 2% (w/v) PS or 2% (w/v) PE, 35 degrees C and pH 6.3. A large number of bacteria and obvious damaged areas were observed on the surface of PS and PE products after inoculated with SW3 for 21 d. The degradation rates of PS and PE by SW3 (21d) were 13.17% and 5.39%, respectively. Manganese peroxidase and lipase were involved in PS and PE degradation by SW3. Through Fourier infrared spectroscopy detection, different functional groups such as carbonyl, hydroxyl and amidogen groups were produced during the degradation of PS and PE by SW3. Moreover, PS and PE were degraded into alkanes, ketones, carboxylic acids, esters and so on detected by GC-MS. Collectively, we have isolated and identified SW3, which can use PS or PE as the only carbon source in MM as well as degrade PS and PE products. This study not only provides a competitive candidate strain with broad biodegradability for the biodegradation of PS and/or PE pollution, but also provides new insights for the study of plastic biodegradation pathways.