Understanding the distribution of soil organic carbon and nitrogen (OC(N)) content, cation exchange capacity (CEC), and specific surface area (SSA) in different soil particle sizes is crucial for studying soil fertility and properties. In this study, we investigated the distribution characteristics of the OC(N), CECand SSA in different particles of yellow–brown soil under different methods. The result revealed that as the particle size decreased, the soil OC(N), SSA and CEC content gradually increase. The content of OC and ON different soil particles ranged from 1.50–28.16 g·kg⁻¹ to 0.18–3.78 g·kg⁻¹, respectively, and exhibited significant differences between different particles. We observed good linear relationships between OC and ON in different particle sizes of yellow–brown soil under different utilization methods, with correlation coefficients ranging from 0.86 to 0.98, reaching a very significant level (n = 12, p < 0.01). The ranges of SSA and CEC in different particles of the four soils were 0.30–94.70 m²·g⁻¹ and 0.70–62.91 cmol·kg⁻¹, respectively. Additionally, we found logarithmic relationships between SSA (CEC) and the equivalent diameter for the four soils, with correlation coefficients (r²) higher than 0.91. Furthermore, there was an extremely significant linear relationship between CEC and SSA of the four soils, with correlation coefficients (r²) of 0.92–0.97 (n = 12, p < 0.01). These results highlight the close relationship between soil particle size and soil OC(N), SSA, and CEC. The conclusions drawn from this study provide valuable data support and a theoretical basis for further understanding soil properties.

Mercury, particularly in its methylated form, poses a significant environmental and health risk in aquatic ecosystems. While the toxicity and bioaccumulation of mercury are well documented, there remains a critical gap in our understanding of the mechanisms governing mercury methylation and demethylation in aquatic environments. This review systematically examines the complex interplay of chemical, biological, and physical factors that influence mercury speciation and transformation in natural water systems. We provide a comprehensive analysis of methylation and demethylation processes, specifically focusing on the dominant role of methanogenic bacteria. Our study highlights the crucial function of hgcAB genes in facilitating mercury methylation by anaerobic microorganisms, an area that represents a frontier in current research. By synthesizing the existing knowledge and identifying key research priorities, this review offers novel insights into the intricate dynamics of mercury cycling in aquatic ecosystems. Our findings provide a theoretical framework to inform future studies and guide pollution management strategies for mercury and its compounds in aquatic environments.

Mercury (Hg) is a pervasive global pollutant whose environmental impact is critically defined by its speciation. This review synthesizes data from 100 studies to quantify the central role of periphyton, a ubiquitous microbial-algal biofilm, in Hg sequestration and transformation. Analyses show that periphyton extracellular polymeric substances (EPS), rich in carboxyl, hydroxyl, and sulfhydryl groups, achieve rapid Hg(II) biosorption within milliseconds, with reported adsorption capacities ranging widely from 27.2 mg/g for fungal components to over 393 mg/g for specific bacterial strains. Simultaneously, the anaerobic microzones of periphyton serve as biochemical reactors where microbial guilds (e.g., sulfate-reducing bacteria and methanogens) mediate methylation via the hgcAB gene cluster and demethylation via the mer operon. A key finding consolidated from the literature is that upon senescence, this mercury-laden biomass can enhance sediment methylmercury (MeHg) concentrations by 54%–514%, creating bioaccumulation hotspots. This review systematically dissects the adsorption mechanisms, environmental drivers, physiological adaptations, and bioremediation applications, highlighting that periphyton’s dual function as a sink and source of MeHg is a pivotal, yet underexplored, dynamic in Hg cycling. We conclude by emphasizing the urgent need to couple micro-scale mechanistic understanding with watershed-level models and to develop in situ monitoring and targated regulation strategies.

Mercury (Hg) is a widespread global pollutant, found throughout the natural environment, posing a health threat to millions of people worldwide. In 2010, the World Health Organization identified mercury as one of the top ten chemicals of major concern for public health (Zhang, 2022). Once mercury enters the ecosystem, its extremely low biodegradability means it can remain in environmental media for decades, accumulating over time and causing irreversible organ damage and cognitive impairments in those exposed. Mercury naturally occurs in the Earth's crust and is mainly released into the surface environment through natural geological processes such as rock weathering and volcanic eruptions. Human activities are also the primary source of mercury release, with key contributors including the steel, cement, gold, non-ferrous metal smelting, chlorine-alkali industries, and sectors directly involved in mercury production (Pavithra et al., 2023).Mercury is an element that exists in multiple forms, commonly known as quicksilver. It can be classified into three main types: elemental mercury (metal), inorganic mercury (such as the highly toxic mercury chloride), and organic mercury (such as the extremely toxic methylmercury). Different forms of mercury exhibit significant differences in toxicity and can severely damage critical human organs, including the central nervous system, digestive tract, immune system, lungs, kidneys, skin, and eyes. In aquatic systems, mercury exists in organic, inorganic, and elemental forms (Zhang, 2023). In the atmosphere, mercury is mostly found in its elemental form, with divalent mercury being the most common oxidation state of the elemental mercury. Mercury is typically released into the environment in its inorganic form, while methylmercury (MeHg) is one of the most neurotoxic substances and predominates in fish. This occurs because inorganic mercury is transformed into methylmercury through various biological and abiological processes in aquatic environments. While microbial methylation is the dominant pathway, abiological processes, such as the photochemical degradation of methylmercury, also significantly influence its environmental cycling and persistence (Donovan et al., 2016). Thus, mercury methylation is a crucial step in the mercury environmental cycle, and it determines the toxicological consequences of mercury release (Wu et al., 2024). Methylmercury has a higher bioavailability than both elemental and inorganic mercury, and it can diffuse from cells and be adsorbed by benthic organisms. These benthic organisms can include zooplankton, small fish, and other small organisms or nonliving entities. Through the food chain, mercury accumulates biologically and is passed on to predators at the top of the food chain (Donadt et al., 2021;Minet et al., 2022). Additionally, studies on wetlands have shown that the production and accumulation of methylmercury are significantly present in floating mats of large aquatic plants (such as Eichhornia crassipes) and waterlogged forest soils in tropical regions (Murphy and Guentzel, 2022).Compared to other metals, mercury is much harder to degrade in ecosystems. Remediation of mercury will typically involve processes like immobilization or removal (Mu, 2023). Techniques such as oxidation, reduction, and adsorption can remove mercury from contaminated sites and also convert harmful mercury into less toxic forms (Veeraswamy et al., 2024). Therefore, understanding the mechanisms behind mercury production and accumulation is crucial. It is urgent to find safe and effective ways to control mercury pollution, protecting both the environment and human health.Periphyton is a microbial community made up of various organisms, including algae, bacteria, fungi, animals, and both organic and inorganic debris. These organisms attach together to organic or inorganic substrates (Zhao et al., 2023), held together by extracellular polymeric substances (EPS) secreted by the matrix. EPS is widely present in various aquatic systems and forms the basis of the food web in aquatic ecosystems. As the main component of surrounding organisms, EPS is a crucial source of carbon and energy that helps maintain the integrity of the periphyton community and enhances microbial activity, including that of mercury methylating bacteria (Xiang et al., 2022). Crucially, the same EPS matrix that supports the periphyton community also governs its interaction with environmental contaminants.Periphyton, as a bioaccumulator or a sensitive receptor of environmental pollutants (Shahzad et al., 2025), has been shown to play a critical role in binding and adsorbing heavy metals due to the various functional groups (such as carboxyl, phospho, amine, sulfhydryl, hydroxyl, etc.) in its EPS (Wang L. et al., 2020).Given the escalating severity of mercury pollution, understanding its biogeochemical cycling in critical environmental compartments is paramount. Periphyton, a ubiquitous and complex microbial-algal consortium, represents such a compartment where the fate of mercury is decisively shaped. This community not only efficiently concentrates and adsorbs mercury ions via its extracellular polymers but also hosts a dynamic microbial consortium that actively transforms them. For instance, sulfate-reducing bacteria (SRB), known mercury methylators found within periphyton, see their composition and methylation rates influenced by the community's nutrient status (Gambardella et al., 2025;Leclerc et al., 2021). Interestingly, under certain conditions, methanogens can emerge as the primary methylators, working synergistically with other microorganisms in this process (Lei et al., 2021). This intricate interplay between adsorption and microbial transformation within periphyton establishes it as a pivotal micro-ecosystem governing mercury speciation, bioavailability, and risk in aquatic environments.As the economy and society continue to develop, the increasing emissions of...

A water body in Guilin was selected for this study. In order to find out the best dosing ratio, we conducted research experiments on combined algae removal methods and obtained a more economical and efficient mixed dosing ratio for treating water bodies. If this solution is replicated, it will contribute to the development of marine and freshwater fisheries; to the construction of a green ecosystem and human public healt.