A comprehensive review published in the journal Biochar on June 11, 2026, examines the colloidal stability of dissolved black carbon (DBC) and its profound implications for environmental fate and pollutant transport. Authored by Fanchao Xu, Jun Zhu, Kun Liu, Minli Wang, Huiting Liu, Jianjun Lian, Xiaolei Qu, and Bingyu Wang, the study addresses a significant knowledge gap in understanding how DBC behaves in aquatic systems. The review synthesizes existing literature to elucidate the interfacial mechanisms that govern DBC aggregation and deposition, highlighting that these processes are critical for carbon sequestration and the movement of adsorbed pollutants.
Dissolved black carbon is operationally defined as the water-soluble fraction of black carbon that passes through a filter with a pore size of 0.1 to 0.70 micrometers. This fraction exhibits high environmental mobility, readily released from black carbon residues through leaching and surface runoff, and extensively transported from soils to aquatic systems such as oceans, bays, lakes, rivers, and estuaries. The molecular definition of DBC varies across studies, reflecting a broad diversity of structural components ranging from condensed aromatic structures rich in polar groups to larger molecular structures containing aliphatic-like and carbohydrate-like components. This structural heterogeneity is a primary driver of the variable colloidal behavior observed in different environmental contexts.
The review emphasizes that the molecular structure of DBC is characterized by high aromaticity and abundant oxygen-containing functional groups. These aromatic and oxygenated functional groups serve as important binding sites for organic pollutants and heavy metals, making DBC an active medium that influences the distribution and response to pollutants in the environment. The high aromatic carbon content relative to aquatic dissolved organic matter, combined with a surface enriched in polar carboxyl groups compared to terrestrial dissolved organic matter, allows DBC to constitute a distinct and critical portion of the dissolved organic matter pool. This unique chemical composition underpins its role as an efficient long-range carrier for assorted pollutants.
Colloidal stability is a key interfacial attribute that controls the fate of DBC in aquatic systems. The review utilizes time-resolved dynamic light scattering measurements to study aggregation behavior, focusing on the attachment efficiency as a key metric for quantifying the tendency of DBC particle aggregation. This metric is determined by normalizing the initial aggregation rate in a specific solution to that in the Diffusion-Limited Aggregation regime, where the aggregation rate constant is independent of electrolyte concentration. A higher attachment efficiency value suggests a less stable colloidal system, indicating a greater propensity for particles to aggregate and settle out of the water column.
The critical coagulation concentration serves as a quantitative metric to compare DBC colloidal stability across various solution chemistries. For divalent cations such as calcium, the critical coagulation concentration of DBC typically ranges between 38.1 mM and 75 mM. This range is notably lower than that of aquatic dissolved organic matter, such as reference humic and fulvic acids, but substantially higher than that of terrestrial dissolved organic matter fractions. This intermediate stability is attributed to the chemical composition of DBC, which exhibits higher aromatic carbon and lower aliphatic carbon than aquatic dissolved organic matter, promoting hydrophobicity and aggregation, while simultaneously being richer in polar carboxyl groups than terrestrial dissolved organic matter, which enhances hydrophilicity and colloidal stability.
The governing mechanisms of DBC colloidal stability are interpreted using the classical Derjaguin-Landau-Verwey-Overbeek theory and its extended form, XDLVO theory. DLVO theory posits that particle aggregation thermodynamics are governed by London-van der Waals and electrostatic interactions. However, the classical DLVO theory fails to adequately describe DBC aggregation in specific scenarios, particularly with divalent cations. The XDLVO theory extends this framework by including Lewis acid-base interactions, which account for polar interactions that can occur in both attractive and repulsive modes. This extended model provides a more accurate thermodynamic perspective on the governing forces, revealing that hydration forces play a crucial role in maintaining colloidal stability in solutions with monovalent and certain divalent cations.
Environmental factors such as ionic composition, pH, organic substances, minerals, and aging processes significantly modulate DBC aggregation. Divalent cations induce more pronounced aggregation than monovalent cations, with destabilization capacity in the order of barium, calcium, and magnesium. Calcium and barium enhance DBC hydrophobicity through strong complexation with oxygen-containing functional groups and promote aggregation via bridging effects. In contrast, magnesium exhibits weaker aggregation capacity due to limited carboxyl complexation. The anion type also influences aggregation, with sulfate ions inducing a stronger aggregation tendency than chloride ions due to higher ionic strength and the promotion of intermolecular hydrogen-bonding network reorganization.
pH dependence is another critical factor, with DBC exhibiting enhanced aggregation under acidic conditions and improved colloidal stability under alkaline conditions. Under acidic conditions, the protonation of surface functional groups reduces surface charge and electrostatic repulsion, facilitating aggregation. Conversely, alkaline conditions increase surface charge density and promote hydration shell formation through DBC-water hydrogen bonding, which inhibits particle attachment. These pH-dependent responses suggest that DBC colloidal stability may undergo significant alterations during pH fluctuations, such as acid mine drainage or acid rain events, with profound implications for the environmental fate of DBC and its associated contaminants.
The environmental implications of DBC colloidal stability extend to the transport of pollutants and the estimation of ocean carbon flux. The presence of heavy metal cations significantly promotes DBC aggregation via strong complexation and cation-pi interactions, leading to pronounced sedimentation and the co-transport of heavy metals to sediments. This process poses a long-term threat to sediment-dwelling organisms and raises concerns about the biomagnification potential of bioavailable heavy metals. Additionally, DBC mediates the decomposition of antibiotic resistance genes in aquatic systems through hydroxyl radical generation, a process strongly correlated with its molecular size. Aggregation-induced changes in particle size distribution may profoundly influence the environmental fate of these contaminants.
During fluvial transport to estuarine systems, DBC undergoes aggregation-mediated conversion to particulate matter, which is ultimately deposited in sediments, reducing its vertical flux in estuarine zones. This sedimentary trapping prevents subsequent transport to oceanic systems, effectively removing DBC and associated pollutants from the dissolved organic matter pool. The DBC/dissolved organic matter ratio has been conventionally employed as a conservative tracer to estimate global DBC fluxes; however, the aggregation behavior of DBC reveals that this ratio demonstrates progressive depletion along salinity gradients. This fractionation process potentially leads to a systematic overestimation of the land-to-ocean DBC flux when using this metric, highlighting the need for more robust predictive models that account for colloidal stability and environmental conditions.
The review concludes that DBC exhibits complex colloidal behaviors fundamentally controlled by its molecular architecture and surface chemistry, which depend on biomass sources, pyrolysis conditions, and environmental parameters. Theoretical frameworks identify electrostatic and Lewis acid-base interactions as the dominant forces driving the unique aggregation behavior of DBC, distinguishing it from conventional dissolved organic matter. Environmental variables collectively modulate these interactions, directly influencing the environmental persistence of DBC, its pollutant carrier effects, and its role in global carbon cycling. The study underscores the importance of understanding these mechanisms for accurate risk assessment and carbon flux estimation.
Future research should focus on developing integrated characterization techniques to provide reliable and comparable multidimensional structural information for DBC. The absence of standardized molecular characterization protocols currently compromises the comparability of published data, while mechanistic insights into contaminant-mediated heteroaggregation remain limited. Developing robust predictive models for the colloidal stability of DBC in natural aquatic systems is essential for forecasting the large-scale transport and sequestration of DBC and associated pollutants. Emerging artificial intelligence techniques offer transformative potential by integrating molecular characterization data with environmental parameters to identify dominant aggregation-influencing factors and develop reliable predictive tools for diverse environmental scenarios.
Subject of Research: Colloidal stability of dissolved black carbon: interfacial mechanisms and environmental implications
Article Title: Colloidal stability of dissolved black carbon: interfacial mechanisms and environmental implications
Article References: Xu, F., Zhu, J., Liu, K., Wang, M., Liu, H., Lian, J., Qu, X., & Wang, B. (2026). Colloidal stability of dissolved black carbon: interfacial mechanisms and environmental implications. Biochar, 8(1), Article 108. https://doi.org/10.1007/s42773-026-00627-7
Image Credits: AI Generated
DOI: 10.1007/s42773-026-00627-7
Keywords: Colloidal, stability, dissolved, black, carbon, interfacial, mechanisms, environmental, implications, scientific research
News Source: Alan Morgan. (November 9, 2026). Review Maps Dissolved Black Carbon Stability Mechanisms. Scienmag.
