Dissolved black carbon, a water-soluble fraction of black carbon produced from incomplete combustion and biochar, has long been viewed as a mobile form of carbon that can move from soils into rivers, lakes, estuaries, and oceans. A new review published in Biochar shows that its journey through the environment is far more complex than simple transport in water.
The review, titled "Colloidal stability of dissolved black carbon: interfacial mechanisms and environmental implications," examines how dissolved black carbon, or DBC, behaves as a colloidal material. Its stability determines whether it remains suspended in water, aggregates into larger particles, or deposits into sediments. These processes directly influence not only the fate of DBC itself, but also the movement of pollutants that attach to it.
"Dissolved black carbon is not just a passive carbon residue in aquatic environments," said the study authors. "Its colloidal behavior can decide whether carbon and associated contaminants travel long distances or become trapped in sediments. Understanding this behavior is essential for predicting environmental risks and carbon cycling."
DBC is widely distributed in natural waters and is released from black carbon residues through leaching and surface runoff. Because it contains aromatic structures and oxygen-containing functional groups, DBC can bind with heavy metals, organic pollutants, antibiotics, and even nanoplastics. When DBC remains stable in water, it can act as a carrier that helps these substances move through aquatic systems. When it aggregates and settles, it can shift pollutants from the water column into sediments, creating localized contamination hotspots and changing exposure risks for benthic organisms.
The review highlights that DBC stability is governed by its molecular structure and surface chemistry, which depend on feedstock source, pyrolysis conditions, extraction conditions, and environmental aging. Using classical DLVO theory and extended XDLVO theory, the authors explain how electrostatic forces, van der Waals attraction, and Lewis acid-base interactions control DBC aggregation. The review notes that short-range acid-base interactions, especially hydration and hydrophobic forces, can be especially important in determining whether DBC remains dispersed or aggregates.
Environmental conditions can strongly alter this balance. Monovalent ions such as sodium often have limited effects, while divalent cations such as calcium, barium, and some heavy metals can destabilize DBC by binding with oxygen-containing groups and promoting particle bridging. pH also matters. Acidic conditions can reduce surface charge and encourage aggregation, while alkaline conditions often improve colloidal stability. Organic substances, minerals, and photoaging can either stabilize or destabilize DBC depending on their interactions with DBC surfaces.
These findings have important implications for water quality, soil remediation, and climate research. Biochar is widely studied as a soil amendment for carbon sequestration and pollutant immobilization, but DBC released from biochar may carry adsorbed pollutants away from treated soils under certain conditions. At the same time, aggregation and deposition of DBC in estuaries may remove a fraction of land-derived carbon before it reaches the ocean, meaning current estimates of land-to-ocean black carbon flux may need refinement.
"The colloidal stability of dissolved black carbon is a missing link between molecular carbon chemistry and large-scale environmental outcomes," the authors said. "Future models of pollutant transport and carbon flux should account for how DBC aggregates, deposits, and interacts with coexisting substances in real environmental waters."
The authors call for integrated characterization methods, stronger mechanistic studies of heteroaggregation in complex waters, and predictive models that combine molecular information with environmental parameters. Such efforts could improve risk assessment, water treatment strategies, and estimates of how black carbon contributes to long-term carbon storage.
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Journal Reference: Xu, F., Zhu, J., Liu, K. et al. Colloidal stability of dissolved black carbon: interfacial mechanisms and environmental implications. Biochar 8, 108 (2026).
https://doi.org/10.1007/s42773-026-00627-7
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About Biochar
Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field.
