In a recent review published in the journal Biochar, authors Fanchao Xu, Jun Zhu, Kun Liu, Minli Wang, Huiting Liu, Jianjun Lian, Xiaolei Qu, and Bingyu Wang systematically synthesized how the structural features, production parameters, and surrounding water chemistry govern the interfacial mechanics and overall environmental fate of dissolved black carbon. Black carbon enters terrestrial and aquatic ecosystems through incomplete biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More combustion, wildfire events, and agricultural biochar additions. The water-soluble portion, termed dissolved black carbon, possesses elevated aromatic carbon content relative to general aquatic organic matter and an abundance of polar oxygenated functional groups compared to terrestrial organic matter. These unique structural properties allow it to remain highly mobile in rivers, bays, and oceans, acting as a potent long-range carrier for priority heavy metals and organic pollutants.

The feedstocks and thermal processing parameters used during biochar production heavily determine the chemical makeup of dissolved black carbon. Biochars derived from herbaceous or cellulose-rich biomass release higher quantities of dissolved black carbon than woody, lignin-rich materials. Furthermore, increasing pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More temperatures reduce the overall concentration of released dissolved black carbon due to enhanced aromatization and structural polymerization. At elevated pyrolysis temperatures, the proportion of hydrogen to carbon decreases, yielding condensed aromatic carbonyl structures characterized by higher graphitization and specific molecular weight distributions. Chemical extraction conditions also modify these structural profiles. Alkaline extraction environments promote the deprotonation of acidic functional groups, significantly enhancing surface hydrophilicity and increasing the total yield of dissolved black carbon compared to neutral or acidic leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More conditions.

Colloidal stability dictates whether dissolved black carbon remains suspended or undergoes aggregation and surface deposition. Time-resolved dynamic light scattering experiments establish the critical coagulation concentration, which quantifies the electrolyte threshold required to eliminate repulsive energy barriers and trigger rapid aggregation. For divalent cations such as calcium, the critical coagulation concentration of dissolved black carbon ranges between thirty-eight and seventy-five millimolar. This stability threshold is lower than that of aquatic dissolved organic matter due to higher aromaticity and hydrophobicity, yet higher than terrestrial soil humic acids owing to abundant polar carboxyl functional groups. Applying Derjaguin-Landau-Verwey-Overbeek theory and extended surface force frameworks demonstrates that electrostatic repulsion and acid-base interactions control these aggregation kinetics. Divalent cations promote particle clumping through charge neutralization and cation bridging mechanisms across carboxylic binding sites.

Environmental aging processes further transform these interfacial dynamics. Sunlight exposure photo-ages dissolved black carbon by introducing oxygenated functional groups, which increases surface negative charge, enhances steric hindrance, and boosts colloidal stability in natural waters. When environmental conditions favor aggregation, dissolved black carbon settles into aquatic sediments along riverine and estuarine pathways. This aggregation-deposition sequence traps both the black carbon and its co-transported contaminants, attenuating dissolved carbon flux to the ocean and creating stable intermediate carbon reservoirs that directly influence global biogeochemical cycles.

Source: 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), 108.