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The relationship between biochar physicochemical characteristics and the adsorption and the degradation of extracellular DNA (eDNA) was studied to assess controls on the fate and transport of eDNA in the environment. Biochar samples were generated by pyrolysis of Chinese herbal medicine residues of sweet wormwood ( Artemisia annua L.) at 500, 600, and 700 °C. Selected physicochemical properties of the biochar were characterized. Adsorption dynamics (adsorption capacity and kinetics) of eDNA to biochar were quantified using several adsorption kinetic and isotherm models. Furthermore, gel electrophoresis was used to detect the impact of biochar on the degradation of eDNA by DNase I. Characterization results indicated that biochar generated from Chinese herbal medicine residues was dominantly aromatic, stable, and polar. Adsorption data showed that the biochar–eDNA interactions were dominated by an electrostatic interaction mechanism. Based on eDNA adsorption capacity and gel electrophoresis of eDNA fragments, we demonstrated that larger eDNA fragments were adsorbed to the biochar and protected from degradation by DNase I. The Chinese herbal medicine residues generated a superior biochar product to adsorb eDNA and protect it from degradation by DNase I. The results of this study provide a mechanistic understanding of factors controlling the fate and transport of eDNA in the environment.

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