Enhancing copper binding property of compost-derived humic substances by biochar amendment: Further insight from two-dimensional correlation spectroscopy.

Little is known about the environmental impacts of biochar (BC) amendment on the immobilization of heavy metals in compost-treated fields. In consequence, this study was designed to explore the effects of BC amendment on the copper (Cu) binding properties of compost-derived humic substances (HS). To this end, unamended and 4.7% (by wet weight) BC-amended compost were incubated in parallel with regular wetting for 6 months. The stability constants for Cu binding, calculated based on the fluorescence quenching technique, were higher for the compost-derived HS with versus without BC amendment. The result suggests that BC addition to compost may intensify the immobilization of heavy metals in a compost-treated field. Copper binding efficacy increased after the incubation with or without BC amendment. However, the enhanced Cu binding efficacy of the BC-amended HS was preserved even after the long-term incubation. Two-dimensional correlation spectroscopy revealed that the short wavelength fulvic-like fluorescence followed by humic-like fluorescence were preferentially associated with Cu binding. However, the range of wavelengths that tracked the binding of Cu were modified after BC amendment. This study evidenced beneficial and synergetic effects of BC amendment on the abatement of the potential environmental risk from heavy metal polluted field on a long-term basis.