Effect of zinc-biochar composite aging on its physicochemical and ecotoxicological properties

The stability of Zn-biochar composites is determined by environmental factors, including the aging processes. This paper focused on the ecotoxicological evaluation of Zn-biochar (Zn-BC) composites subjected to chemical aging. Pristine biochars and composites produced at 500 or 700 degrees C were incubated at 60 and 90 degrees C for six months. All biochars were characterized in terms of their physicochemical (elemental composition, Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and porous structure), ecotoxicological properties (tested with Folsomia candida and Aliivibrio fischeri) and contaminant content (polycyclic aromatic hydrocarbons (PAH), heavy metals (HM) and environmentally persistent free radicals (EPFR)). An increase in the number of surface oxygen functional groups and increased hydrophilicity and polarity of all Zn-BC composites were observed due to oxidation during aging. It was also found that Zn-BC aging at 90 degrees C resulted in a 28-30% decrease in solvent-extractable PAHs (Sigma 16 C-tot PAHs) compared to nonaged composites. The aging process at both temperatures also caused a 10(4) fold reduction in EPFRs in Zn-BC composites produced at 500 degrees C. The changes in the physicochemical properties of Zn-BC composites after chemical aging at 90 degrees C (such as pH and HM content) caused an increase in the toxicity of the composites to Folsomia candida (reproduction inhibition from 19 to 24%) and Aliivibrio fischeri (luminescence inhibition from 96 to 99%). The aging of composites for a long time may increase the adverse environmental impact of BC-Zn composites due to changes in physicochemical properties (itself and its interactions with pollutants) and the release of Zn from the composite.

Automated summary

This study evaluated the Zn-biochar composites after chemical aging, and found that aging process increased the surface oxygen functional groups, hydrophilicity and polarity, and affected the physicochemical properties and toxicity of the composites to organisms and the environment.