Biotoxicity Evaluations of Three Typical Biochars Using a Simulated System of Fast Pyrolytic Biochar Extracts on Organisms of Three Kingdoms

Biochar is a solid material obtained from thermochemical conversion of biomass in an oxygen-limited environment. It is widely used as a soil remediator and carbon sequestrator. However, its biotoxicity to the ecosystem remains unclear. In this study, we assess the toxic effects of three fast pyrolytic biochar extract solutions (rice husk, saw dust, <i>Acorus calamus</i>) on a miocroorganism (<i>Pseudomonas aeruginosa</i>), a plant (<i>Triticum spp.</i>), and an animal (<i>Caenorhabditis elegans</i>). Systematic toxicity tests indicate that the biotoxicity of biochars varies with their biomass sources. Biochars derived from rice husk and sawdust have negligible toxic effects on all the tested organisms, suggesting that biochars obtained from agricultural waste are safe for soil application. By contrast, biochar derived from <i>Acorus calamus</i> shows significant toxicity on all tested organisms at relative high dosage, indicating that risk assessment is necessary before its environmental use. Furthermore, this study found that use of the UV₂₅₄ value is more practical than the SUV₂₅₄ value for evaluation of biochar biotoxicity. Finally, gel permeation chromatography (GPC) suggests that certain small aromatic molecules may be responsible for the toxicity of biochar derived from <i>Acorus calamus