Submicron biochar induces developmental toxicity, oxidative stress, and DNA damage in zebrafish (Danio rerio)

Submicron biochar (submicron-BC) has been widely used in various fields for environmental pollution remediation due to its excellent physicochemical properties. However, its application may cause adverse effects on the environment and aquatic organisms. To investigate the effects of submicron-BC on aquatic organisms, different organic solid wastes were used as feedstocks to produce submicron-BC, and zebrafish was selected as the target test organism. According to the embryonic development experiment, ball-milled sawdust biochar (BSB) prepared at 450 °C was identified as the most toxic submicron-BC. The characterization results by atomic force microscope and scanning electron microscope showed that BSB had irregular spherical surfaces. The embryos were treated with BSB (1,10, and 100 mg/L) for 96 h Its effects on the embryonic development of zebrafish were concentration-dependent and time-dependent. Specifically, BSB led to decreased survival rates, hatching rates, and body length. With the increasing of the concentrations (1,10, and 100 mg/L) and exposure time (1,4, and 7 d) of BSB, the activity of superoxide dismutase, catalase, and glutathione peroxidase initially increased and then decreased, while the content of malondialdehyde continued to rise in adult zebrafish. Comet analysis also showed that BSB caused dose-dependent DNA damage in the liver and gills of adult zebrafish. Humic acid could reduce the content of persistent free radicals in BSB, thus alleviating the toxicity of BSB to the embryo. This work provides a basis for exploring the toxic mechanism and environmental risk assessment of submicron-BC in aquatic ecosystems.