LAUSR

Abstract Sewage sludge biochars (SSBCs) pyrolyzed at 300, 500, and 700 °C (denoted as SS300, SS500 and SS700) were applied for 5-day incubation with wheat to investigate the phytotoxicity of biochars and the specific mechanisms. The properties of the biochars, including the contents of 6 typical potential toxic elements (PTEs) and 16 priority polycyclic aromatic hydrocarbons (PAHs), were carefully examined. SS500 had the highest concentrations of 16 PAHs, while the total content of each PTE increased with increasing heating temperature. Wheat growth was suppressed substantially when the extract of SSBCs was applied at a concentration of 2 g/35 mL, with SS700 being the most toxic. In addition, increasing the concentration of SS700 extract led to increased toxicity. Both principal component analysis (PCA) and linear correlation analysis revealed that PTEs played an important role in determining the phytotoxicity of SSBCs. For the growth of wheat, the root length was the most sensitive to SSBC, followed by the shoot length and the seed germination. This study demonstrated that the growth of plants might be inhibited in the biochar-amended soil that highly leached throughout the years. This inhibition could be alleviated by using biochars produced at lower temperatures and by reducing the amount of biochars.