Toxicological fate of biochar according to feedstock and pyrolysis temperature

This study investigated the effects of feedstock type and pyrolysis temperature on the ecotoxicological properties of biochars through standardized bioassays. Ten feedstocks were pyrolyzed at temperatures ranging from 350 to 650 °C, and were characterized for elemental composition, PAHs, and physicochemical traits. Bioassays with Vibrio fischeri , Pseudokirchneriella subcapitata , Lepidium sativum , and Sorghum saccharatum were performed to assess ecotoxicity. Increasing pyrolysis temperature enhanced surface area, C:N ratio, ash content, and pH; however, feedstock type was the dominant factor influencing biochar properties and toxicity. Although all biochars complied with international thresholds for contaminants, 28 % induced ≥ 50 % inhibition in test organisms, underscoring the importance of ecotoxicological evaluation. Biochars derived from cattle manure, poultry litter, and rice straw exhibited the strongest toxicity, largely attributed to salinity stress from high potassium concentrations. In addition, biochars produced at 350 °C were generally more toxic, presumably due to the presence of volatile organic compounds. These findings underscore the importance of integrating chemical and biological assessments for safe biochar application in agricultural and environmental systems. • The feedstock influence the toxicological fate of biochar. • Pyrolysis temperature has a dominant influence on the toxicological fate of biochar. • Biochars produced from CM, PL, and RS were identified as toxic or highly toxic. • The use of K-rich biochar requires special management.