Assessment of the ecotoxicity of extracts from sugarcane bagasse biochars activated with zinc chloride

Biochar derived from the pyrolysis of biomass is recognized for its carbon sequestration capacity. By adding physical or chemical activation steps, its properties can be enhanced, resulting in activated or modified biochar. However, investigating the possible toxic effects for safer application is necessary. In this study, we aimed to assess the ecotoxicological effects of extracts from biochars prepared from sugarcane bagasse activated with zinc chloride and heat treated at temperatures ranging from 300 to 1000 °C. Using Artemia salina as an indicator of toxicity, we observed variation in mortality ranging from 27.5 % to 100 % as the temperature varied between 1000 and 300 °C. The leachate from the sample prepared at 300 °C, which had the highest zinc content, presented an LC50 of 0.53 w/v. Phytotoxicity tests with Lactuca sativa revealed that extracts from biochars prepared at lower temperatures presented greater phytotoxicity, with reductions in relative germination, relative average radicle growth and the germination index. These results highlight the need to assess the ecotoxicological risks of activated biochar with zinc chloride. The sensitivities of Artemia salina and Lactuca sativa are promising for detecting these effects, suggesting that they are effective approaches for assessing environmental safety. These findings not only broaden our understanding of the adverse effects of activated biochar but also guide safe and sustainable practices for its future application.