Biochar from Sugarcane Straw Reduces the Toxicity of Soils Contaminated with 2,4-D and Fipronil, Isolated and in a Mixture, on Multispecies Microcosms

The intensive use of pesticides causes harmful effects on ecosystems, and remediation techniques can reduce the ecotoxicity of contaminated soils. Sugarcane straw is a feasible feedstock for biochar production, and it is abundant in the ethanol industry. In this sense, this study assessed the application of biochar from sugarcane straw to reduce the ecotoxicity of soils contaminated with the pesticides fipronil and 2,4-D, alone and in a mixture. Tests at the microcosm level (28 days) evaluated the influence of biochar on the terrestrial worm Enchytraeus crypticus and the eudicot plant Eruca sativa L. At the end of the experiment, elutriate solutions were prepared with soil samples to assess responses on E. sativa and on the cladoceran Daphnia similis. Fipronil and 2,4-D decreased the reproduction of E. crypticus in microcosms, particularly on treatments with fipronil. Biochar reduced the ecotoxicity of fipronil in soils, increasing the reproduction of E. crypticus by 43% compared with soils without biochar. However, the control with biochar showed a reproduction reduction of 23% when compared with the control without biochar. In soils with 2,4-D, the germination rates and shoot growth of E. sativa were 2 times greater in biochar-remediated soils compared with untreated soils. Considering the exposure to elutriate, the application of biochar in soils with 2,4-D improved the growth (by 45%) and germination (by 34%) of E. sativa. No effects were identified on D. similis at any exposure scenario. Therefore, sugarcane straw biochar can be a viable alternative for reducing the ecotoxicity of pesticides in soils.