Application of biochar: An approach to attenuate the pollution of the chiral pesticide fipronil and its metabolites in leachate from activated sludge

Abstract The present study investigated the bio-effects and fate of the chiral pesticide fipronil and its three primary metabolites, fipronil desulfinyl, fipronil sulfide and fipronil sulfone on Chlorella pyrenoidosa and Danio rerio in the absence and presence of biochar. The results revealed that fipronil and its metabolites exhibited high toxicity to algae and fish. Enantioselectivity was observed with regard to the toxicity and degradation of fipronil and its metabolites. For Chlorella pyrenoidosa, R-fipronil was more toxic than S-fipronil and degraded preferentially during the toxicity and degradation experiments. For Danio rerio, S-fipronil exhibited higher toxicity than R- and rac-fipronil. The toxicities of fipronil sulfide and sulfone were 3–6 and 5–6 times higher, respectively, than that of rac-fipronil, and the metabolites also exhibited longer persistence. The remediation capacity for water and leachate contaminated by fipronil with the application of biochar was investigated. Biochar significantly mitigated the toxicity of fipronil and its metabolites to nontarget organisms, and reduced residues by 90 % for fipronil, 72 % for sulfone, 65 % for sulfide and 60 % for desulfinyl, whereas mitigation of only 30 %-51 % was observed in the absence of biochar. This study demonstrates that biochar has strong potential as an ideal material for the removal of fipronil and its metabolites from contaminated aquatic environments.