Co-application of biochar and iron-based materials for remediating agricultural soil polluted with metolachlor and s-metolachlor: field research evidence

• Co-application of biochar and iron blocks Metolachlor (MET) and S-MET in soil. • Biochar reduces the bioavailability of MET and S-MET in soil. • Degradation of MET and S-MET in soil by Fe0 and Fe3O4 through de-chlorination. • The co-application of biochar and iron enhances the redox capacity of the system. The performance of the co-application of biochar and iron-based materials (Fe 0 , Fe 3 O 4 ) in remediating metolachlor (MET) pollution, particular the enantiomer S-metolachlor (S-MET), in the field agricultural soils is not yet clear. Therefore, the effects and mechanisms of co-application biochar and iron-based materials (Fe 0 , Fe 3 O 4 ) on the remediation of MET and S-MET in an agricultural soil were investigated through field experiments over a peanut growth period (120 days). Results showed that the application of iron-based materials accelerated the degradation of MET and S-MET adsorbed by biochar (MET 16 %, S-MET 11.63 %). The co-application of both materials reduced the bioavailability of MET and S-MET in the soil, with iron-based materials promoting dechlorination degradation and the co-application enhancing the redox capacity of the system. Biochar (BC) adsorbed MET and S-MET in the soil, thereby delaying their degradation and extending their half-lives by 60–113.5 days, while reducing their bioavailability and the content of pesticide residues in peanuts. The co-application of biochar and iron-based materials exerted control over MET and S-MET contamination in agricultural soils, while also ameliorating soil acidity. This study provides new strategies and scientific evidence for the control of pesticide contamination such as MET and S-MET in agricultural soils.