Toxicity evaluation and degradation of cypermethrin-contaminated soil using biochar and Bacillus cereus amendments

Cypermethrin (Cyp), a persistent synthetic pyrethroid insecticide widely used for insect control. The persistence of Cyp creates toxicity to both humans and the environment This study investigates biochar and Bacillus cereus distinct and collective effects on Cyp -contaminated soil during a 90-day incubation. This study also investigates the effects of different concentrations of Cyp (50, 100, ,500 to 1000 mg kg^-1) on soil physicochemical and biological activities during a 90-day incubation period. Microbial biomass carbon and soil respiration rates decreased significantly across all cypermethrin concentrations, with the most substantial reductions observed at 1000 mg kg^-1. However noticeable variations in soil enzymes and MBC over time during the entire incubation period. On 1st day, the GMean Enz and MBC rate for Cyp treatments (50, 100, ,500 to 1000 mg kg^-1) ranged from 0.98 to 0.63, and 9.06, to 5.03, respectively. Under Cyp pollution, microbial biomass carbon exhibited significant decreases, with the highest inhibition (86.2%) at 1000 mg kg^-1 on 1st day of incubation. Soil respiration rates dropped 77%, at 1000 mg kg^-1, and Integrated biomarker response (IBR) values peaked on day 30, indicating environmental stress. Biochar and Bacillus cereus effectively facilitated the degradation of Cyp, achieving approximately 85% degradation within the first 45 days of the experiment. The combined application of biochar and Bacillus cereus increased soil pH to a neutral level from 5.9, to 7.1, reduced electrical conductivity from 1.41 µS cm^- 1 to 1.20 µS cm^-1, and elevated cation exchange capacity from 1.54 ± 0.04 to 6.18 C mol kg^-1, while also improving organic carbon content to 3.135%. However, the dehydrogenase activity was decresed upto 47% in the combined application and all other enzymes including urasese catlayse and phostasese enzymes with Gmean enzymeatic activities were significantly improved. These findings suggest biochar and bacterial interaction for soil management to enhance soil resilience against pesticide stress.