Soil microbial functional recovery and community resilience driven by biogenic magnetite nanoparticles under carbendazim stress.

The persistence of fungicides in agricultural soils poses a major threat to soil health, as these compounds disrupt microbial communities and compromise key ecosystem functions. Carbendazim, a commonly used systemic fungicide, is known for its ability to inhibit microbial activity and nutrient cycling. This study assessed the capacity of biogenic magnetite nanoparticles to mitigate carbendazim-induced disturbance and facilitate the recovery of soil microbial function. Citrate-stabilized magnetite nanoparticles were applied to an agricultural Andisol intentionally contaminated with carbendazim (10 mg kg⁻¹) under controlled microcosm conditions. Soil enzyme activities related to carbon, nitrogen, and phosphorus cycling (β-glucosidase, urease, acid phosphatase), microbial gene abundances (16S rRNA, amoA, amoB copy number), community structure, and pesticide dissipation kinetics were measured for a 30-day period. Magnetite nanoparticles significantly accelerated carbendazim dissipation, reducing their half-life by approximately 50% compared to pesticide-only treatments. Nanoparticle application partially mitigated the inhibitory effects of carbendazim on soil enzymes. It showed trends towards the recovery of bacterial and nitrifier abundances, with community composition and diversity patterns aligning more closely with those of untreated soils. Co-occurrence network and multivariate analyses of the soil bacterial community, assessed through 16S rRNA amplicon sequencing, revealed patterns indicative of a partial restoration of bacterial interaction structure, with Carb/FeNPs-EC treatments showing increased network connectivity and modularity compared to carbendazim-only soils, approaching the interaction patterns characteristic of undisturbed bacterial assemblages. These findings offer preliminary evidence that biogenic magnetite nanoparticles may reduce pesticide pressure in agricultural soils while supporting microbial functional trends indicative of recovery. The use of onion peel waste as an eco-friendly precursor further highlights the circular potential of this approach. Onion peel is a widely generated agro-industrial by-product particularly rich in polyphenolic compounds, especially quercetin and its derivatives, which act as natural reducing and stabilizing agents during nanoparticle biosynthesis, eliminating the need for toxic chemical reagents and contributing to a lower environmental footprint. This dual role as both a waste valorization strategy and a source of bioactive capping agents warrants further evaluation of this approach as a sustainable soil amendment strategy.