Physical bioturbation coupled with gut-substrate cross-inoculation: A dual-pathway mechanism for enhanced acetochlor degradation in vermifilters.

To mitigate acetochlor (ACT) diffuse pollution in the black soil region of Northeast China, a black soil-gravel biofilter was constructed to investigate how earthworm (Eisenia fetida) bioturbation enhances ACT degradation through coupled physical remodeling and micro-ecological regulation. At an HRT of 72 h, the vermifilter achieved 85.3% aqueous ACT removal and 66.4% solid-phase ACT removal rate, significantly outperforming planted and blank biofilters. In situ Micro-CT showed that earthworm burrowing increased matrix pore connectivity to 20 times that of the blank biofilter, reducing mass transfer resistance and maintaining pollutant bioavailability. High-throughput sequencing revealed that the earthworm gut functioned as a mobile incubator for key degrading bacteria, selectively enriching dechlorinating and dealkylating taxa such as Pseudomonas and Chryseobacterium and reinoculating them into the substrate. Under micro-acidic and nitrogen-rich conditions, the abundance of key transformation genes were higher, enabling complete ACT degradation to the molecular weight product N-(2-ethylphenyl) formamide.