Marine biodegradation of otherwise persistent engineering nylons

<title>Abstract</title> <p>Engineering nylons are generally considered persistent in the environment, including the marine environment. However, some commercially available nylon fishing lines, composed of mass-produced engineering nylon copolymers, unexpectedly exhibit biodegradation in natural seawater, and the mechanisms underlying this behaviour remain unclear. Here, we systematically examined the effect of the composition and structural state of nylon filaments on their marine biodegradation. Accelerated marine biological oxygen demand (BOD) tests revealed substantial marine biodegradation even in highly crystalline, oriented nylon filaments, with structural disruption further enhancing the process. Long-term in situ seafloor exposure experiments under negligible ultraviolet irradiation revealed progressive surface erosion and mechanical deterioration, suggesting degradation under environmentally relevant marine conditions. Additionally, nylon filament biodegradability strongly correlated with water uptake across compositions and structural states, highlighting hydration-mediated accessibility as a key factor linking polymer structure with microbial biodegradation. Molecular and microbiological analyses further confirmed microbial chain scission and high-molecular-weight nylon assimilation, with a newly isolated Dasania species contributing to this process. Therefore, environmental persistence in engineering plastics is not solely determined by polymer chemistry, but also by structure-dependent microbial accessibility, providing new insights into the environmental fate of ghost fishing gear, marine debris, and secondary microplastics.</p>