Toward ecological realism in microplastic toxicology: Intestinal responses to biofilm-colonized microplastics from...

To accurately assess the ecological risks posed by real-world MPs, studies bridging microplastic (MP)-associated biofilms in different environmental compartments and their toxicological consequences are needed. This study investigated 50-week in-situ biofilm development on polyvinyl chloride, polylactic acid, and polyamide 66 (PA66) MPs across the water column and the sediment-water interface (SWI). During colonization in the selected river, the microbial community structures were primarily associated with environmental compartments rather than polymer types. By identifying the highest aging resistance during colonization, PA66 was selected as the model polymer to evaluate the subsequent intestinal toxicity in tilapia (Oreochromis niloticus). Tilapia were exposed to pristine, water-colonized, and SWI-colonized MPs for 14 days, followed by assessments of MP accumulation, gut function biomarkers, 16S gut microbiota profiling, and non-targeted metabolomics. Biofilm colonization increased intestinal MP accumulation by 27.8% (water-colonized) and 24.9% (SWI-colonized) relative to pristine PA66 in the gut, altered digestive enzyme activities, and was associated with compartment-specific gut microbiota dysbiosis and metabolic perturbations. Water-column conditioned MPs were primarily associated with indicators of altered mucosal-related taxa and glycometabolism, whereas SWI conditioning was associated with broader metabolic patterns consistent with oxidative stress and altered nucleotide metabolism. The results suggest that environmental compartment is associated with differences in biofilm-conditioned MP characteristics and biological responses. This study provides novel insights into the compartment-dependent ecological risks of biofilm-colonized MPs and contributes to advancing the paradigm shift toward ecological realism in MP risk assessments.