Carboxyl Surface Modification Attenuates Polystyrene- but Not Poly(methyl methacrylate) Nanoplastic-Induced Gut...

Plastic polymers are widely recognized as significant environmental toxicants through their generation of nanoplastics (NPs), with polystyrene (PS) and poly-(methyl methacrylate) (PMMA) among the most frequently detected in ecosystems. While carboxyl surface modification is known to reduce NP toxicity in some systems, its protective efficacy in intestinal environments remains unclear. This study investigated the comparative effects of pristine PS and PMMA versus their carboxylated derivatives (PS-COOH and PMMA-COOH) on gut dysbiosis in zebrafish larvae. Pathological examination revealed that PS induced the most severe intestinal epithelial damage, which was effectively mitigated by carboxylation. Conversely, PMMA triggered robust gut inflammation, evidenced by significant upregulation of proinflammatory markers IL-1β and NOS2A, effects that persisted despite carboxylation. These differences were correlated with microbiota shifts: PMMA groups significantly enriched opportunistic pathogens (Vibrio and Morganella), while PS-COOH only partially restored microbial balance. Functional analyses identified that carboxylation disrupts key microbial pathways, including amino acid metabolism and NOD-like receptor signaling, which are crucial for maintaining intestinal homeostasis. The roles of gut microbes were further verified by challenging the microbiota-depleted model with Morganella morganii. Our results demonstrate that polymer composition dictates carboxyl modification efficacyprotective for PS but ineffective for PMMAhighlighting the need for material-specific NP safety assessments.