The ecotoxicity of environmental 6PPD exposure to Onychostoma macrolepis: A correlative water–gut microbial framework

Parent 6PPD was detected in Weihe River at concentrations of 1.01–19.82 ng/L. • 6PPD treatment induced intestinal injury, oxidative-stress responses, and gut microbial changes in both fish species. • A correlative water–gut microbial framework was proposed for 6PPD ecotoxicity assessment. • Flavobacterium emerged as a potential microbial biomarker of 6PPD pollution. The tire antioxidant 6PPD is increasingly detected in traffic-impacted aquatic environments, yet its potential effects on native freshwater fish and associated microbial communities in inland river systems remain insufficiently understood. In this study, we combined field sampling at seven sites along the Weihe River, China, with 30-day semi-static laboratory exposure experiments to compare the responses of the native cyprinid Onychostoma macrolepis and the model species Danio rerio . Parent 6PPD was detected at all field sites at concentrations of 1.01–19.82 ng/L. Following exposure to nominal 6PPD concentrations of 1 and 10 μg/L, both fish species exhibited intestinal histopathological alterations, oxidative-stress responses, and treatment-associated restructuring of the gut microbial community. Genus-specific qPCR supported increased absolute abundance of Aeromonas in the 10 μg/L treatment group for both species, whereas Achromobacter abundance decreased in exposed O. macrolepis . In rearing water, Polynucleobacter showed a positive treatment-associated pattern, and SourceTracker analysis indicated greater compositional similarity between matched rearing-water and O. macrolepis gut communities in the 10 μg/L group. In natural river water, Flavobacterium showed the strongest positive site-level association with measured 6PPD concentration among the screened genera. This association remained significant after separate adjustment for multiple environmental covariates, supporting Flavobacterium as a potential microbial biomarker associated with 6PPD contamination. These findings support a correlative water–gut microbial framework and demonstrate the value of incorporating native fish into the ecological assessment of emerging tire-derived contaminants. Download: Download high-res image (152KB) Download: Download full-size image