Elevated PMMA levels in dental clinic wastewater induce retinal developmental toxicity in zebrafish by disrupting dhrs9-mediated retinol metabolism

Dental clinic wastewater has emerged as a significant yet understudied source of microplastic pollution, yet its ecotoxicological risks to aquatic organisms remain poorly characterized. Polymethyl methacrylate (PMMA), the primary matrix material of dental restorative and prosthetic materials, is ubiquitously released during clinical procedures. This study characterized microplastic contamination in wastewater samples from five randomly selected dental clinics and found that PMMA accounted for 12.07% of total detected microplastics and was present in all samples, confirming its status as a ubiquitous dental-derived microplastic pollutant. Subsequently, we evaluated the toxic effects of micron- and nanoscale PMMA (PMMA-MNPs) on zebrafish larvae, revealing that nanoscale PMMA (PMMA-NPs) exhibited significantly greater developmental toxicity than micron-sized particles. Exposure to PMMA-NPs induced concentration-dependent growth retardation, locomotor dysfunction, and ocular developmental defects, including reduced eye area, impaired ocular angiogenesis, and extensive retinal cell apoptosis. Transcriptomic sequencing identified the retinol metabolism pathway as the core dysregulated pathway underlying PMMA-NPs-induced ocular toxicity, with dhrs9 identified as a critical functional mediator. In vivo functional validation using dhrs9 knockdown and mRNA rescue assays demonstrated that dhrs9 deficiency recapitulated PMMA-NPs-induced retinal structural damage and apoptosis, while exogenous dhrs9 mRNA supplementation effectively reversed these toxic effects. Our findings reveal that dental-derived PMMA-NPs induce retinal developmental toxicity in zebrafish by inhibiting dhrs9 expression and disrupting retinol metabolism homeostasis. This study provides the first mechanistic evidence in zebrafish linking dental microplastic exposure to visual system damage in aquatic organisms, offering critical baseline data for the ecological risk assessment and discharge control of dental-source microplastics.