TPhP and nanoplastics impair color preference in adult fish.

Organophosphate ester flame retardants and nanoplastics (NPs) frequently co-occur in aquatic environments; however, their combined effects on fish visual function remain poorly understood. Here, we investigated whether NPs modulate triphenyl phosphate (TPhP)-induced ocular toxicity and color-guided behavior in zebrafish. Fish were exposed to environmentally relevant concentrations of TPhP, NPs, or their mixture (TNP), followed by color preference assays, retinal histopathology, apoptosis analysis, and eye-tissue transcriptomics with targeted gene validation. TPhP exposure significantly disrupted green and red color preferences and altered color-dependent spatial distribution. These behavioral deficits were accompanied by retinal structural damage, including thinning of the inner neuronal and photoreceptor layers, downregulation of opsin-related genes, and increased apoptosis. In contrast, these alterations were partially attenuated under co-exposure conditions. Transcriptomic analyses further revealed distinct molecular signatures under single exposures; TPhP predominantly affected pathways associated with retinal structure, energy metabolism, and junctional integrity, whereas NPs primarily activated inflammation- and cell death-related processes. Co-exposure elicited a broader and more complex transcriptional response, characterized by coordinated reprogramming of immune-inflammatory, metabolic, tight junction, and regulated cell death pathways, suggesting a non-additive interaction between TPhP and NPs. Collectively, these findings demonstrate that NPs reshape TPhP-induced ocular toxicity through complex transcriptional reprogramming rather than simply enhancing or alleviating individual toxic effects. This study highlights the importance of considering mixture-induced molecular adaptation when evaluating the ecological risks of emerging contaminants and supports color-guided behavior as a sensitive endpoint for assessing visual toxicity in aquatic organisms.