Optical toxicity of triphenyl phosphate in zebrafish larvae

Triphenyl phosphate (TPhP) has been shown to cause developmental neurotoxicty. Considering the visual system is a sensitive target, in the present study, we investigated the potential toxicity of TPhP on the visual development and function in zebrafish larvae. Embryos were exposed to 0, 0.1, 1, 10, and 30 μg/L TPhP from 2 to 144 h post-fertilization (hpf). The transcription of photoreceptor opsin genes, and histopathological changes in the retina and visual behavior (optokinetic and phototactic responses) were evaluated. TPhP significantly downregulated the transcription of opsin genes (zfrho, opn1sw1, opn1sw2, opn1mw1, opn1mw2, opn1mw3, opn1mw4, opn1lw1 and opn1lw2) in all exposure groups. Histopathological analysis revealed that the areas of the outer nuclear layer (ONL), inner nuclear layer (INL), and inner plexiform layer (IPL) of the retina were significantly reduced in the 10 and 30 μg/L TPhP groups. The number of ganglion cells was reduced significantly in the 30 μg/L group. The optokinetic response (OKR) and phototactic response showed dose-dependent decreases caused by impaired visual function, which was confirmed by unchanged locomotor activity. The results indicated that exposure to environmentally relevant concentrations of TPhP could inhibit the transcription of genes related to visual function and impair retinal development, thus leading to visual impairment in zebrafish larvae.