Enhanced Bioconcentration of Bisphenol A in the Presence of Nano-TiO<sub>2</sub> Can Lead to Adverse Reproductive Outcomes in Zebrafish

Titanium dioxide nanoparticles (n-TiO<sub>2</sub>) and bisphenol A (BPA) are widespread environmental contaminants in the aquatic environment. We hypothesized that n-TiO<sub>2</sub> may adsorb BPA, and thus modify its bioavailability and toxicity to aquatic organisms. In this study, the bioavailability and toxicity of BPA (0, 2, 20, 200 μg/L) was investigated in the presence of n-TiO<sub>2</sub> (100 μg/L). The n-TiO<sub>2</sub> sorbed BPA and the resulting nanoparticles were taken up by zebrafish, where they translocated to the liver, brain, and gonad tissues. Increased tissue burdens of both BPA and n-TiO<sub>2</sub> were observed following coexposure, and they also caused a reduction in plasma concentrations of estradiol (E<sub>2</sub>), testosterone (T), follicle-stimulating hormone (FSH), and luteinizing hormone (LH). Plasma vitellogenin (VTG) concentrations were significantly increased in males and females upon exposure to BPA. Histological examination of the ovary and testes did not show obvious morphological alterations; however, inhibition of egg production was noted in the presence of n-TiO<sub>2</sub>. The results indicated that n-TiO<sub>2</sub> acts as a carrier of BPA and enhances its bioconcentration in zebrafish, leading to endocrine disruption and impairment of reproduction.