Enhanced bio-concentration of tris(1,3-dichloro-2-propyl) phosphate in the presence of nano-TiO2 can lead to adverse reproductive outcomes in zebrafish

Interactions between organic toxicants and nano-particles in the aquatic environment may modify toxicant bioavailability and consequently the toxicant's fate and toxicity. To evaluate the potential impact of nano-titanium dioxide (TiO2) on the bio-concentration and reproductive endocrine disruption of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) in fish, a comparative bioaccumulation study was conducted on zebrafish (Danio rerio, AB strain) treated with 0, 5.74, 23.6, or 90.7 μg L-1 TDCIPP alone or co-exposed to TDCIPP and 0.09 mg L-1 nano-TiO2 for 21 days. Nano-TiO2 can absorb TDCIPP and nano-TiO2 is taken up into zebrafish. Chemical measurements showed that TDCIPP was bio-concentrated in zebrafish, and the highest level was detected in the liver, followed by the brain and gonads. Compared with TDCIPP treatment, increased tissue burdens of both TDCIPP were observed in the liver, brain, and gonads suggesting that nano-TiO2 adsorbed TDCIPP and acted as a carrier facilitating the uptake and translocation of TDCIPP in tissues. Higher bio-concentration in the presence of nano-TiO2 resulted in a significant decrease in the hepatic-somatic index, gonad-somatic index and brain-somatic index in F0 females but not F0 males. Moreover, a further gender-dependent reduction in testosterone (T), estradiol (E2), follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and induction of plasma vitellogenin (VTG) concentrations in adults were observed following co-exposure. Co-exposure also inhibited egg production and caused significant developmental toxicity in F1 larvae. The results obtained using this multi-marker approach suggested that nano-TiO2 is a carrier of TDCIPP and accelerated its bio-concentration in adult zebrafish, resulting in adverse reproduction outcomes.