Modulation of PFOA (perfluorooctanoic acid) uptake in Daphnia (Daphnia magna) by TiO2 nanoparticles

The hydrophobic surface of plastics adsorbs hydrophobic persistent organic pollutants (POP) such as Perfluorooctanoic acid (PFOA). The potential for hydrophobic nanoparticles such as titanium dioxide (TiO₂) to associate with PFOA and alter accumulation rates has not been investigated. Nanoparticles form ecocorona by adsorption of multiple constituents in water, but few studies have examined if this results in differences in the rate of PFOA accumulation in freshwater animals. We demonstrate the PFOA associates with the hydrophobic surfaces of nano-sized TiO₂ particles and this increases the rate of uptake of PFOA into Daphnia magna. Accumulation of PFOA in daphnia was measurement over multiple concentrations, flux times and particle sizes using a radiotracer-based method (¹⁴C-labelled PFOA). Our results show that TiO₂ NPs have a high sorption capacity for PFOA and PFOA sorption decreased aggregation of TiO₂ as evidenced by a decrease in average hydrodynamic diameter, decreased zeta potential and increased polydispersity index. Uptake of PFOA at 10 μg/L was found to be 45 % higher in the presence of 500 μg/L of 5 nm TiO₂ compared to control PFOA alone uptake. Potentiation of PFOA uptake using 25 nm TiO₂ NPs was 25 % higher than control PFOA alone. PFOA alone (0.5 mg/L) reduced metabolic oxygen consumption (MO₂) in daphnia by 52 %, but exposure to (100 mg/L) 5 nm TiO₂ NPs sorbed with (0.5 mg/L) PFOA decreased metabolic oxygen consumption (MO₂) by ~88 %. These findings show that TiO₂ nanoparticles act as vectors for hydrophobic organic pollutant accumulation and significantly potentiate PFOA accumulation and toxicity in aquatic organisms.