Time-Related Alteration of Aqueous-Phase Anthracene and Phenanthrene Photoproducts in the Presence of TiO 2 Nanoparticles.

Polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO ₂ ) nanoparticles (NPs) are photoactive environmental pollutants that can contaminate aquatic environments. Aqueous-phase interactions between PAHs and TiO ₂ -NPs are of interest due to their emerging environmental relevance, particularly with the deliberate application of TiO ₂ -NPs to remediate pollution events (e.g., oil spills). Our objective was to investigate anthracene (ANT) and phenanthrene (PHE) photoproduct formation and transformation following ultraviolet A (UVA) irradiation in the presence and absence of TiO ₂ -NPs. ANT and PHE solutions were prepared alone or in combination with TiO ₂ -NPs, UVA-irradiated, and either exposed to larval zebrafish or collected for chemical analyses of diverse hydroxylated PAHs (OHPAHs) and oxygenated PAHs (OPAHs). The expression profiles of genes encoding for enzymes involved in PAH metabolism showed PAH-specific and time-dependent inductions that demonstrated changes in PAH and photoproduct bioavailability in the presence of TiO ₂ -NPs. Chemical analyses of PAH/NP solutions in the absence of zebrafish larvae identified diverse photoproducts of differing size and ring arrangements, which suggested photodissociation, recombination, and ring re-arrangements of PAHs occurred either during or following UVA irradiation. Both ANT and PHE solutions showed heightened oxidative potential following irradiation, but TiO ₂ -NP-related increases in oxidative potential were PAH-specific. The exploitation of multiple analytical methods provided novel insights into distinct PAH photoactivity, TiO ₂ -NP influence on photoproduct formation in a PAH-specific manner, and the significant role time plays in photochemical processes.