Time-related formation of bioactive polycyclic aromatic hydrocarbon (PAH) photoproducts upon interaction with TiO2 nanoparticles in the aqueous phase

Abstract

Polycyclic aromatic hydrocarbons (PAHs) and TiO2 nanoparticles (NPs) are environmental pollutants that possess individual photoactivity. Interactions between PAHs and TiO2-NPs can influence the environmental fate, transport, and transformation of PAHs and their photoproducts. PAH and TiO2-NP interactions are of interest due to their emerging environmental relevance, particularly with the deliberate application of TiO2-NPs to remediate pollution events (e.g., oil spills). The objective was to investigate continued PAH photoproduct formation and transformation, both in the absence and presence of TiO2-NPs, following UVA (320-400 nm) irradiation. In order to do this, multiple analytical methods were performed which included identification of PAH-specific photoproducts (e.g., oxygenated PAHs (OPAHs) and hydroxylated PAHs (OHPAHs)), assessing gene expression profiles of specific genes involved in PAH metabolism, and evaluating changes in oxidative potential. Anthracene (ANT), benzo[a]pyrene (BaP), fluoranthene (FLT), phenanthrene (PHE), and pyrene (PYR) solutions were prepared alone or in combination with TiO2-NPs in OECD medium, and UVA (7.26 mW/cm2) irradiated which were then exposed to early life stage zebrafish and collected at specific time-points following UVA irradiation. Gene expression profiles showed PAH-specific and time-dependent induction of genes in exposures of PAHs and altered bioavailability of PAHs and photoproducts in the presence of TiO2-NPs. To explore the diversity of photoproduct formation and transformation following UVA irradiation, a targeted screening of various OHPAHs and OPAHs was performed using gas chromatography-mass spectrometry (GC-MS) at the same time points assessed in zebrafish exposures. Diverse photoproducts of differing size and ring arrangements were identified, which suggested photodissociation, recombination, ring addition, and ring re-arrangements of PAHs occurred either during or following UVA irradiation. PAHs all showed heightened oxidative potential following irradiation, but TiO2-NP-related increases in oxidative potential were PAH-specific. The exploitation of biological responses and analytical chemistry to investigate changes in PAH-specific photochemistry and bioavailability upon interaction with TiO2-NPs following UVA irradiation have provided novel insights into distinct PAH photoactivity, TiO2-NP influence on photoproduct formation in a PAH-specific manner, and the significant role time plays in all of these processes.