Effects of co-exposure to benzo-a-pyrene and cerium dioxide nanoparticles on human lung and placental barriers

• Pollutant toxicity differs between co-exposure by parallel addition and BaP-coated CeO 2 NPs. • CYP1A1 induction by BaP-coated CeO 2 NPs is dose-dependent. • BaP adsorption onto CeO 2 NPs enhances CYP1A1 induction in bronchial cells. • Particle-bound pollutants should be considered in airborne toxicity assessments. Cerium dioxide nanoparticles (CeO 2 NPs) are emerging pollutants widely used for their catalytic properties in diesel fuel and cigarettes. Human exposure to CeO 2 NPs rarely occurs in isolation. Benzo-a-pyrene (BaP), a polycyclic aromatic hydrocarbon co-emitted from diesel engines, tends to adsorb onto CeO 2 NPs in contaminated environments. To better understand their combined effects on both the lung and placental tissues which are critical-barriers for the fetus, we coated CeO 2 NPs with BaP at two different ratios, mimicking environmental exposure. We characterized the physicochemical properties of BaP-coated NPs in bronchial and placental culture media, assessed coating stability and BaP desorption. We evaluated the biological impact of BaP-coated CeO 2 NPs on primary normal human bronchial epithelial cells and purified villous cytotrophoblasts from term human placentas. We compared the response of BaP-coated NPs with that observed under parallel co-exposure, and to individual exposures to BaP and CeO 2 NPs. Bronchial cells exhibited toxicity at lower doses under co-exposure by parallel addition compared to BaP-coated NPs. Cytochrome P450 (CYP1A1) induction varied between tissue barriers, exhibiting a BaP dose-dependent in both tissue models but coating-independent response in trophoblasts, whereas bronchial cells showed a stronger response to BaP adsorbed on CeO₂ NPs. These findings highlight how BaP, when stably associated with CeO 2 NPs, exerts modulated effects depending on the tissue, potentially altering its metabolic kinetics and thus its biopersistence. This study underscores the importance of considering particle-bound pollutants when evaluating the health impact of airborne particulate matter, as this more accurately reflects environmental exposure.