Ultrafine particulate matter emitted from ships drives inflammation and susceptibility to viral infection.

Exposure to ambient airborne particulate matter (PM) has been associated with almost 9 million premature deaths per year worldwide. Ports are essential infrastructure for trade and transport, with over 80% of the world's international trade volume travelling by sea, yet there is little understanding of the potential health effects of PM from ships. Here, we studied the elemental and toxicological characteristics of size-fractionated PM collected at different areas of a busy European mixed-use port. We found that unregulated ultrafine PM, a PM size fraction <100 nm in aerodynamic diameter, originating from a cruise ship source, was highly enriched compared to ultrafine PM from other sites in tracers of heavy fuel oil combustion (V and Ni), with Co identified as a novel tracer. In cell models of airway and alveolar epithelium, this cruise ship-associated ultrafine PM was markedly more pro-inflammatory than PM from other sites, while simultaneously reducing expression of a range of genes associated with the innate antiviral response. Investigation of the effects of the three metals found to be enriched in our cruise ship ultrafine PM showed that these effects could be reproduced by vanadium exposure, which reduced interferon signalling and increased permissiveness to viral infection, facilitating replication of the respiratory viruses rhinovirus-16 and SARS-CoV-2. Our findings suggest that, despite a series of regulations introduced over the last 20 years, cruise ship-associated emissions of PM from heavy fuel oil combustion may exert disproportionate effects on health compared to PM from other sources. In particular, the effects manifest themselves through induction of a response with characteristics of a poor viral infection prognosis. More broadly, current regulations, which neglect PM source- and composition-related variations, and ultrafine PM in general, may need strengthening to better mitigate health effects resulting from exposure to PM.