Cruise ship air pollution could make viral infections worse

Air pollution from cruise ships could be damaging the health of people living in port cities, new research shows.

Southampton researchers found tiny particles in the air that could lead to inflammation and make people more vulnerable to viruses.

The research has now been published in the journal Environment International. 

Studying the air at Southampton's port

The researchers studied tiny dust particles, known as ultrafine particulate matter (PM), in the air within Southampton’s port.

They found the air contained PM enriched with trace elements from the burning of shipping fuel.

Laboratory tests found these particles increase inflammatory signals. They also weaken cells’ defence against viral infections like COVID-19 or the common cold.

Matthew Loxham is Professor of Respiratory Biology and Toxicology at the University of Southampton. He is also part of the NIHR Southampton Biomedical Research Centre (BRC).

“In this research we’ve identified a clear air pollution ‘signature’ coming from cruise ships burning fuel in ports,” he said.

“The ultrafine particles contained in these ships’ emissions can penetrate deeper into the lungs than larger sizes of particulate matter, and may be able to enter the bloodstream. But particles of this size are essentially unregulated and generally not monitored.

“We found that exposure of cells to these particles, and vanadium – the most enriched element in the particles – was both pro-inflammatory and facilitated the replication of viruses.”

Identifying the source

PM is released from a wide range of sources. It is known to affect the respiratory and cardiovascular systems. There is also emerging evidence of associated metabolic, neurological and infection-related harms.

Emissions from ships contribute around eight percent of total global emissions of breathable PM. This has been associated with over 400,000 deaths and 14 million childhood asthma hospitalisations every year.

For the first-time, the researchers carried out an in-depth investigation of the make-up and toxicology of PM within a busy port.

The team chose five sampling sites located around Southampton’s port area. These included a dock gate used for movement of heavy good vehicles, a container ship terminal and a busy cruise terminal.

They also sampled a comparison site to provide a benchmark reading. This was located five kilometres away from the port.

PM samples were collected in the late spring and early summer. They were also collected during the winter at the cruise terminal, during the ‘off-season’ when far fewer cruise ships visit.

At the cruise terminal, researchers found higher levels of vanadium, nickel and cobalt in fine and ultrafine PM during the busy summer season than in the quieter winter months.

Concentrations of these trace elements were also generally higher across the port than at the comparison site.

Dr Nat Easton from the University of Southampton was a coauthor on the paper. She is also part of the NIHR Southampton BRC.

“We saw increases in concentration when the wind was coming from the direction of the ships, and when ship presence was higher,” she said.

“The higher concentrations at the cruise terminal than the rest of the port is perhaps due to increased emissions from ‘hoteling’ cruise ships compared to cargo ships, but difference in fuel origins and berth occupancy times may also play a role.”

The research was funded by the Biotechnology and Biological Sciences Research Council, Leverhulme Trust and Medical Research Council. It was also funded by the NIHR Southampton BRC, Southampton Marine and Maritime Institute, and Southampton Institute for Life Sciences.

Health implications

The researchers conducted a series of laboratory tests. These exposed airway and lung lining cells to the PM they had collected.

In cells exposed to the summer season’s cruise terminal ultrafine PM, they found an increase in the expression of genes relating to an inflammatory response. They also found a decrease in the expression of antiviral response genes.

Additional tests revealed that vanadium may play a role in this. The researchers infected cells from the lungs of healthy donors with human rhinovirus. This virus causes the common cold, and is a leading cause of hospitalisations following asthma attacks. They also used a model of COVID-19 coronavirus infection.

“When exposed to vanadium, the number of copies of both viruses increased,” said Professor Loxham. “This indicates vanadium has a role in diminishing the ability of cells to prevent viral replication. This has potential implications for the severity and spread of infection.”

The researchers say the findings lend weight to calls to reduce emissions from ships in populated areas. This could be achieved by adoption of shoreside power from clean energy sources or carefully selected alternative fuels. Improvement of emissions reduction technology could also play a part.

They also say increased monitoring and regulation of ultrafine PM is needed to protect the health of people living near ports around the world.