The decks of four cruise ships were examined over a two year period without the cruise lines being aware.
Researchers found concentrations of particulate matter (PM) measured were “comparable to concentrations measured in polluted cities, including Beijing and Santiago”.
This means despite being on open water and in the open air, “vacationers and cruise ship staff may be exposed to elevated concentrations of PM,” said Ryan Kennedy, author of the report and an assistant professor at Johns Hopkins University Bloomberg School of Public Health.
”It’s dangerous, it’s not a healthy thing for us to be exposed to,“ Kennedy told CNN.
However, Carnival Cruises disputed the findings.
A spokesperson told Express.co.uk: “These so-called fly-by tests are completely ridiculous, inaccurate and in no way represent reality.
“We test the air quality of our ships and they meet or exceed every requirement.
“The air quality on our ship decks when in port compares favourably with a typical urban or suburban environment.
“Independent testing on our funnels – which is the area where the exhaust originates – further validates our claims.
“This particular organisation, for fundraising purposes, is constantly in search of a problem in our industry even if it has to create fake tests that really have no scientific basis.
“The safety of our guests is our top priority and we undertake our cruises in close coordination with national and international regulatory bodies like the EPA to ensure the utmost safety of our guests and crew.”