The TTC needs to take steps to improve air quality in the city’s subway tunnels, a news Toronto Public Health report says.

The research, released Monday, found levels of fine particulate matter (PM2.5) air pollution in TTC tunnels are elevated and contain high levels of metals that “warrant mitigation.”

Researchers have linked PM2.5 pollution, tiny particles 20 to 30 times smaller than a hair, to the metallic rail dust that is generated when a train’s wheels rub against the tracks.

The report notes there are no current occupational health limits for PM2.5 pollution, but says the levels measured in the subway are expected to be associated with short- and long-term health impacts.

“PM2.5 is a non-threshold contaminant, which means that there is some potential for health impact at all levels of exposure, and any reductions in exposure offer health benefits,” the report says.

The Toronto Board of Health asked for the air quality study in 2017 to look at the health impact on passengers in the subway system.

In an online statement, the City of Toronto wrote that although “the report shows that taking the subway benefits the overall health of all Toronto residents,” it added “that these benefits would be further enhanced by the implementation of short-term and long-term measures to improve subway air quality.”

Among the steps the report recommends the city take include training employees on the subject, continuing to monitor subway air quality and reviewing TTC operations to identify where exposure to PM2.5 could be decreased.

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On Monday, some frequent transit riders and workers of stores inside the subway system expressed concern over the findings.

New mom Sonja Basic, a daily subway user, said she welcome studies informing riders about what they’re being exposed to.

“It’s concerning for my little one, but for myself, I’m not as concerned,” she said, standing on the platform at Queen Station with newborn daughter Amilea nestled in a baby carrier. “I definitely think that something should be done, but I’m not sure how because we can’t all wear masks.”

Behind the counter at a newsstand steps from the entrance to the platform, Mahmud Alam says he’s constantly cleaning the store because of dust.

“There’s a lot of dust,” he said. “After going home I have to clean my eyes and nose.”

Alam said he has not experienced any health issues he can link to working underground, but he’s now wondering about the long run.

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“It could have side effects because you’re inhaling, and who knows what’s in there,” he said.

Meanwhile, Susan Ditchburn, 70, said that even as a senior she isn’t as bothered because she’s only in the tunnel a few minutes per day.

“I’m much more concerned about what I’m breathing around me outside,” she said.

Dr. Eileen de Villa, Toronto’s Medical Officer of Health, will present the report on Jan. 13 at a meeting of city council’s board of health.

The report comes months after the TTC’s own report, released July 10, showed that pollutant levels in the subway system are within exposure limits. At the time, unions representing thousands of transit workers called on the agency to allow employees to use face masks and to do more research on the matter.

“This new report confirms the problems regarding air quality contamination in the subway system are clearly legitimate,” Carlos Santos, president of the Amalgamated Transit Union Local 113, said Monday.

“If the conditions in the subway require many kinds of mitigation for passengers, any reasonable person has to be deeply concerned about what this means for anyone who works there for their living.”

TTC spokesperson Stuart Green acknowledged the city report and said the service “remains fully committed to continuing our world-leading efforts in subway air quality improvement by monitoring the effectiveness of our actions to date and ensuring mitigation is factored in to all aspects of our subway operations and procurement.”

Green added the TTC is well below provincially mandated occupational health regulations, and said tests show “concentrations of certain particulates in the subway air to be up to 10,000 times lower in 2018 than they were when previously tested in 1995.”

Mayor John Tory said he “welcomed this new study so we could confirm that we are on the right track and have current information to help guide future work.”

“I am committed to making sure the TTC continues this work in the existing system and in all future subway projects,” Tory said in a statement.

TTC chair and Coun. Jaye Robinson said the subway is a “safe and environmentally-friendly mode of transportation” and noted that the transit agency is taking action on the issue.

TTC CEO Rick Leary said the agency “will also exchange information and discuss best practices with other large transit systems like New York and London where similar challenges are faced.”

Ilya Bañares is a breaking news reporter, working out of the Star’s radio room in Toronto. Follow him on Twitter: @ilyaoverseas

Jason Miller is a breaking news reporter based in Toronto. Reach him on email: jasonmiller@thestar.ca or follow him on Twitter: @millermotionpic