Mayor John Tory says it’s “not acceptable” that the TTC hasn’t conducted a major air quality study of the subway system in over two decades, and is calling for “objective experts” to determine whether underground pollution poses health risks for riders and transit employees.

Tory made the comments to reporters on Wednesday morning, a day after the release of a new study that found elevated levels of fine particulate matter in Toronto’s subway stations and trains.

The study made no pronouncements on the health impacts of the pollution, and the TTC maintains that the system is safe. In a memo sent to employees the agency said that previous studies have analyzed the same particulate matter and concluded it “does not pose a significant health risk.”

The April 25 memo, signed by chief safety officer John O’Grady, said that in the wake of the new research the TTC “will move quickly” to commission a study of its own, however.

The TTC last conducted a subway air quality study in 1995.

Tory said that the TTC shouldn’t have waited this long to conduct a new test. “It’s not acceptable. That is not a standard that I would be proud to say is one that we’re going to maintain.”

The mayor said he had no reason to doubt the TTC’s assurances that the subway air isn’t hazardous, but he wants more information on the health effects.

“I take them at their word in the sense that I don’t think they would say something that was deliberately untrue,” he said. “But I think what we need to do in light of this particular study is that we have studies done by objective experts, who can assure the public and assure the workers that the subway system and the air quality in the subway system is safe.”

According to a TTC spokesperson, the agency plans to hire an “external service provider” to perform the new study. It’s expected to take place later this year.

The TTC says it has already taken measures to improve air quality, including buying a vacuum work car, and implementing tunnel and station washing programs.

The measures have done little to reassure the TTC’s largest union, which is calling for a “full investigation”.

In a letter sent to TTC CEO Andy Byford on Wednesday, Kevin Morton, secretary-treasurer of Amalgamated Transit Union Local 113, said that “subway workers want to know how the TTC can assure they will not get sick by simply putting in an honest day’s work.”

A meeting between transit unions and TTC management is tentatively scheduled for May 3.

Morton told the Star on Tuesday that he had no evidence any employees have been made sick, but said subway workers have long worried about underground air quality.

Three workers initiated work refusals on Wednesday over concerns about pollution, according to the transit agency.

The research that prompted the controversy was led by Health Canada, and determined that the mean concentration of a substance called PM2.5 in the subway system was 95 micrograms per cubic metre, which was 10-times higher than levels outdoors.

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The particulate matter was heavy on iron, and the study’s authors determined the likely source was “rail dust” generated by friction between the trains’ steel wheels and the tracks.

Experts say that limited exposure to PM2.5 shouldn’t pose a significant risk to healthy people, but under certain conditions it can cause health problems, particularly for people with pre-existing respiratory conditions, the elderly, and young children.

With files from David Rider.