Hamilton health official clarifies impact of July soot: Part of ‘ongoing pollutants’ residents exposed to

Hamilton’s associate medical officer of health is clarifying and putting into context the public health department’s finding there are no short- or long-term impacts linked to the grime coating city neighbourhoods in July.

“We weren’t trying to say that this emission categorically has absolutely no effect on people’s long-term health,” Dr. Bart Harvey told CBC Hamilton on Monday. “We were really putting it in the context that there are ongoing pollutants in Hamilton’s air all the time. All of us are exposed to them.”

In early July, many Hamilton residents reported finding a black soot-like substance on their properties, and on their pets’ and families’ feet.

Black fallout is a perennial issue in Hamilton, particularly near the industrial area, where people have complained about it for decades. However, some residents and elected officials said July’s soot was more pronounced and covered a wider area than usual. 

On Aug. 11, Ontario’s Ministry of the Environment, Conservation and Parks (MECP) said emissions from manufacturer Birla Carbon were “a primary source” of last month’s grime. MECP said it shared its findings with public health. That department addressed the health effects in a news release two days later. 

In addition to reviewing soot samples taken by MECP, Hamilton public health analyzed data from air monitors and emergency rooms to see if people were going to the hospital for related reasons.

Neither indicated short-term health effects such as people seeking urgent medical care for difficulty breathing, Harvey said. 

“It would certainly not be surprising that people may have experienced itchy eyes, sore throats [or] coughs,” he said, but likely not to the degree that they’d go to a doctor.

Harvey said the soot samples mostly contained carbon and other pollutants that are in Hamilton’s airshed “on an ongoing basis.”

WATCH | Residents wonder where soot was coming from:

People in several Hamilton neighbourhoods still don’t know why black soot has been falling on their homes

People living in and around Hamilton’s east end say their homes have been covered in black soot this week. Soot is not a new concern for people in the area, but Ward 4 councillor Tammy Hwang says this time is different, with people further away being affected.

Air quality has been improving in the city, Harvey said, but pollutants including benzo(a)pyrene and polycyclic aromatic hydrocarbons (PAHs) remain, and have been linked to health risks and negative health outcomes.

While we may look at one event in isolation, we have to think about how it compounds with the other exposures that an individual may have.– Matthew Adams, University of Toronto researcher

Harvey pointed to a 2024 public health report on community health in Hamilton that noted air pollutants such as fine particulate matter and sulphur dioxide are associated with short- and long-term health effects.

By one measure, “air pollution was estimated to account for 55 deaths of Hamiltonians in 2018,” the report said. That included approximately 17 deaths due to ischemic heart disease, 13 from chronic obstructive pulmonary disease (COPD) and 11 related to lung cancer. 

Public health’s report said the total could be “much higher,” noting Health Canada modelling indicated about 378 premature deaths could be attributed to air pollution in Hamilton in 2016. 

“Poor air quality can exacerbate symptoms of chronic disease, including COPD and asthma, putting Hamiltonians living with chronic diseases at risk during poor air quality days.”

In 2023, researcher Matthew Adams reported the findings of a two-year study that showed breathing Hamilton’s air is like smoking part of a cigarette every day, when it comes to inhaling the PAH benzo(a)pyrene.

Adams, an associate professor in the University of Toronto’s department of geography and planning, lives in Hamilton’s Dundas area and is familiar with the city’s recurring soot problem, though he says his study didn’t cover it specifically.

Researcher notes exposure by other pollutants

Adams said he was not surprised by the recent news that a McMaster University team sampling soot in 2024 and 2025 found toxic PAHs linked to coal combustion. He said his team found those compounds in the air throughout the city and in greater concentrations near the industrial area. 

The health risk of Hamilton’s air pollution is dependent in part on how much a person breathes, he told CBC Hamilton on Friday. He said children tend to breathe more than adults and are at greater risk of inhaling or ingesting harmful particles. They’re also vulnerable because their bodies are still developing. 

“When I see this grime, children are what come to my mind first,” Adams said, adding one of his own children has asthma. 

“I wouldn’t want her breathing in the amount of soot that someone is able to wipe [it] off of a playground. It seems to me fairly likely that if you were breathing in that air during the event, that it’s likely to exacerbate any ongoing respiratory conditions.”

It’s also important to consider that people are exposed to multiple sources of air pollution, from car exhaust to wildfire smoke, Adams said. 

“While we may look at one event in isolation, we have to think about how it compounds with the other exposures that an individual may have.”

Adams said technologies exist to reduce emissions from industrial sources and he’d like to see those implemented.

Recommendations on how to clean grime

Public health doesn’t have jurisdiction over outdoor air quality, Harvey said, but the department’s supportive of reducing emissions overall. There’s long been an unequal burden in the city, with air pollution tending to be worse closest to industry and major roads in the north end. 

Public health recommends cleaning the grime from last month using soap and water or a mild detergent.

Harvey said wet cleaning avoids stirring up particles that one might then inhale.

Public health also recommends washing any grime-covered produce before eating it, as well as peeling root vegetables and removing the outer leaves or leafy plants.