Passive air sampler
Passive air samplers like these were deployed in nearly 200 locations around the GTA with the help of faculty, staff and students at U of T Scarborough. (Photo by Don Campbell)
Wednesday, August 1 - 2018
Don Campbell

The most comprehensive monitoring of airborne mercury ever done in the Greater Toronto Area (GTA) finds emission levels officially reported to the government can be wildly inaccurate.

“This suggests that the government hasn’t been doing a great job when it comes to accurately monitoring mercury emissions,” says Associate Professor Carl Mitchell, one of the authors of the study.  

The project, done by a team of researchers in U of T Scarborough’s Department of Physical and Environmental Sciences including Professor Frank Wania and PhD David McLagan, deployed nearly 200 air samplers across the GTA with the help of dozens of faculty, staff and students – making it the largest monitoring project ever done on airborne mercury in the world. 

The good news is that mercury concentrations in the GTA continue to be low.

“In terms of acute exposure levels, there’s nothing we should be concerned about whatsoever,” says Mitchell, an expert on contaminant cycling in the environment.  

In fact, in comparing their results to data gathered over the past decade, it seems airborne mercury concentrations have gone down. Mitchell says this is at least partly attributable to Ontario moving away from coal-fired electricity generation in recent years.

The researchers also put the samplers across the GTA near known mercury emission sources identified by Canada’s National Pollutant Release Inventory (NPRI), the public inventory of pollutant releases from waste disposal and recycling facilities. The concentrations they measured did not match well with emissions that are being officially reported to the NPRI.

For example, a hazardous waste facility operated by Aevitas in Ayr just outside of Cambridge, ranks low on the NPRI list but was found to have concentrations 10 times higher (still well below chronic exposure levels) than the average found at other sites. Meanwhile, waste water treatment plants that rank high on the NPRI list were found to have much lower concentrations, suggesting emissions at these facilities are being overestimated.

“It indicates these emissions are not very accurately accounted for, and this has implications for our commitment to the Minamata agreement,” Mitchell says, referring the recent international treaty designed to reduce mercury emissions.

The study also found that gaseous mercury levels were slightly higher in downtown Toronto than in other parts of the GTA, likely due to the concentration of medical facilities downtown.

The extensive monitoring project was made possible through an inexpensive air sampler that was developed at U of T Scarborough. The passive sampler does not rely on electricity and instead works by using the natural movements of air and a carbon material to capture airborne mercury, meaning they were able to deploy many.

Despite low mercury levels, the passive air sampler is so precise that it’s able to determine extremely small differences in concentrations, says Mitchell. As a result, they were able to see tiny increases in concentration levels near waste facilities, crematoriums as well as medical and dental buildings that handle or dispose mercury in various forms. 

“These types of mapping exercises can be used to find so-called fugitive emission sources that are really difficult to find and measure otherwise,” he says.

Mitchell says monitoring mercury is important because it’s a highly toxic pollutant. Mercury released by human activity can be transported in the air across great distances and can eventually be transformed in the environment to methylmercury, the most alarming form from a human health perspective. In humans, it can cause damage to the neurological, immune, cardiovascular and respiratory systems, among others. Fetuses and children are particularly vulnerable because it can hinder the neurological development of the brain.

But, he adds, it’s also important to accurately measure whether or not mercury reduction targets, like those set in the international Minamata agreement, are being met.

The research, which is published in the journal Environmental Research Letters, received funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) and an NSERC Alexander Graham Bell Canada Graduate Scholarship.