Canadian Study Finds Higher Levels of Mercury in Summer

A Ryerson University researcher has found that summer is the peak season for mercury and that higher levels of mercury species exist in the urban atmosphere as compared to rural regions.

Julia Lu, Ph.D., is an associate professor in Ryerson's Department of Chemistry and Biology, where she conducts research identifying and quantifying different forms of trace metals in the environment. Her main focus, however, is mercury. Lu's work has involved such diverse locales as the Canadian Arctic and, more recently, Toronto, Canada's largest city.

Airborne mercury's greatest threat is that it will settle into the surface environment and be converted into the much more toxic organomercury species that can be accumulated and magnified up the food chain.

Lu and her then-graduate students Xinjie Song and Irene Cheng mounted specialized equipment—including air sampling units and a meteorological station—atop a three-storey building on Ryerson's campus in downtown Toronto. From there, the team simultaneously measured three types of mercury:

  • Atmospheric gaseous elemental mercury (GEM),
  • Reactive gaseous mercury (RGM) and
  • Mercury associated with particles less than 2.5 micrometers in size.

In addition to finding higher mercury levels in urban areas, the team discovered those levels seemed to be affected by human-produced emissions rather than chemical and photochemical reactions in the environment. Finally, while the concentrations of all mercury species varied during the year—and were lower in the winter—the amount of GEM spiked in June. This is a concern, according to Lu, because GEM stays in the atmosphere longer and travels further than its chemical counterparts. The result, she believes, is a global-scale problem.

"Sometimes the spikes were as high as what you would find near point sources of mercury," says Lu, citing coal-powered and metal-processing plants as examples. "We need to further our understanding of how cities contribute to the mercury problem. And it's not just GEM that requires attention. Other forms of mercury stay in the atmosphere for a shorter duration and therefore negatively impact local and regional areas."

As next steps, Lu is working to pinpoint sources of mercury in the urban environment.

"Annual Atmospheric Mercury Species in Downtown Toronto, Canada" appeared in a recent edition of the Journal of Environmental Monitoring. Funding for Lu's work is provided by the Canada Foundation for Innovation, the Ontario Ministry of the Environment, the Natural Sciences and Engineering Research Council of Canada, Ryerson's Faculty of Engineering, Architecture and Science, and the Department of Chemistry and Biology.

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