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2007 Research Grant Recipient - Hannah MacDonald

Toxic track record

Photo: Colin P. Laroque
Growing up in Marion Bridge, near Sydney, N.S., Hannah MacDonald heard a lot of stories about and controversy over the Sydney Tar Ponds, one of Canada's most notorious toxic-waste sites. A century of steelmaking and coke production left more than a million tonnes of contaminated soil and sediment in the Muggah Creek Estuary and three other sites, along with lingering questions about its effect on the health of residents.

Now an environmental science student at Mount Allison University, in Sackville, N.B., MacDonald, 21, is still preoccupied with the environmental legacy of the tar ponds. She searched for company records on the steel mill's emissions but was unsuccessful. “The steel plant was on the go for 99 years, but there's no real record of how much pollution was in the area at any one time,” she says. “I wanted to find out how much pollution was in the Sydney area when I was growing up and when my parents and grandparents were growing up.”

MacDonald is instead using dendrochemistry — the study of the chemical composition of tree rings to track air pollution and other environmental changes over time — to understand the extent and plume of airborne pollutants from the steel plant. A region's environmental history is locked within tree rings, she says. “As far as I can tell, it's the best way to see into the past accurately.”

With the assistance of a research grant from The Royal Canadian Geographical Society, MacDonald travelled to Sydney last summer to collect pencil-thin core samples from the most common tree species in the city, including white birch, larch and balsam fir. She started on the grounds of the steel mill (which closed in 2001 and has since been dismantled) and collected samples at 20 sites within a five-kilometre radius of the plant.

She has dated tree rings and analyzed their chemical makeup to detect levels of five heavy metals emitted from the plant: lead, zinc, arsenic, copper and thallium. (So far, she has found lead, zinc and copper in the samples.) Preliminary results show that white birch, a hardwood, picked up more lead and zinc than did softwood trees. MacDonald also noted a decrease in heavy-metal levels after 1988, when the plant’s coke ovens were shut down.

MacDonald’s data collection will lay the foundation for her fourth-year honours research project, which she will start in the fall. Her goal is to create a map of Sydney showing how concentrations of heavy metals throughout the city have changed over time.

— Monique Roy-Sole


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