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The study was produced by the Joint Oil Sands Monitoring (JOSM) program, but two other studies since 2010 have shown increased mercury levels in the area.Larry MacDougal/The Globe and Mail

Bird eggs downstream of Alberta's oil sands have been found to contain rising traces of mercury, with some samples now above the threshold that could be considered dangerous, an Environment Canada study has found.

The study didn't, however, link the cause of rising mercury levels to the growing development in the oil sands – the scientists said further research was required to pinpoint a cause, but "local/regional factors are playing an important role" in mercury presence. It is at least the third peer-reviewed study since 2010 to show mercury levels increasing in the ecosystem in the region.

The study was produced – though not publicized – by the fledgling Joint Oil Sands Monitoring (JOSM) program, a federal-provincial initiative announced in early-2012.

Mercury is common in trace amounts, but chronic human exposure can cause damage to the brain, spinal cord, kidneys, liver and a developing fetus, according to Environment Canada.

Canada this month signed an international treaty pledging to reduce mercury emissions.

Two other studies since 2010 have shown increased levels of mercury in the oil-sands region – one in a major river, the other in lakes as far as 90 kilometres away, though the remote lakes were no more polluted than a typical urban lake. The latest study, published online Sept. 26 by the Environmental Science & Technology journal, shows the mercury level is rising in the eggs of predatory birds, which in turn suggests mercury levels could also be rising in the fish the birds eat.

In most samples, though, the levels are not considered dangerous. "The significance I think is just in terms of the trend itself. When we see mercury levels increasing in the bird eggs, that's something that we obviously need to be aware of," said Craig Hebert, an Environment Canada research scientist and the study's lead author.

The study compared mercury levels in bird eggs, gathered from 2009 to 2012, from two sites in northeastern Alberta, downstream of the oil sands, and those from a site in southern Alberta, far from development. Eggs taken from northeastern Alberta showed an increase in mercury levels, though one species' increase was "non-statistically significant," while the southern Alberta eggs showed a decrease in mercury levels. At one northeastern site downstream of oil sands development, eight of 23 eggs collected in 2012 were found to have a mercury content above a threshold that might be expected to harm sensitive bird species, though not enough to harm the birds being tested, Dr. Hebert said.

In one test, mercury levels had risen two-thirds when compared to an egg sample from 1977, when the oil sands were in their infancy. But researchers stress that they can't pinpoint the cause of the increase. "We can't link the mercury levels we're seeing in these bird eggs specifically to oil sands. Certainly that's one possibility, but there are other possibilities as well," Dr. Hebert said. Those include coal power plants in Asia, which the study says are "an important source of gaseous elemental mercury to North America."

"I think this is really the research question we need to address next – we have to have a much better idea of sources and loadings of mercury into the environment in different areas," Dr. Hebert said.

The peer-reviewed study was produced through the JOSM program, though its online portal didn't publish it, and currently says the data "will be released in the coming months." Environment Canada did accommodate an interview with Dr. Hebert, its researcher, who said the JOSM program is being developed. "There's a lot of work going on now. It's a work in progress, shall we say, but there's lots of activity," he said.

In a statement, Environment Canada said the new monitoring program has increased "geographic coverage of environmental monitoring in the-oil sands region of Alberta, the number of sites monitored, the frequency of sampling (from annual to monthly) and the number of contaminants measured."

Alberta's government shared the study's findings with residents of the Fort Chipewyan and Fort McKay First Nations, near the oil sands, Alberta government spokeswoman Jessica Potter said. They told residents there the bird eggs remain safe to eat. "It's one study. It doesn't necessarily indicate a trend. It's just important that we continue to look into it," Ms. Potter said.

The Canadian Association of Petroleum Producers, an industry lobby group, said it supports increased monitoring that might "evaluate the significance of any trends and to conclusively identify sources." It declined, however, to specifically address the study.

While not pointing to one source, the study did rule out some other possible causes, including dietary change or a recent major forest fire.

"I think what they do a very good job of doing here is ruling out other suspects," Jules Blais, a professor of biology and environmental toxicology at the University of Ottawa, said after reviewing the latest study. The levels found in the bird eggs are "not insignificant," he said, and build on previous findings. "What this does is takes us one step further in showing that the mercury is being acquired by living things."

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