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Canada's oil sands mining operations produce vast and fast-growing quantities of deadly substances, including mercury, heavy metals and arsenic, new data released by Environment Canada shows.

The information on pollutants sheds new light on the environmental toll exacted by Canada's bid to extract oil from bitumen, showing in stark relief how many nasty substances are being laid on the northern Alberta landscape in the process - and how quickly those are growing.

In the past four years, the volume of arsenic and lead produced and deposited in tailings ponds by the country's bitumen mines - run by Syncrude Canada Ltd., Suncor Energy Inc., Canadian Natural Resources Ltd. and Royal Dutch Shell PLC - has increased by 26 per cent. Quantities of some other substances have increased at even faster rates.

The companies also released huge amounts of pollutants into the air last year, including 70,658 tonnes of volatile organic compounds, which can damage the function of human organs and nervous systems, and 111,661 tonnes of sulphur dioxide, a key contributor to acid rain.

The numbers are contained in Environment Canada's national pollutant release inventory, which details the dangerous compounds generated by industrial Canada. New numbers published this weekend track 85 mining facilities that generate tailings and waste rock. Of those, the oil sands produce just under 50,000 tonnes of reportable substances in tailings, or 10 per cent of the total.

Metal ore mines are by far the worst, with 54 per cent, followed by iron ore mines at 25 per cent. Other mines - which include diamond, asbestos and phosphate - generate 5 per cent.

Oil sands operations, however, produced the overwhelming bulk of several dangerous substances: for example, bitumen mines generated nearly all of the Canadian total of acenaphthene, one of a bevy of polycyclic aromatic hydrocarbons released around Fort McMurray. Such substances can cause tumours of the lung, skin and bladder, and some are carcinogens. And their volumes are growing in north-eastern Alberta: companies generated 42 per cent more acenaphthene in 2009 than they did in 2006.

Last year, oil sands mines also produced 322 tonnes of arsenic, 651 tonnes of lead and measurable volumes of mercury, chromium, vanadium, hydrogen sulphide and cadmium.

The numbers "are just ridiculously huge," said Justin Duncan, a staff lawyer with Ecojustice who helped prosecute the 2007 court case that forced Environment Canada to release the data.

"You're talking hundreds of thousands of kilograms of heavy metals going into some of these tailings ponds. If one of these things bursts, it's a catastrophic risk to the Athabasca River system."

The Environment Canada data do not include naphthenic acids, which researchers consider the most toxic component of the effluent brew.

Yet scientists say simply knowing how much pollution is generated by the oil sands does little to show how toxic the mines' tailings are. What's needed is the concentration of the substances - a figure Environment Canada does not provide.

John Giesy, a professor at the University of Saskatchewan and the Canada Research Chair in Environmental Toxicology, points to a potato as an example: a grocery store spud contains 600 to 700 chemicals, some of them carcinogens, but they're in such small quantities that they're not harmful.

"Everything is toxic. It's the concentration that makes the poison," he said.

The actual toxicity of oil sands effluent remains a nascent field of scientific inquiry. But some research that has been carried out by the University of Saskatchewan has found some surprising results. Some older tailings ponds, for instance, are capable of sustaining fish life. And virtually all tailings ponds can sustain invertebrate life; Julie Anderson, a PhD student, has discovered that mosquito-like midges will survive, but not grow, in tailings water.

To allow midges to grow, oil sands wastewater needs to be diluted roughly as much as the effluent from some sewage treatment plants.

And industry says it is working to improve. Travis Davies, spokesman for the Canadian Association of Petroleum Producers, said companies will spend $1-billion in the next year to reduce tailings, "so you have less of these in the environment for any extended period of time."

Environmentalists, however, said the Environment Canada data show the full slate of dangerous compounds emitted by the oil sands and will serve as an important industry barometer.

"More information coming to light is essential, I think, to eventually have a meaningful discussion about the unacceptable risk of these tailings ponds," said Simon Dyer, oil sands program director for the Pembina Institute.

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