In Quebec, and other parts of the country where winter grinds on from November to April, people know that virginal snowfalls are all too soon corrupted, by car oil, muck and garbage.

Cities like Montreal and Toronto gritted their teeth through knifing windchills down to minus 26 degrees Celsius (-15 Fahrenheit) at the weekend and struggled through the latest snowfalls of a brutal winter.

In Montreal, huge banks of dirty ice and snow tower over main roads, parking lots and sidewalks, the legacy authorities battle to ensure frequent snowfalls do not muffle the city's economic heartbeat.

When it comes to snow removal, Montreal is perhaps the best drilled city in the world.

As the snow starts to fall, the city deploys an armoured division of snow blowers, trucks and ploughs to trundle around its streets.

Around 360,000 cubic metres (12.7 million cubic feet) of snow are dumped each winter on the city -- and until 2000, most of that ended up sooner of later in the St Lawrence river.

"That's the way we did it because that was the easiest way to get rid of the snow," said Colin Bilodeau, Service Engineer for Environment Quebec.

"We did that on a very large scale."

But now, in more environmentally sensitive times, it is forbidden to dump snow in the river.

While no formal study has been done on the impact of soiled snow on the river's wildlife, scientists who analysed snow drifts here in 1985 found what was scraped off the streets was much more than just common or garden H2O.

Even before it floated to the ground, snow was contaminated by air pollution, the study found.

And that initial pollution got a lot worse once the snowflakes took their spot in the brown mucky sludge piled by snowploughs at the sides of streets.

Snowbanks suck up gravel, grass, fuel, garbage, paper and engine lubricants as well as metallic compounds like iron and lead spewed out of car exhausts.

And it is not unusual to find other treasure after a sudden snowfall.

When snowblowers get to work "we often find grocery shopping and even blocks of cement buried beneath the drifts," said Bilodeau.

After trying to convince municipalities not to dump snow in water supplies, the provincial authorities started to take enforcement measures in 1997, giving local regions four years to clean up their act.

In Montreal, trucks today dump snow in specially nominated sites where impurities can be hosed out with used water.

In Cap Rouge, near Quebec City, they have gone a little further, developing a heated reservoir, powered by solar energy to melt the snow, before the residue is sent through the sewer system.

TERRA.WIRE