Eco-living: Shocker number one, grit doesn't contain any grit. It's rock salt.

WHEN did you last see a unicorn? I saw one just the other week staring back at me from the mirror. OK, so it wasn't a real unicorn, it was just me holding a giant icicle to my forehead.

Did you have icicles hanging from your guttering? Mine disappeared when my live-in handyman decided the time had come to clear the snow from the roof. I was happy to leave it in situ, seeing as it seemed to be displaying marvellous insulation properties, but the way it was melting through the roof into the house was a bit perplexing.

During this snow-clearing exercise I was delegated the job of ladder holding. This was fine until the icicles started raining down. Would they penetrate my skull if they scored a direct hit? What if I looked up at the wrong moment and got impaled through the eyeball?

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I survived, and the unicorns' horns are no more. Having emerged physically if not mentally unscathed by the Big Freeze, my thoughts turned to the environmental impact of the snowy weather.

Alas, this subject is too vast and full of contradictions. Fewer people were able to drive, hooray! Everyone turned up the heating, boo! So instead we'll focus on one solitary topic: grit.

Shocker number one, grit doesn't contain any grit. It's rock salt. (You knew that already, but here in the sheltered world of unicorns we don't really do science.)

The UK's rock salt supply comes from Cleveland, County Antrim and Cheshire and its primary use is not melting ice on the road but rather producing chlorine gas. Which is used to make PVC. Don't say you never learn anything in this column. We know that PVC isn't the most eco-friendly material but what about using plain old rock salt on the roads?

According to the Environment Agency: "Plants and animals show a wide range of tolerance to chloride and some, which live in saline lakes or coastal rock pools, may be extraordinarily resistant to very high concentrations."

Crabs don't need to worry one little bit about runoff from the roads then. Freshwater fish and amphibians may be a touch more sensitive (as you'll know if you've ever used salt to deter slugs). But as gritting is so infrequent (don't we just know it), exposure is "likely to be low" and any runoff tends to be well diluted.

I came across someone having a rant on a blog about gritting causing coastal plants to migrate inland. I thought this was sci-fi nonsense until I read on the EA site that plants usually found in salt marshes can in fact be found on roadside verges where there's been extensive runoff from rock salt. Fascinating. Other plants and trees don't respond quite so well to a long drink of salty water – they die. As for moose, they flock the salty roads for a lick, potentially causing traffic accidents. What do you mean there aren't any such creatures in Scotland?

What are the alternatives to rock salt? Some swear by wood ash from the fire, although I doubt we've got enough of that to keep trunk roads open. Snow chains are popular in perennially icy countries but by all accounts would grind up our less sturdy roads. Snow tyres seem feasible but, as with councils allocating grit budgets for the year ahead, how many of us are willing to invest in something we might not need? On balance, the road safety and economic benefits of salting the roads appear to outweigh the environmental worries. It also allows those who've begun to think icicles are unicorns' horns to get into the car and drive back to reality.

• This article was first published in Scotland on Sunday on 24 January, 2010