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A Pet-Friendly De-Icer?
The Green Guide—Samuel Frank

Leilani Asks The Green Guide
I am looking for a de-icer that is both pet-friendly and easy on the environment. I've searched the web and have come up with a couple of products, one of which contains magnesium chloride, the other containing carbonyl diamide. I have no idea what these are and whether they are really safe. Salt and dog booties may end up being the best way to go, but certainly not the easiest!

Thanks for any advice,


The Green Guide Responds
The best solution is to avoid de-icers and spread sand or, better yet, gravel: They're not neat, and you should sweep up afterward both for reuse and to keep them out of streams, but their environmental impact is minimal. For trouble spots that need de-icer, we've found one, Safe Paw, that is both environmentally sound and pet-safe. However, there are problems with almost the whole range of other de-icers considered below. Many de-icers, including magnesium chloride, can cause leaching of heavy metals from the soil, bringing them to the surface and into the groundwater. Carbonyl diamide a.k.a. urea can release ammonia and nitrates into the water supply. Save any de-icer for the most dangerous spots, where a small amount will serve to release ice from pavement; apply before ice has built up. As a further preventative measure, if an ice storm is predicted, cover key areas with heavy plastic beforehand. Then take the sheeting up as quickly as possible after the storm to avoid it freezing into place.

The most familiar de-icers are chloride salts. That includes table salt sodium chloride as well as magnesium, calcium, and potassium chlorides. There are variations among the chloride de-icers in terms of minimum effective temperature: A standard sprinkling of sodium chloride only works at temperatures of 18 degrees (F) and up, whereas calcium works at 5 and magnesium at -13, and potassium at only 25 and up (though minimum temperature varies with how much you use). These temperatures correlate with effective speeds magnesium works quickly, potassium slowly. Calcium actually releases heat as it reacts, making it effective in extreme cold.

While chloride salts are common, they are also problematic. They corrode concrete and metal, damage vegetation, and irritate the skin of pets, which can even poison themselves while trying to lick their feet clean. Magnesium and calcium in particular can mark carpets and floors; sodium and potassium are less bad. de-icers also add chloride to the water supply, though a Michigan Department of Transportation study of de-icers found that the environmental impact was in most cases not significant. Nonetheless, they can release heavy metals from soil into ground water and deplete oxygen in small lakes. Some manufacturers and users of magnesium chloride claim it to be pet-safe and non-corrosive, though they generally mean some sophisticated mixture that contains magnesium chloride among other ingredients that reduce its activity. Be sure to read the label carefully before purchasing.

Carbonyl diamide, or urea, is posibly the worst choice for deicing. Urea releases nitrate when it enters the water supply, working just as nitrogen fertilizers do to provide algae with nutrients, encouraging algae blooms and choking out other vegetation as well as fish and shellfish. Toxic ammonia is also released when urea reacts with water. Urea and its variants also severely damage metal (though not concrete) and aren't always effective below 20 degrees F. But those are minor points: It's hardly worth hurting our water (and its inhabitants) just to melt some of it.

One better option is Safe Paw, which is chemically similar to urea but contains nitrate-inhibitors that bind its nitrates to soil and keep it out of the water supply. Safe Paw advertises itself as pet-, child-, and environmentally safe. Like urea, it does not contain chloride, and so does not damage concrete, or lawn and garden vegetation; it is safe with skin contact.

Calcium magnesium acetate is a bit of a wild card. Like potassium chloride, CMA works slowly and only at mild temperatures; still, it's a more effective de-icer than urea and lasts longer than most chloride salts. Better, though, is that it doesn't corrode metal or concrete and doesn't harm vegetation. It has an intermediate effect on the water supply. it can temporarily deplete oxygen in small lakes. That is, it's a problem, but not on the scale of urea. Because CMA biodegrades and isn't especially mobile in soil, it isn't a major threat to most groundwater. If you don't have a pet and you live in not-so-cold climes, CMA might be the de-icer of choice. Of course, alternatives to table salt come with a price many multiples higher and are often more difficult to apply (some come in liquid form; some absorb water from the air and thus cake up); CMA is by far the most expensive of the bunch.