De-icing is defined as removal of snow, ice or frost from a surface. Anti-icing is understood to be the application of chemicals that not only de-ice, but also remain on a surface and continue to delay the reformation of ice for a certain period of time, or prevent adhesion of ice to make mechanical removal easier.

Recently, organic compounds have been developed that reduce the environmental issues connected with salts and have longer residual effects when spread on roadways, usually in conjunction with salt brines or solids. These compounds are generated as byproducts of agricultural operations such as sugar beet refining or the distillation process that produces ethanol. Additionally, mixing common rock salt with some of the organic compounds and magnesium chloride results in spreadable materials that are both effective to much colder temperatures (−34 °C or −29 °F) as well as at lower overall rates of spreading per unit area.

Solar road systems have been used to maintain the surface of roads above the freezing point of water. An array of pipes embedded in the road surface is used to collect solar energy in summer, transfer the heat to thermal banks and return the heat to the road in winter to maintain the surface above 0 °C (32 °F). This automated form of renewable energy collection, storage and delivery avoids the environmental issues of using chemical contaminants.

Deicing salts such as sodium chloride or calcium chloride leach into the soils, where the ions (especially the cations) may accumulate and eventually become toxic to the organisms and plants growing in these soils. The chemicals could also reach water bodies in concentrations that are toxic to the ecosystems. Organic compounds are biodegraded and may cause oxygen-depletion issues. Small creeks and ponds with long turnover time are especially vulnerable.

Propylene glycol used to de-ice aircraft can contaminate drinking water supplies and harm aquatic life. Some airports are now capturing and treating de-icing runoff before allowing it to enter waterways.

The toxicity of deicing fluids is an environmental concern, and research is underway to find less toxic (i.e. non-glycol-based) alternatives.[7] Other strategies can be used to minimize the environmental impact such as collecting used fluid and using the maximum dilution consistent with safety.

See also:
http://en.wikipedia.org/wiki/De-ice

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License and Creative Commons Attribution-ShareAlike License.)