Road Salts an Environmental Concern

Frigid temperatures and large volumes of ice and snow make winter driving conditions in many parts of Canada treacherously slippery. To help make travelling safer, an estimated 4 732 kilotonnes of road salt and calcium chloride are used to de-ice our highways each year. Unfortunately, salt-laden runoff from melting snow can contaminate small nearby lakes, streams and ponds, causing serious concerns over its impact on the plants and animals that live in these bodies of water.

While high levels of road salt have already been proven to have adverse effects on the health of aquatic organisms such as fish, much less is known about the impacts on the benthic, or bottom, layer of aquatic ecosystems. To learn more about this part of the aquatic environment, scientists at Environment Canada's National Water Research Institute in Burlington, Ontario, carried out a benthic study at the Rouge River detention pond in Scarborough, Ontario.

The Rouge River Pond receives runoff from a major multi-lane divided highway (the 401), another smaller highway, and a large urban catchment, and had been identified in previous studies as having elevated salt concentrations in its water column. Although the pond is an engineered structure designed to manage flow and treat stormwater, like many other ponds in urban areas it serves as important habitat for many species of plants, mammals, birds and amphibians.

To find out how elevated salt loadings affected the chemistry of the sediment porewater—the water that fills spaces between the solid sediment particles on the floor of the pond—and to identify impacts on benthic invertebrates, researchers gathered and analyzed samples of the porewater and carried out toxicity tests using a shrimp-like benthic invertebrate, Hyalella azteca.

Their results revealed that when salt-laden water enters a pond or lake it sinks to the bottom and prevents the normal water-mixing process, thereby depriving benthic organisms of a fresh supply of oxygen. The water within the sediments can also attain high concentrations of salt, which, in turn, increases the concentration of heavy metals, such as cadmium, in the porewater. Results of tests on Hyalella azteca showed that the porewater itself was highly toxic, and suggest that the toxicity was caused by metals rather than high levels of chloride.

Although much remains to be done to isolate the specific factors that contribute to porewater toxicity in small urban water bodies, the Rouge River Pond study is an important step toward determining the impacts of road salt on aquatic ecosystems most at risk. These findings are also an important contribution to the body of scientific work currently being carried out to determine whether or not road salts should be considered toxic substances under the Canadian Environmental Protection Act (CEPA).

Results of the CEPA assessment are scheduled for release for public comment in June, and the assessment is to be completed by the end of 2000. Should road salts be identified as toxic, discussions would then follow to identify appropriate measures to mitigate environmental risks, such as reduced usage or complete bans in highly sensitive ecosystem regions.

In order to maintain public safety levels on the nation's highways, Environment Canada is already working with Transport Canada and the provinces on road weather information systems—automatic weather stations that use specialized sensors embedded in the road to measure surface temperature, wetness and residual chemicals. Meteorologists use these data to produce pavement temperature forecasts which, in turn, enable road crews to better plan their winter maintenance operations. These techniques have been shown to increase the safety and efficiency of the road network, while at the same time reducing the use of de-icing chemicals.

Sites web connexes: Participation Canadienne au Mesoscale Alpine Programme RELATED WEB SITES: Polar Bear's Banquet: Article in November/December 1999 issue of Canadian Geographic magazine Environment Canada's Canadian Ice Service.

  Home |  Air |  Atmospheric Science |  Climate Change |  Environmental Action |  Habitat |  Pollution |  Species at Risk |  Technology |  Water |  Weather |  Wildlife