When the weather takes a wintery turn, many cities and municipalities in North America rely on rock salt to deice their roads. Rock salt helps keep roads safe by reducing accidents, but it can also have serious, negative effects on aquatic ecosystems.
Marshes, streams and lakes lie alongside many of the roads and highways that zigzag across North America. Plants and animals inhabit these water bodies and can be exposed to many of the substances we put on those roads.
Rock salt is similar to table salt, made up of sodium and chloride, but coarser. It dissolves quickly on the road, leaving the chloride to flow into nearby waterways.
At low concentrations, chloride is relatively benign. But as concentrations rise, it can be toxic and fatal to aquatic wildlife, including plankton and fish. These ecological changes affect water quality.