As awareness for pollution increases, other forms of pollution are defined. Almost everyone knows about toxic waste and carbon dioxide pollution, but not many people have heard of salt pollution. Salt pollution has been on the increase since the evolution of the automobile. With more pressure on government agencies to keep the highway clear and safe, an increase in the use of salt has developed. It is important to understand why salt is used and how it work as well as the environmental effects to understand the salt pollution problem.
Salt is a necessary and accepted part of the winter environment. It provides safety and mobility for motorists, commercial vehicles and emergency vehicles. Salt is used as the principal deicer because it is the most available and cost-effective deicer. Rock salt is preferred because it is cheap and effective. It costs 20 dollars a ton where as an alternative like calcium magnesium cost around 700 dollars a ton. Some 10 million tons of deicing salt is used each year in the U.S. and about 3 million in Canada.
Salt is used to keep snow and ice from bonding to the pavement and to allow snowplows to remove. When salt is applied to ice and snow it creates a brine that has a lower freezing temperature than the surrounding ice or snow. Salt is the ideal deicing material because it is:
the least expensive deicer
easy to spread
easy to store and handle
harmless to skin and clothing
Salt pollution is broken into two main groups. Water, which includes the effects on ground water, surface water and aquatic life and land.
Most of the salt applied to the roadways eventually ends up in the ground water. It is estimated that 30% to 50% of the salt used travels into the ground water. Salt effect two areas of ground water, chloride concentration and sodium concentration. Chlorides may be present in the form of sodium chloride crystals or as a ion in a solution. Normal concentrations in the water are average around 10 mg/litre. Concentrations found in ground water near major highways have been recorded as high as 250 mg/litre which is around the threshold of taste.
The main factor with ground water pollution is the risk to human health. The raised level in sodium in water can cause high blood pressure and hypertension. With people who already suffer from these problem it is necessary to keep their salt intake relatively low, they should not drink water above 20 mg/liter. Although this is recommended, a study of private well water in Toronto showed that half the wells exceeded this limit, twenty percent exceeded 100 mg/litre and six percent exceeded 250 mg/litre. This increase in sodium and chlorine can also cause problem with water balance in the human body.
As well as surface water, ground water is also affected by road salting. Although the effects are not as great as ground water, they still pose problems to the environment. The problems are based on the salt ions. The salt ions interact with heavy metal that fall to the bottom of the body of water. An example of this is when sodium and chlorine ions compete for mercury to bond with. This cause the release of mercury into the water system. The risk of mercury poisoning is far greater than that of sodium or chlorine. This increase of sodium and chlorine as well as mercury and other heavy metal also cause changes in the pH of water.
The increase of salt around bodies of water also effect aquatic life in the area. Two main areas that are effected are osmotic regulation in fish and the death of micro-biotic life in ponds and lakes. Most fish life can only tolerate a narrow range of salt content in the water. The increase of salt in the water produced by road de-icing cause freshwater fish to swell up with water. The increased salt cause a lower concentration of water in the fishes cells. To compensate, the fishes body takes in water to...