|MadSci Network: Earth Sciences|
Road salt is not necessarily bad for the planet Earth. It can, however, be very bad for the current environment in which we live.
To begin with, salt [chemically: NaCl, a.k.a Sodium(the Na part)Chloride (the Cl part)) is a corrosive substance, which means that it is chemically reactive with other compounds in the environment.
When salt is added to water, it begins dissolving into its ionic components. Specifically, a cation (Na+) and an anion (Cl-). These components are the big troublemakers.
Once salt is applied to a snow and ice covered road, you can sometimes see immediate damage to the environment in the form of salt-burnt plants on the side of the road. When a car drives through the slushy salt solution, it can spray the roadside with large amounts of saltwater. When the salt lands, it begins reacting with other compounds. In this example, they happen to be organic compounds that make up the plant.
The greater problem occurs when large amounts of salt are introduced into ecosystems that cannot readily assimilate it, which effects its accumulation in soil and water. This process can take several years before the accumulations are large enough to be considered a problem.
As salt-laden snow melts and/or is collected for disposal, the resultant meltwater carries the dissolved salt with it. Some of that salt will end up as deposits in surrounding soil, and some of it will end up in larger bodies of water, such as watersheds, wells, lakes and ponds.
Deposited in soil, salt reduces the soil's ability to transport water, which has a direct affect on a plant's ability to take up water. In addition to this, the chloride in the soil may be absorbed by the plant in place of vital nutrients. It may also combine with some of those nutrients, preventing them from reaching the plant.
When salt reaches larger bodies of water and accumulates, it can affect every aspect of the aquatic ecosystem. In watersheds and wells, where many people get drinking water, it can result in increased salt intake. For people with certain medical problems, this is can be very harmful. It would, however, take very high concentrations for this to be a big problem.
In lakes and ponds, salt can affect oxygen levels in the water, which affect aquatic flora and fauna in their ability to take in oxgen. The ions can also give rise to the growth of undesirable forms of algae in the water.
For more information, and more details, please see the following...
From the South Dakota Department of Environment & Natural Resources, Snow Disposal gives a good summary of the harmful effects of salt, as well as the larger issue of snow removal.
From MAD Scientist Archives, a little more on the mechanics of salt and ice:
Re: USING SALT TO MELT ICE
From New Mexico Citizens For Clean Air and Water, a case study entitled Road Salt, Rust, And Dying Trees
Summary Report on Road Salts from the Priority Substances Assessment Program of the Canadian Environmental Protection Act.
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