Re: How is road salt bad for the planet?

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           

And finally...


Summary Report on Road Salts from the Priority Substances Assessment 
Program of the Canadian Environmental Protection Act.

If you have more questions, please feel free to post a follow-up on MAD 
Scientist, or contact me directly.  Thanks for using MAD Scientist.

Joe