I suppose one of the risks of road salt usage is that if there is semi-arid land downstream of the area that applies the roadsalt, that uses the river water for irrigation, then it puts those farmers at risk.
Not all states use Road Salt. Oregon does not.http://www.subaruforester.org/vbulletin/f76/map-states-use-road-salt-27855/
I believe that Washington does use it in the Puget Sound area, but at least that salt only travels a short distance to reach the Pacific Ocean. Other areas in the country have a much longer downstream impact.
I consider the salt to be extremely destructive, and would hope highway officials would pursue alternatives. A non corrosive liquid de-icer is often used here in Oregon.
I also have refused to use salt de-icers for sidewalks.
I was surprised to see on the map that California is listed as using road salt. If the salt is a problem for the agriculture there, I would think they would prohibit the use of road salt, as well as working with all the upstream states, Nevada, Utah, and New Mexico to find alternatives. (most of Idaho's drainage is northward and their application is listed as minimal).
Apparently Australia has been developing salt tolerant wheat varieties. Perhaps the salt will become a natural herbicide.http://www.sciencedaily.com/releases/2010/04/100423094622.htmhttp://www.sciencedaily.com/releases/2012/03/120311150717.htm
Anyway, compared to the approximately 10 million tons of salt used on the roads in the USA each year, a couple of pounds of salt used along a walkway would be pretty insignificant. However, I wouldn't consider it an optimal solution.