Sixteen million tons of sodium chloride was dumped on U.S. roads in 2001. And while all that salt helps keep our roads safe, the salty runoff does have harmful environmental consequences. It stays in water ecosystems for years, possibly drying or killing plants and hurting fish if the concentrations get too high. Other salt dangers are pretty minimal: car manufacturers now dip metal in a zinc sealant to combat salt corrosion and groundwater contamination is rare thanks to better salt-storage and drainage systems. —Sally Atkinson
