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If you live in snowy climes, you probably have a generally positive attitude toward the trucks that salt the roads since driving conditions are typically safer afterward.
The phrase “salting the Earth,” on the other hand, has a decidedly crueler connotation from antiquity—destroying cropland in a way that ensured food could no longer be grown.
Although no ancient civilization probably ever pulled off the logistical feat of intentionally salting a conquered people’s lands, our modern ones may be doing it unintentionally.
Those friendly snowplows (and your sidewalk-shoveling neighbors) are spreading an astounding volume of salt, and it has to go somewhere once it melts.
Road salt became common in the 1940s, and the amount used has increased over time.
The US puts down around 18 million tons of salt each year. Roadsides along highways obviously get dosed with more than their fair share of salt, but salt also runs off (sometimes via storm drains) into streams and lakes where it can accumulate.
That makes road salt a common target in local efforts to protect bodies of water.
Although this has sometimes been studied on the local scale, there hasn’t been much big-picture analysis.
A new study led by the University of Wisconsin-Madison’s Hilary Dugan works to fill in that gap by estimating how widespread salt contamination is in North America.
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