During this seemingly endless winter road crews have been in a continual battle to keep streets and highways safe. Their chief weapon: saltwater. It adheres to the pavement better than bouncing rock salt and keeps ice from forming on top of it. But on some roads this salty solution may contain other potentially harmful substances.

Most state transportation departments mix this brine themselves, using either simple salt and water or natural brine extracted from underground deposits. But in states with conventional natural gas and oil drilling wells, spreading the well wastewater on roads can be a cost-saving way to de-ice. This fluid is called produced brine. Because it circulates among deep rocks and contacts various forms of petroleum, the brine can contain radium, lead or other substances that can be harmful at certain levels of exposure. State regulations of produced brine for de-icing purposes vary greatly, and some experts are calling for more rigorous testing for long-term environmental and health effects. READ MORE

This article originally appeared on Scientific American‘s website on March 5, 2015.