U.S. rivers and streams have become saltier and more alkaline over the last 50 years, posing risks to drinking water by damaging pipelines and other infrastructure, according to a study released on Monday.
As municipal workers dump salt on roads to combat ice and farmers put fertilizer on fields, the runoff has made U.S. waterways saltier and more alkaline, according to the study, which examined decades of data recorded from 232 U.S. Geological Survey monitoring sites.
Salt can also be released by floods that reach sewage systems and spill the contamination into waterways, as well as from brines at hydraulic fracturing - or fracking - operations and oil and gas sites.
The salinity makes water more alkaline, or higher pH, by breaking down concrete, rocks in rivers and minerals in soil and water. The release of the contaminants can cause pipelines to corrode and leach lead into drinking water, while zinc and copper can be leached from rocks and soil in streams. The study found that a combination of salts can do more damage than one salt alone.
"Until now we didn't fully appreciate the role that different salts play in altering the pH of streams and rivers of our country," said Sujay Kaushal, a University of Maryland geologist and the lead scientist of the study, published in the early edition of the Proceedings of the National Academy of Sciences. The study also looked at waterways in southern Canada.
Increased salt levels of waterways was a factor in the lead poisoning crisis in Detroit, in which children were found with high levels of the heavy metal that harms nervous systems in their blood.
The study found that 66 percent of stream and river sites have become more alkaline over the last 50 years. Alkaline water can also cause excessive scaling on the insides of water pipes. Some scaling is desirable as it protects metals from leaching from the pipe, but too much can constrict or block pipes.
Water treatment centers cannot filter out salts, but they use chemicals to fight them. The trouble is that floods and snowstorms are episodic, so it can be hard for the centers to determine the correct amount of additives to use, Kaushal said. Using brine instead of granulated salt for de-icing roads and pre-salting roads ahead of snowstorms can reduce the amount of salt used, he said.
(Reporting by Timothy Gardner; Editing by Susan Thomas)