As winter storms roll through, salts are constantly used to deice roads, parking lots and sidewalks to keep people safe in the winter conditions.
However, new research shows that these salts are contributing to a widely rising problem across the United States: Rivers and streams across the U.S. have become saltier and more alkaline over the past 50 years. Alkaline is defined as having a pH greater than 7 and is less acidic.
A recent study led by a team of University of Maryland (UMD) researchers published these findings on Monday, Dec. 3, in the journal Philosophical Transactions of the Royal Society B: Biological Sciences.
Road deicers are one of the contributors. Fertilizers, salt-heavy diets and other salty compounds that humans indirectly release into waterways also contribute to this condition.
Salty, alkaline freshwater can create big problems for drinking water supplies, urban infrastructure and natural ecosystems.
One of the most notable examples is the water crisis in Flint, Michigan, which shed a light on the growing issue. The city switched its primary water source to the Flint River in 2014, which was highly polluted with salts.
The river’s high salt load combined with the chemical treatments made the water more corrosive. The interaction of the corrosive water and the water treatment caused lead to leach from the water pipes, thus creating the city’s well-documented water crisis.
The same UMD-led team of researchers released a related study in January 2018 that coined the term, “Freshwater Salinization Syndrome.” It was the first study to assess long-term changes in freshwater salinity and pH levels at the continental scale.
The study used data recorded at 232 U.S. Geological Survey (USGS) monitoring sites across the country over the past 50 years. The analysis shows significant increases in both salinization and alkalization.
The study results also suggest a close link between the two properties, with different salt compounds combining to do more damage than any one salt on its own.
The team created the name ‘Freshwater Salinization Syndrome’ because they realized it’s a suite of effects on water quality, with many different salt ions linked together. They didn’t know that before, said Dr. Sujay Kaushal, a professor of geology at UMD and lead author of the study.
“We used to think that when you put salt into a watershed that the salt would wash away and go downstream. Then about 15 years ago, we published the first paper that showed that the salts actually stuck around,” Kaushal said.
The salts were accumulating in soils and groundwater and increasing over time, contributing to long-term trends increasing trends downstream in rivers, lakes and reservoirs. At this time, they first proposed that this was going to be a safe drinking water issue.
“In our recent studies, especially this last study, it really kind of nails it home. Not only does it salinize the drinking water itself, but it also causes the release of all these mixtures of chemicals like the metals, nutrients and other elements that can cause all kinds of different water quality problems,” Kaushal said.
“They’ve even found that the salt releases radium, which is radioactive, and so it’s a much bigger problem than we ever anticipated 15 years ago,” he said.
The more recent study takes a closer look at the global, regional and local consequences of Freshwater Salinization Syndrome. The group found that salty, alkaline freshwater can release a variety of chemicals, including toxic metals and harmful nitrogen-containing compounds, from streambeds and soils in drainage basins.
The results further suggest that many of these chemicals travel together throughout watersheds, forming “chemical cocktails” that can have more devastating effects on drinking water supplies and ecosystems when compared with individual contaminants alone.
The researchers assessed previously published data from rivers in the U.S., Europe, Canada, Russia, China and Iran, substantially expanding the geographic boundaries of the researchers’ previous work.
Their analysis suggests that Freshwater Salinization Syndrome could be a global phenomenon, with the most conclusive support showing a steady trend of increased salt ions in both U.S. and European rivers. These trends trace back at least 50 years, with some data reaching back far enough to support a 100-year trend, according to their research.
“The chemistry is changing very rapidly and is becoming more widespread. It is surprising to me how widespread these changes are occurring,” said study co-author Dr. Gene Likens, president emeritus of the Cary Institute of Ecosystem Studies and a distinguished research professor at the University of Connecticut.
During the snowy, wintry months, states in the mid-Atlantic and Northeast apply road salts to the ground. And this is a primary cause of Freshwater Salinization Syndrome, according to the study.
The team monitored the chemical consequences of road salt by performing detailed field studies in streams located near Washington, D.C., and Baltimore.
“Salt concentrations during the snowstorm were surprisingly high–it was like we were analyzing sea water. But we weren’t expecting such a high corresponding peak in metals,” Kelsey Wood, a geology graduate student at UMD and a co-author of the study said in the press release.
Salt ion concentrations can stay high for months following a storm. This lengthens the amount of time that salt can draw metals from the soil, resulting in harmful cocktails of metals and salts transported far downstream.
“Looking at water quality data over several months in the winter, salt remains high and rarely has a chance to return to baseline before the next storm comes through and more salt is put on the roads,” Kaushal said in the press release.
The group’s latest work highlights the need for new and more comprehensive regulation and pollution management strategies.
“The bottom line of our findings is that when humans add salt to waterways, that salt also releases a lot of dangerous collateral chemicals,” Kaushal said in the press release. “It’s clear that regulatory agencies need to find new ways to address these ‘chemical cocktails’ released by saltier water, rather than looking at individual freshwater pollutants one by one.”
Salts are not currently regulated as a primary contaminant in freshwater and the team is arguing that it should be, Likens said.