Road Salt Contaminates U.S. Waterways in Northern States Year Round
By Brian Bienkowski
As winter sets in across the northern U.S., the road salt that keeps people out of ditches is flowing into rivers at levels that could harm fish and other creatures.
With billions of pounds of salt spread on U.S. roads every year, waterways in the nation’s wintry cities are getting saltier. And, according to new research, the salt—or sodium chloride—in rivers remains toxic not just in winter, but throughout two-thirds of the year.
Photo courtesy of Shutterstock
In icy Wisconsin, where salt is liberally dumped on roads, the Menomonee and the Kinnickinnic have chloride levels in late winter and early spring 10 to 15 times higher than a federal level set to protect fish, amphibians and tiny crustaceans. Toxic concentrations also have been found in rivers, streams and lakes in New York, Maryland, Minnesota, Missouri and several other states.
“It’s likely that many of the organisms in rivers that are sensitive to chloride are simply no longer there,” said Steve Corsi, a research hydrologist with the U.S. Geological Survey (USGS).
Seven of 20 U.S. rivers—four in Wisconsin, one in Ohio and two in Illinois—have average chloride levels that approach or exceed the U.S. Environmental Protection Agency’s guideline for protecting aquatic life, according to the USGS study, which is not yet published. All seven rivers exceeded it on more days in 2006 than in 1991.
The salt stays in rivers and groundwater for years after it’s tossed on roads, said Sujay Kaushal, an associate professor at the University of Maryland who studies road salt in Northeast U.S. streams.
In addition to posing a threat to wildlife, the salt can leach into groundwater, contaminating drinking water supplies.“Even if they quit applying salt now, it would take decades for it to be removed from the system,” Kaushal said.
Yet road salt is considered a necessity in northern states. It is the most efficient and economical way to keep people safe in the winter, said Morton Satin, a vice president at the Salt Institute, a non-profit trade association that advocates for salt.
“We have chosen to live in a northern climate, where we want the same safety in the winter that we have in the summer,” Satin said. “Amazon has to deliver the same packages even when the roads are bad.”
More than 116,000 people in the U.S. are injured and more than 1,300 killed on snowy or icy pavement each year, according to the U.S. Department of Transportation. Road salt reduces snow-induced crashes by about 88 percent, says a Marquette University study.
Salt lowers the freezing point of water, preventing ice and snow from sticking to roads. In addition, cyanide compounds, which also can be toxic, are often added to road salt to prevent it from caking.
The volumes used on U.S. roads have increased each decade since the 1940s. About 617 million pounds were sold per year in the 1940s, and now roughly 35 billion pounds per year.
Some cities, including Madison and Milwaukee, have experimented with beet juice, sand and other “greener” ways to keep ice off roads. But most deicers still contain some chloride, Corsi said. “You may not need to apply as much of them, but they’re way more expensive.”
In Minnesota, the salinity of 39 lakes has mirrored the upward trend of the state’s purchase of road salt. If this trend continues, salinity will double in these lakes in about 50 years, according to University of Minnesota scientists.
In the new USGS research, the rivers were saltiest in the late winter. But the Menomonee and the Kinnickinnic had high concentrations in the summer, too, Corsi said.
“Chloride is very soluble and it’s easy for it to infiltrate the groundwater, the source of the river flow,” said Corsi, who was lead author of the study.
The new findings build on previous USGS research that found that more than half of sites tested in 13 U.S. cities exceeded the EPA’s chloride guideline of 230 parts per million, according to a 2010 USGS study. That guideline is based on chronic exposure levels that reduced the survival of water fleas, rainbow trout and fathead minnows.
Streams tested in Maryland, New York and New Hampshire were “well beyond” the toxicity guideline, Kaushal said. In Missouri, an urban stream, Hinkson Creek, had high levels of chloride linked to reproductive and survival problems for water fleas.
Some of the creatures most sensitive to chloride are amphibians, which are declining worldwide from a variety of environmental threats.
"Road-side aquatic ecosystems in North America are annually polluted with millions of tons of road deicing salts, which threaten the survival of amphibians which live and breed in these habitats,” Utah State University researchers wrote in a study published earlier this year.
Newts exposed in the Utah laboratory to amounts of salt commonly found in roadside streams had severe developmental deformities– bent tails, bent bodies, cysts, missing tails and gills, two heads and shrunken heads.
Also, salamander eggs develop abnormally when exposed. They cannot retain the water needed to avoid freezing and disease.
Wisconsin does not regulate road salt use, and the levels showing up in the state’s rivers are concerning, said Tim Asplund, a monitoring section chief with the Wisconsin Department of Natural Resources.
The state agency, which has been monitoring 42 river sites since the 1980, has found increasing chloride concentrations.
“There are other contributors to chloride concentrations … wastewater treatment facilities, industrial discharges,” Asplund said. “But it’s very likely due to road salt.”
Satin said the salt industry has long known its “biggest long-term problem would be chloride running off into water.”
There are ways to minimize the runoff impact, he said.
“We encourage people to only use the lowest amount they need,” Satin said. “Also, as a country we have not re-engineered our road system in 50 years, we need to take runoff into account in our road design.”
Kaushal agreed, saying that ensuring protection of wetlands and vegetation “provides some line of defense before things get into the river.”
“We need to ask ourselves if we should really be putting more highways, parking lots and houses right on top of rivers,” Kaushal said.
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EcoWatch Daily Newsletter
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For centuries, the delicate silver dove has been a symbol of love and fidelity.
Biodiversity and Habitat Loss<p>Their near extinction is a symbol of the <a href="https://www.dw.com/en/global-biodiversity-outlook-targets-extinction-summit-new-york-pledge/a-54932895" target="_blank">biodiversity crisis</a> in the UK, largely driven by habitat destruction. Britain is now one of the countries with the most <a href="https://www.wwf.org.uk/future-of-UK-nature#:~:text=The%20UK%20is%20one%20of,than%20half%20are%20in%20decline" target="_blank">depleted nature</a> in the world according to the World Wildlife Fund. Half its plant and animal species are in decline and more than <a href="https://www.rspb.org.uk/about-the-rspb/about-us/media-centre/press-releases/let-nature-sing-wales/#:~:text=a%20natural%20tragedy.-,Over%2040%20million%20birds%20have%20vanished%20from%20UK%20skies%20in,unaware%20of%20the%20impending%20danger" target="_blank">40 million birds</a> have vanished in just half a century.</p><p>"[Turtle doves] are the canary in the [coal] mine because there are all these other species before it and after it," said Tree. "It's an umbrella for all the other species that are heading that way."</p><p>Turtle doves migrate south through Europe to sub-Saharan Africa between July and September, ending up in dry woodland and farmland areas of countries like Mali and Senegal for winter. </p><p>Droughts in West Africa and the Sahel region are believed to have contributed to the fall in turtle dove species recorded in northern Europe, with low rainfall reducing supplies of the seeds and insects the birds rely on for energy for the long journey home.</p>
Conservation and Farming<p><a href="https://www.operationturtledove.org/" target="_blank" rel="noopener noreferrer">Operation Turtle Dove,</a> a partnership project of charities including the Essex Wildlife trust, works with landowners and farmers to actively build turtle dove habitat.</p><p>Outten works with <a href="https://www.ebws.org.uk/birdsites/blue-house-farm-ewt-north-fambridge" target="_blank">Blue House Farm</a>, a 660-acre nature reserve in the UK county of Essex, where they have replicated weedy fallow plots. </p><p>"We work on it every year to make sure it's in the condition it needs to be with plants such as clovers and black medic," Outten said. "These plants are native to the landscape and produce the seed the birds feed on." </p><p>The birds eat a wide range of seeds from various plants that would have been abundant 50 or 100 years ago, added Guy Anderson, program manager for species recovery with The Royal Society for the Protection of Birds (RSPB). </p><p>"But it's simply true that with the gradual process of <a href="https://www.dw.com/en/farming-without-pesticides-how-can-we-make-agriculture-greener/a-52216796" target="_blank" rel="noopener noreferrer">intensifying our agricultural production</a>, the availability of those seeds has dropped and dropped," said Anderson.</p><p>Part of the project includes supplementary feeding — providing sources of food in the form of seed or grain. Under the Countryside Stewardship Scheme in England, farmers can receive financial support to create a turtle dove habitat. </p><p>Though they haven't recorded an increase in doves across the sites in the four years of working on the project, Outten said they are seeing improvements in how landowners and farmers manage habitat for the birds. </p>
A Turtle Dove Haven<p>The 3,500-acre Knepp Estate in West Sussex is another project taking a different approach and one of the few places where turtle dove numbers are increasing.</p><p>Isabella Tree and her husband Charlie Burrell converted their intensively farmed land into a rewilding project almost 20 years ago. They have let the land return to nature.</p><p>Just one year after they'd finished <a href="https://www.dw.com/en/uks-most-talented-architects-are-not-human/a-35952128" target="_blank">rewilding</a> the southern part of their property, they heard turtle doves for the first time. It's now a breeding hotspot for the birds with an estimated 19 pairs. Knepp is also home to <a href="https://www.rewildingbritain.org.uk/rewilding/rewilding-projects/knepp-estate" target="_blank" rel="noopener noreferrer">2% of the UK's population</a> of nightingales. </p><p>Tree is critical of supplementary feeding schemes that, in her view, are short term. She questions the chances of turtle doves getting to feed on scattered seeds before other mammals eat them first.</p>
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