Decades of road salting is polluting Mississippi River (waterways research)

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EXCERPTS: . . .  Historically, more snow has meant more road salt. It’s an effective way to clear roads — but also brings cascading environmental impacts as it washes into rivers and streams.

[...] Unlike other pollutants, chloride doesn’t break down in water over time. In other words, once it’s in, there’s no getting it out. Just a teaspoon of salt can pollute five gallons of water forever.

So the increase in chloride in the river isn’t from a recent overabundance of road salt being laid down in the winter months. It has built up over decades. And because it doesn’t break down, it’s all headed down into the Gulf of Mexico.

In a forthcoming report on water quality in the upper river, the Upper Mississippi River Basin Association (UMRBA) found that chloride had increased at least 35 percent across the basin between 1989 and 2018. All 14 sites on the river where chloride was measured, plus one on the Illinois River, which feeds to the Mississippi, showed increases in the pollutant during that time period, according to UMRBA data.

At a Wisconsin Department of Natural Resources monitoring site in Lynxville, about an hour south of La Crosse, chloride levels in the river had increased by more than 60 percent since the 1980s, according to a 2021 study from two Mississippi River water quality specialists with the DNR.

[...] Chloride levels are rising at all 43 DNR river monitoring sites across Wisconsin. “It really shows that we’re not on a sustainable path,” said Shawn Giblin, who coauthored the 2021 DNR study. “You can’t keep having 1 to 4 percent annual increases. You’re eventually going to get to chronic toxicity levels.”

The concept of freshwater becoming saltier, known as freshwater salinization syndrome, isn’t unique to the upper Midwest. In November, the U.S. Environmental Protection Agency said its scientists have been studying the issue because of “dramatic” salt concentration increases in freshwater around the country and globally.

Both the EPA and state environmental agencies set limits for when chloride becomes toxic to aquatic life... (MORE - missing details)

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