The ‘elephant in the room’ hardly surfaces when searching for the cause of toxic levels of salt reaching our waterways. But this article clearly exposes the process. Above is a diagram and text below is an extract:

From Roadways to the River

Michigan, like many states in the Northeast and Midwest United States, is a heavy user of rock salt during the winter months to de-ice roads. While salt water has been applied to prevent public roads from freezing since at least Victorian times, the practice was first applied to modern pavement in New Hampshire in 1938. Within three years, industrial spreaders were being used for dry surface salting and gritting with a total of 5,000 tons of salt being spread on highways nationwide. Today, it’s estimated that upwards of 22 million tons of salt are scattered on US roads annually.

The reason road salt works to de-ice roads is pretty simple. Sodium chloride — or NaCl, the ionic compound that makes up both table salt and pure road salt — is very soluble in water. When it dissolves, it breaks apart into two distinct ions (Na+ and Cl-). These particles disrupt water’s ability to form crystalline ice, lowering the freezing point in proportion to the number of ions floating around. This keeps going until the salt concentration hits about 25%, at which point the freezing temperature of the solution cannot go any lower. Different ionic compounds can be used (calcium chloride is a popular choice when it’s too cold out for sodium chloride to do its thing effectively!), but rock salt has proven cheap and readily available. While this is great for improving driving conditions, it’s unfortunately not so great for the environment.

Rock salt is loaded at a facility near Detroit, Michigan; the city has its own rock salt mine. PHOTOGRAPH BY PAUL SANCYA, AP. Via National Geographic.

When salt is on the road, birds often mistake the crystals for seeds or grit, resulting in toxicosis and death. Deer are also attracted to roads to eat the salt crystals, leading to higher incidents of vehicular accidents and wildlife kills. As warmer temperatures arrive and snow begins to melt, salt splashes and sprays off to the side of the road, entering the soil. Through ion exchange, sodium (Na+) stays within the soil and releases other ions such as Calcium (Ca), Magnesium (Mg), and Potassium (K) into the groundwater, damaging foliage. Runoff washes down storm drains and into reservoirs, endangering sensitive aquatic communities and reducing species diversity.

Although road salt pollution is usually a bigger issue for the surrounding environment and (non-human) organisms that live in it, it can become a real problem for human beings when it comes up against our infrastructure. Chloride (Cl-) from dissolved salt accelerates corrosion, eating away at bridges, power line utilities and parking garage structures — or in the case of Flint, the plumbing that carries their drinking water.

Many countries in the Northern Hemisphere suffer from snowfall and ice which cause many threats to the economy, car crashes, transportation issues of all kinds and danger to life. The cheapness of rock salt to make life easier and safer has been an attractive solution. But now we see we have an anthropogenic action which has caused major crises to our infrastructure, our water supplies and the health of our environment in general.

The ‘best’ sources of quality rock salt production are found in China and the US. Many countries export rock salt, but do not need it themselves, such as Egypt. Germany and Austria have the longest history of salt production. Quebec and Ontario in Canada are big producers. Some countries in South America, such as Brazil are also producers of rock salt. It is a big earner.

A seller of rock salt provides an idea of costs when wishing to procure some for home or city wide use. It may be a country with a high need can produce its own supply, such as Canada. Here in Scotland, where there can be a reasonably high need in winter, there are companies who provide rock salt who compete for contracts with local councils. Here is an example in the UK.

It is about time we phased out the use of rock salt. I realise the loss of income to some economies will be a problem, but it is like supplying arsenic to kill ourselves.

People are trying to address the problem. Read here for example:

Why You Should Consider Using Rock Salt Alternatives

It’s true that millions of tons of rock salt are used each year, but that doesn’t mean that it should be the first item you reach for when looking for a way to improve safety around your home or business.

There are many other products that are even faster acting and more efficient at breaking down snow and ice than traditional rock salt. Because they work so quickly, less of the material is actually needed, leaving less of a footprint on the environment and saving you money.

Even when these other options are combined with rock salt you will be making a positive impact.

But these alternatives have problems all of their own. States in America are trying to find alternatives as the understanding of the disastrous use of rock salt is made apparent on a daily basis.

North America is trying here, but we are a long way from a world wide solution.

Few cities anywhere in the country have as challenging a confluence of winter conditions as Duluth, where steep hills, heavy snowfalls and lake-effect wind and moisture test road maintenance crews.

The Minnesota Department of Transportation has been experimenting with potassium acetate as an alternative to road salt on some of the area’s most heavily used bridges, tunnels and traffic routes near downtown Duluth.

Chris Cheney, maintenance operations superintendent for the department’s Duluth district, said the chemical has shown some promise. It’s better at melting ice in cold temperatures, he said. Salt isn’t effective at melting ice when the temperature falls below about 15 degrees.

Potassium acetate is a liquid solution and costs about three times as much as road salt, Cheney said. But crews are using much less of it than they do road salt, so the cost ends up being about the same, he said.

The environmental impacts of potassium acetate are still unclear. Unlike chloride, the chemical eventually breaks down in the environment, Asleson said, but lab tests have shown it’s toxic to aquatic insects. She said more research is needed.

Connie Fortin, a consultant who trains maintenance crews on smart salting techniques, said there’s no “silver-bullet” de-icer that will replace road salt.

“I think our biggest savings will be in just waste reduction,” Fortin said. “So don’t overapply. Apply it so that it stays on the road.”

We spend billions landing the Rover on Mars, but we cannot allocate appropriate amounts to this urgent problem which has been highlighted by the Flint unfolding story.