When you think of salt and water, the first things that probably pop into mind are either the beach or gargling a heavily salted concoction to stave off a sore throat. Either way, one of the first images that doesn’t pop up - at least for me - is salted winter roads:
When it snows or gets icy, towns will blanket roads and sidewalks with those little chunks of salt to prevent slick spots while walking or driving. But what is put on land doesn’t stay on land. When salt is put on pavement to prevent slick spots, after it’s done it’s job of preventing those slick spots - it has to go somewhere. And that end destination is often our freshwater.
This episode discusses a concept that’s starting to garner some well deserved attention: our inland bodies of water (streams, lakes, ponds, rivers) are getting saltier. This is called salinization, as the water gets saltier. Although this sounds like a distant, foreign topic, it’s actually been suggested as the cause of lead leaching in Flint, Michigan. But what’s causing it, what does it mean for the environment, and why does it matter to you?
Ok, so let’s start at the beginning: streams do naturally have some salt in them, but are receiving way more of it than they’re accustomed to, especially after storms. All because of runoff - water sweeps down asphalt roads or sidewalks, picks up the salt, and dumps it into the body of water it eventually flows into. Like a salty, accumulating snowball.
Stream salinization has the potential to wreak havoc for humans. To see this, all you have to do is look at what happened in Flint, Michigan.
Starting in April of 2014, the residents of the city of Flint were exposed to lead levels dangerous to human health, through their water supply. But what spurred this dangerous lead leaching? In sum, what started it all was a combination of economics and negligence. You see, Flint was broke - and under Michigan law, an emergency manager was appointed to help balance the books and bring the city back ‘out of the red’. One potential solution to their financial woes: adjusting their water supply.
They decided to switch from Detroit water - some of the best drinking water - to the Flint River, and use a treatment facility that hadn’t been in operation in decades. So the problems begin to accumulate fast - switching to a new water source, with new water chemistry, on a tighter budget, and switching back to an old, outdated treatment facility.
But what made the river water so corrosive that it led to massive amounts of lead leaching wasn’t just the fact that industry was dumping some of the byproducts of production into the stream. Instead, it was that much less sinister sounding suspect: salt.
High chloride levels in Flint River meant the water was very corrosive - leading to the corrosion of the pipes that transported drinking water to people’s homes. Because Flint was broke, they hadn’t implemented corrosion control. Corrosion control works by creating the natural buildup of mineral deposits lining the insides of pipes, which prevents the exposure of the pipes to corrosive contaminants found in surface water (and found in especially high concentrations in the Flint River).
I asked some scientists looking at the issue about the solution to freshwater salinization. One thing, they all suggested, was simply: dump less salt.
Remedying this problem isn’t just a function of putting less salt, however; it goes deeper than that. It’s about spreading the awareness that our actions on land influence what happens in our waterways. We don’t act in a vacuum; the things we put out in the environment - whether it be salt, fertilizers, oil spills, or medicine - often end up in our local streams and rivers after rains wash them away. They can end up in the same rivers and streams that we frequently look to for drinking water.
The saying is that you shouldn’t, well, poop where you eat ... what about where you drink?
If you’d like to read more about freshwater salinization, here is an open access (read: free) research article to check out by Kaushal et al. 2018.
Special thanks to Anurag Mantha for describing the science behind the Flint water crisis.