ST. LOUIS — The runoff from years of salting the roads could be affecting the Mississippi River. Currently, chloride is a pollutant found in the river, and the Missouri Department of Natural Resources (MDNR) states on its website that the pollutants are getting worse as the years go by, adding that salt is now part of the problem. 

Chloride poses a significant risk to Missouri’s freshwater lakes and streams. Because chloride does not degrade or settle out of water, prevention is the only option. As a result, lakes and streams are becoming more salty. At high concentrations, salt, and especially the chloride part of salt (sodium chloride), is bad for fish and other aquatic life. Five liters of water are polluted by one teaspoon of salt.

“It is true that road salt used to melt snow can be carried away by runoff and end up in streams that flow into the Mississippi River and add to the amount of chloride in the river,” said Mike Kruse, Environmental Program Supervisor, Total Maximum Daily Load Unit.

He goes on to say that because the Mississippi River is so big, this extra chloride is often diluted and doesn’t cause Missouri’s water quality standards to be broken. 

The Missouri Water Quality Standards Regulations (10 CSR 20-7.031) say that 230 milligrams per liter (mg/L) of chloride is a safe level to protect aquatic life from long-term toxicity and 860 mg/L is a safe level to protect aquatic life from immediate toxicity. 

Chloride is found naturally in lakes and streams, and many animals need it to do important things for their survival. But high levels can cause cells to lose water and nutrients, which can kill fish, amphibians, plants, and other aquatic animals. Excess chloride on land can harm pets, soil, cars, bridges, and other structures.

Kruse said that even though the amount of chloride in the Mississippi River doesn’t go over these limits, some urban streams in the St. Louis area that flow into the river have spikes of chloride that go over these limits during deicing. 

“These streams also experience year-round elevated levels of chloride, but below chronic criteria,” said Kruse. “According to the information we have, the highest levels of chloride in the Mississippi River in Missouri can be found just below St. Louis.”

MDNR has some helpful tips to lessen the chloride pollution:

When clearing snow from walks

  • Apply a liquid deicer before it snows to prevent snow and ice build up.
  • Shovel, snow blow, plow and sweep early and often. The more snow and ice removed, the less salt needed.
  • Less is better. A coffee mug full of salt is adequate for a 20-foot driveway or 10 sidewalk squares. If leftover crystals are visible, the salt has been over-applied. 
  • Use a handheld spreader that applies salt consistently.
  • Wait for warmer weather. When ground temperatures are below 15 degrees F, it’s too cold for ordinary sodium chloride to work. At those temperatures, it’s better to use sand.
  • Use the right deicer. Calcium chloride works at much lower temperatures than sodium chloride.
  • Sweep up extra salt. If it is visible on dry pavement, it is not doing anything and could be washed into water.


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