Chlorides, sulfates, salinity, and dissolved minerals are all forms of “salts” that can harm fish and plant life at high concentrations. For example, the salt applied to roads, parking lots, and sidewalks during our icy winters contains chloride, a water pollutant. When snow and ice melts and runs into lakes and waterways, the salt goes with it. It takes only one teaspoon of road salt to permanently pollute five gallons of water. An estimated 365,000 tons of road salt is applied in the Twin Cities metro area each year. A study by the University of Minnesota found that about 78% of salt applied in the Twin Cities for winter maintenance is either transported to groundwater or remains in the local lakes and wetlands.
Other chloride sources include water softener discharge, which has increased the amount of salt going to wastewater plants. Wastewater facilities are not designed to remove salt. In addition, elevated concentrations of sulfate from mining operations, wastewater plants, or industrial discharges can negatively affect wild rice. Options for treating “salty discharges” are limited and expensive, making pollution prevention and source reduction very important tools in reducing the threats posed by these pollutants.
Currently, there are 21 lakes, 22 streams, and 4 wetlands in Minnesota that have unacceptable levels of chloride.
Learn more about minimizing salt use on winter pavement:
- For winter maintenance professionals — Resources for salt applicators
- For homeowners and citizens — Snow removal: Do it better, cheaper and pollution-free!
What problems does salt cause?
Drinking water
- 75% of Minnesotans rely on groundwater for drinking water. High amounts of salt in groundwater cause drinking water to taste salty, which could restrict its use for drinking. The cost to remove salt from drinking water using reverse osmosis would be expensive.
- Salt in drinking water is a health concern for people with high blood pressure, or hypertension.
- Chloride can be naturally present in Minnesota's groundwater in varying amounts due to the weathering of rocks and varies greatly across the state. However, additional (non-natural) chloride also enters groundwater from deicing salt, fertilizer, water-softening salt, and septic systems.
- Groundwater flows into streams, lakes and wetlands. If the groundwater contains high amounts of chloride, the organisms that live in surface waters can be negatively affected.
The MPCA groundwater report found that:
- 27% of monitoring wells in the Twin Cities metro area in the sand and gravel aquifers had chloride concentrations that were greater than drinking water guidelines set by the EPA (250 mg/L), likely from winter de-icing chemicals.
- 30% of wells in the Twin Cities metro area had chloride concentrations greater than the chronic water quality standard (230 mg/L).
- The source of high chloride concentrations in the Twin Cities metro area and other urbanized areas is likely from salt applied for winter maintenance.
- For more information check out the full report: The Condition of Minnesota’s Groundwater, 2007-2011 or the summary of key findings: The Condition of Minnesota’s Groundwater, 2007-2011: Summary.
Fish and aquatic bugs
- High amounts of chloride are toxic to fish, aquatic bugs, and amphibians.
- Chloride can negatively affect the fish and insect community structure, diversity and productivity, even at lower levels
- Chloride changes the density of water, which can negatively affect the seasonal mixing of lake waters. Mixing increases oxygen levels required by aquatic life.
Plants
- Direct deicing salt splash can kill plants and trees along the roadside.
- Plants can also be harmed by taking up salty water directly through their roots.
- When chloride flows into streams, lakes, and wetlands, it harms aquatic vegetation and can change the plant community structure.
Soil
- Salt may cause soil to lose its ability to retain water, which could lead soil erosion. Increasing sediments going into surface waters can negatively impact aquatic organisms.
- Excess salt can make soil more alkaline and compact, and less permeable, making it more difficult to store nutrients that plants need to grow.
Pets
- Pets may consume de-icing materials by eating them directly, licking their paws, or by drinking snow melt and runoff, which can be harmful to pets.
- Exposure to road salt can cause pets to experience painful irritation, inflammation and cracking of their feet pads.
Wildlife
- Some birds, like finches and house sparrows, have an increased risk of death due to ingesting deicing salt.
- Salt attracts wildlife to roadsides, where they can be hit by cars.
- Deicing salt can cause a decline among populations of salt sensitive species, reducing natural diversity.
Infrastructure
- Chloride corrodes road surfaces and bridges and damages reinforcing rods, increasing maintenance and repair costs.
- Deicing salt accelerates rusting, causing damage to vehicle parts such as brake linings, frames, bumpers.