In 10 seconds: The use of de-icing salts is pushing salt levels in our drinking water above and beyond recommended thresholds. Recent evidence suggests that this is a widespread problem that needs urgent attention.
What are the findings? A recent review has shown that the use of de-icing salts is having a worrying impact on the level of salt in freshwater ecosystems in the US. This is because as snow and ice melt on the roads, the salt mixes with the water and washes into the soil, lakes, streams. Run-off from the roads has also been shown to contaminate drinking water reservoirs and wells. This increase in salt is negatively impacting wildlife and also causing salt levels in our drinking water to rise above and beyond recommended levels which could have detrimental effects on human health.
How big is the problem? De-icing salts were first used in the US in 1938. Since their introduction, their use has increased significantly and today, over 18 million metric tons are applied to roads in the US every year. Salts used on the road are mostly inorganic and include sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl₂). Scientists routinely test the levels of chloride in freshwater to understand the impact that these salts and other pollutants are having on the freshwater ecosystems that provide drinking water for so many. Elevated levels of chloride show that water systems have been polluted by human activities of which road salts are a major contributor. Chloride is also known to corrode water pipes which can increase the levels of toxic metals in the water which was the probable cause of the increased lead concentrations found in drinking water in Flint, Michigan.
What led to this discovery? The researchers collated years of scientific research to help understand just how big an effect de-icing salts are having on freshwater ecosystems. Compiling this information enabled the researchers to look at the bigger picture and see just how widespread and significant this issue is. What they found was that the chloride levels found in freshwater systems all over the US were often exceeding recommended levels and that these salts are also directly causing the increase of other harmful substances such as mercury and lead in drinking water.
What can be done? While the outlook from this review is alarming, the researchers suggest several best management practices that could be used to decrease the amount of salt ending up in our drinking water. One way that salt levels could be reduced is by providing proper storage facilities for the salt before it is used. Many storage facilities store salt directly on the ground which can lead to salt permeating into the soil. Storing salt in facilities with a proper concrete base and a cover would prevent the salt from leaching into the environment in this way. Other methods aim to reduce the amount of salt used and include anti-icing before winter storm events and the use of live-edge snowplows which are more effective at removing snow and ice compared to conventional plows.
OK, and what happens next? While it's clear from the science that road de-icers are having a devastating impact on freshwater ecosystems and human health, they also reduce winter road accidents by 78%. This means that policymakers and environmental managers need to consider solutions that reduce the negative environmental impacts that these salts have while still keeping drivers safe on icy roads. While there is no perfect solution to this problem, several communities have found answers that help reduce the environmental impact of salting their roads without compromising drivers' safety. For example, in Wisconsin, some counties treat their roads with a brine solution. This cut salt use by nearly 60% without an increase in the number of road accidents.
De-icing salts not only impact human health but can also ...
.... reduce the rate at which fish grow. One study demonstrated that exposure to environmentally relevant levels of sodium chloride (NaCl) and calcium chloride (CaCl2) impacted the growth of rainbow trout.
De-icers are not good news for fish at all as research has also shown that higher levels of NaCl can reduce zooplankton populations which are a food source for a lot of aquatic animals.
However, it's not all bad news! Research has shown that Daphnia, a common species of zooplankton, can evolve tolerance to moderate salt levels which could provide a buffer for freshwater food webs against moderate salinization.
Lindy has curated 9 papers saving you 31.5 hours of reading time with a total evidence score of 3 out of 5
The Science Integrity Check of this 3-min Science Digest was performed by Michael Eze.