We are now in the heart of winter in New England. The end is in sight but we are sure to get hit with a few more wintery mixes. For slippery roads during inclement weather, our biggest line of defense is road salt. Road salt is great on dangerous slick roads, walk ways and parking lots and is used often because it is inexpensive, easy to work with and is quite effective. Road salt is made up of 40% sodium and 60% chloride ions. When salt is spread on icy surfaces, salt crystals pull the water molecules out of ice formation and create brine, which continues to speed up the melting process. Road salt is most effective in temperatures 15⁰F and higher, and loses effectiveness in more frigid temperatures. If overused, road salt can cause some problems in the environment and our drinking water.
As the road salt melts, it separates into sodium and chloride ions which then get washed off the roads and into the environment. Along the side of the road, sodium and chloride can alter soil chemistry and kill plants, as well as cause health issues in wildlife that consume it. As the snow and ice melt, the sodium and chloride ions can run off into water supplies. Water contaminated with sodium chloride has a higher density, and tends to settle down at the lower levels. Because of this, it does not receive the dissolved oxygen from the top layer. When the water is void of oxygen, it cannot sustain aquatic life and causes an unhealthy underwater ecosystem.
Chloride ions are completely soluble and there is no natural process of removal, this means they do not break down or get absorbed by vegetation. There is no way to remove chloride from water; it can only be diluted to bring down concentration. The EPA standard for Chloride is 250mg/L, above this it can be toxic to aquatic life. 90% of chloride found in watersheds is from use on roads and parking lots. There are no human health concerns with chloride, but at high levels it can cause an unpleasant taste and can cause corrosion of pipes and plumbing fixtures. High levels of sodium in drinking water can be a concern to people with hypertension that are on a sodium restricted diet. If on a limited diet, it is advised to keep sodium content in drinking water at 20mg/L or below.
Despite the problems it can cause, road salt still remains our first line of defense in slick conditions. It is needed to make roads, parking lots and walkways safe for travel, as icy conditions can be dangerous. The best we can do is to make sure we are using it in a safe and responsible manner.
