Salt Saves Lives on the Roads but Harms Life Down the Road

By Nathan Wolff, Clean Water Institute Intern, Summer 2021

Every winter, the northeastern US sees many episodes of wintery mixes and heavy snowfalls. To keep people on the roads and traveling safely, state Departments of Transportation work around the clock plowing and salting snow and ice. Unfortunately, keeping the roads safe and clear comes with some negative impacts on the environment. In the entire U.S., 37% of drainage areas have experienced increased salinization in the past five decades (Bennett, 2021). Here in Pennsylvania, PennDot has nearly 40,000 miles of roads and almost 96,000 snow-lane miles to maintain. Over the past five winters, they have used an average of 807,766 tons of rock salt on our roads (PennDot, 2022). Although methods of deicing the roads reduce vehicular accidents by 78-87%, we should still concern ourselves with the damage it does to our environment, particularly when salt is used in excess (Hintz et. al., 2021).

Road salts can contaminate drinking water, cause property damage, and harm wildlife (EPA, 2020). When salt finds its way into sources of drinking water the increased salinity can lead to human health risks like high blood pressure and future cardiac issues. Numerous case studies demonstrate contaminated drinking water exceeding thresholds for human salt consumption (EPA, 2020).

Contrary to popular belief, most modern drinking water plants are not equipped to fully remove all chemical contaminants, including excess salts. The main way these drinking water plants remove salts and other contaminants is by reverse osmosis (RO) (Magnus, 2021). RO filtration is very effective, but there are also many practical disadvantages that come with it. Reverse osmosis systems are expensive, they require costly professional maintenance, there are risks bacterial growth due to chlorine removal, and it can waste as much as six times the amount of clean water produced (Magnus, 2021). Most drinking water plants can’t afford to have big and efficient filtration systems, they are often simple and can lack in some areas of filtration, such as desalination. They are never 100% effective so not all salts are removed before we take a drink. Exceedingly high levels of salt can also damage peoples’ vehicles from its corrosive effects: according to AAA, rust caused by winter road salts costs Americans three billion dollars every year (Edmonds, 2017).

The smallest fractions of dissolved road salts can take months to years to travel from roads to nearby streams (Snodgrass et. al., 2017). Northeast stream studies consistently show increasing trends in salt concentration during both summer and winter months (Snodgrass et. al., 2017). Other studies indicate that not all road salt applied in a particular winter season is exported from watersheds within the same year (Snodgrass et. al, 2017). This means every year when roads salts are applied, they accumulate on top of what remains in surrounding lawns, pavements, and sidewalks from the previous year. Considering the amount of rock salt used in the US has tripled since the 1970s, the salt concentration in our environment must be unfathomable (Hintz et al., 2021). We should all be concerned about this and what it means for the ecosystems and wildlife that suffer because of it.

The most common deicing salts are inorganic chlorides with metals such as sodium, calcium, potassium, and magnesium (Hintz et. al, 2021). These salts do not just disappear after the snow and ice is gone. They are washed away as runoff, leaving behind concentrated residues, or ending up in a nearby water source. This harms both the biggest and the smallest wildlife around. Salt residues attract deer species to roadsides as they enjoy licking the salt and increases the probability of vehicle collisions (EPA, 2020). Salinized runoff also results in plumes of contaminated groundwater that adds salt ions to streams year-round (Snodgrass et. al, 2017). At high concentrations, salt can be fatal to zooplankton and macroinvertebrates, which serve as a critical food resource to many fish species. Salinity has been found to negatively affect the abundance of zooplankton in general (Yuan et. al, 2020). Chloride ions are lethal to macroinvertebrates because they compromise important osmoregulatory processes (Fink 2021). Adult fish can build tolerance to periods of increasing salt concentrations, but sub-lethal effects lead to egg mortality (Summers and Valleau, 2022). Fishermen should be alarmed because egg mortality and lack of food decreases total fish abundance. If they can’t survive at birth or eat as growing adults, they will die. Salt also has negative impacts on abiotic components of stream ecosystems such as water mixing. This can lead to salty dead zones down near the streambed (Summers and Valleau, 2022).

Current salt thresholds for the environment are set by the Environmental Protection Agency (EPA). The goal of these standards is to limit how much salt is used to begin with. There are both chronic and acute salt thresholds. Chronic thresholds are for reducing accumulating salt effects that keep getting worse over time, while acute thresholds are used to reduce the amount of salt that gets applied to the roads each year (Hintz et. al, 2021). Unfortunately, our streams are approaching these thresholds at alarming rates. A study by Kaushal et al. (2005) found that 55% of the urban streams they sampled had chloride concentrations 20-30 times higher than the EPA’s chronic thresholds. Contaminated streams can maintain high salt concentrations throughout the summer months, which heavily contributes to these alarming concentrations (Hintz et. al, 2021). The bottom line is that current thresholds are clearly not enough to reduce this environmental problem. Perhaps we can move in a direction towards new technology to help reduce the amount of salt used on our roads in the winter.

One promising solution to our road salt problem may be porous pavement to reduce the amount of salt used on impervious surfaces like typical roads, driveways, sidewalks, and parking lots. Instead of water pooling on the surface and going through freeze-thaw periods, it can soak into the ground naturally. There would be no need to salt these areas anymore because there would be no residual ice patches. A recent study has shown that annual median snow/ice accumulation on porous pavement led to a 77% reduction in annual salt used for maintenance (EPA, 2020). As homeowners, we have the responsibility of taking care of not only our property but the natural ecosystem around it. Instead of carelessly dumping rock salt on our driveways and sidewalks, we should severely reduce how much we use and look to other ways of dealing with ice. An easy way to reduce the amount of salt we use is to clean up snow and sleet as soon as possible, instead of letting it freeze and turn into an icy mess. At that point there is no option but to get chopping and salting. A cool alternative deicer is grape skin compounds. Researchers at Washington State University extracted chemicals from grape skins and made a solution out of it. Their solution melted ice quickly and effectively, all without damaging roads or harming the watershed (Bennett, 2021). This method is great because it turns waste products into environmental solutions. In general, we should continue to practice reducing salt usage on our properties and implement new deicing technologies to address environmental concerns like salination of freshwater sources.                                               
 
 
 
  
Literature Cited
Bennett, Paige. 2021. 8 Sustainable Alternatives to Sidewalk and Road Salts. https://www.ecowatch.com/sustainable-alternatives-winter-salts-2656111075.html
Edmonds, Ellen. 2017. Road De-Icers Cause $3 Billion Annually in Vehicle Rust Damage. AAANewsRoom. https://newsroom.aaa.com/2017/02/road-de-icers-cause-3-billion-annually-vehicle-rust-damage/
Fink, Kendra. Effects of Salt Runoff on Aquatic Macroinvertebrate Colonies. Masters Program-Bemidji State University. 2021. https://www.bemidjistate.edu/directory/wp-content/uploads/sites/16/2021/05/2021.-Fink-K.-Effects-of-salt-runoff-on-aquatic-macroinvertebrate-colonies.pdf
Garrido, S., Ben-Hamadou, R., Santos, A. et al. Born small, die young: Intrinsic, size-selective mortality in marine larval fish. Sci Rep 5, 17065 (2015). https://www.nature.com/articles/srep17065#citeas
Magnus, Jern. 2021. What are the pros and cons of Reverse Osmosis water filters? https://tappwater.co/en/reverse-osmosis-ro-water-filters/
Snodgrass, W. Joel, Joel Moore, Steven M. Lev, Ryan E. Casey, David R. Ownby, Robert F. Flora, and Grant Izzo. Influence of Modern Stormwater Management Practices on Transport of Road Salt to Surface Waters. 2017. Environ. Sci. Technol. 51. 4165-4172. https://pubs.acs.org/doi/abs/10.1021/acs.est.6b03107
Hintz, D. William, Laura Fay, and Rick A. Relyea. Road salts, human safety, and the rising salinity of our fresh waters. Front Ecol Environ. 20 (1). 22-30. https://esajournals.onlinelibrary.wiley.com/doi/10.1002/fee.2433
Kaushal S.S, Groffman P.M., and Likens G.E. 2005. Increased salinization of fresh water in the northeastern United States. P Natl Acad. Sci USA. 102: 13517–20. https://pubmed.ncbi.nlm.nih.gov/16157871/
Summers, Jamie and Robin Valleau. 2022. Road salt is bad for the environment, so why do we keep using it? Queen’s Alumni Review: The Magazine of Queen’s University. https://www.queensu.ca/gazette/alumnireview/stories/road-salt-bad-environment-so-why-do-we-keep-using-it
United States Environmental Protection Agency. Winter is Coming! And with it, tons of salt on our roads. 2020. https://www.epa.gov/snep/winter-coming-and-it-tons-salt-our-roads#:~:text=In%20addition%2C%20road%20salt%20can,fish%2C%20bugs%2C%20and%20amphibians