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The Effect of Rock Salt on Watersheds

Author: Myeesha Begum, Water Quality Specialist, PhD. Environmental Sciences

Cooksville Creek in Mississauga, one of the areas where the highest chloride levels have been recorded in Canada


Run off of rock salt into watersheds has several negative implications. Chloride concentrations from rock salt persists in waters since it does not easily precipitate and is non biodegradable. The Canadian Water Quality Guidelines for the Protection of Aquatic Life stated that the threshold value for chlorine should be 120 mg/l (Breining, 2017). Recently however, chloride levels in water have increased. For example, Toronto rivers have consistently exceeded 5,000 milligrams per litre causing risk to some plant species (Dunn, 2018). In other areas such as Muskoka region of central Ontario, algae remains and microscopic animals (called zooplankton) contained within the region’s lake sediments have become more salt-tolerant than before road salt was widely used. This can bioaccumulate in plankton eating fishes as they can likely die to high chloride concentration (The conversation, 2017).


On the contrary, ethylene glycol does not bioaccumulate or remain in the environment due to its ability to biodegrade aerobically or anaerobically, however it can cause oxygen depletion in receiving waters. Ethylene glycol exerts high levels of biological oxygen demand (BOD) during degradation in surface waters. This process can adversely impact aquatic life by consuming oxygen from aquatic organisms who need it to survive (EPA, 2012). Fortunately, based on the most recent available data from all airports for the 2004-2005 season, the levels of ethylene glycol in effluent streams have been low (Government of Canada, 2015)


Study: Road Salt in Lakes, Rivers May Wipe Out Aquatic Life


References

Breining, G. (2017). We’re pouring millions of tons of salt on roads each winter. Here’s why that’s a problem. Retrieved from

https://www.minnpost.com/politics-policy/2017/11/we-re-pouring-millions-tons-salt-roads-each-winter-here-s-why-s-problem


Dunn, T. (2018). You can taste it': Road salt making GTA rivers, streams as salty as seawater


Environmental protection agency (EPA). (2012). Environmental Impact and Benefit Assessment for the Final Effluent Limitation Guidelines and Standards for the Airport Deicing Category Retrieved from https://www.epa.gov/sites/production/files/2015-06/documents/airport-deicing_environmental-impact-and-benefit-assessment-final-2012.pdf


Health Canada. (2007). ARCHIVED - Priority Substances List Assessment Report for Road Salts. Retrieved from http://hc-sc.gc.ca/ewh-semt//pubs/contaminants/psl2-lsp2/road_salt_sels_voirie/index-eng.php#a261


Government of Canada. (2015). Ethylene Glycol (Final Content). Retrieved from https://www.ec.gc.ca/lcpe-cepa/default.asp?lang=En&n=4B7409ED-1&offset=7


The Conversation. (2017). Road salt is bad for the environment, so why do we keep using it?

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