The widespread use of rock salt has serious environmental and financial consequences. Consider the millions of tons of road salt spread each winter across the continent, and then recall that historically “salting the earth” was a kind of scorched earth policy aimed at rendering a defeated foe’s territory uninhabitable. The practice demonstrated utter contempt for the people and their land, and was also used to punish the families of traitors and other enemies of the state.
Today, rock salt (sodium chloride: NaCl) is not used to intentionally inflict damage, nonetheless its use is plainly harmful. The main side effects of road salt usage are degradation of the environment, particularly soils and vegetation, harm to animals and birds, and disruption of the balance of aquatic life. Contamination of drinking water sources is also a serious concern.
Sodium Chloride concentrations of 200 mg/l can been found as far as 200 metres from roadsides; at only 90 mg/l, concentrations of salt have been shown to harm the bacterial content of soils which disrupts soil structures. These bacteria prevent erosion by aerating soils and promoting plant growth. Soil becomes cloddy and dense, and the ability to retain moisture is diminished.
Plants are also directly affected by both sodium and chloride ions as the presence of these inhibits water absorption and reduces root growth. Nutrients are also less available to the plant in the presence of salt since the plant cannot take up the elements that it needs. The symptoms of chloride poisoning for plants are similar to those of drought (p. 6): stunted growth, browning and premature falling of leaves or needles, dying branches, and shortened lives. Of the 15 principal tree genera making up Canadian forests, 11 are sensitive to road salt and many of these have disappeared from Canadian roadsides.
Birds and other animals are also affected by the high use of salt. Winter songbird mortality has been attributed to salt toxicity as seed-eating birds are unable to distinguish between grit needed for digestion and salt crystals. Additionally, many birds and other animals sometimes experience salt deficiencies and seek out sources of sodium chloride. The abundance of salt at roadways due to highway salting attracts them to a place where they are likely to overshoot their sodium needs. Jasper National Park has recorded kills of elk and big-horn sheep due to salt ingestion, and other places in Canada report moose and deer salt toxicosis. Further, the birds and animals presence in the roadway places them in danger of being struck by speeding vehicles.
Unsurprisingly, aquatic life is also affected by salt run-off, particularly in small streams close to roads. Salt melts ice and snow, which then runs off the road in high concentrations. This decreases oxygen in the water and distorts the aquatic food chain since more salt-tolerant species gain dominance.
Numerous cases (pp. 30-31) have also been reported where drinking water has been contaminated by road salt usage. Wells close to highways or work yards are particularly vulnerable given the high concentration of salts used or stored there. Once the salt is in the environment, it doesn’t just go away, it works its way into groundwater systems and it can take years for the problem to be cleared. It should be remembered that excess dietary sodium is associated with high blood pressure (hypertension) so it is not only plants and animals that are affected by the widespread use of rock salt.
For all of these reasons, Environment Canada stated in 1999:
Based on the available data, it is considered that road salts that contain inorganic chloride salts with or without ferrocyanide salts are entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends. Therefore, it is concluded that road salts that contain inorganic chloride salts with or without ferrocyanide salts are “toxic” as defined in Section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999). (p.3)
Unfortunately, being labelled as toxic does not mean that rock salt is banned in Canada, and it has not officially yet been added to the list of toxic substances. However, steps are being taken to mitigate the effects of rock salt usage, and the Government of Canada has developed a Code of Practice for the Environmental Management of Road Salts as a way to protect the environment while ensuring road safety as well.
It is unlikely that these measures will be enough. Dumping salt into our environment even after we know the damage it causes is akin to the practice of salting the earth in ancient times – only this time, it is ourselves we are showing utter contempt for. It is our home we are making uninhabitable.