How Road Salts Contaminate Freshwater Resources, Threaten Human Health

Releasing salt into the environment has been found to contribute to the pollution of global freshwater resources, according to new research published by the University of Maryland.

The research study, led by Sujay Kaushal, suggests that using salt for things like de-icing roads or land fertilisation for crops releases toxic chemicals into the environment which is putting additional strain on our already vulnerable freshwater supply.

Previous studies led by Sujay Kaushal coined the term ‘Freshwater Salinisation Syndrome’ which refers to the way in which salt can react with soils to release harmful chemicals, metals and broken-down solids. This not only poses a threat to clean water supplies, but also to both human and wildlife populations and ecosystems.

Kaushal, lead author and professor in Geology and Earth System Science at the University of Maryland, said: “We used to think about adding salts as not much of a problem”.

“We thought we put it on the roads in winter and it gets washed away, but we realized that it stuck around and accumulated. Now we’re looking into both the acute exposure risks and the long-term health, environmental, and infrastructure risks of all these chemical cocktails that result from adding salts to the environment, and we’re saying, ‘This is becoming one of the most serious threats to our freshwater supply’”.

By comparing freshwater data worldwide, Kaushal and his team found that there has been an increase in the levels of chloride (which is a key ingredient in road salts) in these freshwater systems. They discovered increased salinity in watersheds, including Passaic River in northern New Jersey, across a 30-year period.

While road salts are a major human-related salt source, aluminium fertilisers, sewage leaks, and water softeners can also release salts into the environment. Saltwater intrusion can also come from indirect sources such as the breakdown of bridges and buildings containing limestone, and rising sea-levels in some coastal regions.

The 2014 Flint, Michigan water crisis provides a clear example of how increased salinity can cause water pipes to corrode allowing heavy metals to pollute drinking water supplies.

According to Kaushal and his team, the risks associated with using salts is just as significant as other major environmental issues such as acid rain and requires the same level of regulation from authorities.

“Ultimately, we need regulation at the higher levels, and we’re still lacking adequate protection of local jurisdictions and water supplies,” Kaushal said.

“We have made dramatic improvements to acid rain and air quality, and we’re trying to address climate change this way. What we need here is a much better understanding of the complicated effects of added salts and regulations based on that. This can allow us to avert a really difficult future for freshwater supplies.”

To reduce the threats associated with Freshwater Salinisation Syndrome, the study points to the significance of using new high-frequency sensor technology to monitor peaks in salinity and water flow in water systems worldwide, to allow scientists to better understand this problem and work towards a solution.