How Road Salt Pollutes Our Nitrates

Rock salt is commonly used to de-ice roads in winter, with around 20 million tons of salt scattered on US roads annually. While this practice improves safety, it also has environmental consequences. When rock salt is applied to roads, it dissolves into snowmelt and stormwater runoff, eventually flowing into storm drains and rivers without treatment. This process leads to the contamination of freshwater streams and ecosystems, causing harm to plants, fish, amphibians, and other aquatic organisms. Additionally, the chloride component of road salt impacts drinking water infrastructure, accelerating corrosion and affecting water taste and quality. The accumulation of salt in the environment poses a growing threat to both ecosystems and human health, with studies indicating an increase in salinity in drainage areas. While road salt helps maintain road safety, its overuse has led to various problems, including water pollution and infrastructure corrosion.

Rock salt is chemically similar to table salt

Rock salt, or sodium chloride, is a mineral with the chemical formula NaCl. It is chemically similar to table salt, which also has the same chemical formula. The primary difference between rock salt and table salt lies in their crystal size and colour. Rock salt forms in very large, chunky crystals, while table salt crystals are much smaller. The larger crystal size of rock salt means it takes longer to dissolve, making it unsuitable for cooking.

Rock salt is typically colourless or white, but its colour can vary depending on impurities. It gets its brownish colour from sand blown in from eastern deserts, but can also be clear, pink, or dark brown due to other geological influences. Rock salt is mined from ancient underground salt deposits that were formed when large lakes and seas dried up millions of years ago. These salt deposits can be hundreds of metres deep and are found in various locations, including Cleveland, County Antrim, and Winsford in the UK.

Table salt, on the other hand, comes almost exclusively from evaporation ponds that remove salt from seawater. While rock salt is used for industrial purposes, such as gritting roads, sidewalks, and parking lots, table salt is commonly used in cooking and seasoning food.

The use of rock salt for de-icing roads has raised environmental concerns. When rock salt is applied to roads, it dissolves into snowmelt and stormwater runoff, eventually flowing into freshwater streams and rivers without treatment. This process increases the salinity of freshwater sources and has negative consequences for aquatic life, infrastructure, and plant health. The sodium chloride in rock salt breaks down into sodium and chloride ions when dissolved in water, and elevated levels of chloride can be toxic to fish, amphibians, and macroinvertebrates.

In conclusion, rock salt and table salt share the same chemical composition but differ in crystal size, colour, and sources. The overuse of rock salt has led to water pollution and environmental damage, highlighting the need for more environmentally friendly de-icing practices.

The use of road salt has increased exponentially

The problems caused by road salt are more significant in highly urbanized areas where chloride levels are much higher due to the large amounts of impermeable land cover. When salt is layered on roads and parking lots in the winter, much of it ends up in waterways. The salt on the pavement dissolves into snowmelt and stormwater runoff, which eventually flows into storm drains that empty into rivers and streams without being treated. This results in freshwater streams becoming increasingly salty each year.

The sodium chloride in the applied salt dissolves into sodium and chloride ions when it comes into contact with water. The chloride component impacts the environment in several ways. Chloride is a persistent pollutant, meaning that once it is in the water, it stays there. As chlorides accumulate, our drinking water is at risk of turning salty. Excessive chloride levels can also accelerate the corrosion of drinking water infrastructure. A 2018 study evaluated various private water supplies in New York near a road salt storage facility and found that rising chloride levels in well water resulted in increased galvanized corrosion of the pipes.

In addition to the problems it causes for drinking water infrastructure, chloride also has consequences for the natural environment. High chloride concentrations are toxic to fish, amphibians, and macroinvertebrates. Even low concentrations of about 150 mg/L can impact aquatic organisms and are correlated with a drop in biodiversity. Sodium ions compete with other cations for negatively charged binding sites on clay particles, so an increase in sodium can cause the release of calcium, potassium, magnesium, and lead into the water.

Road salt contaminates water sources

Rock salt is commonly spread on roads, parking lots, and sidewalks during winter to prevent vehicles from sliding on snow and ice. While this practice is essential for safety, the overapplication of salt poses a significant threat to the environment and water sources.

Road salt, primarily sodium chloride (NaCl), is similar to table salt. When applied to roads, it dissolves into snowmelt and stormwater runoff, eventually flowing into storm drains that empty into rivers and streams without treatment. This process leads to the contamination of freshwater sources, causing an increase in water salinity. A study in 2018 found that 37% of the drainage area in the contiguous US experienced an increase in salinity over the last 50 years, with road salt being the dominant source in colder, humid regions.

The sodium chloride in road salt breaks down into sodium and chloride ions when dissolved in water. These ions have detrimental effects on the environment. Elevated chloride levels are toxic to fish, amphibians, and macroinvertebrates. Even low concentrations of chloride can impact aquatic organisms and reduce biodiversity. Additionally, sodium ions compete with other cations, such as calcium, potassium, and magnesium, leading to their release into the water.

The accumulation of chlorides in water also poses risks to drinking water infrastructure. High chloride levels can accelerate the corrosion of pipes and other plumbing materials, resulting in increased metal leaching and reduced pipe wall thickness. This corrosion can lead to water quality issues and potential health risks for those consuming the water, especially those on low-sodium diets. Furthermore, chlorides can damage roads, bridges, and vehicles, increasing maintenance costs.

To address these issues, some municipalities are adopting more environmentally conscious approaches to de-icing operations, such as using liquid applications instead of salt and implementing application regulators on plow vehicles to reduce salt usage. These initiatives aim to minimize the impact of road salt on water sources and the environment while still maintaining road safety during winter.

Chloride in road salt is toxic to aquatic life

Salt pollution is a threat to freshwater ecosystems. The use of road salt has grown exponentially over the past 70 years, causing various problems for water quality and water-related infrastructure. The exponential increase in road salt usage has led to a corresponding rise in chloride levels, which poses a significant risk to both surface water and groundwater quality.

Chloride is a highly soluble and mobile ion that spreads rapidly throughout a water body once contaminated. It is toxic to aquatic life, including fish, amphibians, and macroinvertebrates, even at relatively low concentrations. For example, chloride levels above 230 mg/L can be toxic to wildlife and impact their growth and reproduction. In addition, high chloride levels can lead to oxygen depletion in water bodies, creating an oxygen-deficient layer detrimental to fish and other aquatic organisms.

The impact of road salt on aquatic life has been observed in various regions. Studies in Wisconsin, Massachusetts, Finland, and Sweden have all shown that road salt runoff negatively affects stream water quality and aquatic organisms. In Finland, chloride concentrations during road salt runoff periods varied over nine-fold within a day, reaching as high as 567 mg/L. In Sweden, road salt had a "profound effect" on soil and stream water chemistry, with salinity increasing directly in proportion to the accumulated application of road salt.

The persistence of chloride in the environment is also a concern. Chloride does not break down naturally, and once it contaminates a water body, it can persist for extended periods. This can lead to long-term toxicity issues for aquatic life and impact the biodiversity of affected water bodies.

To address the environmental impact of road salt, advancements in environmentally friendlier options and practices have been developed. Implementing application regulators on plow vehicles, for instance, can dramatically limit the amount of excess salt used, reducing environmental hazards and costs.

Alternatives to road salt are available

Road salt is a popular de-icing tool because it is widely available, effective, and relatively cheap. However, it is a major cause of environmental damage when it washes into groundwater, lakes, rivers, and streams. The chloride in road salt is a permanent pollutant and corrodes vehicles, bridges and other infrastructure. It is also harmful to pets and dangerous to children who play outside.

The good news is that there are alternatives to road salt that are safer for the environment and infrastructure. One option is to use food byproducts such as pickle juice, cheese brine, beet juice, or sugar beet molasses. These alternatives are effective de-icers, but they usually require added salt to work and can deplete the dissolved oxygen in the water, which is harmful to aquatic life. Another option is to use potassium acetate, which has been shown to be more effective at melting ice in cold temperatures than road salt. While it is more expensive, the fact that less of it is needed means that the cost is similar. However, the environmental impacts of potassium acetate are still unclear, and it has been shown to be toxic to aquatic insects.

For property owners, wood fireplace ash can be used to provide traction and absorb more sunlight due to its darker color. Sand and coffee grinds act in a similar manner to salt and ash. There are also engineered products, such as Ecotraction, that reduce ice and are environmentally friendly.

Local municipalities are also implementing Salt Smart practices to reduce salt use and speed up snow clean-up, such as using liquid applications. Training and certification programs for professionals who clear parking lots and sidewalks are also being developed.

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