Road Salt Poisoning – An Unexpected Hazard to Pets in Winter

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When temperatures drop and the morning gets frosty or even (as this week!) snowy, we often complain that the UK is woefully underprepared for the unexpected annual arrival of winter weather. Yet, when you drive to work on freshly-gritted roads, is this entirely fair? Road salt, or road grit, is used worldwide to help prevent accidents on icy roads. But is this common substance safe for your pets? Today we will answer this question so you and your pet can be safe outside this winter.

What is Road Salt?

The practice of spreading substrate onto the roads appears to have first been recorded in Paris in the early 1900s, mainly helping horses’ hooves (and the very few cars) grip and to melt ice. Since then, its use has exploded in colder regions of the world. In modern times, salt is spread on roads on an industrial scale using salt spreader trucks or from grit bins to be spread by hand.

Initially, cheaper sand or ash was used to grit the roads, but nowadays rock salt (sodium chloride) is the substrate of choice. Other similar chemicals, such as calcium chloride and magnesium chloride, are also used. In the UK, most of this is mined from three sites in Cheshire, North Yorkshire and Northern Ireland. The UK uses around 215,000 tonnes of road salt yearly to de-ice its motorways and main A-roads. However, the reduction of accidents on icy roads is worth the effort.

Rock salt works to make roads safer in two ways. Firstly, by providing physical grip – ice is a smooth surface that tyres and feet struggle to grip to. By adding rough grains of salt on top, more friction is created to provide traction. Secondly, by lowering the freezing temperature of water – when substances are dissolved into a solution (in this case salt into water), the temperature at which the liquid becomes a solid reduces. In practice, this means that the water on the road from snow or rain that usually freezes at 0°c or below will remain liquid up to -10°c when salt is added. For milder winters, this is usually effective to keep the water from freezing, though the efficacy will be limited if it gets any colder. Other additives can be used to lower the freezing temperature further if needed.

Road Salt Toxicity

Because road salt is primarily sodium chloride, excessive ingestion can theoretically lead to hypernatraemia, or sodium toxicity. Sodium is a very important electrolyte for all animals, responsible for helping maintain body water and other electrolyte levels, for transmitting signals along nerves, maintaining blood pressure and helping the heart contract. It is essential for life. The body has a complex system of maintenance to ensure sodium levels remain at the correct level – this is called sodium homeostasis. Most salt enters the body via absorption from food, and excess is primarily excreted via the kidneys.

In most animals, if a large volume of salt is ingested suddenly, the body can compensate and excrete the excess. However, if the volume is significant, the animal is dehydrated or not able to access water, or there is a failure in the body’s ability to process sodium, hypernatraemia can occur. This can be seen with road salt, or other salty things such as seawater, sodium supplements or Play-Dough.

The symptoms of hypernatraemia vary depending on the individual and the degree of hypernatraemia. If very mild or chronic (less likely with road salt ingestion), there may be no symptoms. Milder symptoms include inappetence, lethargy, vomiting and diarrhoea, excessive drinking and urination. More serious hypernatraemia starts to affect the neurological and cardiovascular systems, causing muscle weakness, wobbliness, seizures, comas, and a fast heart rate. Theoretically hypernatraemia can be fatal, though this is rarely the case.

How Can Hypernatraemia Be Diagnosed and Treated?

Diagnosis of hypernatraemia requires blood sampling to measure the sodium level. History taking, such as asking if the pet has been dehydrated or ingested a large volume of road salt recently can help determine the cause.

Treatment is generally supportive and will involve fluids (orally or intravenous) to reduce dehydration and encourage the body to remove excess sodium. Symptomatic control of seizuring, vomiting, diarrhoea and other symptoms may be required as well. If there was an underlying disease, such as diabetes, this may need to be controlled as well.

For pets that ingest road salt, this treatment is usually sufficient to reverse hypernatraemia and return them to normal health.

Is the Risk Significant?

For the average pet, hypernatraemia from road salt is not something you should particularly worry about – the amount of salt consumed from a single lick of road grit is insignificant, and even if it were a larger amount, ready access to fresh water will easily help the body remove the excess. However, if your animal is (or at risk of being) dehydrated, extra care should be taken. This includes very young and elderly animals, cats, and those with diseases causing dehydration (vomiting, diarrhoea, diabetes mellitus, kidney disease, urinary tract disease, etc.) or on drugs causing excessive urination like steroids. If these animals ingest a large amount of salt, the relative concentration in a dehydrated body will be higher than in a physiological normal animal, potentially leading to hypernatraemia.

Are There Other Risks from Road Salt

As well as the risk of toxicity, the more common risk associated with road salt is the damage to the paws when walked on. Pet paws are very sensitive, and the grit can cause irritation and pain when walked on. The salt itself can also dehydrate the paws, leading to cracking and damage. This could lead to infection in the feet.

How to Avoid Road Salt Toxicity and Sore Paws

There are a few tips you can consider to keep your pet safe from road salt this winter.

Avoidance is easiest, so walking your dog in areas where grit hasn’t been spread will minimise the risk. This will, of course, depend on the area you walk in. And this strategy will be much harder for cats who like to roam. Still, consider in advance if there are any new salt-free places you may be able to take you pet to.

If avoidance is not possible, try protecting them from the salt with protective paw balms (good for amenable cats), boots (probably less useful for cats!), or muzzles to prevent licking the salt. This ensures they can have fun outside without excessive contact with the road salt.

It’s a good idea anytime your pet comes back from outside to rinse their paws with warm water and dry them thoroughly. This washes off the salt and other contaminants and prevents them drying out. Using some pad moisturiser afterwards can keep the pads supple.

You can also purchase pet safe de-icer, with magnesium or calcium chloride as the main ingredient, preventing the risk of hypernatraemia if ingested. Other homemade chemical de-icers can also be effective, or simple sand for grip (though remember to wash your pet’s paws after to avoid irritation).