The Killer Coolant

The leaves are turning, the days are getting shorter and there is a definite nip to the air, signalling that it’s time to get our cars ready for the ice and cold. Antifreeze is an essential ingredient for a functional car during Canadian winters, but what’s good for cars can be a disaster for wildlife. At the BC node of the CWHC we see a few cases of fatal antifreeze toxicity every year in a variety of wildlife ranging from ground squirrels and raccoons to bears and coyotes.

The vast majority of antifreeze is made up of 95% ethylene glycol, which is diluted to 50% in vehicle cooling systems. Ethylene glycol is extremely toxic to all animals, including humans. Less than a teaspoon (5mL) of undiluted antifreeze is enough to kill a cat, and less than a quarter cup (125 mL) can kill an adult human. Not only is it dangerous to wildlife because it is toxic in small amounts, but it also tastes sweet, and has a low freezing point so it is liquid when water is ice, which attracts animals to consume it.  To help deter consumption by children, the BC government has required a “bittering agent” to be added to antifreeze since 2011, but the effects of this on consumption by wild animals is unknown.

The most common clinical signs reported in cases submitted to the CWHC BC are neurological signs such as incoordination, difficulty moving the hind end, and sometimes seizures. One raccoon was submitted with a history of “unusual friendliness”.

Once ingested, ethylene glycol is rapidly absorbed, reaching peak blood concentrations in about three hours. Symptoms for this period are mild, typically resembling intoxication with alcohol. Over the course of the next several hours ethylene glycol is metabolized by the liver and kidneys, and that is when it becomes a real problem. Accumulation of one of the metabolites, glycolic acid, results in a severe metabolic acidosis (decreased blood pH) and renal tubular necrosis (kidney failure). Accumulation of a later metabolite, oxalate, also contributes to renal tubular necrosis and is deposited as crystals in the renal tubules. The result is fatal in a few hours to days.

Figure 1: Kidney of a bear that died from ethylene glycol (antifreeze) toxicity. Note the damaged renal tubules containing numerous bright crystals that shine under polarized light. H&E – polarized light

Careful storage, handling and disposal of antifreeze as well as switching to antifreeze that contains propylene glycol, which is much less toxic, are all ways to decrease the risk of antifreeze toxicity in people, pets and wildlife. The best disposal is recycling. In BC we are fortunate that there are 339 depots across BC that will take your unwanted or used antifreeze; find one near you HERE (and across Canada HERE).

Contributed by: Glenna McGregor, Wildlife Pathologist, CWHC-BC

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