I love obscure facts. The best, obscure facts are those which are relatively important, and make people wonder why they remain obscure. Eating a penny can kill a dog. There’s a good. one. Yes, just one penny. You see the average US Penny minted after the latter half of 1982, has a mass of 2.5 grams. 97.5% of that mass is zinc. That equals about 2.4g (2,400mg). The LD50 for zinc, or dose at which 50% of animals that have ingested zinc will die is 100mg per kg of body weight. That means, that half of the 24kg (53lb) dogs who eat one penny, will die–if not treated. This is a little smaller than an average Golden Retriever. I know you are wondering what the year a penny was minted has to do with anything. You are also probably wondering exactly how a penny might be deadly. You also may want to know if a penny can kill your baby.
For the exact mecahnism by which pennies kill, unfortunately, you may need to look elsewhere. Nobody knows for sure how zinc does what it does to dogs. We do know, however, that it causes the destruction of red blood cells in the dog leading to a low red blood cell count. This condition, which may be caused by other factors such as autoimmune diseases, certain drugs, and other toxins, is known as hemolytic anemia. Hemolytic anemia in dogs is ugly. Victims typically present to their vets very lethargic and jaundiced (Note the color of the gums and eyeball in the image). It can be quite frightening. The part we don’t understand yet, is how zinc brings about this destruction. There are theories, but nobody really knows for sure. The fact that zinc causes this destruction, however, is very well established, and unfortunately, veterinarians see thousands of these cases every year. I, alone, have seen approximately 10 in the past 3 years.
A quick search on Google will convince you that zinc toxicity from US pennies minted after 1982 is not a major problem. The majority of sites listed discuss the danger to dogs.
Why pennies minted after 1982? The answer is a bit of a history lesson. It turns out, the composition of the US penny has changed over time. Here’s the rundown from the US Mint:
- The composition was pure copper from 1793 to 1837.
- From 1837 to 1857, the cent was made of bronze (95 percent copper, and five percent tin and zinc).
- From 1857, the cent was 88 percent copper and 12 percent nickel, giving the coin a whitish appearance.
- The cent was again bronze (95 percent copper, and five percent tin and zinc) from 1864 to 1962.
(Note: In 1943, the coin’s composition was changed to zinc-coated steel. This change was only for the year 1943 and was due to the critical use of copper for the war effort. However, a limited number of copper pennies were minted that year. You can read more about the rare, collectible 1943 copper penny in “What’s So Special about the 1943 Copper Penny.”)
- In 1962, the cent’s tin content, which was quite small, was removed. That made the metal composition of the cent 95 percent copper and 5 percent zinc.
- The alloy remained 95 percent copper and 5 percent zinc until 1982, when the composition was changed to 97.5 percent zinc and 2.5 percent copper (copper-plated zinc). Cents of both compositions appeared in that year.
So, zinc toxicity is becoming more common, as a greater proportion of the pennies in circulation are toxic. Should we call the US Mint and ask them to change the composition of the penny to one less toxic to dogs? I think we should. Please call:
Office of Public Affairs
Tell him that you read about it on davidbessler.com.