Non-Toxic Antifreeze

by Ann Backus, MS

Have you seen an ad for non-toxic antifreeze? Well, a recent Hamilton Marine ad in Fishermen’s Voice got me thinking: What about this stuff? Shouldn’t we be encouraging it for the fishing community?

November is about the right time to be hauling-out or winterizing the boat. So maybe it’s a good time to dig into some information about anti-freeze for water-based cooling systems.

Ethylene glycol and propylene glycol are two common antifreeze liquids. They are both odorless and colorless but ethylene glycol is also slightly sweet – hold that thought. Both are somewhat more viscous (thick) than their antifreeze cousins, ethanol and methanol.

Both ethylene glycol and propylene glycol are miscible in water, that is they don’t separate out like an olive oil and vinegar dressing for your salad does. Both lower the freezing point of water - the characteristic we are looking for in an anti-freeze. Both increase the boiling point of water, which is a benefit when the temperature of the cooling water could potentially reach the boiling point of water, 212 degrees Fahrenheit. What you don’t want in your cooling system is steam and bubbles of air.

When you purchase anti-freeze, the solution is already a mixture of water and either ethylene or propylene glycol. This is a good thing because in their pure form both are flammable at a temperature just higher than the boiling point of water. Note: Don’t plan to mix-up your own antifreeze.

Clearly, there are a number of similarities across these two chemicals made up of carbon, hydrogen and oxygen. Where do the similarities end?

Ethylene glycol is considered toxic. It is hazardous if ingested (swallowed) and can cause skin and eye irritation. According to the Safety Data Sheet for undiluted ethylene glycol from ScienceLab.com “over-exposure can result in death.” It can effect the kidneys, liver, and central nervous system. The likelihood that it will cause cancer has not been determined for animals or humans, but animals find its “sweet” taste attractive and will get sick. If ingested by a person or a pet, the poison center should be contacted.

Propylene glycol, however, is non-toxic. It can cause skin and eye irritation, so gloves and goggles are advised during use; if contact occurs on skin or eyes they should be washed and flushed for at least five minutes. Ingestion will make a person sick and the poison center should be contacted, however, propylene glycol is broken down in the body to metabolites common to the human body such as pyruvic acid, acetic acid, and lactic acid. A forth metabolite, propionaldehyde, is potentially hazardous, hence the importance of medical help. However, various sources state that a large quantity of propylene glycol would be required to cause “perceptible health damage” to humans.

Interestingly enough, the US Food and Drug Administration (FDA) has classified propylene glycol as “generally recognized as safe” for use as a food additive. It is found in ice cream, frozen desserts and other foods. It is safe for use in dog food, but cats become anemic if it is in their food. (Check your pet food labels.)

However, there is one interesting caution that is especially important for fishermen. Propylene glycol is hazardous to the aquatic environment. The mechanism of impact on the aquatic environment is of interest. In addition to being harmful to the fish and shellfish through ingestion of the propylene glycol, it is known that the microbiota in water consume large amounts of oxygen when they degrade propylene glycol. The result is a substantial decrease in the amount of dissolved oxygen available to the fish. In the most extreme case and over the long term, the pelagic fish will leave the area for areas more rich in oxygen and eventually the depleted dissolved oxygen may impact the bottom feeders.

OK, back to the good news. Non-toxic antifreeze is excellent for winterizing engines and potable water systems; it is non-corrosive. It is very much safer for humans and the environment than ethylene glycol. Read the labels on the containers, use the product cautiously with regard to your own exposure, and don’t dispose of used or excess product into the aquatic environment. You can mix it with that extra kitty litter, saw dust, or other absorbent and throw it in the trash.

Enjoy the winter!

Ann Backus, MS, is an Instructor in Occupational Safety and Director of Outreach in the Department of Environmental Health at the Harvard T.H. Chan School of Public Health, Boston, MA. She may be reached by phone at (617) 432-3327 or by email at abackus@hsph.harvard.edu