|Photo by Sealle, used under CC BY 2.0 license.|
There is a much subtler form of this that can be done with inanimate objects. "Don't put sulfur mustard in your body! It's a chemical weapon!" Sulfur mustard is indeed a chemical weapon. Of course, sulfur mustard is also an early chemotherapy drug which worked precisely because it is a cellular poison. So the advice to categorically refuse to put it in your body under any circumstance is somewhat misguided (now we have some better drugs- though I'm no oncologist). This brings me to the interesting case of antifreeze. I recently read a story about dog owners suing Purina, the pet food manufacturer, alleging in part that the practice of adding propylene glycol to dog food killed their dogs. The article correctly states that propylene glycol is a component in antifreeze. This is where I tell you, in no uncertain terms, that antifreeze has an unfair reputation. Sorta. Kinda. It's a long story, so let's get to it.
What's In a Name?
What's in a name? that which we call a rose
By any other name would smell as sweet;
-William Shakespeare. Romeo and Juliet, Act II, SceneII.A few days ago I wrote about the Food Babe, and she has made much about the presence of propylene glycol in certain foods. She states that it is a component of antifreeze, and that we should be very afraid. As others have pointed out however, propylene glycol (which is in antifreeze, I'll get to this in a second) is distinct, and completely different from propylene glycol alginate which is what is actually in the foods she's highlighting. You see, in chemistry, these seemingly small differences in words are absolutely devastatingly critical. The International Union of Pure and Applied Chemistry (IUPAC) is in charge of coming up with the international standards for naming chemical compounds, and because chemicals are so diverse, the naming rules can get incredibly complicated. What you need to know is that just because chemicals sound similar, or even rhyme, it doesn't even mean that they are at all related.
Take bromine, for example. It's a toxic gas. Theobromine is an important component of chocolate. So it should be similar, or at least have some bromine in it, right? No. Theobromine is named after the scientific name for the cocoa plant, Theobroma cacao in which it was first discovered. There is absolutely no relationship to bromine, the element. In fact, it's much more closely related to caffeine.
This brings us to alginates. Alginates are actually derived from kelp, they're gel-like sugary substances. They're useful for many, many things. Since they're derived from kelp and seaweed, which we've been eating for centuries, we don't mind putting them in food. So propylene gylcol is not the same as propylene glycol alginate. They're just not the same.
Even when compounds are similar, it doesn't mean that they're not radically different in the effect they will have on the human body. A similar naming story is methanol and alcohol. If you take fruits and certain vegetables, and allow them to ferment, they produce a bitter, combustible substance we know as alcohol. The chemical name for alcohol is ethanol or ethyl alcohol. If you're desperate enough for alcohol that you decide to hack apart your furniture and ferment the wood, what you'll get is a related compound once known as wood alcohol, an better known to chemists as methanol or methyl alcohol. The names, and even the structures, of ethanol and methanol are incredibly similar.
The effects could not be more different. Alcohol will intoxicate you. It's so good at this we sell it by the bottle in various flavors. It's poisonous, of course, so we tell you that you should be careful not to drink too much, but a lot of people risk it anyway. Methanol is also poisonous, but if you drink a glass of methanol, you won't just be intoxicated, but blinded. Methanol breaks down in the body to form highly toxic compounds. Homeless alcoholics, finding themselves without money to purchase quality alcohol have succumbed to the effects of ingesting methanol, since its effects are initially similar and it smells similar. It's also generally not taxable, which makes it cheap. Whether you drink alcohol is your business, but you should never, under any circumstances, drink methanol as a substitute.
In chemistry, a rose by any other word might kill you.
Bait and Switch.
One of the main components of antifreeze has long been the sickly sweet, and absolutely toxic compound ethylene glycol. Ethylene glycol is toxic to humans but the "glycol" in its name is actually a hint that it's in a class of compounds known as diols. Its sweetness has lead to it being used as a poison of choice by various cruel individuals. So that's it then? Case closed. Antifreeze is bad for you and anyone who puts it in food is a bad person, right?
Not exactly. Precisely because ethylene glycol is so toxic, and because it's bad for the environment, there has been a move to use a related compound in antifreeze: Propylene glycol. The idea is that it will keep your car running, but if leaks, it won't be as bad for plants and animals. Remember the difference between alcohol and ethanol? There's a similar one here. If you've eaten ice cream in the past ten years, chances are you've ingested some propylene glycol. In fact, the FDA has stated the propylene glycol, in small amounts, is safe. When you ingest it, your body breaks it down into lactic acid, which your body knows how to deal with since it makes lactic acid every time you exercise.
The problem is that even though the toxicity of a lot of brands of antifreeze has gone down, people are still behaving as if having the same product as a food additive is a monstrosity, even though the only reason it's in antifreeze is precisely because it's less toxic. You can't win for losing, sometimes. Antifreeze was (and still is) highly toxic, so we've make it less toxic by using something that could be considered a food additive, and the response has been to look at food and go, "There's antifreeze in there!" If we somehow figured out how to clear clogged drains with coffee, then people would turn around and go, "Did you know that they sell coffee with drain cleaner in it?!"
Of course, antifreeze still has a bunch of other toxic compounds in it, including methanol, so it should go without saying that you shouldn't drink it.
Hair of the Dog
Here's the thing about the news story: It doesn't smell right. I don't know anything about the toxicity of various substances in dogs, but the plaintiffs' cases sound a lot like attribution error, where people pick seemingly linked events and tie them together. These days, you put up a Facebook post saying dog food killed your pet, and everyone whose dog dies of similar symptoms checks to see if they have the same dog food. If they don't, they don't say anything. If they do, they become another data point that seems to confirm a trend. I don't think that Purina actually does very much different from its competitors, and if propylene glycol kills dogs, then why only Purina dog food? There are cheaper, far more corner-cutting brands out there that no one is accusing of anything.
I'm not saying that Purina is in the clear, and that I know for certain that their food has always been safe. I'm not even saying that propylene glycol is probably okay for dogs. I am pointing out that claiming it contains "an antifreeze chemical" is a lawyer's gambit, not a scientific evaluation of how harmful it is. If you've ever drank tea, no matter how pure and natural, you've ingested large quantities of a chemical commonly used in sewage treatment: Water. See how ridiculously easy it is?
Losing a pet is tragic, and I have sympathy for the owners who have lost pets. I have pets of my own. Still, it's important to analyze a news story critically, and look at what is being said by who. Nothing against lawyers, but lawyers are not paid to make scientifically accurate statements, and neither are their very-coached clients. It is also incredibly useful to think generally in these situations. Are other manufacturers probably doing the same thing? Why only Purina brand? What could they be doing different? Why deny it? (This one isn't as obvious as it seems.) Who are the lawyers? Who are the plaintiffs?
The conclusion you reach may be different from mine, and I don't think that would be entirely unreasonable- just don't base it purely on the fact that propylene glycol happens to be in antifreeze.