If you recently threw out your black plastic spatula, as several news articles urged us to do (“Your favorite spatula could kill you” was a real headline), you might want to see if you can dig it back out of the trash. They were based on a study whose most dramatic finding has turned out to be a miscalculation.
To be fair, the general idea hasn’t been debunked; plastic contains a multitude of chemicals whose potential health effects aren’t well understood. And the black spatula study did identify a serious issue in plastic manufacturing. But the problem is literally 1/10th as big as the news stories led us to believe.
The original study—which makes some good points even when the mathematical error is corrected—focused on the use of flame retardants in plastic. Flame retardants are just what they sound like: chemicals that make it harder for materials to catch fire. Electronic components like computers are often made with flame retardants for safety.
Flame retardants, especially a family of them called brominated flame retardants, are suspected of causing potential health issues (like cancer) and may accumulate in the environment. If these are being used in manufacturing, they should be kept away from places where people might consume them. And that’s where this study comes in.
The authors suspected that black plastic from electronics was being recycled into other items, like kitchen utensils. And they found that that is indeed the case.
As Canada’s National Post reported, chemist Joe Schwarzc took a closer look at the numbers in the study, and found an error—the kind you probably made a ton of on your grade school science papers. (I know I did.) It relates to the dosage of the chemical BDE-209. The reference dose means—very roughly, and there is nuance to this definition—the amount of the chemical that’s considered probably safe to consume each day.
The authors of the paper looked at the reference dose for BDE-209, which was 7,000 nanograms per kilogram of a person’s body weight. They multiplied that out for a 60-kilogram person (132 pounds, the size of a small adult), and then compared that to their findings of 34,700 nanograms per day of exposure from kitchen utensils. Whoa—34,700 is really darn close to the reference dose of 42,000 nanograms per day! That’s definitely cause for concern.
But that math was missing a zero. The reference dose actually multiplies out to 420,000 nanograms. That makes 34,700 nanograms not 83% of the reference dose, but 8.3%. Potentially still a concern, but not nearly to the same degree. The journal posted a correction, in which the authors say “We regret this error and have updated it in our manuscript. This calculation error does not affect the overall conclusion of the paper.”
That overall conclusion was that “when toxic additives are used in plastic, they can significantly contaminate products, made with recycled content, that do not require flame retardancy.” The authors also called for more research and regulation to be sure that plastic items are made with safer materials. And those do sound like fair points to make.
