How a simple math error sparked unnecessary panic about black plastic

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The simple arithmetic error that unnecessarily sent countless plastic spatulas into the trash over a toxic chemical scare came to light a few days ago as Joe Schwarcz, director of McGill University’s Office for Science and Society, sat reading a research paper in his office in the Otto Maass Chemistry building on Montreal’s Sherbrooke Street.

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“I follow everything on plastics, that’s one of my areas,” the well-known chemist and science popularizer said in an interview. He’s also a “stickler for detail on numbers,” so when he saw 60 multiplied by 7,000 to get 42,000, his eyes widened. “I’m not bad at math,” he said.

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Plastics rarely make news like this. From Newsmax to Food and Wine, and from the Daily Mail to CNN, the media uptake was enthusiastic on a paper published in October in the peer-reviewed journal Chemosphere.

“Your cool black kitchenware could be slowly poisoning you, study says. Here’s what to do,” said the LA Times. “Yes, throw out your black spatula,” said the San Francisco Chronicle. Salon was most blunt: “Your favorite spatula could kill you,” it said.

The study, by researchers at the advocacy group Toxic-Free Future, sought to determine whether black plastic household products sold in the U.S. contain brominated flame retardants, fire-resistant chemicals that are added to plastics for use in electronics, such as televisions, to prevent accidental fires.

The hypothesis was that these chemicals are in black plastic kitchenware because electronic waste, such as televisions, is sometimes recycled back into household items, such as spatulas. Ironically, this is because black plastic is not recyclable by traditional means because it does not reflect the infrared light used in sorting machines, but it is commercially desirable, so producers seek out cheap sources from recycled electronics, often in Asia.

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Through a series of estimates and laboratory experiments, the researchers in Chemosphere aimed to measure how much of this flame retardant toxin was getting out of the spatulas during cooking and into the human body.

The study noted there are concerns about these chemicals causing cancer, disrupting the endocrine system of hormones, and other kinds of toxicity affecting the nervous and reproductive systems.

The study estimated that using contaminated kitchenware could cause a median intake of 34,700 nanograms per day of Decabromodiphenyl ether, known as BDE-209. That is far more than the bodily intake previously estimated from other modes, such as ingesting dust.

The trouble is that, in the study’s section on “Health and Exposure Concerns,” the researchers said this number, 34,700, “would approach” the reference dose given by the United States Environmental Protection Agency.

A reference dose is a sort of limit on safe exposure to a toxin, informed in this case by studies on mice.

The paper correctly gives the reference dose for BDE-209 as 7,000 nanograms per kilogram of body weight per day, but calculates this into a limit for a 60-kilogram adult of 42,000 nanograms per day. So, as the paper claims, the estimated actual exposure from kitchen utensils of 34,700 nanograms per day is more than 80 per cent of the EPA limit of 42,000.

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That sounds bad. But 60 times 7,000 is not 42,000. It is 420,000. This is what Joe Schwarcz noticed. The estimated exposure is not even a tenth of the reference dose. That does not sound as bad.

“I think it does change the flavour of the whole thing somewhat when you’re off by a factor of ten in comparing something to the reference value,” he said.

Lead author Megan Liu, science and policy manager at Toxic-Free Future, described the mistake as a “typo” and said her co-authors have submitted a correction to the journal. The error remains in the online version but Liu said she anticipates it will be updated soon.

“However, it is important to note that this does not impact our results,” Liu told National Post. “The levels of flame retardants that we found in black plastic household items are still of high concern, and our recommendations remain the same.”

National Post also covered this report in the first instance, with the headline: “Should you toss your black plastic spatula? What a new study says about toxic chemicals.”

There is an old newspaper joke, known as Betteridge’s Law, that every headline phrased as a question can be correctly answered with the word “No.” But things are rarely so simple, especially in using science to inform health policy, even if some of the arithmetic is dodgy.

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As Schwarcz points out, it appears the study’s hypothesis is correct, that black plastic recycled out of electronic devices, mostly in Asia, is getting back into the American supply chain for household kitchen items, including spatulas.

So if you’re keen on eliminating these chemicals in any amount, chucking the black plastic kitchenware is a start, even if not as effective as the erroneous calculation suggests.

But it is another example of science being led astray in describing risk. Schwarcz does not generally like measurements of risk expressed in percentages. Absolute numbers tend to be more useful, as in this study. He gives the example of a lottery ticket. If you have one lottery ticket, your chances of winning are, say, one in a million. If you buy another, your chances of winning have increased by 100 per cent, which sounds like a lot until you realize they are still just two in a million.

“Risk analysis is a sketchy business in the first place, very difficult to do, especially if you don’t express units properly,” Schwarcz said. “You can make things sound worse.”

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There was also no need to use nanograms as the unit of measurement in this study, Schwarcz said, which gave unit amounts in the tens of thousands. The more common micrograms would have given units in the tens.

“It’s a common thing in scientific literature, especially in ones that try to call attention to some kind of toxin,” Schwarcz said.

“All of this merits attention,” he said. “But you have to do it properly, and you have to make sure your numbers are correct before you scare the pants off people.”

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