The Study That Called Out Black Plastic Utensils Had a Major Math Error

Despite the correction, the study's authors stand by their conclusions about the risks of certain kitchen utensils.

Editors of the environmental chemistry journal Chemosphere have posted an eye-catching correction to a study reporting toxic flame retardants from electronics wind up in some household products made of black plastic, including kitchen utensils. The study sparked a flurry of media reports a few weeks ago that urgently implored people to ditch their kitchen spatulas and spoons. Wirecutter even offered a buying guide for what to replace them with.

The correction, posted Sunday, will likely take some heat off the beleaguered utensils. The authors made a math error that put the estimated risk from kitchen utensils off by an order of magnitude.

Specifically, the authors estimated that if a kitchen utensil contained middling levels of a key toxic flame retardant (BDE-209), the utensil would transfer 34,700 nanograms of the contaminant a day based on regular use while cooking and serving hot food. The authors then compared that estimate to a reference level of BDE-209 considered safe by the Environmental Protection Agency. The EPA's safe level is 7,000 ng—per kilogram of body weight—per day, and the authors used 60 kg as the adult weight (about 132 pounds) for their estimate. So, the safe EPA limit would be 7,000 multiplied by 60, yielding 420,000 ng per day. That's 12 times more than the estimated exposure of 34,700 ng per day.

However, the authors missed a zero and reported the EPA's safe limit as 42,000 ng per day for a 60 kg adult. The error made it seem like the estimated exposure was nearly at the safe limit, even though it was actually less than a tenth of the limit.

"[W]e miscalculated the reference dose for a 60 kg adult, initially estimating it at 42,000 ng/day instead of the correct value of 420,000 ng/day," the correction reads. "As a result, we revised our statement from 'the calculated daily intake would approach the U.S. BDE-209 reference dose' to 'the calculated daily intake remains an order of magnitude lower than the U.S. BDE-209 reference dose.' We regret this error and have updated it in our manuscript."

Unchanged Conclusion

While being off by an order of magnitude seems like a significant error, the authors don't seem to think it changes anything. "This calculation error does not affect the overall conclusion of the paper," the correction reads. The corrected study still ends by saying that the flame retardants "significantly contaminate" the plastic products, which have "high exposure potential."

Ars has reached out to the lead author, Megan Liu, but has not received a response. Liu works for the environmental health advocacy group Toxic-Free Future, which led the study.

The study highlighted that flame retardants used in plastic electronics may, in some instances, be recycled into household items.

"Companies continue to use toxic flame retardants in plastic electronics, and that's resulting in unexpected and unnecessary toxic exposures,” Liu said in a press release from October. "These cancer-causing chemicals shouldn't be used to begin with, but with recycling, they are entering our environment and our homes in more ways than one. The high levels we found are concerning."

BDE-209, aka decabromodiphenyl ether or deca-BDE, was a dominant component of TV and computer housings before it was banned by the European Union in 2006 and some US states in 2007. China only began restricting BDE-209 in 2023. The flame retardant is linked to carcinogenicity, endocrine disruption, neurotoxicity, and reproductive harm.

Uncommon Contaminant

The presence of such toxic compounds in household items is important for noting the potential hazards in the plastic waste stream. However, in addition to finding levels that were an order of magnitude below safe limits, the study also suggested that the contamination is not very common.

The study examined 203 black plastic household products, including 109 kitchen utensils, 36 toys, 30 hair accessories, and 28 food serviceware products. Of those 203 products, only 20 (10 percent) had any bromine-containing compounds at levels that might indicate contamination from bromine-based flame retardants, like BDE-209. Of the 109 kitchen utensils tested, only nine (8 percent) contained concerning bromine levels.

"[A] minority of black plastic products are contaminated at levels >50 ppm [bromine]," the study states.

But that's just bromine compounds. Overall, only 14 of the 203 products contained BDE-209 specifically.

The product that contained the highest level of bromine compounds was a disposable sushi tray at 18,600 ppm. Given that heating is a significant contributor to chemical leaching, it's unclear what exposure risk the sushi tray poses. Of the 28 food serviceware products assessed in the study, the sushi tray was only one of two found to contain bromine compounds. The other was a fast food tray that was at the threshold of contamination with 51 ppm.

This story originally appeared on Ars Technica.

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