The simple math error is...?
TL;DR: They overstated the dose by a factor of 10 due to an "error" multiplying two numbers.
From linked article (link in the subject article) emphasis added:
In the study, researchers estimated that using black plastic kitchenware could cause an intake of 34,700 nanograms a day of decaBDE. But, in a section of the study on “Health and Exposure Concerns,” the researchers said that amount “would approach” the established safe exposure limit set by the EPA (also known as a reference dose).The study notes that the reference dose for decaBDE is 7,000 nanograms per kilogram of body weight a day; the reference dose for a 60-kilogram (132-pound) adult, it calculated, would be 42,000 nanograms a day. That would put this exposure at more than 80% of the EPA’s limit.
Here’s the thing: The math was incorrect. Sixty multiplied by 7,000 is actually 420,000, not 42,000. As a result, the exposure amount of 34,700 nanograms a day of decaBDE from black plastic is less than a 10th of the established EPA limit.