Bostonians who watch WBZ-TV News saw something last night that’s all too common in our national discussion about trace levels of mercury in tuna: a television reporter who can’t grasp the concept of multiplying  by 10. WBZ’s Paula Ebben whipped up pointless fear about “troubling levels of mercury” in a handful of pieces of sushi her staff bought from local vendors. “The most troublesome results,” Ebben insisted: “Three of our samples tested above the Food and Drug Administration’s ‘Action Level,’ which means they contain so much mercury [that] the agency could take legal action…” But without a clue about what the FDA’s “Action Level” means, and how the magic number 10 is involved, WBZ ended up serving up nothing but panic.
Here’s the FDA’s own description of its “Action Level” for mercury in fish, a definition that hasn’t changed since at least 1994:

FDA’s action level of 1 ppm [part-per-million] for methyl mercury in fish was established to limit consumers’ methyl mercury exposure to levels 10 times lower than the lowest levels associated with adverse effects [to health]… FDA based its action level on the lowest level at which adverse effects were found to occur in adults. This is because the level of exposure was actually lower than the lowest level found to affect fetuses, affording them greater protection. [emphasis added]

So although the FDA’s “Action Level” is 1 ppm, the lowest level associated with adverse health effects is ten times higher. There’s that tricky math problem that has baffled reporters at The New York Times, the Chicago Tribune, ABC News, Newsweek, and now the good people at WBZ. And they’ve all forgotten to mention that the medical literature contains zero cases of fish-related mercury poisoning from eating commercial catches in the United States.
There were other problems with the WBZ story as well. One quoted doctor claimed that traces of mercury may “virtually eliminate” the heart-protective benefits of eating fish. He also insisted that the idea of selenium in fish protecting against mercury contamination is still “very preliminary.” But the evidence for the first statement consists of a single anomalous study. The evidence for the second consists of about 300 pieces of published research.

It may be too much to expect journalists to be well-versed in toxicology (or basic arithmetic). But here’s hoping their Google searching skills improve to the point where we’ll see fewer examples of what otherwise seafood-savvy Bostonians had to endure last night.