With an eye to the imminent release of the first federal controls on mercury emissions from power plants, the Sierra Club has released a new smartphone app, Safe Sushi, that lists 38 varieties of seafood, from aji (horse mackerel) to uni (sea urchin roe) and measures each one’s mercury level. It is available for both the iPhone and Android-based models.

(In the case of uni, the app points out that even though the mercury levels are low, it is “unsustainably harvested” and should be avoided.)

Mercury is a neurotoxin; even in smaller doses, it can affect children’s brain development and I.Q. scores. In the 19th century, the use of mercury by haberdashers for treating felt for hats led to high levels of exposure and erratic behavior, inspiring the character of the Mad Hatter in Lewis Carroll’s “Alice in Wonderland.”

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