The "holiday" began in Colorado in 1986, simply as an excuse for "crazy" or whimsical behaviors, especially involving the wearing of hats. When I posted this photo online, a friend in Brazil immediately commented with the Portuguese version of the term, and some virtual chuckles followed.
As detailed in a Mad Hatter Day article in the Panache section of Economic Times, the manic character is associated with Lewis Carroll's Alice in Wonderland, though he never used that exact name for his character the Hatter. The article explains why today's date is used to celebrate the character.
It errs, however, in associating the "madness" of haberdashers with their use of lead; mercury was the real culprit, as mentioned in the video above. It is an easy mistake to have made: both are metals known to be neurotoxins, and in reality the toxicity of mercury is gravely serious. In fact, I am justifying the time I am spending on this blog post by the fact that I am sharing it with my Environmental Regulations class later this morning. We will make some comparisons between mercury and dichlordiphenyltrichloroethane, which we have been studying for the past few weeks.
Mercury and DDT are different in many ways, but both are subject to biomagnification in fatty tissue and were in use for decades before their toxicity was understood. Both exemplify the limitations of free markets when managing environmental risks.