“Twinkle, twinkle, little bat, how I wonder what you’re at.” So starts the Mad Hatter in Lewis Carroll’s Alice’s Adventures in Wonderland at a tea party he shares with the March Hare and the Dormouse. He also asks, “Why is a raven like a writing desk?” As Alice finds out, there is no answer to this riddle. These nonsensical quips by the Mad Hatter suggest that his eponymous name is well deserved. Most likely, it was his occupation that poisoned him.
When felt hats became popular in Europe around the start of the 17th century, hat makers used mercury in the manufacturing process. This made it easier to create a smooth, even felt. Felting (or carroting) involved treating animal fur or wool with a solution of mercuric nitrate to create a mat of fibers that could be molded into complex shapes—pressed and shaped into a hat form. By the 19th century, it was recognized that hatters were at risk of mercury poisoning, and some attempts were made to regulate its use in the hat-making industry. But it wasn’t until the 20th century that the use of mercury in hat-making was essentially phased out.
Mercury is toxic, and exposure to its vapors gave rise to neurological symptoms such as tremors, memory loss, and odd behaviors that typified the expression ‘mad as a hatter.’ It is a formable poison as the vapors can cross the blood-brain barrier leading to significant toxicity.
Mercury exists in three toxicologically significant forms: elemental, inorganic, and organic compounds. Elemental mercury is the only metal liquid at room temperature and is sometimes referred to as quicksilver. For example, thermometers, barometers, and fluorescent bulbs contain the elemental form of mercury, while inorganic mercury can be found in products used as disinfectants and fungicides. Organic forms of mercury, such as methylmercury, are present in sea and freshwater through both environmental contamination and natural processes. Fish can concentrate mercury via the food chain, which results in various amounts of methylmercury in the flesh, depending on what they eat and how long they live. The higher up the food chain, the more mercury. Guidelines on safe fish consumption, particularly for pregnant and nursing mothers, are available. Species such as swordfish and King mackerel should be avoided or limited as they contain higher concentrations of methylmercury than, for example, flounder or salmon.
Significant mercury poisoning of local residents, including pregnant women and children, occurred in Minamata, Japan, in the late 1950s. Contaminated wastewater from a nearby chemical plant was released in Minamata Bay and Shiranui Sea. Fish and shellfish living in the polluted waters were consumed by residents and produced severe poisoning. The methylmercury poisoning caused ataxia (impaired balance and coordination), numbness of the hands and feet, and muscle weakness. Central nervous system (brain) changes were also observed in the congenital form of the disease, and children were born with deafness, blindness, gnarled limbs, and severe intellectual disabilities.
Proper disposal of mercury-containing thermometers, fluorescent light bulbs, thermostats, and any other household or industrial items is essential for keeping the environment mercury free. The Cheshire cat was right. He thought that both the Hatter and the March Hare were mad.
And neither played basketball.