In a stuffy milliner’s workshop in Danbury, Conn., a hat maker brushed a solution of mercury nitrate over a set of rabbit furs. This was the first step of several that the hatmaker would perform to transform the furs into the stiff felt hats in fashion in the late 18th century. As he worked, the milliner breathed in vapors from the muggy air.
Over time, this milliner and others in his profession began to develop a frightening set of symptoms. First, uncontrollable muscular tremors and twitching wracked their bodies. Their vision began to distort, their speech and thought became confused. Some even advanced to hallucinations and other psychotic symptoms.
The onset of such dramatic symptoms in hatmakers eventually coined the term “mad hatters.” These milliners were being poisoned by the mercury that their trade called for. Eventually, after a study of mercury toxicity confirmed it as the cause, mercury was banned in the United States in hat making in 1941.
Mercury inhibits the actions of selenium-dependent enzymes in the body, causing the myriad of symptoms displayed by the “mad hatters.” One of these enzymes normally breaks down adrenaline. As a result, those suffering from mercury poisoning often have symptoms of sweating, a fast heartbeat and high blood pressure.
Seated next to gold on the periodic table, mercury is unique among metals in that it is a liquid at room temperature. Its silvery appearance and ability to flow like water earned it the nickname quicksilver.
The accumulation of mercury in the environment poses a major concern today. Mercury is deposited into the environment by the improper disposal of mercury-containing items, coal plant emissions and volcanoes. Plants and animals accumulate low levels of mercury from contaminated soil, water and atmosphere. Predators then acquire large amounts of mercury by consuming these contaminated prey. This process, called biomagnification, results in significant concentrations of mercury at the levels of higher animals in the food chain, including humans.
Long before its toxicity was understood, mercury was valued in many cultures. In Islamic Spain, mercury was used to fill decorative pools, and may have even been used as divination mirrors in bowls during the classic period of Mayan civilization. Ancient Greeks, Romans and Egyptians also used mercury in cosmetics, which sometimes resulted in deformed faces.
Although once used for many things in modern society, including mascara, thermometers and electronics, its use is being phased out in many applications due to this accumulation and toxicity. However, the use of mercury in fluorescent light bulbs is still increasing.