Not long ago, I came across an article about the detection of hazardous elements such as Mercury and Arsenic in traditional Chinese medicinal herbs. It reminded me of my experience during chemistry practical lessons with my students, especially when the experiments involved the use of mercury thermometers. Despite having conducted the same lesson many times, I was always tense and stress, not because of the fear of not being able to complete the lesson, but rather I was worried that someone might accidentally break the thermometer, as mercury is deemed to be toxic.
For most of my years as a Chemistry teacher, no one seemed to be interested to know why mercury is toxic, most are quite happy with just accepting it as a fact and making sure that proper precautions is taken when working with the thermometers, until one day, I was prompted to find out the reason when a student raised the question ‘Why is mercury toxic?’.
Mercury is a fascinating element, the fact that it is a liquid metal at room temperature reminds me of the T-1000 cyborg in the movie, Terminator 2. The ancient Greeks, intrigued by the properties of the metal, named the element after the fleet messenger of God, Mercury. The Chinese mistakenly thought that it could bestow immortality.
After searching through books and the internet, I realised that it was the vapour and not the element which is dangerous. Mercury vapour can be hazardous, especially to the young. Breathing in too much of the vapour may lead to damage to the brain, kidney and lungs and symptoms include tremors, emotional changes, insomnia, muscle atrophy, disturbances in sensations, changes in nerve responses, and performance deficits on tests of cognitive function.
Surprisingly, mercury vapour is not its most toxic form. In the 1950s, dozens of people died and thousands experienced symptoms of mercury poisoning in the Japanese village of Minamata. It was found out that a nearby chemical plant, has been using mercury during its production of the organic compound, acetylene and, in the process discharging the element into the ocean. But mercury is insoluble in water, it turns out that microorganisms in the ocean convert the mercury to a highly toxic compound, methyl mercury, which in turn contaminated the fish, leading to humans being infected when they ingested the fish.
Mercury causes its effects by binding to and deactivates critical enzymes in our body. In order to have this effect, it must enter the bloodstream of our body. The vapour form of mercury or the soluble methyl mercury can accomplished this easily.
So what happen if there is a mercury spillage in the laboratory, usually the laboratory technician will ensure that the students are kept away from the spillage and sprinkle sulfur powder over the spillage since sulfur binds strongly to mercury. The waste can then be removed carefully and discarded properly.
Harada, M. (1995). Minamata disease: methylmercury poisoning in Japan caused by environmental pollution. Critical Reviews in Toxicology, 25(1), 1–24. http://doi.org/10.3109/10408449509089885