Why is Mercury so poisonous?
I’m assuming, like me, you were always told the same thing as a child: “Don’t bite on the thermometer!” You might assume your parents were being overzealous as usual, exaggerating so you pay attention. But having witnessed the ensuing panic after my little sister bit into one, I started thinking maybe there was something to this.
But what is it about Mercury that makes it do dangerous? Often called Quicksilver, its physical properties make it the stuff of stories! The symbol for mercury on the periodic table is Hg from the Greek “hydragynum” which translates to watery silver: this is where the secret lies. Silver is a metal and we generally have a specific idea of what metals are like: hard and strong and generally always in a solid state. Mercury is the only metal that is liquid at standard temperature and pressure: in fact it is the metal that can remain liquid in the widest range of conditions. This is mostly due to the abnormal behaviour of the electrons orbiting the atom and makes it one of the only 5 elements to be liquid in a normal state.
But the real dangerous property of mercury is its density. 13.5 times denser than water, its liquid and gas forms are highly poisonous. When inhaled or ingested, Mercury can accumulate in the body, slowly degrading the membranes of important organs like the brain, nervous system, kidneys or liver. It can cause varying effects from eye irritation and vomiting to DNA and chromosomal damage. Mercury can be found naturally in the environment, present around the world as cinnabar. Although it has always been released into the environment through normal weathering, the recent rise in its quantity on the globe has many people worried. As it is not naturally found in food, there is a worry that we could be ingesting dangerous amounts of it simply as a result of the natural food chain, fish being the main concern.
There has been a huge effort to minimise the mercury danger, whether it be its atmospheric concentration or finding new tools to replace its use in day-to-day life. A wide range of non-mercury thermometers are now available, especially as mercury thermometers have been banned in the US and some EU countries.
The other day I broke one of the last remaining mercury thermometers in my lab. Not in my mouth thank god, just dropped it on the floor. A million little beads of silver scattered everywhere and I have to admit I was a little stumped as to what to do. Once thing: don’t hoover it up or use a broom, you’ll just disperse the beads even further. But it is possible to merge the beads together by pushing them along the floor and making a bit pool of mercury. It actually is quite cool! Luckily we have ways of disposing of toxic chemicals in research labs, but don’t mess around with it at home, your parents were right to be a pain!