Why is mercury poisonous? It can damage the nervous system, kidneys, liver, and immune systems of people and animals.
Mercury is a heavy metal. Heavy metals are metals that are very dense and have a high atomic number. Mercury has an atomic number of 80. It melts at -38.83℃, which means it is liquid at room temperature. It boils at 356.62℃. When it is heated, it expands very consistently, which is why it is used in non-digital thermometers. All heavy metals are toxic to us, except for bismuth.
All mercury is toxic to us, but there are different forms of mercury and some forms are more toxic than others. Elemental mercury is pure mercury that is liquid at room temperature. This is what you will find in a thermometer. It also has many other uses, from electrical switches to mining. Then there is inorganic mercury. This is formed when mercury combines with other elements, like sulphur or oxygen. They can occur naturally or then can be created through industrial processes. Some cosmetics used to use inorganic mercury. Lastly, there is organic mercury. This is when mercury combines with carbon and it is a process that can be carried out inside living organisms. Microscopic organisms can convert mercury into methylmercury, and this is the most dangerous for us.
We can be exposed to elemental mercury through its vapor. It is not likely that someone will inject mercury as a whole, but when it is vaporized, it can be inhaled very easily. This is the worry if you break a thermometer or work somewhere mercury is used in an industrial process. We are not likely to be exposed to inorganic mercury unless we actually work with it directly. Organic mercury is the one we are most likely to be exposed to and the two most common ways are through eating fish and shellfish, and through pollution.
When mercury gets into the sea or lakes and rivers, microorganisms convert it into methylmercury. Larger fish or shellfish eat these organisms and pick up the methylmercury. As it goes up the food chain, more and more methylmercury builds up until the fish at the very top, sharks, dolphins, whales, and very large fish, contain large amounts of methylmercury. When we eat those fish, that methylmercury goes in to us. So, how does it get into the sea? It gets there through pollution. Fossil fuels, such as coal, contain mercury. When we burn fossil fuels, the mercury is released into the atmosphere. It is estimated that 3,000 tons of mercury is released into the atmosphere from power stations every year. The rest of the mercury in the atmosphere comes from volcanoes and natural weathering. Once the mercury is in the atmosphere, we can breathe it in, or it can sink down into the oceans, where microorganisms turn it into methylmercury.
All three types of mercury can be poisonous, but organic mercury, particularly methylmercury is the worst. Elemental mercury is dangerous, but it is not absorbed into our bodies very easily. It is far more dangerous when it is inhaled as a vapor because it passes through the lungs and into the bloodstream far more easily. Methylmercury is the most dangerous because our bodies absorb it very easily and because we have a far larger chance of being exposed to it in such large quantities.
Once mercury vapor or methylmercury are in the bloodstream, they travel to the liver, the kidneys, and up into the brain. Methylmercury is able to cross the blood brain barrier and enter the brain. Once there, it starts to build up. Mercury is harmful in any organ that it settles in because it can stop the production of proteins and hamper with the cell’s mitochondria. It also interferes with thioredoxin reductase, which is responsible for using vitamins to prevent damage to the cells from oxidization. The brain uses a large amount of the body’s total oxygen and therefore has a much larger amount of damage from oxidization. Mercury prevents the body from fixing this and parts of the brain can die. Mercury also disrupts neurotransmitters, shutting down parts of the brain and parts of the nervous system. Sufferers can lose their eyesight, senses, and even the ability to walk. Death can follow.
Methylmercury can be transmitted to babies along the placenta and can cause an enormous amount of brain damage. Minamata Bay in Japan is a sad example of this. The Chisso Corporation released methylmercury into the bay for 30 years. The number of children born with neurological disease skyrocketed.
Here’s an extra thing I found out. The Mad Hatter in Alice in Wonderland made more sense when the book was written because a lot of hatters were mad. From the 18th to the 20th century, hat makers used mercury to stiffen the felt they used in their hats. From the constant contact with mercury, many of them developed mercury poisoning and went mad. Many hatters were mad. And this is what I learned today.
Image By Bionerd – Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=4972709
Sources
https://faculty.washington.edu/chudler/merc.html
https://www.atsdr.cdc.gov/sites/toxzine/mercury_toxzine.html
https://www.who.int/news-room/fact-sheets/detail/mercury-and-health
https://my.clevelandclinic.org/health/diseases/23420-mercury-poisoning
https://en.wikipedia.org/wiki/Mercury_poisoning
https://en.wikipedia.org/wiki/Mercury_(element)
https://www.cdc.gov/biomonitoring/pdf/Mercury_FactSheet.pdf
https://dec.vermont.gov/sites/dec/files/wmp/SolidWaste/Documents/alittlebit.pdf
https://www.thermofisher.com/blog/metals/infographic-bismuth-the-heaviest-among-heavy-metals/