80
mercury200.59
by Tori Blakeman
M
ercury, an element that can be both deadly and unassailably safe. Knowing the difference might save you from madness.
Mad Hatter’s Disease. We’ve all heard of it. It’s at the centre of Lewis Carroll’s famous Mad Hatter character in Alice in Wonderland, and affects the protagonist in the new hit podcast, S-town. I’m also sure most of us have been announced ‘as mad as a hatter’ before, after a particularly silly moment or two.
Both elemental and methylmercury are extremely toxic to the central and peripheral nervous systems, as they are able to penetrate the blood-brain barrier. If ingested or inhaled, mercury can get into the cells of the nervous system where it reduces cellular processes such as RNA production and protein synthesis, ultimately leading to cellular degeneration and cell death.
It turns out that hatters did go mad, thanks to poisoning from mercury (Hg); the naturally occurring element that is found in air, water and soil. Old England hat-makers of the Victorian era used mercury to stabilise wool when felting fur from animals such as rabbits. It was this technique that exposed hat-makers to long-term inhalation of the element, which ended up causing chronic neurological damage. Due to such poisonous effects, mercury has largely been phased out from many processes and products in which it was once commonplace: batteries, lamps, thermometers, light bulbs and felt production are some examples. It has now even made the World Health Organisation’s top 10 list of chemicals posing a major public health concern. Despite this, today the element is still, surprisingly, present in commonplace medicine, such as in silver dental fillings and as a preservative in vaccines. So, why has mercury been phased out for some uses, but not others? Mercury exists in various forms, all of which have varying toxic effects. Elemental mercury, the raw element found within the Earth’s crust, is pretty safe when left untouched. That is, until it’s released into the atmosphere by volcanic activity, or, more likely, human activity such as coal burning. Once in the environment, elemental mercury is naturally broken down by bacteria into its organic form, methylmercury.
8
I, Science
The symptoms of mercury poisoning vary according to exposure, but are largely determined by the areas of the nervous system most vulnerable to the element: the sensory spinal ganglia and the cerebellum. The sensory spinal ganglia are the nerve fibres that relay information from the muscle and skin to the spinal cord, conveying feelings such as pain, temperature and touch. The cerebellum is the area of the brain situated at the back of the head, at the top of your neck, and is important in maintaining posture, and coordinating and learning movements. Exposure to even small amounts of mercury can therefore cause serious health problems, affecting senses as well as movement. If inhaled regularly, the famous Mad Hatter’s disease, or Erethism
mercurialis as its medically known, manifests as tremors, pathological shyness, irritability, depression and delirium. Even worse, chronic ingestion can have profound effects in the form of Minamata disease. Between 1932 and 1968 in Minamata, Japan, vast quantities of mercury were released into the sea as chemical waste from factories, causing methylmercury to accumulate in the tissue of fish and shellfish. Entirely unaware, the local fishing population continued to consume their seafood, resulting in widespread insanity, paralysis, comas and even death. The contamination was so far reaching that fish today are still ridden with mercury, and the consumption of fish and shellfish is now the most common reason for exposure to methylmercury. Yes, mercury is present in seafood, but no, you will not get Minamata disease if you eat it. The amount of mercury ingested via seafood today is approximately 0.3 grams in a lifetime; far too small to cause a problem. Unless, perhaps, if you’re a member of a subsistence fishing population from Brazil, Canada, China, Columbia or Greenland, where up to 17 in 1000 children can present with cognitive impairment. The not-so-toxic form of mercury is ethylmercury, found in thiosermal, which is used in very small amounts as a preservative in some vaccines and pharmaceuticals. The reason ethylmercury isn’t as poisonous as other forms is that once it is within the body, it is rapidly broken down and so does not accumulate within the cells. There is therefore no reason to worry about mercury poisoning the next time you get a vaccine. The World Health Organisation has continually reviewed the use of thiosermal in vaccines and always reaches the same conclusion; that it poses absolutely no health risk. The mercury used in dental fillings has no health risk either. Mercury is present here as an amalgam comprising of about 50% mercury, combined with silver and small amounts of copper, zinc or tin. Amalgamating the metal like this renders it inert, and therefore non-toxic. There remain concerns of mercury vapour release on chewing, however, all studies to present have been inconclusive. Mercury is a fascinating element that has been utilised for millennia for numerous reasons. Considering its toxic effects, it is essential that mercury science now shifts to reducing its use and anthropogenic release to relieve danger to both health and the environment.
www.isciencemag.co.uk