Mercury is one of the most peculiar elements we know, and we have known about it for about 4,000 years. One of the few liquid metals at room temperature along with cesium, gallium and francium; all discovered in more recent years, mercury (from the Greek hydrargyros, liquid silver) is a heavy metal with atomic number 80 and symbol Hg that is located right next to thallium in the periodic table, and with which it shares certain characteristics that make it very interesting, to say the least.
Mercury can exist naturally in two forms: its metallic form with its characteristic liquid shine is the best known, previously widely used in thermometers, barometers and any instrument to measure pressure and/or temperature; and its organic form in the form of mercuric sulfides, also known as cinnabar.
In its metallic form it is considered not too toxic, due to the difficulty it presents to be absorbed by the body, except when it is heated above 40° C, then it produces highly toxic and corrosive vapors that can be inhaled, ingested or enter the body through the skin and mucous membranes.
The problem with mercury stems from its affinity to react with sulfur groups that are part of a large number of metabolic enzymes in the human body, thus interfering with the normal metabolism of the individual. The main sources of mercury responsible for metal poisoning are usually mercuric chloride, mercuric chloride, mercuric oxide and mercuric cyanide, in addition to their organic compounds.
The symptoms of acute mercury poisoning can be divided into two groups: those that occur in the mouth and gastrointestinal tract (GIT) and are the first to be perceived, ranging from a metallic aftertaste in the mouth, burning and constriction of the throat, as well as as pain in the GIT, constant nausea and vomiting; and systemic symptoms, which it shares with the rest of the heavy metals and range from anxiety, palpitations, increased blood pressure and kidney damage.
High exposures to mercury deplete cellular reserves of selenium available for the synthesis of thioredoxin reductase and other selenoenzymes that prevent oxidative damage caused by free radicals, and whose sustained lack causes brain cells to malfunction, eventually leading to death. On the other hand, mercury is stored in the kidneys, causing kidney damage that eventually causes uremic syndrome, an alteration in biochemical and physiological functions during the development of end-stage renal failure. Other symptoms of metal buildup in the blood include blindness, cerebral palsy, deafness, growth problems, and impaired mental and lung function.
Organic mercury compounds are often far more harmful than the element itself: the most dangerous, dimethylmercury, is so toxic that even a drop spilled on the skin can kill. The most important, due to the effects on the life and health of millions of humans today, is methylmercury, or MeHg+, a metal cation formed by a methyl group (CH3) and a mercury atom. This is a byproduct of countless human processes, from making paints and coatings to burning garbage. Methylmercury accumulates in water, where it passes into fish and shellfish, where it concentrates up the food chain until it is ingested by humans when we consume large species of predatory fish, such as salmon or tuna.
The best-known case of this condition occurred in Minamata Bay in Japan in the 1940s, from which derives the common name for methylmercury poisoning, Minamata disease, a neurotoxic disorder caused by ingestion of contaminated marine products. with methylmercury compounds whose main symptoms include sensory disturbances, ataxia, concentric contraction of the visual field, and hearing disorders. If a mother is exposed to high levels of methylmercury during pregnancy, her baby may suffer from fetal Minamata disease, and may show different symptoms than the adult version of the condition. More than 3,000 people have died from this disease, and cases of poisoning from ingestion of organic mercury continue to rise each year.
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