Mercury poisoning

• 1. Introduction

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  On the 14th of August 1996, Karen Wetterhahn, a chemistry professor at Dartmouth College, spilled a small amount of dimethylmercury onto her latex glove. She was a specialist working with a substance she understood. Five months later she began to feel the symptoms of mercury poisoning. Aggressive chelation therapy, a treatment that binds metals so the body can clear them, could not stop the damage. She died a few months after that from a neurodegenerative disease caused by the mercury.

  Her case is among the strangest in the long record of mercury poisoning. That record includes Chinese emperors, hat makers, Japanese fishing towns and people who simply eat a lot of tuna. How can one metal behave so differently depending on its chemical form? Why can the damage stay hidden for months after the exposure? And how did a substance once swallowed as medicine end up the subject of an international treaty?

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• 2. Three Faces of Mercury

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  Quicksilver, the shiny liquid metal, is surprisingly gentle when swallowed. Animal data suggest that less than 0.01 percent of ingested liquid mercury crosses an intact gut. Even in attempted suicides by injection into a vein, systemic poisoning did not follow, though the metal physically blocked blood vessels at the injection site and in the lungs.

  The vapor of that same metal is the most hazardous form. Roughly 80 percent of inhaled mercury vapor is absorbed through the lungs and carried around the body. Skin takes up only about 1 percent as much as the lungs do. Workers breathing air with concentrations between 0.7 and 42 micrograms per cubic metre developed tremors, weaker thinking and disturbed sleep.

  Mercury salts form the second family. Calomel, the name for mercurous chloride, is far less soluble in water than mercuric chloride, so mercuric salts are generally the more acutely toxic. Both mainly harm the gut and the kidneys. They cross into the brain poorly, so serious neurological damage needs heavy or continuous exposure. Mercuric cyanide is a particular menace. It has been used in murders because it delivers cyanide poisoning alongside the mercury.

  The third family, the organic compounds, is much more dangerous than the metal or its salts. These compounds are linked to damage in the brain and liver. Dimethylmercury is the worst of them, and a few microliters on the skin can kill.

  Methylmercury is the organic form that most people actually meet. Ethylmercury is a different case. It comes from the preservative ethylmercurithiosalicylate, once used as an antiseptic and a vaccine preservative, and it leaves the blood with a half-life of seven to ten days. Indoor latex paints once carried phenylmercuric acetate and phenylmercuric nitrate as mildew killers, until toxicity cases led to their removal in 1990. Ethylmercury is presumed to enter the brain by simple diffusion, without the transporter that methylmercury is thought to use.

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• 3. Inside the Body

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  Thioredoxin reductase is an enzyme that mercury shuts down at a concentration of only 9 nanomolar. This enzyme restores vitamins C and E and other antioxidants to the form in which they can fight oxidative damage. Mercury blocks it for good, along with other enzymes that depend on selenium. The brain burns oxygen at a high rate and so produces many reactive oxygen molecules, which leaves its cells especially reliant on those enzymes.

  High mercury exposure drains the cell's supply of selenium, the element needed to build these protective enzymes. Because this selenium drain is slow, symptoms in adults can appear weeks or months after exposure. The first sign is typically paresthesia, a tingling or numbness of the skin. Severe effects follow quickly, sometimes ending in coma and death. The damage seems to track the peak level of mercury, not how long the exposure lasted.

  Mercury also disables a second chemical, S-adenosyl methionine, which helps the body break down catecholamines such as adrenaline. The result is heavy sweating, a persistently fast heartbeat, extra saliva and high blood pressure. These signs can look like pheochromocytoma or Kawasaki disease, so doctors may misread them.

  Children show their own pattern. Cheeks, nose and lips turn red, and hair, teeth and nails can fall out. Light becomes painful, and muscles go weak. Some patients feel pain, burning or a crawling sensation under the skin that doctors call formication.

  In another route to harm, methylmercury raises antibodies against myelin basic protein and glial fibrillary acidic protein. The immune system then attacks the insulation around nerves, and the central nervous system declines. In fetuses and infants the consequences are the worst, with serious birth defects and nerve sheaths that fail to form properly.

  Experiments on pregnant rodents hint at a longer shadow. Methylmercury given during gestation left behavioral effects that appeared in adulthood, and sometimes only in old age. The prefrontal cortex and dopamine signaling may be especially sensitive.

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• 4. Emperors and Elixirs

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  Neolithic artists who worked with the red mineral cinnabar already show signs of mercury poisoning. Humans have been grinding this mineral for a very long time. In China, alchemists later fed it to the powerful in the hope of granting health or immortality.

  Qin Shi Huang, the first emperor of unified China, is reported to have died in 210 BC after swallowing mercury pills meant to give him eternal life. In 859, Emperor Xuanzong of Tang died after being given cinnabar treated with fire. His court alchemists brushed off worries about his health and sanity. They pointed to medical texts describing itching, formication, swelling and weak muscles as proof the elixir was curing hidden ailments. Today those are recognized as symptoms of mercury poisoning. The emperor grew irritable and paranoid.

  Pliny the Elder, writing in his Natural History, was blunter. He noted that "it is a fact generally admitted that cinnabar is a poison" and warned against using it in medicine. He also described workers who polished it and tied loose masks of bladder skin over their faces to avoid breathing the dust. That is one of the earliest mentions of protective equipment.

  Calomel was a popular Victorian medicine that contained mercury, and it hurt many patients it was meant to help. In her 1859 autobiography, the Scottish seamstress Elizabeth Storie described a life of disability. A doctor had given her prolonged doses of calomel for a mild childhood illness. In 1862 an American Civil War soldier named Carleton Burgan suffered similar disfiguring harm after calomel treatment for an infection. Abraham Lincoln, for years and into the early part of his presidency, took a common mercury-rich medicine called blue mass.

  On the 5th of September 1920, the silent film actress Olive Thomas swallowed mercury capsules dissolved in an alcoholic solution at the Hotel Ritz in Paris. Her husband, Jack Pickford, brother of Mary Pickford, had syphilis, and mercury was a treatment of the time. Controversy remains over whether she meant to kill herself or took the external preparation by mistake. She died a few days later at the American Hospital in Neuilly.

  Children suffered most from calomel in their teething powders. The resulting illness, infantile acrodynia, takes its name from Greek words for extremity and pain, and it leaves the hands and feet painful and pink. It is also called pink disease. Cases fell sharply after calomel was dropped from most teething powders in 1954.

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• 5. Trades That Poison

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  The old saying "mad as a hatter" probably points to milliners, who used mercury compounds to make felt hats in the 18th and 19th centuries. The Mad Hatter of Alice in Wonderland is presumed to have been inspired by an eccentric furniture dealer named Theophilus Carter. Carter did not suffer from mad hatter disease, though Lewis Carroll would have known of the dementia seen among hatters.

  Gilders paid a worse price. They coated objects with a gold and mercury amalgam and then heated it so the mercury vaporized and left the gold behind. During the building of Saint Isaac's Cathedral alone, an estimated 60 men died from gilding the main dome.

  The Swedish chemist Carl Scheele, a pioneer of 18th-century chemical research, died at 43 from mercury poisoning caused by his own work.

  In 1810, the British ships HMS Triumph and HMS Phipps salvaged a large load of liquid mercury from a wrecked Spanish vessel near Cadiz, Spain. The bladders holding it soon burst, and the metal spread through both ships as liquid and vapor. Sailors developed tremors, paralysis, heavy salivation, tooth loss, skin problems and lung complaints. Henry Plowman, the surgeon on Triumph, concluded that the sickness came from breathing the mercury-laden air. He had the lower deck gun ports opened when safe, banned sleeping on the orlop, and kept symptomatic men out of the lower deck. Windsails channeled fresh air below day and night. William Burnett, M.D., published a report on the effects of mercurial vapor in 1823.

  The German chemist Alfred Stock studied mercury poisoning from 1923 to 1926 and was poisoned himself, along with his colleagues. His laboratory equipment, including diffusion pumps, float valves and manometers, all contained mercury. Spilled mercury had also lodged in cracks in the linoleum floor. He founded a committee in Berlin to examine suspected cases and coined the term micromercurialism.

  In the late 1930s, workers in a seed-packaging factory in Norwich, England, breathed methylmercury used as a seed disinfectant and pesticide. A study of them gave the condition the name Hunter-Russell syndrome.

  The trade continues today. In Ghana, small independent gold miners called galamsey face high risk because their processing methods are crude. Neighboring French-speaking countries have similar workers called orpailleurs. No official count exists, but observers believe 20,000-50,000 people work as galamsey, including many women who act as porters. Similar problems have been reported among Indonesian gold miners.

  On the 19th of March 2008, Tony Winnett, aged 55, inhaled mercury vapor while using liquid mercury to separate gold from computer parts. He died ten days later. His Oklahoma home was so contaminated that it had to be gutted.

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• 6. Poisoned Waters

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  In 1950s Japan, industrial discharges of mercury into rivers and coastal waters caused outbreaks of methylmercury poisoning in several places. The best-known were in Minamata and Niigata. In Minamata alone, more than 600 people died of what became known as Minamata disease. More than 21,000 people filed claims with the Japanese government, and almost 3,000 were certified as having the disease. In 22 documented cases, pregnant women who ate contaminated fish showed mild symptoms or none, yet gave birth to infants with severe developmental disabilities.

  In Ontario, Canada, the Grassy Narrows and Whitedog peoples were poisoned across generations by fish from the Wabigoon-English River system. The Dryden Chemical Company had discharged more than 9,000 kg of mercury directly into the river, and it kept polluting the air with mercury until 1975.

  The worst single event came in rural Iraq in 1971-72. Villagers made bread from grain that had been treated with a methylmercury fungicide meant only for planting. At least 6,530 people were poisoned and at least 459 died.

  In India, a study by the Centre for Science and Environment and the Indian Institute of Toxicology Research examined Singrauli, the country's energy capital. It found that mercury is slowly entering people's homes, food, water and even blood.

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• 7. Fish and Fire

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  Tuna and swordfish carry more mercury than smaller fish because mercury climbs the food web. This process is called biomagnification. Eating fish is by far the largest source of mercury ingested by people. The US FDA and EPA tell women of childbearing age, nursing mothers and young children to avoid swordfish, shark, king mackerel and Gulf of Mexico tilefish entirely. They also advise limiting albacore tuna to 6 oz per week and other fish and shellfish to 12 oz per week.

  Fish are not simply a danger, though. A 2006 review of the risks and benefits found that for adults one to two servings a week outweigh the risks, with a few exceptions among species. Avoiding fish could cause excess deaths from coronary heart disease and weaker neural development in children. Epidemiological studies link ocean fish eaten during pregnancy, and the selenium, omega-3 fatty acids, iodine and vitamin D it supplies, to better outcomes. Child IQs rose by 4-6 points in one association.

  The balance tips in places where people live almost entirely on fish. In certain fishing communities, rates of mercury poisoning among children have reached 1.7 per 100. In Japan, Tetsuya Endo of the Health Sciences University of Hokkaido tested whale meat bought in the whaling town of Taiji. He found mercury more than 20 times the acceptable Japanese standard.

  The mercury in the sea has to come from somewhere. Coal-burning power plants and other human sources produce about half of atmospheric mercury, and volcanoes and other natural sources produce the rest. An estimated two-thirds of the human share comes from burning fuel, mostly coal. A 2021 study of European soils found high concentrations near abandoned mines at Almaden in Spain, Mt. Amiata in Italy, Idrija in Slovenia and Rudnany in Slovakia. High levels also appeared near coal-fired plants.

  Cosmetics bring another route. Some skin whitening products contain mercury(II) chloride, which passes readily through the skin into the blood. In Hong Kong in 2002, two such products held between 9,000 and 60,000 times the recommended dose. Mercury in cosmetics is illegal in the United States, but imports slip in, and the FDA has warned against them.

  Broken fluorescent lamps release vapor, because the liquid inside evaporates at room temperature. The EPA recommends leaving the room and airing it for at least 15 minutes after a bulb breaks. A 1987 report described a 23-month-old toddler with peeling, reddened fingers and toes. The acrodynia was traced to a carton of 8-foot bulbs that had broken in a potting shed near a nursery, where the child often played.

  Traditional medicines, including some Ayurvedic and Traditional Chinese remedies, can contain mercury and other heavy metals. In Romania, occult practices involving liquid mercury put roughly 200 people a year into the National Poisoning Centre.

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• 8. Treatment and Rules

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  Whole-blood mercury is typically under 6 micrograms per liter, yet a diet rich in fish can push it above 200. Blood testing is of little help for suspected elemental or inorganic poisoning because mercury leaves the blood quickly. Doctors prefer 24-hour urine collections for chronic exposure. Chelation therapy itself raises urine mercury, which makes those samples hard to read. For organic mercury, blood or hair is more reliable than urine.

  Treatment starts by finding and removing the source. Contaminated clothes come off, skin is washed with soap and water, and eyes are flushed with saline when needed. Before organic chelating agents existed, many nineteenth and early twentieth century doctors gave salts of iodide by mouth, a practice heavily promoted by Louis Melsens.

  The chelators used for acute inorganic poisoning include DMSA, DMPS, D-penicillamine and dimercaprol. Only DMSA is FDA-approved for children. Studies found no clear clinical benefit from DMSA for mercury vapor poisoning. No chelator is approved for methylmercury or ethylmercury, but DMSA is used most often for severe methylmercury cases because it is taken by mouth, has fewer side effects and outperformed the others. Glutathione and N-acetylcysteine are recommended by some physicians, yet they have been shown to raise mercury concentrations in the kidneys and the brain.

  Chelation can also kill if given wrongly. In August 2005, a five-year-old boy died of cardiac arrest after receiving edetate disodium, the wrong form of EDTA, which caused hypocalcemia.

  Some effects can be partly or fully reversed if selenium is restored before oxidative damage spreads too far. Autopsy findings put the half-life of inorganic mercury in the human brain at 27.4 years. Heavy or prolonged exposure can do irreversible damage, especially to fetuses, infants and young children. Young's syndrome is believed to be a long-term result of early childhood mercury poisoning. The EPA classes mercuric chloride and methylmercury as possible human carcinogens.

  Spills at home call for care, because mercury is hard to gather and clumsy cleanup can enlarge the exposure. Powdered sulfur can be spread over a spill to form a solid that lifts from surfaces more easily than the liquid.

  In 1999, the CDC and the American Academy of Pediatrics asked vaccine makers to remove thiomersal, an organomercury preservative, as quickly as possible. They were following the precautionary principle. The move still fed confusion and a controversy over autism. A 2004 Institute of Medicine committee favored rejecting a causal link, and autism rates kept rising after thiomersal left childhood vaccines. No accepted scientific evidence shows that it causes autism.

  Regulation has tightened elsewhere. The European Union has banned the export of mercury and some of its compounds since the 15th of March 2011 and most uses of the metal, with an exception for fluorescent bulbs. The exception came under pressure from Germany, the Netherlands and Hungary, countries tied to the big bulb makers General Electric, Philips and Osram.

  The Minamata Convention on Mercury was signed on the 22nd of April 2016, which was Earth Day. That date was also the sixtieth anniversary of the discovery of the disease that gave the treaty its name.

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