31. Mercury Poisoning

Summary Mercury is a heavy metal and the 67th most common element in the earth’s crust. Its unique chemical properties have led to its use in a number of industries including laboratory equipment (thermometers), medical equipment (blood pressure cuffs and preservatives), dental amalgams, fluorescent lights, chlorine production, and gold and silver mining. Burning coal creates the majority of the mercury humans are exposed to. Mercury has no known physiological role in humans. Exposure to mercury can result in nerve damage, brain damage, problems with walking, hearing, and seeing, skin rashes, kidney disease, and breathing problems. Mercury is particularly detrimental to the developing fetus. Avoiding mercury exposure in the expecting mother and young children are of paramount importance. Morbidity and Mortality Inhalation of large amounts of elemental mercury can lead to acute respiratory distress syndrome and death. Large inorganic mercury exposure can cause profound gastrointestinal disturbance, severe dehydration, end stage renal disease, and death (lethal dose 30 to 50 mg/kg). Dimethylmercury is so toxic that only a few drops onto the skin caused the death of Karen Wetterhahn, a chemistry professor. Methylmercury can bioaccumulate to high levels in humans that are continually exposed. Such individuals will develop ataxia, neuropathy, and sensory impairment, which can progress to severely altered mentation, paralysis, coma, and even death. Lower doses of methylmercury during fetal and childhood development can result in substantially lower IQs. Story - Between 1932 and 1968, the Chisso Corp. released wastewater contaminated with mercury into Minamata Bay, Japan. This accumulated in local marine wildlife. Those who ingested the contaminated seafood often developed a severe neurological illness called Minamata disease. Around 1800 people died from this catastrophe. - In 1971 in Iraq around 100,000 tons of grain intented for planting was treated with methylmercury as a fungicide. This grain was then used to bake bread instead. This resulted in thousands of hospitalizations and atleast 400 deaths. Key Points 1. Mercury has no physiological role in humans. All of its different forms have toxic risks. 2. Elemental, inorganic, and organic mercury compounds have very different pharmacology and toxicological effects. 3. Organic mercury can readily cross the placenta and blood brain barrier. Compounds like methylmercury can have profound effects on the neurological development of fetuses and children. 4. Methylmercury is accumulating in our water, largely from burning coal. This mercury bio-accumulates up the food chain. Apex predators can develop very high mercury levels as a result. 5. Pregnant women, woman of childbearing age, and young children should avoid the consumption of apex ocean predators. Consumption of other fish should be limited to < 12 oz a week in these at-risk groups. References - Young-Jin Sue. Mercury. Chapter 95. Goldfrank’s Toxicological Emergencies, 11th Ed. 2019 - Harada M. Minamata disease: methylmercury poisoning in Japan caused by environmental pollution. Crit Rev Toxicol. 1995 - Mercury and Health. WHO. Available at: https://www.who.int/news-room/fact-sheets/detail/mercury-and-health - Minamata Convention on Mercury. Available at: https://www.mercuryconvention.org/ - Wikipedia. Mercury, Mercury Poisioning, Mad as a hatter, Minamata disease, Minimata convention, Karen Wetterhahn.