see also:

• toxicology
• Curr Probl Pediatr Adolesc Health Care. 2010. Mercury Exposure and Children’s Health

• mercury is a heavy metal which accumulates in the body and also becomes more concentrated in animals higher in the food chain
• mercury has no known physiologic benefits
• high levels may cause toxicity and can affect babies in utero as well as during lactation

• in the late 19th century, the term “mad as a hatter” was used to denote mercury poisoning in hat makers
• mercury was frequently used in medicines such as diuretics, antiseptics, laxatives and to treat syphilis, as well as use in the home and industry
  • mercury as Calomel (insoluble mercuric chloride) was commonly used in teething powders and as worm medication until c1955
    • it seems intestinal actions could cause it to be absorbed in certain situations causing Pink disease (infantile acrodynia) which occurred in 1 in 500 exposed children and was especially prevalent in Australia, North America, and Central Europe in the 1st half of the 20th century and was 1st described in literature in 1903 although cases in Australia predate this time by at least two decades.
      • it may be linked to autism spectrum disorders in grandchildren of the affected - a 2011 study showed the prevalence rate of ASD among the grandchildren of pink disease survivors (1 in 25) to be significantly higher than the comparable general population prevalence rate (1 in 160) ¹⁾
  • merbromin, an organic form of mercury bromide, was the main constituent of the water based Mercurochrome 1% solution which was painted topically on abrasions and burns as an antiseptic and was banned in US as an over the counter medicine in 1998 as it contained trace amounts of mercury - still used in Third World countries
  • thimerosal was used in the alcohol-based antiseptic Merthiolate and also contained trace amounts of mercury - still used in Third World countries, it is also used as a preservative in vaccines, although this use has largely disappeared
• elemental mercury was used in the far majority of thermometers, barometers and sphygmomanometers until phased out from 2001 in many countries
  • although trialled since 1620's, mercury thermometers were not commercially made until 1717 when Daniel Gabriel Fahrenheit finally made a version which was better than spirits
  • the typical “fever thermometer” contains between 0.5-3g of elemental mercury, however, swallowing this amount of mercury would pose little danger but the inhaling of the vapour could lead to health problems
• large fish such as shark (eg. “flake”), swordfish, white albacore tuna, king mackerel, especially if caught in industrial waters can have high levels of mercury which are then eaten by humans
• amalgam (“silver”) tooth fillings, are half mercury and are still common in dentistry
• in 1961, it was found to be the cause of Minamata disease in Japan due to a factory discharged inorganic mercury into the water where bacteria methylated it and fish ingested it
• prior to 1990, many paints contained mercury as an antimildew agent

• the classic triad found in chronic mercury toxicity is tremors, gingivitis, and erethism
  • it has been suggested that chronic mercury poisoning in infants due to mercury containing teething powders may be the cause of Young's syndrome
• inorganic mercurial salts are often caustic when ingested
• mercury damages the nervous system through several potential mechanisms:
  • binds to sulfhydryl groups and incapacitates key enzymes involved in the cellular stress response, protein repair, and oxidative damage prevention
  • methylmercury disrupts the muscarinic cholinergic systems in the brainstem and occipital cortices
  • methylmercury also inactivates sodium-potassium adenosine triphosphatase (Na+/K+-ATPase), which leads to membrane depolarization, calcium entry, and eventual cell death
  • methylmercury may sequester selenium and thus disrupt cellular biochemical pathways that use selenium as an enzymatic cofactor
  • dysregulation of the nitric oxide system in rodents
  • several pathways may be simultaneously activated to cause apoptosis
• direct renal toxic effect

• ingested elemental mercury is not absorbed at all hence swallowing a mercury thermometer is not going to cause mercury poisoning HOWEVER, oral ingestion of elemental mercury may lead to significant environmental contamination as the mercury is passed unabsorbed through the GI tract and expelled in the faeces
• mercurial compounds are variably absorbed with usual absorption rates of 2-10%, although some organic forms such as methylmercury (eg. in fish from contaminated waters) has ~90% absorption!
  • organic mercurial compounds are mainly excreted in the faeces
  • biological half-life of methylmercury is approximately 65 days
• inorganic mercurial salt poisoning and caustic burns may occur with ingestions of button batteries
• mercury has been detected in 45% of high-fructose corn syrup samples
• mercury is also present in some uncontrolled substances such as skin-lightening creams and Chinese herbal medicines

• mercury vapour is well absorbed through inhalation and as it is lipid soluble, it is easily transported:
  • into RBC's where catalase converts it to inorganic mercuric form which is not lipid soluble and does not readily cross the BBB
  • across the blood brain barrier where it becomes trapped in the CNS by ionisation to mercuric forms
• inhalation of mercury vapour may lead to metal fume fever
• inhalational exposure may occur when people vacuum or sweep mercury spills in an enclosed space
• newer compact, energy-efficient fluorescent lights contain substantial mercury concentrations, making breakages with subsequent release a source of exposure

• long term exposure to dermal inorganic mercurial salts can cause toxicity

• acute onset:
  • fatigue, weakness
  • fever, chills
  • dizziness, headache
  • abdominal cramping
  • dyspnea
  • dysuria
  • ejaculatory pain

• acute onset:
  • ashen-gray mucous membranes secondary to precipitation of mercuric salts
  • hematochezia
  • vomiting
  • severe abdominal pain
  • hypovolemic shock
• systemic effects onset several hours and may last days:
  • metallic taste
  • stomatitis
  • gingival irritation
  • foul breath
  • loosening of teeth
  • renal tubular acidosis (RTA) leading to oliguria or anuria
• chronic phase - erethism:
  • irritability
  • excitability
  • anxiety
  • insomnia
  • social withdrawal

• onset is usually days to weeks after exposure when the target enzymes become depleted
• organic mercury targets various parts of the brain - mainly the cerebral cortex and cerebellum
• most are neurologic features:
  • paraesthesiae occurs early esp. perioral and facial
  • peripheral neuropathy with preferential loss of large myelinated nerve fibers
  • headache
  • scotomata
  • ataxia
  • hearing loss
  • dysarthria
  • cognitive impairment and memory loss
  • tremor
  • movement disorders
  • psychiatric disturbances
  • severe exposure results in paralysis and death
• in utero exposure:
  • low birth weight
  • seizure disorders
  • profound developmental delay
  • incomplete visual loss (eg. tunnel vision) or total blindness
  • hearing loss
• childhood exposure:
  • use of calomel-containing teething powders prior to 1955 has been implicated as a cause of Young's syndrome
  • motor impairment
  • visual loss
  • hearing loss
  • developmental delay
  • seizure disorders

• the mercury in calomel teething powders was recognised as the probable cause after a study in 1945 which led to the cessation of these teething powders in 1955 and a resultant massive drop in cases
• possibly a genetic or physiologic sensitivity to mercury as only 1 in 500 exposed children developed pink disease
  • low glutathione levels may be a risk factor ²⁾
• most commonly reported symptoms included:
  • irritability
  • neurosis
  • photophobia
  • hyperhidrosis
  • hypotonia
  • ataxia
  • digestive problems (including loss of weight, loss of appetite, vomiting, and constipation)
  • anaemia
  • excessive salivation
  • respiratory problems
  • lethargy
  • extreme misery
  • slurring/loss of speech
  • loosening/loss of teeth
  • swollen extremities
  • marked reddening of the extremities, particularly the hands and feet (acrodynia)
• 10-33% mortality rate
• survivors appeared to have complete recovery but some developed Young's syndrome and it appears some may have developed autism spectrum disorder

• remove from contaminated air if inhalational, and remove contaminated clothing
• activated charcoal and whole bowel irrigation may be indicated for acute ingestions or inorganic or organic mercurial compounds
• FBE to help exclude GIT blood loss
• U&E to help exclude renal tubular acidosis (RTA)
• blood mercury levels are useful in acute poisonings but not chronic poisonings
• hair mercury levels are more inicative of chronic poisonings
• surgical removal of subcutaneous metallic mercury or ingested mercury that has become ledged in bowel may be indicated
• chelation Rx may be indicated
  • 2,3-dimercaptosuccinic acid (DMSA or succimer)
  • polythiol is a nonabsorbable resin that can theoretically help in facilitating the removal of methylmercury
  • BUT note that chelation removes only a small portion of the body's mercury stores and risks may outweigh its benefits
• neostigmine may help motor function in methylmercury toxicity as this toxicity may lead to acetylcholine deficiency
• avoid further exposures - ie. avoid eating fish high in mercury content such as larger fish / sharks