Can be elemental mercury in gaseous form
In the following, uptake, distribution and excretion as well as the resulting health risks for the three forms of mercury (elemental mercury, inorganic mercury salts, organic mercury compounds) are each considered separately.
Metallic (elemental) mercury
Inhaled mercury vapors are approximately 80 percent absorbed through the lungs. In its elemental form, mercury can cross the blood-brain barrier and the placental barrier.
After resorption through the lungs, the elemental mercury quickly turns into inorganic mercury compounds in erythrocytes, in the liver and in the brain (Ed2+) oxidized. Ed2+-Ions can barely cross the blood-brain barrier and the placental barrier. They bind to sulfur-containing biomolecules, such as glutathione, hemoglobin and enzymes, the function of which is impaired in this way. Unoxidized elemental mercury can be exhaled through the lungs.
From the dental amalgam used for tooth fillings, mercury can get further into the body in two ways: on the one hand, the fillings give off mercury vapor, on the other hand, abrasion and corrosion processes also contribute to the mercury load. In the past, between 3.9 and 21 micrograms of mercury entered the body in this way per day, today the exposure is between 3 and 12 micrograms (Commission Human Biomonitoring 1999).
Nocturnal unconscious teeth grinding (bruxism) and chewing gum can increase the daily intake by a factor of 5 to 20.
Ingested metallic mercury is practically not absorbed from the gastrointestinal tract. Mercury from a clinical thermometer broken in the mouth is therefore toxicologically harmless. On the other hand, mercury leaked from clinical thermometers can evaporate and lead to severe poisoning, especially in small, poorly ventilated rooms (Feer's disease in small children!).
Inorganic mercury salts
Inorganic mercury salts are absorbed from the gastrointestinal tract to about 2-15 percent. Substances that are readily soluble in water are absorbed better than those with low water solubility. The toxicity also varies accordingly: calomel, which is hardly soluble in water (mercury-I chloride), is significantly less toxic than the readily soluble sublimate (mercury-II chloride).
The highest concentrations of inorganic mercury salts are found in the kidneys. There the mercury ions bind to the sulfur-rich protein metallothionein. Inorganic mercury also accumulates in the liver, pituitary gland and some other brain areas.
The excretion of the mercury ions (ed2+) occurs predominantly through the urine, with a high intake also through the stool.
Due to their high fat solubility, organic mercury compounds are absorbed from the gastrointestinal tract to over 90 percent. They are also well absorbed through the skin and lungs.
Organic mercury is evenly distributed in the body, it can cross the blood-brain barrier and the placenta barrier. Organic mercury is converted to Hg2 + by microorganisms in the large intestine, which is then excreted in the stool. The remaining (unconverted) organic mercury is absorbed.
About 90 percent of the organic mercury is excreted in the stool. In addition, organic mercury compounds are also stored in the hair.
The half-life of organic mercury in the blood is 30 to 70 days. In some organs it may be in the range of years. The daily intake from food is estimated at 3 micrograms of mercury (predominantly as methyl mercury). With a fish-rich diet, it can increase to around 14 micrograms per day.
Toxicity depending on the mercury compound and intake
How mercury exposure affects health depends on which form of mercury (elemental, inorganic, organic) has been ingested and whether it is acute or chronic. Ultimately, in addition to the total amount of mercury supplied, the concentration in the individual target organs is also decisive.
Acute poisoning with elemental mercury and inorganic mercury salts
Inhaling large amounts of mercury vapor initially damages the lungs. Concentrations of more than 1 milligram of mercury per cubic meter of air are considered critical. They can lead to coughing, shortness of breath and severe inflammation of the bronchi and lungs. The oral ingestion of inorganic mercury salts quickly becomes noticeable through a metallic taste and increased salivation (hypersalivation).
As the disease progresses, the entire gastrointestinal tract is burned with vomiting and diarrhea. As a result, severe electrolyte shifts occur, which can lead to shock. Acute kidney failure also occurs. Central nervous symptoms appear later. The lethal dose for an adult is around 1 to 4 grams.
Chronic poisoning with elemental mercury and inorganic mercury salts
In the past, professionally exposed people - such as hat makers who worked with mercury-stained fur and felt - were generally considered crazy ("Mad Hatter" from Alice in Wonderland). Much newer knowledge about chronic mercury poisoning also comes from occupational medicine.
Key symptoms for long-term inhalation exposure to mercury vapor are tremor (beginning with finely pounded finger tremors), pathologically increased excitability and inflammation of the mucous membrane of the dental arches (gingivitis). In further occupational medical studies on chronic mercury intoxication, damage to various other organs was observed. Affected are the central nervous system with impaired short-term memory and coordination, the sensory system with color vision disorders, the peripheral nervous system and the kidneys with glomerulonephritis due to the formation of immune complexes.
Autoimmune kidney disease is also rare. There is also a risk of skin sensitization, but allergic reactions are rare.
Studies at amalgam-processing dentists have shown that poor working conditions can impair fertility.
In children, chronic intoxication leads to the - now rare - picture of Feer's disease (synonym: Feer's neurosis, Selter-Swift-Feer disease, acrodynia, pink disease). Apparently the organism, especially the brain, is more sensitive to relatively small amounts of mercury in small children than is the case in adults. There have been repeated case reports of small children who have developed severe clinical pictures at urine concentrations below 50 micrograms per liter.
The symptoms are characterized by cerebral, vegetative and dermatological symptoms: pronounced hypotension, later refusal to walk, stand and sit, uncomfortable, sullen, miserable behavior, motor-related apathy, muscle and limb pain, loss of appetite, weight loss, nighttime sleep disorders, somnolence during the day, increased sweating, pronounced itching, increased blood pressure, photophobia; symmetrical reddening (acrodynia, pink disease) on the nose and on the hands and feet (von Mühlendahl 1990 and 1991).
Acute and chronic toxicity of organic mercury compounds
Our knowledge of the dangerousness of organic mercury compounds comes mainly from two environmental disasters: the illegal discharge of mercury compounds into the Minamata Bay (Japan) and the mass poisoning in Iraq from seeds stained with mercury that were mistakenly used to make bread.
Organic mercury compounds mainly act on the nervous system. There are visual disturbances (blurred vision, restricted field of vision), hearing disturbances (hearing loss, restricted understanding of words) and sensory disturbances (fingers, toes), followed by problems with walking and arm motor functions (see overview in F. Schweinsberg, 2002).
The transition between acute and chronic poisoning is fluid. Organic mercury ingested during pregnancy affects child development. The effects on the unborn child have been well studied in several studies. Compared to adults, children are 5 to 10 times more sensitive to organic mercury, which manifests itself in motor and cognitive developmental disorders:
"The first symptoms were delayed learning to walk and speak. In four to seven-year-old children of stressed mothers, hearing loss, increased muscle tone in the legs, increased tendon reflex (only in boys) and ataxia. The most sensitive reactions were observed in seven-year-olds in neurophysiological tests (. ..). " (Commission Human Biomonitoring 1999).
In two large studies carried out on the Faroe Islands and the Seychelles, the question of what influence the regular consumption of fish and seafood (mean content approx. 0.3 milligrams per kilogram of fish) during pregnancy that is significantly contaminated with mercury on child development has.
The Faroe Islands study provided evidence that the higher the mercury concentration, the development deficits in the children: In 7-year-olds, neuropsychological tests showed abnormalities when the (organo-) mercury content in the mother's hair exceeded 10 milligrams per kilogram. Changes in the areas of attention, memory and language occurred even with even lower values. It has not yet been clarified why such developmental disorders were not observed in the Seychelles study.
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