Mercury in any form is poisonous. Mercury is a most dangerous heavy metal to human second only to uranium. In clinical practice very seldom toxic level of uranium detected but toxic level of mercury is very prevalent. Study on polar bear in north-pole indicates toxic level of mercury due to food chain through migratory birds that feeding on sea-food. Environmental exposure usually coming from sea-food especially fish and amalgam tooth filling. Three teeth filling with amalgam (contain 51% mercury), mercury in the stool generally detected forty times higher than allowable level by WHO.
Poisoning can result from mercury vapor inhalation, mercury ingestion, mercury injection, and absorption of mercury through the skin.
Mercury toxicity most commonly affecting the neurologic, gastrointestinal and renal organ systems. Half-life of mercury in the brain is estimated to be about 25 years.
Heart muscle analysis in those who died of myocardial infarction usually contains five or more times higher mercury level than non-heart related death. In cardiomyopathy, the level of mercury in heart muscle can be higher by thousands of times. Breast cancer tissue generally much higher mercury level than in fibro-adenoma cases.
Virtually mercury can cause all kind of symptoms especially nerve and cognitive symptoms (but not all symptoms can be caused by mercury)
The most deadly form of mercury is methylmercury where 90% of any methylmercury ingested is absorbed into the bloodstream from the GastroIntestinal tract.
Organic mercury compounds, specifically methylmercury, are concentrated in the food chain. Fish from contaminated waters are the most common source. Industrial mercury pollution is often in the inorganic form, but aquatic organisms and vegetation in waterways such as rivers, lakes, and bays convert it to deadly methylmercury. Fish eat contaminated vegetation, and the mercury becomes biomagnified in the fish. Fish protein binds more than 90% of the consumed methylmercury so tightly that even the most vigorous cooking methods cannot deplete the toxic effect.
Minamata disease is an example of organic toxicity. In 1955, a factory discharged inorganic mercury into the water upstream. The mercury was methylated by bacteria and subsequently ingested by fish. Researchers in Japan correlated elevated mercury levels with the features of the Minamata disease in Minamata Bay. Local villagers ate the fish and began to exhibit signs of neurologic damage, such as visual loss, hearing loss, and ataxia. Twenty thousand people affected by numbness in extremities, mouth, sensory problem, incoordination, difficulty walking, fatigue, tremors, seizures, slurred speech, hand eye incoordination, lack of concentration, diminished vision, hearing, partial paralysis, jerking movements, difficulty swallowing, convulsions, brain damage, death, poor judgement. 1400 people died. Babies exposed to the methylmercury in utero were the most severely affected.
Iraqi grain incicdence. 1971 Drought – Iraq imported wheat for seedling from Mexico, 178,000 tons, treated with methyl mercury. To warn that they were not meant for consumption, skull and cross bone labeled on gunny sack. Some people made into bread 6,000 people sick, 450 died.
Children expose in womb manifested as cerebral palsy, mental retardation, weakness, seizures, visual loss, delayed development.
Manifestation of Mercury toxicity
Mercury has devastating neurologic consequences as a primary outcome of methyl mercury intoxication; unfortunately, these are relatively resistant to treatment. Complications include the following:
- Psychiatric disturbances
- Sensory loss
- Chronic paresthesias
- Visual disturbance – Eg, scotomata, visual field constriction
- Paresthesias (early signs)
- Hearing loss
- Perioral and facial paresthesias
- Mental deterioration
- Muscle tremor
- Movement disorders
- Paralysis and death – With severe exposure
- Acute perioral and facial paresthesias
- Respiratory distress and nonspecific dermatitis
- Extremity numbness eventually appears, along with headache, fatigue, and tremor
- Ataxia and dysarthria can also be observed Ataxia
- Visual-field loss
- Hearing loss
- Problems with walking
- Psychiatric disturbances
Organic mercury poisoning usually results from ingestion of contaminated food. The long-chain and aryl forms of organic mercury have similar toxic characteristics as inorganic mercury. The onset of symptoms usually is delayed (days to weeks) after exposure.
Chronic low level induce more subtle symptoms and usually miss to be detected if not tested. Organic mercury targets enzymes by blocking essential mineral. Essential minerals are co-factors for enzymes activation. Enzymes reduce ‘activation energy” ten to ten thousand fold. “Activation energy” is minimum energy required for a chemical process to occur. Hence mercury affecting almost all enzymes due to its strong electromagnetically, and the depletion of these enzymes must occur before the onset of symptoms.
Babies exposed in utero are the most severely affected. They are affected by low birth weight, seizure disorders, profound developmental delay, incomplete visual loss (including tunnel vision) or total blindness, and hearing loss.
Neurologic damage in the form of diffuse and widespread neuronal atrophy is most severe in patients exposed in utero. Long-term studies may indicate that even prenatal exposure at low concentrations can cause subtle, but detectable, decrements in the areas of motor function, language, and memory.
Necrosis of the proximal tubules is a common direct renal toxic effect. Unexplained renal abnormalities with neuropsychiatric disturbances should prompt the physician to consider mercury toxicity.
Sources of mercury poisoning
Causes of elemental mercury toxicity include the following:
- Calibration instruments
- Chlor-alkali production
- Dental amalgams
- Ethnomedical practices
- Fingerprinting products
- Fluorescent and mercury lamps
- Infrared detectors
- Jewelry industry
- Neon lamps
- Paper pulp production
- Silver and gold production
- Semiconductor cells
Exposure to organic mercury is primarily through ingestion of contaminated fish. Persons who consume large amounts of seafood from contaminated waters have an increased risk of toxicity.
The causes of organic mercury toxicity also include the following:
- Embalming agents
- Farming industry
- Germicidal agents
- Insecticidal products
- Laundry products
- Diaper products
- Paper manufacturing
- Pathology products
- Histology products
- Seed preservation
- Wood preservatives
The causes of inorganic mercury toxicity include the following:
- Antisyphilitic agents
- Acetaldehyde production
- Chemical laboratory work
- Fur hat processing
- Ink manufacturing
- Mercury vapor lamps
- Mirror silvering
- Perfume industry
- Spermicidal jellies
- Tattooing inks
- Taxidermy production
- Vinyl chloride production
- Wood preservation
Acute exposure caused by inhaled elemental mercury can lead to pulmonary symptoms. Initial signs and symptoms, such as fever, chills, shortness of breath, metallic taste, and pleuritic chest pain. Other possible symptoms include stomatitis, lethargy, confusion, and vomiting. In addition, elemental mercury can also be injected, causing a life-threatening pulmonary embolism.
Recovery is usually without sequela, but pulmonary complications of inhaled toxicity may include interstitial emphysema, pneumatocele, pneumothorax, pneumomediastinum, and interstitial fibrosis. Fatal acute respiratory distress syndrome (ARDS) has been reported following elemental mercury inhalation.