Heavy Metal Poisoning: Mercury

Mercury is the only metal which is present in liquid form. The toxicity of low level organic mercury exposure is mainly manifested by neurobehavioral performance. Mercury is excreted in urine and feces and has a ½ life in blood of about 60 days. But, deposits in the kidney and brain may remain for many years. Elemental mercury (Hg°) is not absorbed well. But, it can volatilize into highly absorbable vapor. Inorganic mercury is absorbed through the gastro intestinal tract and skin. Organic mercury is well absorbed by ingestion and inhalation and it is a major source of mercury poisoning.

Sources of Mercury poisoning: Metallic, mercuric mercury (Hg°, Hg+, Hg2+) and mercurous mercury exposures occur in some chemical, metal-processing, electrical equipment industries and automotive industries. Mercury is also present in thermometers, dental amalgams and batteries. Mercury can also be spread by waste incineration. Mercury present in environment is converted to organic mercury from inorganic mercury by bacteria. This organic mercury is than taken up by planktons, algae and fungi which are food for sea fishes like tuna, swordfish, and other pelagic fish. These sea foods when consumed by humans in large amount can lead to slow mercury poisoning.

Toxicity: Acute inhalation of mercury vapor can cause pneumonitis and pulmonary edema (water in lungs) which may cause death. It can also cause polyneuropathy and CNS (central nervous system) symptoms. Acute ingestion of inorganic mercury can cause gastroenteritis, nephritic syndrome, acute renal failure, hypertension, and cardiovascular collapse. Death usually occurs at a dose of 10–42 mg/kg. Acute ingestion of organic mercury causes gastroenteritis, arrhythmias (rhythm disturbance of heart beat), and lesions in the basal ganglia and gray matter. Chronic inhalation of mercury vapor causes CNS toxicity (mercurial erethism) lower exposures impair renal function, motor speed, memory, coordination.

High exposure of mercury during pregnancy can cause severe mental retardation due to derangement of fetal neuronal migration. Mild exposures of mercury during pregnancy (from fish like tuna, swordfish, and other pelagic fish consumption) are associated with reduced neurobehavioral performance in offspring.

Dimethylmercury is highly toxic (supertoxic) and is found in research labs. A few drops of exposure via skin absorption or inhaled vapor can cause severe cerebellar degeneration which lead to death.

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