Mercury poisoning: The metallic element mercury is poisonous to humans. Mercury poisoning can occur in both acute and chronic forms.
Acute mercury poisoning (which today is less common) is associated with ulcerations of the stomach and intestine and with toxic changes in the renal (kidney) tubules. Anuria (failure to form urine) and anemia may occur.
Chronic mercury poisoning can cause diarrhea, slowed reflexes, poor coordination, ataxia (wobbliness), tremor, impaired vision, and emotional instability.
Death and illness from mercury poisoning have long been recognized. The expression "mad as a hatter" came from the occupational hazard of hat makers in the 1800's who were poisoned by mercury salts used in the making of felt hats. Consumption of food contaminated with methylmercury in the second half of the 20th century resulted in death or illness for thousands of people around Minimata Bay, Japan.
Minamata disease is, in fact, the name of a disorder caused by methylmercury poisoning that was first described in the inhabitants of Minamata Bay and resulted from their eating fish contaminated with mercury industrial waste. The disease is characterized by peripheral sensory loss, tremors, dysarthria, ataxia, and both hearing and visual loss.
Even the unborn child is at risk from Minimata disease. methylmercury readily crosses the placenta from mother to fetus and is teratogenic, particularly to the developing brain. Children born with Minimata disease can have growth deficiency, microcephaly (an abnormally small head), severe mental retardation and be deaf and blind.
Minimata disease has not been confined to Minimata where the source of the mercury was primarily from eating fish caught in the contaminated Bay. Other sources of maternal exposure to methylmercury have included flour made from seed grain treated with methylmercury (which affected at least 6,500 people in Iraq) and meat from animals raised on mercury-tainted grain (in New Mexico, USA).
Mercury is discharged into the air by such sources as coal-burning power plants, incinerators, and mining. It eventually contaminates waterways where it is converted by bacteria into methylmercury. This molecule collects in the fatty tissues of fish and the animals that eat fish. Fish are the major dietary source of mercury, but it can also enter the body in other ways including diet, dental fillings, pharmaceuticals and contact with mercury metal or its compounds.
The FDA/EPA Fish Consumption Advisory informs women who may become pregnant, pregnant women, nursing mothers and the parents of young children about how to get the positive health benefits from eating fish and shellfish lower in mercury (for example, shrimp, canned light tuna, salmon, pollock, and catfish), while minimizing mercury exposure by avoiding types of fish that are higher in mercury (for example, shark, swordfish, tilefish and king mackerel).