Mercury poisoning, hydrargyria, or mercurialism, is a disease caused by exposure to mercury or its compounds. Mercury (chemical symbol Hg) is classified as a heavy metal that occurs in several forms, and some forms are especially neurotoxic, but all forms can produce toxic effects in high enough doses.
In adults, acute mercury toxicity symptom onset starts with sensory disturbance followed by visual field constriction, ataxia, cognitive decline, and death.
Exposure to toxic levels of mercury vapor in adults causes the classic triad of erethism (bizarre behavior, eg, excessive shyness or aggression), tremor, and gingivitis. The cardinal neurologic sign of toxic vapor exposure is tremor that may be accompanied by a variety of neuropsychological effects ranging from emotional lability at high exposure levels to subtle performance deficits at lower levels.
Toxic effects include damage to the brain (mainly at the occipital cortex and cerebellum),
kidney, and lungs, and can result in several diseases, including acrodynia, (pink disease) characterized by pain and pink discoloration of the hands and feet in children, Hunter-Russell syndrome (methylmercury poisoning), and Minamata disease (named after the methlymercury poisoning epidemic that occurred amoung the people living along Minamata Bay in Japan).
Acrodynia consists of irritability, photophobia, redness of the hands and feet, high blood pressure, failure to thrive, and sometimes death. Because elemental mercury is heavier than air, it will tend to settle near the floor, putting crawling infants and toddlers at greater risk. Infants have occasionally incurred pink disease from minute drops of mercury in hospital isolettes as a result of broken thermometers.
Hunter-Russell syndrome (methylmercury poisoning) is characterized by paresthesias, visual field constriction, ataxia, impaired hearing, and speech impairment. The term Hunter-Russell syndrome derives from a study of mercury poisoning among workers in a seed packing factory in Norwich, England in the late 1930s who breathed methylmercury that was being used as a seed disinfectant and preservative.
Minamata disease is a neurological syndrome caused by severe methyl mercury poisoning that produces ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision, and damage to hearing and speech. In extreme cases, insanity, paralysis, coma and death follow within a few weeks after the onset of symptoms.
The fetal brain is especially susceptible to damage from exposure to mercury, and in Minamata, Japan, pregnant women who consumed methylmercury contaminated fish manifested mild or no symptoms but gave birth to infants with severe developmental disabilities, including cerebral palsy,mental retardation, and seizures. This is called congenital Minamata disease.