Mercury is present in numerous chemical forms. Elemental mercury itself is toxic and cannot be broken down into less hazardous compounds. Elemental or inorganic forms can be transformed into organic (especially methylated) forms by biological systems. Not only are these methylated mercury compounds toxic, but highly bioaccumulative as well. The increase in mercury as it rises in the aquatic food chain results in relatively high levels of mercury in fish consumed by humans. Widespread poisoning of Japanese fisherman and their families occurred in Minamata, Japan in the 1950's as a result of consumption of methyl mercury contaminated fish. Today, we continue to be exposed to mercury in our diets, primarily from fish and shellfish. As a result, the U.S. Food and Drug Administration (FDA) has an action level for mercury of 1 part per million (ppm) in fish and the Michigan Department of Public Health issues fish consumption advisories to anglers when mercury levels exceed 0.5 ppm in fish tissue.
Widespread industrial production of mercury, along with lack of careful handling and disposal practices, has contributed to environmental contamination. The U.S. Environmental Protection Agency (EPA) has made efforts to regulate the continued release of mercury into the environment. EPA regulates industrial discharges to air and water, as well as regulating some aspects of mercury waste disposal. In 1976, EPA banned most pesticide uses of mercury - with the exceptions of fungicidal uses in paints and outdoor fabrics, and for control of Dutch Elm disease. In 1990, mercury use as a fungicide in interior latex paint was halted by the EPA. This action stemmed from requests by Michigan officials after a child was poisoned from over formulated mercury-containing paint used in his home. More recently, the use of mercury compounds in exterior latex paint has also been halted.
In addition to the early workers in the cinnabar mines, modern workers in industries using mercury are at risk from overexposure. The Occupational Safety and Health Administration (OSHA) has been reviewing the current occupational exposure standard of 0.1 mg/m3 (milligrams per cubic meter of air) to determine if they should reduce the 8 hour acceptable exposure limit to 0.05 mg/m3. Although no regulatory limit exists for airborne exposure to mercury outside of an occupational setting, the EPA suggests that 0.3 ug/m3 (micro-grams per cubic meter of air) of mercury is a no-effect level (or reference dose = Rfd) for chronic inhalation exposure.
Workplace exposure to mercury occurs through inhalation of contaminated air, direct skin contact with liquid mercury, or oral exposure through contaminated hands, food, etc. A recent edition of the television show 60 Minutes highlighted concerns about mercury exposure in patients receiving silver dental fillings with mercury-containing amalgam. Insufficient scientific evidence exists at this time to either support or refute the claims that dental fillings may result in harmful exposure to mercury.
Accidents have resulted in several cases of mercury poisoning in Michigan in the past two years. Four members of a Lincoln Park family were killed after one member attempted to refine dental amalgam in his home while attempting to recover silver. High levels of mercury were found throughout the house, including wrapped food inside the freezer. The entire house had to be demolished and disposed of in a hazardous waste landfill.
A number of children have developed mercury poisoning after playing with small vials of mercury which they found at home or school. These children were hospitalized when symptoms became so severe that they could not longer walk. One contamination incident involved closing a school for weeks and entailed environmental investigation of residences, cars, school buses and day care centers.
In the human body, mercury accumulates in the liver, kidney, brain, and blood. Mercury may cause acute or chronic health effects. Acute exposure (i.e., short term, high dose) is not as common today due to greater precautions and decreased handling. However, severe acute effects may include severe gastrointestinal damage, cardiovascular collapse, or kidney failure, all of which could be fatal. Inhalation of 1-3 mg/m3 for 2-5 hours may cause headaches, salivation, metallic taste in the mouth, chills, cough, fever, tremors, abdominal cramps, diarrhea, nausea, vomiting, tightness in the chest, difficulty breathing, fatigue, or lung irritation. Symptoms may be delayed in onset for a number of hours.
Chronic effects include central nervous system effects, kidney damage and birth defects. Genetic damage is also suspected.
Nervous system effects. These are the most critical effects of chronic mercury exposure from adult exposure as they are consistent and pronounced. some elemental mercury is dissolved in the blood and may be transported across the blood/brain barrier, oxidized and retained in brain tissue. Elimination from the brain is slow, resulting in nerve tissue accumulation. Symptoms of chronic mercury exposure on the nervous system include: Increased excitability, mental instability, tendency to weep, fine tremors of the hands and feet, and personality changes. The term "Mad as a Hatter" came from these symptoms which were a result of mercury exposure in workers manufacturing felt hats using a mercury-containing process.
Kidney effects: Kidney damage includes increased protein in the urine and may result in kidney failure at high dose exposure.
Birth defects: Neurologic damage from methyl mercury. The manifestations of mild exposure include delayed developmental milestones, altered muscle tone and tendon reflexes, and depressed intelligence.
Mercury exposure in children can cause a severe form of poisoning termed acrodynia. Acrodynia is evidenced by pain in the extremities, pinkness and peeling of the hands, feet and nose, irritability, sweating, rapid heartbeat and loss of mobility.