Mercury exposure in humans results primarily from eating fish that contain methylmercury.

• About 85% of adults in the United States consume fish and shellfish at least once a month
• 40% consume fish and shellfish weekly
• For high-end consumers, it is estimated that 87% of their exposure to mercury comes from eating seafood.

Mercury is primarily a neurotoxin, which means it attacks the central nervous system. Its effects are often subtle enough not to be recognized immediately, but more and more people are learning that their health problems could be due to mercury exposure. Nervous system problems can include impaired coordination, tremors, irritability, memory loss, depression, blurred vision and a tingling sensation in the skin. Other symptoms include fatigue, headache, decreased concentration and muscle or joint pain.

Adverse health effects from mercury in fish diets can range from subtle nervous system effects to more serious poisoning, depending on how much and how often fish is eaten and how much mercury is in the fish.

An EPA scientist estimated that one in six pregnant women has enough mercury in her blood to pose neurological risks to her developing baby. This means that hundreds of thousands of newborns each year in the United States may be exposed to enough mercury to hinder nervous system development.

Perhaps the greatest concern about mercury is its effect on the early development of the fetus and later effects on childhood development. Methylmercury can travel across the placenta from the mother to the fetus, meaning exposure to the dangerous poison often begins in the womb during a baby's most vulnerable developmental period. Children and fetuses are also harmed by lower concentrations of mercury than it takes to hurt adults.

• Mercury can cause irreversible impairment to brain function in children in the womb and as they grow.
• Infants and children exposed to toxic doses of mercury have problems with attention span, language, visual-spatial skills, memory and coordination.
• Very high exposure levels in children can lead to brain damage, mental retardation, blindness, seizures, and speech problems.
  
• Exposure also appears to weaken the heartbeat and the developing immune system.

Cardiovascular Disease

At least 12 scientific studies have linked mercury to cardiovascular disease including increased blood pressure, irregular and increased heart rate, and increased rates of death from heart attacks.

Infertility

Mercury is among a group of chemicals that can cause infertility according to the National Research Council. It is believed that mercury exposure can lead to spontaneous abortions.

Kidney Damage and Cancer

Mercury causes kidney damage and is classified as a "Possible Human Carcinogen" by the EPA and IARC.
While there is inadequate information to draw a conclusion based on human studies, it has been shown to cause kidney tumors in male laboratory mice.

• Dr. Jane Hightower, a physician in San Francisco noticed that many of her patients were experiencing symptoms related to mercury exposure, including depression, loss of scalp hair, metallic taste, headaches, arthritic pain, irritability, tremors, and numbness and tingling in the hands and feet. In some cases, the symptoms were so severe that the patients were having trouble earning a living or doing well in school. After several tests and dietary studies, she linked the symptoms to diets high in seafood. These are what two of Dr. Hightower's patients experienced:
• A surgeon had tremors so bad she was afraid she'd have to give up operating.
• A geophysicist was forced to quit work, noting severe memory problems and the inability to think. He also suffered from slurred speech and poor balance. Though he stopped eating fish, he suffered permanent brain damage of a type almost always associated with heavy metal exposure.
• In May, 2004, Donna Elrick was interviewed by a TV news program in the Washington, D.C. area. She had been losing her short- and long-term memory. After a visit to her doctor, the cause was determined to be high levels of mercury, linked to her high-fish diet.
• "Love of fish almost kills a man," blared the headlines in Duluth, Minnesota in early 1993. Henry (Buddy) Henk, Jr. suffered from sores that would not heal, leg and back pain, eventual loss of feeling in his legs, and a loss of 100 lbs. He was hospitalized and suffered from hallucinations. He "didn't recognize his own wife" and "ground his teeth down to the bone." His physicians could not determine a diagnosis until his wife mentioned that his diet was high in fish from a lake a few miles from his home. He was tested and discovered to have "severe mercury toxicity."
• Oceana Wavemakers share their experiences.