Mercury is a metal that is liquid at room temperature. Most compounds containing mercury are poisonous. Methylmercury is an organic form of mercury that has been used to preserve seed grain. Methylmercury can also be produced from metallic mercury or mercury compounds in bodies of water by the action of bacteria. Outbreaks of methylmercury poisoning have occurred following ingestion of treated seed grain, from meat from animals fed treated seedgrain, or from fish in waters contaminated with methylmercury, such as Minamata Bay in Japan.

The fetus and young infants are very sensitive to methylmercury's effects. Methylmercury causes central nervous system (CNS -- i.e., the brain and spinal cord) damage and the severity of the damage depends on the extent of the exposure. Many of the CNS effects are similar to those seen in cerebral palsy, and methylmercury is thought to cause a form of cerebral palsy.

In January, 2001, the FDA issued a warning to pregnant women, women who may become pregnant, nursing mothers, and small infants to avoid fish that may contain unsafe levels of methylmercury. These fish include larger, longer-lived fish, such as swordfish, king mackerel, shark, or tilefish. The FDA especially warns against non-commercial fish, or fish caught by friends and family, and the Agency recommends that consumers check their local or state health departments for warnings against locally-caught, non-commercial fish.

• history of exposure to methylmercury (possibly in the womb)
• cerebral palsy
• growth deficiency
• microcephaly (small head)
• deafness
• blindness