The highest mercury levels tend to be found in warm-water species, like bass or perch. Unlike such toxic contaminants as dioxin or PCBs, which concentrate in the skin or fat, mercury cannot be cooked out or cut out of a fish before it is eaten. When humans eat contaminated fish, the mercury moves quickly through the stomach and intestines. It readily crosses the blood stream to the brain, where it attacks the central nervous system. In pregnant women, mercury crosses the placenta and enters the fetus.
Exposure is more dangerous for children, because more of the mercury passes into their brains.
Humans eliminate mercury through the urine and feces. However, it may take months for the body to purge itself after mercury consumption is halted. That means a woman who becomes pregnant may pass mercury on to her unborn child during a critical period of fetal development, even if she hasn't eaten fish for months. Original content in this site by Lori Haugen, graphics by Kathy Jungjohann, Guy Gannett New Media.