Mercury is a naturally-occurring metal which is mined and used in the production of chlorine gas and caustic soda. It is also used in thermometers, barometers, batteries, and electrical switches. A large source is both hospital and municipal waste incinerators. Mercury damages the nervous system. In high amounts, mercury can cause severe mental and physical retardation in a baby.
Lower amounts can delay walking and talking, and can cause other effects, such as learning deficits.
Choose younger, smaller fish to eat. Generally, larger, older fish have more contamination. For example, lake trout live for up to 10 years, so they may contain more contaminants than chinook salmon, which only live three to four years. Fish that eat other fish also build up more contaminants. Walleye and northern pike, for example, tend to have high levels of mercury.