Fish consumption is the primary pathway of mercury exposure. Most human intake of mercury comes from eating certain types of fish or seafood containing a form of mercury called “methylmercury.” When mercury enters water bodies, it can be converted to “methylmercury” and enter the aquatic food chain, where it bioaccumulates in fish tissue. The magnitude of human exposure to methylmercury depends on the level of mercury in the fish consumed and the amount of fish eaten.
There is disagreement over the level of mercury considered “safe.” At certain levels, mercury is a developmental neurotoxin—it can adversely affect nervous system function and the development of fetuses. Yet, there is disagreement as to what level of exposure presents a threat to public health.
In 1996, EPA established a mercury “reference dose”—the amount of a substance that can be safely consumed over a lifetime—of 0.1 micrograms per kilogram of body weight per day. The U.S. Food and Drug Administration, the Agency for Toxic Substances and Disease Registry, and the World Health Organization have recommended regulatory levels that are significantly less stringent that EPA’s.