Fish and shellfish are excellent sources of protein and omega-3 fatty acids that offer a number of health benefits. However, eating fish may expose people to various contaminants, including methylmercury,
which can be harmful to a person’s health if they are highly concentrated. Consumers are thus faced
with the dilemma: choosing between thehealth benefits and possible risks from eating fish.
Exposure to methylmercury varies according to the kind of fish consumed and the region where the fish originate. Because methylmercury accumulates up the food web, higher concentrations are found in large fish (tuna and swordfish, for example) that are at higher levels on the food chain. Freshwater fish, including bass, walleye, and pickerel from sources in the United States can also contain significant concentrations of mercury as a result of airborne contamination. The vast majority of Americans are not exposed to
unsafe levels of methylmercury, but pregnant women who consume large amounts of predatory fish (e.g.,
swordfish, shark, tilefish, and king mackerel) may expose their developing fetuses to it. Prenatal exposures that exceed the established safe “reference dose” can cause an IQ deficit; abnormal muscle tone; or impaired motor function, attention, and visualspatial performance in the child.
Assessing potential exposure to mercury is a challenge. Currently, the EPA is responsible for regulating
all the industrial mercury released into the air and surface water; the U.S. Food and Drug Administration
is responsible for monitoring levels of mercury in commercially sold fish; and the Agency for Toxic
Substances and Disease Registry evaluates the potential risk of methylmercury to humans. All
three agencies have used different risk assessment methods, data sets, uncertainty factors and guidelines to assessexposure to toxicants. The National Research Council report Toxicological Effects of Methyl mercury (2000)
identifies the most appropriate studies and approachesto assess the risk of methylmercury. It also recommends conducting an exposure assessment of the U.S. population to provide a more cohesive picture of the distribution of methylmercury nationally and regionally