How are people exposed to methylmercury and what are methylmercury's health effects?

How people are exposed.  Methylmercury, an organic form of mercury, is the form of mercury that people are most commonly exposed to.  Nearly all methylmercury exposures occur through eating fish and shellfish. Microscopic organisms convert inorganic mercury into methylmercury, which accumulates up the food chain in fish, other fish-eating animals, and people.  Some fish contain more methylmercury than others; big fish that eat smaller fish tend to contain more methylmercury. Certain species of commercially available saltwater fish, such as shark, swordfish, kingfish and tilefish, can contain high levels of methylmercury.

• Learn more about how mercury enters the environment and how it moves through the food chain:  http://www.epa.gov/mercury/exposure.htm#1 

Health effects of methylmercury.  Outbreaks of methylmercury poisonings have made it clear that adults, children, and developing fetuses are at risk from ingestion exposure to mercury. During these poisoning outbreaks some mothers with no symptoms of nervous system damage gave birth to infants with severe disabilities; as a result, it became clear that the developing nervous system of the fetus may be more vulnerable to methylmercury than is the adult nervous system. Mothers who are exposed to methylmercury and breast-feed their babies may also expose their infant children through their milk.

More information: 

• Mercury health effects: http://www.epa.gov/mercury/effects.htm
• Agency for Toxic Substances and Disease Registry (ATSDR) toxicological profile for mercury: http://www.atsdr.cdc.gov/toxprofiles/tp.asp?id=115&tid=24

What you can do.  In 2004, EPA and the Food and Drug Administration issued advice about how often women who might become pregnant, women who are pregnant, nursing mothers and young children should eat certain types of fish.  By following the advisory, parents can reduce their unborn or young child's exposure to the harmful effects of methylmercury, while at the same time maintaining a healthy diet that includes the nutritional benefits of fish and shellfish.

• Read the advice:  http://water.epa.gov/scitech/swguidance/fishshellfish/outreach/advice_index.cfm

States issue fish advisories that tell consumers about how often they should eat certain types and quantities of locally caught fish.

• Find state and local advisories for specific bodies of water: http://fishadvisoryonline.epa.gov/General.aspx
• Learn more about state and local advisories: http://water.epa.gov/scitech/swguidance/fishshellfish/fishadvisories/general.cfm#tabs-4

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