Too much of a good thing (fish): methylmercury case study.

Methylmercury is an environmental toxicant that has been shown to cause neurologic damage in both children and adults if ingested in sufficiently high quantities. Poisoning outbreaks in Japan and Iraq have revealed serious effects on developing fetuses at levels far below those that produced clinical signs or symptoms in the mothers. Therefore, health guidance values for methylmercury, such as the chronic oral minimal risk level (MRL) of the Agency for Toxic Substances and Disease Registry, have been set by governmental agencies at levels that would protect fetuses. Since adults are less sensitive than fetuses, chronic intakes within an order of magnitude of the MRL generally have been considered to represent no health risk to otherwise healthy adults. The present report of suspected mercury intoxication in a 53-year-old female suggests that some individuals might be susceptible to adverse health impacts of methylmercury at intakes just 7 to 15 times the MRL.