Let's start with researchers from the Harvard School of Public Health who reported in the February 2002 Journal of Occupational and Environmental Medicine that they could not find mercury-related health effects among a group of regular swordfish consumers.
In 2006, Phil Davidson from the University of Rochester Medical School, presented results of a unique 10-year study of more than 700 children living in the Seychelles Islands. The children's mothers averaged 12 meals of fish a week – about 10 times the average fish consumption of individuals in the United States – and those fish contained high levels of methylmercury. Yet cognitive tests on the children, taken multiple times over the years, found no cognitive defects or other maladies normally attributed to mercury absorption.
Our own EPA has said "Human-caused U.S. mercury emissions are estimated to account for roughly 3 percent of the global total, and U.S. coal-fired power plants are estimated to account for only about 1 percent." The main sources of mercury in the environment are erosion into rivers of naturally-occurring mercury and volcanoes.
We do know that exposure to extremely high levels of mercury can be harmful. There were mass poisonings in Japan's Minamata Bay in the 1950s and in Iraq in the 1970s. However, the former was due to direct methylmercury discharge to the bay, and the latter was due to people eating seed corn that was supposed to be planted that had been fumigated with methylmercury.
Now there are people who try to link an illness to mercury in the environment; but they ignore the more important potential root cause. What licit and illicit drugs were the parents ingesting prior to and - in the mother's case - post conception?
My favorite in the mercury discussions is people like Carol Browner, who was a vocal critic of president Bush's administration's plans to reduce mercury emissions. She doesn't like to mention that she was the EPA Chief under President Clinton, and she did nothing to reduce mercury emissions.
My favorite mercury-related quote comes from Steven Milloy, the editor of a website devoted to battling "junk science" and author of several books on the subject. Speaking about Ms. Browner (and Ms. Clinton and Ms. Boxer, who were at the same rally) he asked plainly: "Show me the person in the U.S. who has gotten sick from eating fish because of mercury. Where are the bodies? Where are the illnesses?"
I do not know of any.