We have known the effects of mercury since the 16^th century when the "Mad Hatters Syndrome" originated. Because the hat making process used mercury as a fabric preservative, the hat makers were exposed daily to mercury and developed neurological defects. More recently, in 1955-56, Japan noted many deaths, birth defects, and health problems linked with mercury exposure after mercury laden industrial wastewater poisoned fish and shellfish. Over 60 people died and 200,000 were estimated to have been adversely affected.⁹ In 1971-72 serious health problems associated with mercury exposure arose in Iraq when consumption of baked bread from grain treated with a mercury fungicide killed 400 and hospitalized 6000.¹⁰ These occurrences provide the baselines for concern by the Indiana Department of Health, the EPA, and other public health and environmental institutions.

The fish consumption advisory is published in reaction to high levels of mercury in fish. The high levels of mercury in the fish are likely a result of decades of mercury emissions in the environment. Mercury enters our lakes, rivers, and streams through air deposition and from direct discharges in some cases. In an aquatic system, mercury then enters the food chain. This is how contamination presents a problem for humans. Mercury, once in the aquatic system is converted to organic mercury by bacteria. The organic form of mercury, methylmercury, is easily absorbed in animals and the human body. Once methlymercury is produced, it can be taken up by microscopic organisms in the sediments or water. It concentrates as it moves up the food chain from microscopic plants to microscopic animals to forage fish to predator fish then to humans and wildlife that eat the fish. Since mercury accumulates in tissues, its concentration increases with every higher level in the food chain in a process called bioaccumulation. The organic form of mercury, once converted, can also be absorbed through fish gills and skin.

Figure 5

Source: Government of Canada, 1991
Toxic Chemicals in the Great Lakes & Assoc. Effects

The fish consumption advisory warns people against eating large predator fish and bottom feeders. As explained above the larger fish tend to have higher levels of mercury. Bottom feeders, like carp, eat large amounts of organisms in the sediments and also have higher mercury levels.

Today over 1.6 million American women and children are at risk for mercury poisoning.⁸ People who rely on fish for food, recreational anglers, and people who have a preference for eating large amounts of fish are also at risk for health problems from consuming mercury-contaminated fish.

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