Human Health Effects Research Program
The Great Lakes, which consist of Lakes Superior, Michigan, Huron, Erie, and Ontario, are collectively the largest inland body of freshwater on this planet. The lakes contain 22,000 cubic kilometers of water, or one-fifth of the freshwater on the earth's surface, and cover 94,250 square miles in the United States and Canada. Approximately 10% of the U.S. population lives within the Great Lakes basin, which include eight U.S. states (Illinois, Indiana, Ohio, Pennsylvania, Michigan, Minnesota, New York, and Wisconsin) and Canada .
For over 200 years, the Great Lakes basin has been used as a resource for industry, agriculture, shipping, and recreation. The physical nature of the basin and the long retention time of the lakes combine to make this huge freshwater resource a repository for chemical by-products of all the previously described activities. Despite the size of the lakes, the long retention time makes them especially sensitive to pollution. Less than one percent of the total volume of water in the system flows out of the St. Lawrence River each year, leaving toxic pollutants to accumulate in bottom sediments and fish.
More than 1,000 chemicals have been detected in the waters of the Great Lakes . Researchers have identified 362 contaminants in the waters, sediment, and biota in quantifiable amounts; approximately one-third have been evaluated for potential toxic effects . Although the levels of some of these chemicals have declined, they are still a cause of great concern to the Great Lakes ecosystem and human health.
In 1985, 11 of the most persistent and widespread toxic substances were identified as "critical" Great Lakes pollutants by the International Joint Commission (IJC)  (Table 1). These 11 substances tend to accumulate in aquatic organisms eaten by Great Lakes fish. With the exception of alkylated lead and methylmercury, these substances are stored in fatty tissues of fish and become more concentrated over time.
Eight of these chemicals are organochlorine compounds known to bond strongly to body fat and, therefore, to accumulate in fatty tissues and other body organs of fish predators. Contaminated fish are then consumed by other wildlife species and humans. The transport of these substances through the food chain allows them to persist and biomagnify within the aquatic food chain, thereby making them available to higher forms of life (Figure 1).
The IJC has identified 42 areas of concern (AOC) in the Great Lakes basin; toxic substances detected in these areas exceed the limits or guidelines of the Great Lakes Water Quality Agreement . Thirty one of these 42 areas are within the borders of the United States (Figure 2).
Potential environmental pathways of human exposure to Great Lakes pollutants include inhalation of air; ingestion of water, foodstuffs, or contaminated soil; and dermal contact with water or airborne particulates. Multimedia analyses indicate that the majority of human exposure to chlorinated organic compounds (80-90%) comes from the food pathway, a lesser amount (5-10%) from air, and minute amounts (less than 1%) from water [6,7].
Most of the data available on human exposure to toxic substances in the Great Lakes come from analyses of contaminant levels in drinking water and sport fish. The consumption of contaminated sport fish and wildlife can significantly increase human exposure to the Great Lakes critical pollutants. A spectrum of these major contaminants has been identified in cooked Great Lakes fish . Investigators have demonstrated that blood serum levels of these contaminants are significantly increased in consumers of contaminated Great Lakes sport fish compared to people who do not eat such fish or who consume very small amounts of fish [9,10,11,12,13,14].
Several investigators have shown that exposure from fish far outweighs atmospheric, terrestrial, or water column sources [15, 8, 13]. These patterns may vary for populations living in the vicinity of industrial areas such as refineries or smelting plants.
Because of the persistence and widespread presence of these Great Lakes pollutants in the environment, toxic effects in wildlife have been observed (Table 2) . Results from epidemiologic investigations also suggest that adverse human health effects, i.e., reproductive, developmental, behavioral, neurologic, endocrinologic, and immunologic, may result from exposure to Great Lakes pollutants [17, 18, 20, 19, 20, 21, 22, 23, 24].