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TEACH Water Pollution in the Great Lakes

3 | Effects of water pollution

Water pollution affects the health of the waterway, the health of the organisms living in and around the waterway, and, eventually, the health of humans. The effects of water pollution can range from aquatic deformities to contaminated fish to "dead" lakes.

Click for larger image Aquatic diseases and deformities
As virtual "canaries in a gold mine," the deteriorating health of fish and wildlife speaks volumes about the need to clean up the Great Lakes. Heavy metals such as mercury and lead, and human-made organic chemicals such as pesticides, biomagnify as they move up the food chain, resulting in tumors and death for predatory animals, such as lake trout, herring gulls, and even humans.

Toxic pollutants can also alter the genetic makeup of an organism, resulting in either death or extreme deformities. Studies have found cormorants suffering from cross-billed syndrome at rates 42 percent times the natural occurence, while terns exhibit birth defects from dioxin, PCBs and furan exposure at 31 times the normal levels. Other examples of deformities include large fish tumors and three-legged frogs.

Human health issues
Persistant Organic Pollutants, or POPs, such as dioxin, PCBs and DDT, are chemical substances that persist in the environment and bioaccumulate through the food web; therefore, POPs can also cause sickness and disease in humans, who are at the end of the food chain. People who regularly consume a lot of fish will have larger levels of toxic chemicals in their bodies than those who only eat fish occasionally. While scientists are still studying the effects of high chemical levels in humans, studies have suggested that toxic chemicals can lead to reproductive problems, cancer and neurological disorders.

People who are most at risk of health problems due to contaminated fish consumption are those with weakened immune systems, including children, pregnant women and the elderly. Those in the "high-risk" category should either abstain from eating Great Lakes fish, or only eat one meal consisting of fish every week or month, depending on the type of fish. Each state/province in the Great Lakes region publishes a yearly fish advisory; of the 1,400 fish consumption advisories in the United States, more than 1,000 are found in the eight Great Lakes states. See GLIN's fish advisory page for more information.

Other human health issues related to water pollution include drinking water contamination and skin infection, caused by bacterial contamination.

Eutrophication
Before Europeans arrived in the Great Lakes region, the Great Lakes were mainly oligotrophic lakes, meaning they contained little plant nutrients and were continuously cool and clear due to their immense size and depth. Oligotrophic lakes can support high levels of animal life and receive proper amounts of nutrients, mainly phosphorous and nitrogen, from natural sources, such as decomposing plant matter.

European settlement and industrialization changed all of that. The amount of nutrients entering the Great Lakes has intensified greatly, mainly due to increased urbanization and agriculture, leading to increased biological growth, or eutrophication. Under eutrophic conditions, nutrient loading (more nutrients than the waterbody can handle) stimulates excessive plant growth, which in turn decreases the amount of oxygen in the water and eventually kills off certain species of animal life. Other pollution-tolerant species, such as worms and carp, grow more rapidly; thus, the ecological balance of the lake is significantly altered.

Graphic: Tumor on long-nosed sucker found in the Great Lakes.

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