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The 10 worst forms of pollution

By: Bryan Nelson on July 7, 2010, 1:05 p.m.
Two men look out over a polluted lake

Photo: Daniel Berehulak/Getty Images

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Untreated sewage

Lackluster sewage treatment in some parts of the world is a major source of disease and water contamination. In Latin America only 15 percent of wastewater is treated, and sewage treatment is virtually unheard of in sub-Saharan Africa. In addition to the sanitation hazard, untreated sewage also allows for redistribution and accumulation of other pollutants in the water table.