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The 10 worst forms of pollution

Small plane dips low to spray a field

Photo: santiago nicolau/Flickr

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Agricultural pollution

Pesticides, chemicals and untreated manure are the most dangerous forms of agricultural pollution because they end up in the water supply. Excessive agricultural runoff can prompt the growth of large algal blooms, which starve waterways of oxygen and create "dead zones." Excessive erosion can also be a problem, and even accidental milk spillage from dairies can be a serious contaminant. According to the Environmental Protection Agency, half of all surface water pollution in the U.S. is attributable to agricultural sources.