Nitrates as pollutants

Nitrates are used in chemical fertilizers. When applied to fields much of nitrates often filter through the soil to the water table where they contaminate the drinking supply. In rivers, streams, estuaries and seas nitrates encourage the proliferation of algae, which stifle other, more various plants and fish. Nitrates turn to nitrites in water and in human stomach and is suspected of causing stomach cancer and other diseases.