Nitrates as pollutants

Peroxyacetyl nitrates
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. Nitrates turn to nitrites in water and in human stomach and is suspected of causing stomach cancer and other diseases. In rivers, streams, estuaries and seas nitrates encourage the proliferation of algae, which stifle other, more various plants and fish. The concentration of 50mg of nitrates per litre of water is considered by the European Commission to be the maximum permissible level for water for human consumption.
According to a 1992 EU/ECE report, the nitrate content in groundwater in shallow wells in the Netherlands, Belgium, Denmark and Germany is above the acceptable drinking water limit and will only reach an acceptable level in 25 to 50 years' time under present management regimes.
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(E) Emanations of other problems