Nitrogen is often added to fertilizers, because without it plants could not live.
Contamination occurs when there is more nitrate in the soil than plants can absorb.
The excess is carried through the soil into groundwater supplies by rainwater and irrigation. Naturally, agricultural areas, where heavy farming is performed, tend to have more nitrate-contaminated water supplies than other areas. However, contamination can also occur from surface water runoff and from septic tanks leaching into wells. Hemoglobin performs the vital function of carrying oxygen to all parts of the body. When nitrite combines with hemoglobin, methemoglobin is formed, which does not carry oxygen.