The runoff problem is often greatest when manure is used as a fertilizer, such as it is now in many sites in the US where large commercial farms are used to produce pigs and chickens and these companies provide the manure to farms who grow the animals for them. Nitrate represents the most oxidized chemical form of nitrogen found in natural systems. Nitrate is one of the most water soluble anions known. Nitrate is also defined as fertilizer consisting of sodium nitrate or potassium nitrate. Nitrate is converted in the gut to nitrite, which then combines with hemoglobin to form methemoglobin, thus decreasing the ability of the blood to carry oxygen.
Infants are more susceptible to nitrate toxicity than older children or adults.
Fatalities are rare, but subacute methemoglobinemia can be asymptotic while affecting development, making the condition particularly insidious. Nitrate concentration is monitored in municipal water supplies world-wide, and in foodstuffs, to prevent exposure of populations to harmful or toxic levels. In addition, nitrate-containing wastes are produced by many industrial processes including paper and munitions manufacturing. Because agriculture is implicated in the nitrate pollution problem, farmers and rural communities are the most threatened populations. Consumer concern and awareness regarding the quality and safety of water, food and the environment is well established.