Used in agriculture, pharmaceuticals and meat processing, nitrates and nitrites are compounds containing nitrogen and oxygen. Closely related in chemical structure, the difference is in the number of oxygen molecules: nitrates have three. If a nitrate ion is reduced by having an oxygen atom removed, a nitrite ion is formed. Nitrites can be oxidized, meaning an oxygen atom is added, to form nitrates. Bacteria in soil, meats, septic tanks and human intestines readily convert nitrates and nitrites into other biologically active compounds.
Nitrates and Nitrites in Agriculture
Nitrate fertilizers are indispensable to modern agriculture. Farmers add nitrates and nitrites to the soil in the form of packaged fertilizer products or animal manure. Bacteria in the soil convert nitrate and nitrite compounds into other nitrogen containing compounds which crops can easily absorb and use.
Nitrates and Nitrites Cure Meat
Nitrates and nitrites are essential to the taste and preservation of meat. Sodium nitrite, sodium nitrate or potassium nitrate is added to meat in the first step of the curing process. Curing occurs when the nitrite compounds are converted to nitrous oxide gas. This gas kills germs, including the bacteria which causes botulism. Nitrous oxide also reacts with the hemoglobin of the blood still in the meat. This reaction creates the pink color and characteristic taste of cured meat.
Nitrates in fertilizer dissolve in rain or irrigation water. Eventually, they find their way into ground water, wells, streams, rivers and lakes. Warm weather and high levels of nitrates in rivers and lakes may lead to algae blooms and fish kills, where large numbers of fish die in water. Excess nitrates in well water, rivers and lakes eventually enter human drinking water
Effect on Human Health
Although nitrates and nitrites are directly applied to meats in the curing process, humans get more of these compounds from vegetable sources. Bacteria in the human intestine converts nitrates to nitrites. Then they convert nitrites into nitrous oxide or ammonia. Just as nitrous oxide gas reacts with meat hemoglobin, it has a toxic reaction with human blood hemoglobin. Nitrous oxide converts human hemoglobin to methemoglobin. Methemoglobin does not carry oxygen in red blood cells as well as normal hemoglobin does. Less oxygen is available for body tissues to function. The victim becomes cyanotic: his lips and skin develop a purple or bluish tint. This can be fatal to infants who drink formula contaminated with nitrates and nitrites.
Nitrates and nitrites are not just found in foods. Some anti-diarrheal products contain bismuth subnitrate. The heart medications nitroglycerin and isosorbide dinitrate are nitrite sources as well. Nitrites levels will also rise in those who abuse inhalants such as amyl nitrite. Nitrites may enter the body through the antibacterial silver nitrites as well.