Nitrates and nitrites are nitrogen-oxygen compounds that exist widely in the environment as part of the natural nitrogen cycle. Nitrate is the more stable form, typically found in soil and water, while nitrite is more reactive. Although these compounds are necessary for plant growth, excessive exposure can lead to nitrate poisoning. This poisoning occurs when the compounds interfere with the blood’s ability to transport oxygen, causing a form of chemical suffocation.
How Nitrates Affect the Body
Nitrate is relatively harmless until it is converted into nitrite, its more toxic counterpart. This conversion mainly occurs in the gastrointestinal tract, often facilitated by certain bacteria. Infants under six months are particularly vulnerable because their digestive systems contain bacteria highly efficient at reducing nitrate to nitrite.
Once in the bloodstream, nitrite interacts with hemoglobin, the protein in red blood cells responsible for carrying oxygen. Nitrite acts as an oxidizing agent, changing the iron in hemoglobin from the functional ferrous state to the ferric state. This oxidized hemoglobin is called methemoglobin, which is unable to bind to and transport oxygen effectively.
When methemoglobin levels rise significantly, the condition is known as methemoglobinemia. This severely reduces the oxygen supply to the body’s tissues, leading to cellular hypoxia.
Primary Sources of Nitrate Exposure
A primary source of high nitrate exposure is contaminated drinking water, especially for people who rely on private well water. These sources are not regulated like public water systems. Agricultural runoff containing nitrogen fertilizers and animal manure is a common cause of groundwater contamination. Septic systems and human waste can also introduce nitrate into shallow groundwater sources.
Dietary sources are another significant route of exposure. Many vegetables naturally accumulate high concentrations of nitrate from the soil, particularly leafy greens like spinach, celery, and lettuce. The concentration varies widely depending on the plant type, soil conditions, and fertilizer use.
Nitrates and nitrites are also intentionally added to cured meats, such as bacon and deli meats, where they function as preservatives. Nitrites prevent the growth of harmful bacteria and help maintain the color and flavor of the meat. While overall dietary intake of nitrate often comes from vegetables, cured meats contribute directly to nitrite exposure.
Identifying the Symptoms of Poisoning
The physical symptoms of nitrate poisoning result directly from the blood’s reduced oxygen-carrying capacity. The most noticeable sign in severe cases is cyanosis, a grayish-blue discoloration of the skin, lips, and nail beds. This color change results from the presence of methemoglobin.
Symptoms vary based on the percentage of methemoglobin present in the blood. Levels below 15% may not produce noticeable signs, though cyanosis can begin to appear. As concentrations rise to between 20% and 50%, a person may experience headaches, dizziness, fatigue, and an elevated heart rate.
Concentrations exceeding 50% can lead to confusion, seizures, and depressed mental status. Infants are at particularly high risk for severe symptoms, which manifest as lethargy, irritability, and poor feeding. Levels above 70% methemoglobin are often fatal due to profound tissue hypoxia.
Treatment and Risk Mitigation Strategies
Immediate medical treatment for significant nitrate poisoning involves the intravenous administration of Methylene Blue. This chemical antidote enhances a natural pathway in the red blood cells. Methylene Blue is converted into leukomethylene blue, which acts as an electron donor. This process directly reduces the ferric iron in methemoglobin back to the functional ferrous state. This reaction quickly restores the blood’s ability to carry oxygen, often reversing symptoms within minutes.
To mitigate the risk of exposure, testing private well water is an effective measure, especially for vulnerable populations. The maximum contaminant level for nitrate in drinking water is 10 milligrams per liter (mg/L). Water exceeding this level should not be used for preparing infant formula. Reducing the intake of cured and processed meats can also help lower overall exposure.