The Difference Between Nitrate and Nitrite
Nitrate ($NO_3^-$) and nitrite ($NO_2^-$) are both nitrogen-oxygen chemical compounds that play a role in the natural nitrogen cycle. The key difference lies in their chemical structure and stability. Nitrates consist of one nitrogen atom bonded to three oxygen atoms, making them more stable and less reactive than nitrites, which have one nitrogen atom and two oxygen atoms. In oxygenated environments, such as surface water and most public water systems, nitrite is rapidly oxidized and converted into the more stable nitrate. This is why contamination is more frequently detected as high nitrate levels, which can then be converted to nitrite inside the human body. However, in environments with low oxygen, like stagnant wells, nitrite can persist.
How Nitrite Enters the Water Supply
Contamination of drinking water with nitrite is primarily the result of human activities and natural processes that disrupt the nitrogen cycle. Sources include:
- Agricultural Runoff: The overuse of nitrogen-based fertilizers and the presence of animal manure can cause high concentrations of nitrates and nitrites to leach into groundwater or run off into surface water.
- Failing Septic Systems: Septic tanks and drainfields that are poorly maintained or located too close to a well can contaminate the groundwater with human sewage.
- Industrial Waste: Some manufacturing processes, such as those for munitions and explosives, can produce and release nitrogenous waste into the environment.
- Natural Sources: Certain aquifers may naturally have higher levels of nitrogen compounds from the erosion of rock deposits.
- Poor Well Construction: Shallow wells or those with damaged casings and fittings are highly susceptible to contamination from surface-level sources.
Health Risks of Nitrite in Drinking Water
While most healthy adults can tolerate the small amounts of nitrite they are exposed to, high levels present significant health concerns. The most serious risk is for infants under six months of age, who can develop methemoglobinemia, commonly known as "blue baby syndrome".
Methemoglobinemia
In infants, the less acidic stomach environment and certain gut bacteria can convert ingested nitrate to nitrite more readily than in adults. Once in the bloodstream, nitrite reacts with hemoglobin, the molecule responsible for carrying oxygen, oxidizing it into methemoglobin. Methemoglobin cannot effectively transport oxygen, leading to oxygen deprivation in the body's tissues. Symptoms include a bluish discoloration of the skin and lips, weakness, shortness of breath, and in severe cases, loss of consciousness or death. Medical attention is required immediately if these symptoms appear.
Other Vulnerable Groups
Pregnant women and individuals with certain health conditions, such as peptic ulcers, chronic gastritis, or specific genetic deficiencies, are also more susceptible to the effects of nitrite exposure. Long-term exposure for decades may also increase the risk of certain cancers, as nitrite can form carcinogenic N-nitroso compounds in the body under certain conditions.
Regulatory Standards for Drinking Water
To protect public health, regulatory agencies have established Maximum Contaminant Levels (MCLs) for nitrite in drinking water. In the United States, the Environmental Protection Agency (EPA) has set the MCL for nitrite at 1 mg/L (or 1 part per million). The World Health Organization (WHO) has a guideline value of 3 mg/L. Public water systems are required to regularly monitor and treat their water to ensure these standards are met. However, private wells are not subject to the same regulations, and testing is the responsibility of the well owner.
Testing for Nitrite in Your Water
Since nitrite is colorless, odorless, and tasteless, testing is the only reliable way to know if it is present in your water supply.
- Home Test Kits: These kits use color-changing strips or reagents that react to the presence of nitrite. They are a cost-effective option for initial screening.
- Certified Laboratory Analysis: For the most accurate results, water samples should be sent to a certified laboratory. Many local health departments can provide test kits and refer you to a lab for testing. Well water owners are often advised to test annually.
Comparison of Nitrite Removal Methods
| Method | Effectiveness | Mechanism | Application | Important Note |
|---|---|---|---|---|
| Reverse Osmosis | Highly Effective (Removes >95%) | Pushes water through a semi-permeable membrane that filters out nitrite molecules. | Point-of-use (at a single faucet) or whole-house systems. | Needs regular maintenance to remain effective. |
| Distillation | Highly Effective | Boils water, captures the steam, and condenses it back into liquid, leaving contaminants behind. | Primarily point-of-use for small quantities of water. | Energy-intensive and slow. |
| Ion Exchange | Very Effective | Uses charged resins to swap out contaminant ions like nitrite for less harmful ones. | Point-of-use or whole-house systems available. | Requires disposal or regeneration of the resin. |
| Boiling | Ineffective & Harmful | Concentrates nitrite and other contaminants as water evaporates. | NOT recommended for any level of nitrite contamination. | Significantly increases the danger of contaminated water. |
How to Reduce Your Risk of Nitrite Exposure
For those on a private well, or living in an area with known contamination risks, proactive measures are key:
- Test Your Water Annually: Get your well water tested yearly for both nitrate and nitrite. Test more frequently if there are nearby land use changes.
- Identify and Mitigate Contamination Sources: Locate and address potential sources like failing septic systems, nearby animal waste storage, or improper fertilizer application.
- Use Certified Treatment Systems: If your water tests high for nitrite, install a certified water treatment system such as reverse osmosis, distillation, or ion exchange.
- Use an Alternative Water Source for Infants: If your well water is contaminated, use bottled water or water from an approved municipal source for preparing infant formula and cooking for babies under six months.
Conclusion
While the answer to "does drinking water have nitrite?" is yes, the key takeaway is that levels are typically low and tightly regulated in public water systems. The primary risk is from contamination, particularly in private well water. The dangers, especially for infants susceptible to methemoglobinemia, are severe and should not be ignored. By understanding the sources of contamination, having your water regularly tested, and using effective removal methods, you can ensure the safety of your drinking water for everyone, especially the most vulnerable. For further information on the health effects of nitrites, consult reliable sources such as the Centers for Disease Control and Prevention.
Further Reading
For an authoritative resource on the health effects of nitrate and nitrite, visit the CDC's archive: Nitrate/Nitrite Toxicity: What Are the Health Effects from...
