Nitrogen is fundamental to all life, forming the structure of DNA, proteins, and chlorophyll. Toxicity occurs when this substance exceeds a safe concentration or when its chemical structure is altered. Nitrogen toxicity manifests in two distinctly different ways: exposure to the inert gas under pressure, or exposure to highly reactive chemical compounds. Understanding these two mechanisms—one involving pressure and the other a chemical reaction in the bloodstream—is key to grasping the full scope of nitrogen-related health risks.
Nitrogen Narcosis From Pressurized Gas
Nitrogen narcosis is a reversible alteration of consciousness caused by inhaling nitrogen gas (\(\text{N}_2\)) at high partial pressures, primarily encountered during deep-sea diving. As a diver descends, increased ambient pressure forces more nitrogen to dissolve into the body’s tissues. This excess dissolved gas is highly soluble in lipids within the central nervous system, interfering with the normal transmission of nerve impulses and producing a state similar to anesthetic intoxication.
Symptoms can begin to become noticeable at depths of around 30 meters (98 feet), though individual susceptibility is highly variable. Initial signs often involve impaired judgment, difficulty concentrating, and short-term memory loss. As the pressure increases with depth, the effects worsen, leading to euphoria, anxiety, or inappropriate behavior, which has earned the condition the nickname “rapture of the deep.” The danger lies in the diver’s inability to make rational decisions, which can lead to life-threatening errors. The symptoms of narcosis are completely and rapidly reversed by ascending to a shallower depth, allowing the gas to diffuse out of the tissues.
Nitrate and Nitrite Poisoning From Chemical Compounds
This form of nitrogen toxicity arises from the ingestion of nitrogen-containing compounds, specifically nitrates (\(\text{NO}_3^-\)) and nitrites (\(\text{NO}_2^-\)). Nitrates are commonly found in contaminated well water due to agricultural runoff from fertilizers or septic system leakage. Nitrites are also used as preservatives in cured meats, or they can form in the body when ingested nitrates are converted by bacteria.
The primary danger of this toxicity is the induction of methemoglobinemia, a life-threatening condition where the blood’s ability to carry oxygen is severely compromised. Ingested nitrites, or nitrites converted from nitrates, act as powerful oxidizing agents that react with the iron in hemoglobin. This reaction converts the iron from its normal ferrous state (\(\text{Fe}^{2+}\)) to the oxidized ferric state (\(\text{Fe}^{3+}\)), forming methemoglobin. Methemoglobin cannot bind to and transport oxygen effectively, leading to tissue oxygen deprivation.
Infants under six months of age are especially vulnerable because their digestive systems are more prone to converting nitrates to nitrites, and they have lower levels of the enzyme needed to reverse the conversion. Symptoms include cyanosis—a bluish discoloration of the skin and lips—and shortness of breath, which is why the condition is sometimes referred to as “blue baby syndrome.”
Prevention and Risk Mitigation
Preventing Nitrogen Narcosis
Mitigating the risk of nitrogen narcosis involves strict adherence to depth limits and careful gas planning. Recreational divers typically limit their depth to a maximum of 30 to 40 meters when breathing standard compressed air. For deeper or more technical dives, the nitrogen content of the breathing gas can be reduced by substituting a portion of it with helium, creating a mixture called Trimix. Helium is a less narcotic gas than nitrogen, allowing divers to descend to greater depths while maintaining cognitive function. Divers must also avoid factors that increase susceptibility, such as fatigue, alcohol, and anxiety, and should immediately ascend to a shallower depth if any symptoms of narcosis are recognized.
Preventing Nitrate and Nitrite Poisoning
Preventing nitrate and nitrite poisoning requires a focus on water source safety, particularly for private wells. The United States Environmental Protection Agency (EPA) recommends a maximum contaminant level of 10 milligrams per liter for nitrate-nitrogen in drinking water, a standard set to protect infants. Well owners should have their water tested annually for nitrate levels, as this chemical cannot be seen, smelled, or tasted.
If well water tests above the safe limit, it should not be used to prepare infant formula, as boiling the water will not remove the nitrate and will actually increase its concentration. Using bottled water or a public municipal source for infants under six months is the simplest and safest alternative. Techniques like reverse osmosis or distillation can be used to treat contaminated water, but standard carbon filters are ineffective against nitrates.