Nitrates and nitrites are nitrogen-containing chemical compounds found throughout the natural world. Nitrates are water-soluble and serve as a nutrient source for plants, making them part of the natural nitrogen cycle. Nitrites are less stable and often serve as an intermediate step in nitrogen conversion. While both occur naturally, high concentrations in water and food generally result from human activities. This article provides practical steps to reduce exposure in your home water supply and diet.
Identifying Nitrate Sources and Health Concerns
The primary route for nitrate contamination is the excessive use of nitrogen-based fertilizers in agriculture, which is carried by water into groundwater supplies. Livestock manure and wastewater from septic systems also contribute significantly, allowing nitrate to leach easily through the soil due to its high solubility. Private wells drawing from shallow groundwater are at increased risk for elevated nitrate levels, especially if they are poorly maintained or located near a contamination source.
The concern with nitrate arises when it is converted to nitrite through bacterial action. Nitrite interferes with the blood’s ability to carry oxygen by reacting with hemoglobin to form methemoglobin. This condition, methemoglobinemia, limits oxygen transport and is particularly dangerous for infants under six months of age, leading to “blue baby syndrome.”
For adults, long-term consumption of high nitrate levels has been associated with chronic health issues. Nitrites can react with compounds in the digestive tract to form N-nitroso compounds, also called nitrosamines. These nitrosamines are linked to certain cancers, including those of the digestive tract and the thyroid. Pregnant women are also advised to limit exposure, as they may be more susceptible to the effects of high nitrate concentrations.
Water Treatment Methods for Nitrate Removal
Since nitrates are invisible, odorless, and tasteless, the only reliable way to determine if your water supply is safe is through regular testing. Private well owners should test their water for nitrates annually, especially if the well is shallow or located near farming or a septic system. Knowing the exact concentration is necessary to select an appropriate treatment system, as effectiveness can be reduced by extremely high initial levels.
Two household technologies are effective for removing nitrates from drinking water: reverse osmosis (RO) and ion exchange. Reverse osmosis systems work by forcing water under pressure through a semi-permeable membrane with fine pores. The membrane acts like a selective filter, rejecting the larger nitrate ions while allowing purified water to pass through.
RO systems are installed as a point-of-use solution, treating water at a single tap, such as the kitchen sink. They offer a high rejection rate (83 to 92 percent removal), but the process is inherently slow and produces a concentrated waste stream that must be flushed down the drain. This water inefficiency is a necessary trade-off for the purified drinking water produced.
The other effective option is an anion exchange unit, which operates similarly to a standard water softener. The system contains resin beads pre-charged with a non-harmful anion, usually chloride or sulfate. As nitrate-contaminated water flows over the resin, it captures the negatively charged nitrate ions and releases the chloride or sulfate ions into the water.
Anion exchange systems are often installed as a point-of-entry treatment to purify all the water entering a home, but they require periodic regeneration. During this cycle, a salt solution is used to flush the accumulated nitrate from the resin and recharge it with fresh chloride ions. The system requires low sulfate concentrations, as the resin may preferentially exchange sulfates over nitrates, limiting the system’s ability to reduce nitrate levels.
A misconception is that boiling water removes nitrate contamination. Since nitrate is a dissolved mineral, boiling causes water to evaporate, which concentrates the remaining nitrate in the reduced volume. This process makes the contaminated water more dangerous. An alternative source of low-nitrate water, such as bottled water, should be used for infant formula if testing reveals high levels. Standard carbon filters, found in many common water pitchers, are also ineffective at removing nitrate ions.
Dietary Strategies for Reducing Intake
Dietary intake of nitrate comes from two main sources: vegetables and processed meats. Vegetables, especially leafy greens like spinach, lettuce, and arugula, and root vegetables such as carrots and beets, are the largest source of dietary nitrates, accounting for about 80% of total intake. However, the naturally occurring nitrates in vegetables are often accompanied by antioxidants like Vitamin C, which can inhibit the formation of harmful nitrosamines in the body.
In contrast, processed or cured meats like bacon, hot dogs, and deli meats use sodium nitrite or potassium nitrite as preservatives to prevent bacterial growth and maintain color. When these meats are cooked at high temperatures, the nitrites can react with the meat’s amino acids to form nitrosamines, which are the compounds associated with increased health risks. Reading product labels and choosing uncured meats without added nitrates or nitrites is a practical step to reduce exposure from this source.
For high-nitrate vegetables, preparation methods can help reduce the final consumed amount. Because nitrate is water-soluble, cooking methods that involve water, such as boiling or blanching, can reduce nitrate content by up to 40 to 80 percent if the cooking water is discarded. Conversely, methods that evaporate water, such as steaming or baking without discarding the water, will concentrate the nitrate content.
Proper storage is an effective way to manage potential nitrite exposure from vegetables. Nitrate in cooked vegetables can be converted into the more harmful nitrite by bacteria present in the environment. To prevent this conversion, cooked leftovers should be refrigerated within two hours, as storing them at room temperature allows bacteria to multiply and rapidly increase nitrite levels. Refrigeration at 0 to 4 degrees Celsius significantly slows the bacterial activity, delaying nitrite formation for up to 72 hours.