Nitrates are nitrogen-based compounds that exist as part of the natural nitrogen cycle in soil and water systems. While they are naturally occurring and function as an important nutrient for plant life, their concentration in water sources can become significantly elevated through human activity. Because nitrate contamination is typically invisible, odorless, and tasteless, routine testing of water supplies is the only method to identify its presence and protect public health from its documented risks.
Sources of Nitrate Contamination
Elevated nitrate levels result from nitrogen being introduced into the environment faster than natural systems can process it. The largest source is agricultural activity, which contributes nitrogen through synthetic fertilizers and the application of animal manure. When fertilizer is over-applied or not fully utilized by plants, the excess nitrate is highly water-soluble and easily leaches through the soil into groundwater aquifers.
This contamination is recognized as non-point source pollution, originating from a diffuse area rather than a single discharge point. Other sources include poorly maintained septic systems and sewage lines, which release nitrogen-rich waste into the subsurface. Industrial wastewater discharges and the erosion of natural geological deposits also contribute to the overall nitrate load.
Health Consequences of Nitrate Exposure
Testing water for nitrates addresses the acute health hazard posed to infants under six months of age. When ingested, nitrate is converted by bacteria in the digestive system into nitrite. This conversion is more pronounced in infants due to their less acidic digestive tracts, which favor the growth of nitrate-reducing bacteria.
Nitrite enters the bloodstream and interferes directly with oxygen transport. It reacts with the iron in hemoglobin, oxidizing it from its ferrous (Fe²⁺) state to its ferric (Fe³⁺) state. This altered form, known as methemoglobin, cannot bind oxygen effectively, leading to methemoglobinemia.
Methemoglobinemia, or Blue Baby Syndrome, rapidly causes symptoms like shortness of breath and bluish-gray skin discoloration due to oxygen deprivation. The condition is potentially fatal if untreated, making infant protection the basis for drinking water standards. Long-term exposure to elevated nitrate levels may also be associated with increased risks for chronic conditions in adults, including links to gastric, colorectal, and thyroid cancers.
Regulatory Limits and Water Standards
Regulatory standards, established by the U.S. Environmental Protection Agency (EPA), enforce testing to protect public health. The EPA set the enforceable Maximum Contaminant Level (MCL) for nitrate-nitrogen in public drinking water supplies at 10 milligrams per liter (mg/L). This standard is set to prevent methemoglobinemia in infants.
Public water systems must regularly test their water to ensure levels remain below the MCL. These mandatory regulations do not apply to private well owners, who are responsible for their own drinking water safety. For private wells, the EPA’s 10 mg/L standard serves as a safety reference, and owners should conduct periodic testing.
Methods for Detecting Nitrates
Water quality professionals use various techniques to determine nitrate concentration, ranging from field assessments to laboratory procedures. For quick initial screening, colorimetric test kits or strips are often used. These methods involve a chemical reaction that changes the color of the sample, which is then compared to a reference chart to estimate the nitrate level.
For regulatory compliance, water samples must be analyzed by a certified laboratory using advanced instrumentation. Common laboratory techniques include spectrophotometry, which measures the light absorbed by nitrate ions. Ion chromatography (IC) is also used; this method separates and measures the concentration of nitrate ions, offering reliable quantification.
Preventing and Treating Nitrate Contamination
Once high nitrate levels are detected, the response involves source management and water treatment. Large-scale prevention focuses on agricultural best management practices, such as optimizing fertilizer application to reduce leaching into groundwater. Proper siting and maintenance of septic systems also reduce nitrogen entering the water table.
For individual homeowners whose water exceeds the 10 mg/L limit, several treatment systems can effectively remove the contaminant.
Reverse Osmosis (RO)
Reverse osmosis (RO) systems work by forcing water through a semi-permeable membrane that rejects the nitrate ions, producing clean drinking water.
Anion Exchange
Anion exchange uses specialized resin beads to swap nitrate ions for harmless ions like chloride.
Distillation
Distillation is also effective, as it boils the water and condenses the purified steam, leaving the nitrate behind.