What Is Nitrosamines?

Nitrosamines are a class of nitrogen-containing organic compounds characterized by an N-nitroso functional group attached to an amine structure. In drinking water, the most widely studied member is N-nitrosodimethylamine, commonly called NDMA, but other compounds such as N-nitrosodiethylamine, N-nitrosomorpholine, N-nitrosopyrrolidine, and N-nitrosopiperidine may also occur. Because this profile addresses nitrosamines as a group, there is no single chemical formula, chemical symbol, or CAS number that applies to all of them.

In the drinking water field, nitrosamines are important because some can form during disinfection, especially where chloramines are used to maintain a residual in the distribution system. Unlike the more familiar regulated disinfection byproducts such as trihalomethanes and haloacetic acids, nitrosamines are usually measured at nanogram-per-liter levels rather than microgram-per-liter levels. Even at these very low concentrations, they are a high-priority concern because several nitrosamines have shown strong carcinogenicity in animal studies.

Nitrosamines are not normally added intentionally to drinking water. They form when specific nitrogen-containing precursors react under conditions created by water treatment and distribution. Precursors may include dimethylamine and other low-molecular-weight amines, quaternary amine polymers, certain ion-exchange resin residuals, wastewater-derived organic nitrogen, algal organic matter, industrial inputs, and degradation products from personal care and pharmaceutical compounds.

Scientific Identity

Nitrosamines belong to the broader family of N-nitroso compounds. Their defining structural feature is the nitroso group, generally written as N–N=O, bonded to an amine nitrogen. NDMA, for example, has two methyl groups attached to the nitrosated nitrogen, while NDEA has two ethyl groups. This structural difference affects volatility, polarity, adsorption behavior, analytical recovery, and treatment response.

From a water chemistry perspective, nitrosamines are unusual among disinfection byproducts. Many classic chlorination byproducts form through halogen substitution and oxidation of natural organic matter. Nitrosamines, by contrast, arise from reactions involving organic nitrogen, inorganic nitrogen species, and nitrosating intermediates. Monochloramine, dichloramine, dissolved oxygen, nitrite, and reactive nitrogen species can all influence formation depending on source water chemistry and treatment conditions.

Most drinking water nitrosamines are small, polar, uncharged organic molecules. NDMA is highly soluble and poorly adsorbed by standard granular activated carbon compared with larger hydrophobic organic chemicals. This is one reason nitrosamines require special attention: treatment strategies that perform well for many organic contaminants may not fully remove already-formed NDMA.

How Nitrosamines Enters Drinking Water

Nitrosamines enter drinking water primarily by formation during treatment and distribution rather than by direct contamination alone. The highest concern is usually associated with chloramination, where chlorine and ammonia are combined to form chloramine disinfectants. Chloramines are valuable because they produce lower trihalomethane levels and persist longer in distribution systems, but they can promote nitrosamine formation when suitable amine precursors are present.

Formation can begin in the treatment plant and continue in storage tanks, transmission mains, and distribution pipes. Wastewater-impacted rivers, reservoirs receiving treated effluent, and source waters influenced by urban runoff often contain more dissolved organic nitrogen and trace amines. When these waters are chloraminated, NDMA and related nitrosamines may form during long contact times.

Treatment chemicals can also contribute precursors. Certain cationic polymers used in coagulation, clarification, sludge handling, or membrane pretreatment may contain amine structures that can act as NDMA precursors if not carefully selected and dosed. Anion exchange resins, amine-functionalized treatment media, and some rubber or elastomeric materials in contact with chlorinated water have also been investigated as possible sources in specific systems.

Ozonation is not usually the classic route for nitrosamine formation in the same way chloramination is, but ozone can alter organic nitrogen precursors and, under some conditions, contribute to downstream nitrosamine potential. Advanced treatment trains for potable reuse therefore evaluate how ozone, biological filtration, chlorination, and chloramination interact rather than assessing each process in isolation.

Occurrence and Exposure

Public exposure occurs mainly by ingestion of finished drinking water containing trace nitrosamines. Inhalation and dermal exposure during showering are generally less important for NDMA than for volatile trihalomethanes, although exposure assumptions vary by compound. Drinking water concentrations are typically reported in ng/L, and analytical methods must be sensitive enough to distinguish true occurrence from background contamination or sample artifacts.

Nitrosamine occurrence is most often investigated in systems using chloramines, systems with long distribution residence time, and systems treating wastewater-impacted source water. Potable reuse projects, indirect reuse reservoirs, groundwater recharge projects using advanced treated wastewater, and utilities downstream of municipal wastewater discharges may conduct more extensive monitoring because precursor levels can be elevated.

Private wells are not usually a major nitrosamine concern unless the well water is disinfected with chloramine-like conditions, influenced by wastewater, or treated with materials that release amine precursors. However, small systems that switch disinfectants, add ammonia, use packaged treatment chemicals, or rely on long storage times can develop site-specific nitrosamine issues even if source water concentrations are low.

Health Effects and Risk

The health concern for nitrosamines is driven mainly by cancer risk. NDMA and several related nitrosamines have produced tumors in multiple animal species at different target organs, including the liver. Toxicological agencies commonly classify NDMA as a probable human carcinogen or similarly high-concern carcinogenic compound based on strong animal evidence and mechanistic understanding of metabolic activation.

Nitrosamines generally require metabolic activation in the body to form reactive intermediates capable of damaging DNA. This DNA-reactive mode of action is why very low drinking water concentrations can be relevant in risk assessment. The exact potency differs among individual nitrosamines; NDMA and NDEA are among the better-studied and more potent members, while data for some less common nitrosamines are more limited.

Short-term health effects from drinking water nitrosamine levels are not the usual concern. The primary issue is long-term exposure over many years. Risk managers therefore focus on minimizing formation, controlling precursors, and maintaining concentrations as low as reasonably achievable, especially in systems where monitoring shows recurrent NDMA detection.

Risk should not be interpreted as a reason to avoid disinfection. Proper disinfection prevents acute waterborne disease, which is an immediate and serious public health threat. The goal is to disinfect effectively while reducing nitrosamine formation through optimized treatment chemistry, precursor control, and distribution system management.

Testing and Monitoring

Nitrosamines require specialized laboratory analysis because they occur at extremely low concentrations and can be affected by sampling artifacts. Routine field test kits for chlorine, pH, hardness, or nitrate cannot measure nitrosamines. Testing should be performed by a qualified laboratory experienced in disinfection byproduct analysis at ng/L reporting limits.

In the United States, EPA Method 521 is commonly referenced for determination of several nitrosamines in drinking water using solid phase extraction and gas chromatography with tandem mass spectrometry. Some laboratories also use validated liquid chromatography-tandem mass spectrometry methods or other jurisdiction-approved methods. The target analyte list often includes NDMA, NDEA, N-nitrosodi-n-propylamine, N-nitrosodi-n-butylamine, N-nitrosopyrrolidine, N-nitrosopiperidine, and N-nitrosomorpholine.

Sampling must be carefully controlled. Chlorine or chloramine residuals are typically quenched using approved preservatives so nitrosamines do not continue forming in the sample bottle. Laboratories may specify amber glass bottles, chilled shipment, avoidance of rubber or plastic contamination, and short holding times. Because false positives or contamination can occur at ng/L levels, field blanks, trip blanks, duplicates, and matrix spikes may be important in investigative monitoring.

Utilities often monitor both finished water and distribution system locations. In chloraminated systems, nitrosamine levels may increase with water age, so storage tanks, dead-end mains, and distant sampling sites are important. Precursor testing can also be useful; formation potential tests expose water to controlled chloramination conditions to estimate whether source water or treatment chemicals contain nitrosamine-forming precursors.

Treatment Methods

Nitrosamine control is most successful when it prevents formation rather than relying only on removal after formation. Once NDMA is present, conventional treatment barriers may be limited. A strong program combines precursor reduction, disinfectant strategy, activated carbon where appropriate, and distribution system control.

Activated carbon deserves careful interpretation. Point-of-entry GAC can reduce certain organic precursors before household distribution, but if the public water already contains NDMA formed in the municipal system, standard residential carbon may not provide dependable removal. Point-of-use carbon at a kitchen tap may lower some organic contaminants and improve taste, but nitrosamine claims should be supported by independent testing for NDMA or the specific nitrosamine of concern.

Treatment optimization is usually the best first-line strategy for public water systems. Utilities may change the point of ammonia addition, use free chlorine contact before chloramination to oxidize precursors, avoid overfeeding polymer, improve filter performance, lower water age, flush low-flow areas, or modify storage tank operation. For potable reuse or highly impacted source waters, advanced trains using ozone, biological activated carbon, membranes, UV, and carefully managed final disinfection may be required.

Regulations and Guidelines

Regulatory treatment of nitrosamines varies widely by country, state, province, and water program. In many jurisdictions, there is no single enforceable maximum contaminant level for “total nitrosamines” as a class. Instead, monitoring or guidance often focuses on individual compounds, especially NDMA.

In the United States, the EPA has not established a federal primary drinking water maximum contaminant level for NDMA or total nitrosamines. However, nitrosamines have been included in federal occurrence monitoring and contaminant candidate evaluations, and EPA health risk information is used by states and utilities when assessing low-level detections. Some U.S. states, including California, have developed notification levels, response levels, public health goals, or monitoring expectations for NDMA and selected related nitrosamines. These values are not uniform and should be checked against the current state drinking water program.

The World Health Organization has published drinking water guideline information for NDMA, and some national agencies have adopted their own health-based values. Canada, Australia, European countries, and local potable reuse programs may apply different criteria depending on toxicological assumptions, analytical capability, and risk management policy. Because limits and advisory values differ, the correct benchmark for a water result depends on the jurisdiction and the specific nitrosamine measured.

For utilities, nitrosamines are often managed through disinfection byproduct control plans rather than through a simple end-point compliance number. Monitoring results are interpreted alongside chloramine operation, total organic carbon, dissolved organic nitrogen, ammonia, nitrite, water age, and precursor studies.

Related Contaminants

Frequently Asked Questions

Are nitrosamines the same as NDMA?

No. NDMA is one member of the nitrosamine family and is the compound most often discussed in drinking water. A nitrosamine test panel may include NDMA, NDEA, N-nitrosomorpholine, N-nitrosopyrrolidine, and other related compounds.

Why are chloraminated systems more associated with nitrosamines?

Chloramines can react with amine-containing precursors to form nitrosating intermediates that produce NDMA and related compounds. The risk increases when source water contains wastewater-derived organic nitrogen, when treatment chemicals add amine precursors, or when distribution water age is long.

Will an activated carbon filter remove nitrosamines?

Activated carbon can help remove some nitrosamine precursors, especially larger or more hydrophobic organic compounds, but it is often weak for already-formed NDMA. A household carbon filter should not be relied on for nitrosamine control unless it has documented performance for the specific compound and conditions.

Can boiling water remove nitrosamines?

Boiling is not an effective control method for nitrosamines in drinking water. It does not reliably destroy them under normal household conditions and can concentrate other nonvolatile contaminants as water volume decreases.

What should I do if nitrosamines are reported in my water system?

Review the specific compound, concentration, sampling location, and applicable state or national guidance value. Because nitrosamines are usually a utility-scale disinfection chemistry issue, contact the water supplier for its control plan, monitoring history, and any treatment optimization steps being implemented.