Fact-checked by Grok 2 weeks ago

Chloramines

Chloramines are chemical compounds containing one or more chlorine atoms directly bonded to a nitrogen atom, derived from ammonia (inorganic chloramines) or organic amines (organic chloramines).^[1] The inorganic chloramines include monochloramine (NH₂Cl), dichloramine (NHCl₂), and trichloramine (NCl₃). These compounds form through the reaction of hypochlorous acid (or chlorine) with ammonia in aqueous solutions, with the specific species depending on the chlorine-to-ammonia ratio and pH conditions.^[1] Monochloramine is the predominant form used in applications due to its relative stability and lower volatility compared to the other two, which are more reactive and prone to decomposition.^[2] Chloramines have been used as disinfectants in drinking water treatment since the early 1900s, initially to address taste and odor issues associated with free chlorine.^[3] In water treatment, chloramines serve as secondary disinfectants to maintain residual protection against pathogens in distribution systems, offering longer persistence than free chlorine while producing fewer disinfection byproducts like trihalomethanes.^[4] They are generated in situ at water treatment plants by adding ammonia to chlorinated water, typically at concentrations up to 4 mg/L, and are regulated by the U.S. Environmental Protection Agency under the maximum residual disinfectant level of 4 mg/L as chlorine.^[5] Beyond drinking water, chloramines find limited industrial uses, such as in hydrazine synthesis for rocket fuels and as bleaching agents in textiles or pulp, though global production remains modest.^[5] Chemically, monochloramine appears as a colorless to pale yellow liquid with a strong pungent odor, a melting point of -66°C, and high solubility in water, though it is unstable in pure form and can decompose explosively above -50°C.^[6] Dichloramine and trichloramine exhibit greater instability; dichloramine is oily and volatile, while trichloramine is a yellow explosive liquid that hydrolyzes rapidly in water, contributing to odors in poorly managed pools.^[7] Human exposure primarily occurs through ingestion of treated drinking water or inhalation in indoor swimming pools, where chloramines can cause respiratory irritation at concentrations exceeding 0.5 mg/m³, though they pose minimal risk at standard regulatory levels and are classified as non-carcinogenic by the International Agency for Research on Cancer.^[5] Special precautions are advised for aquariums, dialysis patients, and certain industrial settings due to potential toxicity.^[8]

Introduction

Definition and Nomenclature

Chloramines are a class of chemical compounds in which one or more hydrogen atoms attached to a nitrogen atom in ammonia or an amine are substituted by chlorine atoms, resulting in the formation of nitrogen-chlorine (N-Cl) bonds.^[7] These compounds can be inorganic, derived from ammonia (NH₃), or organic, derived from amines containing carbon-based groups. The N-Cl bond in chloramines is typically polar covalent, distinguishing them from other chlorine-containing species. For inorganic chloramines, the general formula is NH_{3-n}Cl_n, where n ranges from 1 to 3, reflecting the progressive replacement of hydrogen atoms by chlorine.^[7] Organic chloramines follow structures such as R-NHCl, R-NCl₂, or R₂NCl, where R represents an organic substituent like an alkyl or aryl group.^[7] Nomenclature for inorganic chloramines is based on the number of chlorine atoms: monochloramine for NH₂Cl, dichloramine for NHCl₂, and nitrogen trichloride (or trichloramine) for NCl₃.^[7] Organic chloramines are named as N-chloro derivatives of the parent amine or amide, such as N-chlorosuccinimide, which features an N-Cl bond within a cyclic imide structure.^[9] Unlike hypochlorites, which contain oxygen-chlorine (O-Cl) bonds—often in the form of hypochlorous acid (HOCl) or its salts—chloramines involve direct N-Cl linkages, leading to differences in reactivity and stability.^[10] This structural distinction affects their chemical behavior, with chloramines generally exhibiting lower oxidizing power compared to O-Cl compounds.^[10]

Historical Development

The existence of monochloramine, a key chloramine compound, was first recognized in the early 19th century, with initial observations of its formation during reactions involving ammonia and chlorine derivatives.^[5] Early synthetic efforts focused on related compounds, such as the preparation of trichloramine noted by chemist Pierre-Louis Dulong in 1813, though stable isolation of monochloramine proved challenging due to its reactivity.^[11] In the early 20th century, German chemist Friedrich Raschig advanced the synthesis of monochloramine through his development of the Raschig process for hydrazine production, patented in 1906, which involved reacting sodium hypochlorite with ammonia to generate chloramine intermediates under controlled conditions.^[12] This method laid foundational techniques for chloramine production, influencing later industrial and disinfection applications. By the 1910s, chloramines began transitioning to practical use in water treatment; the first documented application occurred in 1915 at the Ottawa, Ontario waterworks, where monochloramine was employed to improve disinfection residuals and reduce taste issues associated with free chlorine.^[13] In the United States, Denver implemented monochloramine treatment in 1917, marking the initial adoption, with wider use as a secondary disinfectant emerging in the 1930s to maintain longer-lasting residuals in distribution systems.^[13]^[14] A pivotal shift occurred in the 1970s following the discovery of disinfection byproducts, notably trihalomethanes (THMs), formed during chlorination of organic matter, as identified by researchers like J. J. Rook in 1974.^[15] This led to the U.S. Environmental Protection Agency's 1979 Total Trihalomethane Rule, which set limits on THM levels and encouraged alternatives like chloramination to mitigate byproduct formation while preserving disinfection efficacy.^[15] By the 2000s, chloramines had become the primary disinfectant in water systems serving more than one-fifth of the U.S. population, reflecting regulatory-driven preferences for reduced THM risks.^[4] As of 2025, chloramines remain in use by approximately 25% of large U.S. public water systems.^[4]

Chemical Properties

General Structure and Stability

Chloramines are a class of compounds derived from ammonia or amines in which one or more N-H bonds are replaced by N-Cl bonds, resulting in the general formula RNHCl, RNCl₂, or RNClR', where R and R' are hydrogen or organic groups. The N-Cl bond is polar covalent, with chlorine's higher electronegativity (3.16) compared to nitrogen (3.04) leading to a partial negative charge on chlorine and a partial positive charge on nitrogen, which contributes to the bond's reactivity. Typical N-Cl bond lengths in chloramines are approximately 1.75 Å, as observed in monochloramine (NH₂Cl).^[16] The N-Cl bond is significantly weaker than the N-H bond, with dissociation energies around 200 kJ/mol for chloramines compared to about 390 kJ/mol for N-H in ammonia, making the N-Cl linkage prone to homolytic or heterolytic cleavage.^[17]^[18] The stability of chloramines is influenced by several environmental factors. At neutral to slightly alkaline pH (7-8.5), chloramines like monochloramine are relatively stable, but they decompose rapidly in acidic conditions (pH < 6) via disproportionation to hydrochloric acid, ammonia, and nitrogen gas, or in strongly basic conditions (pH > 10) to hypochlorite and ammonia.^[19] Temperature also plays a key role, with higher temperatures accelerating decomposition; for instance, monochloramine's half-life decreases from over 300 hours at 4°C to about 75 hours at 25°C at pH 7.5.^[19] Substituents on the nitrogen atom affect stability, with electron-donating groups (e.g., in amine-type N-Cl) enhancing it compared to electron-withdrawing groups (e.g., in imide-type), following the order amine > amide > imide for N-Cl bond persistence in N-halamines.^[20] In general, inorganic chloramines exhibit lower stability than their organic counterparts due to the absence of stabilizing alkyl or aryl groups, leading to faster hydrolysis and decomposition. For example, monochloramine in water has a half-life ranging from several hours to days under typical drinking water conditions (pH 7-8, 10-20°C), while organic chloramines can persist longer, sometimes exceeding 48 hours depending on structure.^[6]^[21] Spectroscopic techniques provide key insights into chloramine structure. In infrared (IR) spectroscopy, the N-Cl stretching vibration appears in the range of 700-800 cm⁻¹, as characteristic of the bond's low force constant; for monochloramine, it is observed around 780 cm⁻¹. Basic nuclear magnetic resonance (NMR) data include ¹H NMR signals for protons on nitrogen in NH₂Cl near 5-6 ppm in aqueous solution, reflecting the deshielding effect of the electronegative chlorine, while ¹⁵N NMR shifts for chloramines typically occur in the 300-400 ppm range relative to ammonia, indicating the electronic perturbation from N-Cl bonding.^[22]

Reactivity and Decomposition

Chloramines function as mild oxidizing agents, exhibiting lower oxidation-reduction potentials than free chlorine, which renders them less aggressive in disinfection applications but still capable of reacting with reduced species. In redox processes, the chlorine in chloramines maintains a +1 oxidation state, allowing them to oxidize substrates such as iodide to iodine or participate in electron transfer reactions with organic compounds. These interactions with natural organic matter can lead to the formation of nitrogenous disinfection byproducts, including haloacetonitriles, which arise from the incorporation of nitrogen from chloramines into chlorinated organics.^[23] Hydrolysis represents a key decomposition pathway for monochloramine, governed by the reaction:

\mathrm{NH_2Cl + H_2O \rightarrow [NH_3](/page/Ammonia) + [HOCl](/page/Hypochlorous_acid)}

This process is relatively slow at neutral pH, with a half-life exceeding centuries under typical conditions, but its rate increases significantly at higher pH values due to enhanced nucleophilic attack by hydroxide ions.^[7] For dichloramine and trichloramine, hydrolysis is more rapid in acidic environments, contributing to their instability and conversion to other species like ammonia and hypochlorous acid. Thermal decomposition of chloramines occurs at elevated temperatures, yielding products such as chlorine gas (Cl₂), nitrogen gas (N₂), and hydrochloric acid (HCl), with monochloramine breaking down above -50°C into nitrogen, chlorine, and traces of trichloramine.^[7] Photolytic decomposition, induced by ultraviolet irradiation at wavelengths like 254 nm, degrades all inorganic chloramines (NH₂Cl, NHCl₂, NCl₃) into nitrite (NO₂⁻), nitrate (NO₃⁻), nitrous oxide (N₂O), and ammonium (NH₄⁺), with quantum yields varying by wavelength and pH—favoring nitrate at low pH and nitrite at high pH.^[24] In atmospheric contexts, trichloramine serves as a significant precursor to chlorine radicals (Cl·) through photolysis, with recent observations in urban environments like Beijing and New Delhi showing mixing ratios up to 124 pptv and contributions exceeding 30% to ground-level Cl· production during low-pollution periods.^[25] Chloramines interact dynamically with ammonia in aqueous systems, particularly during breakpoint chlorination, where excess chlorine oxidizes initial chloramine formations (e.g., monochloramine) and residual ammonia, ultimately producing nitrogen gas and eliminating combined chlorine residuals at a chlorine-to-ammonia weight ratio of approximately 10:1 at pH 7.^[26] This process involves sequential redox steps, including the disproportionation of dichloramine to N₂, N₂O, and NCl₃. The redox potential for the monochloramine-ammonia couple (NH₂Cl/NH₃) is approximately 0.8 V under standard conditions, reflecting chloramines' moderate oxidizing strength relative to free chlorine (E° ≈ 1.4 V).^[27]

Inorganic Chloramines

Monochloramine

Monochloramine (NH₂Cl) is the primary inorganic chloramine employed in water treatment due to its relative stability compared to other chloramines. It forms through the chlorination of ammonia under controlled conditions, serving as a key disinfectant that provides longer-lasting residuals than free chlorine. Unlike dichloramine and trichloramine, monochloramine predominates at higher pH levels (around 7–8) and chlorine-to-nitrogen ratios near 3:1 to 5:1, making it the favored species in practical applications.^[7]^[5] Preparation of monochloramine typically involves the reaction of ammonia with hypochlorous acid or chlorine in aqueous solution: NH₃ + HOCl → NH₂Cl + H₂O. This process occurs rapidly with a rate constant of approximately 6.1 × 10⁶ M⁻¹ s⁻¹ at 25°C and is optimized at pH values above 8 with a hypochlorite-to-ammonia molar ratio less than 1 to minimize formation of dichloramine or trichloramine. In industrial water treatment settings, monochloramine is generated in situ by sequentially adding ammonia to pre-chlorinated water, ensuring a weight ratio of chlorine to ammonia-nitrogen between 3:1 and 5:1 for efficient production without excess free chlorine.^[7]^[5] Physically, monochloramine appears as a colorless to yellow liquid with a strong pungent odor and has a melting point of -66°C. It is highly soluble in water, as well as in alcohol and ether, though only slightly soluble in carbon tetrachloride and benzene. Due to its inherent instability, pure monochloramine decomposes explosively above -50°C and is sensitive to light, temperature, and pH changes, often breaking down in dilute solutions to nitrogen, hydrochloric acid, and ammonium chloride.^[5]^[28] Monochloramine exhibits unique reactivity characterized by slower disinfection kinetics than hypochlorous acid—approximately 10⁴ times less effective—but greater persistence in water systems, allowing sustained antimicrobial activity. It selectively oxidizes sulfhydryl (-SH) groups in proteins and enzymes, converting them to disulfides or higher oxidation states, which disrupts microbial metabolic processes; the extent of this oxidation depends on the molar ratio of monochloramine to sulfhydryl and is pH-dependent. This targeted reactivity with thiols, rather than rapid reaction with a broad range of organics, contributes to its role in controlling biofilm formation without the rapid decay seen in free chlorine.^[7]^[29] Analytical detection of monochloramine residuals relies on methods that distinguish it from free chlorine, with the DPD (N,N-diethyl-p-phenylenediamine) colorimetry being the most widely used. In this approach, monochloramine reacts with DPD in buffered solution to produce a red-colored indamine dye, measured spectrophotometrically at 515 nm; it is quantified as combined chlorine by subtracting free chlorine readings (without potassium iodide) from total chlorine readings (with potassium iodide). This method achieves detection limits around 0.02 mg/L as Cl₂ and is standardized for water quality monitoring, though interferences from metals like copper or manganese require sample pretreatment. Alternative techniques include amperometric titration at pH 3.5–4.5 using potassium iodide, where monochloramine liberates iodine proportional to its concentration.^[7]^[5]

Dichloramine and Trichloramine

Dichloramine (NHCl₂) and trichloramine (NCl₃) are higher chlorinated inorganic chloramines formed during the reaction of ammonia with chlorine or hypochlorite under conditions favoring excess chlorination. Dichloramine is produced at chlorine-to-nitrogen (Cl:N) molar ratios of approximately 2:1, as in the reaction \ce{NH3 + 2HOCl -> NHCl2 + 2H2O}.^[30] Trichloramine forms at higher ratios, around 3:1 molar Cl:N, such as through further chlorination of dichloramine or direct reaction with excess hypochlorous acid.^[31] These species are transient in water treatment, appearing briefly before decomposing due to their inherent instability, unlike the more persistent monochloramine.^[19] Physically, dichloramine manifests as a yellow oil with a predicted density of 1.429 g/cm³ and a boiling point of 115–117°C at reduced pressure (15 Torr); it is highly reactive and unstable even at ambient conditions. Trichloramine appears as a yellow, oily liquid that is explosive in its pure form, with a density of 1.653 g/mL, melting point of −40°C, boiling point of 71°C, and a pungent, chlorine-like odor.^[32] The instability of these compounds distinguishes them from lower chloramines. Dichloramine undergoes rapid decomposition, yielding primarily nitrogen gas (N₂) and hydrochloric acid (HCl) through pathways involving oxidation and disproportionation reactions leading to nitrogen-containing products such as N₂ and nitrate.^[33]^[34] In the presence of excess ammonia, it often produces monochloramine as an intermediate. Trichloramine exhibits even greater hazard, being highly explosive upon shock or heating, and it is a key contributor to the irritating "chlorine smell" in chlorinated environments due to its volatility and odor.^[35]

Organic Chloramines

Synthesis and Structures

Organic chloramines are typically synthesized through the N-chlorination of primary or secondary amines using chlorinating agents such as sodium hypochlorite (NaOCl) or N-chlorosuccinimide (NCS). The reaction with NaOCl proceeds rapidly under basic conditions, where the amine (R-NH₂ or R₂NH) reacts with hypochlorite to form the corresponding N-chloroamine (R-NHCl or R₂NCl) and sodium hydroxide, as exemplified by the second-order kinetics with rate constants around 1.52 × 10⁵ L·mol⁻¹·min⁻¹ at high pH.^[36] NCS serves as a milder, electrophilic chlorinating agent, particularly effective for N-chlorination of amines like benzylamine, involving direct transfer of Cl⁺ to the nitrogen lone pair, yielding stable N-chloro products under controlled conditions without requiring aqueous media.^[37] The molecular structures of organic chloramines feature the characteristic N-Cl bond, which can adopt cyclic or acyclic configurations depending on the amine precursor. In acyclic forms, the N-Cl is directly attached to alkyl or aryl groups (e.g., R-NCl-R'), while cyclic variants incorporate the N-Cl within ring systems for enhanced rigidity, such as in hydantoins where the chloramine is part of a five-membered imidazolidine-2,4-dione framework. Aromatic substituents often provide resonance stabilization to the N-Cl bond through delocalization involving the π-system of the aryl ring, which interacts with the electronegative chlorine, reducing bond polarity and improving overall structural integrity.^[38] A notable example is trichloroisocyanuric acid (TCCA), a cyclic N-chloro compound with the formula (C₃Cl₃N₃O₃), featuring three N-Cl bonds in a symmetric triazine ring derived from isocyanuric acid, which acts as a stable reservoir for chlorine release.^[39] Compared to inorganic chloramines like NH₂Cl, organic variants exhibit greater persistence due to the stabilizing influence of carbon-based substituents, which sterically hinder decomposition pathways and modulate the N-Cl bond strength, allowing for prolonged activity in solution.^[7] This enhanced stability is particularly evident in cyclic structures like TCCA, which resists hydrolysis and maintains efficacy over extended periods, unlike the more reactive inorganic forms that decompose rapidly in water.^[7] Spectroscopic identification of organic chloramines often relies on UV-Vis absorption, where the N-Cl chromophore produces characteristic bands around 250-280 nm attributable to n→σ* transitions in the N-Cl bond, enabling straightforward detection and quantification in complex matrices.^[40]

Common Examples

One prominent example of an organic chloramine is N-chlorosuccinimide (NCS), a white solid compound employed as a mild chlorinating and oxidizing agent in organic synthesis for reactions such as allylic chlorination and alpha-halogenation of carbonyls.^[41] It exhibits a melting point of 148–150 °C and is valued for its stability under controlled conditions, enabling selective transformations without excessive side reactions.^[42] Another key organic chloramine is chloramine-T, the sodium salt of N-chlorotoluene-4-sulfonamide, which features a sulfonamide group attached to an aromatic toluene ring. This compound possesses antiseptic properties and is utilized as a mild disinfectant in topical applications due to its ability to release active chlorine slowly.^[43] Its low toxicity profile supports its use in medical and pharmaceutical contexts, where it acts as an oxidizing agent with minimal adverse effects at therapeutic concentrations.^[44] Halogenated hydantoin derivatives, such as 1,3-dichloro-5,5-dimethylhydantoin (DCDMH), represent cyclic organic chloramines that function as slow-release disinfectants in recreational water systems like swimming pools. These compounds provide sustained chlorine delivery over extended periods, maintaining effective sanitization levels while the hydantoin backbone decomposes gradually.^[45] Organic chloramines like these offer biodegradability advantages over inorganic counterparts, as their carbon-based structures facilitate natural breakdown into non-persistent residues in environmental settings.^[46]

Disinfection Applications

Drinking Water Treatment

Chloramination is a widely employed disinfection method in municipal drinking water treatment, involving the sequential addition of chlorine gas or hypochlorite followed by ammonia to form primarily monochloramine (NH₂Cl) as the residual disinfectant. This process typically occurs after primary filtration and aims to maintain a stable disinfectant throughout the distribution system, with common dosages ranging from 1 to 4 mg/L as chlorine to achieve a chlorine-to-ammonia weight ratio of approximately 3:1 to 5:1.^[4]^[8] The resulting monochloramine provides effective control against bacterial pathogens while minimizing the formation of harmful disinfection byproducts compared to free chlorine alone.^[19] One key advantage of chloramination is its ability to reduce the production of trihalomethanes (THMs) and other regulated disinfection byproducts, which form when free chlorine reacts with natural organic matter in source water; studies show chloramine-treated water can have significantly lower THM levels under similar conditions.^[47] Additionally, monochloramine's greater chemical stability allows for a longer-lasting residual in extended distribution networks, reducing the risk of microbial regrowth and biofilm formation in pipes compared to free chlorine, which dissipates more rapidly.^[4] This persistence is particularly beneficial in large urban systems where water travel times can exceed several days. Despite these benefits, chloramination presents challenges, including slower inactivation rates for certain pathogens such as the protozoan Cryptosporidium parvum, which requires significantly higher contact times or supplementary treatments like filtration for effective removal, as monochloramine alone achieves only limited log reductions even at elevated concentrations. Another concern is the risk of nitrification in distribution systems, where residual ammonia promotes the growth of nitrifying bacteria, potentially leading to decreased disinfectant residuals, pH drops, and increased corrosion if not managed through monitoring and ammonia control strategies.^[48] Additionally, research published in 2024 identified chloronitramide anion as a previously unknown byproduct of chloramination, present in many US water systems at concentrations of 1–120 μg/L, though its health impacts are still being evaluated.^[49] In the United States, chloramines are used by approximately 25-30% of community water systems serving over 20% of the population, according to recent EPA surveys, reflecting their adoption to comply with disinfection byproduct regulations.^[4] In Europe, chloramine use is limited due to preferences for alternatives like ozone or chlorine dioxide, which offer effective disinfection with potentially fewer byproduct concerns in groundwater-dominated supplies.^[50]

Swimming Pools and Spas

In swimming pools and spas, chloramines form when chlorine-based disinfectants react with nitrogen-containing compounds introduced by swimmers, such as sweat, urine, and body oils, leading to the buildup of monochloramine (NH₂Cl) and other species.^[51] This reaction is exacerbated in recreational waters where bather loads are high, resulting in combined chlorine levels that can impair disinfection efficacy if not managed.^[52] To mitigate accumulation, operators employ breakpoint chlorination, which involves adding sufficient chlorine—typically 10 times the measured combined chlorine concentration—to oxidize and eliminate chloramines, restoring free chlorine residuals.^[53]^[54] A primary concern with chloramines, particularly trichloramine (NCl₃), is its role in causing eye and skin irritation among swimmers and staff, manifesting as redness, stinging, and discomfort often misattributed to free chlorine.^[55] Trichloramine is also responsible for the characteristic "chlorine smell" in pools, which arises from its volatile nature rather than chlorine itself, signaling elevated byproduct levels.^[56] In indoor facilities, trichloramine's high volatility leads to greater airborne concentrations near the water surface, heightening exposure risks in enclosed spaces.^[57] Effective management includes maintaining free chlorine levels between 1 and 3 parts per million (ppm) as recommended by the Centers for Disease Control and Prevention (CDC), alongside combined chlorine below 0.4 ppm to minimize irritation.^[58]^[59] Adjunctive technologies such as ultraviolet (UV) light or ozone systems can break down chloramines without solely relying on chemical shocking, enhancing overall water quality by targeting nitrogen precursors and volatile byproducts.^[53] For indoor pools and spas, adequate mechanical ventilation is essential to dilute airborne trichloramine, with systems designed to extract air at deck level to prevent accumulation in breathing zones.^[60] These strategies collectively reduce user impacts while ensuring safe recreational use.

Health and Environmental Impacts

Human Health Effects

Acute exposure to chloramines, particularly through inhalation of volatile forms like trichloramine in indoor swimming pool environments, can cause irritation of the eyes, nose, throat, and upper respiratory tract, leading to symptoms such as coughing, wheezing, and shortness of breath among pool workers and frequent swimmers.^[61] Dermal contact with chloramines may result in skin irritation, and epidemiological studies have linked such exposures to exacerbated asthma symptoms, with evidence suggesting occupational asthma development in pool attendants exposed to airborne chloramines.^[62] These effects are typically reversible upon removal from exposure, though high concentrations from accidental mixing of chlorine and ammonia can induce pneumonitis without long-term pulmonary damage.^[7] Chronic exposure to chloramines raises concerns regarding potential mutagenicity, with the U.S. Environmental Protection Agency noting inconclusive results from assays showing marginal mutagenic activity in bacteria like Bacillus subtilis and Salmonella typhimurium, but no clear genotoxic effects in mammalian cells.^[7] Byproducts formed during chloramine decomposition, such as cyanogen chloride, pose additional risks as potent irritants that cause severe eye and respiratory tract burning, lacrimation, and choking effects at concentrations below 1 ppm, rapidly metabolizing to cyanide and disrupting oxygen utilization in tissues.^[63] Children and individuals with pre-existing asthma represent vulnerable groups, exhibiting heightened susceptibility to respiratory symptoms and increased asthma onset risk from cumulative chloramine exposure in chlorinated pools, with odds ratios up to 3.7 for upper airway irritation in atopic children.^[64] Although no specific OSHA permissible exposure limit exists for monochloramine, occupational guidelines recommend maintaining airborne concentrations below 0.5 ppm to minimize irritation risks, aligning with limits for related chlorine compounds.^[65] Recent 2024 research highlights decomposition products of chloramines, including the newly identified chloronitramide anion prevalent in U.S. tap water treated with inorganic chloramines, which computational modeling links to potential chronic toxicity, prenatal developmental harm, and oxidative stress through reactive species generation.^[66] Additionally, studies on organic chloramines formed during algal blooms indicate they may induce cellular oxidative stress and toxicity, warranting further evaluation of long-term human health implications.^[67]

Environmental and Regulatory Concerns

Chloramines pose significant risks to aquatic ecosystems, primarily due to their toxicity to fish and other sensitive organisms. Monochloramine, the most common form used in water treatment, can cause gill damage and disrupt oxygen transport in fish when concentrations exceed 0.02 mg/L, leading to stress, inflammation, and mortality in species like trout and salmon.^[68]^[69] For this reason, dechloramination is essential for aquarium and aquaculture systems, where water must be treated with reducing agents or filters to neutralize residuals below 0.1 mg/L before use.^[70] While chloramines exhibit low bioaccumulation potential due to their reactivity with organic matter and rapid decay in natural environments, their persistence in treated water systems can lead to the formation of harmful byproducts. Unlike free chlorine, monochloramine hydrolyzes slowly, maintaining residuals for extended periods in distribution networks, which increases the risk of N-nitrosodimethylamine (NDMA) production—a probable human carcinogen classified by the U.S. EPA as posing risks at low ng/L levels.^[71]^[72] NDMA forms during chloramination of precursors like dimethylamine, raising ecological concerns for downstream water bodies where treated effluents are discharged.^[73] Regulatory frameworks address these environmental risks through limits on residuals and byproducts. In the United States, the EPA's Stage 2 Disinfectants and Disinfection Byproducts Rule (2006), with proposed revisions announced in 2025 to potentially enhance monitoring of disinfection byproducts including considerations for toxicity weighting, sets a maximum residual disinfectant level of 4.0 mg/L for chloramines while requiring compliance averages below this to minimize ecological exposure.^[74]^[75] In the European Union, the Drinking Water Directive indirectly limits chloramine use by capping chlorite and chlorate byproducts at 0.25 mg/L and emphasizing chlorine residuals, with monochloramine guidelines at 3 mg/L in member states like the UK to protect aquatic life.^[76] Some regions, such as certain U.S. municipalities like Hannibal, Missouri, have prohibited chloramines in favor of alternative disinfectants due to persistent toxicity and byproduct issues.^[77] Mitigation strategies focus on removal and surveillance to reduce environmental discharge. Granular activated carbon (GAC) filtration effectively breaks down chloramines through catalytic reduction, requiring extended contact times compared to chlorine removal, and is widely used in wastewater effluents to protect receiving waters.^[78] Ongoing monitoring of disinfection byproducts (DBPs) like NDMA, mandated under EPA and EU rules, ensures residuals do not exceed safe thresholds, with advanced treatment like UV irradiation or biofiltration employed in high-risk areas to prevent ecological harm.^[79]^[80]

References

[1]
Chloramine - Some Drinking-water Disinfectants and Contaminants ...
Chloramine, also known as monochloramine, is an inorganic nitrogen compound with chlorine atoms, used as a disinfectant in drinking water.Missing: definition | Show results with:definition
[2]
Chloramines as a disinfectant - Lenntech
Inorganic chloramines are formed when dissolved chlorine and ammonia react. During this reaction three different inorganic chloramines are formed; ...
[3]
Chloramines Water Disinfection - Nebraska Extension Publications
They are composed of three chemicals: monochloramine, dichloramine and trichloramine. Monochloramine is preferred for water disinfection because of its biocidal ...
[4]
Chloramines in Drinking Water | US EPA
Mar 14, 2025 · Chloramines are disinfectants formed when ammonia is added to chlorine, used to treat drinking water, and are safe when meeting EPA standards. ...Missing: properties | Show results with:properties
[5]
Monochloramine | ClH2N | CID 25423 - PubChem - NIH
Chloramine is used as a chemical intermediate in the synthesis of various amines and hydrazine(1) and as a disinfectant in drinking water for systems in which ...
[6]
[PDF] DRINKING WATER CRITERIA DOCUMENT FOR Chloramines
Mar 8, 1994 · For a discussion of rates of formation and breakdown of chloramines see the Physical and Chemical Properties Section and the Uses of Chloramines ...
[7]
About Water Disinfection with Chlorine and Chloramine - CDC
Feb 14, 2024 · Chloramines are a group of chemical compounds that contain chlorine and ammonia. The type of chloramine used to kill germs in drinking water is ...Missing: definition | Show results with:definition
[8]
N-chlorosuccinimide as a novel agent for biofouling control in the ...
N-chlorosuccinimide as a novel agent for biofouling control in the polyamide reverse ... Recently, we reported an N-halamine (a group of organic chloramine) ...
[9]
N-Chloramines, a Promising Class of Well-Tolerated Topical Anti ...
The latter can be divided into chloramines, with a saturated carbon atom adjacent to the N-Cl function, -CH2-NCl-, and chloramides or chlorimides, with one and ...
[10]
THE CHEMISTRY OF CHLORAMINES - jstor
actions (19), the first of which is the formation of monochloramine,. 2NH3 + Ob = NH2CI + NH4CI. INTERRELATION OF CHLORAMINES. In the average treatment of ...Missing: synthesis | Show results with:synthesis<|separator|>
[11]
Olin Raschig process - Wikipedia
The Olin Raschig process is a chemical process for the production of hydrazine. The main steps in this process, patented by German chemist Friedrich Raschig ...Missing: Fritz 1920s
[12]
Why Are So Many People Talking About Monochloramine?
It was first used in water treatment in the mid-1910s; the City of Ottawa first used chloramines in 1915. Denver, Colorado, started using monochloramine ...Missing: 19th | Show results with:19th
[13]
Monochloramines and Disinfection Byproducts in Drinking Water
Jul 25, 2012 · Monochloramine has been used in the U.S. as a secondary disinfectant since the 1930s. While the EPA does not know the absolute number of people ...
[14]
FAQs • How do chloramines affect fish? - Deltona, FL
Major U.S. cities such as Denver and Minneapolis have been using chloramines since the 1940s. ... Will chloramines affect swimming pools? No. You will still need ...
[15]
A Review on the 40th Anniversary of the First Regulation of Drinking ...
The 1979 THM regulation established that the combined concentration of the four THMs (chloroform, BDCM, DBCM, and bromoform) should not exceed an annual average ...
[16]
CCCBDB compare calculated bond lengths
Bond Length (Å). Lowest value, NCl, nitrogen monochloride, 1.626. Highest value, NH2Cl, chloramine, 1.744. Calculated Bond lengths. Click on entry for all ...
[17]
The nitrogen-chlorine bond has an average bond dissociation energ...
The nitrogen-chlorine bond has an average bond dissociation energy of 200 kJ/mol. Calculate the highest wavelength of photons that can initiate the dissociation ...Missing: chloramines | Show results with:chloramines
[18]
Common Bond Energies (D - Wired Chemist
Bond, D (kJ/mol), r (pm). N-N, 167, 145. N=N, 418, 125. N≡N, 942, 110. N-O, 201, 140. N=O, 607, 121. N-F, 283, 136. N-Cl, 313, 175. P-P, 201, 221. P-O, 335, 163.Missing: chloramines | Show results with:chloramines
[19]
Chloramines in Drinking Water - Guideline Technical Document for ...
Nov 23, 2018 · As a secondary usage, monochloramine has been used for the organic synthesis of amines and substituted hydrazines used as pharmaceutical ...
[20]
https://pubs.acs.org/doi/10.1021/ct050364u
[21]
Organic chloramines in drinking water: An assessment of formation ...
Apr 15, 2016 · The stability of different organic chloramines has been reported to be quite variable, ranging from a half-life of 13 min to more than 48 h ( ...
[22]
MS and NMR Analysis of Isotopically Labeled Chloramination ...
May 9, 2024 · We have developed a model chloramination reaction using compounds which share structural features with DOM in conjunction with 15N-labeled ...Introduction · Experimental Section · Results and Discussion · Conclusions
[23]
Precursors and factors affecting formation of haloacetonitriles and ...
This study investigated the precursors and factors affecting formation of haloacetonitriles (HANs) and chloropicrin (TCNM) during chlorination/chloramination ...
[24]
UV Photodegradation of Inorganic Chloramines - ACS Publications
All three chloramines can be degraded by UV irradiation, and the quantum yields for these processes are wavelength-dependent.Missing: thermal | Show results with:thermal
[25]
Chloramine chemistry as a missing link in atmospheric chlorine cycling
Oct 29, 2025 · Chlorine radicals (Cl·) profoundly affect atmospheric oxidation capacity. Chloramines, especially trichloramine, are emerging precursors of Cl·.
[26]
Breakpoint Chlorination - an overview | ScienceDirect Topics
Breakpoint chlorination is defined as a process in which chlorine reacts with ammonia in multiple stages to ultimately convert ammonia into nitrogen gas, ...
[27]
Water chlorination chemistry: nonmetal redox kinetics of chloramine ...
Water chlorination chemistry: nonmetal redox kinetics of chloramine and nitrite ion ... Reactivity of chlorine dioxide with amino acids, peptides, and proteins.
[28]
[PDF] Chloramines | Canada.ca
unstable liquid with a melting point of –66°C. Monochloramine is soluble in cold water, alcohol and ether and slightly soluble in carbon tetrachloride and.Missing: properties | Show results with:properties
[29]
Oxidation of sulfhydryl groups by monochloramine - ScienceDirect
A study was undertaken to evaluate the compound's reactions with sulfhydryl (−SH) groups. The extent of oxidation of these groups was dependent upon the molar ...Missing: reactivity | Show results with:reactivity
[30]
[PDF] NDMA Formation during Chlorination and Chloramination of ...
Jan 16, 2008 · When chloramines are prepared at Cl/N molar ratio <1.5:1, NH2Cl and NHCl2 coexist without the presence of free chlorine following eq. 1 with an ...
[31]
Differentiation and Quantification of Free Chlorine and Inorganic ...
However, it has been demonstrated that organic chloramines interfere with titrimetric determinations of free chlorine ( 7, 8) and cannot be differentiated from ...
[32]
Nitrogen trichloride | Cl3N | CID 61437 - PubChem
3.2.1 Physical Description. Liquid · 3.2.2 Color / Form. Yellow, oily liquid; explodes · 3.2.3 Odor. Pungent · 3.2.4 Boiling Point. 71 °C · 3.2.5 Melting Point. -40 ...
[33]
Dichloramine decomposition in the presence of excess ammonia
The decomposition of dichloramine, producing primarily nitrogen gas and monochloramine, was initiated by mixing solutions of dichloramine and monochloramine ...Missing: instability | Show results with:instability
[34]
Guidelines for Canadian Drinking Water Quality - Canada.ca
Feb 7, 2020 · Dichloramine undergoes a series of decomposition and oxidation reactions to form nitrogen-containing products, including nitrogen, nitrate ...
[35]
Trichloramine - American Chemical Society
Aug 30, 2016 · It is much more responsible for pools' “chlorine smell” than chlorine itself. In an article on disinfection byproducts in swimming pools related ...
[36]
Nitrogen trichloride - Wikipedia
Odor · chlorine-like ; Density, 1.653 g/mL ; Melting point, −40 °C (−40 °F; 233 K) ; Boiling point, 71 °C (160 °F; 344 K).
[37]
Chloronitramide anion is a decomposition product of inorganic ...
Nov 21, 2024 · We report chloronitramide anion (Cl–N–NO 2 − ) as a previously unidentified end product of inorganic chloramine decomposition.
[38]
Continuous formation of N-chloro-N,N-dialkylamine solutions in well ...
Dec 2, 2015 · The rate of reaction of NaOCl and amines at high pH is very fast with a second order rate constant, kobs of 1.52 × 105 L·mol−1·min−1 ...
[39]
Kinetic study of the formation of N -chloro compounds using N
Aug 10, 2025 · The reaction of benzylamine with N-chlorosuccinimide involves addition of the amine to electrophilic chlorine to yield N-chlorobenzylamine and ...
[40]
Antimicrobial N-Halamine Polymers and Coatings: A Review of ...
For organic polymers, N-halamine moieties can be divided into cyclic and acyclic structures. ... Structures of some cyclic organic N-halamines; X = Cl or Br or H.Missing: stabilization | Show results with:stabilization
[41]
Trichloroisocyanuric Acid: A Safe and Efficient Oxidant
As seen from the structure TCCA belongs to the large group of N-chloroimides and amides which is a subgroup of the more general N-chloroamines. N-chloroamines ...
[42]
Organic chloramines attenuation and disinfection by-product ...
May 19, 2022 · UV irradiation at 254 nm could effectively degrade OCs by 96.6% after 60 min, mainly because N-Cl bond had significant UV absorption at 250-280 nm.Missing: spectroscopy chromophores
[43]
Chlorosuccinimide | C4H4ClNO2 | CID 31398 - PubChem
4 Melting Point. 150 °C. Haynes, W.M. (ed.). CRC Handbook of ... N-Chlorosuccinimide's production and use as a chlorinating agent in organic synthesis ...
[44]
What is N-Chlorosuccinimide? - ChemicalBook
Mar 25, 2021 · Properties. Melting point 148-150 °C(lit.) Density 1,65 g/cm3. Refractive index 1.4378 (estimate). Fp >110°C. Storage temp. Store at +2°C to +8 ...
[45]
Chloramine-T: Uses, Interactions, Mechanism of Action - DrugBank
Sep 30, 2018 · Tosylchloramide, also known as chloramine-T, is a chlorinated and deprotonated sulfonamide used as a mild disinfectant. It is not stable in the ...
[46]
Uses of Chloramine-T - ChemicalBook
Aug 18, 2022 · It's a inexpensive, low toxic and mild oxidizing agent, and it also acts as a source of nitrogen anions and eletrophilic cations.<|control11|><|separator|>
[47]
1,3-Dichloro-5,5-dimethylhydantoin | C5H6Cl2N2O2 - PubChem
A maximal level of 10 ppm has been recommended for its use as a sanitizing agent in swimming pools. This limit is based on accidental swallowing of 100 to 200 ...
[48]
Hydantoin in eco-friendly cleaners
Jan 13, 2025 · Biodegradability: Hydantoin is biodegradable, meaning that it breaks down naturally in the environment without causing long-term pollution.Missing: chloramine | Show results with:chloramine
[49]
[PDF] What does EPA see as the advantages of using monochloramine?
Feb 24, 2009 · Water treated with monochloramine contains reduced levels of regulated disinfection byproducts compared to water treated with chlorine. 3.
[50]
[PDF] Nitrification - U.S. Environmental Protection Agency
Typically, the blended Cl2:NH3-N ratio will increase after blending. Most often this is due to dilution of the ammonia fraction in the chloraminated water.
[51]
https://www.cdc.gov/healthy-swimming/prevention/preventing-eye-irritation-from-pool-chemicals.html
[52]
Preventing Eye Irritation from Pool Chemicals - CDC
May 28, 2025 · Chlorine is used in pools to kill germs, but it can also combine with sweat, dirt, and pee to create chemical irritants called chloramines.Key Points · Prevention Tips · Prevent Chloramines From...Missing: guidelines | Show results with:guidelines
[53]
[PDF] chloramine quick guide 2025 - NACCHO
What are the prevention strategies? Swimmer Hygiene. Chloramines need nitrogen to form. Swimmers can help reduce nitrogen inputs by showering before entering ...
[54]
Chloramines and Pool Operation | Healthy Swimming - CDC
Jun 23, 2025 · Make sure the swimming area is well-ventilated, because superchlorination (also known as "breakpoint chlorination") increases off gassing of the ...
[55]
[PDF] HOW TO SHOCK THE POOL (CHLORINATE TO BREAKPOINT)
Chloramines can usually be eliminated from the pool water by performing breakpoint chlorination with chlorine or super oxidation with a non-chlorine oxidizer.Missing: structure | Show results with:structure
[56]
Prevalence of Ocular, Respiratory and Cutaneous Symptoms ... - NIH
Chloramines, especially trichloramine, are considered the causal agent for irritated eye, nose and throat symptoms, as well as asthma, in swimmers and subjects ...
[57]
The chlorine hypothesis: fact or fiction? - PMC - NIH
NCl3 is formed when organic matter (eg, sweat, urine) brought by swimmers in the water reacts with the chlorine, and is often responsible for the chlorine smell ...
[58]
Exposure to trichloramine and respiratory symptoms in indoor ...
Trichloramine is the most volatile and is easily released into the air. It is considered to be irritating to the eye and upper airway 1. ... However, the chemical ...
[59]
Operating and Managing Public Pools, Hot Tubs and Splash Pads
Jan 10, 2025 · CDC has the following guidance to help prevent the spread of germs ... Chloramines and Pool Operation · Pool Chemical Safety · Surf Venue ...
[60]
Combined Chlorine (Chloramines) - CMAHC
The owner shall ensure the AQUATIC facility takes action to reduce the level of combined chlorine (chloramines) in the water when the level exceeds 0.4 ...
[61]
Deck level air extraction and its impact on trichloramine ...
Sep 1, 2023 · In indoor swimming pools, NCl3 must be removed from the breathing zones with mechanical ventilation. Since it tends to accumulate at the water ...
[62]
Inorganic chloramines: a critical review of the toxicological and ...
Monochloramine is soluble and stable in water and the dominating inorganic chloramine in chlorinated water sources. No clinical effects were seen in healthy ...<|separator|>
[63]
Occupational asthma caused by chloramines in indoor swimming ...
The first series of three workers who developed occupational asthma following exposure to airborne chloramines in indoor chlorinated swimming pools is reported.Missing: dermal | Show results with:dermal
[64]
Cyanogen chloride (CK): Systemic Agent | NIOSH - CDC
Cyanogen chloride (CK) has strong irritant and choking effects. Its vapors are extremely irritating and corrosive. Cyanogen chloride (CK) is a chemical warfare ...
[65]
Chlorinated Pool Attendance, Atopy, and the Risk of Asthma ... - NIH
Use of indoor chlorinated pools especially by young children interacts with atopic status to promote the development of childhood asthma. These findings further ...
[66]
[PDF] exposure to Chloramine - NJ.gov
Chloramine can irritate skin, eyes, nose, throat, and lungs. Breathing it can cause coughing, shortness of breath, and potentially pulmonary edema. No exposure ...
[67]
A new concern raised from algal bloom: Organic chloramines in ...
Aug 15, 2024 · Theoretical predictions and toxicological tests suggest that organic chloramines may cause oxidative or toxic pressure to bacteria or cells.
[68]
Environmental Diseases of Aquatic Animals in Aquatic Systems
Both compounds are highly toxic to fish, with adverse effects occurring at chlorine concentrations as low as 0.02 mg/L and mortality at 0.04 mg/L. A simple ...Missing: threshold | Show results with:threshold
[69]
5.5.1. Chlorination in Depth - Aquarium Science
Chlorine is 100 to 1000 times more toxic than ammonia. Chlorine kills exposed tissues like the gills of the fish outright. When the cells in the gills of the ...
[70]
[PDF] Chloramines and Fish - City of Sioux Falls
Chloramine residuals in water used to keep fish should be kept below 0.1 mg/L. ... Chloramines are a combination of chlorine and ammonia and both can be toxic to ...Missing: threshold | Show results with:threshold
[71]
[PDF] Monochloramine in Drinking-water - World Health Organization (WHO)
The peak plasma level was reached 8 h following administration, with an elimination half-life from plasma of 39 h (31). Monochloramine is metabolized to the ...
[72]
NDMA formation during drinking water treatment - ScienceDirect.com
May 15, 2016 · According to USEPA's Integrated Risk Information System (IRIS), NDMA is considered carcinogenic at low ng/L levels. California currently has a 3 ...
[73]
The role of chloramine species in NDMA formation - ADS
N-nitrosodimethylamine (NDMA), a probable human carcinogen disinfection by-product, has been detected in chloraminated drinking water systems.
[74]
Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules
Jul 1, 2025 · The Stage 2 DBPR strengthens public health protection by tightening compliance monitoring requirements for Trihalomethanes (TTHM) and Haloacetic ...
[75]
National Primary Drinking Water Regulations: Stage 2 Rule
Jan 4, 2006 · EPA believes the Stage 2 DBPR will reduce the potential risks of cancer and reproductive and developmental health effects associated with DBPs.
[76]
Regulation drinking water disinfection EU - Lenntech
Chlorine is added for residual disinfection. Great Britain is one of few European countries that use chloramines for residual disinfection in the ...
[77]
Citizens across the country question chloramines in drinking water
Apr 19, 2021 · Hannibal, Missouri, and Poughkeepsie, New York, are among the cities that have dropped the controversial chemical in favor of new water treatment systems.
[78]
Mitigating Disinfection Byproducts: Chloramination or Granular ...
Aug 11, 2025 · A second reason to reconsider the reliance on chloramines to control DBP exposure is that chloramines are responsible for substantial ...
[79]
[PDF] Disinfectants and Disinfection Byproducts Rules (Stage 1 and Stage 2)
The Stage 1 DBPR analytical and monitoring requirements for chlorine, chloramines, bromate, chlorine dioxide and chlorite apply to all CWSs and NTNCWSs that add ...
[80]
Formation and removal of disinfection by-products in a full scale ...
Feb 20, 2020 · Activated carbon (GAC) is considered as an advanced treatment for NOM removal through adsorption and/or biodegradation (Yang et al., 2010, Chili ...