Disinfection by-product
Encyclopedia
Disinfection by-products (DBPs) result from reactions between organic and inorganic matter in water with chemical treatment agents during the water disinfection process.
, chlorine dioxide
, and chloramine
, are strong oxidising agents introduced into water in order to destroy pathogenic microbes, to oxidise taste/odour-forming compounds, and to form a disinfectant residual so as water may reach the consumer tap safe from microbial contamination. These disinfectants may react with naturally present fulvic and humic
acids, amino acids, and other natural organic matter, as well as iodide and bromide ions, to produce a range of DBPs such as the trihalomethanes (THMs), haloacetic acids
(HAAs), and chlorite
(which are regulated in the US), and so-called "emerging" DBPs such as halonitromethanes, haloamides, halofuranones, iodo-acids, iodo-THMs, nitrosamines, and others.
Chloramine has become a popular disinfectant in the US, and it has been found to produce N-nitrosodimethylamine (NDMA), which is a possible human carcinogen, as well as highly genotoxic iodinated DBPs, such as iodoacetic acid, when iodide is present in source waters.
Residual chlorine (and other disinfectants) may also react further within the distribution network —both by further reactions with dissolved natural organic matter and with biofilms present in the pipes. In addition to being highly influenced by the types of organic and inorganic matter in the source water, the different species and concentrations of DBPs vary according to the type of disinfectant used, the dose of disinfectant, the concentration of natural organic matter and bromide/iodide, the time since dosing, temperature, and pH of the water.
Swimming pools using chlorine have been found to contain trihalomethanes, although generally they are below current EU standard for drinking water (100 micrograms per litre). Concentrations of trihalomethanes (mainly chloroform
) of up to 0.43 ppm have been measured. In addition, trichloramine has been detected in the air above swimming pools, and it is suspected in the increased asthma observed in elite swimmers. Trichloramine is formed by the reaction of urea (from urine and sweat) with chlorine and gives the indoor swimming pool its distinctive odor. Salt-water pools generate higher levels of trihalomethanes (mainly bromoform
) than freshwater chlorine pools with levels measured of close to 1.3 ppm.
, for example, produces ketones, carboxylic acids, and aldehydes, including formaldehyde. Bromide in source waters can be converted by ozoneinto bromate
, a potent carcinogen that is regulated in the United States, as well as other brominated DBPs.
As regulations are tightened on established DBPs such as THMs and HAAs, drinking water treatment plant may switch to alternative disinfection methods. This change will alter the distribution of classes of DBP's.
, chloramination
, ozonation, or treatment with chlorine dioxide. Many hundreds of DBPs exist in treated drinking water and at least 600 have been identified.The low levels of many of these DBPs, coupled with the analytical costs in testing water samples for them, means that in practice only a handful of DBPs are actually monitored. Increasingly it is recognised that the genotoxicities and cytotoxicities of many of the DBPs not subject to regulatory monitoring, (particularly iodinated, nitrogenous DBPs) are comparatively much higher than those DBPs commonly monitored in the developed world (THMs and HAAs).
, but not for congenital anomalies (birth defects). Early-term miscarriages have also been reported in some studies.The exact putative agent remains unknown, however, in the epidemiological studies since the number of DBPs in a water sample are high and exposure surrogates such as monitoring data of a specific by-product (often total trihalomethanes) are used in lieu of more detailed exposure assessment. The World Health Organization
has stated that "the risk of death from pathogens is at least 100 to 1000 times greater than the risk of cancer from disinfection by-products (DBPs)" {and} the "risk of illness from pathogens is at least 10 000 to 1 million times greater than the risk of cancer from DBPs".
has set Maximum Contaminant Levels (MCLs) for bromate
, chlorite
, haloacetic acids and total trihalomethane
s (TTHMs). In Europe, the level of TTHMs has been set at 100 micrograms per litre, and the level for bromate to 10 micrograms per litre, under the Drinking Water Directive. No guideline values have been set for HAAs in Europe. The World Health Organization has established guidelines for several DBPs, including bromate, bromodichloromethane, chlorate, chlorite, chloroacetic acid, chloroform, cyanogen chloride, dibromoacetonitrile, dibromochloromethane, dichloroacetic acid, dichloroacetonitrile, NDMA, and trichloroacetic acid.
Chlorination disinfection by-products
Chlorinated disinfection agents such as chlorineChlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, chlorine dioxide
Chlorine dioxide
Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching....
, and chloramine
Chloramine
Chloramines are derivatives of ammonia by substitution of one, two or three hydrogen atoms with chlorine atoms. Monochloramine is an inorganic compound with the formula NH2Cl. It is an unstable colourless liquid at its melting point of -66° temperature, but it is usually handled as a dilute...
, are strong oxidising agents introduced into water in order to destroy pathogenic microbes, to oxidise taste/odour-forming compounds, and to form a disinfectant residual so as water may reach the consumer tap safe from microbial contamination. These disinfectants may react with naturally present fulvic and humic
Humic acid
Humic acid is a principal component of humic substances, which are the major organic constituents of soil , peat, coal, many upland streams, dystrophic lakes, and ocean water. It is produced by biodegradation of dead organic matter...
acids, amino acids, and other natural organic matter, as well as iodide and bromide ions, to produce a range of DBPs such as the trihalomethanes (THMs), haloacetic acids
Haloacetic acids
Haloacetic acids are carboxylic acids in which a halogen atom takes the place of a hydrogen atom in acetic acid. Thus, in a monohaloacetic acid, a single halogen would replace a hydrogen atom. For example, chloroacetic acid would have the structural formula CH2ClCO2H. In the same manner, in...
(HAAs), and chlorite
Chlorite
The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:...
(which are regulated in the US), and so-called "emerging" DBPs such as halonitromethanes, haloamides, halofuranones, iodo-acids, iodo-THMs, nitrosamines, and others.
Chloramine has become a popular disinfectant in the US, and it has been found to produce N-nitrosodimethylamine (NDMA), which is a possible human carcinogen, as well as highly genotoxic iodinated DBPs, such as iodoacetic acid, when iodide is present in source waters.
Residual chlorine (and other disinfectants) may also react further within the distribution network —both by further reactions with dissolved natural organic matter and with biofilms present in the pipes. In addition to being highly influenced by the types of organic and inorganic matter in the source water, the different species and concentrations of DBPs vary according to the type of disinfectant used, the dose of disinfectant, the concentration of natural organic matter and bromide/iodide, the time since dosing, temperature, and pH of the water.
Swimming pools using chlorine have been found to contain trihalomethanes, although generally they are below current EU standard for drinking water (100 micrograms per litre). Concentrations of trihalomethanes (mainly chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
) of up to 0.43 ppm have been measured. In addition, trichloramine has been detected in the air above swimming pools, and it is suspected in the increased asthma observed in elite swimmers. Trichloramine is formed by the reaction of urea (from urine and sweat) with chlorine and gives the indoor swimming pool its distinctive odor. Salt-water pools generate higher levels of trihalomethanes (mainly bromoform
Bromoform
Bromoform is a pale yellowish liquid with a sweet odor similar to chloroform, a halomethane or haloform. Its refractive index is 1.595 . Bromoform is produced naturally by phytoplankton and seaweeds in the ocean and this is thought to be the predominant source to the environment...
) than freshwater chlorine pools with levels measured of close to 1.3 ppm.
By-products from non-chlorinated disinfectants
Several powerful oxidising agents are used in disinfecting and treating drinking water, and many of these also cause the formation of DBPs. OzoneOzone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
, for example, produces ketones, carboxylic acids, and aldehydes, including formaldehyde. Bromide in source waters can be converted by ozoneinto bromate
Bromate
The bromate anion, BrO, is a bromine-based oxoanion. A bromate is a chemical compound that contains this ion. Examples of bromates include sodium bromate, , and potassium bromate, .Bromates are formed many different ways in municipal drinking water...
, a potent carcinogen that is regulated in the United States, as well as other brominated DBPs.
As regulations are tightened on established DBPs such as THMs and HAAs, drinking water treatment plant may switch to alternative disinfection methods. This change will alter the distribution of classes of DBP's.
Occurrence
DBPs are present in most drinking water supplies that have been subject to chlorinationChlorination
Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
, chloramination
Chloramination
Chloramination is the treatment of drinking water with a chloramine disinfectant. Both chlorine and small amounts of ammonia are added to the water one at a time which react together to form chloramine , a long lasting disinfectant...
, ozonation, or treatment with chlorine dioxide. Many hundreds of DBPs exist in treated drinking water and at least 600 have been identified.The low levels of many of these DBPs, coupled with the analytical costs in testing water samples for them, means that in practice only a handful of DBPs are actually monitored. Increasingly it is recognised that the genotoxicities and cytotoxicities of many of the DBPs not subject to regulatory monitoring, (particularly iodinated, nitrogenous DBPs) are comparatively much higher than those DBPs commonly monitored in the developed world (THMs and HAAs).
Health effects
Epidemiological studies have looked at the associations between exposure to DBPs in drinking water with cancers, adverse birth outcomes and birth defects. Meta-analyses and pooled analyses of these studies have demonstrated consistent associations for bladder cancer and for babies being born small for gestational ageSmall for gestational age
Small for gestational age babies are those who are smaller in size than normal for the baby's sex and gestational age, most commonly defined as a weight below the 10th percentile for the gestational age.-Terminology:...
, but not for congenital anomalies (birth defects). Early-term miscarriages have also been reported in some studies.The exact putative agent remains unknown, however, in the epidemiological studies since the number of DBPs in a water sample are high and exposure surrogates such as monitoring data of a specific by-product (often total trihalomethanes) are used in lieu of more detailed exposure assessment. The World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
has stated that "the risk of death from pathogens is at least 100 to 1000 times greater than the risk of cancer from disinfection by-products (DBPs)" {and} the "risk of illness from pathogens is at least 10 000 to 1 million times greater than the risk of cancer from DBPs".
Regulation and monitoring
The United States Environmental Protection AgencyUnited States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
has set Maximum Contaminant Levels (MCLs) for bromate
Bromate
The bromate anion, BrO, is a bromine-based oxoanion. A bromate is a chemical compound that contains this ion. Examples of bromates include sodium bromate, , and potassium bromate, .Bromates are formed many different ways in municipal drinking water...
, chlorite
Chlorite
The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:...
, haloacetic acids and total trihalomethane
Trihalomethane
Trihalomethanes are chemical compounds in which three of the four hydrogen atoms of methane are replaced by halogen atoms. Many trihalomethanes find uses in industry as solvents or refrigerants. THMs are also environmental pollutants, and many are considered carcinogenic...
s (TTHMs). In Europe, the level of TTHMs has been set at 100 micrograms per litre, and the level for bromate to 10 micrograms per litre, under the Drinking Water Directive. No guideline values have been set for HAAs in Europe. The World Health Organization has established guidelines for several DBPs, including bromate, bromodichloromethane, chlorate, chlorite, chloroacetic acid, chloroform, cyanogen chloride, dibromoacetonitrile, dibromochloromethane, dichloroacetic acid, dichloroacetonitrile, NDMA, and trichloroacetic acid.