Disinfection by-products (DBPs) result from
chemical reaction
A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...
s between organic and inorganic matter in water with chemical treatment agents during the
water disinfection
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...
process.
Chlorination disinfection byproducts
Chlorinated
disinfection agents such as
chlorine
Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
and
monochloramine
Monochloramine, often called chloramine, is the chemical compound with the formula NH2Cl. Together with dichloramine (NHCl2) and nitrogen trichloride (NCl3), it is one of the three chloramines of ammonia. It is a colorless liquid at its melting p ...
are strong
oxidizing agent
An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ). In ot ...
s introduced into water in order to destroy
pathogenic
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
microbes, to oxidize taste/odor-forming compounds, and to form a
disinfectant residual so water can reach the consumer tap safe from microbial contamination. These disinfectants may react with naturally present
fulvic and
humic Humic substances (HS) are organic compounds that are important components of humus, the major organic fraction of soil, peat, and coal (and also a constituent of many upland streams, dystrophic lakes, and ocean water). For a long era in the 19th an ...
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
In chemistry, trihalomethanes (THMs) 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 environ ...
(THMs),
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 structur ...
(HAAs),
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 drinki ...
, and
chlorite
The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorous ac ...
(which are regulated in the US), and so-called "emerging" DBPs such as
halonitromethanes,
haloacetonitriles,
haloamides,
halofuranones,
iodo-acids such as
iodoacetic acid
Iodoacetic acid is a derivative of acetic acid. It is a toxic compound, because, like many alkyl halides, it is an alkylating agent.
It reacts with cysteine residues in proteins. It is often used to modify SH-groups to prevent the re-formation ...
, iodo-THMs (
iodotrihalomethanes),
nitrosamine
In organic chemistry, nitrosamines (or more formally ''N''-Nitrosamines) are organic compounds with the chemical structure , where R is usually an alkyl group. They feature a nitroso group () bonded to a deprotonated amine. Most nitrosamines are ...
s, 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 Genotoxicity is the property of chemical agents that damage the genetic information within a cell causing mutations, which may lead to cancer. While genotoxicity is often confused with Mutagen, mutagenicity, all mutagens are genotoxic, but some geno ...
iodinated DBPs, such as iodoacetic acid
Iodoacetic acid is a derivative of acetic acid. It is a toxic compound, because, like many alkyl halides, it is an alkylating agent.
It reacts with cysteine residues in proteins. It is often used to modify SH-groups to prevent the re-formation ...
, 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 (i.e. water age), 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, or trichloromethane, is an organic compound with chemical formula, formula Carbon, CHydrogen, HChlorine, Cl3 and a common organic solvent. It is a colorless, strong-smelling, dense liquid produced on a large scale as a precursor to ...
) 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.
Byproducts from non-chlorinated disinfectants
Several powerful oxidizing agents are used in disinfecting and treating drinking water, and many of these also cause the formation of DBPs. Ozone
Ozone (), or trioxygen, is an inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , breaking down in the lo ...
, for example, produces ketones, carboxylic acids, and aldehydes, including formaldehyde. Bromide in source waters can be converted by ozone into 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 drinki ...
, 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 plants 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 chlorination Chlorination may refer to:
* Chlorination reaction
In chemistry, halogenation is a chemical reaction that entails the introduction of one or more halogens into a compound. Halide-containing compounds are pervasive, making this type of transform ...
, chloramination, ozonation, or treatment with chlorine dioxide
Chlorine dioxide is a chemical compound with the formula ClO2 that exists as yellowish-green gas above 11 °C, a reddish-brown liquid between 11 °C and −59 °C, and as bright orange crystals below −59 °C. It is usually ...
. 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 recognized 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).][
In 2021, a new group of DBPs known as halogenated pyridinols was discovered, containing at least 8 previously unknown heterocyclic nitrogenous DBPs. They were found to require low pH treatments of 3.0 to be removed effectively. When their ]developmental
Development of the human body is the process of growth to maturity. The process begins with fertilization, where an egg released from the ovary of a female is penetrated by a sperm cell from a male. The resulting zygote develops through mitosi ...
and acute toxicity
Acute toxicity describes the adverse effects of a substance that result either from a single exposure or from multiple exposures in a short period of time (usually less than 24 hours). To be described as ''acute'' toxicity, the adverse effect ...
was tested on zebrafish
The zebrafish (''Danio rerio'') is a freshwater fish belonging to the minnow family ( Cyprinidae) of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio (and thus often ...
embryos, it found to be slightly lower than those of halogenated benzoquinones Benzoquinone (C6H4O2) is a quinone with a single benzene ring. There are 2 (out of 3 hypothetical) benzoquinones:
* 1,4-Benzoquinone, most commonly, right image (also ''para''-benzoquinone, ''p''-benzoquinone, ''para''-quinone, or just quinone)
* ...
, but dozens of times higher than of commonly known DBPs such as tribromomethane and iodoacetic acid
Iodoacetic acid is a derivative of acetic acid. It is a toxic compound, because, like many alkyl halides, it is an alkylating agent.
It reacts with cysteine residues in proteins. It is often used to modify SH-groups to prevent the re-formation ...
.
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 age
Small for gestational age (SGA) newborns are those who are smaller in size than normal for the gestational age, most commonly defined as a weight below the 10th percentile for the gestational age.
Causes
Being small for gestational age is broadly ...
, 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
The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of h ...
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)" 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 Agency
The Environmental Protection Agency (EPA) is an independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it be ...
has set Maximum Contaminant Levels (MCLs) for 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 drinki ...
, chlorite
The chlorite ion, or chlorine dioxide anion, is the halite with the chemical formula of . A chlorite (compound) is a compound that contains this group, with chlorine in the oxidation state of +3. Chlorites are also known as salts of chlorous ac ...
, haloacetic acid 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 struc ...
s and total trihalomethane
In chemistry, trihalomethanes (THMs) 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 environment ...
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.
See also
* Stuart W. Krasner
References
{{DEFAULTSORT:Disinfection By-Product
Chlorine
Drinking water
Water pollution
Water treatment