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Acrylamide (or acrylic
amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...
) is an
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon- hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
with the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
CH2=CHC(O)NH2. It is a white odorless solid, soluble in
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
and several organic solvents. From the chemistry perspective, acrylamide is a vinyl-substituted
primary amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a compound with the general formula , where R, R', and R″ represent organic groups or hydrogen atoms. The amide group is called a peptide bond when it is ...
(CONH2). It is produced industrially mainly as a precursor to
polyacrylamide Polyacrylamide (abbreviated as PAM) is a polymer with the formula (-CH2CHCONH2-). It has a linear-chain structure. PAM is highly water-absorbent, forming a soft gel when hydrated. In 2008, an estimated 750,000,000 kg were produced, mainly f ...
s, which find many uses as water-soluble thickeners and flocculation agents. Acrylamide forms in burnt areas of
food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ...
, particularly
starchy foods Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets, ...
like
potatoes The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae. Wild potato species can be found from the southern United ...
, when cooked with high heat, above . Acrylamide is highly toxic, linked to cancer in animal testing though not likely to be
carcinogenic A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive sub ...
for humans, but its main derivative polyacrylamide is nontoxic. The possibility that this innocuous polymer contains traces of its hazardous precursor has long attracted attention. Because acrylamide is volatile and hazardous, it is mainly handled as an aqueous solution.


Production

Acrylamide can be prepared by the hydration of
acrylonitrile Acrylonitrile is an organic compound with the formula and the structure . It is a colorless, volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecular ...
: :CH2=CHCN + H2O → CH2=CHC(O)NH2 This reaction is catalyzed by sulfuric acid, various metal salts, and the enzyme
nitrile hydratase Nitrile hydratases (NHases; ) are mononuclear iron or non-corrinoid cobalt enzymes that catalyse the hydration of diverse nitriles to their corresponding amides R-C≡N + H2O → R-C(O)NH2 Metal cofactor In biochemistry, cobalt is in gener ...
. In 2008, an estimated 750,000,000 kg of polyacrylamide were produced, mainly using the enzymatic route.


Uses

The majority of acrylamide is used to manufacture various polymers, especially
polyacrylamide Polyacrylamide (abbreviated as PAM) is a polymer with the formula (-CH2CHCONH2-). It has a linear-chain structure. PAM is highly water-absorbent, forming a soft gel when hydrated. In 2008, an estimated 750,000,000 kg were produced, mainly f ...
. This water-soluble polymer, which has very low toxicity, is widely used as thickener and flocculating agent. These functions are valuable in the purification of drinking water, corrosion inhibition, mineral extraction, and paper making. Polyacrylamide gels are routinely used in medicine and biochemistry for purification and assays.


Toxicity and carcinogenicity

Acrylamide can arise in some cooked foods via a series of steps by the reaction of the amino acid
asparagine Asparagine (symbol Asn or N) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the depro ...
and glucose. This condensation, one of the Maillard reactions, followed by dehydrogenation produces ''N''-(D-glucos-1-yl)-L-asparagine, which upon
pyrolysis The pyrolysis (or devolatilization) process is the thermal decomposition of materials at elevated temperatures, often in an inert atmosphere. It involves a change of chemical composition. The word is coined from the Greek-derived elements ''p ...
generates some acrylamide. The discovery in 2002 that some cooked foods contain acrylamide attracted significant attention to its possible biological effects. IARC, NTP, and the
EPA 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 ...
have classified it as a probable carcinogen. Although epidemiological studies (as of 2019) suggest that dietary acrylamide consumption does not significantly increase people's risk of developing
cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...
, genomic analysis has revealed widespread contribution of acrylamide exposure to human carcinogenesis.


Europe

According to the EFSA, the main toxicity risks of acrylamide are "Neurotoxicity, adverse effects on male reproduction, developmental toxicity and
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subst ...
icity". However, according to their research, there is no concern on non- neoplastic effects. Furthermore, while the relation between consumption of acrylamide and cancer in rats and mice has been shown, it is still unclear whether acrylamide consumption has an effect on the risk of developing cancer in humans, and existing epidemiological studies in humans are very limited and do not show any relation between acrylamide and cancer in humans. Food industry workers exposed to twice the average level of acrylamide do not exhibit higher cancer rates.


HEATOX (heat-generated food toxicants) study in Europe

The Heat-generated Food Toxicants (HEATOX) Project was a
European Commission The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body ...
-funded multidisciplinary research project running from late 2003 to early 2007. Its objectives were to "estimate health risks that may be associated with hazardous compounds in heat-treated food, nd tofind cooking/processing methods that minimize the amounts of these compounds, thereby providing safe, nutritious, and high-quality food-stuffs."Heat-generated Food Toxicants; Identification, Characterisation and Risk Minimisation
(PDF) . Retrieved on 2012-06-11.
It found that "the evidence of acrylamide posing a cancer risk for humans has been strengthened,"HEATOX project completed – brings new pieces to the Acrylamide Puzzle
(PDF) . Retrieved on 2012-06-11.
and that "compared with many regulated food carcinogens, the exposure to acrylamide poses a higher estimated risk to European consumers." HEATOX sought also to provide consumers with advice on how to lower their intake of acrylamide, specifically pointing out that home-cooked food tends to contribute far less to overall acrylamide levels than food that was industrially prepared, and that avoiding overcooking is one of the best ways to minimize exposure at home.


United States

Acrylamide is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S.
Emergency Planning and Community Right-to-Know Act The Emergency Planning and Community Right-to-Know Act of 1986 is a United States federal law passed by the 99th United States Congress located at Title 42, Chapter 116 of the U.S. Code, concerned with emergency response preparedness. On Octo ...
(42 U.S.C. 11002), and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities. Acrylamide is considered a potential occupational carcinogen by U.S. government agencies and classified as a Group 2A carcinogen by the IARC. The
Occupational Safety and Health Administration The Occupational Safety and Health Administration'' (OSHA ) is a large regulatory agency of the United States Department of Labor that originally had federal visitorial powers to inspect and examine workplaces. Congress established the agenc ...
and the
National Institute for Occupational Safety and Health The National Institute for Occupational Safety and Health (NIOSH, ) is the United States federal agency responsible for conducting research and making recommendations for the prevention of work-related injury and illness. NIOSH is part of the ...
have set dermal occupational exposure limits at 0.03 mg/m3 over an eight-hour workday.


Opinions of health organizations

The
American Cancer Society The American Cancer Society (ACS) is a nationwide voluntary health organization dedicated to eliminating cancer. Established in 1913, the society is organized into six geographical regions of both medical and lay volunteers operating in more tha ...
says that
laboratory studies Science and technology studies (STS) is an interdisciplinary field that examines the creation, development, and consequences of science and technology in their historical, cultural, and social contexts. History Like most interdisciplinary fie ...
have shown that acrylamide is likely to be a carcinogen, but that evidence from epidemiological studies suggests that dietary acrylamide is unlikely to raise the risk of people developing cancer. 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 o ...
(WHO) has set up a clearinghouse for information about acrylamide that includes a database of researchers and data providers; references for research published elsewhere; information updates about the current status of research efforts; and updates on information relevant to the health risk of acrylamide in food.


Hazards

Acrylamide is also a skin irritant and may be a
tumor initiator Tumor initiation is defined as "a process in which normal cells are changed so that they are able to form tumors". It is the first phase in tumor development. Mutagens, substances that cause cancer can be tumor initiators. See also * Tumor promo ...
in the skin, potentially increasing risk for skin cancer. Symptoms of acrylamide exposure include
dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...
in the exposed area, and
peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...
. Laboratory research has found that some
phytochemical Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. The name comes . Some phytochemicals have been used as poison ...
s may have the potential to be developed into drugs which could alleviate the toxicity of acrylamide.


Occurrence in food and associated health risks

left, Glycidamide is the dangerous metabolite produced from acrylamide, which in turn is produced by heating certain proteins.


Mechanism of action

Acrylamide is metabolized to the genotoxic derivative glycidamide. On the other hand, acrylamide and glycidamide can be detoxified via conjugation with
glutathione Glutathione (GSH, ) is an antioxidant in plants, animals, fungi, and some bacteria and archaea. Glutathione is capable of preventing damage to important cellular components caused by sources such as reactive oxygen species, free radicals, pe ...
.


Discovery of acrylamide in foods

Acrylamide was discovered in foods, mainly in
starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diets ...
y foods, such as
potato chip A potato chip (North American English; often just chip) or crisp (British and Irish English) is a thin slice of potato that has been either deep fried, baked, or air fried until crunchy. They are commonly served as a snack, side dish, or app ...
s (UK: ''potato crisps''),
French fries French fries ( North American English), chips ( British English), finger chips (Indian English), french-fried potatoes, or simply fries, are '' batonnet'' or '' allumette''-cut deep-fried potatoes of disputed origin from Belgium and France ...
(UK: ''chips''), and bread that had been heated higher than . Production of acrylamide in the heating process was shown to be temperature-dependent. It was not found in food that had been boiled, or in foods that were not heated. Acrylamide has been found in roasted barley tea, called ''mugicha'' in Japanese. The
barley Barley (''Hordeum vulgare''), a member of the grass family, is a major cereal grain grown in temperate climates globally. It was one of the first cultivated grains, particularly in Eurasia as early as 10,000 years ago. Globally 70% of barley ...
is roasted so it is dark brown prior to being steeped in hot water. The roasting process produced 200–600 micrograms/kg of acrylamide in mugicha. This is less than the >1000 micrograms/kg found in potato crisps and other fried whole potato snack foods cited in the same study and it is unclear how much of this is ingested after the drink is prepared. Rice cracker and
sweet potato The sweet potato or sweetpotato ('' Ipomoea batatas'') is a dicotyledonous plant that belongs to the bindweed or morning glory family, Convolvulaceae. Its large, starchy, sweet-tasting tuberous roots are used as a root vegetable. The young ...
levels were lower than in potatoes. Potatoes cooked whole were found to have significantly lower acrylamide levels than the others, suggesting a link between food preparation method and acrylamide levels. Acrylamide levels appear to rise as food is heated for longer periods of time. Although researchers are still unsure of the precise mechanisms by which acrylamide forms in foods, many believe it is a byproduct of the Maillard reaction. In fried or
baked Baking is a method of preparing food that uses dry heat, typically in an oven, but can also be done in hot ashes, or on hot stones. The most common baked item is bread but many other types of foods can be baked. Heat is gradually transferred " ...
goods, acrylamide may be produced by the reaction between
asparagine Asparagine (symbol Asn or N) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the depro ...
and reducing sugars (
fructose Fructose, or fruit sugar, is a ketonic simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorb ...
,
glucose Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, usi ...
, etc.) or reactive
carbonyl In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups. A compound containin ...
s at temperatures above . Later studies have found acrylamide in black olives, dried plums, dried pears,
coffee Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world. Seeds of ...
, and
peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible Seed, seeds. It is widely grown in the tropics and subtropics, important to both small ...
s. The US FDA has analyzed a variety of U.S. food products for levels of acrylamide since 2002.


Public awareness

On April 24, 2002, the Swedish National Food Administration announced that acrylamide can be found in baked and fried starchy
food Food is any substance consumed by an organism for nutritional support. Food is usually of plant, animal, or fungal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals. The substance is ...
s, such as
potato chips A potato chip (North American English; often just chip) or crisp (British and Irish English) is a thin slice of potato that has been either deep fried, baked, or air fried until crunchy. They are commonly served as a snack, side dish, or a ...
, breads, and
cookie A cookie is a baked or cooked snack or dessert that is typically small, flat and sweet. It usually contains flour, sugar, egg, and some type of oil, fat, or butter. It may include other ingredients such as raisins, oats, chocolate chips, ...
s. Concern was raised mainly because of the probable
carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subst ...
ic effects of acrylamide. Sales of chips in Sweden decreased by 30–50 percent during the following three days after the announcement. On August 26, 2005,
California attorney general The attorney general of California is the state attorney general of the Government of California. The officer's duty is to ensure that "the laws of the state are uniformly and adequately enforced" (Constitution of California, Article V, Sectio ...
Bill Lockyer William Westwood Lockyer (born May 8, 1941) is a retired American politician from California, who held elective office from 1973 to 2015, as State Treasurer of California, California Attorney General, and President Pro Tempore of the Californi ...
filed a lawsuit against four makers of
french fries French fries ( North American English), chips ( British English), finger chips (Indian English), french-fried potatoes, or simply fries, are '' batonnet'' or '' allumette''-cut deep-fried potatoes of disputed origin from Belgium and France ...
and
potato chips A potato chip (North American English; often just chip) or crisp (British and Irish English) is a thin slice of potato that has been either deep fried, baked, or air fried until crunchy. They are commonly served as a snack, side dish, or a ...
H.J. Heinz Co. The H. J. Heinz Company is an American food processing company headquartered at One PPG Place in Pittsburgh, Pennsylvania. The company was founded by Henry J. Heinz in 1869. Heinz manufactures thousands of food products in plants on six contine ...
, Frito-Lay,
Kettle Foods Inc. Kettle Foods, Inc. is an American manufacturer of potato chips, based in Salem, Oregon, United States, with a European and Middle East headquarters in Norwich, United Kingdom. As of 2006 they were the largest natural potato chip brand in the ...
, and
Lance Inc. Lance is an American brand of snack foods owned by the Snyder's-Lance company headquartered in Charlotte, North Carolina. As of 2018, Snyder's-Lance is owned by Campbell's. Merger On July 22, 2010, Lance announced that it would merge with Snyder's ...
– to reduce the risk to consumers from consuming acrylamide. The lawsuit was settled on August 1, 2008, with the food producers agreeing to cut acrylamide levels to 275 parts per billion in three years, to avoid a Proposition 65 warning label. The companies avoided trial by agreeing to pay a combined $3 million in fines as a settlement with the California attorney general's office. In 2016, the UK
Food Standards Agency , type = Non-ministerial government department , nativename = , nativename_a = , nativename_r = , logo = Food Standards Agency.svg , logo_width = , logo_caption = , seal = , seal_width = , seal_caption = , picture = , picture_width = , ...
launched a campaign called "Go for Gold", warning of the possible cancer risk associated with cooking potatoes and other starchy foods at high temperatures. In 2018, a judge in California ruled that the
coffee Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world. Seeds of ...
industry had not provided sufficient evidence that acrylamide contents in coffee were at safe enough levels to not require a Proposition 65 warning.


Acceptable limits

Although acrylamide has known toxic effects on the nervous system and on fertility, a June 2002 report by the
Food and Agriculture Organization The Food and Agriculture Organization of the United Nations (FAO)french: link=no, Organisation des Nations unies pour l'alimentation et l'agriculture; it, Organizzazione delle Nazioni Unite per l'Alimentazione e l'Agricoltura is an intern ...
of the
United Nations The United Nations (UN) is an intergovernmental organization whose stated purposes are to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmonizi ...
and 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 o ...
attempting to establish basic
toxicology Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating expos ...
( threshold limit value,
no-observed-adverse-effect level The no-observed-adverse-effect level (NOAEL) denotes the level of exposure of an organism, found by experiment or observation, at which there is no biologically or statistically significant increase in the frequency or severity of any adverse effe ...
s, tolerable daily intake, etc.) concluded the intake level required to observe
neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or or ...
(0.5 mg/kg body weight/day) was 500 times higher than the average dietary intake of acrylamide (1 μg/kg body weight/day). For effects on fertility, the level is 2,000 times higher than the average intake. From this, they concluded acrylamide levels in food were safe in terms of neuropathy, but raised concerns over human carcinogenicity based on known carcinogenicity in laboratory animals. Pre-treatment of potato slices by asparaginase prior to frying reduced the acrylamide contents in the processed chips up to 81% compared to untreated control.


Occurrence in cigarettes

Cigarette smoking is a major acrylamide source. It has been shown in one study to cause an increase in blood acrylamide levels three-fold greater than any dietary factor.


See also

*
Acrydite Acrydite is a phosphoramidite that allows the synthesis of oligonucleotides with a methacryl group at the 5' end (less commonly 3' or internal). Acryl oligonucleotides have been tested, but the acryl group is not stable to storage. Acrydite-modif ...
: research on this compound casts light on acrylamide *
Acrolein Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is a colorless liquid with a piercing, acrid smell. The smell of burnt fat (as when cooking oil is heated to its smoke point) is caused by glycerol in the burning fa ...
*
Alkyl nitrites In organic chemistry, alkyl nitrites are a group of organic compounds based upon the molecular structure , where R represents an alkyl group. Formally they are alkyl esters of nitrous acid. They are distinct from nitro compounds (). The first ...
* Deep-frying *
Deep fryer A deep fryer (also referred to as a deep fat fryer), is a kitchen appliance used for deep frying. Deep frying is a method of cooking by submerging food into oil at high heat, typically between temperatures of . While commonly used in commercial ...
* Vacuum fryer * Substance of very high concern * Heterocyclic amines *
Polycyclic aromatic hydrocarbons A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. P ...


References


Further reading

*


External links

{{Consumer food safety Carboxamides Hazardous air pollutants IARC Group 2A carcinogens Monomers Reproductive toxicants Suspected fetotoxicants