Formalin, an aqueous solution of formaldehyde (40% formaldehyde by volume or 37% formaldehyde by weight) combined with a stabilizer, is used to preserve biological specimens and tissue samples, as an embalming fluid, and in dilute form as a disinfectant or antibacterial wash.
Formaldehyde under ordinary conditions is a colorless flammable gas with a pungent and irritating odor. It dissolves easily in water but readily escapes from the water in its gaseous form. It occurs in the environment as an intermediate byproduct of the combustion of methane gas, of forest fires, of automobile exhaust, and of tobacco smoke. When formaldehyde is produced in the upper atmosphere as the result of the action of sunlight and oxygen on atmospheric methane, it becomes part of smog. In 1969, interstellar formaldehyde was first detected by a team of radio astronomers at the National Radio Astronomy Observatory. In 2014, astronomers at the Llano de Chajnantor Observatory in the Atacama Desert in Chile detected the presence of formaldehyde in the comae (envelopes surrounding the comets' nuclei) of two comets.
In living organisms, formaldehyde is produced in minute amounts during the metabolism of amino acids and can be detected in human blood. Formaldehyde does not, however, remain in the environment for long periods of time; it is readily broken down by sunlight or by bacteria in the soil or water. It does not accumulate in aquatic organisms or in the mammalian food chain. In humans, formaldehyde is quickly metabolized and converted into formic acid. The greatest danger that formaldehyde poses to human health is chronic (long-term) inhalation of its vapor.
Pure formaldehyde is a colorless gas at room temperature. It freezes at -134°F (-92°C) and boils at -6°F (-21°C) but can become explosive at temperatures above 122°F (50°C). Formalin boils at a temperature of 205°F (96°C). Most people can begin to detect the smell of formaldehyde at a concentration of 0.05 parts per million (ppm); eye irritation begins at levels of 0.5 ppm and higher. Occupational exposure is limited to 0.3 ppm, according to standards set by the National Institute for Occupational Safety and Health (NIOSH). The U.S. Environmental Protection Agency (EPA) has set an upper limit of 0.016 ppm formaldehyde in the air in any of the agency's new buildings.
Formaldehyde was first discovered in 1859 by Alexander Butlerov (1828–1886), a Russian chemist. It was first produced by August Wilhelm von Hofmann (1818–1892), a German chemist, by passing methanol vapor over a heated platinum wire. A metal catalyst is still used in the commercial production of formaldehyde by the formox process.
Formaldehyde was first produced commercially in Germany in the 1880s and then in France, Belgium, and the United States by the early 1900s. Early production was in small lots, usually between 10 and 45 pounds and was used primarily to make formalin for embalming and preserving medical specimens.
The use of formaldehyde in the manufacture of plastics began in 1907, when Belgian chemist Leo Baekeland (1863–1944) used a resin made with formaldehyde to produce Bakelite, the first hard moldable plastic. In the 1940s, German manufacturers produced the first commercial-grade particleboard using formaldehyde, which led to its widespread use in the furniture and construction industries and a vastly increased demand for formaldehyde. Almost all formaldehyde produced as of 2018 was used in industrial applications.
Formaldehyde is present in low levels in the human body itself as well as in the natural environment, which means that all people worldwide have modest levels of exposure to it. In the developed countries, formaldehyde is rarely encountered in its pure form except in factories in which it is produced as a precursor to manufacturing synthetic resins and other chemical compounds. As of 2002, at least 8.7 million tons of formaldehyde were manufactured worldwide each year, and the amount has increased since then, although exact figures for the rate of production were not available as of 2018.
Most people do not suffer serious health effects from exposure to formaldehyde vapor in the home or office environment, although infants, the elderly, and people with asthma or other respiratory disorders may feel uncomfortable. Workers in industries that produce or use formaldehyde, particularly those in the particleboard and synthetic coatings industries, are at greatest risk of serious health effects. As of 2018, about 4 million people worked in the 12,000 plants located across Canada and the United States that either produced or used formaldehyde.
More than 99% of the formaldehyde produced industrially is used to make different types of resins and other industrial chemicals; it is a useful compound for this purpose because it is a stable molecule that binds tightly with other substances and thus links them together. Phenolic, urea, and melamine resins are used as adhesives and binders in the manufacture of paper and pulp, furniture, and synthetic fibers; in textile finishing; and in making plastics and coatings. Polyacetal resins are also used in the manufacture of plastics. In addition to its role in the manufacture of resins, formaldehyde is used as an intermediate step in the production of such chemicals as 1,4 butanediol (used as a solvent and to make certain types of plastics) and methylene diphenyl diisocyanate (used to make polyurethane paints and foams).
Slightly less than 1% of manufactured formaldehyde is used for embalming or for medical and forensic purposes. It can be used as a tissue fixative and preservative; as an antibacterial and antifungal agent to treat aquarium fish infected by parasites; to prevent contamination of vaccines by viruses and bacteria during the production process; as a topical application for removing skin warts; and as a source of compounds used to prevent the growth of bacteria in cosmetics, creams, and other personal care products. Last, formaldehyde is added to animal feeds to keep the feed free of Salmonella bacteria, which can cause severe digestive disorders in farm animals.
Interstellar formaldehyde has attracted growing interest on the part of astronomers and astrochemists because of its usefulness as a probe for studying dust particles in interstellar clouds.
Formaldehyde can enter the human or natural environment in several ways:
Exposure to formaldehyde can produce the following symptoms:
In regard to the risk of cancer, formaldehyde has been considered a suspected or known carcinogen since the early 2000s. The International Agency on Research for Cancer (IARC) classified formaldehyde as a cause of nasopharyngeal cancer in 2004 and a cause of myeloid leukemia in 2012, based on data from animal studies and European workers exposed to formaldehyde. In June 2011, the twelfth edition of the National Toxicology Program (NTP) report on carcinogens changed the status of formaldehyde from “reasonably anticipated to be a human carcinogen” to “known to be a human carcinogen”.
In 2018, however, a U.S. study that summarizes investigations carried out since 2011 reported that “new findings are consistently negative, and integration of all available evidence challenges the earlier conclusions that formaldehyde causes leukemia.” A Korean study, also published in 2018, stated that “additional evidence is needed to confirm the relationship between formaldehyde exposure and nasopharyngeal cancer.” One reason for the ongoing debate about formaldehyde as a carcinogen is that many industrial workers exposed to it are exposed to a mixture of other chemicals as well. In addition, the mechanisms by which formaldehyde is thought to cause cancer were not completely understood as of 2018.
There is some evidence from European researchers that occupational exposure to formaldehyde may be associated with an increased risk of amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease. A group of Danish physicians reported in 2017 that formaldehyde exposure is associated with a 1.3-fold increase in the rate of ALS among male workers. Further studies were under way as of 2018.
The National Institute of Occupational Safety and Health (NIOSH) recommends the following measures to prevent health problems from exposure to formaldehyde:
NIOSH recommends the following treatments for exposure to formaldehyde:
Most people exposed to formaldehyde vapor in homes or offices do not suffer lasting ill effects, although people with asthma or chronic obstructive pulmonary disease may experience increased wheezing or difficulty breathing. There were at least six known cases of human suicides resulting from ingesting formalin as of 2018, with lethal doses ranging between four and five ounces.
Additional precautions for safety in regard to formaldehyde include the following:
See also Agency for Toxic Substances and Disease Registry ; Sick building syndrome ; Smog .
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U.S. Environmental Protection Agency (EPA), 1200 Pennsylvania Ave. NW, Washington, DC, 20460, (202) 564-4700, https://www.epa.gov .
Rebecca J. Frey, PhD