Synthetic Formaldehyde “known to be a human carcinogen” in common indoor pollutant and contaminant in foods

Formaldehyde (systematic name methanal) is an organic compound with the formula CH₂O and structure H−CHO. The compound is a pungent, colorless gas that polymerizes spontaneously into paraformaldehyde. It is stored as aqueous solutions (formalin), which consists mainly of the hydrate CH₂(OH)₂. It is produced commercially as a precursor to many other materials and chemical compounds. In 2006, the global production rate of formaldehyde was estimated at 12 million tons per year. It is mainly used in the production of industrial resins, e.g., for particle boards and coatings. Small amounts also occur naturally.

Formaldehyde is produced industrially by the catalytic oxidation of methanol. The most common catalysts are silver metal, iron(III) oxide, iron molybdenum oxides [e.g. iron(III) molybdate] with a molybdenum-enriched surface or vanadium oxides. In the commonly used formox process, methanol and oxygen react at c. 250–400 °C in the presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the chemical equation:

2 CH₃OH + O₂ → 2 CH₂O + 2 H₂O

The silver-based catalyst usually operates at a higher temperature, about 650 °C. Two chemical reactions on it simultaneously produce formaldehyde: shown above and the dehydrogenation reaction:

CH₃OH → CH₂O + H₂

In principle, formaldehyde could be generated by oxidation of methane, but this route is not industrially viable because the methanol is more easily oxidized than methane.

In Biochemistry - Formaldehyde is produced via several enzyme-catalyzed routes. Living beings, including humans, produce formaldehyde as part of their metabolism. Formaldehyde is key to several bodily functions (e.g. epigenetics), but its amount must also be tightly controlled to avoid self-poisoning.

Occurrence

Processes in the upper atmosphere contribute up to 90% of the total formaldehyde in the environment. Formaldehyde is an intermediate in the oxidation (or combustion) of methane, as well as of other carbon compounds, e.g. in forest fires, automobile exhaust, and tobacco smoke. When produced in the atmosphere by the action of sunlight and oxygen on atmospheric methane and other hydrocarbons, it becomes part of smog. Formaldehyde has also been detected in outer space.

Formaldehyde and its adducts are ubiquitous in nature. Food may contain formaldehyde at levels 1–100 mg/kg. Formaldehyde, formed in the metabolism of the amino acids serine and threonine, is found in the bloodstream of humans and other primates at concentrations of approximately 50 micromolar.

Formaldehyde does not accumulate in the environment, because it is broken down within a few hours by sunlight or by bacteria present in soil or water. Humans metabolize formaldehyde quickly, converting it to formic acid, so it does not accumulate. It nonetheless presents significant health concerns, as a contaminant.

Formaldehyde is classified as a carcinogen (agents in the environment capable of contributing to cancer growth). Additionally, it can cause respiratory and skin irritation upon exposure.

Industrial applications

Formaldehyde is a common precursor to more complex compounds and materials. In approximate order of decreasing consumption, products generated from formaldehyde include urea formaldehyde resin, melamine resin, phenol formaldehyde resin, polyoxymethylene plastics, 1,4-butanediol, and methylene diphenyl diisocyanate. The textile industry uses formaldehyde-based resins as finishers to make fabrics crease-resistant.

When treated with phenol, urea, or melamine, formaldehyde produces, respectively, hard thermoset phenol formaldehyde resin, urea formaldehyde resin, and melamine resin. These polymers are permanent adhesives used in plywood and carpeting. They are also foamed to make insulation, or cast into molded products. Production of formaldehyde resins accounts for more than half of formaldehyde consumption.

Disinfectant and biocide

An aqueous solution of formaldehyde can be useful as a disinfectant as it kills most bacteria and fungi (including their spores). It is used as an additive in vaccine manufacturing to inactivate toxins and pathogens. Formaldehyde releasers are used as biocides in personal care products such as cosmetics. Although present at levels not normally considered harmful, they are known to cause allergic contact dermatitis in certain sensitized individuals.

Aquarists use formaldehyde as a treatment for the parasites Ichthyophthirius multifiliis and Cryptocaryon irritans. Formaldehyde is one of the main disinfectants recommended for destroying anthrax.

Formaldehyde is also approved for use in the manufacture of animal feeds in the US. It is an antimicrobial agent used to maintain complete animal feeds or feed ingredients Salmonella negative for up to 21 days.

Formaldehyde is commonly used to disinfect (via fumigating, sprinklers, and spray sleds) poultry and swine confinement buildings, egg hatcheries, rooms, railway cars, mushroom houses, tools, and equipment. Formaldehyde is a valuable packaged preservative in the food and beverage industry.

Safety

Because of its widespread use, toxicity, and volatility, formaldehyde poses a significant danger to human health. In 2011, the US National Toxicology Program described formaldehyde as "known to be a human carcinogen".

Chronic inhalation

However, concerns are associated with chronic (long-term) exposure by inhalation as may happen from thermal or chemical decomposition of formaldehyde-based resins and the production of formaldehyde resulting from the combustion of a variety of organic compounds (for example, exhaust gases). As formaldehyde resins are used in many construction materials, it is one of the more common indoor air pollutants. At concentrations above 0.1 ppm in air, formaldehyde can irritate the eyes and mucous membranes. Formaldehyde inhaled at this concentration may cause headaches, a burning sensation in the throat, and difficulty breathing, and can trigger or aggravate asthma symptoms.

In the residential environment, formaldehyde exposure comes from several routes; formaldehyde can be emitted by treated wood products, such as plywood or particle board, but it is produced by paints, varnishes, floor finishes, and cigarette smoking as well. In July 2016, the U.S. EPA released a prepublication version of its final rule on Formaldehyde Emission Standards for Composite Wood Products. These new rules impact manufacturers, importers, distributors, and retailers of products containing composite wood, including fiberboard, particleboard, and various laminated products, who must comply with more stringent record-keeping and labeling requirements.

In the building environments, formaldehyde levels are affected by several factors. These include the potency of formaldehyde-emitting products present, the ratio of the surface area of emitting materials to volume of space, environmental factors, product age, interactions with other materials, and ventilation conditions. Formaldehyde is emitted from a variety of construction materials, furnishings, and consumer products.

Other routes

Formaldehyde occurs naturally, and is "an essential intermediate in cellular metabolism in mammals and humans." According to the American Chemistry Council, "Formaldehyde is found in every living system—from plants to animals to humans. It metabolizes quickly in the body, breaks down rapidly, is not persistent, and does not accumulate in the body."

In humans, ingestion of as little as 30 milliliters (1.0 US fl oz) of 37% formaldehyde solution can cause death. Other symptoms associated with ingesting such a solution include gastrointestinal damage (vomiting, abdominal pain), and systematic damage (dizziness). Testing for formaldehyde is done by blood and/or urine by gas chromatography–mass spectrometry. Other methods include infrared detection, gas detector tubes, etc., of which high-performance liquid chromatography is the most sensitive.

Contaminant in food

Scandals have broken in both the 2005 Indonesia food scare and 2007 Vietnam food scare regarding the addition of formaldehyde to foods to extend shelf life. In 2011, after a four-year absence, Indonesian authorities found foods with formaldehyde being sold in markets in a number of regions across the country. In August 2011, at least at two Carrefour supermarkets, the Central Jakarta Livestock and Fishery Sub-Department found cendol containing 10 parts per million of formaldehyde. In 2014, the owner of two noodle factories in Bogor, Indonesia, was arrested for using formaldehyde in noodles. 50 kg of formaldehyde was confiscated. Foods known to be contaminated included noodles, salted fish, and tofu. Chicken and beer were also rumored to be contaminated. In some places, such as China, manufacturers still use formaldehyde illegally as a preservative in foods, which exposes people to formaldehyde ingestion. In the early 1900s, it was frequently added by US milk plants to milk bottles as a method of pasteurization due to the lack of knowledge and concern regarding formaldehyde's toxicity.

In 2011 in Nakhon Ratchasima, Thailand, truckloads of rotten chicken were treated with formaldehyde for sale in which "a large network", including 11 slaughterhouses run by a criminal gang, were implicated. In 2012, 1 billion rupiah (almost US$100,000) of fish imported from Pakistan to Batam, Indonesia, were found laced with formaldehyde.

Formalin contamination of foods has been reported in Bangladesh, with stores and supermarkets selling fruits, fishes, and vegetables that have been treated with formalin to keep them fresh. However, in 2015, a Formalin Control Bill was passed in the Parliament of Bangladesh with a provision of life-term imprisonment as the maximum punishment as well as a maximum fine of 2,000,000 BDT but not less than 500,000 BDT for importing, producing, or hoarding formalin without a license.