Formaldehyde (systematic name: methanal) is a chemical compound with the formula CH2O. It is the simplest aldehyde. Formaldehyde also exists as the cyclic trimer trioxane and the polymer paraformaldehyde. It exists in water as the hydrate H2C(OH)2. Aqueous solutions of formaldehyde are referred to as formalin. "100%" formalin consists of a saturated solution of formaldehyde (this is about 40% by volume or 37% by mass) in water, with a small amount of stabilizer, usually methanol to limit oxidation and polymerization. A typical commercial grade formalin may contain 10–12% methanol in addition to metallic impurities such as aluminium (3 ppm), iron (1 ppm) and copper (1 ppm). Annual world production of formaldehyde (about 2005) was 21 million tonnes (46 billion pounds).[2]

In view of its widespread use, toxicity, and volatility, exposure to formaldehyde is a significant consideration for human health.[3]

Formaldehyde is a common building block for the synthesis of 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.[3]

When reacted with phenol, urea, or melamine formaldehyde produces, respectively, hard thermoset phenol formaldehyde resin, urea formaldehyde resin, and melamine resin, which are commonly used in permanent adhesives such as those used in plywood or carpeting. It is used as the wet-strength resin added to sanitary paper products such as (listed in increasing concentrations injected into the paper machine headstock chest) facial tissue, table napkins, and roll towels. They are also foamed to make insulation, or cast into moulded products. Production of formaldehyde resins accounts for more than half of formaldehyde consumption.

Formaldehyde is also a precursor to polyfunctional alcohols such as pentaerythritol, which is used to make paints and explosives. Other formaldehyde derivatives include methylene diphenyl diisocyanate, an important component in polyurethane paints and foams, and hexamine, which is used in phenol-formaldehyde resins as well as the explosive RDX.

The textile industry uses formaldehyde-based resins as finishers to make fabrics crease-resistant.[8]

Formaldehyde has been found as a contaminant in several bath products, at levels from 54–610 ppm: it is thought to arise from the breakdown of preservatives in the products.[9]

Miscellaneous applications

Formaldehyde is a common component of many uses. Formaldehyde, along with 18 M (concentrated) sulfuric acid (the entire solution often called the Marquis reagent), is used as an MDMA "testing kit" by such groups as Dancesafe as well as MDMA consumers. The solution alone cannot verify the presence of MDMA but reacts with many other chemicals that the MDMA tablet itself may be adulterated with. The reaction itself produces colors that correlate with these components.

As a 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 also used as a preservative in vaccines. Formaldehyde solutions are applied topically in medicine to dry the skin, such as in the treatment of warts. Many aquarists use formaldehyde as a treatment for the parasites Ichthyophthirius multifiliis and Cryptocaryon irritans.[10]

Formaldehyde preserves or fixes tissue or cells by irreversibly cross-linking primary amino groups in proteins with other nearby nitrogen atoms in protein or DNA through a -CH2- linkage. This is exploited in ChIP-on-chip transcriptomics experiments. Formaldehyde is also used as a denaturing agent in RNA gel electrophoresis, preventing RNA from forming secondary structures.

In photography

Formaldehyde is still used in low concentrations for process C-41 (color negative film) stabilizer in the final wash step,[11] as well as in the process E-6 pre-bleach step, to obviate the need for it in the final wash.

Tissue fixative and embalming agent

Formaldehyde solutions are used as a fixative for microscopy and histology. Formaldehyde-based solutions are also used in embalming to disinfect and temporarily preserve human and animal remains. It is the ability of formaldehyde to fix the tissue that produces the tell-tale firmness of flesh in an embalmed body. In post mortem examinations a procedure known as the "sink test" involves placing the lungs of an animal in an aqueous solution of fomaldehyde; if the lungs float it suggests the animal was probably breathing or able to breathe at the time of death.

Several European countries restrict the use of formaldehyde, including the import of formaldehyde-treated products and embalming. The European Union is considering a complete ban on the use of formaldehyde as a biocide (including embalming) under the Biocidal Products Directive (98/8/EC).[12][13] Countries with a strong tradition of embalming corpses, such as Ireland and other colder-weather countries, have raised concerns. Despite reports to the contrary,[14] no decision on the inclusion of formaldehyde on Annex I of the Biocidal Products Directive for product-type 22 (embalming and taxidermist fluids) had been made as of September 2009.[15]

Occupational exposure to formaldehyde by inhalation is mainly from three types of sources: thermal or chemical decomposition of formaldehyde-based resins, formaldehyde emission from aqueous solutions (for example, embalming fluids), and the production of formaldehyde resulting from the combustion of a variety of organic compounds (for example, exhaust gases). Formaldehyde can be toxic, allergenic, and carcinogenic.[2] Because formaldehyde resins are used in many construction materials it is one of the more common indoor air pollutants.[19] At concentrations above 0.1 ppm in air formaldehyde can irritate the eyes and mucous membranes, resulting in watery eyes.[20] Formaldehyde inhaled at this concentration may cause headaches, a burning sensation in the throat, and difficulty breathing, as well as triggering or aggravating asthma symptoms.[21][22]

Formaldehyde is classified as a probable human carcinogen by the U.S. Environmental Protection Agency. The International Agency for Research on Cancer (IARC) has determined that there is "sufficient evidence" that occupational exposure to formaldehyde causes nasopharyngeal cancer in humans.[2] The United States Environmental Protection Agency (EPA) allows no more than 16 ppb formaldehyde in the air in new buildings constructed for that agency.[23] The Federal Emergency Management Agency (FEMA) has also announced limits on the formaldehyde levels in trailers purchased by that agency.[24]

Formaldehyde can cause allergies and is part of the standard patch test series. People with formaldehyde allergy are advised to avoid formaldehyde releasers as well (e.g., Quaternium-15, imidazolidinyl urea, and diazolidinyl urea).[25] Formaldehyde has been banned in cosmetics in both Sweden and Japan.[citation needed]

REFERENCE:
http://en.wikipedia.org/wiki/Formaldehyde