Formaldehyde

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This article is about the chemical compound. For the 1993 rock album, see Formaldehyde (album).
Formaldehyde
File:Formaldehyde-2D.svg
File:Formaldehyde-3D-balls-A.png
File:Formaldehyde-3D-vdW.png
IUPAC name
methanal
Other names
formol, methyl aldehyde, methylene oxide, methanal
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number 50-00-0 YesY
ChemSpider 692
EC-number 200-001-8
RTECS number LP8925000
ATCvet code QP53AX19
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InChI Script error: No such module "collapsible list".
style="background: #F8EABA; text-align: center;" colspan="2" | Properties[1]
Molecular formula CH2O
Molar mass 30.03 g mol−1
Appearance colorless gas
Melting point

-92 °C (pure)
−15 °C (37% solution)

Boiling point

-21 °C (pure)
96 °C (37% solution)

Solubility in water very high (see text)
Dipole moment 2.33 D
style="background: #F8EABA; text-align: center;" colspan="2" | Structure
Molecular shape trigonal planar
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
MSDS ICSC 0275
EU Index 605-001-00-5
EU classification Toxic (T)
Carc. Cat. 3
R-phrases R23/24/25 R34 R40 R43
S-phrases (S1/2) S26 S36/37/39 S45 S51
NFPA 704
2
3
2
Flash point flammable gas
Autoignition
temperature 		430 °C (806 °F)
Explosive limits 7–73%
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Related aldehydes acetaldehyde
propionaldehyde
Related compounds methanol
formic acid
 YesY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Formaldehyde (systematic name: methanal) is an organic compound with the formula CH2O. As the simplest aldehyde, it is an important precursor to many other chemical compounds, especially for polymers. In 2005, annual world production of formaldehyde was estimated to be 23 million tons (46 billion pounds).[2] In view of its widespread use, toxicity and volatility, exposure to formaldehyde is a significant consideration for human health.[3]

Forms of formaldehyde

Formaldehyde is more complicated than many simple carbon compounds because it adopts different forms. Formaldehyde is a gas at room temperature, but the gas readily converts to a variety of derivatives. These derivatives generally behave similarly to gaseous formaldehyde and are used in industry. One important derivative is the cyclic compound trioxane, the "trimer" of formaldehyde with formula is (CH2O)3. When dissolved in water, formaldehyde converts to H2C(OH)2, a diol (i.e. a compound with two hydroxy groups). 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 degree of polymerization. A typical commercial grade formalin may contain 10–12% methanol in addition to various metallic impurities. The diol also exists in equilibrium with a series of short polymers (called oligomers), depending on the concentration and temperature. The infinite polymer formed from formaldehyde is called paraformaldehyde. The cyclic trimer is called metaformaldehyde (or 1,3,5-trioxane).

Occurrence

Formaldehyde is a naturally occurring substance in the environment made of carbon, hydrogen and oxygen. Natural processes in the upper atmosphere may contribute up to 90 percent of the total formaldehyde in the environment. Formaldehyde is an intermediate in the oxidation (or combustion) of methane as well as other carbon compounds, e.g. forest fires, in automobile exhaust, and in 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 (see below).

Formaldehyde, as well as its oligomers and hydrates are rarely encountered in living organisms. Methanogenesis proceeds via the equivalent of formaldehyde, but this one-carbon species is masked as a methylene group in methanopterin. Formaldehyde is the primary cause of methanol's toxicity, since methanol is metabolised into toxic formaldehyde by alcohol dehydrogenase. 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, so it does not accumulate, and is converted to formic acid in the body.

Small amounts of formaldehyde are produced in case of incomplete combustion of methane gas.

Interstellar formaldehyde

Main article: Interstellar formaldehyde

Formaldehyde was the first polyatomic organic molecule detected in the interstellar medium[4] and since its initial detection has been observed in many regions of the galaxy. Because of the widespread interest in interstellar formaldehyde it has recently been extensively studied, yielding new extragalactic sources.[5] A proposed mechanism for the formation is the hydrogenation of CO ice, shown below.[6]

H + CO → HCO
HCO + H → H2CO (rate constant = 9.2 × 10−3 s−1)

Formaldehyde appears to be a useful probe for astrochemists due to its low reactivity in the gas phase and to the fact that the 110←111 and 211←212 K-doublet transitions are rather clear.

Synthesis and industrial production

Formaldehyde was first reported by the Russian chemist Aleksandr Butlerov (1828–86) and was conclusively identified by August Wilhelm von Hofmann.[7]

Formaldehyde is produced industrially by the catalytic oxidation of methanol. The most common catalysts are silver metal or a mixture of an iron and molybdenum or vanadium oxides. In the more commonly used FORMOX process methanol and oxygen react at ca. 250–400 °C in presence of iron oxide in combination with molybdenum and/or vanadium to produce formaldehyde according to the chemical equation:[2]

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: that shown above and the dehydrogenation reaction:

CH3OH → H2CO + H2

In principle formaldehyde could be generated by oxidation of methane, but this route is not industrially viable because the formaldehyde is more easily oxidized than methane.[2]

Organic chemistry

Formaldehyde is a building block in the synthesis of many other compounds of specialised and industrial significance. It exhibits most of the chemical properties of other aldehydes but is more reactive. For example it is more readily oxidized by atmospheric oxygen to formic acid (formic acid is found in ppm levels in commercial formaldehyde). Formaldehyde is a good electrophile, participating in electrophilic aromatic substitution reactions with aromatic compounds, and can undergo electrophilic addition reactions with alkenes and aromatics. Formaldehyde undergoes a Cannizzaro reaction in the presence of basic catalysts to produce formic acid and methanol.

Examples of organic synthetic applications

Condensation with acetaldehyde affords pentaerythritol, a chemical necessary in synthesizing PETN, a high explosive.[8] Condensation with phenols gives phenol-formaldehyde resins. With 4-substituted phenols one obtains calixarenes.[9]

When combined with hydrogen sulfide it forms trithiane.[10]

3CH2O + 3H2S → (CH2S)3 + 3H2O

Uses

Industrial applications

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.[2] The textile industry uses formaldehyde-based resins as finishers to make fabrics crease-resistant.[11] Formaldehyde-based materials are key to the manufacture of automobiles, and used to make components for the transmission, electrical system, engine block, door panels, axles and brake shoes. The value of sales of formaldehyde and derivative products was over $145 billion in 2003, about 1.2% of the Gross Domestic Product (GDP) of the United States and Canada. Including indirect employment, over 4 million work in the formaldehyde industry across approximately 11,900 plants in the U.S. and Canada.[12]

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. 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.[13]

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.[14]

Formaldehyde is used to inactivate bacterial products for toxoid vaccines (vaccines that use an inactive bacterial toxin to produce immunity). It is also used to kill unwanted viruses and bacteria that might contaminate the vaccine during production.[15] Urinary tract infections are also often treated using a derivative of formaldehyde (methenamine), a method often chosen because it prevents overuse of antibiotics and the resultant development of bacterial resistance to them. Some topical creams, cosmetics and personal hygiene products also contain derivatives of formaldehyde as the active ingredients that prevent the growth of potentially harmful bacteria.

Tissue fixative and embalming agent

Formaldehyde preserves or fixes tissue or cells by reversibly 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.

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 formaldehyde; if the lungs float it suggests the animal was probably breathing or able to breathe at the time of death.

Formaldehyde solutions are commonly used as a biological preserving medium, usually for smaller specimens.

Several European countries restrict the use of formaldehyde, including the import of formaldehyde-treated products and embalming. Starting September 2007, the European Union banned the use of formaldehyde due to its carcinogenic properties as a biocide (including embalming) under the Biocidal Products Directive (98/8/EC).[16][17] Countries with a strong tradition of embalming corpses, such as Ireland and other colder-weather countries, have raised concerns. Despite reports to the contrary,[18] 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.[19]

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 (the drug ecstasy) "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.

In photography, formaldehyde is still used in low concentrations for process C-41 (color negative film) stabilizer in the final wash step,[20] as well as in the process E-6 pre-bleach step, to obviate the need for it in the final wash.

Formaldehyde is used extensively in the woodworking and cabinet-making industries. Formaldehyde is used in the glues which bond particle-board together. The particle board is used underneath wood veneer and plastic laminate. Cabinets, bank counters, and veneered and laminated woodwork all use particle board containing formaldehyde under the plastic laminate and wood veneer.

Safety

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.[3] Because formaldehyde resins are used in many construction materials it is one of the more common indoor air pollutants.[21] At concentrations above 0.1 ppm in air formaldehyde can irritate the eyes and mucous membranes, resulting in watery eyes.[22] 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.[23][24] Studies by the National Academy of Sciences and the Institute of Medicine failed to show an association between formaldehyde exposure and asthma.[25]

The primary exposure concern is for the workers in the industries producing or using formaldehyde. As far back as 1987, the U.S. EPA classified it as a probable human carcinogen and after more studies the WHO International Agency for Research on Cancer (IARC), in 1995, also classified it as a probable human carcinogen. Further information and evaluation of all known data led the IARC to reclassify formaldehyde as a known human carcinogen [26] associated with nasal sinus cancer and nasopharyngeal cancer, and possibly with leukemia in June 2004[27].

The United States Environmental Protection Agency (EPA) allows no more than 16 ppb formaldehyde in the air in new buildings constructed for that agency.[28] A U.S. Environmental Protection Agency study found a new home measured 0.076 ppm when brand new and 0.045 ppm after 30 days.[29] The Federal Emergency Management Agency (FEMA) has also announced limits on the formaldehyde levels in trailers purchased by that agency.[30] The EPA recommends the use of “exterior-grade” pressed-wood products to limit formaldehyde exposure since pressed-wood products containing formaldehyde resins are often a significant source of formaldehyde in homes.[27]

For most people, irritation from formaldehyde is temporary and reversible, though 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).[31] Formaldehyde has been banned in cosmetics in both Sweden and Japan.[citation needed] The eyes are most sensitive to formaldehyde exposure: The lowest level at which many people can begin to smell formaldehyde is about 0.3 ppm. In controlled chamber studies, individuals begin to sense eye irritation at about 0.5 ppm; 5 to 20 percent report eye irritation at 0.5 to 1 ppm; and greater certainty for sensory irritation occurred at 1 ppm and above. While some agencies have used a level as low as 0.1 ppm as a threshold for irritation, the expert panel found that a level of 0.3 ppm would protect against nearly all irritation. In fact, the expert panel found that a level of 1.0 ppm would avoid eye irritation—the most sensitive endpoint—in 75-95% of all people exposed.[25]

European ban

There are several web articles claiming that formaldehyde has been banned from manufacture or import into the European Union (EU) under REACH (Registration, Evaluation, Authorization, and restriction of Chemical substances) legislation. This appears to be misinformation, as official EU chemical databases contradict these claims as of February 19, 2010. This misconception has gained some ground. Formaldehyde is not listed in the Annex I of Regulation (EC) No 689/2008 (export and import of dangerous chemicals regulation), nor on a priority list for risk assessment. However, formaldehyde is banned from use in certain applications (preservatives for liquid-cooling and processing systems, slimicides, metalworking-fluid preservatives, and antifouling products) under the Biocidal Products Directive.[32][33]

FEMA trailer incidents

Hurricane Katrina & Rita

In the U.S. the Federal Emergency Management Agency (FEMA) provided travel trailers and mobile homes starting in 2006 for habitation by residents of the U.S. gulf coast displaced by Hurricane Katrina and Hurricane Rita. Some of the people who moved into the trailers complained of breathing difficulties, nosebleeds, and persistent headaches. Formaldehyde-catalyzed resins were used in the production of these homes.

The United States Centers For Disease Control and Prevention (CDC) performed indoor air quality testing for formaldehyde[34] in some of the units. On February 14, 2008 the CDC announced that potentially hazardous levels of formaldehyde were found in many of the travel trailers and mobile homes provided by the agency.[35][36] The CDC's preliminary evaluation of a scientifically established random sample of 519 travel trailers and mobile homes tested between Dec. 21, 2007 and Jan. 23, 2008 (2+ years after manufacture) showed average levels of formaldehyde in all units of about 77 parts per billion (ppb). Long-term exposure to levels in this range can be linked to an increased risk of cancer and, at levels above this range, there can also be a risk of respiratory illness. These levels are higher than expected in indoor air, where levels are commonly in the range of 10-20 ppb, and are higher than the Agency for Toxic Substance Disease Registry (ATSDR, division of the CDC) Minimal Risk Level (MRL) of 8 ppb.[37] Levels measured ranged from 3 ppb to 590 ppb.[38]

FEMA, which requested the testing by the CDC, said it would work aggressively to relocate all residents of the temporary housing as soon as possible. Lawsuits are being filed against FEMA as a result of the exposures.[39]

Iowa Floods of 2008

Also in the U.S., problems arose in trailers again provided by FEMA to residents displaced by the Iowa floods of 2008. A couple months after moving to the trailers, occupants reported violent coughing, headaches, as well as asthma, bronchitis, and other problems. Tests showed that in some trailers, levels of formaldehyde exceeded the limits recommended by the U.S. Environmental Protection Agency and American Lung Association.[40][41] The associated publicity has resulted in additional testing to begin in November.[42]

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. Foods known to be contaminated include noodles, salted fish, tofu, and rumors of chicken and beer. In humans, it is known to have a number[quantify] of detrimental effects and there is limited evidence of a carcinogenic effect.[3] Testing for formaldehyde is by blood and/or urine by gas chromatography-mass spectrometry. Other methods include infrared detection, gas detector tubes, etc., of which HPLC is the most sensitive [43] 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 regarding formaldehyde's toxicity. This resulted in numerous deaths in both orphanages and homes, particularly in the Midwestern states, where infants were fed the tainted milk, and resulted in a high death rate at several large orphanages in northern America.[citation needed]

See also

References

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External links

Consumer food safety
Adulterants/Food contaminants

3-MCPD · Aldicarb · Cyanide · Formaldehyde · Lead poisoning · Melamine · Mercury in fish · Sudan red dye

Toxins/Poisons
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ar:فورمالدهيد

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  1. ↑ Weast, Robert C., ed. (1981), CRC Handbook of Chemistry and Physics (62nd ed.), Boca Raton, FL: CRC Press, pp. C–301, E–61, ISBN 0-8493-0462-8 .
  2. ↑ 2.0 2.1 2.2 2.3 Günther Reuss, Walter Disteldorf, Armin Otto Gamer, Albrecht Hilt “Formaldehyde” in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a11_619
  3. ↑ 3.0 3.1 3.2 "Formaldehyde", Formaldehyde, 2-Butoxyethanol and 1-tert-Butoxypropan-2-ol (PDF), IARC Monographs on the Evaluation of Carcinogenic Risks to Humans 88, Lyon, France: International Agency for Research on Cancer, 2006, pp. 39–325, ISBN 92-832-1288-6 . "Formaldehyde (gas)", Report on Carcinogens, Eleventh Edition (PDF), U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, 2005 .
  4. ↑ Zuckerman, B.; Buhl, D.; Palmer, P.; Snyder, L. E. (1970), "Observation of interstellar formaldehyde", Astrophys. J., 160: 485–506, doi:10.1086/150449 .
  5. ↑ Mangum, Jeffrey G.; Darling, Jeremy; Menten, Karl M.; Henkel, Christian (2008), "Formaldehyde Densitometry of Starburst Galaxies", Astrophys. J., 673 (2): 832–46, doi:10.1086/524354 .
  6. ↑ Woon, David E. (2002), "Modeling Gas-Grain Chemistry with Quantum Chemical Cluster Calculations. I. Heterogeneous Hydrogenation of CO and H2CO on Icy Grain Mantles", Astrophys. J., 569: 541–48, doi:10.1086/339279 .
  7. ↑ Read, J. (1935), Text-Book of Organic Chemistry, London: G Bell & Sons .
  8. ↑ Schurink, H. B. J. (1925), "Pentaerythritol", Org. Synth., 4: 53 ; Coll. Vol., 1: 425  Missing or empty |title= (help).
  9. ↑ Gutsche, C. D.; Iqbal, M. (1993), "p-tert-Butylcalix[4]arene", Org. Synth. ; Coll. Vol., 8: 75  Missing or empty |title= (help).
  10. ↑ Bost, R. W.; Constable, E. W. (1936), "sym-Trithiane", Org. Synth., 16: 81 ; Coll. Vol., 2: 610  Missing or empty |title= (help).
  11. ↑ Formaldehyde in Clothing and Other Textiles (PDF), Existing Chemicals Information Sheet, Australian National Industrial Chemicals Notification and Assessment Scheme, October 2007, retrieved 2009-09-01 .
  12. ↑ Economic Importance, Formaldehyde Council. 2009. Accessed on April 14, 2010.
  13. ↑ No More Toxic Tub: Getting Contaminants Out Of Children’s Bath & Personal Care Products (PDF), Campaign for Safe Cosmetics, March 2009 .
  14. ↑ Francis-Floyd, Ruth (April 1996), Use of Formalin to Control Fish Parasites ([dead link]), Institute of Food and Agricultural Sciences, University of Florida .
  15. ↑ Center for Disease Control: Vaccines
  16. ↑ Directive 98/8/EC of the European Parliament and of the Council of 16 February 1998 concerning the placing of biocidal products on the market. OJEU L123, 24.04.1998, pp. 1–63. (consolidated version to 2008-09-26)
  17. ↑ Commission Regulation (EC) No 2032/2003 of 4 November 2003 on the second phase of the 10-year work programme referred to in Article 16(2) of Directive 98/8/EC of the European Parliament and of the Council concerning the placing of biocidal products on the market, and amending Regulation (EC) No 1896/2000. OJEU L307, 24.11.2003, p. 1–96. (consolidated version to 2007-01-04)
  18. ↑ Patel, Alkesh (2007-07-04), Formaldehyde Ban set for 22 Sept 2007, WebWire .
  19. ↑ European chemical Substances Information System (ESIS) entry for formaldehyde, retrieved 2009-09-01 .
  20. ↑ Process C-41 Using Kodak Flexicolor Chemicals – Publication Z-131, Kodak, retrieved 2009-09-01 .
  21. ↑ Indoor Air Pollution in California (PDF), Air Resources Board, California Environmental Protection Agency, July 2005, pp. 65–70 .
  22. ↑ Formaldehyde, Occupational Safety and Health Administration, August 2008, retrieved 2009-09-01 .
  23. ↑ Formaldehyde Reference Exposure Levels (PDF), California Office Of Health Hazard Assessment, December 2008 .
  24. ↑ Formaldehyde and Indoor Air, Health Canada, August 2005, ISBN 0815511299, retrieved 2009-09-01 .
  25. ↑ 25.0 25.1 Formaldehyde and Facts About Health Effects (PDF). Formaldehyde Epidemiology, Toxicology and Environmental Group. August 2002. Accessed on April 25, 2010.
  26. ↑ IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Volume 88 (2006) Formaldehyde, 2-Butoxyethanol and 1-tert-Butoxypropan-2-ol (pdf, html), WHO Press, 2006( English ) 
  27. ↑ 27.0 27.1 Formaldehyde and Cancer Risk 
  28. ↑ Testing for Indoor Air Quality, Baseline IAQ, and Materials ([dead link]), Environmental Protection Agency .
  29. ↑ Residential Indoor Air Formaldehyde Testing Program: A Pilot Study," M. Koontz, et al, prepared for U.S. EPA, 1996
  30. ↑ Evans, Ben (2008-04-11), FEMA limits formaldehyde in trailers, Boston.com, retrieved 2008-09-04 .
  31. ↑ Formaldehyde allergy, DermNet NZ, New Zealand Dermatological Society, June 2009, retrieved 2009-09-01 .
  32. ↑ European Union Bans formaldehyde/formalin within Europe (PDF), European Commission's Environment Directorate-General, September 2007, pp. 1–3 .
  33. ↑ ESIS (European Chemical Substances Information System), European Commission Joint Research Centre Institute for Health and Consumer Protection, February 2009 
  34. ↑ CFC.gov
  35. ↑ Formaldehyde Levels in FEMA-Supplied Trailers
  36. ↑ Mike Brunker (2006-07-25), Are FEMA trailers ‘toxic tin cans’?, MSNBC 
  37. ↑ ATSDR - Minimal Risk Levels for Hazardous Substances (MRLs)
  38. ↑ FEMA: CDC Releases Results Of Formaldehyde Level Tests
  39. ↑ Kunzelman, Michael. "Suit Filed Over FEMA Trailer Toxins". The Washington Post. Retrieved 2010-05-02. 
  40. ↑ Megan Terlecky (2008-10-24), How We Tested for Formaldehyde ([dead link]), KGAN-TV 
  41. ↑ NIGEL DUARA (2008-10-21), FEMA disputes formaldehyde study of Iowa trailers, Associated Press [dead link]
  42. ↑ Cindy Hadish (2008-10-24), FEMA meets with mobile home residents over health concerns ([dead link]), Cedar Rapids Gazette 
  43. ↑ Moise Ngwa (2010-10-25), formaldehyde testing (PDF), Cedar Rapids Gazette 
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