Formaldehyde

Chemical Name

  • Formaldehyde
  • Formalin
  • Morbicid acid
  • Methyl aldehyde
  • Methylene oxide
  • Formol

IUPAC / CAS

Methanal / 50-00-0

Physical and Chemical Properties

Formaldehyde occurs as a natural product in the environment. It is a monoaldehyde, colorless gas with a pungent odor. It is soluble in water, ethanol and diethylether. It has a molecular weight at 30.03. Its melting   point is - 117 ºC and its boiling point of -19.3 ºC. Formaldehyde gas readily polymerizes at room temperature and atmospheric pressure. Formaldehyde solution (formalin) consists of 34 % to 38% (wt/wt) of Methanal and methanol (to delay polymerization). In presence of sunlight, formaldehyde gas gets photo-oxidized to carbon dioxide. Hence its presence in the atmosphere is very short lived.

Mode of Action

Formaldehyde is an extremely reactive chemical agent and acts by forming a chemical bond with the primary amide and the amino groups of protein molecules. Thus, in vitro, it reacts with proteins, DNA and RNA. It can penetrate the thick wall of spores and hence has long been considered a sporicidal agent. Even at low concentrations, formaldehyde acts against spores and prevents germination.  Formaldehyde also has mutagenic potential. Its action on the carboxyl, sulphydryl and the hydroxyl groups makes it a strong alkylating agent as well. It forms protein – DNA cross linkages and hence inhibits DNA synthesis in micro-organisms. The above action on nucleic acids like DNA and RNA has been demonstrated by experimental studies on viruses like SV40.

Activity Spectrum

Formaldehyde belongs to the aldehyde group of disinfectants and steriliants. It has a wide spectrum of activity and is commonly used in industries and health care outfits. It is bactericidal, sporicidal as well as virucidal in nature but acts much more slowly as compared to Gluteraldehyde, which is the other widely used aldehyde from this group. Formaldehyde is either used as a liquid agent or in combination with low pressure steam for the above purpose.

Advantages

It has a wide spectrum of activity and can even destroy spore forms which are the most resistant morphological forms of bacteria. 10% formalin with 0.5% sodium tetraborate is used for sterilizing clean metal instruments. Formaldehyde gas has been used for sterilization of heat sensitive devices like catheters. 10% formalin has long been used for preservation of pathological specimens as it preserves the cellular morphology.

Disadvantages

The gas is irritant and toxic when inhaled. When solutions are used for surface disinfection, vapors given out from the surface can injure the respiratory mucosa. This can be nullified by the use of ammonia vapor after disinfection has been completed. It is also a skin irritant.

Toxicity and Side Effects in Humans

Formaldehyde is an irritant to the eyes, nose and the respiratory mucosa. It is also a strong sensitizer and leads to allergic reactions of the skin and the respiratory tract. Contact dermatitis occurs when exposed to more than 2% formaldehyde solutions.  The liquid and vapor of formaldehyde are inflammable.
Formaldehyde is known to be a human carcinogen. Numerous animal and human studies have proven the carcinogenic effects of exposure to formaldehyde. Human epidemiological studies indicate an increase in oronasal and nasopharyngeal carcinomas in individuals exposed to formaldehyde. It has been associated with undifferentiated or squamous cell carcinomas. The genotoxic effects of formaldehyde along with its ability to initiate cell proliferation are the main events responsible for its carcinogenic potential. Formaldehyde reacts with DNA to form DNA to protein linkages (DPX) which in turn inhibits synthesis and repair of DNA. This also induces mutations which may contribute to cell proliferation. Experimental studies on human buccal cells have shown that exposure to formaldehyde cause micronuclei formation and induce chromosomal aberrations. This is called clastogenic damage. Induction of cell proliferation by formaldehyde is the other key event responsible for tumorogenesis.

Regulatory Information

Over the years formaldehyde has become an extremely regulated product.

  • 1991 - The US, Environmental Protection Agency (EPA) classified formaldehyde as a B1 ‘probable’ human carcinogen.
  • The U.S Department of Labor’s Occupational Safety and Health Administration (OSHA) has established a Permissible Exposure Levels (PEL) to 0.75 parts per million (ppm) at the workplace.
  • International Agency for Research on Cancer (IARC) – classified formaldehyde under the Group 2A as a ‘probable’ human carcinogen.
  • In 2004, IARC upgraded formaldehyde to Category 1 (known human) carcinogen from group 2A, inlight of mounting scientific evidence towards its carcinogenic effects in humans.
  • The World Health Organization (WHO) recommends an air quality guideline of 0.1 mg/m3 for a 30 minute period to avoid significant sensory irritation in the general population.

Safety Measures

  • Protective clothing in the form of respiratory masks, gowns and protective eye wear are recommended in industries and health care establishments where formaldehyde exposure is common.
  • If there is a spill, immediately extinguish all open flames and evacuate the area.
  • If any part of the body or clothes get contaminated with formalin, remove the clothes and wash the body part with a mild soap and water for at least 15 mins.
  • If the eye is affected, irrigate the eye cold water at the eyestation.
  • When formalin gas is inhaled and it causes respiratory irritation,  fresh air must be inhaled in an upright position. If required artificial ventilatory support may be needed. The symptoms of lung oedma appear after a few hours of inhaling the gas in which case the patient needs to be hospitalised at least for 24 hours under observation.

References:

  1. McDonnell G, Russell D. Antiseptics and Disinfectants : Activity, Action and Resistance. Clin Microbiol Rev 1999; 12(1): 147 - 179
  2. Air quality guidelines for Europe – second edition. Copenhagen, WHO Regional Office for Europe, Denmark, 2001.