Sources and health implications
Formaldehyde is a major chemical building block in polymer chemistry, with numerous applications in the manufacture of construction products. It is used as a component of urea-formaldehyde foam insulation and is also present in many timber products as a component of glues and resins used in the manufacture of chipboard, plywood and furniture. Formaldehyde is used is now world-wide. For example, production in the United States of America alone exceeds 4 million tones per year (36) about half of which is used for the production of urea-formaldehyde and phenol-formaldehyde resins and in foam insulation.
With a boiling point of -19°C, formaldehyde is highly volatile at room temperatures, leading to the possibility of high concentrations in the indoor environment. It has a strong pungent odour, which acts as a warning against prolonged exposure to high concentrations. Moderate levels of exposure have irritant effects to the nose, throat, lung and eyes; at higher levels of concentration for prolonged periods (such as those associated with workers exposed to formaldehyde in the workplace) pathological changes to nasal mucosa have been reported (36). Allergenic skin reactions have also been reported in men chronically exposed to formaldehyde-containing materials. Finally, in high concentrations, the inhalation of formaldehyde is a potential carcinogen on the nasal mucosa: according to IARC (20), formaldehyde is probably carcinogenic to humans.
Factors influencing exposure
Data on acute toxicity are mainly from epidemiological studies of occupationally exposed populations and residents of buildings constructed of materials containing formaldehyde, and from controlled human exposure studies (37). Occupational exposure contributes to total exposure, for example, a high occupational exposure (e.g. in formaldehyde or resin production) of 1 mg/m3 for a 25 per cent time-weighted period would give a daily intake of about 5 mg per day (37).
The possible routes of exposure to formaldehyde are ingestion, inhalation, dermal absorption. Inhalation via ambient air, indoor air, or from smoking is the major route of exposure. Of the three, inhalation of the indoor air is the major route of entry with releases from chipboard and other building and furnishing materials constituting the bulk of the exposure (37) Furthermore occupants of prefabricated buildings incorporating chipboard are likely to inhale 2-3 times as much formaldehyde as occupants of conventional buildings (37).
Acceptable exposure levels
Regulations of different countries now limit workplace exposures to between 0.5 mg/m3 and 2.0 mg/m3; while Sweden has specified domestic maxima to 0.1 mg/m3 for new homes and 0.7 mg/m3 for old homes; indoor concentrations ranging from 0.1 to 0.8 mg/m3 in houses and mobile homes with urea formaldehyde foam insulation are commonly found (36). It has been found that 0.5 mg/m3 is sufficient to produce nasal irritation; that the no-effect level is 2 mg/m3; and that at dosages of 5.6 mg/m3, rats developed nasal tumours. There is thus only a small margin between the upper permitted exposure levels and the levels at which carcinogenicity has been demonstrated.
The highly volatile nature of formaldehyde means that while early concentration in the indoor environment may be high, the level of concentration will fall rapidly. For example, the level of concentration within a week following the application of a floor finish using formaldehyde can fall to less than one-sixth of its level shortly after application (38). Thus, while workers need protection during application, occupants can effectively be protected by delaying occupancy long enough for the emission to have reached an acceptable level. Adequate ventilation both during construction and occupation can ensure that unacceptable concentrations do not arise. Respiratory protective equipment should be used whenever necessary. Building codes and production and processing regulations should take into account the numerous sources that may contribute to indoor formaldehyde, levels which include: insulating materials, chipboard and plywood, and fabrics. Other sources are cigarette smoke, heating and cooking.
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