Toxicological evaluation and limit values for Methyl-tertiary-butyl ether (MTBE), Formaldehyde, Glutaraldehyde, Furfural

1. General description

1.2 Physical / chemical properties

Formaldehyde is produced commercially by the catalytic oxidation of methanol. The widest use is in the production of resins with urea, phenol and melamine. Formaldehyde-based resins are used as adhesives and impregnating resins in the manufacture of particle-board, plywood, furniture, and other wood products. The resins are also used in the textile, leather, rubber, and cement industries. Further, formaldehyde is used in the chemical industry as an intermediate in a variety of chemical synthesis. Formaldehyde itself is used for preservation and disinfection e.g. by embalming of biological specimens. It is used as an antimicrobial agent in many cosmetics products e.g. soaps, shampoos, hair preparations deodorants, lotions, and make-ups. (IARC 1995).

Formaldehyde is ubiquitous in the environment; it is an important endogenous substance that occurs in most life forms. In humans, as well as in other animals, formaldehyde is an essential metabolic intermediate in all cells in the biosynthesis of purines, thymidine, and certain amino acids. (IARC 1995).

Formaldehyde is formed by photooxidation of hydrocarbons in the troposphere where naturally occurring methane is the most important source for the production. The non-urban background level of formaldehyde is <1 mg/m³ with a mean of about 0.5 mg/m³.

Formaldehyde together with other aldehydes contributes about 12% of the volatile organic compounds in automobile exhaust from gasoline cars; diesel exhaust contains about 5% aldehydes (Larsen et al. 1997). Levels in urban areas with anthropogenic hydrocarbon and aldehyde emissions from traffic are reported to 1-20 mg/m³ (IARC 1995).

In streets with dense traffic in Copenhagen, average and maximum levels of 4.3 and 8.3 mg/m³ have been reported during a winter period (Granby et al. 1997). Higher levels would be expected during summer months.

Formaldehyde levels in rainwater are reported to 0.1-0.2 mg/kg. Drinking water normally contains <0.1 mg/l (IPCS 1989). Formaldehyde in drinking water is mainly formed by oxidation of natural organic (humic) matter during ozonation and chlorination or it enters the water from polyacetal plastic fittings. Up to 30 mg/l has been found in ozonated drinking water (WHO 1996).

No information is available concerning formaldehyde in soil.

There is some natural formaldehyde in raw food. Fruits and vegetables typically contain 3-60 mg/kg (e.g. pear: 60 mg/kg and apple: 17 mg/kg); milk and milk products about 1 mg/kg; meat and fish 6-20 mg/kg and shellfish 1-100 mg/kg. (IARC 1995, IPCS 1989).

In air, formaldehyde photolyses and reacts rapidly with reactive free radicals. The half-life in sunlight is a few hours. Because of high water solubility formaldehyde may be transferred to and eliminated with the rain. (HSDB 1996).

When released into water, formaldehyde will biodegrade to low levels within few days. Due to a low Henry´s Law constant of 3.7 x 10^-7 atm m³/mole volatilisation from water should not be significant. Little adsorption to sediment would be expected to occur. In nutrient-enriched sea-water there is a long lag period (approximately 40 hours) prior to measurable loss of formaldehyde by presumably biological processes. The fate of formaldehyde in ground water is unknown. (HSDB 1996).

Formaldehyde is easily biodegradable in soil. The adsorption coefficient to soil is very low, thus mobility is high and leaching may easily occur (IPCS 1989).

1.6 Human exposure

Humans are mainly exposed to formaldehyde by inhalation of ambient and indoor air containing formaldehyde. Indoor air may contain much higher levels than ambient air due to evaporation of formaldehyde from furniture, paint and building constructions. Levels between 10 and 1000 mg/m³ have been reported. The contribution from various atmospheric environments to the average human daily intake has been calculated to be 0.02 mg/day for outdoor air, 0.5-2 mg/day for indoor conventional buildings, and up to 1-10 mg/day for buildings with sources of formaldehyde. Smoking 20 cigarettes per day contributes with an additional exposure of about 1 mg formaldehyde. (IPCS 1989).

The quantity of formaldehyde ingested in food depends on the composition of the meal and may, for an average adult, range from 1.5 to 14 mg/day (IPCS 1989).

Humans are dermally exposed to formaldehyde in connection with use of various cosmetic products containing formaldehyde. The absorption from dermal exposure is estimated to be negligible (IPCS 1989).