Report No FR0067

S Hunt and J K Fawell

Feb 1990



To review the information on the toxicity of formaldehyde with reference to drinking water and to discuss the setting of a drinking water guide level for the compound.


There is a need to provide water suppliers with sound guidance on the maximum levels of toxic substances that should be permitted in drinking water. The WHO is undertaking a review of its drinking water guidelines for a number of substances. This review is part of the UK water industry's contribution to that process of establishing new guidelines based on a sound scientific assessment of the latest available data.


There are no data on the occurrence of formaldehyde in treated water. The main focus of attention has been on the presence formaldehyde in air, so most data concern exposure by the inhalation route. Formaldehyde is of moderate acute toxicity. There is little indication that formaldehyde is carcinogenic by oral or dermal exposure, but some evidence that it can cause cancer in rats and mice following inhalation by irritating the nasal epithelium. There is evidence of mutagenicity in vitro, but not in vivo.


Formaldehyde is carcinogenic in rats following inhalation, and there is a suggestion that it may be a tumour promoter in the gastrointestinal tract. However, the concentrations of formaldehyde used in this study were high and, in view of the evidence for its mode of action in the nasal epithelium, it seems probable that the promoting action is linked to irritation. An additional uncertainty factor should be applied to the calculation of a guide value to take this into account.


The report reviews the toxicology of formaldehyde and considers how it may relate to the safety of drinking water. Formaldehyde has clearly been shown to be carcinogenic in rats following inhalation. There is little evidence to suggest that formaldehyde is a carcinogen in rats by the oral route (although papilloma were reported in the stomach in one study) or in man by the inhalation route. There is some evidence that formaldehyde may be a tumour promoter in the gastrointestinal tract.

A WHO classification of 2B, that is 'possibly carcinogenic to humans' may therefore be appropriate for this compound.

An additional point to consider is the potential for formaldehyde in water to induce gastrointestinal irritation and nausea in man, effects not easily modelled in animal toxicity studies. Although there are no specific data on gastrointestinal irritation following oral exposure to comparatively low levels of formaldehyde it may be prudent to include a further uncertainty factor to eliminate any such possibility, when attempting to set a guide level in drinking water.

Formaldehyde exposure by the oral and inhalation routes should be considered as separate events because potential effects tend to occur at the site of exposure and not systemically. There is a paucity of information available on levels in water and data available on food are also limited.

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