Setting an indoor air exposure limit for formaldehyde: Factors of concern
Introduction
Formaldehyde has a pungent, suffocating odor (NIOSH, 1997). Its odor is detected and/or recognized by most human beings at concentrations below 1 ppm2 (reviewed by Arts et al., 2006a); the odor threshold for formaldehyde has been reported to be between 0.04 and 0.4 ppm in most cases (Gemert van, 2003).
Formaldehyde is irritating to the eyes and respiratory tract at low concentrations. This is caused by a chemosensory effect, i.e. interaction with local nerve endings (Nervus Trigeminus), which is called trigeminal stimulation or more commonly sensory irritation (see reviews by Paustenbach et al., 1997, Arts et al., 2006a). Sensory irritation leads to reflex responses such as sneezing, lacrimation, rhinorrhea, coughing, vasodilatation and changes in the rate and depth of respiration. The latter results in a decrease in the total amount of inhaled material resulting in a protective effect to the individual. Trigeminus stimulation is not necessarily an indication of cell or tissue damage. At higher concentrations formaldehyde will lead to cytotoxic reactions; this cytotoxic respiratory tract irritation is a localized pathophysiological response to a chemical, involving local redness, swelling, or itching (Arts et al., 2006b).
Formaldehyde is also a genotoxicant (IARC, 2006), and increased numbers of DNA–protein cross-links have been found in the upper respiratory tract of monkeys, and in the rat nasal mucosa following inhalation exposure (Casanova et al., 1991, Casanova et al., 1994). In long-term inhalation studies in rats, an exposure level of 1 ppm did not induce respiratory epithelial hyper/metaplasia in nasal tissues, whereas levels of 2–3 ppm did induce slight respiratory epithelial hyper/metaplasia. Levels of about 6 ppm and higher induced extensive hyper/metaplasia, necrosis, and severe rhinitis. An increased incidence of nasal cell carcinomas was seen from about 10 ppm, concomitant with clear cytotoxic effects (reviewed in Arts et al., 2006a), indicating that cytotoxicity is a prerequisite for the induction of carcinogenic effects.
The objective of this review is to evaluate the advised indoor air limit of 1 μg/m3 (0.8 ppb) formaldehyde by the European Commission (the INDEX project; Kotzias et al., 2005) taking into account the odor, (sensory) irritation and the mode of action resulting in the carcinogenicity of formaldehyde. Due to this level of 1 μg/m3 being lower than the levels generally encountered in rural areas and also being lower than the level found in the exhaled air of humans (Moser et al., 2005, Wehninger et al., 2007, Kushch et al., 2008), there is therefore a clear need to evaluate this advised indoor air limit. The studies on which this proposed limit is based, and the assessment factors used will be evaluated.
Section snippets
Evaluation
An indoor air limit of 1 μg/m3 (0.8 ppb) formaldehyde was established by the European Commission (the INDEX project; Kotzias et al., 2005). This level has been based on a threshold for nose and throat irritation of 0.1 mg/m3 (0.08 ppm; LOAEL), a NOAEL of 0.03 mg/m3 (0.025 ppm) and an assessment factor of 30. The latter consists of a factor of 10 for intra-species variation and a factor of 3 due to children being possibly more sensitive than adults.
This evaluation focuses on three major points:
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Are the
Discussion and conclusion
The critical health effect of formaldehyde exposure at low concentrations is sensory irritation. In volunteers, eye irritation is observed first at levels of 1 ppm and higher (reviewed by Paustenbach et al., 1997, Arts et al., 2006a). Also in the study by Lang et al. (2008), it was shown that peaks of 1 ppm were most likely responsible for the induction of eye irritation, as minimal objective eye irritation was observed only at a level of 0.5 ppm with peaks of 1 ppm. Eye irritation was not seen at
Acknowledgments
The authors thank Mark Kean, AkzoNobel T&E, Arnhem, the Netherlands, for editing the paper and the FormaCare sector group of CEFIC, Brussels, Belgium for the financial contribution to perform this evaluation. The views in this paper, however, are those of the authors and do not necessarily reflect the views of the industries presented by the FormaCare sector group.
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Present address: Akzo Nobel T&E, Arnhem, The Netherlands.