This report contains the collective views of an international group of experts and does not necessarily represent the decisions or the stated policy of the United Nations Environment Programme, the International Labour Organization, or the World Health Organization.

First draft prepared by R.G. Liteplo, R. Beauchamp, M.E. Meek, Health Canada, Ottawa, Canada, and R. Chénier, Environment Canada, Ottawa, Canada

Published under the joint sponsorship of the United Nations Environment Programme, the International Labour Organization, and the World Health Organization, and produced within the framework of the Inter-Organization Programme for the Sound Management of Chemicals.

World Health Organization

Geneva, 2002

The International Programme on Chemical Safety (IPCS), established in 1980, is a joint venture of the United Nations Environment Programme (UNEP), the International Labour Organization (ILO), and the World Health Organization (WHO). The overall objectives of the IPCS are to establish the scientific basis for assessment of the risk to human health and the environment from exposure to chemicals, through international peer review processes, as a prerequisite for the promotion of chemical safety, and to provide technical assistance in strengthening national capacities for the sound management of chemicals.

The Inter-Organization Programme for the Sound Management of Chemicals (IOMC) was established in 1995 by UNEP, ILO, the Food and Agriculture Organization of the United Nations, WHO, the United Nations Industrial Development Organization, the United Nations Institute for Training and Research, and the Organisation for Economic Co-operation and Development (Participating Organizations), following recommendations made by the 1992 UN Conference on Environment and Development to strengthen cooperation and increase coordination in the field of chemical safety. The purpose of the IOMC is to promote coordination of the policies and activities pursued by the Participating Organizations, jointly or separately, to achieve the sound management of chemicals in relation to human health and the environment.

WHO Library Cataloguing-in-Publication Data

Formaldehyde.

(Concise international chemical assessment document ; 40)

1.Formaldehyde - adverse effects 2.Risk assessment 3.Environmental exposure

I.International Programme on Chemical Safety II.Series

ISBN 92 4 153040 5         (NLM Classification: QV 225)

ISSN 1020-6167

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Concise International Chemical Assessment Documents (CICADs) are the latest in a family of publications from the International Programme on Chemical Safety (IPCS) — a cooperative programme of the World Health Organization (WHO), the International Labour Organization (ILO), and the United Nations Environment Programme (UNEP). CICADs join the Environmental Health Criteria documents (EHCs) as authoritative documents on the risk assessment of chemicals.

International Chemical Safety Cards on the relevant chemical(s) are attached at the end of the CICAD, to provide the reader with concise information on the protection of human health and on emergency action. They are produced in a separate peer-reviewed procedure at IPCS. They may be complemented by information from IPCS Poison Information Monographs (PIM), similarly produced separately from the CICAD process.

CICADs are concise documents that provide summaries of the relevant scientific information concerning the potential effects of chemicals upon human health and/or the environment. They are based on selected national or regional evaluation documents or on existing EHCs. Before acceptance for publication as CICADs by IPCS, these documents undergo extensive peer review by internationally selected experts to ensure their completeness, accuracy in the way in which the original data are represented, and the validity of the conclusions drawn.

The primary objective of CICADs is characterization of hazard and dose–response from exposure to a chemical. CICADs are not a summary of all available data on a particular chemical; rather, they include only that information considered critical for characterization of the risk posed by the chemical. The critical studies are, however, presented in sufficient detail to support the conclusions drawn. For additional information, the reader should consult the identified source documents upon which the CICAD has been based.

Risks to human health and the environment will vary considerably depending upon the type and extent of exposure. Responsible authorities are strongly encouraged to characterize risk on the basis of locally measured or predicted exposure scenarios. To assist the reader, examples of exposure estimation and risk characterization are provided in CICADs, whenever possible. These examples cannot be considered as representing all possible exposure situations, but are provided as guidance only. The reader is referred to EHC 170¹ for advice on the derivation of health-based guidance values.

While every effort is made to ensure that CICADs represent the current status of knowledge, new information is being developed constantly. Unless otherwise stated, CICADs are based on a search of the scientific literature to the date shown in the executive summary. In the event that a reader becomes aware of new information that would change the conclusions drawn in a CICAD, the reader is requested to contact IPCS to inform it of the new information.

The flow chart shows the procedures followed to produce a CICAD. These procedures are designed to take advantage of the expertise that exists around the world — expertise that is required to produce the high-quality evaluations of toxicological, exposure, and other data that are necessary for assessing risks to human health and/or the environment. The IPCS Risk Assessment Steering Group advises the Co-ordinator, IPCS, on the selection of chemicals for an IPCS risk assessment, the appropriate form of the document (i.e., EHC or CICAD), and which institution bears the responsibility of the document production, as well as on the type and extent of the international peer review.

The first draft is based on an existing national, regional, or international review. Authors of the first draft are usually, but not necessarily, from the institution that developed the original review. A standard outline has been developed to encourage consistency in form. The first draft undergoes primary review by IPCS and one or more experienced authors of criteria documents to ensure that it meets the specified criteria for CICADs.

The draft is then sent to an international peer review by scientists known for their particular expertise and by scientists selected from an international roster compiled by IPCS through recommendations from IPCS national Contact Points and from IPCS Participating Institutions. Adequate time is allowed for the selected experts to undertake a thorough review. Authors are required to take reviewers’ comments into account and revise their draft, if necessary. The resulting second draft is submitted to a Final Review Board together with the reviewers’ comments.

A consultative group may be necessary to advise on specific issues in the risk assessment document.

The CICAD Final Review Board has several important functions:

• to ensure that each CICAD has been subjected to an appropriate and thorough peer review;
• to verify that the peer reviewers’ comments have been addressed appropriately;
• to provide guidance to those responsible for the preparation of CICADs on how to resolve any remaining issues if, in the opinion of the Board, the author has not adequately addressed all comments of the reviewers; and
• to approve CICADs as international assessments.

Board members serve in their personal capacity, not as representatives of any organization, government, or industry. They are selected because of their expertise in human and environmental toxicology or because of their experience in the regulation of chemicals. Boards are chosen according to the range of expertise required for a meeting and the need for balanced geographic representation.

Board members, authors, reviewers, consultants, and advisers who participate in the preparation of a CICAD are required to declare any real or potential conflict of interest in relation to the subjects under discussion at any stage of the process. Representatives of nongovernmental organizations may be invited to observe the proceedings of the Final Review Board. Observers may participate in Board discussions only at the invitation of the Chairperson, and they may not participate in the final decision-making process.

This CICAD on formaldehyde was prepared jointly by the Environmental Health Directorate of Health Canada and the Commercial Chemicals Evaluation Branch of Environment Canada based on documentation prepared as part of the Priority Substances Program under the Canadian Environmental Protection Act (CEPA). The objective of assessments on Priority Substances under CEPA is to assess potential effects of indirect exposure in the general environment on human health as well as environmental effects. This CICAD additionally includes information on occupational exposure. Data identified as of the end of December 1999 (environmental effects) and January 1999 (human health effects) were considered in this review.² Other reviews that were also consulted include IARC (1981, 1995), IPCS (1989), RIVM (1992), BIBRA Toxicology International (1994), and ATSDR (1999). Information on the nature of the peer review and availability of the source document (Environment Canada & Health Canada, 2001) and its supporting documentation is presented in Appendix 1. It should be noted, as indicated therein, that the biologically motivated case-specific model for exposure–response analyses for cancer included in this CICAD was the product of a joint effort involving the US Environmental Protection Agency (EPA), Health Canada, the Chemical Industry Institute of Toxicology (CIIT), and others. The product of this collaborative effort superceded the content of a draft CICAD on formaldehyde prepared previously by the Office of Pollution Prevention and Toxics of the US EPA, on the basis of health-related toxicological information published prior to1992. Information on the peer review of this CICAD is presented in Appendix 2. This CICAD was approved as an international assessment at a meeting of the Final Review Board, held in Geneva, Switzerland, on 8–12 January 2001. Participants at the Final Review Board meeting are listed in Appendix 3. The International Chemical Safety Card for formaldehyde (ICSC 0275), produced by the International Programme on Chemical Safety (IPCS, 2000), has also been reproduced in this document.

Formaldehyde (CAS No. 50-0-0) is a colourless, highly flammable gas that is sold commercially as 30–50% (by weight) aqueous solutions. Formaldehyde enters the environment from natural sources (including forest fires) and from direct human sources, such as automotive and other fuel combustion and industrial on-site uses. Secondary formation also occurs, by the oxidation of natural and anthropogenic organic compounds present in air. The highest concentrations measured in the environment occur near anthropogenic sources; these are of prime concern for the exposure of humans and other biota. Motor vehicles are the largest direct human source of formaldehyde in the environment of the source country (Canada). Releases from industrial processes are considerably less. Industrial uses of formaldehyde include the production of resins and fertilizers.

When formaldehyde is released to or formed in air, most of it degrades, and a very small amount moves into water. When formaldehyde is released into water, it does not move into other media but is broken down. Formaldehyde does not persist in the environment, but its continuous release and formation result in long-term exposure near sources of release and formation.

The focus of the human health assessment is airborne exposure, due primarily to the lack of representative data on concentrations in media other than air and limited data on effects following ingestion.

Extensive recent data are available for concentrations of formaldehyde in air at industrial, urban, suburban, rural, and remote locations in the source country (Canada). There are fewer but still considerable data on concentrations in indoor air, which are higher. Data on concentrations in water are more limited. Although formaldehyde is a natural component of a variety of foodstuffs, monitoring has generally been sporadic and source directed. Based on available data, the highest concentrations of formaldehyde occurring naturally in foods are in some fruits and marine fish. Formaldehyde may also be present in food due to its use as a bacteriostatic agent in production and its addition to animal feed to improve handling characteristics. Formaldehyde and formaldehyde derivatives are also present in a wide variety of consumer products to protect the products from spoilage by microbial contamination. The general population is also exposed during release from combustion (e.g., from cigarettes and cooking) and emission from some building materials, such as pressed wood products.

Since formaldehyde (also a product of intermediary metabolism) is water soluble, highly reactive with biological macromolecules, and rapidly metabolized, adverse effects resulting from exposure are observed primarily in those tissues or organs with which formaldehyde first comes into contact (i.e., the respiratory and aerodigestive tract, including oral and gastrointestinal mucosa, following inhalation or ingestion, respectively).

Sensory irritation of the eyes and respiratory tract by formaldehyde has been observed consistently in clinical studies and epidemiological surveys in occupational and residential environments. At concentrations higher than those generally associated with sensory irritation, formaldehyde may also contribute to the induction of generally small, reversible effects on lung function.

For the general population, dermal exposure to concentrations of formaldehyde, in solution, in the vicinity of 1–2% (10 000–20 000 mg/litre) is likely to cause skin irritation; however, in hypersensitive individuals, contact dermatitis can occur following exposure to formaldehyde at concentrations as low as 0.003% (30 mg/litre). In North America, less than 10% of patients presenting with contact dermatitis may be immunologically hypersensitive to formaldehyde. Although it has been suggested in case reports for some individuals that formaldehyde-induced asthma was attributable to immunological mechanisms, no clear evidence has been identified. However, in studies with laboratory animals, formaldehyde has enhanced their sensitization to inhaled allergens.

Following inhalation in laboratory animals, formaldehyde causes degenerative non-neoplastic effects in mice and monkeys and nasal tumours in rats. In vitro, formaldehyde induced DNA–protein crosslinks, DNA single-strand breaks, chromosomal aberrations, sister chromatid exchange, and gene mutations in human and rodent cells. Formaldehyde administered by inhalation or gavage to rats in vivo induced chromosomal anomalies in lung cells and micronuclei in the gastrointestinal mucosa. The results of epidemiological studies in occupationally exposed populations are consistent with a pattern of weak positive responses for genotoxicity, with good evidence of an effect at site of contact (e.g., micronucleated buccal or nasal mucosal cells). Evidence for distal (i.e., systemic) effects is equivocal. Overall, based on studies in both animals and humans, formaldehyde is weakly genotoxic, with good evidence of an effect at site of contact, but less convincing evidence at distal sites. Epidemiological studies taken as a whole do not provide strong evidence for a causal association between formaldehyde exposure and human cancer, although the possibility of increased risk of respiratory cancers, particularly those of the upper respiratory tract, cannot be excluded on the basis of available data. Therefore, based primarily upon data derived from laboratory studies, the inhalation of formaldehyde under conditions that induce cytotoxicity and sustained regenerative proliferation is considered to present a carcinogenic hazard to humans.

The majority of the general population is exposed to airborne concentrations of formaldehyde less than those associated with sensory irritation (i.e., 0.083 ppm [0.1 mg/m³]). However, in some indoor locations, concentrations may approach those associated with eye and respiratory tract sensory irritation in humans. Risks of cancer estimated on the basis of a biologically motivated case-specific model for calculated exposure of the general population to formaldehyde in air based on the sample exposure scenario for the source country (Canada) are exceedingly low. This model incorporates two-stage clonal growth modelling and is supported by dosimetry calculations from computational fluid dynamics modelling of formaldehyde flux in various regions of the nose and single-path modelling for the lower respiratory tract.

Environmental toxicity data are available for a wide range of terrestrial and aquatic organisms. Based on the maximum concentrations measured in air, surface water, effluents, and groundwater in the sample exposure scenario from the source country and on the estimated no-effects values derived from experimental data for terrestrial and aquatic biota, formaldehyde is not likely to cause adverse effects on terrestrial or aquatic organisms.

Formaldehyde (CH₂O) is also known as methanal, methylene oxide, oxymethylene, methylaldehyde, oxomethane, and formic aldehyde. Its Chemical Abstracts Service (CAS) registry number is 50-00-0.

At room temperature, formaldehyde is a colourless gas with a pungent, irritating odour. It is highly reactive, readily undergoes polymerization, is highly flammable, and can form explosive mixtures in air. It decomposes at temperatures above 150 °C. Formaldehyde is readily soluble in water, alcohols, and other polar solvents. In aqueous solutions, formaldehyde hydrates and polymerizes and can exist as methylene glycol, polyoxymethylene, and hemiformals. Solutions with high concentrations (>30%) of formaldehyde become turbid as the polymer precipitates (IPCS, 1989). As a reactive aldehyde, formaldehyde can undergo a number of self-association reactions, and it can associate with water to form a variety of chemical species with properties different from those of the pure monomolecular substance. These associations tend to be most prevalent at high concentrations of formaldehyde; hence, data on properties at high concentrations are not relevant to dilute conditions.

Values reported for the physical and chemical properties of formaldehyde are given in Table 1. Additional physical/chemical properties are presented in the International Chemical Safety Card reproduced in this document.

Pure formaldehyde is not available commercially but is sold as 30–50% (by weight) aqueous solutions. Formalin (37% CH₂O) is the most common solution. Methanol or other substances are usually added to the solution as stabilizers to reduce the intrinsic polymerization of formaldehyde (IPCS, 1989; Environment Canada, 1995). In solid form, formaldehyde is marketed as trioxane [(CH₂O)₃] and its polymer paraformaldehyde, with 8–100 units of formaldehyde (IPCS, 1989).

Selected methods for the determination of formaldehyde in air, food, and wood are presented in Table 2 (IARC, 1995). The most widely used methods for the detection of formaldehyde are based on spectrophotometry, but other methods, such as colorimetry, fluorimetry, high-performance liquid chromatography, polarography, gas chromatography, infrared detection, and gas detector tubes, are also used. Organic and inorganic chemicals, such as sulfur dioxide and other aldehydes and amines, can interfere with these methods of detection. The most sensitive of these methods is flow injection (Fan & Dasgupta, 1994), which has a detection limit of 9 ppt (0.011 µg/m³). Another commonly used method is high-performance liquid chromatography, which offers a detection limit of 0.0017 ppm (0.002 mg/m³) (IARC, 1995). Gas detector tubes and infrared analysers are often used for monitoring workplace atmospheres and have a sensitivity of about 0.33–0.42 ppm (0.4–0.5 mg/m³) (IARC, 1995).

Data on sources and emissions primarily from the source country of the national assessment on which the CICAD is based (i.e., Canada) are presented here as an example. Sources and patterns of emissions in other countries are expected to be similar, although quantitative values may vary.

Formaldehyde is formed primarily by the combustion of organic materials and by a variety of natural and anthropogenic activities. Secondary formation of formaldehyde occurs in the atmosphere through the oxidation of natural and anthropogenic volatile organic compounds (VOCs) in the air. While there are no reliable estimates for releases from natural sources and for secondary formation, these may be expected to be much larger than direct emissions from anthropogenic activities. However, highest concentrations have been measured near key anthropogenic sources, such as automotive and industrial emissions (see section 6.1.1).

Formaldehyde occurs naturally in the environment and is the product of many natural processes. It is released during biomass combustion, such as forest and brush fires (Howard, 1989; Reinhardt, 1991). In water, it is also formed by the irradiation of humic substances by sunlight (Kieber et al., 1990).

As a metabolic intermediate, formaldehyde is present at low levels in most living organisms (IPCS, 1989; IARC, 1995). It is emitted by bacteria, algae, plankton, and vegetation (Hellebust, 1974; Zimmermann et al., 1978; Eberhardt & Sieburth, 1985; Yamada & Matsui, 1992; Nuccio et al., 1995).

Anthropogenic sources of formaldehyde include direct sources such as fuel combustion, industrial on-site uses, and off-gassing from building materials and consumer products.

Although formaldehyde is not present in gasoline, it is a product of incomplete combustion and is released, as a result, from internal combustion engines. The amount generated depends primarily on the composition of the fuel, the type of engine, the emission control applied, the operating temperature, and the age and state of repair of the vehicle. Therefore, emission rates are variable (Environment Canada, 1999a).

Based on data for 1997 reported to the National Pollutant Release Inventory, on-road motor vehicles are the largest direct source of formaldehyde released into the Canadian environment. Data on releases from on-road vehicles were estimated by modelling (Mobile 5C model), based on assumptions outlined in Environment Canada (1996). The amount estimated by modelling to have been released in 1997 from on-road motor vehicles was 11 284 tonnes (Environment Canada, 1999b). While Environment Canada (1999b) did not distinguish between gasoline-powered and diesel-powered vehicles, it has been estimated, based on emissions data from these vehicles, that they account for about 40% and 60% of on-road automotive releases, respectively. Aircraft emitted an estimated 1730 tonnes, and the marine sector released about 1175 tonnes (Environment Canada, 1999b). It can be expected that the rates of release of formaldehyde from automotive sources have changed and will continue to change; many current and planned modifications to automotive emission control technology and gasoline quality would lead to decreases in the releases of formaldehyde and other VOCs (Environment Canada, 1999b).

Other anthropogenic combustion sources (covering a range of fuels from wood to plastics) include wood-burning stoves, fireplaces, furnaces, power plants, agricultural burns, waste incinerators, cigarette smoking, and the cooking of food (Jermini et al., 1976; Kitchens et al., 1976; Klus & Kuhn, 1982; Ramdahl et al., 1982; Schriever et al., 1983; Lipari et al., 1984; IPCS, 1989; Walker & Cooper, 1992; Baker, 1994; Guski & Raczynski, 1994). Cigarette smoking in Canada is estimated to produce less than 84 tonnes per year, based on estimated emission rates (IPCS, 1989) and a consumption rate of approximately 50 billion cigarettes per year (Health Canada, 1997). Canadian coal-based electricity generating plants are estimated to emit 0.7–23 tonnes per year, based on US emission factors (Lipari et al., 1984; Sverdrup et al., 1994), the high heating value of fuel, and Canadian coal consumption in 1995 (D. Rose, personal communication, 1998). A gross estimate of formaldehyde emissions from municipal, hazardous, and biomedical waste in Canada is 10.6 tonnes per year, based on measured emission rates from one municipal incinerator in Ontario (Novamann International, 1997; Environment Canada, 1999a).

Industrial releases of formaldehyde can occur at any stage during the production, use, storage, transport, or disposal of products with residual formaldehyde. Formaldehyde has been detected in emissions from chemical manufacturing plants (Environment Canada, 1997b,c, 1999a), pulp and paper mills, forestry product plants (US EPA, 1990; Fisher et al., 1991; Environment Canada, 1997b, 1999a; O’Connor & Voss, 1997), tire and rubber plants (Environment Canada, 1997a), petroleum refining and coal processing plants (IARC, 1981; US EPA, 1993), textile mills, automotive manufacturing plants, and the metal products industry (Environment Canada, 1999a).

Total environmental releases in Canada from 101 facilities were 1423.9 tonnes in 1997, with reported releases to different media as follows: 1339.3 tonnes to air, 60.5 tonnes to deep-well injection, 19.4 tonnes to surface water, and 0 tonnes to soil. From 1979 to 1989, about 77 tonnes were spilled in Canada as a result of 35 reported incidents. Releases of formaldehyde to groundwater from embalming fluids in bodies buried in cemeteries are expected to be very small based on groundwater samples and the estimated loading rates of six cemeteries in Ontario (Chan et al., 1992). In the USA in 1992, total releases of formaldehyde to environmental media from certain types of US industries were approximately 8960 tonnes, of which approximately 58%, 39%, 2%, and 1% were released to the atmosphere, to underground injection sites, to surface water, and to land, respectively (TRI, 1994).

Formaldehyde has been detected in the off-gassing of formaldehyde products such as wood panels, latex paints, new carpets, textile products, and resins. While emission rates have been estimated for some of these sources, there are insufficient data for estimating total releases (Little et al., 1994; NCASI, 1994; Environment Canada, 1995). In some countries, there have been regulatory and voluntary initiatives to control emissions from building materials and furnishings, since these are recognized as the major sources of elevated concentrations of formaldehyde in indoor air.

Formaldehyde is formed in the troposphere by the photochemical oxidation of many types of organic compounds, including naturally occurring compounds, such as methane (IPCS, 1989; US EPA, 1993) and isoprene (Tanner et al., 1994), and pollutants from mobile and stationary sources, such as alkanes, alkenes (e.g., ethene, propene), aldehydes (e.g., acetaldehyde, acrolein), and alcohols (e.g., allyl alcohol, methanol, ethanol) (US EPA, 1985; Atkinson et al., 1989, 1993; Grosjean, 1990a,b, 1991a,b,c; Skov et al., 1992; Grosjean et al., 1993a,b, 1996a,b; Bierbach et al., 1994; Kao, 1994).

Given the diversity and abundance of formaldehyde precursors in urban air, secondary atmospheric formation frequently exceeds direct emissions from combustion sources, especially during photochemical air pollution episodes, and it may contribute up to 70–90% of the total atmospheric formaldehyde (Grosjean, 1982; Grosjean et al., 1983; Lowe & Schmidt, 1983). In California, USA, Harley & Cass (1994) estimated that photochemical formation was more important than direct emissions in Los Angeles during the summertime days studied; in winter or at night and in the early morning, direct emissions can be more important. This was also observed in Japan, where the concentrations of formaldehyde in the central mountainous region were not associated directly with motor exhaust but rather were associated with the photochemical oxidation of anthropogenic pollutants occurring there through long-range transport (Satsumabayashi et al., 1995).

Formaldehyde is produced commercially from methanol. The primary methanol oxidation processes use metal catalyst (silver now, previously copper) or metal oxide catalyst (ATSDR, 1999). Similar methods of production are used in many countries worldwide. Table 3 shows the production of formaldehyde by selected countries, with the highest amounts originating from the USA and Japan.

In 1996, the domestic production of formaldehyde in Canada was approximately 222 000 tonnes (Environment Canada, 1997bc); in 1994, domestic production in the USA was 3.6 million tonnes (Kirschner, 1995). The production of formaldehyde worldwide in 1992 was estimated at approximately 12 million tonnes (IARC, 1995).

Total Canadian domestic consumption of formaldehyde was reported at about 191 000 tonnes for 1996 (Environment Canada, 1997b). Formaldehyde is used predominantly in the synthesis of resins, with urea-formaldehyde (UF) resins, phenolic-formaldehyde resins, pentaerythritol, and other resins accounting for about 92% of Canadian consumption. About 6% of uses were related to fertilizer production, while 2% of the formaldehyde was used for various other purposes, such as preservatives and disinfectants (Environment Canada, 1997b). Formaldehyde can be used in a variety of industries, including the medical, detergent, cosmetic, food, rubber, fertilizer, metal, wood, leather, petroleum, and agricultural industries (IPCS, 1989), and as a hydrogen sulfide scavenger in oil operations (Tiemstra, 1989).

Formaldehyde is often added to cosmetics, in which it acts as a preservative and an antimicrobial agent. Its use in cosmetics is regulated or voluntarily restricted. In Canada, for example, formaldehyde is acceptable for use in non-aerosol cosmetics, provided the concentration does not exceed 0.2% (R. Green, personal communication, 1994). It is also included in the Cosmetic Notification Hot List, with the recommendation to limit its concentration in cosmetics to less than 0.3%, except for fingernail hardeners, for which a maximum concentration of 5% applies (A. Richardson, personal communication, 1999).

In the agriculture industry, formaldehyde has been used as a fumigant, as a preventative for mildew and spelt in wheat, and for rot in oats. It has also been used as a germicide and fungicide for plants and vegetables and as an insecticide for destroying flies and other insects. In Canada, formaldehyde is registered as a pesticide under the Pest Control Products Act; about 131 tonnes are applied annually for pest control. Approximately 80% of the slow-release fertilizer market is based on UF-containing products (ATSDR, 1999; HSDB, 1999). In Canada, there are currently 59 pest control products containing formaldehyde registered with the Pest Management Regulatory Agency. Formaldehyde is present as a formulant in 56 of these products, at concentrations ranging from 0.02% to 1% by weight. Formaldehyde is an active ingredient in the remaining three products, at concentrations ranging from 2.3% to 37% in the commercially available products (G. Moore, personal communication, 2000).

Formaldehyde is also used as an antibacterial agent in processing of foodstuffs. For example, the Food and Drugs Act allows up to 2 ppm (i.e., 2 mg/kg) formaldehyde in maple syrup resulting from the use of paraformaldehyde to deter bacterial growth in the tap holes of maple trees in Canada (M. Feeley, personal communication, 1996). Formaldehyde is also registered as a feed under the Feed Act in Canada.

The sections below summarize the available information on the distribution and fate of formaldehyde released into the environment. More detailed fate information is provided in Environment Canada (1999a).

Formaldehyde emitted to air primarily reacts with photochemically generated hydroxyl radicals in the troposphere or undergoes direct photolysis (Howard et al., 1991; US EPA, 1993). Minor processes include reactions with nitrate radicals, hydroperoxyl radicals, hydrogen peroxide, ozone, and chlorine (US EPA, 1993). Small amounts of formaldehyde may also transfer into rain, fog, and clouds or be removed by dry deposition (Warneck et al., 1978; Zafiriou et al., 1980; Howard, 1989; Atkinson et al., 1990; US EPA, 1993).

Reaction with the hydroxyl radical is considered to be the most important photooxidation process, based on the rate constants and the concentrations of the reactants (Howard et al., 1991; US EPA, 1993). Factors influencing the atmospheric lifetime of formaldehyde, such as time of day, intensity of sunlight, temperature, etc., are mainly those affecting the availability of hydroxyl and nitrate radicals (US EPA, 1993). The atmospheric half-life of formaldehyde, based on hydroxyl radical reaction rate constants, is calculated to be between 7.1 and 71.3 h (Atkinson, 1985; Atkinson et al., 1990). Products that can be formed from hydroxyl radical reaction include water, formic acid, carbon monoxide, and the hydroperoxyl/formaldehyde adduct (Atkinson et al., 1990).

Photolysis can take two pathways. The dominant pathway produces stable molecular hydrogen and carbon monoxide. The other pathway produces the formyl radical and a hydrogen atom (Lowe et al., 1980), which react quickly with oxygen to form the hydroperoxyl radical and carbon monoxide. Under many conditions, the radicals from photolysis of formaldehyde are the most important net source of smog generation (US EPA, 1993). When the rates of these reactions are combined with estimates of actinic radiance, the estimated half-life of formaldehyde due to photolysis is 1.6 h in the lower troposphere at a solar zenith angle of 40° (Calvert et al., 1972). A half-life of 6 h was measured based on simulated sunlight (Lowe et al., 1980).

The nighttime destruction of formaldehyde is expected to occur by the gas-phase reaction with nitrate radicals (US NRC, 1981); this tends to be more significant in urban areas, where the concentration of the nitrate radical is higher than in rural areas (Altshuller & Cohen, 1964; Gay & Bufalini, 1971; Maldotti et al., 1980). A half-life of 160 days was calculated using an average atmospheric nitrate radical concentration typical of a mildly polluted urban centre (Atkinson et al., 1990), while a half-life of 77 days was estimated based on measured rate constants (Atkinson et al., 1993). Nitric acid and formyl radical have been identified as products of this reaction. They react rapidly with atmospheric oxygen to produce carbon monoxide and hydroperoxyl radicals, which can react with formaldehyde to form formic acid. However, because of this rapid back-reaction, the reaction of nitrate radicals with formaldehyde is not expected to be a major loss process under tropospheric conditions.

Overall half-lives for formaldehyde in air can vary considerably under different conditions. Estimations for atmospheric residence time in several US cities ranged from 0.3 h under conditions typical of a rainy winter night to 250 h under conditions typical of a clear summer night (assuming no reaction with hydroperoxyl radicals) (US EPA, 1993). During the daytime, under clear sky conditions, the residence time of formaldehyde is determined primarily by its reaction with the hydroxyl radical. Photolysis accounted for only 2–5% of the removal.

Given the generally short daytime residence times for formaldehyde, there is limited potential for long-range transport of this compound. However, in cases where organic precursors are transported long distances, secondary formation of formaldehyde may occur far from the actual anthropogenic sources of the precursors (Tanner et al., 1994).

Because of its high solubility in water, formaldehyde will transfer into clouds and precipitation. A washout ratio (concentration in rain/concentration in air) of 73 000 at 25 °C is estimated by Atkinson (1990). Gas-phase organic compounds that have a washout ratio of greater than 105 are generally estimated to be efficiently "rained out" (California Air Resources Board, 1993). Based on the washout ratio, the wet deposition (removal of gases and particles by precipitation) of formaldehyde could be significant as a tropospheric loss process (Atkinson, 1989). However, Zafiriou et al. (1980) estimated that rainout was responsible for removing only 1% of formaldehyde produced in the atmosphere by the oxidation of methane. Warneck et al. (1978) showed that washout is important only in polluted regions. Nevertheless, it is expected that wet deposition can lead to a somewhat shorter tropospheric lifetime of formaldehyde than that calculated from gas-phase processes alone.

In water, formaldehyde is rapidly hydrated to form a glycol. Equilibrium favours the glycol (Dong & Dasgupta, 1986); less than 0.04% by weight of unhydrated formaldehyde is found in highly concentrated solutions (Kroschwitz, 1991). In surface water or groundwater, formaldehyde can be biodegraded (US EPA, 1985; Howard, 1989). Incorporated into atmospheric water, formaldehyde or its hydrate can be oxidized.

Formaldehyde is degraded by various mixed microbial cultures obtained from sludges and sewage (Kitchens et al., 1976; Verschueren, 1983; US EPA, 1985). Formaldehyde in lake water decomposed in approximately 30 h under aerobic conditions at 20 °C and in approximately 48 h under anaerobic conditions (Kamata, 1966). Howard et al. (1991) estimated half-lives of 24–168 h in surface water and 48–336 h in groundwater based on scientific judgement and estimated aqueous aerobic biodegradation half-lives.

When incorporated from air into cloud water, fog water, or rain, formaldehyde can react with aqueous hydroxyl radicals in the presence of oxygen to produce formic acid, water, and hydroperoxide (aqueous). The formaldehyde glycol can also react with ozone (Atkinson et al., 1990).

Because of its low organic carbon/water partition coefficient (K_oc) and high water solubility, formaldehyde is not expected to significantly sorb to suspended solids and sediments from water. Biotic and abiotic degradation are expected to be significant processes affecting the fate of formaldehdye in sediment (US EPA, 1985; Howard, 1989).

Formaldehyde is not expected to adsorb to soil particles to a great degree and would be considered mobile in the soil, based on its estimated K_oc. According to Kenaga (1980), compounds with a K_oc of <100 are considered to be moderately mobile. Formaldehyde can be transported to surface water through runoff and to groundwater as a result of leaching. Parameters other than K_oc affecting its leaching to groundwater include the soil type, the amount and frequency of rainfall, the depth of the groundwater, and the extent of degradation of formaldehyde. Formaldehyde is susceptible to degradation by various soil microorganisms (US EPA, 1985). Howard et al. (1991) estimated a soil half-life of 24–168 h, based on estimated aqueous aerobic biodegradation half-lives.

In view of the very low bioconcentration factor of 0.19, based on a log octanol/water partition coefficient (K_ow) of 0.65 (Veith et al., 1980; Hansch & Leo, 1981), formaldehyde is not expected to bioaccumulate. When examined, bioconcentration was not observed in fish or shrimp (Stills & Allen, 1979; Hose & Lightner, 1980).

Fugacity modelling was carried out to provide an overview of key reaction, intercompartment, and advection (movement out of a system) pathways for formaldehyde and its overall distribution in the environment. A steady-state, non-equilibrium model (Level III fugacity model) was run using the methods developed by Mackay (1991) and Mackay & Paterson (1991). Assumptions, input parameters, and results are presented in Mackay et al. (1995) and Environment Canada (1999a).

Based on formaldehyde’s physical/chemical properties, Level III fugacity modelling indicates that when formaldehyde is continuously discharged into one medium, most of it can be expected to be present in that medium (Mackay et al., 1995; DMER & AEL, 1996). However, given the uncertainties relating to use of pseudo-solubility, hydration in water, and the complex atmospheric formation and degradation processes for formaldehyde, quantitative estimates of mass distribution are not considered reliable.

Data on concentrations in the environment primarily from the source country of the national assessment on which the CICAD is based (i.e., Canada) are presented here as a basis for the sample risk characterization. Patterns of exposure in other countries are expected to be similar, although quantitative values may vary.

6.1.1 Ambient air

Formaldehyde was detected (detection limit 0.042 ppb [0.05 µg/m³]) in 3810 of 3842 24-h samples from rural, suburban, and urban areas, collected at 16 sites in six provinces surveyed from August 1989 to August 1998 (Environment Canada, 1999a). Concentrations ranged from below the detection limit (0.042 ppb [0.05 µg/m³]) to maxima of 22.9 ppb (27.5 µg/m³) for eight urban sites, 10.03 ppb (12.03 µg/m³) for two suburban sites, 7.59 ppb (9.11 µg/m³) for two rural sites considered to be affected by urban and/or industrial influences, and 8.23 ppb (9.88 µg/m³) for four rural sites considered to be regionally representative. Long-term (1 month to 1 year) mean concentrations for these sites ranged from 0.65 to 7.30 ppb (0.78 to 8.76 µg/m³). The single highest 24-h concentration measured was 22.9 ppb (27.5 µg/m³), obtained for an urban sample collected from Toronto, Ontario, on 8 August 1995. Available data indicate that levels are highest between June and August, and there is no evidence that concentrations of formaldehyde were systematically increasing or decreasing at these sites over this 9-year period (Health Canada, 2000).

Atmospheric measurements made in 1992 during the dark winter and sunlit spring of an extremely remote site at Alert, Nunavut, ranged from 0.033 to 0.70 ppb (0.04 to 0.84 µg/m³) on a 5-min basis (detection limit 0.033 ppb [0.04 µg/m³]), with a mean of 0.40 ppb (0.48 µg/m³) (De Serves, 1994).

In air near a forest products plant in Canada, the maximum 24-h average concentrations for three 3-month periods between March 1995 and March 1996 ranged from 1.43 to 3.67 ppb (1.71 to 4.40 µg/m³) (detection limit not specified) (Environment Canada, 1997b).

6.1.2 Indoor air

Data concerning concentrations of formaldehyde in residential indoor air from seven studies conducted in Canada between 1989 and 1995 were examined (Health Canada, 2000). Despite differences in sampling mode and duration (i.e., active sampling for 24 h or passive sampling for 7 days), the distributions of concentrations were similar in five of the studies. The median, arithmetic mean, 95th percentile, and 99th percentile concentrations of the pooled data (n = 151 samples) from these five studies were 25, 30, 71, and 97 ppb (30, 36, 85, and 116 µg/m³), respectively (Health Canada, 2000). In view of the potential for less dilution from indoor sources in Canadian residential structures owing to lower average air exchange rates due to energy conservation, levels of formaldehyde in indoor air in residences located in warmer climates might be expected to be less. Identified values measured in non-workplace indoor air in other countries are, however, similar to those reported here.

Concurrent 24-h measurements in outdoor air and indoor air of Canadian residences were available from some of these studies. Average concentrations of formaldehyde were an order of magnitude higher in indoor air than in outdoor air, indicating the presence of indoor sources of formaldehyde and confirming similar findings in other countries (IPCS, 1989; ATSDR, 1999). Information concerning the presence of environmental tobacco smoke (ETS) in the homes sampled was available from some of these studies; however, there was no clear indication that concentrations of formaldehyde were greater in homes where ETS was present. Acetaldehyde, rather than formaldehyde, is the most abundant carbonyl compound in mainstream and sidestream cigarette smoke. Based on data from the USA and elsewhere, ETS does not increase concentrations of formaldehyde in indoor air, except in areas with high rates of smoking and minimal rates of ventilation (Godish, 1989; Guerin et al., 1992).

Data from several studies indicate that various cooking activities may contribute to the elevated levels of formaldehyde sometimes present in indoor air (Health Canada, 2000). In recent work from the USA, the emission rate of formaldehyde from meat charbroiling over a natural gas-fired grill in a commercial facility was higher (i.e., 1.38 g/kg of meat cooked) than emission rates of all other VOCs measured except for ethylene (Schauer et al., 1999).

6.1.3 Water

Representative data concerning concentrations in drinking-water in Canada were not available. The concentration of formaldehyde in drinking-water is likely dependent upon the quality of the raw source water and purification steps (Krasner et al., 1989). Ozonation may slightly increase the levels of formaldehyde in drinking-water, but subsequent purification steps may attenuate these elevated concentrations (Huck et al., 1990). Elevated concentrations have been measured in US houses equipped with polyacetal plumbing elbows and tees. Normally, an interior protective coating prevents water from contacting the polyacetal resin (Owen et al., 1990). However, if routine stress on the supply lines results in a break or fracture of the coating, water may contact the resin directly. The resultant concentrations of formaldehyde in the water are largely determined by the residence time of the water in the pipes. Owen et al. (1990) estimated that at normal water usage rates in occupied dwellings, the resulting concentration of formaldehyde in water would be about 20 µg/litre. In general, concentrations of formaldehyde in drinking-water are expected to be less than 100 µg/litre (IPCS, 1989; IARC, 1995).

Concentrations of formaldehyde in raw water from the North Saskatchewan River were measured at the Rossdale drinking-water treatment plant in Edmonton, Alberta, Canada. Concentrations between March and October 1989 averaged 1.2 µg/litre, with a peak value of 9.0 µg/litre. These concentrations were influenced by climatological events such as spring runoff, major rainfall events, and the onset of winter, as evidenced by concentration increases during spring runoff and major rainfall and concentration decreases (<0.2 µg/litre) following river freeze-up (Huck et al., 1990).

Anderson et al. (1995) measured formaldehyde concentrations in the raw water of three drinking-water treatment pilot plants in Ontario, Canada. The study included three distinct types of surface waters, covering a range of characteristics and regional influences: a moderately hard waterway with agricultural impacts (Grand River at Brantford), a soft, coloured river (Ottawa River at Ottawa), and a river with moderate values for most parameters, typical of the Great Lakes waterways (Detroit River at Windsor). Concentrations were less than the detection limit (1.0 µg/litre) and 8.4 µg/litre in raw water samples collected on 2 December 1993 and 15 February 1994, respectively, from the Detroit River. In the Ottawa River, concentrations were below the detection limit (1.0 µg/litre) in three profiles taken between 12 April and 7 June 1994. In the Grand River, a mean concentration of 1.1 µg/litre was obtained for seven sampling dates between 11 May and 21 June 1994.

The highest reported concentration from one of the four plants reporting releases for 1997 (Environment Canada, 1999b) was a 1-day mean of 325 µg/litre, with a 4-day mean of 240 µg/litre (Environment Canada, 1999a).

Extensive monitoring of groundwater from a Canadian site of production and use of formaldehyde included 10 samples in which formaldehyde concentrations were below the detection limit (50 µg/litre) and 43 samples with concentrations ranging from 65 to 690 000 µg/litre (mean of two duplicates) from November 1991 to February 1992 (Environment Canada, 1997b). Data had been collected as part of a monitoring programme to delineate the boundaries of groundwater contamination at the facility and were used to design a groundwater containment and recovery system. Formaldehyde was not detected in samples taken from outside the contaminated zone.

Quarterly analyses of five monitoring wells on the property of a Canadian plant that produces UF resins were carried out during 1996–1997. Concentrations ranged from below the detection limit (50 µg/litre) to 8200 µg/litre, with an overall median of 100 µg/litre. Concentrations for different wells indicated little dispersion from wells close to the source of contamination (Environment Canada, 1997b).

Groundwater samples collected from wells downstream from six cemeteries in Ontario, Canada, contained concentrations of formaldehyde of 1–30 µg/litre (detection limit not specified), although a blank sample contained 7.3 µg/litre in these analyses (Chan et al., 1992).

Concentrations of formaldehyde in rain ranged from 0.44 µg/litre (near Mexico City) to 3003 µg/litre (during the vegetation burning season in Venezuela; anthropogenic sources). Mean concentrations ranged from 77 µg/litre (in Germany) to 321 µg/litre (during the non-burning season in Venezuela). In snow, concentrations of formaldehyde ranged from 18 to 901 µg/litre in California, USA. A mean snow concentration of 4.9 µg/litre is reported for Germany. In fog water, concentrations of 480–17 027 µg/litre have been measured in the Po valley, Italy, with a mean of 3904 µg/litre (Environment Canada, 1999a).

6.1.4 Sediment and soil

No data were identified on concentrations of formaldehyde in sediments in the source country (Canada).

Concentrations in soil were measured at manufacturing plants that use phenol/formaldehyde resins. At a plywood plant, six soil samples collected in 1991 contained formaldehyde concentrations of 73–80 mg/kg, with a mean of 76 mg/kg (detection limit not specified) (G. Dinwoodie, personal communication, 1996). At a fibreglass insulation plant, formaldehyde was not detected (detection limit 0.1 mg/kg) in soil samples collected in 1996 from six depths at four industrial areas on-site. Formaldehyde was also not detected in samples taken from a non-industrial site 120 km away from the plant.

6.1.5 Biota

No data were identified on concentrations of formaldehyde in biota in the source country (Canada).

6.1.6 Food

There have been no systematic investigations of levels of formaldehyde in a range of foodstuffs as a basis for estimation of population exposure (Health Canada, 2000). Although formaldehyde is a natural component of a variety of foodstuffs (IPCS, 1989; IARC, 1995), monitoring has generally been sporadic and source directed. Available data suggest that the highest concentrations of formaldehyde naturally occurring in foods (i.e., up to 60 mg/kg) are in some fruits (Möhler & Denbsky, 1970; Tsuchiya et al., 1975) and marine fish (Rehbein, 1986; Tsuda et al., 1988).

Formaldehyde develops postmortem in marine fish and crustaceans, from the enzymatic reduction of trimethylamine oxide to formaldehyde and dimethylamine (Sotelo et al., 1995). While formaldehyde may be formed during the ageing and deterioration of fish flesh, high levels do not accumulate in the fish tissues, due to subsequent conversion of the formaldehyde formed to other chemical compounds (Tsuda et al., 1988). However, formaldehyde accumulates during the frozen storage of some fish species, including cod, pollack, and haddock (Sotelo et al., 1995). Formaldehyde formed in fish reacts with protein and subsequently causes muscle toughness (Yasuhara & Shibamoto, 1995), which suggests that fish containing the highest levels of formaldehyde (e.g., 10–20 mg/kg) may not be considered palatable as a human food source.

Higher concentrations of formaldehyde (i.e., up to 800 mg/kg) have been reported in fruit and vegetable juices in Bulgaria (Tashkov, 1996); however, it is not clear if these elevated levels arise during processing. Formaldehyde is used in the sugar industry to inhibit bacterial growth during juice production (ATSDR, 1999). In a study conducted by Agriculture Canada, concentrations of formaldehyde were higher in sap from maple trees that had been implanted with paraformaldehyde to deter bacterial growth in tap holes (Baraniak et al., 1988). The resulting maple syrup contained concentrations up to 14 mg/kg, compared with less than 1 mg/kg in syrup from untreated trees.

In other processed foods, the highest concentrations (i.e., 267 mg/kg) have been reported in the outer layer of smoked ham (Brunn & Klostermeyer, 1984) and in some varieties of Italian cheese, where formaldehyde is permitted for use under regulation as a bacteriostatic agent (Restani et al., 1992). Hexamethylenetetramine, a complex of formaldehyde and ammonia that decomposes slowly to its constituents under acid conditions, has been used as a food additive in fish products such as herring and caviar in the Scandinavian countries (Scheuplein, 1985).

Concentrations of formaldehyde in a variety of alcoholic beverages ranged from 0.04 to 1.7 mg/litre in Japan (Tsuchiya et al., 1994) and from 0.02 to 3.8 mg/litre in Brazil (de Andrade et al., 1996). In earlier work conducted in Canada, Lawrence & Iyengar (1983) compared levels of formaldehyde in bottled and canned cola soft drinks (7.4–8.7 mg/kg) and beer (0.1–1.5 mg/kg) and concluded that there was no significant increase in the formaldehyde content of canned beverages due to the plastic inner coating of the metal containers. Concentrations of 3.4 and 4.5 mg/kg in brewed coffee and 10 and 16 mg/kg in instant coffee were reported in the USA (Hayashi et al., 1986). These concentrations reflect the levels in the beverages as consumed.

Formaldehyde is used in the animal feed industry, where it is added to ruminant feeds to improve handling characteristics. The food mixture contains less than 1% formaldehyde, and animals may ingest as much as 0.25% formaldehyde in their diet (Scheuplein, 1985). Formalin has been added as a preservative to skim milk fed to pigs in the United Kingdom (Florence & Milner, 1981) and to liquid whey (from the manufacture of cheddar and cottage cheeses) fed to calves and cows in Canada. Maximum concentrations in the milk of cows fed whey with the maximum level of formalin tested (i.e., 0.15%) were up to 10-fold greater (i.e., 0.22 mg/kg) than levels in milk from control cows fed whey without added formalin (Buckley et al., 1986, 1988). In a more recent study, the concentrations of formaldehyde in commercial 2% milk and in fresh milk from cows fed on a typical North American dairy total mixed diet were determined. Concentrations in the fresh milk (i.e., from Holstein cows, morning milking) ranged from 0.013 to 0.057 mg/kg, with a mean concentration (n = 18) of 0.027 mg/kg, while concentrations in processed milk (i.e., 2% milk fat, partly skimmed, pasteurized) ranged from 0.075 to 0.255 mg/kg, with a mean concentration (n = 12) of 0.164 mg/kg. The somewhat higher concentrations in the commercial 2% milk were attributed to processing technique, packaging, and storage, but these factors were not assessed further (Kaminski et al., 1993).

The degree to which formaldehyde in various foods is bioavailable following ingestion is not known.

6.1.7 Consumer products

Formaldehyde and formaldehyde derivatives are present in a wide variety of consumer products (Preuss et al., 1985) to protect the products from spoilage by microbial contamination. Formaldehyde is used as a preservative in household cleaning agents, dishwashing liquids, fabric softeners, shoe care agents, car shampoos and waxes, carpet cleaning agents, etc. (IPCS, 1989). Levels of formaldehyde in hand dishwashing liquids and liquid personal cleansing products available in Canada are less than 0.1% (w/w) (A. McDonald, personal communication, 1996).

Formaldehyde has been used in the cosmetics industry in three principal areas: preservation of cosmetic products and raw materials against microbial contamination, certain cosmetic treatments such as hardening of fingernails, and plant and equipment sanitation (Jass, 1985). Formaldehyde is also used as an antimicrobial agent in hair preparations, lotions (e.g., suntan lotion and dry skin lotion), makeup, and mouthwashes and is also present in hand cream, bath products, mascara and eye makeup, cuticle softeners, nail creams, vaginal deodorants, and shaving cream (IPCS, 1989; ATSDR, 1999).

Some preservatives are formaldehyde releasers. The release of formaldehyde upon their decomposition is dependent mainly on temperature and pH. Information on product categories and typical concentrations for chemical products containing formaldehyde and formaldehyde releasers was obtained from the Danish Product Register Data Base (PROBAS) by Flyvholm & Andersen (1993). Industrial and household cleaning agents, soaps, shampoos, paints/lacquers, and cutting fluids comprised the most frequent product categories for formaldehyde releasers. The three most frequently registered formaldehyde releasers were bromonitropropanediol, bromonitrodioxane, and chloroallylhexaminium chloride (Flyvholm & Andersen, 1993).

Formaldehyde is present in the smoke resulting from the combustion of tobacco products. Estimates of emission factors for formaldehyde (e.g., µg/cigarette) from mainstream and sidestream smoke and from ETS have been determined by a number of different protocols for cigarettes in several countries.

A range of mainstream smoke emission factors from 73.8 to 283.8 µg/cigarette was reported for 26 US brands, which included non-filter, filter, and menthol cigarettes of various lengths (Miyake & Shibamoto, 1995). Differences in concentrations reflect differences in tobacco type and brand. More recent information is available from the British Columbia Ministry of Health from tests conducted on 11 brands of Canadian cigarettes. Mainstream smoke emission factors ranged from 8 to 50 µg/cigarette when tested under standard conditions.³

Levels of formaldehyde are higher in sidestream smoke than in mainstream smoke. Guerin et al. (1992) reported that popular commercial US cigarettes deliver approximately 1000–2000 µg formaldehyde/cigarette in their sidestream smoke. Schlitt & Knöppel (1989) reported a mean (n = 5) formaldehyde content of 2360 µg/cigarette in the sidestream smoke from a single brand in Italy. Information from the British Columbia Ministry of Health from tests conducted on 11 brands of Canadian cigarettes indicates that emission factors from sidestream smoke ranged from 368 to 448 µg/cigarette.³

Emission factors for toxic chemicals from ETS, rather than from mainstream or sidestream smoke, have also been determined. This is in part due to concerns that emission factors for sidestream smoke may be too low for reactive chemicals such as formaldehyde, due to losses in the various apparati used to determine sidestream smoke emission factors. Daisey et al. (1994) indicated that ETS emission factors for formaldehyde from six US commercial cigarettes ranged from 958 to 1880 µg/cigarette, with a mean of 1310 ± 349 µg/cigarette. Data concerning emission factors for formaldehyde from ETS produced by Canadian cigarettes were not identified.

Formaldehyde-releasing agents provide crease resistance, dimensional stability, and flame retardance for textiles and serve as binders in textile printing (Priha, 1995). Durable-press resins or permanent-press resins containing formaldehyde have been used on cotton and cotton/polyester blend fabrics since the mid-1920s to impart wrinkle resistance during wear and laundering. Hatch & Maibach (1995) identified nine major resins used. These differ in formaldehyde-releasing potential during wear and use.

Priha (1995) indicated that formaldehyde-based resins, such as UF resin, were once more commonly used for crease resistance treatment; more recently, however, better finishing agents with lower formaldehyde release have been developed. Totally formaldehyde-free crosslinking agents are now available, and some countries have legally limited the formaldehyde content of textile products. In 1990, the percentage of durable-press fabric manufactured in the USA finished with resins rated as having high formaldehyde release was 27%, about one-half the percentage in 1980, according to Hatch & Maibach (1995). It has been reported that the average level contained by textiles made in the USA is approximately 100–200 µg free formaldehyde/g (Scheman et al., 1998).

Piletta-Zanin et al. (1996) studied the presence of formaldehyde in moist baby toilet tissues and tested 10 of the most frequently sold products in Switzerland. One product contained more than 100 µg/g, five products contained between 30 and 100 µg/g, and the remaining four products contained less than 30 µg formaldehyde/g.

The emission of formaldehyde from building materials has long been recognized as a significant source of the elevated concentrations of formaldehyde frequently measured in indoor air. Historically, the most important indoor source among the many materials used in building and construction has been urea-formaldehyde foam insulation (UFFI), which is produced by the aeration of a mixture of UF resin and an aqueous surfactant solution containing a curing catalyst (Meek et al., 1985). UFFI was banned from use in Canada in 1980 and in the USA in 1982, although the US ban was subsequently overturned.

Pressed wood products (i.e., particleboard, medium-density fibreboard, and hardwood plywood) are now considered the major sources of residential formaldehyde contamination (Godish, 1988; Etkin, 1996). Pressed wood products are bonded with UF resin; it is this adhesive portion that is responsible for the emission of formaldehyde into indoor air. The emission rate of formaldehyde is strongly influenced by the nature of the material. Generally, release of formaldehyde is highest from newly made wood products. Emissions then decrease over time, to very low rates, after a period of years (Godish, 1988).

Concentrations of formaldehyde in indoor air are primarily determined by such factors as source strength (i.e., mass of substance released per unit time or per unit area), loading factors (i.e., the ratio of the surface area of a source [e.g., a particleboard panel] to the volume of an enclosed area [e.g., a room] where the source is present), and the presence of source combinations (Godish, 1988). Emission rates for formaldehyde from pressed wood products determined by emission chamber testing in Canada (Figley & Makohon, 1993; Piersol, 1995), the United Kingdom (Crump et al., 1996), and the USA (Kelly et al., 1999) are now typically less than 0.3 mg/m² per hour (Health Canada, 2000).

Formaldehyde release from pressed wood materials is greater in mobile homes than in conventional housing, as mobile homes typically have higher loading ratios (e.g., exceeding 1 m²/m³) of these materials. In addition, mobile homes can have minimal ventilation, are minimally insulated, and are often situated in exposed sites subject to temperature extremes (Meyer & Hermanns, 1985).

The use of scavengers (e.g., urea) to chemically remove unreacted formaldehyde while the curing process is taking place has been investigated as a control measure. Other reactants could be used to chemically modify the formaldehyde to a non-toxic derivative or convert it to a non-volatile reaction product. There has also been work to effectively seal the resin and prevent the residual formaldehyde from escaping (Tabor, 1988). Surface coatings and treatments (e.g., paper and vinyl decorative laminates) can significantly affect the potential for off-gassing and in some cases can result in an order of magnitude reduction in the emission rates for formaldehyde from pressed wood products (Figley & Makohon, 1993; Kelly et al., 1999). On the other hand, high emissions of formaldehyde during the curing of some commercially available conversion varnishes (also known as acid-catalyst varnishes) have been reported. An initial emission rate of 29 mg formaldehyde/m² per hour was determined for one product (McCrillis et al., 1999).

Emission rates for formaldehyde from carpets and carpet backings, vinyl floorings, and wall coverings in the source country (Canada) are now generally less than 0.1 mg/m² per hour (Health Canada, 2000).

This sample exposure estimation is based primarily on data on concentrations in the environment from the source country of the national assessment on which the CICAD is based (i.e., Canada) as a basis for the sample risk characterization. Owing to the ubiquitous sources of formaldehyde, which are likely similar in most countries, the overall magnitude of relative contributions from various sources of exposure presented here are expected to be reasonably representative of those in other parts of the world.

Estimates of the total daily intake of formaldehyde by six age groups of the general population of Canada were developed primarily to determine the relative contributions from various media. These estimates indicate that the daily intake of formaldehyde via inhalation is consistently less than that estimated for the ingestion of foodstuffs. However, it should be noted that critical effects associated with exposure to formaldehyde occur primarily at the site of first contact (i.e., the respiratory tract following inhalation and the aerodigestive tract, including oral and gastrointestinal mucosa, following ingestion) and are related to the concentration of formaldehyde in media to which humans are exposed, rather than to the total intake of this substance. For this reason, effects of exposure by inhalation and ingestion are addressed separately.

Due primarily to limitations of available data as a basis for characterization of exposure via ingestion, the principal focus of the assessment is airborne exposure. The less representative assessment for ingestion involves comparison of the concentration of formaldehyde in a limited number of food products with a tolerable concentration (ingestion).

A subset of data from the National Air Pollution Surveillance programme was selected to represent the range and distribution of concentrations to which the general population of Canada is currently assumed to be exposed via inhalation of outdoor air (Table 4).

Pooled data (n = 151) from five studies in which concentrations of formaldehyde were measured in the indoor air of residences in Canada between 1989 and 1995 were the basis for the range and distribution of concentrations to which the general population of Canada is currently assumed to be exposed via inhalation of residential indoor air (Health Canada, 2000) (Table 4).

The distribution of the time spent outdoors is arbitrarily assumed to be normal in shape with an arithmetic standard deviation of 2 h. In the probabilistic simulation, this distribution is truncated at 0 h and 9 h. The time spent indoors is calculated as 24 h minus the time spent outdoors. Individuals residing in warmer climates may spend a greater amount of time outdoors.

Estimates of the distribution of time-weighted 24-h concentrations of formaldehyde to which the general population is exposed were developed using simple random sampling (Monte Carlo analysis) with Crystal Ball™ Version 4.0 (Decisioneering, Inc., 1996) and simulations of 10 000 trials.

Two simulations were run. The parameters for the simulations and estimates of the median, arithmetic mean, and upper percentiles of the distributions of 24-h time-weighted average concentrations of formaldehyde determined from these probabilistic simulations are summarized in Table 5. Based on the assumptions underlying these probabilistic simulations, the estimates summarized in Table 5 indicate that one of every two persons would be exposed to 24-h average concentrations of formaldehyde in air of 20–24 ppb (24–29 µg/m³) or greater (i.e., median concentrations). Similarly, 1 in 20 persons (i.e., 95th percentile) would be exposed to 24-h average concentrations of formaldehyde in air of 67–78 ppb (80–94 µg/m³) or greater.

Based on limited data from the USA, concentrations in drinking-water may range up to approximately 10 µg/litre, in the absence of specific contributions from the formation of formaldehyde by ozonation during water treatment or from leaching of formaldehyde from polyacetal plumbing fixtures. One-half this concentration (i.e., 5 µg/litre) was judged to be a reasonable estimate of the average concentration of formaldehyde in Canadian drinking-water, in the absence of other data. Concentrations approaching 100 µg/litre were observed in a US study assessing the leaching of formaldehyde from domestic polyacetal plumbing fixtures, and this concentration is assumed to be representative of a reasonable worst case.

Similarly, very few data are available with which to estimate the range and distribution of concentrations of formaldehyde in foods to which the general population in Canada is exposed. According to the limited available data, concentrations of formaldehyde in food are highly variable. In the few studies of the formaldehyde content of foods in Canada, the concentrations of formaldehyde were within the range <0.03–14 mg/kg (Health Canada, 2000). However, the proportion of formaldehyde in foods that is bioavailable is unknown. Formaldehyde is a metabolite of methanol (IPCS, 1997).

Since the principal focus of the source document was on exposure in the general environment, the following provides only a brief overview of occupational exposure to formaldehyde. Occupational exposure to formaldehyde occurs in all workplaces, as the sources (e.g., combustion) are ubiquitous. Although it is not possible to accurately estimate the number of people

occupationally exposed to formaldehyde worldwide, it is likely to be several millions in industrialized countries alone (IARC, 1995). Industries with greatest potential exposure include health services, business services, printing and publishing, manufacture of chemicals and allied products, apparel and allied products, paper and allied products, personal services, machinery except clerical, transport equipment, and furniture and fixtures (IARC, 1995).

Formaldehyde occurs in occupational environments mainly as a gas. Formaldehyde-containing particles can also be inhaled when paraformaldehyde or powdered resins are being used in the workplace (IARC, 1995). These resins can also be attached to carriers, such as wood dust. Exposure may also occur dermally when formalin solutions or liquid resins come into contact with skin.

Exposure concentrations are highly variable between workplaces. The reported mean concentrations in the air of factories producing formaldehyde-based resins vary from <1 to >10 ppm (<1.2 to >12 mg/m³) (IARC, 1995). Formaldehyde-based glues have been used in the assembly of plywood and particleboard for over 30 years, and concentrations in these factories were usually >1 ppm (>1.2 mg/m³) before the mid-1970s but have been below that level more recently (IARC, 1995). The development of glues with lower formaldehyde content and better ventilation has reduced concentrations to about 1 ppm (1.2 mg/m³) or below (Kauppinen & Niemelä, 1985). Furniture varnishes may contain UF resins dissolved in organic solvents. As a result, workers are continuously exposed to an average level of about 1 ppm (1.2 mg/m³), but the levels have decreased slightly since 1975 (Priha et al., 1986). Coating agents and other chemicals used in paper mills may contain formaldehyde as a bactericide. The average levels related to lamination and impregnation of paper in mills in the USA, Sweden, and Finland were usually below 1 ppm (1.2 mg/m³), but variation can occur depending on the type of resin used and the product manufactured (IARC, 1995).

Formaldehyde has been used in the textile industry to produce crease-resistant and flame-retardant fabrics. These fabrics release formaldehyde into the air of the plants, leading to average concentrations of 0.2–2 ppm (0.24–2.4 mg/m³) in the late 1970s and 1980s. Measurements from the 1980s indicate that levels are dropping owing to the lower content of formaldehydes in fabrics (IARC, 1995).

Formaldehyde-based resins are commonly used as core binders in foundries. The mean levels of formaldehyde in core-making and post-core-making operations in the 1980s in Sweden and Finland were usually below 1 ppm (1.2 mg/m³). Formaldehyde-based plastics are used in the production of electrical parts, dishware, and various other products. The concentrations measured in such industries have usually been below 1 ppm (1.2 mg/m³), but much higher concentrations may occur, especially in factories creating moulded plastic products (IARC, 1995). The heating of bake-drying paints and soldering as well as the coating and development of photographic films can lead to the release of small amounts of formaldehyde in the workplace, but levels are usually well below 1 ppm (1.2 mg/m³) (IARC, 1995). Formaldehyde can also be released or formed during the preservation of fur, leather, barley, and sugar beets and during many other industrial operations. Some of these activities can result in heavy exposures, with high peak exposure occurring many times per day.

Formaldehyde is used as a tissue preservative and disinfectant in embalming fluids. The concentration of formaldehyde in the air during embalming is variable, but the mean level is about 1 ppm (1.2 mg/m³) (IARC, 1995). The mean concentrations of formaldehyde measured in hospitals range from 0.083 to 0.83 ppm (0.1 to 1.0 mg/m³), but the measurements were made during disinfection, which usually takes a relatively short time. Formalin solution is commonly used to preserve tissue samples in histopathology laboratories. The concentrations are sometimes high, but the mean level during exposure is about 0.5 ppm (0.6 mg/m³) (IARC, 1995).

Occupational exposure to formaldehyde may also occur in the construction industry, agriculture, forestry, and the service sector. Specialized workers can be exposed to very high concentrations. For example, workers who varnish wood floors are exposed to mean levels of 2–5 ppm (2.4–6.0 mg/m³) during each coat. Each worker may complete 5–10 coats of varnish per day (IARC, 1995). Formaldehyde is used in agriculture as a preservative for fodder and as a disinfectant for brooding houses. Although exposure is high at the time of application (7–8 ppm [8.4–9.6 mg/m³]), the annual exposure from this source remains very low (Heikkilä et al., 1991). Lumberjacks can also be exposed to formaldehyde from the exhaust of their chainsaws; however, the average exposure in Sweden and Finland was <0.1 ppm (<0.12 mg/m³) (IARC, 1995).

Formaldehyde is formed endogenously during the metabolism of amino acids and xenobiotics. In vivo, most formaldehyde is probably bound (reversibly) to macromolecules.

Owing to its reactivity with biological macromolecules, most of the formaldehyde that is inhaled is deposited and absorbed in regions of the upper respiratory tract with which the substance comes into first contact (Heck et al., 1983; Swenberg et al., 1983; Patterson et al., 1986). In rodents, which are obligate nose breathers, deposition and local absorption occur primarily in the nasal passages; in oronasal breathers (such as monkeys and humans), they likely occur primarily in the nasal passages and oral mucosa, but also in the trachea and bronchus. Species-specific differences in the actual sites of uptake of formaldehyde and associated lesions of the upper respiratory tract are determined by complex interactions among nasal anatomy, ventilation, and breathing patterns (e.g., nasal versus oronasal) (Monticello et al., 1991).

Formaldehyde produces intra- and intermolecular crosslinks within proteins and nucleic acids upon absorption at the site of contact (Swenberg et al., 1983). It is also rapidly metabolized to formate by a number of widely distributed cellular enzymes, the most important of which is NAD⁺-dependent formaldehyde dehydrogenase. Metabolism by formaldehyde dehydrogenase occurs subsequent to formation of a formaldehyde–glutathione conjugate. Formaldehyde dehydrogenase has been detected in human liver and red blood cells and in a number of tissues (e.g., respiratory and olfactory epithelium, kidney, and brain) in the rat.

Due to its deposition principally within the respiratory tract and rapid metabolism, exposure to concentrations of formaldehyde of 1.9 ppm (2.3 mg/m³), 14.4 ppm (17.3 mg/m³), or 6 ppm (7.2 mg/m³) has not been shown to result in an increase in concentrations of formaldehyde in blood in humans, rats, and monkeys, respectively (Heck et al., 1985; Casanova et al., 1988).

In animal species, the half-life of formaldehyde (administered intravenously) in the circulation ranges from approximately 1 to 1.5 min (Rietbrock, 1969; McMartin et al., 1979). Formaldehyde and formate are incorporated into the one-carbon pathways involved in the biosynthesis of proteins and nucleic acids. Owing to the rapid metabolism of formaldehyde, much of this material is eliminated in the expired air (as carbon dioxide) shortly after exposure. Excretion of formate in the urine is the other major route of elimination of formaldehyde (Johansson & Tjälve, 1978; Heck et al., 1983; Billings et al., 1984; Keefer et al., 1987; Upreti et al., 1987; Bhatt et al., 1988).

Information on non-neoplastic effects associated with the repeated inhalation or oral exposure of laboratory animals to formaldehyde is summarized in Tables 6 and 7, respectively.