INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 89
FORMALDEHYDE
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Geneva, 1989
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WHO Library Cataloguing in Publication Data
Formaldehyde.
(Environmental health criteria ; 89)
1.Formaldehyde
I.Series
ISBN 92 4 154289 6 (NLM Classification: QV 225)
ISSN 0250-863X
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR FORMALDEHYDE
1. SUMMARY AND CONCLUSIONS
1.1. Physical and chemical properties, and analytical methods
1.2. Sources of human and environmental exposure
1.3. Environmental transport, distribution, and transformation
1.4. Environmental levels and human exposure
1.5. Kinetics and metabolism
1.6. Effects on organisms in the environment
1.7. Effects on experimental animals
1.8. Effects on man
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
2.2. Physical and chemical properties
2.3. Conversion factors
2.4. Analytical methods
3. SOURCES IN THE ENVIRONMENT
3.1. Natural occurrence
3.2. Man-made sources
3.2.1. Production levels and processes
3.2.1.1 World production figures
3.2.1.2 Manufacturing processes
3.2.2. Uses
3.2.2.1 Aminoplastics (urea-formaldehyde resins and
melamine formaldehyde resins
3.2.2.2 Phenolic plastics (phenol formaldehyde resins)
3.2.2.3 Polyoxymethylene (polyacetal plastics)
3.2.2.4 Processing formaldehyde to other compounds
3.2.2.5 Medical and other uses
3.2.3. Sources of indoor environmental exposure
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1. Transport, and distribution
4.2. Transformation
4.2.1. Special products of degradation under specific conditions
4.2.2. Microbial degradation
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
5.1.1. Air
5.1.1.1 Air in the vicinity of industrial sources and
in urban communities
5.1.1.2 Emissions from industrial plants
5.1.1.3 Emissions from furnaces
5.1.1.4 Emissions from motor vehicles
5.1.2. Water
5.1.3. Soil
5.1.4. Food
5.2. Indoor air levels
5.2.1. Indoor exposure from particle boards
5.2.2. Indoor air pollution from urea-formaldehyde foam
insulation (UFFI)
5.2.3. Indoor air pollution from phenol-formaldehyde plastics
5.2.4. Exposure to indoor air containing cigarette smoke
5.3. General population exposure
5.3.1. Air
5.3.1.1 Smoking
5.3.2. Drinking-water
5.3.3. Food
5.3.4. Other routes of exposure
5.4. Occupational exposure
6. KINETICS AND METABOLISM
6.1. Absorption
6.1.1. Inhalation
6.1.1.1 Animal data
6.1.1.2 Human data
6.1.2. Dermal
6.1.3. Oral
6.2. Distribution
6.3. Metabolic transformation
6.4. Elimination and excretion
6.5. Retention and turnover
7. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
7.1. Microorganisms
7.2. Aquatic organisms
7.3. Terrestrial organisms
7.4. Plants
8. EFFECTS ON EXPERIMENTAL ANIMALS AND IN VITRO TEST SYSTEMS
8.1. Skin and eye irritation; sensitization
8.2. Single exposures
8.3. Short-term exposures
8.3.1. Inhalation studies
8.3.2. Oral studies
8.4. Long-term exposure and carcinogenicity
8.4.1. Inhalation
8.4.2. Dermal studies
8.4.3. Oral studies
8.5. Mutagenicity and related end-points
8.6. Reproduction, embryotoxicity, and teratogenicity
8.7. Mechanisms of carcinogenicity
8.7.1. Reactions with macromolecules
8.7.2. Cytotoxicity and cell proliferation
9. EFFECTS ON MAN
9.1. Sources of exposure
9.2. General population exposure
9.2.1. Sensory effects
9.2.2. Toxic effects
9.2.3. Respiratory effects
9.2.4. Dermal, respiratory tract, and systemic sensitization
9.2.4.1 Mucosal effects
9.2.4.2 Skin effects
9.2.4.3 Respiratory tract sensitization
9.2.4.4 Systemic sensitization
9.2.4.4.1 Allergic reaction following the
dental use of paraformaldehyde
9.2.5. Skin irritation
9.2.6. Genotoxic effects
9.2.7. Effects on reproduction
9.2.8. Other observations in exposed populations
9.2.9. Carcinogenic effects
10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT
10.1. Evaluation of human health risks
10.2. Evaluation of effects on the environment
10.3. Conclusions
11. RECOMMENDATIONS
11.1. Recommendations for future research
11.2. Recommendations for preventive measures
12. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR FORMALDEHYDE
Members
Professor O. Axelson, Department of Occupational Medicine, University
Hospital, Linköping, Sweden
Dr Birgitta Berglund, Department of Psychology, University of
Stockholm, Stockholm, Sweden
Professor D. Calamari, Institute of Agricultural Entomology, Faculty
of Agriculture, Milan, Italy ( Vice-Chairman )
Dr Ildiko Farkas, National Institute of Hygiene, Budapest, Hungary
Dr V.J. Feron, TNO-CIVO Toxicology and Nutrition Institute, AJ Zeist,
Netherlands
Dr O.J. Grundler, BASF AG, Ludwigshafen, Federal Republic of Germany
Professor J.M. Harrington, Institute of Occupational Health, University
of Birmingham, Birmingham, United Kingdom
Dr H.D. Heck, Chemical Industry Institute of Toxicology, Research
Triangle Park, USA
Dr R.F. Hertel, Fraunhofer Institute for Toxicology and Aerosol
Research, Hanover, Federal Republic of Germany ( Rapporteur )
Professor F. Klaschka, Department of Dermatology, Clinic and Polyclinic
in the Steglitz Clinic of the Free University of Berlin, Berlin
(West)
Dr Y. Kurokawa, Division of Toxicology, National Institute of Hygienic
Sciences, Tokyo, Japan
Dr Mathuros Ruchirawat, Department of Pharmacology, Faculty of Science,
Mahidol University, Bangkok, Thailand
Dr A. Schaich Freis, Danish National Institute of Occupational Health,
Copenhagen, Denmark
Dr A. Shaker, Environmental and Occupational Health Center, Ministry of
Health, Cairo, Egypt
Dr J.A.J. Stolwijk, Department of Epidemiology and Public Health, Yale
University School of Medicine, New Haven, USA ( Chairman )
Dr U. Thielebeule, Bezirks Hygiene Inspection, Rostock, German Demo-
cratic Republic
Observers
Dr J.C. Aubrun, (representing the European Council of Chemical Manu-
facturers) Courbevoie, France
Dr A. Basler, Federal Health Office, Berlin (West)
Dr J.-C. Berger, Health and Safety Directorate, Commission of the
European Communities, Luxembourg
Dr M.A. Cooke, University of Aston, Birmingham, United Kingdom
Mr W.R. Gaffey (representing Formaldehyde Institute), Department of
Medicine and Environmental Health, Monsanto Company, St. Louis, USA
Dr P. Messerer, BASF AG, Occupational Medicine and Health Protection,
Ludwigshafen, Federal Republic of Germany
Dr M.G. Penman (representing the European Chemical Industry Ecology
and Toxicology Centre), ICI, Central Toxicology Laboratory,
Macclesfield, United Kingdom
Dr N. Petri, BASF AG, Ludwigshafen, Federal Republic of Germany
Mr V. Quarg, Federal Ministry for Environment, Nature Conservation and
Nuclear Safety, Bonn, Federal Republic of Germany
Dr A.G. Smith (representing the European Chemical Industry Ecology and
Toxicology Centre), Ciba Geigy (UK), Macclesfield, United Kingdom
Dr K. Ulm, Institute for Medical Statistics and Epidemiology of the
Technical University of Munich, Munich, Federal Republic of Germany
Dr G. Vollmer, Federal Ministry for Environment, Nature Conservation
and Nuclear Safety, Bonn, Federal Republic of Germany
Secretariat
Dr D. Kello, Environmental Health Division, World Health Organization,
Regional Office for Europe, Copenhagen, Denmark
Dr E. Smith, International Programme on Chemical Safety, World Health
Organization, Geneva, Switzerland
Dr Linda Shuker, Division on Environmental Carcinogenesis, Inter-
national Agency for Research on Cancer, Lyons, France
NOTE TO READERS OF THE CRITERIA DOCUMENTS
Every effort has been made to present information in the criteria
documents as accurately as possible without unduly delaying their pub-
lication. In the interest of all users of the environmental health cri-
teria documents, readers are kindly requested to communicate any errors
that may have occurred to the Manager of the International Programme on
Chemical Safety, World Health Organization, Geneva, Switzerland, in
order that they may be included in corrigenda, which will appear in
subsequent volumes.
* * *
A detailed data profile and a legal file can be obtained from the
International Register of Potentially Toxic Chemicals, Palais des
Nations, 1211 Geneva 10, Switzerland (Telephone no. 7988400 -
7985850).
ENVIRONMENTAL HEALTH CRITERIA FOR FORMALDEHYDE
A WHO Task Group on Environmental Health Criteria for Formaldehyde
met at the Fraunhofer Institute for Toxicology and Aerosol Research,
Hanover, Federal Republic of Germany, from 9 to 13 November, 1987.
Professor U. Mohr opened the meeting and welcomed the members on behalf
of the host Institute, and Dr G. Vollmer spoke on behalf of the Federal
Government, which sponsored the meeting. Dr D. Kello, opened the meet-
ing on behalf of the Director-General, World Health Organization and
Dr E. Smith addressed the meeting on behalf of the three cooperating
organizations of the IPCS (UNEP/ILO/WHO). The Task Group reviewed and
revised the draft criteria document and made an evaluation of the risks
for human health and the environment of exposure to formaldehyde.
The drafts of this document were prepared by DR R.F. HERTEL and
DR G. ROSNER of the Fraunhofer Institute for Toxicology and Aerosol
Research, Hanover, Federal Republic of Germany. Available international
and national reviews of formaldehyde were consulted during the
preparation of the criteria document and are listed in the Appendix.
Dr E. Smith of the IPCS Central Unit was responsible for the overall
scientific contents of the document and Mrs M.O. Head of Oxford for the
editing.
The efforts of all who helped in the preparation and finalization
of the document are gratefully acknowledged.
* * *
Partial financial support for the publication of this criteria
document was kindly provided by the United States Department of Health
and Human Services, through a contract from the National Institute of
Environmental Health Sciences, Research Triangle Park, North Carolina,
USA - a WHO Collaborating Centre for Environmental Health Effects. The
United Kingdom Department of Health and Social Security also generously
contributed to the costs of printing.
1. SUMMARY AND CONCLUSIONS
1.1 Physical and Chemical Properties, and Analytical Methods
Formaldehyde is a flammable, colourless and readily polymerized gas
at ambient temperatures. The most common commercially available form is
a 30-50% aqueous solution. Formaldehyde is readily soluble in water,
alcohols, and other polar solvents, but has a low degree of solubility
in non-polar fluids.
Methanol or other substances are usually added to the solutions as
stabilizers to reduce intrinsic polymerization.
Formaldehyde decomposes at 150 °C into methanol and carbon monox-
ide; in general it is highly reactive with other chemicals. In sun-
light, it is readily photo-oxidized to carbon dioxide. It has a very
low n -octanol/water partition coefficient as well as a low soil-
absorption coefficient. The Henry constant is relatively high at
0.02 Pa x m3/mol.
Chemical analysis for formaldehyde involves direct extraction from
solid and liquid samples while absorption and/or concentration by ac-
tive (filtration) or passive (diffusion) sampling is necessary for air
samples. A variety of absorbants is available. The most widely used
methods of analysis are based on photometric determination. Low concen-
trations in air can be detected, after appropriate absorption, by means
of high performance liquid chromatography.
1.2 Sources of Human and Environmental Exposure
Formaldehyde is present in the environment as a result of natural
processes and from man-made sources. It is formed in large quantities
in the troposphere by the oxidation of hydrocarbons. Minor natural
sources include the decomposition of plant residues and the transform-
ation of various chemicals emitted by foliage.
Formaldehyde is produced industrially in large quantities and used
in many applications. Two other important man-made sources are automo-
tive exhaust from engines without catalytic converters, and residues,
emissions, or wastes produced during the manufacture of formaldehyde or
by materials derived from, or treated with it.
It has been calculated that the average rate of global production
from methane in the troposphere is of the order of 4 x 1011 kg/year,
while the total industrial production in recent years has been about
3.5 x 109 kg/year; the emission from automotive engines has not been
quantifiable on a global basis.
Formaldehyde has a variety of uses in many industries, it has medi-
cal applications as a sterilant and is used as a preservative in con-
sumer products, such as food, cosmetics, and household cleaning
agents.
One of the most common uses is in urea-formaldehyde and melamine-
formaldehyde resins. Urea-formaldehyde foam is used to insulate
buildings (UFFI); it can continue to emit formaldehyde after instal-
lation or constituting a source of persistent emission. Phenolic plas-
tics and polyacetal plastics are also important fields of application,
but are not expected to release formaldehyde.
There are several indoor environmental sources that can result in
human exposure including cigarettes and tobacco products, furniture
containing formaldehyde-based resins, building materials containing
urea-formaldehyde resins, adhesives containing formaldehyde used for
plastic surfaces and parquet, carpets, paints, disinfectants, gas
cookers, and open fireplaces.
Indoor areas of special importance are hospitals and scientific
facilities where formaldehyde is used as a sterilizing and preserving
agent, and living spaces, such as schools, kindergartens, and mobile
homes or apartments where there may be uncontrolled emissions of
formaldehyde from tobacco smoking, building materials, and furniture.
1.3 Environmental Transport, Distribution, and Transformation
Air is the most relevant compartment in the formaldehyde cycle,
most of the production and/or emissions, and degradation processes
occurring in the atmosphere.
Photolysis and reaction with hydroxyl radicals rapidly remove
formaldehyde from the atmosphere. The calculated half-life of each
process is a matter of hours, according to environmental conditions.
Transport of formaldehyde over distances is probably not of great
importance, nevertheless some organic compounds (air pollutants or
natural) from which formaldehyde can be derived are more stable and can
contribute to the formation of formaldehyde over considerable dis-
tances. The compound can be dissolved in the atmosphere in cloud and
rainwater and can be adsorbed as an atmospheric aerosol.
The value of the Henry constant suggests that formaldehyde in
aqueous solution is less volatile than water and that volatilization
from an aquatic environment is not expected under normal environmental
conditions. The high water solubility and the low n -octanol/water par-
tition coefficient suggest that adsorption on suspended solids and
partition in sediments is not significant. In water, formaldehyde is
rapidly (days) biodegraded by several species of microorganisms, pro-
vided the concentration is not too high. Formaldehyde is also readily
biodegradable in the soil. Because the soil adsorption coefficient is
very low, leaching occurs easily and mobility in soil is very high.
As it has a low n -octanol-water partition coefficient (log Pow),
formaldehyde is not be expected to bioaccumulate in aquatic organisms.
Furthermore, aquatic organisms are able to metabolize and transform it
through various metabolic pathways.
1.4 Environmental Levels and Human Exposure
Air concentrations of formaldehyde, near the ground in coastal,
mountain, or oceanic areas, ranged from 0.05 to 14.7 µg/m3, and the
majority of concentrations were within the range 0.1-2.7 µg/m3. In
the presence of man-made inputs, but away from any industrial
plants, mean values ranged from 7 to 12 µg/m3 with a few peaks up to
60-90 µg/m3. Data from different parts of the world were in good
agreement.
Rain water contains 110-174 µg/litre with peaks as high as
310-1380 µg/litre.
Emissions of formaldehyde from industrial processes vary widely
according to the types of industry. A considerable amount of formalde-
hyde comes from the exhaust emissions of motor vehicles, but this
varies greatly according to country and the grade of fuel.
There is some natural formaldehyde in raw food, levels ranging from
1 mg/kg up to 90 mg/kg, and accidental contamination of food may occur
through fumigation, the use of formaldehyde as a preservative, or
through cooking.
Tobacco smoke as well as urea-formaldehyde foam insulation and
formaldehyde-containing disinfectants are all important sources of
indoor formaldehyde.
Indoor air levels (non-workplace), measured in various countries,
depended on several factors, but mainly on the age of the building and
the building materials, the type of construction, and the ventilation.
They varied widely with different situations, but most ranged from a
minimum of 10 µg/m3 up to a maximum of 4000 µg/m3. In some cases,
low values were found in rooms with substantial sources of formaldehyde
emission. Disinfection of areas of hospitals produced the highest
levels, up to 20 000 µg/m3, but the personnel carrying out disin-
fection wear protective equipment and the areas are not occupied until
formaldehyde levels have fallen to 1.2 mg/m3 (1 ppm) and below. Levels
in rooms in which there is tobacco smoking can exceed 100 µg/m3.
The contributions of various atmospheric environments to the aver-
age human daily intake has been calculated to be 0.02 mg/day for out-
door air, 0.5-2 mg/day for indoor conventional buildings, < 1-10 mg/day
for buildings with sources of formaldehyde, 0.2-0.8 mg/day for work
places without occupational use of formaldehyde, 4 mg/day for work
places using formaldehyde, and 0-1 mg/day for environmental tobacco
smoke. Smoking 20 cigarettes per day corresponds to an intake of
1 mg/day through inhalation.
The formaldehyde concentration in drinking-water is generally
about 0.1 mg/litre resulting in a mean daily intake of 0.2 mg/day. The
quantity of formaldehyde ingested in food depends on the composition of
the meal and, for an average adult, may range from 1.5 to 14 mg/day.
1.5 Kinetics and Metabolism
Formaldehyde is readily absorbed in the respiratory and gastro-
intestinal tracts. Dermal absorption of formaldehyde appears to be very
slight. Increases in blood concentrations of formaldehyde were not de-
tected in rats or human beings exposed to formaldehyde through inha-
lation, because of rapid metabolism.
The metabolites of formaldehyde are incorporated into macromol-
ecules via one-carbon pathways or are eliminated in the expired air
(CO2) and urine. Formaldehyde that escapes metabolism can react with
macromolecules at the site of entry. DNA-protein cross-links have been
detected in tissues exposed directly to formaldehyde, but not in
tissues remote from the absorption site.
1.6 Effects on Organisms in the Environment
Formaldehyde is used as a disinfectant to kill viruses, bacteria,
fungi, and parasites, but it is only effective at relatively high
concentrations.
Algae, protozoa, and other unicellular organisms are relatively
sensitive to formaldehyde with acute lethal concentrations ranging
from 0.3 to 22 mg/litre. Aquatic invertebrates showed a wide range of
responses; some crustaceans are the most sensitive with median effec-
tive concentration (EC50) values ranging from 0.4 to 20 mg/litre. In
96-h tests on several fish species, the LC50 of formaldehyde for
adults ranged from a minimum of about 10 mg/litre to a maximum of sev-
eral hundred mg/litre; most species showed LC50 values in the range of
50-100 mg/litre. The responses of various species of amphibians are
similar to those of fish with median acute lethal concentrations
(LC50) ranging from 10 to 20 mg/litre for a 72-h exposure.
No data are available on long-term aquatic studies.
Eggs and larvae of some cattle parasites were killed by formal-
dehyde solution (1-5%) and some nematodes by a 37% solution, whereas
other nematodes were unaffected. In ruminant mammals, formaldehyde
protects dietary protein from microbial proteolysis in the rumen and
increases the efficiency of utilization of amino acids.
Few data are available on the effects of formaldehyde on plants.
However, from the agricultural use of urea-formaldehyde fertilizers, it
appears that, at recommended concentrations, formaldehyde does not
alter nitrogen and carbohydrate metabolism in plants, but that high
doses have negative effects on soil metabolism. Formaldehyde impairs
pollen germination.
1.7 Effects on Experimental Animals
Acute inhalation exposure of rats and mice to formaldehyde at very
high concentrations (120 mg/m3) produced salivation, dyspnoea,
vomiting, spasms, and death. At a concentration of 1.2 mg/m3, eye
irritation, decreased respiratory rate, increased airway resistance,
and decreased compliance appeared. Mice were more sensitive than
rats.
Short-term, repeated exposures (7-25 mg/m3) of rats produced
histological changes in the nasal epithelium, such as cell degener-
ation, inflammation, necrosis, squamous metaplasia, and increased cell
proliferation.
There is growing evidence that it is concentration rather than dose
that determines the cytotoxic effects of formaldehyde on the nasal
mucosa of rats; concentrations below 1 mg/m3 do not lead to cell
damage and hyperplasia.
Dose-related lesions observed in long-term, repeated inhalation
exposure (2.4, 6.7, or 17.2 mg/m3) were dysplasia and squamous meta-
plasia of the respiratory and olfactory epithelia, which regressed to
some extent after cessation of exposure.
Formaldehyde produced nasal squamous cell carcinomas in rats
exposed to high concentrations (17.2 mg/m3), which also caused severe
tissue damage. The concentration - response curve was extremely non-
linear with a disproportionate increase in tumour incidence at higher
concentrations. A low, but not statistically significant, incidence of
nasal tumours occurred at 6.7 mg/m3. No tumours were found at other
sites. Mice developed squamous cell carcinomas of the nasal cavity with
long-term exposure to 17.2 mg/m3, but this finding was not statisti-
cally significant. No tumours were found at other sites. No tumours
were found in hamsters.
Long-term oral administration of formaldehyde (0.02-5% in the
drinking-water) to rats was found to induce papillomas in the fore-
stomach.
Several skin initiation/promotion studies with formaldehyde did not
produce evidence of skin carcinogenicity in mice; the results with
respect to promotion were either negative or inconclusive.
1.8 Effects on Man
Formaldehyde has a pungent odour detectable at low concentrations,
and its vapour and solutions are known skin and eye irritants in human
beings. The common effects of formaldehyde exposure are various symp-
toms caused by irritation of the mucosa in the eyes and upper airways.
In the non-industrial indoor environment, sensory reactions are typical
effects, but there are large individual differences in the normal popu-
lation and between hyperreactive and sensitized people.
There are a few case reports of asthma-like symptoms caused by
formaldehyde, but none of these demonstrated a sensitization effect
(neither Type I nor Type IV) and the symptoms were considered to be due
to irritation. Skin sensitization is induced only by direct skin
contact with formaldehyde solutions in concentrations higher than
20 g/litre (2%). The lowest patch test challenge concentration in an
aqueous solution reported to produce a reaction in sensitized persons
was 0.05% formaldehyde.
The available human evidence indicates that formaldehyde does not
have a high carcinogenic potential. While some studies have indicated
an excess of cancer in exposed individuals or populations, only nasal
or nasopharyngeal tumours are likely to be causally related to formal-
dehyde exposure.
Formaldehyde does not have any adverse effects on reproduction and
is not teratogenic.
Formaldehyde in vitro interferes with DNA repair in human cells,
but there are no data relating to mutagenic outcomes.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1 Identity
Chemical formula: CH2O [HCHO]
Chemical structure: H
|
C = O
|
H
CAS registry number: 50-00-0
RTECS registry number: LP 8925000
UN number: 1198, 2209, 2213
EC numbers: 605-001-01 (solution 5% to < 25%)
605-001-02 (solution 1% to < 5%)
605-001-005 (solution > 25%)
IUPAC name: Methanal
Common synonyms: formaldehyde, methanal, methylene oxide,
oxymethylene, methylaldehyde, oxomethane
Common names for solutions
of formaldehyde: Formalin, Formol
Formaldehyde is a colourless gas at normal temperature and press-
ure, with a relative molecular mass of 30.03.
The most common commercially available form is a 30-50% aqueous
solution. Methanol or other substances are usually added to the sol-
ution as stabilizers to reduce intrinsic polymerization. The concen-
tration of methanol can be up to 15%. The concentration of other
stabilizers is of the order of several 100 mg/litre. Concentrated
liquid formaldehyde-water systems containing up to 95% formaldehyde are
obtainable, but the temperature necessary to maintain solution and
prevent separation of polymer increases from around room temperature to
120 °C as the solution concentration increases.
In solid form, formaldehyde is marketed as trioxane (CH2O)3,
and its polymer, paraformaldehyde, with 8-100 units of formaldehyde.
Paraformaldehyde has become technologically important.
2.2 Physical and Chemical Properties
Formaldehyde is a flammable, colourless, reactive, and readily
polymerized gas at normal temperature. The heat of combustion for
formaldehyde gas is 4.47 Kcal per gram. It forms explosive mixtures
with air and oxygen at atmospheric pressure. Flammability is reported
to range from 12.5 to 80 volume %, a 65-70% formaldehyde-air mixture
being the most readily flammable.
Formaldehyde is present in aqueous solutions as a hydrate and tends
to polymerize. At room temperature and a formaldehyde content of 30%
and more, the polymers precipitate and render the solution turbid.
Formaldehyde decomposes into methanol and carbon monoxide at
temperatures above 150 °C, although uncatalysed decomposition is slow
below 300 °C.
Under atmospheric conditions, formaldehyde is readily photo-
oxidized in sunlight to carbon dioxide. It reacts relatively quickly
with trace substances and pollutants in the air so that its half-life
in urban air, under the influence of sunlight, is short. In the absence
of nitrogen dioxide, the half-life of formaldehyde is approximately
50 min during the daytime; in the presence of nitrogen dioxide, this
drops to about 35 min (Bufalini et al., 1972).
Some physical and chemical properties of formaldehyde are presented
in Table 1.
Table 1. Physical and chemical properties of formaldehydea
------------------------------------------------------------
Relative molecular mass 30.03
Relative gas density (air = 1) 1.04
Melting point (°C) -118b
Boiling point (°C) -19.2b
Explosivity range in air (vol %) 7-73
(g/m3) 87-910
n -octanol/water partition -1
coefficient) (log Pow)
Specific reaction rate (k) with 15.10-18 m3/mol x s
OH radical (k OH )
Distribution water/air: Henry 0.02 Pa. m3/mol
constant (H)
Vapour pressure 101.3 kPa at -19 °C
52.6 kPa at -33 °C
------------------------------------------------------------
a Modified from: BGA (1985).
b From: Diem & Hilt (1976) and IARC (1982).
From: Neumüller (1981) and Windholz (1983).
2.3 Conversion Factors
1 ppm formaldehyde = 1.2 mg/m3 at 25 °C, 1066 mbar
1 mg formaldehyde/m3 = 0.83 ppm
A number of other conversion factors have been cited but, for this
draft, 0.83 has been used.
2.4 Analytical Methods
The most widely used methods for the determination of formaldehyde
are based on photometric measurements. Methods for the sampling and
determination are summarized in Table 2. The type of sampling depends
on the medium in which the formaldehyde is to be determined.
Direct and indirect methods can be used for sampling formaldehyde
in air. Indirect sampling (by means of a grab sample) is used when
formaldehyde is present in extremely low concentrations or where sam-
pling sites are removed from analytical laboratories. However, lack of
preconcentration means that a very sensitive analytical technique is
needed and there may also be absorption on the wall of the collecting
container. Alternatively, the sample may be preconcentrated by passing
air (active sampling) through an absorbing liquid. The collection ef-
ficiency of some liquids is reported in NRC (1981):
Water 80-85% (85% with ice bath)
1% aqueous bisulfite 94-100% (with ice bath)
3-methyl-2-benzothiazolene
hydrazine (MBTH) 84-92%
Chromotropic acid in concen-
trated sulfuric acid 99%
Concentrated sulfuric acid 99%
Formaldehyde in air may be collected in an absorbing medium by dif-
fusion (passive sampling). Aqueous or 50% 1-propanol solutions are used
for formaldehyde sampling. For active sampling, aqueous solutions and
solutions containing sulfite, 3-methyl-2-benzothiazolonehydrazone
(MBTH), chromotropic acid, or 2,4-dinitrophenylhydrazine (DNPH) are
generally used as the absorbing solution (Stern, 1976). For passive
sampling, sodium bisulfite (Kennedy & Hull, 1986), triethanolamine
(Prescher & Schönbude, 1983), and DNPH (Geisling et al., 1982) are used
and sorbents such as silica gel, aluminium oxide, and activated carbon,
sometimes specially pretreated, may be useful for taking samples at the
work place (DFG, 1982).
Table 2. Sampling and analytical methods for formaldehydea
--------------------------------------------------------------------------------------------------------
Method Sampling Analysis Sensitivity mg/litre (ppm) Interferences
15-min long-term
--------------------------------------------------------------------------------------------------------
Chromotropic acid: midget spectrophotometry 0.19 (0.16) 0.05 (0.04) phenol, other
NIOSH 3500 impinger (1 h) organic substances
Paraosaniline midget spectrophotometry 0.02 (0.02) 0.0006 (0.0005) sulfur dioxide
(original) impinger (8 h)
Paraosaniline midget spectrophotometry 0.05 (0.045) 0.0012 (0.001) sulfur dioxide
(modified) impinger (8 h)
Paraosaniline continuous colorimetric 0.06 (0.05) NA sulfur dioxide
(TGM-555)
MBTH absorber spectrophotometry 0.12 (0.10) 0.0036 (0.003)
(8 h)
Acetylacetone midget spectrophotometry 0.12 (0.10) --- other aldehydes,
spectrophotometric impinger amines, Sulfur
dioxide
Acetylacetone midget fluorimetry 0.05 (0.04) --- other aldehydes,
fluorimetric impinger amines, Sulfur
dioxide
2.4-DNPH aqueous midget HPLC 0.00007 0.000018 (0.000015)
ethanol impinger (0.00006) (1 h)
2.4-DNPH coated adsorbent HPLC 1.58 (1.32) 0.12 (0.10)
adsorbent tube (3 h)
NIOSH 3501 midget polarography 1.94 (1.62) 0.32 (0.27) other aldehydes
impinger (1.5 h)
OSHA acidic midget polarography 0.12 (0.10) 0.012 (0.01) acetaldehyde
hydrazine impinger (2.5 h)
-------------------------------------------------------------------------------------------------------
Table 2 (contd).
-------------------------------------------------------------------------------------------------------
Method Sampling Analysis Sensitivity mg/litre (ppm) Interferences
15-min long-term
-------------------------------------------------------------------------------------------------------
NIOSH 2502 reactive gas chromatography 9.38 (7.82) 0.6 (0.5)
adsorbent (4 h)
MIRAN continuous infrared 0.5 (0.4) NA multiple
Draeger reactive visual 0.6 (0.5) NA
adsorbent
Passive reactive spectrophotometry 3.84 (3.2) 0.12 (0.1)
monitor 3M adsorbent (CA) (8 h)
DuPont reactive spectrophotometry 9.6 (8) 0.3 (0.25)
adsorbent (CA) (8 h)
Air Quality reactive spectrophotometry 8.04 (6.7) 0.25 (0.21)
Research adsorbent (CA) (8 h)
Envirotech moist spectrophotometry 0.86 (0.72) 0.07 (0.06) other aldehydes
adsorbent (PUR) (8 h)
-------------------------------------------------------------------------------------------------------
a Modified from: Consensus Workshop on Formaldehyde (1984).
In 1981, the US National Institute of Occupational Safety and
Health (NIOSH) developed a solid-sorbent sampling method in which
samples collected can be stored for at least 14 days, at room tempera-
ture, before analysis, without loss of the analyte (Blade, 1983).
A method for the specific and sensitive determination of formal-
dehyde and other aldehydes and ketones in air has been described by
Binding et al. (1986). The specificity is based on subsequent high per-
formance liquid chromatographic separation. In air samples of 5 litres,
the detection limit is 0.05 ml/m3. The method is suitable for deter-
mining 5-min short-term values, as well as for continuous sampling over
a whole work shift.
A sensitive method for the determination of formaldehyde is based
on the Hantzsch reaction between acetylacetone (2,4-pentanedione) am-
monia and formaldehyde to form 3,5-diacetyl-1,4-dihydrolutidine. For-
maldehyde concentration can be determined colorimetrically (Nash, 1953)
or, more sensitively, by fluorimetry (Belman, 1963). The method is sub-
ject to interference by oxides of nitrogen, sulfur dioxide and ozone
but is less subject to interference by phenol than the chromotropic
acid method.
Photometric assay, using the sulfite-pararosaniline or the chromo-
tropic acid method, is usually applied to determine formaldehyde in
air. Automated analytical equipment has been developed.
Suitable analytical methods for monitoring air in the work-place
environment have been developed and recommended by the German Research
Society, DFG (1982) and by NIOSH (1984).
Menzel et al. (1981) described a special continuously-operating
measuring device, developed for determining formaldehyde in particle
boards for classification purposes; equipment for continuous measure-
ments using the pararosaniline method is available (Lyles et al.,
1965).
A simple colour reaction for the identification of urea formalde-
hyde resins and diisocyanates, carried out on the surface of wood-based
panels, has been described by Schriever (1981). This is based on the
reaction with p -dimethyl-aminocinnamaldehyde (DACA), resulting in a
red colour for both the resins and diisocyanates. The reaction of
purpald with formaldehyde is used to distinguish between urea formalde-
hyde resins and diisocyanates and it is possible to identify diiso-
cyanates when mixed with urea formaldehyde resins.
Water sampling may be by means of grab samples. Where water or
individual effluents are not homogeneous several subsamples may be
collected at different times from different sampling locations and
combined for analysis. If sample storage is necessary it should be
frozen or at least kept at 4 °C to prevent biological or chemical
degradation of formaldehyde. An organic solvent is used for extraction
of formaldehyde prior to analysis.
Concentrations of formaldehyde in the air in the range of
0.05-40 mg/m3 can be determined by the use of gas-detector tubes which
contain a colour reagent (Leichnitz, 1985). They cannot be relied upon
in the presence of other substances, e.g., tobacco smoke or below a
concentration of 0.05 mg/m3.
Formaldehyde can be extracted from foods using a solvent, such as
isopetane, or by steam distillation and extraction with ether. Before
extraction foodstuffs may be pulverized or homogenized.
The Association of Official Analytical Chemists (AOAC, 1984)
recommends the Helmer-Fulton Test (registration No. 20.081) for the
determination of formaldehyde in food and a spectrophotometric method
(Nash's reagent B; registry no. 31203) for the determination of formal-
dehyde in maple syrup.
3. SOURCES IN THE ENVIRONMENT
3.1 Natural Occurrence
Formaldehyde is naturally formed in the troposphere during the
oxidation of hydrocarbons. These react with OH radicals and ozone to
form formaldehyde and/or other aldehydes as intermediates in a series
of reactions that ultimately lead to the formation of carbon monoxide
and dioxide, hydrogen, and water (Zimmermann et al., 1978; Calvert,
1980).
Of the hydrocarbons found in the troposphere, methane occurs in the
highest concentration (1.18 mg/m3) in the northern hemisphere. Thus,
it provides the single most important source of formaldehyde (Lowe et
al., 1981).
Terpenes and isoprene, emitted by foliage, react with the OH radi-
cals, forming formaldehyde as an intermediate product (Zimmermann et
al., 1978). Because of their short life-times, this potentially impor-
tant source of formaldehyde is only important in the vicinity of vege-
tation (Lowe et al., 1981). The processes of formaldehyde formation and
degradation are discussed in section 4.
Formaldehyde is one of the volatile compounds formed in the early
stages of decomposition of plant residues in the soil (Berestetskii et
al., 1981).
3.2. Man-Made Sources
The most important man-made source of formaldehyde is automotive
exhaust from engines not fitted with catalytic converters (Berglund et
al., 1984; Guicherit & Schulting, 1985).
3.2.1 Production levels and processes
Table 3. World production figures for formaldehyde
--------------------------------------------------------
Year Area Quantity
(million kg)
--------------------------------------------------------
1978 USA, 16 companies 1073
1978 Canada, 4 companies 88
1979 USA, 16 companies 1003
1983 USA 905
1983 Germany, Federal Republic of,
11 companies 534
1983 Japan, 24 companies 403
1983 Major producing countries total 3200
1984 Major producing countries total 5780
1985 USA, 13 companies 941
--------------------------------------------------------
3.2.1.1 World production figures
The total production figures for formaldehyde are calculated on a
100% formaldehyde basis, though a variety of concentrations and forms
are produced. In 1984, the overall production capacity of major indus-
trial countries was approximately 5780 million kg/year (European Eco-
nomic Community 1700 kg/year, other Western European countries 530, USA
1440, Japan 640, other Asian countries and Australia 1240, Latin
America 230). Formaldehyde is also produced in Africa and the USSR. No
production figures for formaldehyde are available for eastern industri-
alized countries (Izmerov, 1982). Table 3 shows actual production fig-
ures for some western industrialized countries.
3.2.1.2 Manufacturing processes
Formaldehyde is produced by oxidizing methanol using two dif-
ferent procedures: (a) oxidation with silver crystals or silver
nets at 600-720 °C; and (b) oxidation with iron molybdenum oxides at
270-380 °C. Formaldehyde can be produced as a by-product of hydrocarbon
oxidation processes (Walker, 1975), but this method is not used commer-
cially.
Formaldehyde is an inexpensive starting material for a number of
chemical reactions, and a large number of products are made using for-
maldehyde as a base. Thus, it is important in the chemical industry.
3.2.2 Uses
Products manufactured using formaldehyde as an intermediate product
are listed in Table 4.
In animal nutrition, formaldehyde is used to protect dietary pro-
tein in ruminants (section 7.3). In the USA, formaldehyde is used as a
food additive to improve the handling characteristics of animal fat and
oilseed cattle food mixtures by producing a dry free-flowing product
(US FDA, 1980). Urea formaldehyde fertilizer is used in farming as a
source of nitrogen to improve the biological activity of the soil
(section 7.1).
3.2.2.1 Aminoplastics (urea formaldehyde resins and melamine formalde-
hyde resins)
Reaction of formaldehyde with urea or melamine yields urea formal-
dehyde (UF) or melamine formaldehyde (MF) (condensation process). These
synthetic resins are then delivered in solution or powder form at vari-
ous concentrations for further processing.
Table 4. Products produced with formaldehyde as a compounda
-----------------------------------------------------------------------------
Intermediate product Product
-----------------------------------------------------------------------------
urea formaldehyde resins particleboard, fibreboard, plywood,
paper treatment, textile treatment,
moulding compounds, surface coatings,
foam
phenolic resins plywood adhesives, insulation,
foundry binders
melamine resins surface coatings, moulding compounds,
laminates, wood adhesives
hexamethylenetetramine phenolic thermosetting, resin curing
agents, explosives
trimethylolpropane urethanes, lubricants, alkyd resins,
multifunctional acrylates
1,4-butanediol tetrahydrofuran, butyrolactone,
polybutylene terephthalate
polyacetal resins auto applications, plumbing components
pentaerythritol alkyd resins, synthetic lubricants,
tall oil esters, foundry resins,
explosives
urea formaldehyde concentrates controlled release fertilizers
-----------------------------------------------------------------------------
a From: Archibald (1982).
In the Federal Republic of Germany, about 70% of the total amount
of aminoplastics produced, i.e., 170 000 tonnes of formaldehyde per
annum, is used as glue in the manufacture of particle boards. These
boards are mostly manufactured from urea formaldehyde resins, the
water resistance of which is less than that of other resins, but is
sufficient for use in enclosed areas. About 10% of the aminoplastic
glues used are melamine-urea-formaldehyde resins, i.e., products where
melamine and urea are co-condensed with formaldehyde. Melamine resins
are more damp-proof than urea resins, but they are also more expens-
ive.
Formaldehyde can be released from such wood products over a long
period, even years, at a continuously declining rate. This occurs es-
pecially if the particle board material has become wet due to careless
handling, e.g., in construction work. The emission is composed of the
excess of formaldehyde used during actual production of the wood prod-
ucts and that produced by hydrolytic cleavage of unreacted methylol
groups in the resins. Melamine formaldehyde resins are generally more
stable and the amounts of formaldehyde emitted from them are much lower
(Deppe, 1982).
Aminoplastics are also used as glue for plywood and in the manufac-
ture of furniture. Paper saturated with aminoplastics and with a high
melamine-formaldehyde-resin content is used to coat surfaces of par-
ticle boards. Aminoplastics are used to increase the wet strength of
certain products in the paper industry.
Urea formaldehyde resins are used as urea formaldehyde foam insu-
lation (UFFI), or as reinforcing foams in the insulation of buildings
and in mining, where hollow areas are filled with foam. UFFI is pro-
duced by the aeration of a mixture of urea formaldehyde resin and an
aqueous surfactant solution containing a phosphoric acid curing cata-
lyst (Meek et al., 1985). This type of foam can emit formaldehyde, even
after completion of work, depending on factors such as process and
installation, age of building materials, temperature, and humidity.
Condensed aminoplastics of very low relative molecular mass serve
as textile treatments to make cotton and fabrics containing synthetic
fibres creaseproof and permanently pressed. In the USA, it is estimated
(CPSC, 1979) that approximately 85% of all fabrics used in the clothing
industry have been treated in this way. Extremely stable aminoplastics
are used in order to ensure that they will not degrade during the life-
time of the articles. Formaldehyde concentrations ranging from 1 to
3000 mg/kg were found in such fabrics in the early years of this type
of use (Schorr et al., 1974). However, residues of free formaldehyde
from the manufacturing process can largely be removed by heat treatment
with washing during the textile finishing process. In the last 10
years, the processing of finishing agents in the textile industry has
improved and textiles treated with formaldehyde-containing finishing
agents contain very little free formaldehyde and cannot cause allergic
contact dermatitis (Bille, 1981).
Compounds similar to those used in finishing textiles are used in
the tanning of leather. Another field of application is for amino-
plastics mixed with rock or wood dust, fibres, or synthetic pulp in
hard materials manufactured by hot moulding. They are used in electri-
cal engineering, e.g., in light switches, sockets, and in parts of
electrical motors; in mechanical engineering; in the motor-vehicle
industry; and for household articles, e.g., camping dishes, parts of
electrical household appliances, lamps, and plumbing components.
Aminoplastics are used in the paint industry as carriers in
binders for special types of lacquer and paint, e.g., for cars. In
agriculture, they are used as preservatives. They are also used in
carpet-cleaning agents in the form of foam resin.
The fields of application of aminoplastics in the Federal Republic
of Germany are given in Tables 5 and 6.
3.2.2.2 Phenolic plastics (phenol formaldehyde resins)
Phenolic plastics are synthetic resins in which formaldehyde is
condensed with phenols. Phenol, resorcinol, and cresols are among the
phenolic components. Owing to the stable binding of phenol and formal-
dehyde, formaldehyde should not be emitted from the final products made
of phenolic plastics, as long as there is no free formaldehyde
present.
As in the case of aminoplastics, the wood-working industry is a
major consumer.
Table 5. Uses of melamine formaldehyde resins in the Federal Republic of
Germany during 1981-82a
------------------------------------------------------------------
Area of use Proportion as Consumption
% of resin of formaldehyde
consumption (tonnes)
------------------------------------------------------------------
Adhesive resins for timber 30 12 000
products, especially particle
boards (adhesives)
Resin varnishes 36 14 500
Hardenable moulding material 10 4 000
for plastic products
Raw materials for paints 8 3 000
Paper and textile finishing 5 2 000
Other 11 4 500
------------------------------------------------------------------
a From: BASF (1984).
Other major areas of application are the production of hard
materials, similar to those produced from aminoplastics, as a moulding
material, and as a binder in enamel, paints, and lacquers.
Phenolic plastics are used as binders in the production of insu-
lating materials from rock wool or glass fibres, in brake linings,
abrasive materials, and moulded laminated plastics. They also serve as
binding agents for moulding sand in foundries. Fields of application of
phenolic plastics in the Federal Republic of Germany are listed in
Table 7.
Emissions of formaldehyde are produced when processing phenolic
plastics at high temperatures. Phenol and formaldehyde emissions during
moulding led to complaints in previous decades about annoying smells.
Now, resins have been improved to meet work-place environment standards
and emissions should not cause annoyance.
3.2.2.3 Polyoxymethylene (polyacetal plastics)
Polyoxymethylenes (POM) are another type of plastics produced by
polymerizing formaldehyde. Like the final products from phenolic plas-
tics, articles made of polyoxymethylene are not expected to emit
formaldehyde.
Polyoxymethylenes are harder, tougher, and longer-lasting than
other plastics and are used in many areas of application in which met-
allic materials were previously used. They are used in producing motor-
vehicle and machine parts that are subjected to mechanical or thermal
stress, parts for precision and communication engineering, parts for
household appliances, and plumbing fixtures.
Table 6. Uses of urea formaldehyde resins in the Federal Republic of
Germany during 1981-82a
------------------------------------------------------------------
Area of use Proportion as Consumption of
% of resin formaldehyde
consumption (tonnes)
------------------------------------------------------------------
Adhesive resins for timber 80 160 000
products, especially particle
boards (adhesives)
Paper finishing 4 8 000
Hardenable moulding material 4 8 000
for plastic products
Textile finishing 3 6 000
Resin varnishes for impregnating, 2 4 000
e.g., moulded, laminated plastics
Foam resins 2 4 000
for: building insulation 0.2
mining 1.0
amelioration 0.4
carpet-cleaning products 0.3
other purposes 0.1
Raw materials for paints 2 4 000
Binding agents for fibre 1 2 000
mats, etc.
Foundry resins 1 2 000
Other 1 2 000
------------------------------------------------------------------
a From: BASF (1984).
3.2.2.4 Processing formaldehyde to other compounds
Formaldehyde is an important raw material in the industrial syn-
thesis of a number of organic compounds.
In the Federal Republic of Germany during 1981-82, the chemical
industry processed 34% of all formaldehyde products to the following
derivative substances (BASF, 1984):
- 1,4 butane diol 10%
- pentaerythritol 6%
- methylenediphenyldiisocyanate 5%
- trimethylolpropane and neopentylglycol 4%
- hexamethylenetetramine 2%
- chelating agents (NTA, EDTA) 2%
- miscellaneous (e.g., dyes, dispersion, 5%
pesticides, perfumes, vitamins)
Table 7. Uses of phenolic plastic resins in the
Federal Republic of Germany during 1981-82a
------------------------------------------------------------------
Area of use Proportion as Consumption of
% of resin formaldehyde
consumption (tonnes)
------------------------------------------------------------------
Hardenable moulding material 23 9000
for plastic products
Adhesive resins for timber 20 8000
products, especially particle
boards (adhesives)
Binding agents for rock wool, 17 7000
glass wool, etc.
Raw materials for paints 14 5500
Foundry resins 7 3000
Resin varnishes for impregnating, 4 1500
e.g., moulded, laminated plastics
Abradant binders, e.g., for 3 1000
sandpaper
Binding agents for friction 3 1000
surfaces, e.g., brake linings
Rubber chemicals 2 1000
Other 7 3000
------------------------------------------------------------------
a From: BASF (1984).
3.2.2.5 Medical and other uses
The use of formaldehyde in medical and other fields is relatively
small (1.5% of the total production) compared with its use in the manu-
facture of synthetic resins and chemical compounds. However, its use in
these areas is of great significance for human beings, since it occurs
either as free formaldehyde and can therefore be easily liberated and
affect people (e.g., when used as a disinfectant) or it may reach many
people via various consumer goods, such as preservatives and cosmetics.
The use of formaldehyde for the preservation of organic material is of
historical importance.
Examples of fields of application are listed in Table 8.
Table 8. Use of products containing formaldehyde in medicinal
and other technical areasa
-------------------------------------------------------------------------
Area Use
-------------------------------------------------------------------------
Detergents and cleaning Preservative in soaps, detergents, cleaning
agents industry agents
Cosmetics industry Preservative in soaps, deodorants, shampoos,
etc; additive in nail hardeners and products
for oral hygiene
Sugar industry Infection inhibitor in producing juices
Medicine Disinfection, sterilization, preservation of
preparations
Petroleum industry Biocide in oil well-drilling fluids; auxiliary
agent in refining
Agriculture Preservation of grain, seed dressing, soil
disinfection, rot protection of feed, nitrogen
fertilizer in soils, protection of dietary
protein in ruminants (animal nutrition)
Rubber industry Biocide for latex; adhesive additive; anti-
oxidizer additive also for synthetic rubber
Metal industry Anti-corrosive agent; vehicle in vapour
depositing and electroplating processes
Leather industry Additive to tanning agents
Food industry Preservation of dried foods; disinfection of
containers; preservation of fish and certain
oils and fats; modifying starch for cold
swelling
Wood industry Preservative
Photographic industry Developing accelerator; hardener for gelatin
layers
-------------------------------------------------------------------------
a Modified from: BASF (1984).
(a) Disinfectants and sterilizing agents
At present, formaldehyde is the disinfectant with the broadest ef-
ficiency; its virucidal property makes it indispensable for disinfec-
tion in the clinical field. It is an important active substance in dis-
infectants that kill and inactivate microorganisms and are used in the
prevention and control of communicable diseases and hospital infections
(BGA, 1982). Agents containing formaldehyde are marketed as concen-
trated solutions and must be diluted appropriately by the user. These
concentrates usually contain 6-10% formaldehyde, occasionally up to
30%. The formaldehyde contents of the diluted mixtures lie between 0.3
and 0.5% and, in exceptional cases, 0.9%. Application of the solutions
is supposed to kill pathogenic organisms on the surfaces of objects.
The ensuing effect is proportional to the concentration of formal-
dehyde, length of application, and temperature (Spicher & Peters,
1981). The objects to be disinfected are either placed in the formal-
dehyde solution (e.g., disinfecting linen in washing machines) or wiped
and/or sprayed with the solutions. When disinfecting a room, a formal-
dehyde solution is either vaporized or atomized. Disinfecting in a
formaldehyde chamber and gas sterilization both work on a similar
principle, that is a mixture of formaldehyde and water vapour is pumped
into a special air-tight chamber in which the objects to be disinfected
or sterilized have been placed. This method is also used to disinfect
incubators for premature babies and haemodialysis equipment.
(b) Medicines
Pharmaceutical products containing formaldehyde are rarely used for
disinfecting the skin and mucous membranes, but formaldehyde is added
to pharmaceutical products as a preservative.
Root canal filling sealants containing paraformaldehyde are used in
dental surgery.
(c) Cosmetics
Formaldehyde is used as a preservative in cosmetics and in nail-
hardening agents. Traces can be found in cosmetics resulting from the
disinfecting of apparatus used in their manufacture. Furthermore, pro-
ducts containing formaldehyde are used for other purposes, e.g., anti-
perspirants and skin-hardening agents. The formaldehyde content of some
cosmetics has been reported to be up to 0.6% and is as high as 4.5% in
nail hardeners (Marzulli & Maibach, 1973; Consensus Workshop on Formal-
dehyde, 1984). Concentrations in dry-skin lotion, creme rinse, and
bubble bath oil are in the range of 0.4-0.6%. Present regulatory values
are given in section 11.
Formaldehyde is considered technically superior to a number of
other preservatives, especially in products with a high water content,
e.g., shampoos. As a preservative, formaldehyde also assures that the
product is germ-free, prevents microbial contamination during pro-
duction and packaging, multiplication of residual organisms during
storage, and re-contamination during use.
(d) Consumer goods and other products
The use of formaldehyde in consumer goods is intended to protect
the products from spoilage by microbial contamination.
It is used as a preservative in household cleaning agents, dish-
washing liquids, fabric softeners, shoe-care agents, car shampoos and
waxes, carpet cleaning agents, etc. As a rule, the formaldehyde concen-
tration is less than 1%. Disinfecting cleaning agents contain higher
concentrations (up to 7.5%) and are diluted before use.
Flooring adhesives contain formaldehyde. It is added to paper,
leather, dyes, wood preservatives, sealing agents for parquet floors,
as a preservative with fungicidal and bactericidal properties (see also
Table 4).
Formaldehyde is a component of reactive resins (urea formaldehyde
resins, melamine formaldehyde resins, phenol formaldehyde resins,
benzoguanomine formaldehyde, and polymers on a methyloacylamide and/or
methylomethacrylamide basis), which control the hardening properties of
lacquers and varnishes and are essential for the surface properties of
the treated products. The resins used for these purposes contain free
formaldehyde at concentrations of up to 3%, this means up to 0.3% in
ready-to-use varnishes (BASF, 1983). This free formaldehyde is emitted
during application. Thermal degradation of resins during the baking of
paints may cause additional emissions of formaldehyde.
3.2.3 Sources of indoor environmental exposure
The major man-made sources affecting human beings are in the indoor
environment. Primary sources include cigarette smoke, particle board
and plywood, furniture and fabrics, gases given off by heating systems,
and cooking.
Thus, the indoor levels of formaldehyde differ clearly from the
concentrations in the outdoor air. Indoor concentrations are influenced
by temperature, humidity, ventilation rate, age of the building, prod-
uct usage, presence of combustion sources, and the smoking habits of
occupants. When considering the indoor presence of formaldehyde, it is
necessary to differentiate between:
- Hospitals or other scientific facilities, where formaldehyde has to
be used as a disinfectant or preservative; and
- All other indoor areas, especially living spaces, schools, kinder-
gartens, and mobile homes where there may be uncontrolled emissions
of formaldehyde from sources such as smoking, building materials,
and furniture. This sector presents the specific problems in indoor
areas.
Possible sources of indoor formaldehyde emissions are:
- cigarettes and other tobacco products;
- particle boards;
- furniture; urea formaldehyde foam insulation (UFFI);
- gas cookers;
- open fireplaces;
- other building materials made with adhesives containing
formaldehyde, such as plastic surfaces and certain parquet
varnishes;
- carpeting, drapes, and curtains;
- paints, coatings, and wood preservatives; and
- disinfectants and sterilizing agents.
Other products containing formaldehyde do not noticeably contribute
to indoor exposure because of their stable formaldehyde binding, e.g.,
plastic articles made by moulding, or because of their low rate of
emission, e.g., cosmetics. Data are summarized in Tables 15 and 16
(section 5.2).
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1 Transport and Distribution
The degradation of methane is a major source of the natural back-
ground concentration of formaldehyde in the atmosphere. Since methane
is widely distributed naturally and has a half-life of several years,
formaldehyde is formed on a global scale.
Fig. 1 provides a survey of processes that may contribute to for-
maldehyde concentrations in ambient air.
Formaldehyde is a highly reactive compound with a half-life in the
atmosphere of about 1-3 h in the sunlit troposphere at 30° N at mid-day
(Bufalini et al., 1972; Lowe & Schmidt, 1983). Therefore, transpor-
tation of formaldehyde over distances is probably not of great import-
ance.
The organic compounds from which formaldehyde is derived are usual-
ly much more stable. Thus, emissions of organic air pollutants can con-
tribute to the formation of formaldehyde over considerable distances.
Various photochemical models have also been used to predict formal-
dehyde distribution in the troposphere, but the computed values are
difficult to compare, because of the different assumptions used to
generate the models.
Lowe et al. (1981) estimated a chemical life-time for formaldehyde
using the following reactions for formaldehyde formation (Levy, 1971):
CH4 + OH -> CH3 + H2O (1)
CH3 + O2 + M -> CH3O2 + M (2)
CH3O2 + NO -> NO2 + CH3O (3)
CH3O + O2 -> HCHO + HO2 (4)
Wofsy et al. (1972) considered that reaction (3) was unlikely and
suggested that methyl hydroperoxide (CH3OOH) could be an intermediate
in the reaction series producing formaldehyde.
CH3O2 + HO2 -> CH3OOH + O2 (5)
CH3OOH + hv -> CH3O + OH (6)
CH3O + O2 -> HCHO + HO2 (7)
For the purposes of estimating a chemical life-time for formal-
dehyde in the troposphere, reactions (1)-(4) are assumed, with reaction
(1) as the rate-limiting step. Hence, the rate of formaldehyde pro-
duction (P) from methane can be written as:
P = K1 [OH] x [CH4] (8)
Using K1 = 2.4 x 10-12 e-1710/T (Lowe et al., 1981), OH pro-
files for latitude 45 °N (Logan, 1980), and a mean tropospheric methane
mixing ratio of 1.18 mg/m3, equation (5) can be numerically inte-
grated over a 10-km high troposphere to yield an average column formal-
dehyde production rate, due to methane oxidation, of 9 x 10-5 g/cm2
per year.
Similar results are obtained using a mean tropospheric OH concen-
tration of 6.5 x 105 molecules/cm3 (Volz et al., 1981) with a mean
methane mixing ratio of 1.18 mg/m3 giving a column formaldehyde pro-
duction in a 10-km high troposphere of 8 x 10-5g/cm2 per year. This
is equivalent to an average world production rate of formaldehyde from
methane of 4 x 1011 kg/year, which greatly exceeds the total indus-
trial formaldehyde production rate (6 x 109 kg/year).
Various processes contribute to the removal of formaldehyde from
tropospheric air. The action of solar ultraviolet radiation on formal-
dehyde results in its photolysis via two channels (Moortgat et al.,
1978; Calvert, 1980).
HCHO + h v -> H2 + CO (9)
-> H + HCO (10)
Formaldehyde is also removed from the troposphere by reaction with
the OH radical (Stief et al., 1980).
HCHO + OH -> HCO + H20 (11)
HCO + O2 -> HO2 + CO (12)
Through the reaction series (1)-(4) and reactions (9)-(12), CO and
H2 are produced in the atmosphere via formaldehyde as an intermediate
product. The destruction of one methane molecule leads to the pro-
duction of approximately one formaldehyde molecule and ultimately to
the production of a CO molecule. The series of reactions also results
in a net production of HO2 radicals, resulting in an overall increase
in the chemical reactivity of the atmosphere.
From equations (9), (10), and (11), it follows that the chemical
destruction of formaldehyde (D) is given by:
D = [HCHO][K11[OH] + J9 + J10] = [HCHO] (13)
tau
where K11 is the rate constant of equation (11), J9 and J10 are the
photodissociation coefficients for equations (9) and (10) and tau [s]-1
is the chemical life-time of formaldehyde in the lower troposphere.
Substituting J9+J10 = 4.5 x 10-5 s -1 (mean estimated from Calvert,
1980), K11 = 1.05 x 10-11 (Stief et al., 1979), and [OH] = 5 x 106
molecules/cm3 (Logan et al., 1981) into equation (13) yields an
average chemical life-time for formaldehyde in the lower troposphere
during daylight, of 3 h. Under atmospheric conditions in the presence
of nitrogen dioxide (NO2), the half-life of formaldehyde was found to
be 35 min (Bufalini et al., 1972).
At ground level in the atmosphere, reaction with the OH radical is
the dominant removal process for formaldehyde. However, in the first
few kilometres of the troposphere, the importance of the OH radical as
a removal process decreases with altitude and the photodissociation
coefficients J9 and J10 increase in importance.
Formaldehyde is also removed from the troposphere by rainout
(gaseous constituents of the atmosphere are absorbed during the forma-
tion of cloud droplets), washout (falling raindrops scavenge gases,
particles, and aerosols from the atmosphere), and by deposition at the
surface. However, these processes are only of minor importance in the
free troposphere. For example, from formaldehyde measurements made in
rainwater collected at an equatorial site in the Pacific, Zafiriou et
al. (1980) estimated that rainout was responsible for removing only 1%
of the formaldehyde produced in the atmosphere by the oxidation of
methane. In addition, Warneck et al. (1978) showed that washout, as a
removal process for gaseous formaldehyde in the troposphere, is import-
ant only in polluted regions and may be ignored in unpolluted air.
Dry deposition at the surface is usually defined by a deposition
velocity, (vo (cm/second)), and the flux (fo) to the surface may be
estimated by:
fo = vo x [HCHO]o (14)
where [HCHO]o is the mean formaldehyde concentration above the
surface.
The deposition velocity depends on the surface. For example, from
measurements made at an equatorial Pacific atoll, Zafiriou et al.
(1980), deduced a value for vo of 0.4 cm/second at the ocean surface.
The mean formaldehyde mixing ratio, [HCHO]o, measured during
an oceanographic expedition in the north and south Atlantic, was
0.29 x 10-3 mg/m3, corresponding to a concentration of 5.9 x 109 mol-
ecules/cm3 (Lowe et al., 1981). With a deposition velocity of
0.4 cm/second, equation (14) suggests a loss due to deposition at the
ocean surface of 2.4 x 109 molecules/cm2 per second or about 4% of
the column formaldehyde production from methane oxidation calculated
above. Although vo for formaldehyde is expected to vary with wind vel-
ocity, it is unlikely to exceed 1 cm/second. Hence, loss of formal-
dehyde from the troposphere due to deposition will only be important
near the surface itself.
More recently, consideration has been given to the possibility of
how much formaldehyde indirectly contributes to the overacidification
of precipitation (Richards et al., 1983). Formaldehyde reacts with
sulfur dioxide (SO2) and gives off relatively concentrated hydroxy-
methanesulfonic acid, whereby SO2 may contribute to the acid content
of precipitation without preceding oxidation to sulfuric acid, which is
a relatively slow process. More in-depth investigations have to be
carried out, in order to ascertain to what extent this process is
important for acid formation.
4.2 Transformation
4.2.1 Special products of degradation under specific conditions
Highly carcinogenic bis(chloromethyl)ether can be produced by a
condensation reaction between formaldehyde and hydrogen chloride
(Thiess et al., 1973; Nelson, 1977; Albert et al., 1982; Sellakumar et
al., 1985). The maximum equilibrium concentration of bis(chloro-
methyl)ether generated from atmospheric formaldehyde and hydrogen
chloride was estimated to reach 4 x 10-16 ppb; it was concluded that
this represented little impact on human health (NRC, 1981). According
to Keefer & Roller (1973), formaldehyde is able to catalyze nitro-
sation of a series of secondary amines to carcinogenic nitrosamines or
N -nitroso-compounds.
4.2.2 Microbial degradation
Formaldehyde released into the aquatic environment appears to
undergo relatively rapid biodegradation. Kamata (1966) examined the
biodegradation of formaldehyde in natural water obtained from a stag-
nant lake in Japan. Under aerobic conditions, known quantities of added
formaldehyde were decomposed in ca. 30 h at 20 °C, anaerobic decompo-
sition required ca. 48 h. No decomposition was noted in sterilized
water.
Various activated sludges and microorganisms isolated from acti-
vated sludges have been shown to be very efficient in degrading formal-
dehyde in aqueous effluents, providing the formaldehyde concentration
does not exceed 100 mg/litre (Verschueren, 1983). Essentially complete
degradation is achieved in 48-72 h, if the proper temperature and nu-
trient conditions are maintained (Kitchens et al., 1976). Grabinska-
Loniewska (1974) isolated 44 bacteria strains from an industrial acti-
vated sludge and found that formaldehyde was used as a sole carbon
source by various Pseudomonas strains but not by strains of
Achromobacter , Flavobacterium , Mycobacterium , or Xanthomonas . Several
studies have revealed significant degradation of formaldehyde by mixed
cultures obtained from sludges and settled sewage (Heukelekian & Rand,
1955; Hatfield, 1957; Sakagami & Yokoyama, 1980; Speece, 1983; Behrens
& Hannes, 1984), while in other studies, little or no degradation has
been found (Placak & Ruchhoft, 1947; Gerhold & Malaney, 1966; Belly &
Goodhue, 1976; Kalmykova & Rogovskaya, 1978; Chou et al., 1979).
A number of pure culture studies have shown that formaldehyde is
biologically degradable. Cell extracts of Pseudomonas methanica and
Methylosinus trichosporium (Patel et al., 1979) and cell-free extracts
of yeast strains of the Candida sp. are able to oxidize formaldehyde
(Fujii & Tonomura, 1972, 1974, 1975; Sahm, 1975; Pilat & Prokop, 1976).
Cell extracts of Pseudomonas oleovorans (Sokolov & Trotsenko, 1977),
Pseudomonas putida Cl (Hohnloser et al., 1980), Hansenula polymorpha
(Van Dijken et al., 1975), Methylococcus capsulatus (Patel & Hoare,
1971), Methanobacterium thermoautotrophicum , M. voltae and M.
jannaschii (Escalante-Semerena & Wolfe, 1984) and Alcaligenes faecalis
(Marion & Malaney, 1963) can also oxidize formaldehyde.
Yamamoto et al. (1978) isolated 65 strains of methanol-utilizing
bacteria from seawater, sand, mud, and weeds of marine origin and found
that all were able to use formaldehyde as a sole carbon source for
growth. In contrast, Kimura et al. (1977) found that 336 strains of
bacteria, isolated from coastal seawater and mud, could not use formal-
dehyde as a sole carbon source for growth.
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1 Environmental Levels
5.1.1 Air
Measurements in maritime air yielded average formaldehyde concen-
trations of < 1-14 µg/m3 (Table 9).
Table 9. Measurements of aldehyde mixing ratios in the air
near the grounda
-----------------------------------------------------------------------------
Location RCHO HCHO Number Reference
of
measure-
(µg/m3) ments
-----------------------------------------------------------------------------
Baltic sea coast - 0.7-2.7 5 Hadamczik (1947)
Panama 1.2-4.8 - ? Lodge & Pate (1966)
Antarctica <0.6-12 - ? Breeding et al. (1973)
Panama <0.3-3.7 - ? Breeding et al. (1973)
Amazon Basin 1.2-7.4 - ? Breeding et al. (1973)
Irish west coast - 0.1-0.5 5 Platt et al. (1979)
Eastern Indian Ocean - < 1-14 63 Fushimi & Miyake (1980)
Central Pacific - 0.1-0.8 7 Zafiriou et al. (1980)
South Africa - 0.3-1.0 5 Neitzert & Seiler
(1981)
Irish west coast - 0.1-0.6 36 Lowe et al. (1981)
Bürserberg, Austria - 0.05-2.3 55 Seiler (1982)
-----------------------------------------------------------------------------
a Modified from: Lowe et al. (1981).
Higher values were generally obtained in the equatorial zone and
the Pacific (Fushimi & Miyake, 1980; Guderian, 1981; Seiler, 1982).
Measurements of the Nuclear Research Centre (Jülich, Federal Republic
of Germany), carried out with different measurement procedures in the
North and South Atlantic, yielded values of 0.1 µg/m3 and less (Lowe
et al., 1981). In the vicinity of the Pacific islands, values of up to
14 µg/m3 were reported (Fushimi & Miyake, 1980). However, it should
be borne in mind that considerable technical difficulties are involved
in measuring such low concentrations, with ensuing uncertainties.
The values measured in continental air are higher (0-16 µg/m3).
Measurements in Bürserberg, Austria, at 1250 m above sea level (Seiler,
1982), showed a mean value of 0.6 µg/m3 with a variation range of
0.05-2.3 µg/m3.
Measurements made by the Federal Environmental Agency at
Deuselbach, Hunsrück, Federal Republic of Germany, have proved to be
representative for the air in the rural areas of Central Europe
(Seiler, 1982). The mean value was about 1.5 µg/m3, ranging from
0.1 to 4.5 µg/m3 (Seiler, 1982). The lowest values were measured when
there was a rapid inflow of maritime air over extended periods. The
elevated values were probably due to man-made organic compounds that
had been transported long distances. Values of 6 µg/m3 generally ap-
pear together with increased concentrations of carbon monoxide and
sulfur dioxide, indicating man-made air pollution. Man-made emissions
dominate in the highly industrialized areas of Central Europe (Ehhalt,
1974).
Pronounced diurnal concentrations of formaldehyde are recognizable.
A typical example is given in Fig. 2. The resulting values are higher
in summer than in winter. They vary from season to season because of
the variation in intensity of the ultraviolet radiation.
5.1.1.1 Air in the vicinity of industrial sources and in urban communities
Estimated formaldehyde concentrations in emissions from various
sources are summarized in Table 10.
Table 10. Estimated formaldehyde concentrations in emissions
from various sourcesa
-------------------------------------------------------------
Emission source Formaldehyde level
-------------------------------------------------------------
Natural gas combustion
Home appliances and 2400-58 800 µg/m3
industrial equipment
Power plants 15 000 µg/m3
Industrial plants 30 000 µg/m3
Fuel-oil combustion 0-1.2 kg/barrel oil
Coal combustion
Bituminous < 0.005-1 g/kg coal
Anthracite 0.5 g/kg coal
Power plant, industrial and
commercial combustion
Incinerators
Municipal 0.3-0.4 g/kg refuse
Small domestic 0.03-64 g/kg refuse
Backyard 11.6 g/kg (max) refuse
Oil refineries
Catalytic cracking units 4.27 kg/barrel oil
Thermofor units 2.7 kg/barrel oil
Mobile sources
Automobiles 0.2-1.6 g/litre fuel
Diesel engines 0.6-1.3 g/litre fuel
Aircraft approximately 0.3-0.5 g/litre
fuel
-------------------------------------------------------------
a From: Kitchens et al. (1976).
Motor vehicle exhaust from automobiles not equipped with catalyzers
is the major source of formaldehyde in ambient outdoor air (Kitchens et
al., 1976).
Only a few highly industrialized areas, which are also areas with
heavy traffic, have been covered completely by measurements of the for-
maldehyde burden. In one such area in the Federal Republic of Germany
(Ludwigshafen-Frankenthal), annual mean values of 7-12 µg formalde-
hyde/m3 were measured during 1979-84. The annual mean value was the
arithmetic average of all half-hour values measured within a year
(long-term value). Peak concentrations in certain subareas, one square
km in size, ranged from 16 to 69 mg/m3. These were based on the 95-
percentile, i.e., 5% of the measured values were allowed to be in
excess of the prescribed parameters for concentrations in ambient air
(MSGU RP, 1984). The majority of subareas showed 95-percentile values
of about 25 µg/m3.
A mean value of 7 µg/m3 was determined in 1971-73 for the 43
measurement points in the Lower Main District, Federal Republic of
Germany, which is a radial measuring network with downtown
Frankfurt/Main (Federal Republic of Germany) as its centre. This was
based on 1-h measurements (n = 862). The 95% value of the cumulative
frequency distribution was 18 µg/m3, and the 4 highest single values
were 69, 65, 59, and 52 µg/m3 (Lahmann, 1977).
In another area at Mainz-Budenheim (Federal Republic of Germany),
continuous exposure to 8-20 µg/m3 was measured, with short-term
values of 23-99 µg/m3. Analysis of the causes of these high levels
showed that they were not only caused by industrial emissions. Individ-
ual measurements showed a correlation with carbon monoxide levels and
were not season-dependent. Hence, it can be assumed that motor vehicles
not equipped with catalyzers are responsible, to a considerable extent,
for the concentrations in ambient air (section 5.1.1.2). Usually, con-
centrations in ambient air are below 1 µg/m3. Data on concentrations
of formaldehyde in ambient air are presented in Table 11.
Formaldehyde concentrations in ambient air in areas with a high
level of air pollution, away from the vicinity of industrial plants,
are presented in Table 12.
Ambient air concentrations of formaldehyde, measured in Los
Angeles, California, during the autumn in 1961 and 1966, were
0.006-0.197 mg/m3 (Kitchens et al., 1976) and a daily average of
0.06-0.148 mg/m3 (Patterson et al., 1976), respectively. Concen-
trations of formaldehyde in the Los Angeles area ranged from 0.003 to
0.167 mg/m3 in 1969 (Kitchens et al., 1976). More recent air measure-
ments taken during 1979 in Los Angeles indicated levels of less than
18.5 µg formaldehyde/m3 (Versar Inc., 1980).
The results of continuous analyses of formaldehyde concentrations
in ambient air at the National Autoexhaust Monitoring Station at
Kasumigaseki in Tokyo were studied by Matsumura et al. (1979). The
hourly, daily, monthly, and yearly average concentrations were 1-88,
1-34, 3.7-23, and 5.5-12.6 µg/m3 (1-73, 1-28.4, 3.1-19.1, and 4.6-
10.5 ppb), respectively, with a 9-year average value of 8.5 µg/m3
(7.1 ppb). Daily average concentrations showed logarithmic normal
distribution. Ratios of the daily to hourly average concentrations
were about 1 to 2. The daily maximum value was observed at around noon
and the yearly maximum was found during June and August.
Richards et al. (1983) collected cloud water samples in the Los
Angeles Basin during 5 aircraft flights (altitude not reported) and
found a median of 2 mg formaldehyde/litre (68 µmol/litre) (range, 11-
142 µmol/litre).
Measurements taken in 4 cities in New Jersey showed median daily
concentrations in the range of 4.67-8.12 µg/m3 (Cleveland et al.,
1977).
A study in Switzerland showed formaldehyde concentrations of
11.4-12.3 µg/m3 in street air (Wanner et al., 1977). Maritime air in
the northern part of the Federal Republic of Germany has been reported
to contain formaldehyde at levels of 0.12-8 µg/m3 (Platt et al.,
1979).
Tanner & Meng (1984) observed strong seasonal variations in the
levels of formaldehyde, maximum levels being observed in the summer.
The formaldehyde samples were collected at an unidentified northeast
coastal site in the USA, using an impinger containing acetonitrile and
DNPH; they were analysed using high-pressure liquid chromatography.
The concentrations ranged from 1 to 58 µg/m3 (0.9 to 48 ppbv) with an
overall mean of 9 µg/m3 (7.5 ppbv). The monthly average ambient
levels were:
equivalent to:
July/August: 1982: 15.8 ppbv, 16 samples 16 µg/m3
October/November:1982: 4.4 ppbv, 24 samples 4 µg/m3
March: 1983: 3.8 ppbv, 59 samples 4 µg/m3
April: 1983: 11.2 ppbv, 11 samples; and 11 µg/m3
May: 1983: 12.2 ppbv, 25 samples 12 µg/m3
Table 11. Levels of formaldehyde in ambient aira
---------------------------------------------------------------------------------------------------------
Country Sampling area % of Analytical Source HCHOb Comment Reference
samples method (µg/m3)
---------------------------------------------------------------------------------------------------------
Federal Eifel Region - 2,4 dinitrophe- easterly 5.0- Within boundary Schmidt &
Republic (51°N, 6°E) nylhydrazine winds 6.1 layer Lowe
of from indus- 0.37 above boundary (1981)
Germany trial area; layer
westerly 0.12 5-7 km altitude
maritime
winds
Federal Mainz-outskirts 8 glass fibre automobiles 0.063 formaldehyde Klippel &
Republic of city; 54 filters some auto- 0.037- aerosol only Warneck
of Deuselbach-rural mobile 0.39 (1978)
Germany industry
France Paris roadside 2,4-dinitrophe- automobiles 41- total aldehydes Favart et
nylhydrazine 120 al. (1984)
Ireland Mace Head and 28 glass fibre maritime air 0.049- formaldehyde Klippel &
Loop Head filters 0.082 aerosol only Warneck
located on (1978)
shoreline
Italy Northern - near 15 2,4-dinitrophe- 7.06 De Bortoli
Swiss border nylhydrazine et al.
(1985)
Nether- Terschelling 350 chromatropic acid 7.4 Guicherit &
lands Island - small at each method Schulting
population; site (1985)
Delft - small
city; Rotterdam -
heavily industrialized
---------------------------------------------------------------------------------------------------------
Table 11 (contd).
---------------------------------------------------------------------------------------------------------
Country Sampling area % of Analytical Source HCHOb Comment Reference
samples method (µg/m3)
---------------------------------------------------------------------------------------------------------
USA Rural Illinois 30 3-methyl-2- - <1.2- total Breeding
and Missouri; benzothiazolone 5.0 aldehydes et al.
3 samples hydrazone (1973)
1 m above ground,
1 sample 20-15 m
above tree tops
USA Los Angeles- 31 30 or 60 litres - 49.1 July-November, Altshuller
downtown of air at 1 litre 55.3 1960 & McPherson,
per min through Sept-Nov. 1961 (1963)
20 ml of 0.1%
chromotropic acid
in conc. H2SO4
USA Riverside, 32 Fournier-transform < 5- Tuazon et
California infrared system 12 al. (1978)
USA Lennox, Calif., 36 Microimpinger industrial 0.6- levels between Grosjean &
roof top method with emissions 48.6 07h30 and 20h00 Swanson,
Azusa, Calif., 36 2,4-dinitro- photo- 0.9- during air pol- (1983)
roof top phenylhydra- chemical 43 lution episode
zine pollutants
Los Angeles 20 4.5- between 9h30 and
Area 70.1 16h20 during air
pollution episode
USA Bayonne, hourly dichlorosulfit- automobiles 17.2- range of max. Cleveland
Camden, samples omercurate 20.0 levels from 4 et al.
Elizabeth between complex and acid sites (1977)
and Newark, May 1 and bleached pararo- 4.7- range of average
New Jersey Sept. 30, saniline hydro- 8.1 levels from
1974 chloride 4 sites
---------------------------------------------------------------------------------------------------------
a Modified from: Meek et al. (1985).
b Unless other specified, mean or ranges.
Table 12. Measurements of formaldehyde in ambient air in areas remote
from industrial emission sourcesa
--------------------------------------------------------------------------------------------------------
Location Period Mean value Maximum Remarks Reference
or range value
(ug/m3) (ug/m3)
--------------------------------------------------------------------------------------------------------
Federal Republic of Germany
Berlin 1973-74 0.6 18 118-h mean Lahmann &
2.1 32 119-h mean Prescher
Berlin - Airport 2.2 29 72-h mean (1979)
Berlin - Steglitz 1966-67 39 243-h mean Lahmann & Prescher
Berlin - Tempelhof 1973-74 0.5 12 71-h mean (1979)
Frankfurt - Airport 1983 9-11 23 half-hour mean BGA (1985)
Frankfurt - City 1983 7-13 9-25 BGA (1985)
Köln - Neumarkt December 1975 2.3 8.5 95-percentile Deimel (1978)
June 1978 8.2 18.3 95-percentile Deimel (1978)
June 1978 23.1 rush-hour traffic Deimel (1978)
Mainz - University 1979 4.4 7.5 65 measurements Seiler (1982)
Mainz - Finthen 1979-80 1.6 3.8 33 measurements Seiler (1982)
Switzerland
Street air 1976 11.4-12.3 - Wanner et al. (1977)
USA
California 1960-80 8-70 160 Versar Inc.(1986)
Los Angeles, California 1961-66 6-197 - Kitchens et al.
(1976)
Northeastern coastal site 1982-83 1-48 - Tanner & Meng
(1984)
--------------------------------------------------------------------------------------------------------
a From: BGA (1985).
5.1.1.2 Emissions from industrial plants
(a) Chemical industry
The following emission factors per metric tonne of formaldehyde
produced by formaldehyde-manufacturing plants in the Federal Republic
of Germany are given on a 100% basis (section 3.2.1.1).
Silver catalyst process with afterburning of flue gas in power
plant and gas displacement devices: 0.003-0.008 kg/metric tonne formal-
dehyde produced; silver catalyst process with flaring of off-gas,
without gas displacement devices: 0.05-0.2 kg/metric tonne produced;
metal-oxide catalyst process without afterburning: approximately
0.5 kg/metric tonne produced; metal-oxide catalyst process with after-
burning but without gas displacement devices: 0.08-0.2 kg/metric tonne
produced.
(b) Wood-processing industry
Several studies are available that deal with formaldehyde emissions
at particle board factories in the Federal Republic of Germany (WKI,
1978; Marutzky et al., 1980; Schaaf, 1982).
In 1980, the emissions in the exhaust air of several plants reached
a mean value of 40 mg formaldehyde/m3 off-gases. No measures had been
taken at any of the plants to clean the off-gases. Pilot studies at a
particle board factory showed that a concentration (pure gas) of less
than 20 mg/m3 could be obtained using bioabsorption equipment. Mean-
while, the emittable formaldehyde content of the resins used was
further reduced, resulting in even lower formaldehyde concentrations in
the off-gases (BGA, 1985).
5.1.1.3 Emissions from furnaces
Incomplete combustion in furnaces is also a cause of formaldehyde
emission (Schmidt & Götz, 1977). Various types of furnaces differ
considerably in their emission of formaldehyde, depending on the rate
of combustion.
Investigations on a small solid-fuel boiler running on wood
(Schriever et al., 1983) showed that there was a formaldehyde concen-
tration of more than 1000 mg/m3 in the gaseous emission during the
first phase of combustion, i.e., that of degasification. During the
subsequent burning-out phase, the emissions of formaldehyde were about
50-100 mg/m3.
Lipari et al. (1984) measured formaldehyde emissions in the exhaust
gases of a free-standing wood-burning fireplace in the laboratory.
When burning green ash (quartered logs), values of 708 mg/kg wood were
found; the formaldehyde content of the exhaust gases, when burning red
oak, ranged from 89 mg/kg (quartered logs) to 326 mg/kg (split wood).
It is likely that wood burning in the home is a major source of primary
aldehydes during the winter.
In the Federal Republic of Germany, it is estimated that about 2.8
million tonnes of firewood off-gas are consumed in small heating
systems for heating buildings. On the basis of an average formaldehyde
concentration of 100 mg/m3 firewood, an overall annual emission of
approximately 1000 tonnes of formaldehyde has been calculated.
5.1.1.4 Emissions from motor vehicles
Formaldehyde is also emitted as a product of incomplete combustion
by internal combustion engines. The amounts emitted depend greatly on
the operating conditions. Very high values are reached in emissions
from a cold engine. Kitchens et al. (1976) reported a formaldehyde
emission of 700 mg/litre gasoline or diesel fuel. Given an assumed
average value for gasoline consumption of 23 million tonnes and for
diesel fuel consumption of 13 million tonnes in the Federal Republic of
Germany, the total formaldehyde emission would be 35 000 tonnes per
year. Hence, motor vehicles are by far the most important source of
formaldehyde emission. The use of exhaust catalytic converters reduces
the emissions to less than one-tenth. Emission factors of between 1.8
and 2.4 mg/km have been reported for the USA (VDA, 1983).
Four-stroke engines, running on alcohol, emit more aldehydes than
similar engines fuelled with petrol. The formaldehyde concentration in
the exhaust fumes can be reduced by a factor of 10 by installing
exhaust catalytic converters in vehicles powered with methanol, but the
concentration is still higher than that of vehicles with petrol-burning
engines. Emission factors of about 250-300 mg/km have been given for
vehicles with methanol-burning engines without an exhaust catalyser
(Menrad & König, 1982). The odour of such amounts of formaldehyde is
perceptible near the vehicle. Diesel engines also emit formaldehyde;
diesel oil produces 1-2 g aldehydes/litre of which 50-70% is
formaldehyde (Guicherit & Schulting, 1985).
5.1.2 Water
In the atmosphere, formaldehyde is absorbed during the formation of
cloud droplets ("rainout") or scavenged by falling raindrops
("washout"). Some concentrations in rainwater and aerosols are
given in Table 13. When the rainfall continued for a long period,
remaining concentrations in the air of 0.05 µg/m3 (detection limit:
0.03 µg/m3) were found by Seiler (1982). Concentrations in
rainwater at a remote site in the central equatorial Pacific averaged
8 ± 2 µg/kg (Zafiriou et al., 1980). Kitchens et al. (1976) reported
concentrations of 0.31-1.38 mg/litre.
Table 13. Formaldehyde concentrations in rainwater and
aerosola
-------------------------------------------------------
Location (year) Rainwater Aerosol
concentration concentration
(mg/litre) (ng/m3)
-------------------------------------------------------
Mainz, Federal Republic 0.174 ± 0.085 -
of Germany (1974-77)
Deuselbach, Federal 0.141 ± 0.048 40.9 ± 26.0
Republic of (1974-76)
Ireland (1975, 1977) 0.142 ± 0.059 5.36 ± 2.4
Irelandb (1977) 0.111 ± 0.059 -
-------------------------------------------------------
a From: Klippel & Warneck (1978).
b Very clean air.
Fish-culture activities are also a source of formaldehyde in the
aquatic environment. Formalin is one of the most widely and frequently
used chemicals for treating fish with fungal or ectoparasitic infec-
tions. After use, formaldehyde solutions are often discharged into the
hatchery effluent (NRC, 1981).
5.1.3 Soil
Formaldehyde is formed in the early stages of plant residue
decomposition in soil (Berestetskii et al., 1981). It is degraded by
certain bacteria in the soil, and therefore bioaccumulation does not
occur. Completely polymerized urea-formaldehyde resins persist in the
environment and do not emit formaldehyde. Partially polymerized conden-
sation products of low relative molecular mass degrade gradually, thus
releasing formaldehyde vapour that can be broken down by soil micro-
flora (Kitchens et al., 1976; Hsiao & Villaume, 1978).
5.1.4 Food
There is some natural formaldehyde in raw food. Formaldehyde
concentrations in various food are given in Table 14.
Table 14. Formaldehyde content of foodstuffs
-----------------------------------------------------------------------------
Food Formaldehyde content Reference
(mg/kg)
-----------------------------------------------------------------------------
Fruits and vegetables
pear 60a (38.7)b Möhler & Denbsky (1970)
apple 17.3 (22.3) Tsuchiya et al. (1975)
cabbage 4.7 (5.3) Tsuchiya et al. (1975)
carrot 6.7 (10) Tsuchiya et al. (1975)
green onion 13.3 (26.3) Tsuchiya et al. (1975)
spinach 3.3 (7.3) Tsuchiya et al. (1975)
tomato 5.7 (7.3) Tsuchiya et al. (1975)
white radish 3.7 (4.4) Tsuchiya et al. (1975)
Meat
pig 20 Florence & Milner (1981)
sheep 8 Mills et al. (1972)
poultry 5.7 Möhler & Denbsky (1970)
Milk and milk products
goat's milk 1 Mills et al. (1972)
cow's milk up to 3.3 Möhler & Denbsky (1970)
cheese up to 3.3 Möhler & Denbsky (1970)
Fish
freshwater (fumigated) 8.8 Möhler & Denbsky (1970)
sea (fumigated) 20 Möhler & Denbsky (1970)
cod (frozen) 20 Rehbein (1986)
shrimp (live) 1 Radford & Dalsis (1982)
crustacea 1-60 Cantoni et al. (1977)
(Mediterannean)
crustacea (ocean) 3-98 Cantoni et al. (1977)
-----------------------------------------------------------------------------
a Analysis by chromotropic acid.
b Analysis using Schiff's reagent.
Accidental contamination can occur through fumigation (e.g., in
grain) or by using formaldehyde-containing food additives.
Hexamethylenetetramine has been reported to decompose gradually to
formaldehyde under acidic conditions or in the presence of proteins
(Hutschenreuter, 1956; WHO, 1974a). Its use is not recommended when
there is a possibility that nitrate might also be present in food,
because of the risk of nitrosamine formation (WHO, 1974b).
Formaldehyde can be introduced into food through cooking and
especially through smoking of food, from utensils, and as a combustion
product; it can be eluted from formaldehyde-resin plastic dishes with
water, acetic acid, and ethanol in amounts directly proportional to the
temperature (Table 15, 16).
Release of formaldehyde may increase with the repeated use of
melamine resin tableware (Table 16). The molar concentration ratio of
formaldehyde to melamine (y), in 4% acetic acid maintained at 95 °C for
30 min in melamine cups, decreases biexponentially between the first
and fifth treatments according to the following formula: 1n y = -1.0755
ln x + 2.2462, where x = the number of times that the heat treatment is
repeated. After the sixth treatment, the value of y is reported to
remain constant (Inoue et al., 1987).
Daily intake of formaldehyde through food is difficult to evaluate,
but a rough estimate from available data is in the range of 1.5-14
mg/day for an average adult, most of it in a bound and unavailable
form.
5.2 Indoor Air Levels
Indoor air levels of formaldehyde in various countries were
presented during the International Conference on Indoor Air Quality in
Stockholm (Berglund et al., 1984).
A survey of indoor air quality under warm weather conditions, in a
variety of residences in Houston, Texas, USA, not selected in response
to occupant complaints, revealed a distribution of indoor formaldehyde
concentrations ranging from < 0.01 to 0.35 mg/m3, with an arithmetic
mean of 0.08 mg/m3 (Stock & Mendez, 1985). Levels in approximately
15% of the monitored residences exceeded 0.12 mg/m3. Formaldehyde
levels depended on the age and structural type of the dwelling. These
factors were not independent and reflected the influence of more funda-
mental variables, i.e., the rate of exchange of indoor and outdoor air
and the overall emission potential of indoor materials. The results of
this survey suggested that considerable population exposure to excess
(>0.12 mg/m3) formaldehyde concentrations might have occurred in the
residential environment, indicating the need for improved control
strategies.
Hawthorne et al. (1984) measured formaldehyde levels in 40 East-
Tennessee homes. Levels in older houses averaged 0.048 mg/m3 while
those in houses less than 5 years old averaged 0.096 mg/m3.
The effects of foliage plants on the removal of formaldehyde from
indoor air in energy-efficient homes is discussed in section 7.3.
Measurements made in living areas, schools, hospitals, and other
buildings are listed in Table 17 to 19.
Table 15. Migration of formaldehyde from melamine and urea-resin tableware (mg/litre) into
different solvents. Detection limit 0.4 mg/litrea.
--------------------------------------------------------------------------------------------
Resin Temperature Water 4% Acetic acid 15% Ethanol 35% Ethanol
30 minb 30 minc 30 minb 30 minc 30 minb 30 minc 30 minb 30 minc
--------------------------------------------------------------------------------------------
25 °C n.d.d n.d. n.d. n.d. n.d. n.d. n.d. n.d.
60 °C n.d. n.d. 0.5 n.d. 0.4 n.d. n.d. n.d.
Melamine 70 °C n.d. n.d.
resin 80 °C 0.5 1.4 0.6 3.0 0.5 1.6 0.5 1.4
90 °C 2.2 2.6
100 °C 2.6 5.2 0.8 8.9 0.5 4.6 0.5 4.8
--------------------------------------------------------------------------------------------
25 °C 0.4 0.4 0.4 0.5 0.5 0.5 0.4 0.5
60 °C 2.9 4.3 3.1 8.3 3.1 3.8 2.9 4.1
Urea 70 °C 5.0 13.0
resin 80 °C 9.1 23.4 9.6 126.0 7.4 30.0 8.6 28.2
90 °C 13.0 39.2
100 °C 18.0 48.2 27.6 648.0 19.0 54.0 18.5 50.4
--------------------------------------------------------------------------------------------
a From: Homma (1980).
b Standing at room temperature.
c Maintained at a definite temperature.
d Not detected.
Table 16. Migration from melamine cups with 4% acetic acid
concentration in the migration solutiona
-------------------------------------------------------------------
Conditions Melamine Formaldehyde
mg/litre mg/litre
-------------------------------------------------------------------
60 °C, 30 min 0.5 ± 0.6 ndb
Microwave oven 1.5 min (90 °C)
and stood at room temperature for
30 min (60 °C) 1.7 ± 1.2 (1.1 ± 0.4)
95 °C, 30 min
repetition 1 9.5 ± 3.1 (4.1 ± 0.8)
2 28.1 ± 6.0 (12.0 ± 2.6)
3 37.7 ± 10.3 (17.3 ± 3.4)
5 46.4 ± 13.9 (19.4 ± 2.8)
7 50.4 ± 3.6 (22.2 ± 2.2)
-------------------------------------------------------------------
a From: Ishiwata et al. (1986).
b Not detected.
Tobacco smoke contains an average of 48 mg formaldehyde/m3 and is
an important source of formaldehyde in indoor air. Two cigarettes
smoked in a 30 m3 room increased the formaldehyde level to more than
0.1 mg/m3 (Jermini et al., 1976). Formaldehyde from tobacco smoke is
absorbed by furniture, carpets, and curtains, and only slowly desorbed
if the formaldehyde concentration in the indoor air decreases. Par-
ticle boards and, to a lesser extent, urea-formaldehyde-foam insulation
(UFFI) were also listed as causes of increased indoor exposure. Disin-
fectant products may cause high exposure. These sources of emission
are described in Table 17, 18, and 19.
Formaldehyde concentrations in 49 Dutch houses and 3 old peoples'
homes where no UF-foam or particle board had been used were analysed by
Cornet (1982). The houses were of different construction types and
periods, in which it could be established that no particle board as
construction material nor UF-foam had been used. However, several of
these houses had particle board furniture. Overall, construction types
and conditions of use were typical for Dutch circumstances. Average
formaldehyde concentrations were 65 µg/m3, ranging mainly from 30 to
100 µg/m3. Ventilation rates ranged usually from 0.3-1.5 air changes per
hour in living rooms and 0.2-1.2 in bedrooms. During the measurements
no smoking took place.
No clear correlations could be established between the amount of
particle board present in furnishings, ventilation rates, and formal-
dehyde concentrations.
5.2.1 Indoor exposure from particle boards
Nuisance from bad smells led to complaints by students and teachers
in several new schools in Köln, Federal Republic of Germany, in 1975
and 1976. Formaldehyde concentrations of up to 1.2 mg/m3 were measured
with the windows closed (Deimel, 1978). A combination of ceilings and
furniture made of particle boards and insufficient ventilation was the
cause of these high indoor concentrations (Anderson et al., 1975).
There have been complaints from schools, kindergartens, private homes,
and, especially in the USA, mobile homes. Formaldehyde concentrations
of more than 0.12 mg/m3 and sometimes more than 1.2 mg/m3 were
measured.
During the 1970s, increased use of UF-bonded particle board
as a construction material in The Netherlands resulted in many
consumer complaints, attributed to formaldehyde. In 1978, a level of
120 µ