INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 49
ACRYLAMIDE
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Labour Organisation, or the World Health Organization.
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the International Labour Organisation,
and the World Health Organization
World Health Orgnization
Geneva, 1985
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR ACRYLAMIDE
1. SUMMARY AND RECOMMENDATIONS FOR FURTHER RESEARCH
1.1. Summary
1.1.1. Properties, uses, and analytical methods
1.1.2. Environmental sources and environmental
transport and distribution
1.1.3. Environmental levels and exposures
1.1.4. Metabolism of acrylamide
1.1.5. Effects on man and animals
1.1.6. Mutagenicity and carcinogenicity
1.1.7. Teratogenicity and reproduction
1.1.8. Dose-effect and dose-response relationships
1.1.9. Evaluation of health risks for man
1.2. Recommendations for further research
1.2.1. Analysis
1.2.2. Exposure
1.2.3. Metabolism and indicators of exposure
1.2.4. Effects
2. PROPERTIES AND ANALYTICAL METHODS
2.1. Identity
2.2. Chemical and physical properties
2.3. Sampling and analytical methods
3. SOURCES IN THE ENVIRONMENT
3.1. Production levels, processes, and uses
3.1.1. World production
3.1.2. Production processes
3.1.3. Uses
3.2. Release into the environment
3.3. Disposal of wastes
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1. Transport in the environment
4.2. Biomagnification and bioconcentration
4.3. Transformation
5. ENVIRONMENTAL LEVELS AND EXPOSURES
5.1. Environmental levels
5.1.1. Ambient air and soil
5.1.2. Water
5.1.3. Food
5.2. General population exposure
5.3. Occupational exposure
6. KINETICS AND METABOLISM
6.1. Experimental animal studies
6.1.1. Absorption and distribution
6.1.2. Metabolism
6.1.3. Elimination and excretion
6.1.3.1 Elimination
6.1.3.2 Excretion
6.2. Human studies
7. EFFECTS ON ANIMALS
7.1. Neurological effects
7.1.1. Neurobehavioural effects
7.1.2. Electrophysiological effects
7.1.2.1 Peripheral effects
7.1.2.2 Central nervous system effects
7.1.3. Morphological effects
7.1.4. Biochemical effects
7.1.4.1 Effects on axonal transport
7.1.4.2 Effects on energy production
and neuronal metabolism
7.1.4.3 Effects on CNS neurochemistry
7.2. In vitro toxicity studies
7.3. Effects on other organs
7.4. Genotoxic effects and carcinogenicity studies
7.4.1. Mutagenicity and other related short-term tests
7.4.2. Carcinogenicity studies
7.5. Teratogenicity and reproductive studies
7.6. Factors modifying effects
7.6.1. Chemical modification of acrylamide toxicity
7.6.2. Age
7.6.3. Sex differences
7.6.4. Species
7.7. Dose-response and dose-effect relationships
7.7.1. Dose-response relationships
7.7.2. Dose-effect relationships
7.7.2.1 Manifestations of neuropathy
7.7.2.2 Electrophysiological effects
7.7.2.3 Morphological effects
7.7.2.4 Effects on axonal transport
7.7.2.5 Neurobehavioural effects
8. EFFECTS ON MAN
8.1. Clinical studies and case reports
8.2. Epidemiological studies
8.3. Dose-effect and dose-response relationships
9. EFFECTS ON ORGANISMS IN THE ENVIRONMENT
9.1. Aquatic organisms
9.1.1. Invertebrates
9.1.2. Fish and amphibia
9.2. Terrestrial plants
9.3. Microorganisms
10. STRUCTURE-NEUROTOXICITY RELATIONSHIPS
11. EVALUATION OF HEALTH RISKS FOR MAN AND EFFECTS
ON THE ENVIRONMENT FROM EXPOSURE TO ACRYLAMIDE
11.1. General considerations
11.2. Assessment of exposure
11.3. Assessment of adverse effects
11.4. Exposure of the environment
11.5. Occupational exposure
REFERENCES
WHO TASK GROUP ON ACRYLAMIDE
Members
Dr N. Aldridge, Medical Research Council, Carshalton, Surrey,
United Kingdom (Chairman)
Dr M. Berlin, Monitoring and Assessment Research Centre,
University of London, London, United Kingdom
Prof J. Cavanagh, Institute of Neurology, London, United
Kingdom
Dr K. Hashimoto, Department of Hygiene, School of Medicine,
Kanazawa University, Ishikawa, Japan (Vice-Chairman)
Dr D.G. Hatton, US Food and Drug Administration, Department of
Health and Human Services (Rapporteur)
Prof M. Ikeda, Department of Environmental Health, Tohoku
University School of Medicine, Sendai, Japan
Dr P. Le Quesne, National Hospital for Nervous Diseases,
London, United Kingdom
Prof A. Massoud, Ain Shams University, Cairo, Egypt
Dr P.K. Ray, Industrial Toxicology Research Centre, Lucknow,
India
Prof I.V. Sanotsky, Research Institute of Industrial Hygiene
and Occupational Diseases, USSR Academy of Medical
Sciences, Moscow, USSR
Dr H.A. Tilson, Laboratory of Behavioral and Neurological
Toxicology, NIEHS, Research Triangle Park, North Carolina,
USA
Representatives from Other Organizations
Mr S. Batt, Monitoring and Assessment Research Centre,
University of London, London, United Kingdom
Dr L. Shukar, Monitoring and Assessment Research Centre,
University of London, London, United Kingdom
Mr J.D. Wilbourn, International Agency for Research on Cancer,
Unit of Carcinogen Identification and Evaluation, Lyons,
France
WHO Secretariat
Dr M. Draper, International Programme on Chemical Safety,
World Health Organization, Geneva, Switzerland
Dr E.M.B. Smith, International Programme on Chemical Safety,
World Health Organization, Geneva, Switzerland (Secretary)
Ms A. Sunden, International Register of Potentiallly Toxic
Chemicals, Geneva, Switzerland
NOTE TO READERS OF THE CRITERIA DOCUMENTS
While every effort has been made to present information in
the criteria documents as accurately as possible without unduly
delaying their publication, mistakes might have occurred and are
likely to occur in the future. In the interest of all users of
the environmental health criteria documents, readers are kindly
requested to communicate any errors found 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.
In addition, experts in any particular field dealt with in
the criteria documents are kindly requested to make available to
the WHO Secretariat any important published information that may
have inadvertently been omitted and which may change the
evaluation of health risks from exposure to the environmental
agent under examination, so that the information may be
considered in the event of updating and re-evaluation of the
conclusions contained in the criteria documents.
* * *
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. 988400 -
985850)
ENVIRONMENTAL HEALTH CRITERIA FOR ACRYLAMIDE
Following the recommendations of the United Nations
Conference on the Human Environment held in Stockholm in 1972,
and in response to a number of World Health Assembly resolutions
(WHA23.60, WHA24.47, WHA25.58, WHA26.68), and the recommendation
of the Governing Council of the United Nations Environment
Programme, (UNEP/GC/10, 3 July 1973), a programme on the
integrated assessment of the health effects of environmental
pollution was initiated in 1973. The programme, known as the WHO
Environmental Health Criteria Programme, has been implemented
with the support of the Environment Fund of the United Nations
Environment Programme. In 1980, the Environmental Health
Criteria Programme was incorporated into the International
Programme on Chemical Safety (IPCS). The result of the
Environmental Health Criteria Programme is a series of criteria
documents.
A WHO Task Group on Environmental Health Criteria for
Acrylamide was held at the British Industries Biological Research
Association (BIBRA), Carshalton, Surrey, United Kingdom, from
3-5 December, 1984. Dr E.M.B. Smith opened the meeting on behalf
of the Director-General. The Task Group reviewed and revised the
draft criteria document and made an evaluation of the health risks
of exposure to acrylamide.
The initial draft was prepared by DR M. BERLIN with the
assistance of DR L. SHUKAR and MR S. BATT of the MONITORING AND
ASSESSMENT RESEARCH CENTRE (MARC) London, United Kingdom.
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 UK Department of Health
and Social Security generously supported the cost of printing.
1. SUMMARY AND RECOMMENDATIONS FOR FURTHER RESEARCH
1.1. Summary
1.1.1. Properties, uses, and analytical methods
Acrylamide is a white crystalline solid produced from
acrylonitrile, which is present as a residue in technical grades
of acrylamide at concentrations ranging from 1 to 100 mg/kg.
Acrylamide readily undergoes polymerization, resulting in a
highly cross-linked insoluble gel of polyacrylamide. Commercial
polyacrylamide contains 0.05 - 5.0% acrylamide. Hydroquinone
monomethylether, t-butylpyrocatechol, N-phenyl-2-naphthylamine,
and copper (ion) may be used as stabilizers.
Acrylamide is mainly used in the production of polymers and
copolymers for various purposes. Polyacrylamides are useful as
flocculents in the treatment of waste water and the purification
of drinking-water. Acrylamide is also used as a grouting agent
and in the construction of dam foundations and tunnels.
Methods for the determination of acrylamide in polymers, air,
water, and biological materials have been devised using gas
chromatography, high-performance liquid chromatography, and
differential pulse polarography. No method has so far been
described for the determination of either acrylamide bound to
blood and tissue proteins or its metabolites in the urine.
The reported sensitivity for the determination of acrylamide
in air, using gas chromatography, is 5 µg/m3 and, using electron
capture and flame ionization detection, 30 µg/m3. Sampling of
acrylamide (vapour and dust) in air is performed using midget
impingers. Determination of acrylamide in polyacrylamide can be
accomplished, with a sensitivity of less than 1 mg/kg, using
differential pulse polarography. The detection limit for
acrylamide in water is 0.1 µg/litre, using electron capture gas
chromatography after derivatization, though the recovery of
acrylamide is rather poor. Derivatization followed by high-
performance liquid chromatography is less sensitive (0.2 µg/litre),
but is more suitable for the routine analysis of both natural and
polluted water. Free acrylamide in biological samples such as
plasma and tissue homogenates can be determined, by electron
capture-gas chromatography, with a detection limit of 10
µg/litre.
1.1.2. Environmental sources and environmental transport and
distribution
All acrylamide in the environment is man-made, the main
source being the release of the monomer residues from
polyacrylamide used in water treatment or in industry. The most
important environmental contamination results from the use of
acrylamide in soil grouting, because of contamination of ground
water. Chemical decontamination of acrylamide-containing liquid
wastes and solids is possible, but the costs, in most instances,
are high.
Because it is highly soluble in water, acrylamide is
extremely mobile in the aqueous environment and is readily
leachable in soil. It is unlikely to enter and be transported in
the atmosphere to any significant extent, because of its low
vapour pressure. Biodegradation is likely to occur.
A wide variety of microbes possess the ability to degrade
acrylamide. However, there is a latent period of several days
before there is any significant degradation. The residence
period for acrylamide may be of the order of days, weeks, or
months, in rivers and coastal areas of low microbial activity.
The half-life in aerobic soil, which is of the order of several
days at 20 °C, increases with decreasing temperature.
Acrylamide is unlikely to be removed during sewage treatment
and has been shown to pass through waterworks mainly unchanged.
1.1.3. Environmental levels and exposures
Because polyacrylamide is used in water treatment, residues
of acrylamide may be found in potable water. In most countries,
such residues are limited to 0.25 µg/litre by maintaining the
concentration of acrylamide monomer in the polyacrylamide used
for water treatment at 0.05%. Concentrations of acrylamide in
effluents from polyacrylamide-using factories generally range
from less than 1 to 50 µg/litre. However, 1.5 mg
acrylamide/litre has been measured downstream from industrial
effluent discharges. Levels reported in receiving streams and
rivers are variable and dependent on the extent of dilution. A
level of 0.3 µg/litre was detected at a waterworks intake
downstream from an effluent discharge from a clay pit. In the
vicinity of local grouting operations, high levels of acrylamide
may be found in wells and ground water; a concentration of 400
mg/litre was reported in one such well.
Monitoring of acrylamide concentrations in air and soil close
to 6 acrylamide-producing plants in the USA failed to demonstrate
any acrylamide in the air (detection limit 0.1 µg/m3) or in the
soil (detection limit 0.02 mg/kg).
Polyacrylamides are also used in the washing and packaging of
prepacked foods and vegetables. The US Food and Drug
Administration has limited the amount of monomer in
polyacrylamide for use in paper or cardboard in contact with food
to 0.2% (2 g/kg). In the Federal Republic of Germany, the level
of polyacrylamide used in foodstuff packaging is limited to 0.3%
(3 g/kg) and the level of residual acrylamide monomer to 0.2%
(2 g/kg)a.
-------------------------------------------------------------------
a Bundesministerium für Jugend, Familie und Gesundheit,
personal communication, 1984.
Occupational exposure to acrylamide occurs mainly through
skin absorption and inhalation in acrylamide-producing plants.
Personal sampling in such plants has shown average levels in
workplace air of about 0.6 mg/m3, with a range of 0.1 - 3.6 mg/m3
in heavily-exposed areas. Measurements resulting from stationary
sampling were generally 2 - 3 times lower. This indicates the
importance of taking work procedures into account in the
assessment of exposure. Published figures from the USA indicate
that about 20 000 workers may be exposed to acrylamide. Although
exposure levels have not been reported for grouters, the
potential for hazard from this use is probably greater than from
other uses, because of the uncontrolled nature of the exposure.
1.1.4. Metabolism of acrylamide
Acrylamide is readily absorbed by ingestion, inhalation, and
through the skin. Absorbed acrylamide is distributed in body
water compartments and passes through the placental barrier. In
rats, biotransformation of acrylamide occurs through glutathione
conjugation and through decarboxylation. At least 4 urinary
metabolites have been found in rat urine, of which mercapturic
acid and cysteine- S-propionamide have been identified.
Acrylamide and its metabolites are accumulated (protein-bound) in
both nervous system tissue and blood (bound to haemoglobin).
Accumulation in the liver and kidney as well as the male
reproductive system has also been demonstrated. The results of
animal studies indicate that acrylamide is largely excreted as
metabolites in urine and bile. Because of the enterohepatic
circulation of biliary metabolites, faecal excretion is minimal.
Two-thirds of the absorbed dose is excreted with a half-life of a
few hours. However, protein-bound acrylamide or acrylamide
metabolites in the blood, and possibly in the central nervous
system, have a half-life of about 10 days. The net elimination
in urine of acrylamide metabolites is constant in the rat and is
independent of dose within the range 1 - 200 mg/kg body weight.
Acrylamide has been identified in rat milk during lactation.
There are no data indicating any major differences in acrylamide
metabolism between man and other mammals.
1.1.5. Effects on man and animals
Acrylamide is toxic and an irritant. Cases of acrylamide
poisoning show signs and symptoms of local effects due to
irritation of the skin and mucous membranes and systemic effects
due to the involvement of the central, peripheral, and autonomic
nervous systems. Local irritation of the skin or mucous
membranes is characterized by blistering and desquamation of the
skin of the hands (palms) and feet (soles) combined with blueness
of the hands and feet. Effects on the central nervous system are
characterized by abnormal fatigue, sleepiness, memory
difficulties, and dizziness. With severe poisoning, confusion,
disorientation, and hallucinations occur. Truncal ataxia is a
characteristic feature, sometimes combined with nystagmus and
slurred speech. Excessive sweating in the limb extremities is a
common observation.
Signs of central nervous system and local skin involvement
may precede peripheral neuropathy by as much as several weeks.
Peripheral neuropathy can involve loss of tendon reflexes,
impairment of vibration sense, loss of other sensation, and
muscular wasting in peripheral parts of the extremities. Nerve
biopsy shows loss of large diameter nerve fibres as well as
regenerating fibres. Autonomic nervous system involvement is
indicated by excessive sweating, peripheral vasodilation, and
difficulties in micturition and defaecation. After cessation of
exposure to acrylamide, most cases recover, although the course
of improvement is prolonged and can extend over months to years.
In animal studies, early changes in visual-evoked potentials
(VEP), preceding clinical signs, as well as changes in
somatosensory-evoked potentials (SEP), have been seen.
Morphological studies have revealed degenerative changes
principally in peripheral nerve axons, with less severe changes
in the longer fibres of the central nervous system. Degeneration
of Purkinje cells has been observed in chronically-intoxicated
animals. The changes are most pronounced in the nerve endings of
myelinated sensory fibres. The nerve endings show enlarged
"boutons terminaux" and a widespread enlargement of nerve terminals
from the accumulation of neurofilaments. This occurs in both the
peripheral and central nervous systems. Impairment of retrograde
and, to a lesser degree, anterograde axonal transport has been
found in sensory fibres, and interference with glycolysis and
protein synthesis, the latter preceding the onset of clinical
signs, has been observed in biochemical studies. Studies of
neurotransmitter distribution and receptor binding in the brains of
rats have revealed changes induced by acrylamide. In rats, changes
in the concentration of neurotransmitters and in striatal dopamine
receptor binding have been related to behavioural changes.
Degenerative changes in renal convoluted tubular epithelium
and glomeruli and fatty degeneration and necrosis of the liver
have been seen in monkeys given large doses of acrylamide. In
rats, impairment of hepatic porphyrin metabolism has been
observed.
1.1.6. Mutagenicity and carcinogenicity
Acrylamide (> 99% pure) was not mutagenic in Salmonella
typhimurium in the presence or absence of a metabolic activation
system.
Acrylamide of unknown purity induced chromosomal aberrations
in the spermatocytes of male mice and was reported to increase
cell transformation frequency in Balb 3T3 cells, in the presence
of a metabolic activation system.
Acrylamide was shown to be an initiator for skin tumours in
mice when administered by various routes. It increased the
incidence of lung tumours in mice-screening assays.
A 2-year study on rats administered acrylamide in the
drinking-water has been conducted but has not been fully reported
or evaluated.
No epidemiological data on cancer due to exposure to
acrylamide are available and, from the available data, it is not
possible to form a conclusion concerning the carcinogenicity of
acrylamide.
1.1.7. Teratogenicity and reproduction
There is no evidence in either man or animals of any gross
teratogenic effects resulting from acrylamide exposure.
Absorption of acrylamide by the fetus has been demonstrated in
animal (pig, dog, rabbit, rat) studies. Oral administration of
acrylamide, between the 7 - 16th days of gestation in rats,
decreased the binding of dopamine receptors in the striatal
membranes in 2-week-old pups, a fact that may be explained by
postnatal exposure through lactation as well as prenatal effects.
Degeneration of seminiferous tubules, and chromosome aberrations
in spermatocytes have been seen in acrylamide-treated male mice.
Depressed plasma levels of testosterone and prolactin have also
been observed. However, fertility studies have not been
reported.
1.1.8. Dose-effect and dose-response relationships
A total of over 60 cases of acrylamide poisoning in man have
been reported in the literature. No human epidemiological
studies relating exposures to effects are available; the current
lack of methods for biological monitoring or assessing the extent
of exposure makes such studies impossible. From clinical
experience, it appears that acute exposure to high doses of
acrylamide induces signs and symptoms of effects on the central
nervous system, whereas peripheral neuropathy is a feature of
long-term cumulative exposure to smaller doses. Peripheral signs
of neuropathy appear after a latent period. This latent period
is dose-dependent and decreases with increasing dose. In animal
studies, the onset of peripheral neuropathy parallels the
accumulation of acrylamide bound to protein in the nervous system
and, similarly, acrylamide bound to haemoglobin in erythrocytes.
The LD50 was of the same order of magnitude for all mammals
studied.
A statistically-significant increase in the incidence of
mesothelioma of the scrotal cavity was observed in rats after
long-term (2-year) administration in the drinking-water of
acrylamide at 0.5 mg/kg body weight per day. There are no
reports of increases in any other types of tumour at this dose
level. However, administration over 2 years of 2 mg
acrylamide/kg body weight per day not only increased the
incidence of a variety of tumour types (both benign and
malignant) but also decreased the life expectancy in both male
and female rats. The smallest long-term dose of acrylamide
reported in one study to be associated with adverse neurological
effects in rats was 1 mg/kg body weight per day. This dose caused
morphological changes in the sciatic nerves.
1.1.9. Evaluation of health risks for man
There are insufficient epidemiological data regarding
occupational or environmental exposure to acrylamide to serve as
a basis for a quantitative risk evaluation. Experimental animal
data indicate that there are no major species differences among
mammals with respect to acrylamide metabolism or sensitivity to
its neurotoxic effects. Extrapolation from animal dose-effect
data suggests that an absorbed dose of 0.12 mg/kg body weight per
day (derived from total dose to surface area data) could cause
adverse neurological effects in man. As acrylamide is readily
absorbed through the skin and by inhalation and ingestion, these
effects are probably independent of the route of exposure.
Applying a safety factor of 10 to the extrapolated minimum dose
for neurological effects would indicate that an absorbed dose of
0.012 mg/kg body weight per day should not be exceeded. Animal
data are not sufficient to draw any conclusions concerning the
carcinogenicity of acrylamide. Acrylamide is associated with
adverse effects on testicular function in experimental animals.
No data regarding these effects in human beings are available.
Biological monitoring would be the method of choice in the
assessment of human exposure to acrylamide, particularly as skin
absorption is the major route of exposure. So far, no such
method has been devised, though results of experimental animal
studies indicate that the level of acrylamide bound to
erythrocytes in blood is a measure of the absorbed dose.
The most suitable method for the early assessment of adverse
effects in human beings exposed to acrylamide is the
electrophysiological examination of peripheral nerves, such as
measurements of both sensory and motor nerve action potential
amplitudes and electromyography (EMG). The sensitivity of this
method is strongly enhanced if pre-exposure baseline measurements
have been performed. Quantitative assessment of vibration
sensation offers considerable promise as a sensitive and easily
applicable method. The results of experimental animal studies
indicate that other electrophysiological procedures or parameters
such as sensory and visual evoked potentials may also be useful.
Exposure of the environment to acrylamide is mainly limited
to the contamination of water. Grouting operations may
contaminate drinking-water supplies. Special precautions must
therefore be taken to limit ground water contamination and, where
necessary, to prevent its use as drinking-water. Effluents from
industries producing or using polyacrylamide, communal sewage
plants, and from waterworks may also contaminate drinking-water
supplies, if they are taken from polluted water sources. The
current limit for the acrylamide content of drinking-water in
many countries is 0.25 µg/litre. The acrylamide content of
drinking-water can be maintained at an acceptable level by
limiting the amount of acrylamide monomer in the polyacrylamide
used for water treatment to 0.05%. Under exceptional conditions,
swimming in water close to industrial effluents containing
acrylamide may present a hazard.
Preventive measures, such as the enclosure of production
procedures and the wearing of protective clothing, should be used
to prevent occupationally-exposed workers absorbing more than
0.012 mg/kg body weight per day. The concentration in the
workroom air should not exceed 0.1 mg/m3. Ventilated face masks
may be used to prevent inhalation of acrylamide. It is possible
that underlying neurological disease and/or the administration of
neuroactive drugs might alter human sensitivity to acrylamide
but, in the absence of definite evidence that this has occurred,
no specific recommendations can be made.
1.2. Recommendations for Further Research
1.2.1. Analysis
A method for the determination of acrylamide, bound to
haemoglobin in red blood cells, should be devised to provide a
means for the biological monitoring of human exposure to
acrylamide. No methods for assessing the concentration of
acrylamide metabolites in urine are available; such analyses
would be useful for the assessment of recent exposure, and
methods should be devised.
1.2.2. Exposure
The development of biological monitoring methods would be
useful in the routine screening of occupationally-exposed
workers.
1.2.3. Metabolism and indicators of exposure
To evaluate fully the health effects and risks associated
with acrylamide exposure, it is important to elucidate the
mechanism of neurotoxicity. Both the proximal toxic agent and
the primary biochemical lesion need to be identified. Studies
should be carried out to investigate further the relationship
between the concentration of the toxic moiety in the central
nervous system and possible indicators of exposure, such as the
concentration of erythrocyte-bound acrylamide or metabolites in
the urine.
1.2.4. Effects
Further studies on animals are required to establish the no-
observed-adverse-effect levels for morphological changes in the
central nervous system and to assess the carcinogenic potential
of acrylamide.
Provided that methods for the biological monitoring of
acrylamide exposure can be devised, epidemiological studies
should be performed to relate exposure to both neurological
effects and to the incidence of cancer in acrylamide-exposed
workers. Electrophysiological methods, such as the measurement
of visual and sensory-evoked potentials, that have proved to be
useful in experimental animal studies, should be evaluated in
human studies. More experience is needed in assessing the
sensitivity and value of quantitative sensory testing. Further
studies should be performed to design suitable procedures for the
health monitoring of an occupationally-exposed population.
Further animal studies are needed on the effects of acrylamide on
the developing nervous system and the process of ageing.
2. PROPERTIES AND ANALYTICAL METHODS
2.1. Identity
Chemical structure: H H O H
| | || |
C = C - C - N
| |
H H
Chemical formula: C3H5NO
Synonyms: acrylic amide, akrylamide, propen-
amide, propenoic acid amide
CAS registry number: 79-06-1
RTECS registry number: AS 3325000
Relative molecular mass: 71.08
2.2. Chemical and Physical Properties
Acrylamide is a white, odourless, crystalline solid that is
highly soluble in water and reacts through its amide group or
double bond. Reactions of the amide group include hydrolysis,
dehydration, and alcoholysis. The Diels-Alder reaction,
polymerization, and the addition of nucleophilic reactants across
the conjugated ethylenic bond are characteristic reactions. The
chemical is stable in solution at room temperature and does not
polymerize spontaneously. Commercial solutions of the monomer may
be stabilized with hydroquinone, t-butylpyrocatechol, N-phenyl-2-
naphthylamine, or other antioxidants (Windholz et al., 1976). In
addition to carbamoylethylation and hydrolysis to acrylic acid,
acrylamide readily undergoes polymerization and copolymerization
resulting in a highly cross-linked insoluble gel. The physical
properties of acrylamide are summarized in Table 1.
Polyacrylamide is a white, odourless solid, soluble in water,
insoluble in solvents such as methanol, ethanol, and hexane, and
at least 1% soluble in glycerol, ethyl acetate, glacial acetic
acid, and lactic acid. The polymer is safe in relation to both
fire and explosion (Bikales, 1973). Levels of residual
acrylamide monomer in polyacrylamide range from 0.05 to 5%,
depending on the intended use of the product (Croll et al.,
1974).
The level of residual acrylonitrile monomer in polyacrylamide
has been estimated to be approximately 1 mg/kg (1 ppm). In
addition to polyacrylamide, N-hydroxymethylacrylamide and
N,N'-methylenebisacrylamide are produced commercially from
acrylamide. The levels of residual acrylamide in these products
are not known.
Table 1. Physical properties of acrylamide
-------------------------------------------------------------
Appearance white crystals
Relative molecular mass 71.08
Melting point 84.5 ± 0.3 °C
Vapour pressure 0.009 kPa at 25 °C
0.004 kPa at 40 °C
0.09 kPa at 50 °C
Boiling point 87 °C at 0.267 kPa
103 °C at 0.667 kPa
125 °C at 3.33 kPa
Heat of polymerization 19.8 Kcal/mole
Density 1.122 g/cm at 30 °C
Solubility in g/litre acetone 631
solvent at 30 °C benzene 3.46
chloroform 26.6
ethanol 862
ethylacetate 126
n-heptane 0.068
methanol 155
water 2155
Conversion factor
1 ppm acrylamide in air = 5 mg/m3
-------------------------------------------------------------
Adapted from: Bikales (1973).
2.3. Sampling and Analytical Methods
A number of sampling methods have been devised for
acrylamide, though no one technique has proved suitable for
collecting both aerosol and vapour. A portable pump with a
membrane filter has been used to collect samples of acrylamide
aerosol, and midget fritted glass bubblers have been used for the
determination of acrylamide vapour in air. Silica-gel sampling
tubes with membrane filters and midget impingers have been used
to collect both dust and vapour, the use of midget impingers
being more efficient than sampling tubes for vapour collection.
However, a method for sampling gaseous acrylamide using a
specially-designed sampling tube packed with Flucin-F as the
solid absorbent has been reported (Suzuki & Suzumura, 1977).
A variety of methods has been reported in the literature for
determining levels of acrylamide in environmental media and
biological tissues. Those shown in Table 2 represent the most
sensitive and/or most widely-used methods. Acrylamide reacts
with diazomethane in methanol-ether solution to form a pyrazoline
derivative that can react with 4-dimethylaminocinnamaldehyde to
form a brightly coloured (purple) Schiff base complex (Mattocks,
1968). This reaction is not specific for acrylamide and is
insufficiently sensitive for determination in environmental
media.
Acrylamide can be converted to its 2,3-dibromopropionamide
derivative for use with the electron capture detector (ECD). For
waste water, as little as 0.1 µg acrylamide/litre (as its 2,3-
dibromopropionamide derivative) has been detected by this method
(Croll & Simkins, 1972). The detection limit for biological
samples was 20 µg/litre in a biological extract of 0.5 ml (Poole et
al., 1981). Levels of 0.1 mg acrylamide/kg (0.1 ppm) in polymer or
impinger samples (Skelly & Husser, 1978) and 0.2 µg/litre (as the
2,3-dibromopropionamide derivative) in natural and polluted water
samples (Brown & Rhead, 1979) can be determined by means of the UV
detection of acrylamide after separation by high-performance liquid
chromatography (HPLC). Differential pulse polarography can be used
to determine acrylamide residues in polyacrylamide with a detection
limit of less than 1 mg/kg (1 ppm) (Betso & McLean, 1976). Dust
and airborne samples (collected by particle and vapour filtration
in a water impinger) have also been analysed by this technique with
a reported sensitivity of 0.5 µg/litre in the final extract (NIOSH,
1976).
The gas chromatography (GC) method using the 2,3-
dibromopropionamide derivative and the selective and sensitive
ECD are the most suitable for trace level determination of
acrylamide in environmental and biological samples though, for
the analysis of water samples (natural and polluted), the assay
of the derivative by HPLC has several advantages over ECGLC.
These include the suitability for routine analysis, speed of
determination, and stability of the calibration curve using
different UV lamps and columns (Brown & Rhead, 1979).
Methods for determining impurities found in commercial
acrylamide (acrylate, ammonium salts, acrylonitrile,
nitrilotrispropionamide, and butanol insolubles) have been
described by Norris (1967).
Table 2. Analytical techniques for determining acrylamide concentrations in environmental media and
biological tissues
---------------------------------------------------------------------------------------------------------
Technique Sensitivity Application Comments Reference
---------------------------------------------------------------------------------------------------------
Titration precision assay of commercial interference by acrylic Norris (1967)
(bromate- ± 0.3% product (sales acid, ethyl acrylate,
bromide method) specification) N,N'-methylene-bis-
acrylamide
Bromination/elec- 5 µg/m3 determination of no interference reported; NIOSH (1976)
tron capture gas acrylamide vapour in air conversion efficiencies
chromatography from monomer to brominated
derivative unknown
Flame ionization 0.05 - 5 mg/m3 determination of using sampling tube Suzuki &
detector; gas (0.01 - 1 ppm) acrylamide vapour in air packed with Flusin-F Suzumura (1977)
chromatography treated with phosphoric
(FID/GC) acid), the recovery of
acrylamide = 82 - 86%
High-performance 0.1 mg/kg (a) determination of acryl- no prior separation of Skelly & Husser
liquid chroma- (0.1 ppm) amide monomer in polyacryl- impurities is required; (1978)
tography amide; (b) acrylamide in recovery of acrylamide
(reverse phase) wipe and impinger samples = 96%
Direct current optimum range determination of monomeric interference by acrylo- MacWilliams
(DC) polaro- = 0.01 - 0.5% acrylamide in poly- nitrile; cationic and et al. (1965)
graphy (100 - 5000 acrylamide anionic species
mg/kg)
Differential < 1 mg/kg determination of monomeric interference by acrylo- Betso & McLean
pulse polaro- acrylamide in poly- nitrile, ethyl acrylates, (1976)
graphy (DPP) acrylamides cationic and anionic
species; some substituted
acrylamides; recovery of
acrylamide > 90%
---------------------------------------------------------------------------------------------------------
Table 2. (contd.)
---------------------------------------------------------------------------------------------------------
Technique Sensitivity Application Comments Reference
---------------------------------------------------------------------------------------------------------
Bromination/electron optimum range determination at low concentrations Croll & Simkins
capture-gas chromat- = 0.1 µg/litre of acrylamide (> 0.25 µg/litre) (1972)
ography - 1 mg/litre in water analytical interferences
must be removed; conversion
to derivative varies with
water quality; recovery of
acrylamide = 34 - 66%
Bromination/high- 0.2 µg/litre determination of interference by natural Brown & Rhead
performance liquid acrylamide in organic compounds; (1979)
chromatography natural and recovery of acrylamide (as
(reverse phase) polluted water derivative) = 70 ± 9%
Colorimetry 0.1 µg/ml urine analysis interference by aldehydes Mattocks (1968)
(0.1 ppm) ketones, pyrroles, indoles,
hydrazines, chromatic
amines
Bromination/electron 20 µg/litre determination of only suitable for Poole et al.
capture-gas chromat- (corresponding acrylamide in measuring unbound (free) (1981)
ography to a final biological samples: acrylamide; recovery of
derivatized (a) plasma acrylamide 80-90% (in the
extract of (b) tissue concentration range 10 -
0.5 ml from a homogenates 1000 ppb)
0.5 ml tissue
homogenate)
---------------------------------------------------------------------------------------------------------
3. SOURCES IN THE ENVIRONMENT
There is no evidence that acrylamide or its commercially
significant derivatives are directly produced in the environment.
3.1. Production Levels, Processes, and Uses
3.1.1. World production
Acrylamide was first produced in 1893 in Germany, and
commercial production began in 1954. The annual production of
acrylamide in the USA for 1979, 1980, and 1981 was approximately
30 000, 35 000, and 37 000 tonnes, respectively. The estimated
production of acrylamide in Japan for 1984 was approximately 36 000
tonnes (Kagaken Kogyo Nippo, 1980). The Stanford Research
Institute estimated the total annual production capacity of firms
manufacturing acrylamide in 1982 to be 63 500 tonnes. Conway et
al. (1979) forecast an increase in the level of production over the
next few years.
3.1.2. Production processes
Acrylamide monomer is produced commercially by either the
sulfuric acid hydration or the catalytic hydration of
acrylonitrile. Since its introduction in the early 1970s, the
catalytic process has become the preferred process, and has been
the only process used in the USA since 1981 (US EPA, 1981). It
possesses many advantages over the sulfate process in that high-
purity acrylamide is produced (99.5 - 99.9% compared with 98%),
there are no undesirable by-products, the conversion efficiency
is greater (97% compared with 80%), and an expensive acrylamide
purification step is avoided (Conway et al., 1979; US EPA, 1981).
In the catalytic process, acrylonitrile is hydrated to
acrylamide in the following reaction:
Catalyst
(copper)
CH2 = CHCN + H2O ------------> CH2 = CHCONH2
70 - 120 °C
This is essentially a continuous process in which unreacted
acrylonitrile is recycled back to the reactor. Acrylonitrile and
the catalyst are removed from the product by evaporation and
filtration, respectively. The aqueous acrylamide solution
produced requires no further treatment or purification.
Polymerization inhibitors are not required at any stage in the
process (Davis et al., 1976). A typical 50% aqueous acrylamide
solution produced by this process contains 48 - 52% acrylamide
and a maximum of 0.05% of polymer (ECT, 1978). Residual
acrylonitrile has been reported at levels between 1 and 100 mg/kg
(i.e., up to 0.01%) (US EPA, 1980a).
Although monomer manufacture does not generate large volumes
of by-products, acrylamide-containing waste streams are generated
during polyacrylamide production (Conway et al., 1979).
3.1.3. Uses
The major use of acrylamide and its derivatives is in the
production of polymers and copolymers for various purposes. In
the USA, the only large-scale use of acrylamide, other than in
the manufacture of polymers, is as a chemical grout; this
consumed 1100 tonnes (3%) of domestically-produced monomer in
1980 (US EPA, 1980a). The relative amounts of acrylamide used in
water treatment may vary from country to country. The various
uses of acrylamide monomer, domestically produced and imported,
are summarized in Fig. 1.
Polyacrylamides are used as flocculents to separate solids
from aqueous solutions in mining operations, in the disposal of
industrial wastes, and in the purification of water supplies
(Tilson, 1981). The largest market for acrylamide polymers is in
the treatment of sewage and wastewater (40% of total acrylamide
production in 1973 in the USA) (Blackford, 1974).
Numerous derivatives of acrylamide appear in the literature.
The two most commercially important are N-hydroxymethyl-
acrylamide and N,N-methylenebisacrylamide. N-hydroxymethyl-
acrylamide is used in the textile industry as a cross-linking
agent and N,N-methylenebisacrylamide is used mainly as a
copolymer in acrylamide grout and in the manufacture of
photo-polymer printing plates. Some of the minor uses of
polyacrylamides are summarized in Table 3.
Table 3. Minor uses of polyacrylamides
-----------------------------------------------------------------------
Coal dust loss preventative Pigment-binding resins
Coal floatation Polyester laminating resins
Dental fillers Printing pastes
Drilling fluid additives Propellant binders
Elastomer curing agent Rodent repellents
Electro-refining Shaving creams
Emulsion stabilizers Soil stabilizers
Flooding agents for petroleum Suspending agents
recovery Textile resins for warp sizing,
Hair sprays printing, shrinkproofing, anti-
Ion-exchange polymers static treatments, binding non-
Leather-treating agents woven fabrics, improving dye
Moulding resins to increase receptivity, increasing dimen-
strength, raise softening temp- sional stability of viscose
erature, or to serve as plasti- rayon
cizing components Thickening agents
Paper additives and resins for Gel electrophoretic separation
faster draining, improved filler of biochemicals
retention, coating, sizing, wet
and dry strength improvements
-----------------------------------------------------------------------
From: US EPA (1981).
3.2. Release into the Environment
Acrylamide monomer may enter the environment from a number of
sources. Because closed systems are now used in acrylamide
manufacture (section 3.1.2), production processes are unlikely to
be a source of environmental contamination, except in the event
of a leak from the reactor.
Contamination of water by acrylamide, discharged in effluent
from industries using or manufacturing polyacrylamide, has been
reported (Croll et al., 1974; Conway et al., 1979; Brown et al.,
1980b).
Another potential source is the release of acrylamide monomer
residues from polyacrylamide flocculents used in processes such
as sludge or conditioning of oil tailings and clarification of
waste and drinking-waters. Croll et al. (1974) demonstrated
that, in many water-treatment processes, acrylamide is not
removed (section 4.3).
Localized contamination may also arise from the use of
acrylamide in grouting operations. The technology exists for the
in situ cross-linking of the polymer as opposed to the monomer
in such operations, thereby decreasing environmental exposure.
However, it is not known to what extent this technique is
employed (US EPA, 1980a).
Direct contamination from spills and leaks may also occur
during transportation, storage, use, and disposal of either
acrylamide or polyacrylamide (Conway et al., 1979).
The Dow Chemical Company has estimated that releases of
acrylamide monomer into the environment during manufacture and
use could amount to 95 tonnes annually. A draft report prepared
for the US EPA estimated a higher figure of 250 tonnes (US EPA,
1978).
3.3. Disposal of Wastes
Decontamination of solid and liquid wastes containing
acrylamide may be achieved by chemical means, e.g., using
potassium permanganate or ozone (Croll et al., 1974) or by
biological degradation (Davis et al., 1976; Arai et al., 1981).
Acrylamide waste may be disposed of by incineration, provided
nitrogen oxides are scrubbed from flue gases (HBTHC, 1981).
However, the cost of removing a large percentage of acrylamide in
waste streams is high.
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1. Transport in the Environment
Acrylamide and its monomeric analogues have a high mobility
in an aqueous environment and are readily leachable in soil.
Acrylamide may travel great distances in the ground water of deep
rock aquifers, where biodegradability is reportedly absent
(Conway et al., 1979). Lande et al. (1979) found acrylamide to
have a higher mobility (leaching) and lower rate of degradation
in sandy soils than in clay soils. Since grouting with acrylamide
is recommended for sandy soils, a potential hazard for ground water
contamination may exist. However, no studies have been made of its
behaviour in subsurface soil where most grouting applications take
place. Acrylamide is unlikely to enter and be distributed in the
atmosphere to any significant extent, because of its low vapour
pressure. Biodegradation is liable to occur to some extent;
acrylamide should not be regarded as a persistent substance,
although its rate of degradation may vary with environmental
conditions (Davis et al., 1976).
4.2. Biomagnification and Bioconcentration
Solubility, partition coefficients, and polarity will affect
the fate of acrylamide analogues. Since many acrylamides are
highly water soluble and are degraded by microorganisms (Brown et
al., 1980c), it is unlikely that they will bioconcentrate in food
chain organisms in significant quantities (Metcalf et al., 1973;
Neely et al., 1974). Log Po/w (n-octanol/water partition
coefficient), based on methods of Hansch & Leo (1979), yields an
approximate value of -1.65 (US EPA, 1980a). This value indicates
that the solubility of acrylamide in water is very high compared
with its solubility in lipids. Thus, it is considered that
bioconcentration of organisms in the fatty tissues will be
minimal. Similarly, on the basis of its water solubility,
biomagnification of acrylamide in the food chain is not expected
(Metcalf et al., 1973).
4.3. Transformation
A wide variety of microbes possess the ability to degrade
acrylamide (Croll et al., 1974; Lande et al., 1979; Brown et al.,
1980a) under light or dark, anaerobic or aerobic conditions.
However, periods of several days may elapse prior to any
significant degradative losses (Conway et al., 1979; Brown et
al., 1982). An amidase-producing microorganism belonging to the
genus Rhodococcus (strain 10 021R), isolated from the sewage of
an acrylamide plant, was found to convert acrylamide monomer
(even in an acrylamide gel stabilizer) into the less toxic
acrylic acid. This microorganism was found to be non-virulent in
experimental animals (even at high doses) and hence, its possible
use in the control of environmental pollution has been suggested
(Arai et al., 1981).
The residence period of acrylamide may be of the order of
days, weeks, or months in a river of low microbial activity.
Brown et al. (1980a) also showed that degradation rates in
samples of river water, continuously exposed to low levels of
acrylamide (6 - 50 µg/litre), were faster than those in river
samples not previously exposed. Acrylamide entering a water
course may be present for several days (Brown et al., 1980a).
Under aerobic conditions, acrylamide has been shown to be readily
degraded in fresh water by bacteria, with a half-life of 55 - 70
h, after acclimatization of the bacteria to the compound for 33 -
50 h (Conway et al., 1979). Half-lives in estuarine or salt
water are slightly longer (Croll et al., 1974). Cherry et al.
(1956) studied the effects of acrylamide (10 mg/litre) on the
chemical oxygen demand (COD) in filtered river water. The
initial half-life was approximately 5 days. When the samples were
re-exposed to acrylamide, the COD decreased more rapidly. Croll et
al. (1974) monitored the concentration of acrylamide in river water
containing acrylamide at 8 µg/litre. After a time-lag of
approximately 100 h, the acrylamide degraded rapidly. The addition
of acrylamide at 10 µg/litre to natural waters, which had already
been exposed to acrylamide, resulted in a shorter time-lag and
faster degradation rates.
In laboratory experiments, acrylamide was not adsorbed by
sewage sludge, natural sediments, clays, peat, or synthetic
resins over the pH range 4 - 10. Therefore, removal by this
means seems unlikely unless converted to a less polar and/or
charged compound. Temporary entrainment in a polymeracrylamide-
particle matrix may occur during flocculation processes, and rapid
leaching will occur should such a matrix remain in contact with
water for a period of time (Brown et al., 1980c). Polyacrylamide
is used for the conditioning of waterworks sludge. Since 92 - 100%
of the residual acrylamide in the polymer is leached out in the
sludge-conditioning process, care must be taken to ensure that any
conditioned sludge supernatant which is returned to the main flow,
does not raise the acrylamide concentration in finished water above
acceptable levels. A removal rate of 75% was calculated by Croll
et al. (1974) for an overloaded sewage works receiving an
acrylamide effluent of 1.1 mg/litre.
Lande et al. (1979) found a faster rate of degradation and
lower mobility of acrylamide in silt clay soils than in clay
loam, loamy fine sand, or loam. Acrylamide is recommended for
grouting on sandy soils, in which it has a relatively low rate of
degradation and a high mobility. Unfortunately, no studies have
been carried out on the behaviour of acrylamide in subsurface
soil where most grouting applications take place.
The half-life of acrylamide in aerobic silt loam was of the
order of 20 - 45 h at a concentration of 25 mg/kg and a
temperature of 22 °C, and 94.5 h at 500 mg/kg and 20 °C.
Increasing the acrylamide concentration or decreasing the
temperature increased the half-life (Lande et al., 1979;
Abdelmagid & Tabatabai, 1982). The behaviour of acrylamide
(100 mg/kg) in soil-plant systems was investigated by Nishikawa
et al. (1979). Acrylamide decomposed mainly by hydrolysis to
form acrylic acid. In upland farming conditions (aerobic
conditions), there was a rapid decrease in total organic carbon
(TOC), up to 15 days after application, whereas in wet-land
(rice) conditions, the decrease was slow. These fluctuations in
TOC under both types of farming conditions corresponded closely
to the changes in TOC originating from acrylamide and acrylic
acid (Nishikawa et al., 1979).
Polyacrylamide may be hydrolysed, but acrylamide monomer is
not formed in solutions. Some photosensitized polymerization is
possible for certain acrylamide derivatives. However, major
modification of the molecule as a consequence of
chemical/photochemical reaction seems unlikely (Davis et al.,
1976).
5. ENVIRONMENTAL LEVELS AND EXPOSURES
5.1. Environmental Levels
5.1.1. Ambient air and soil
The results of monitoring studies in the USA, performed near
6 plants producing acrylamide and/or polyacrylamides, showed
average acrylamide levels in the air of less than 0.2 µg/m3, in
either vapour or particulate form, and less than 0.02 mg/kg (0.02
ppm) in soil or sediment samples (Going, 1978).
5.1.2. Water
The Committee on New Chemicals for Water Treatment in the
United Kingdom recommended that: commercial polyacrylamide used in
the treatment of drinking-water should not contain more than 0.05%
acrylamide monomer, the average amount of polymer added to water
should not exceed 0.5 mg/litre, and the maximum dose should not
exceed 1.0 mg/litre (UK Ministry of Housing and Local Government,
1969).
Although limits have been recommended for the amount of
polyacrylamide used in the clarification of drinking-water, much
higher levels may be encountered in other uses, where polymers
with a higher monomer content are used at much higher levels.
For example, polyacrylamides used for effluent treatment may
contain monomer levels of between 1 and 50 g/kg (Croll et al.,
1974). If effluent from such processes were to enter water
subsequently treated for public supply, then the acrylamide
concentration derived from the raw water source might be higher
than that resulting from the clarification process. The
acrylamide contents of effluents from several industries using
polyacrylamide are shown in Table 4.
Brown et al. (1980b) did not detect any acrylamide in
effluents from the china-clay industry, after several months of
polymer use (analytical detection limit, 0.2 µg/litre). Croll et
al. (1974) detected 16 µg acrylamide/litre in the effluent from a
clay pit, which resulted in an acrylamide level of 1.2 µg/litre in
the receiving stream. Further downstream at a waterworks intake,
this level had dropped to 0.3 µg/litre.
Environmental monitoring at sites of acrylamide and
polyacrylamide production in the United Kingdom and the USA
indicates that levels of acrylamide reaching surface waters from
industrial effluent would generally be difficult to detect below
1 µg/litre (Croll & Simkins, 1972; Going & Thomas, 1979). A
value of 1.5 mg/litre was recorded by Going (1978) in a small
stream receiving effluent directly downstream from a
polyacrylamide producing plant in the USA. High levels have also
been found in the vicinity of local grouting operations (Croll et
al., 1974). Igisu et al. (1975) reported a level of 400 mg
acrylamide/litre in well-water in Japan that had been
contaminated from a grouting operation 2.5 metres away.
Table 4. Concentrations of acrylamide in some industrial effluents
-----------------------------------------------------------------------
Effluent Acrylamide Reference
concentration
(µg/litre)
-----------------------------------------------------------------------
Colliery A; tailings lagoon 42 Croll et al. (1974)
Colliery B; tailings lagoon 39 Croll et al. (1974)
Colliery C; coal washing; 1.8 Croll et al. (1974)
effluent lagoon
Colliery/coking plant effluent 0.74 Croll et al. (1974)
Paper mill A; treated effluent 0.47 Croll et al. (1974)
Paper mill B; treated effluent 1.2 Croll et al. (1974)
Clay pit 16.0 Croll et al. (1974)
Paper mill A & B; treated effluent < 1.0 Brown et al. (1980b)
Paper mill A & B; process water < 1.0 Brown et al. (1980b)
Paper mill C; treated effluent 14.4 Brown et al. (1980b)
Paper mill C; process water 45.4 Brown et al. (1980b)
-----------------------------------------------------------------------
No acrylamide (detection limit 4 µg/litre) was detected in
process waters from a sewage works, either before or after
polymer addition (Brown et al., 1980a). In another works,
samples of vacuum- and pressure-filtered sewage sludge,
conditioned with polyacrylamide, were found to contain up to 0.1
µg acrylamide/litre. On the basis of the acrylamide content and
polymer dosage, these filtrates would have contained up to 25 µg
acrylamide/litre, had no degradation and/or adsorption occurred
(Croll et al., 1974).
The fate of acrylamide monomer in waterworks sludge
conditioning (using the polymer) was investigated by Croll et al.
(1974). In 2 waterworks, between 74 and 87% of acrylamide
(residual monomer from the polymer) passed into the recovered
water. This water was either returned directly to the waterworks
intake or disposed of as an effluent. No acrylamide was detected
by Brown et al. (1980b) in process waters from a waterworks using
polyacrylamide for effluent treatment (detection limit 0.2
µg/litre). The authors also investigated the effects of
accidental polymer overdosing. A maximum concentration of 8.6 µg
acrylamide/litre was detected in backwash water, 30 min after
spiking with 100 times the normal polymer dosage. The effluent
was diluted approximately 12 times, in river water 500 metres
downstream from the discharge (0.7 µg/litre). Such effluents
from over-loaded water- or sewage sludge-conditioning works could
present a hazard to water supplies taken downstream of the
effluent discharge (Croll et al., 1974).
5.1.3. Food
The US Food and Drug Administration has established a maximum
acrylamide residue level of 0.2% (2 g/kg) for acrylamide polymers
used in paper or paperboard in contact with foodstuffs (Bikales,
1973). Similarly, in the Federal Republic of Germany, the
Federal Health Authority have recommended that the level of
polyacrylamide used as an agent for retention (Table 3) in
foodstuff packaging should not exceed 0.3%. This should not
include more than 0.2% monomer. The use of polyacrylamides in the
washing of pre-packed foods and vegetables and the clarification
and stabilization of wines has been described (MacWilliams, 1973;
Croll et al., 1974). In the USA, polyacrylamide used in the
washing of fruits and vegetables must not contain more than 0.2% (2
g/kg) acrylamide monomer (IRPTC, 1983). No data regarding the
levels of acrylamide in foods or the potential effects that such
contamination might have on the environment are available. Brown
et al. (1980b) mentioned the possibility of acrylamide consumption
by farm animals, via feed containing industrial or sewage sludges.
5.2. General Population Exposure
The general population is potentially exposed to acrylamide
by inhalation, skin absorption, water, and by ingestion of food.
In the Federal Republic of Germany, the level of residual
monomer in polyacrylamide used in hair sprays is limited to 0.01%
(0.1 g/kg)a.
5.3. Occupational Exposure
Information on occupational exposure to acrylamide is sparse.
In 1976, NIOSH estimated that approximately 20 000 workers might
be exposed to acrylamide in the USA; however, there is no
indication that this figure included grouting workers and Conway
et al. (1979) estimated that this group of workers could number
at least 2000 by 1980. A large number of laboratory workers are
also potentially exposed to acrylamide during the preparation of
polyacrylamide gels for electrophoresis. Although exposure
levels have not been reported for grouters, the potential for
hazard from this use is probably greater than that from other
uses because of the uncontrolled nature of the grouters'
exposure.
No epidemiological studies are available, and only limited
air monitoring data (Vistron Company, USA), on acrylamide
concentrations in the workplace. Stationary air sampling
showed acrylamide concentrations ranging from 0.1 to 0.4 mg/m3
for a control room, from 0.1 to 0.9 mg/m3 for a bagging room,
and from 0.1 to 0.4 mg/m3 for a processing area. The sampling
was performed during an 8-h working day, and the values cited
represented weekly averages. In another factory in the USA,
personal sampling (4 h) revealed acrylamide exposure levels of
0.76 mg/m3 and 0.52 mg/m3 for 2 packers, 0.48 mg/m3 for a
reactor operator, and 0.52 mg/m3 for a dryer operator (NIOSH,
1976). In another factory, both personal sampling and stationary
sampling were performed during 1974-75. Personal sampling
concentrations ranged from 0.1 to 3.6 mg/m3, with the highest
concentrations seen in the bagging area. The median value for
all personal monitoring data was 0.6 mg/m3, while the stationary
-------------------------------------------------------------------
a Bundesministerium für Jugend, Familie und Gesundheit, 1984.
sampling showed concentrations ranging from 0.1 to 0.3 mg/m3.
Thus, in 2 factories, the personal sampling measurements were
between 2 and 3 times higher than stationary sampling measurements
(NIOSH, 1976).
A recommended threshold limit value/time-weighted average
(TLV/TWA) for acrylamide in workroom air is 0.3 mg/m3 and the
short-term exposure limit (TLV-STEL) is 0.6 mg/m3 (ACGIH,
1984). Other recommended occupational exposure levels (for
acrylamide in workroom air) for various countries are shown in
Table 5.
Table 5. Occupational exposure levels for acrylamide in workroom
air of various countriesa
--------------------------------------------------------------------
Country Exposure limit Category of Notation
(mg/m3) limitb
--------------------------------------------------------------------
Australia 0.3 TWAc Sd
Belgium 0.3 S
Finland 0.3 TWA S
Germany, Federal 0.3 MAKe Sf
Republic of
Hungaryg 0.3 TWA
1.5 STEL
Italy 0.3 TWA S
Japan 0.3 MACh S
Netherlands 0.3 TWA S
Sweden 0.3 TWA S
0.9 STELi
Switzerland 0.3 MAC S
United Kingdom 0.3 TWA S
0.6 STEL
USA
(a) NIOSH/OSHA 0.3 PELj S
(b) ACGIH 0.3 TWA S
0.6 STEL
USSRk 0.2 MAC
Yugoslavia 0.3 TWA S
--------------------------------------------------------------------
a From: ILO (1980) and IRPTC (1983).
b Category of limit: broad definition of type of limit stated.
For exact meaning of terms, refer to individual country
requirements.
c TWA (time-weighted average): a mean exposure limit averaged
generally over a working day whereby, within prescribed limits,
excursions above the level specified are permitted, provided
they are compensated for by excursions below the level specified.
d SI: specified as a skin irritant.
e MAK: maximum worksite concentration.
Table 5. (contd.)
--------------------------------------------------------------------
f S (skin absorption): this designation refers to the potential
contribution of cutaneous absorption either by airborne or, more
particularly, by direct contact.
g From: Hungary, State Ministry of Health (1978).
h MAC: maximum allowable concentration.
i STEL (short-term exposure limit): a maximum concentration
allowed for a short specified duration.
j PEL: permissible exposure limit.
k From: USSR, Ministry of Health (1979).
Note: Occupational exposure levels and limits are derived in
different ways, possibly using different data and expressed
and applied in accordance with national practices. These
aspects should be taken into account when making comparisons.
6. KINETICS AND METABOLISM
6.1. Experimental Animal Studies
6.1.1. Absorption and distribution
Acrylamide has been reported to induce neurotoxic effects in
many animal species following absorption via the respiratory,
dermal, and oral routes (Hamblin, 1956). The absorption and
distribution of acrylamide applied dermally to rabbits was
studied by Hashimoto & Ando (1975). A single 30-min application
of a 10 - 30% aqueous solution of [1-14C]-acrylamide rapidly
penetrated the skin (auto-radiography showed a concentration of
14C in the hair follicles) and appeared in the blood in 2 forms,
mainly protein-bound, and in a free water-soluble form. About
50% of the radioactivity in the blood was associated with the
protein-bound fraction, 24 h after cessation of contact. This
value increased to about 90%, when there was daily contact with
acrylamide (30-min duration) for 7 days. Similar patterns of
distribution were observed after intravenous (iv) administration.
In rats, Hashimoto & Aldridge (1970) found that the highest
levels of radioactivity after a single iv dose (100 mg/kg body
weight) were in whole blood. After 24 h, the plasma contained
little radiolabel and in vitro binding to haemoglobin was
demonstrated; this suggested that the protein-bound radioactivity
in the blood was associated with the red blood cells. By 14
days, the majority of free/soluble radiolabel had disappeared in
both blood and tissues. However, the protein-bound radiolabel
remained at 100% and 25% of the 24-h levels in blood and tissues,
respectively. During the 48 h following an iv dose of [1,3-14C]-
acrylamide at 50 mg/kg (Young et al., 1979), the concentration of
radiolabel decreased in selected rat tissues but increased in red
blood cells to a plateau that was between 10 and 90 times higher
than the levels in the other tissues examined.
Miller et al. (1982) determined the extractable fraction of
parent acrylamide in tissues obtained from rats, at various time
intervals after an iv dose of [14C]-acrylamide at 10 mg/kg body
weight. Values, which ranged from 85 to 100% at 15 min,
decreased as time progressed (10 - 50% at 12 h and less than 1%
after 24 h). The extractable fraction from the blood was only
50% at 15 min and less than 1% at 12 h. Covalent binding of
acrylamide to cysteine residues in rat haemoglobin was
demonstrated by Hashimoto & Aldridge (1970) and binding occurred
at the 4 active sulphydryl groups in the haemoglobin molecule. It
seems likely that the non-extractable fraction in vivo is due to
this reaction or its metabolites.
The only biological component that has substantial irreversible
binding and has been found to concentrate acrylamide (as 14C) is
the red blood cell. Pastoor & Richardson (1981) found that 3 h
after iv administration to rats, uptake of acrylamide by red blood
cells was essentially complete and had plateaued. The plateau
level was closely correlated with dose (r2 = 0.995) and was
determined to be 2.0 ± 0.2% of the dose per ml of red blood
cells. After iv administration of 10 mg [14C]-acrylamide/kg body
weight, the binding to erythrocytes in rats plateaued at 12% of
the dose and accounted for essentially all of the 14C in the
blood (Miller et al., 1982). When acrylamide was given to rats
(30 mg/kg body weight per day), the blood concentration rose to a
plateau of about 400 mg/kg, on day 9 (Young et al., 1979).
Measurements of unbound acrylamide in the blood of rats given
a single iv dose indicated that acrylamide is distributed
throughout total body water within 30 min (Edwards, 1975a).
Fetal absorption of acrylamide has been reported in various
mammalian species demonstrating the permeability of the placenta
(section 7.5) (Edwards, 1976a; Ikeda et al., 1983). Miller et
al. (1982) studied the distribution and fate of orally-
administered [14C]-acrylamide (10 mg/kg body weight) in rats.
An absorption phase, which had peaked by the end of the first
hour, was observed in liver, fat, kidney, and testis. Acrylamide
is highly soluble in water and poorly soluble in lipids.
Concentration in particular tissues is due, either to covalent
binding to particular proteins, or to an accumulation of
metabolites, e.g., in the liver and kidney. The concentration of
radiolabel in neural tissue (brain, spinal cord, and sciatic
nerve) did not differ significantly from that in non-neural
tissue, except for that in red blood cells (Poole et al., 1981;
Miller et al., 1982). Ando & Hashimoto (1972) reported that the
distribution of radiolabel in the sciatic nerve was 2.5 times
greater in the distal half of this tissue. Acrylamide has also
been reported to concentrate in the sciatic nerve terminals, with
accumulation taking place directly from the blood stream
(Hashimoto, 1980). Hashimoto & Aldridge (1970) detected a
considerable amount of protein-bound radioactivity in the brain
and spinal cord of rats, 14 days after a single iv dose (100
mg/kg body weight) of [14C]-acrylamide. They suggested that this
finding could be significant if protein binding were involved in
the primary lesion.
6.1.2. Metabolism
The biotransformation of acrylamide has been shown to be
mainly mediated through glutathione conjugation (Pastoor et al.,
1980; Dixit et al., 1981a; Miller et al., 1982). Studies by
Dixit et al. (1981a) established that the reaction of acrylamide
with glutathione occurs by both non-enzymic and enzymic
(catalysed by glutathione- S-transferase (GST) (EC 2.5.1.18))
reactions and occurs in both the liver and the brain. Edwards
(1975a) demonstrated biliary excretion of a glutathione conjugate
of acrylamide ( S-beta-propionamido-glutathione) after iv
administration to rats. In studies by Miller et al. (1982), 15%
of the dose (as total 14C) was excreted in the bile within 6 h of
oral administration to rats; only 1% was parent acrylamide.
Miller et al. (1982) detected at least 4 urinary metabolites
after the oral administration of [14C]-acrylamide to rats. The
major metabolite was mercapturic acid ( N-acetyl-cysteine- S-
propionamide), which accounted for 48% of the dose. Unmetabolized
acrylamide (2%) and 3 non-sulfur-containing metabolites (total
14%) were also present in the urine; cysteine- S-propionamide was
identified as a urinary metabolite by Dixit et al. (1982).
Glutathione conjugation is presumed to be a detoxifying
process, since Dixit et al. (1980a) demonstrated an earlier onset
of toxicity after depletion of hepatic glutathione stores and
Edwards (1975b) found that the glutathione conjugate did not
induce any neurotoxic effects. Concurrent administration of
methionine (involved in the synthesis of glutathione) with
acrylamide has also been shown to reduce the neurotoxic potency
of acrylamide (Hashimoto & Ando, 1971). Inhibition of GST by
acrylamide has been reported by Dixit et al. (1981b), Mukhtar et
al. (1981), and Das et al. (1982). Thus, acrylamide may inhibit
not only its own detoxification, but also that of other toxic
xenobiotics along this pathway. Pre-exposure of rats to
acrylamide has been shown to inhibit the biliary excretion of
methylmercury, which requires glutathione for its
biotransformation (Refsvik, 1978).
Hashimoto & Aldridge (1970) reported that 6% of an iv dose
of [1-14C]-acrylamide, was exhaled by rats as [14C]-carbon
dioxide (14CO2), for 8 h after administration. No exhaled
14CO2 was detected by Miller et al. (1982) using
[2,3-14C]-acrylamide. It would appear, therefore, that
acrylamide is metabolized, to a small extent, by cleavage of
the carbonyl group. Apparently, the remaining 2-carbon
fragment is not metabolized to carbon dioxide.
Efforts to demonstrate the role of the microsomal mixed-
function oxidase (MFO) (EC 1.14.14.1) system in the
biotransformation of acrylamide have not been successful. There is
evidence suggesting that, under in vitro conditions, a reactive
metabolite of acrylamide is formed by the MFO system, which
inhibits aniline hydroxylase activity and cytochrome P-450 in rats
(Ortiz et al., 1981). In vivo studies by Das et al. (1982) also
demonstrated a decrease in hepatic MFO enzyme levels. Similar
studies on mice by Nilsen et al. (1978) demonstrated a reduction in
only one form of hepatic cytochrome P-450 (P-45047), without any
change in the total amount of cytochrome P-450. A reduction in
both cutaneous and hepatic aryl hydrocarbon hydroxylase (AHH)
activity was observed in mice following topical application of
acrylamide (Mukhtar et al., 1981). Edwards et al. (1978) reported
a 15% depletion of microsomal cytochrome P-450 in rats after a
single subcutaneous (sc) dose of acrylamide. This observation was
accompanied by a 100% increase in liver porphyrins; there is
evidence that reactive metabolites of allyl groups formed via
cytochrome P-450 are responsible for the abnormal degradation of
haem (Ortiz de Montellano & Mico, 1980).
SKF 525A is an inhibitor of hepatic mixed-function oxidases
(decreased detoxification or bioactivation) while phenobarbital
increases them (increases bioactivation and/or detoxification)
and also induces glutathione S-transferases (detoxification).
Kaplan et al. (1973) reported that pretreatment of rats with SKF
525A, to inhibit hepatic mixed-function oxidase activity,
enhanced the neurological effects and lethality of acrylamide.
On the other hand, acrylamide-induced changes in striatal
dopaminergic receptors were completely prevented by SKF 525A
(Agrawal et al., 1981a). With regard to the effects of hepatic
microsomal inducers on the development of acrylamide neuropathy,
Kaplan et al. (1973) reported a significantly delayed onset of
ataxia after ip administration of acrylamide following
pretreatment of rats with phenobarbital (or DDT), while Edwards
(1975b) failed to obtain similar results after oral
administration. Hashimoto & Tanii (1981) reported that
phenobarbital treatment reduced neuro- and testicular toxic
effects due to acrylamide, or selected analogues in mice.
However, Kaplan et al. (1973) found that the delayed onset of
neurotoxicity was accompanied by a greater degree of peripheral
nerve injury in pretreated animals. In studies by Tanii &
Hashimoto (1981), phenobarbital pretreatment did not increase the
rate of in vitro metabolism of acrylamide, but increased the
rate of reaction of acrylamide with glutathione by some 40%.
Because it has not yet been established whether the biological
effects of acrylamide are due to the parent compound or to a
bioactivated derivative, it is difficult to interpret the results
of these studies.
6.1.3. Elimination and excretion
6.1.3.1. Elimination
Acrylamide (as total 14C) was eliminated from rat tissues
in a biphasic manner (Miller et al., 1982). In the first
component, the elimination half-life in most tissues was less
than 5 h and, in the second, 8 days or less. Testes and skin had
slower elimination rates with initial half-lives of 8 and 11 h,
respectively. An interesting observation was that the
elimination of radiolabel in neural tissue did not differ
significantly from that in non-neural tissue.
The amount of 14C in blood remained constant at 12% of the
dose for up to 7 days. However, 14C in plasma was eliminated
very rapidly. The terminal elimination half-life for acrylamide
in blood (as 14C) was reported by Pastoor & Richardson (1981) to
be about 10 days, which is close to the figure of 13 days
suggested by Hashimoto & Aldridge (1970).
In contrast to the kinetics for total 14C, the elimination of
parent acrylamide fitted a monoexponential curve. The half-life
of parent acrylamide in blood was 1.7 h (Miller et al., 1982),
which is comparable with the figure of 1.9 h reported by Edwards
(1975a). Pastoor & Richardson (1981) estimated that the half-
life of plasma acrylamide was approximately 2.5 h. They also
observed that the semi-log plasma elimination curves became more
linear as the dose increased from 2 to 20 mg/kg body weight (iv
administration), which implied a saturation of elimination
pathways at higher doses. The elimination of parent acrylamide
from tissues corresponded with that seen in the blood. Within 24
h, no detectable levels were found in any tissue (Miller et al.,
1982). The conclusion is that the half-life for parent
acrylamide in blood and tissues makes it unlikely that this form
accumulates in the body.
6.1.3.2. Excretion
The excretion half-life of parent acrylamide in rat urine
was 7.8 h (Miller et al., 1982) (section 6.1.1). Using
[1-14C]-acrylamide, Hashimoto & Aldridge (1970) reported that
approximately 6% of the dose was exhaled as 14CO2. In an
extensive study of the kinetics of both orally- and iv-administered
[2,3-14C]-acrylamide, it was shown that the rate of elimination
of the radiolabel in urine was independent of the route of
administration. Within 24 h, about two-thirds of the dose was
excreted in the urine and three-quarters in 7 days. Faecal
excretion was small (4.8% in 24 h and 6% by 7 days). Since 15%
of the dose appeared in the bile within 6 h, acrylamide or its
derivatives must undergo enterohepatic circulation. Thus,
approximately 80% of the radiolabel was excreted within 7 days
and, of this, a very large proportion (90%) was in the form of
metabolites.
When [14C]-acrylamide was given to rats daily by gavage or
in the drinking-water at 30 mg/kg body weight per day, the daily
excretion of radioactivity in the urine was nearly constant
during the 14-day period (Young et al., 1979), most of the dose
being excreted as 2 major metabolites together with a small
amount of the parent compound. Miller et al. (1982) reported
that the excretion rates of radiolabel in urine, following
administration of 1 - 100 mg acrylamide/kg body weight were
independent of dose, implying zero order elimination kinetics.
Excretion of both free and protein-bound [14C] acrylamide has
been demonstrated in the milk of rats, during lactation (section
7.5) (Walden & Schiller, 1981).
6.2. Human Studies
Limited data are available on absorption, distribution,
elimination, and metabolism in human beings, and these have
mainly been derived from clinical observations in cases of
poisoning. The findings in animal studies that acrylamide is
readily absorbed, whatever the route of exposure, is supported by
clinical observations. The majority of human cases of acrylamide
poisoning reported in the literature have occurred through skin
absorption (Fujita et al., 1961; Auld & Bedwell, 1967; Garland &
Patterson, 1967; Morviller, 1969; Graveleau et al., 1970;
Takahashi et al., 1971; Cavigneaux & Cabasson, 1972; Davenport et
al., 1976; Mapp et al., 1977). Poisoning by ingestion of
contaminated water has also been reported (Igisu et al., 1975),
indicating efficient gastrointestinal absorption of acrylamide.
However, quantitative data on absorption or excretion in human
beings are not available at present. There are no methods for
determining acrylamide or its metabolites in blood or excreta,
and such methods are urgently needed. Animal data suggest that
the concentration of acrylamide in red blood cells might serve as
an index of body burden of acrylamide (Edwards, 1976b; Pastoor &
Richardson, 1981). However, no studies are available on the
relationship between the blood concentration of acrylamide and
its toxic effects or on human urinary excretion of acrylamide and
its metabolites.
7. EFFECTS ON ANIMALS
7.1. Neurological Effects
Regardless of species, nearly all studies on acrylamide
intoxication involve manifestations of various degrees of
neurotoxicity; however, it must be emphasized that polyacrylamide
itself is not neurotoxic. Some effects of acute acrylamide
intoxication are shown in Table 6. Results of experimental
animal studies suggest that central nervous system (CNS) effects
predominate in acute acrylamide poisoning, whereas, on repeated
administration of divided doses, signs of peripheral neuropathy
become more evident (Le Quesne, 1980). The general toxicological
profile of poisoning, following prolonged exposure to repeated
doses, includes tremors, incoordination, ataxia, muscular
weakness, distended bladder, and loss of weight. In acute
single-dose studies on cats, Kuperman (1958) described ataxic
tremors together with severe tonic-clonic convulsions and other
signs of diffuse central excitation. With prolonged intoxication
in cats, incoordination was the first malfunction observed,
followed by limb weakness (McCollister et al., 1964; Le Quesne,
1980). The development of neuropathy usually begins with the
involvement of the distal parts of limbs and slowly progresses to
the proximal regions of the body.
7.1.1. Neurobehavioural effects
Numerous investigators have used neurobehavioural techniques
to detect and quantify the neurotoxic effects of acrylamide,
including effects on motor and sensory function, on-going
performance, and cognitive processes.
The procedures and the effects of acrylamide on neuromotor
function in rats are listed in Table 7 according to sensitivity,
i.e., the lowest cumulative dose required to produce a
significant alteration. Motor dysfunction, as measured by
impaired rotarod performance, hind-limb splay, and hind-limb
weakness, can be observed in the dose range 100 - 320 mg/kg. In
other procedures involving a conditioned motor response, such as
food-reinforced, schedule-controlled behaviour (VI or FR), changes
in performance have been observed in the dose range 25 - 75 mg/kg.
Tilson et al. (1979) associated neuromuscular weakness with
histopathological alterations, i.e., loss of fibres and axonal
swelling in peripheral nerves, both during dosing and following
cessation of exposure. Other studies with mice have also shown
that motor dysfunction can be quantified using neurobehavioural
procedures that assess motor coordination and neuromuscular
strength (Gilbert & Maurissen, 1982; Teal & Evans, 1982).
Table 6. Clinical signs of acute acrylamide intoxication in mammals
--------------------------------------------------------------------------------------------------------
Species Route Dose Mortality Clinical signs Reference
(mg/kg
body weight)
--------------------------------------------------------------------------------------------------------
Mouse oral 100 - 1000 - postural and motor incoordination; Kuperman (1957)
convulsions; death
Mouse dermal (40% sol.) 100% 50% mortality within 45 min Novikova (1979)
Rat oral 100 - 200 - tremor; general weakness; death Fullerton & Barnes
(1966)
Rat ip 100 - 1000 - ataxia; general weakness; death Kuperman (1958)
Rat oral 126 0/5 slight weight loss; coma McCollister et al.
(1964)
Rat oral 256 5/5 death within 24 h McCollister et al.
(1964)
Guinea-pig oral 126 1/4 tremors; pupil dilation McCollister et al.
(1964)
Guinea-pig oral 252 4/4 death within 24 h McCollister et al.
(1964)
--------------------------------------------------------------------------------------------------------
Table 6. (contd.)
--------------------------------------------------------------------------------------------------------
Species Route Dose Mortality Clinical signs Reference
(mg/kg
body weight)
--------------------------------------------------------------------------------------------------------
Rabbit sc 500 - postural and motor incoordination; Kuperman (1957)
convulsions; death
Rabbit oral 63 0/4 slight weight loss McCollister et al.
(1964)
Rabbit oral 126 1/4 tremors; pupil dilation McCollister et al.
(1964)
Rabbit oral 252 4/4 death within 24 h McCollister et al.
(1964)
Rabbit dermal 500 - 1000 1/5 oedema; death McCollister et al.
(1964)
Cat iv or ip 65 - 70 - postural and motor incoordination Kuperman (1957)
Cat iv 5000 - general weakness; circulatory Kuperman (1957)
collapse; death
Cat ip 100 - unconsciousness after 24 h; severe McCollister et al.
effects or death (1964)
Dog oral 100 - convulsions; postural and motor Kuperman (1957)
incoordination
--------------------------------------------------------------------------------------------------------
Table 7. Summary of effects of acrylamide on motor function of rats
----------------------------------------------------------------------
Test Route Least effective Reference
cumulative dose
(mg/kg)
----------------------------------------------------------------------
Taste aversion oral 10 Anderson et al.
(1982)
Food-reinforced gavage 25 Tilson & Squibb
variable-interval (1982)
(VI) responding
Open-field ip 50 Gipon et al.
rearing (1977)
Altered gait ip 50 Jolicoeur et al.
(1979)
Food-reinforced gavage 75 Tilson et al.
fixed-ratio (FR) (1980)
Horizontal motor ip 100 Gipon et al.
activity (1977)
Hind-limb gavage 100 Tilson & Cabe
weakness (1979)
Hind-limb splay ip 150 Edwards &
Parker (1977)
ip 200 Jolicoeur et al.
(1979)
(oral) 280 Edwards &
diet Parker (1977)
Rotarod ip 300 Gipon et al.
(1977)
ip 320 Kaplan & Murphy
(1972); Kaplan
et al. (1973)
Inclined board gavage 500 Fullerton &
Barnes (1966)
Running wheel (oral) 550 Lewkowski et al.
activity diet (1978)
Motor activity gavage 600 Tilson et al.
(automex) (1979)
---------------------------------------------------------------------------
Responses associated with appetitive and/or consummatory
behaviour have also been used to quantify acrylamide-induced
toxicity. Teal & Evans (1982) found that administration of
acrylamide for 30 days produced a considerable increase in
periodic milk-licking, even in severely intoxicated animals.
These effects are presumed to be associated with disturbances in
water balance (Gipon et al., 1977) and may be associated with
alterations in thirst and hunger regulation in the hypothalamus.
Blunting of tactile sensitivity is recognized as an early
effect following exposure to acrylamide; such sensory signs
usually precede motor involvement. Recently, Maurissen et al.
(1983) used operant psychophysical techniques to assess vibratory
or electrical stimuli applied to the fingertips. Monkeys dosed
orally with 10 mg/kg acrylamide, 5 days per week, for up to 9
weeks, were found to exhibit impaired vibration sensitivity
before the onset of neuromuscular effects. Sensory effects were
evident for several months after dosing ceased. Sural nerve
biopsies did not reveal a clear association between loss of nerve
fibres and degree of sensory loss. These and other data suggest
that vibration sensory loss is probably due to dysfunction of the
end-organ receptors. Spencer & Schaumburg (1977) reported that
the generator potential of the Pacinian corpuscle was decreased
by acrylamide exposure at a time when pathology was not evident.
Maurissen et al. (1983) also found that sensitivity to the
electrical stimulus did not change, suggesting that acrylamide
differentially affected the mechanoreceptors. Studies on rats
have shown that acrylamide does not markedly affect
responsiveness to thermal stimuli, even when motor dysfunction is
present (Pryor et al., 1983).
Anderson et al. (1982) studied the effects of acrylamide on
conditioned taste aversion, considered to be due to interoceptive
effects discernible by the animal. Taste aversion was observed
following a single dose of acrylamide given by gavage, suggesting
that acrylamide can induce effects at doses much lower than those
required to induce neurohistopathological changes, and the
neurological substrates or processes involved may be different
from those mediating the expression of central peripheral distal
axonopathy.
Where animals survived the effects of acute poisoning,
recovery was usually rapid and complete (Spencer & Schaumburg,
1974b). Similarly, after long-term poisoning, neuropathy was
reversible, though recovery was often slow (McCollister et al.,
1964; Hopkins & Gilliatt, 1971).
7.1.2. Electrophysiological effects
7.1.2.1. Peripheral effects
Various electrophysiological parameters have been used to
help characterize the development of the lesion in acrylamide-
induced peripheral neuropathy. Fullerton & Barnes (1966)
administered repeated doses (20 - 30 and 10 - 14 mg acrylamide/kg
body weight per day) to rats. Concomitant with the appearance of
major clinical symptoms (after 3 weeks on the high dose and 12
weeks on the low dose), the maximal motor conduction velocity
(MCV) was reduced significantly by about 20%. Similar reductions
in MCV have been reported for cats (29%) and monkeys (24%) by
Leswing & Ribelin (1969) and dogs (11%) by Satchell et al. (1982)
with various dosage regimens and durations of exposure. The
reduction in MCV has been correlated with selective degeneration
of the fast-conducting, large-diameter fibres (Fullerton &
Barnes, 1966; Hopkins & Gilliatt, 1971; Spencer & Schaumburg,
1974b).
Hopkins & Gilliatt (1971) carried out serial conduction
studies on motor and sensory nerves in baboons, given relatively
large total amounts of acrylamide (10 or 15 mg per day for
several months). Conduction velocity became reduced in all
nerves, the greatest reduction being 38% in the anterior tibial
nerve. This occurred when there had already been considerable
reduction in the amplitude of the evoked muscle action potential.
The authors also studied recovery of conduction velocity and
action potential amplitude on cessation of intoxication. In a
severely affected baboon treated with 15 mg acrylamide/kg body
weight per day for 94 days, the amplitude of the nerve action
potentials was still reduced after 1 year, but, after 2 years, it
had returned to 80% of normal. The amplitude of the muscle
action potentials of less severely affected baboons (receiving
acrylamide at 10 mg/kg body weight per day for 89 or 115 days)
returned to normal within 2 - 3 months.
Sumner & Asbury (1974) measured conduction velocities in
single sensory nerve fibres in acrylamide-intoxicated cats. They
reported that the earliest change was failure of muscle spindle
(type 1a) and Golgi tendon organ (type 1b) afferent terminals to
initiate impulses. An important conclusion of the single fibre
study was that no reduction in conduction velocity could be
demonstrated in surviving nerve fibres or in the proximal parts
of fibres that had degenerated peripherally. These findings
confirm the suggestion that reduction in MCV is due to
degeneration of the largest, most rapidly conducting nerve
fibres. Lowndes et al. (1978) studied the changes in the
responses of primary and secondary endings of muscle spindles
during the early stages of acrylamide intoxication in the cat.
They reported that the earliest detectable change was an elevated
threshold and diminished response of muscle spindle endings,
which occurred prior to abnormalities in neuromuscular function.
These findings confirmed previous data that large diameter
sensory fibres are involved early in the toxicity. Surviving
axons did not display any slowing of conduction velocity.
Von Burg et al. (1981) determined the conduction velocities
of sensory and motor nerves, both in vivo and in vitro, in
mice administered acrylamide (300 mg/kg body weight per week,
ip). Despite an early decrease in isolated sensory (sural) nerve
conduction velocity, a significant reduction (13%) was not
observed until the third week of treatment, when tibial nerve MCV
was also reduced (20%). Similarly, significant in vivo
differences in conduction velocity were not observed until the
third week, when the conduction velocities of the sciatic-sural
and sciatic-tibial nerves were reduced by 24% and 43%,
respectively, although a reduced velocity of the sciatic-sural
nerve was first observed after 2 weeks of treatment.
Anderson (1981) studied nerve action potentials using
isolated sural and sciatic nerves from rats given a cumulative
dose of 100 mg/kg body weight. A change in the waveform of the
sural nerve action potential and an increase in the relative
refractory period were observed as little as 24 h after a single
dose of 100 mg/kg body weight. In a further study (Anderson,
1982), no effects were observed on sciatic nerve action
potential, amplitude, or velocity 24 h after administration of
25 - 100 mg/kg body weight, despite a significant increase in the
duration of the evoked muscle action potential. The significance
of these findings in the context of early nerve changes is not
clear.
7.1.2.2. Central nervous system effects
There have been relatively few electrophysiological studies
on the central nervous system. Kuperman (1958) found
electroencephalographic (EEG) abnormalities in acrylamide-treated
cats prior to the development of ataxia (Table 8). These studies
clearly indicated that the primary neural locus was subcortical
and it was proposed that this locus was the mesencephalic
tegmentum. The effects of acrylamide on spinal cord function
were investigated in the cat by Goldstein & Lowndes (1979).
Animals receiving 7.5 mg acrylamide/kg body weight per day were
observed to have a reduced unconditioned spinal monosynaptic
reflex (MSR), when the cumulative dose reached 75 mg/kg body
weight, with no observable signs of peripheral neuropathy.
Boyes & Cooper (1981) measured the far-field somato-sensory-
evoked potentials (SSEPs) in acrylamide-intoxicated rats in order
to determine the location of dysfunction in the specific
somatosensory pathway. The results indicated that damage may
have occurred throughout the ascending somato-sensory system
without damage to cortical areas.
Table 8. Dose-effect relationship between EEG change and signs of acrylamide intoxication in catsa
------------------------------------------------------------------------------------------------------
Daily dose Number of Number Days to 25% Cumulative dose resulting in:
(mg/kg cats showing 25% increasec 25% increaseb Maximum Ataxiac First neurolog-
body frequency (range) increasec (mg/kg) ical deficit
weight) increaseb (mg/kg) (mg/kg) (range in mg/kg)
------------------------------------------------------------------------------------------------------
15 5 4 4.5 ± 2 60 - 75 86 ± 11 95 ± 4 75 - 105
25 9 6 3.3 ± 25 25 - 75 71 ± 11 104 ± 15 50 - 100
40 6 6 2.8 ± 29 40 - 80 80 ± 0 80 ± 0 40 - 80
65 5 4 1.3 ± 7 65 65 ± 0 65 ± 0 65
Total 25 20
------------------------------------------------------------------------------------------------------
a Adapted from: Kuperman (1958).
b Asynchronous high-frequency pattern.
c Mean ± percent SD.
Short-latency somatosensory evoked potentials (SLSEP) in
monkeys during acrylamide intoxication were studied by Arezzo et
al. (1982). The potential produced by activity at the rostral
end of the fasiculus gracilis (SLSEP2) was reduced, before
abnormalities were detected in other central tracts or peripheral
nerves.
Electrophysiological evidence of damage to optic nerve
components was reported by Vidyasagar (1981). Alterations in
visual-evoked potentials (VEPs) in female monkeys (macaque) were
reported by Merigan et al. (1982) following short-term acrylamide
exposure. VEP latencies were prolonged after 20 daily doses (10
mg/kg body weight per day), well before overt signs of toxicity
appeared.
7.1.3. Morphological effects
The histopathological effects of acrylamide in peripheral
nerves were investigated by Fullerton & Barnes (1966). At doses
inducing clinical effects in animals (section 7.1.2.1), primary
axonal degeneration was observed with secondary demyelination of
the sciatic, tibial, median, and ulnar nerves (as seen in
Wallerian degeneration). Distal nerve segments were more
severely affected than proximal segments. Medium- to large-
diameter fibres (8 - 9 µm) were more susceptible to degeneration.
Hopkins & Gilliatt (1971) also reported that the longest and
largest fibres (10 - 16 µm) of both motor and sensory nerves were
most severely affected in acrylamide-intoxicated baboons (19
mg/kg body weight per day for 118 days). No abnormalities were
reported in the proximal sciatic nerve or spinal cord in animals
exhibiting severe peripheral axonal (distal) degeneration
(Fullerton & Barnes, 1966).
Ultrastructural changes in the nerves of cats, administered
3 mg acrylamide/kg body weight per day in the drinking-water (252 -
294 days), were studied by Schaumburg et al. (1974). Tissue
biopsies from hind feet, after completion of the study, showed a
loss of all types of myelinated fibres in distal nerves. Only a
few small and large myelinated nerve fibres were seen in plantar
nerve twigs and most fibres had completely degenerated (bands of
Bungner). Many unmyelinated nerve fibres were present. Most of
the muscle fibres were vacuolated and shrunken.
In studies by Gipon et al. (1977), significant swelling in
terminal axons and arborizations in rat muscle were reported at a
cumulative dose of acrylamide of 550 mg/kg body weight (50 mg/kg,
every other day). At this dose, 50 - 60% of large peripheral
nerve fibres showed signs of degeneration. No histological
abnormalities were reported in the spinal cord, but the
techniques employed may not have been adequate.
Axonal degeneration in cats given 10 mg acrylamide/kg body
weight per day was evident by 49 days and was preceded by massive
accumulation of neurofilaments and enlarged mitochondria in the
peripheral nerve fibres, which were evident by 22 days (Prineas,
1969). Similar findings were reported in the sciatic nerves of
adult and suckling rats (4 - 12 injections of acrylamide at 50
mg/kg body weight, 3 doses per week), when no evidence of
abnormalities could be seen by light microscopy (Suzuki & Pfaff,
1973). Accumulation of neurofilaments and invaginations of the
axolemna have also been observed under similar conditions in dogs
(Thomann et al., 1974; Satchell et al., 1982).
In a study by Schaumburg et al. (1974), morphological changes
in the terminals of sensory and motor nerve fibres were examined
in the paws of cats administered acrylamide intraperitoneally at
10 mg/kg body weight per day, for 7 - 32 days. Pacinian
corpuscle axons in the hind feet were the first terminals to
display degeneration. The first change was a loss of filopod
axonal processes, sometimes accompanied by neurofilamentous
hyperplasia. The axolemna disappeared and the axoplasm was
phagocytosed by inner core cells. Shortly afterwards, changes
were seen in juxtaposed Pacinian corpuscles, followed by
degeneration of primary annulospiral endings of muscle spindles,
secondary muscle spindle endings, and motor nerve terminals, in
that order. All these endings accumulated neurofilaments prior
to degeneration. These results not only demonstrated
ultrastructural changes prior to clinical signs, but also that
sensory nerve terminals were more sensitive than motor nerve
terminals. Unmyelinated fibres in somatic nerves were observed
to be relatively resistant to the effects of acrylamide.
Concurrent with axonal degeneration and secondary myelin
breakdown, Suzuki & Pfaff (1973) reported the appearance of
endoneural macrophages and a proliferation of Schwann cells in
the sciatic nerves of adult rats after 26 injections of
acrylamide (50 mg/kg body weight, 3 doses per week). After 4
injections, microscopic examination revealed myelin figures in
Schwann cells and enlarged fibres within the sciatic nerve. These
changes became more prominent after 8 injections. Examination of
nerves from rats receiving 26 injections revealed numerous axonal
sprouts growing within the Schwann cells. Honeycomb-like
interdigitation of Schwann cell-axon networks was observed prior to
hind limb weakness in acrylamide-intoxicated rats (Spencer &
Schaumburg, 1977). Ultrastructural observations in mice led to the
suggestion that Schwann cell damage occurred after the onset of
axonal demyelination (Von Burg et al., 1981).
Accumulation of smooth endoplasmic reticulum (SER) and other
organelles within peripheral and central nervous system neuronal
axons has been reported following acrylamide exposure (Cavanagh &
Gysbers, 1981; Chrétien et al., 1981). Such accumulation in
tibial nerves was observed several days before the onset of
axonal degeneration (Cavanagh & Gysbers, 1981). The same changes
have, however, been observed in other toxic neuropathies and are
probably of a non-specific nature.
Regenerating fibres have been found in nerves of rats
administered repeated low doses of acrylamide, as shown by the
presence of fibres with inappropriately short internodal lengths
for their diameter (Fullerton & Barnes, 1966). In long-term
acrylamide intoxication, regeneration may occur simultaneously
with continuing degeneration, but the regeneration is severely
retarded. Kemplay & Cavanagh (1984) reported a prolonged
inhibition of spontaneous sprouting from motor end-plates at the
neuromuscular junction in female rats. This inhibition was
apparent 24 h after a single dose (90 mg/kg body weight) and
lasted for 4 weeks. Acrylamide also reduced the number and
length of reactionary terminal sprouts following partial
denervation.
Degeneration in large sympathetic and parasympathetic and,
therefore, probably sensory-myelinated fibres, demonstrating the
involvement of the autonomic nervous system in acrylamide
neuropathy, has been observed (Post & McLeod, 1977a). Studies in
cats showed impaired neural control of the mesenteric vascular
bed of a type indicating damage to post-ganglionic unmyelinated
fibres (Post & McLeod, 1977b). Acrylamide has been shown to
cause megaoesophagus in greyhounds (Satchell & McLeod, 1981) due
to impairment of mechanoreceptors, the afferent fibres of which
pass through the vagus nerve (Satchell et al., 1982).
Ultrastructural changes in the cell bodies (perikarya) of
dorsal root ganglia (DRG) in cats that had received a cumulative
dose of 320 mg acrylamide/kg body weight subcutaneously, at 10
mg/kg body weight per day, were studied by Prineas (1969). A
disturbance in granular endoplasmic reticulum (GER), a breakdown
in polyribosomes, ribosomal dislocation, and an increase in the
amount of electron-dense material in the cytoplasm were reported.
Using light microscopy, Sterman (1982) detected a spectrum of
perikaryal changes in both large and small neurons of lumbar DRG
in rats administered a cumulative dose of acrylamide at 350 mg/kg
body weight (50 mg/kg body weight per day). These changes
occurred prior to significant peripheral nerve damage and
included nuclear eccentricity, peripherally-located Nissl bodies,
and increased numbers of perineuronal cells. In a further study,
Sterman (1983) observed ultrastructural changes between days 5
and 9 of acrylamide treatment (50 mg/kg body weight per day).
Quantitative morphometric study revealed significant perikaryal
modifications after 5 - 6 days of treatment, which had progressed
by 8 - 9 days. Qualitatively, altered profiles had nuclear
eccentricity and capping, marked changes in mitochondrial
morphology, and modifications of ribosomes and Nissl granules.
Neurons that appeared normal by light microscopy often displayed
ultrastructural changes.
The results of microscopic examination of the brain and/or
spinal cord have been reported in acrylamide-intoxicated rats
(Fullerton & Barnes, 1966), mice (Bradley & Asbury, 1970), cats
(Kuperman, 1958; McCollister et al., 1964), dogs (Thomann et al.,
1974), and monkeys (McCollister et al., 1964). No abnormalities
attributable to acrylamide were reported in these studies.
Prineas (1969) demonstrated ultrastructural changes in nerve
fibres and boutons terminaux in the anterior spinal grey matter
after subcutaneous injection of a cumulative dose of 320 mg
acrylamide/kg body weight (10 mg/kg per day). Small myelinated
fibres frequently contained excessive numbers of neurofilaments
associated with local fibre swelling. Similarly, 5 - 15% of the
boutons terminaux were enlarged and contained large numbers of
neurofilaments. At the cervical level, in the latter stages of
intoxication (between 32 and 49 days), there were pronounced
changes in the gracile nucleus. Small myelinated fibres
displayed neurofilamentous hyperplasia, many mitochondria, dense
body and fine granular material, and unusual tubulo-vesicular
profiles. Myelin degeneration and axonal abnormalitie