PA-560/2-76-008
INVESTIGATION OF SELECTED
POTENTIAL ENVIRONMENTAL CONTAMINANTS:
ACRYLAMIDES
August 1976
FINAL REPORT
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, D.C. 20460
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EPA- 560/2-76-008 TR 76-507
INVESTIGATION OF SELECTED POTENTIAL
ENVIRONMENTAL CONTAMINANTS:
ACRYLAMIDES
Leslie N. Davis
Patrick R. Durkin
Philip H. Howard
Jitendra Saxena
July 1976
Final Report
Contract No. 68-01-3127
SRC No. L1255-07
Project Officer:
Frank J. Letkiewicz
Prepared for:
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, D.C. 20460
Document is available to the public through the
National Technical Information Service, Springfield,
Virginia 22151
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NOTICE
This report has been reviewed by the Office of Toxic Substances, EPA,
and approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Environmental Protection
Agency, nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
ii
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TABLE OF CONTENTS
Executive Summary ix
I. Physical and Chemical Data 1
A. Structure and Properties 1
1. Chemical Structure 1
2. Physical Properties of Pure Material 2
3. Properties of Commercial Materials 10
4. Principal Contaminants in Commercial Products 10
B. Chemistry 13
1. Reactions Involved in Production and Uses 13
2. Hydrolysis, Oxidation, and Photochemistry 16
3. Other Chemistry 18
II. Environmental Exposure Factors 19
A. Production and Consumption 19
1. Quantity Produced 19
2. Producers, Major Distributors and Importers, Sources 20
of Import, and Production Sites
3. Production Methods and Processes 22
4. Market Prices 27
5. Market Trends 28
B. Uses 28
1. Major Uses 28
2. Minor Uses 31
3. Discontinued Uses 34
4. Projected or Proposed Uses 34
5. Possible Alternatives to Uses 35
C. Environmental Contamination Potential 36
1. General 36
2. From Production 36
3. From Transport and Storage 37
4. From Use 38
5. From Disposal 40
6. Potential Inadvertent Production of the Chemical in 42
Other Industrial Processes as a By-Product
7. Potential Inadvertent Production in the Environment 42
iii
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Table of Contents
(continued)
Page
D. Current Handling Practices and Control Technology 43
1. Special Handling in Use 43
2. Methods of Transport and Storage 44
3. Disposal Methods 46
4. Accident Procedures 46
5. Current Controls and Technology Under Development 48
E. Monitoring and Analysis 48
1. Analytical Methods 48
2. Current Monitoring 54
III. Health and Environmental Effects 56
A. Environmental Effects 56
1. Persistence 56
a. Biological Degradation, Organisms, and Products 56
b. Chemical Degradation 60
2. Environmental Transport 60
3. Bioaccumulation and Biomagnification 62
B. Biological Effects 63
1. Toxicity and Clinical Studies in Man 63
a. Occupational Studies 63
b. Neurophysiology and Pathology of Occupational 67
Exposures
c. Other Human Studies 69
2. Effects on Non-Human Mammals 69
a. Absorption, Distribution, and Elimination 69
b. Metabolism 75
c. Acute Toxicity 78
(i) Acrylamide 78
(ii) Substituted Acrylamides 83
d. Subacute and Chronic Toxicity 85
iv
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Table of Contents
(continued)
(i) Acrylamide - Gross Toxic Effects and 86
Dose-Response Relationships
(ii) Acrylamide - Structural Changes 103
(iii) Acrylamide - Functional Changes 109
(iv) Acrylamide Analogs 111
e. Sensitization, Repeated Doses 117
f. Teratogenicity 118
g. Mutagenicity 118
h. Carcinogenicity 118
i. Behavioral Effects 120
j. Possible Synergisms and Other Drug Interactions 120
k. Field Studies 121
3. Effects on Other Vertebrates 121
4. Effects on Invertebrates 122
5. Effects on Plants 123
6. Effects on Microorganisms 123
7. In Vitro and Biochemical Studies 123
a. Effects on Isolated Organs 123
b. Effect on Cell Cultures (Non-Microbial) 123
c. Effect on Isolated Organelles and Cell Homogenates 124
d. Effects on Purified Enzymes and Isolated Enzyme 124
Systems
e. Effects on Nucleic Acids and Proteins 124
IV. Regulations and Standards 127
A. Current Regulation 127
1. Food, Drug, and Pesticide Authorities 127
2. OSHA 128
3. Other Federal, State, and County Regulations 128
4. Foreign Countries 128
B. Consensus and Similar Standards 128
1. TLV 128
2. Public Exposure Limits 128
3. Other 128
V. Summary and Conclusions 130
REFERENCES 135
v
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LIST OF TABLES
Number Page
1 Physical Properties of Acrylamide and Related Compounds 3
2 Solubilities of Acrylamides and Selected Derivatives 4
3 Acrylamide and Commercial Specifications for Selected Acrylamide 11
Derivatives
4 Rates of Acid and Base-Catalyzed Hydrolysis of Acrylamide 17
5 Polyaerylamide Produced and Sold in the United States 20
6 Producers of Acrylamide Monomer 20
7 Producers of Acrylamide Derivatives 21
8 Producers of Acrylamide Polymers 21
9 Catalytic Hydration Process for Acrylamide Production 26
10 Current Market Prices for Acrylamide Products 27
11 Uses of Polyacrylamide 31
12 The Effect of Some Water Treatment Processes on 6 yg 1 41
Acrylamide
13 Respirators Suitable For Work With Acrylamide 44
14 Summary of Assay Techniques Applicable to Acrylamide 53
15 Concentrations of Acrylamide in Some Industrial Effluents 55
16 Standard 5-Day BOD Test with Acrylamide Using Different Types 58
of Seeds
17 The Degradation of Acrylamide by Sewage Effluent 59
18 Main Signs and Symptoms of Occupational Acrylamide Intoxication in 64
Six Cases in England
19 Symptoms of Acrylamide Intoxication in Fifteen Cases of Industrial 66
Exposures from Japan
20 Distribution of [14C] in Tissues of Rats After Single Intravenous 72
Injections of [1-14C] Acrylamide and [1-11+C] N-Me thy lol aery lamide
vi
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List of Tables
(continued)
Number Page
21 [14C] in Nucleic Acids Isolated From Rat Brain and Liver After 73
a Single Dose of [1-14C] Acrylamide to Rats
22 Acute Toxicity of Acrylamide to Various Mammals 79
23 Acute Toxicity of Substituted Acrylamides 84
24 Acrylamide Doses Producing Early Signs of Peripheral Neuropathy 87
in Various Mammals
25 Development of Ataxia After Repeated Intraperitoneal Injections of 88
Acrylamide to Cats
26 Effects of Repeated Acrylamide Exposure on Rats 93
27 Effects of Repeated Acrylamide Exposure on Cats 95
28 Effects of Repeated Acrylamide Exposure on Primates 97
29 Recovery Periods In Mammals After Severe Acrylamide Intoxication 98
30 The Effect of Age on the Onset of and Recovery from Acrylamide 100
Intoxication in Rats
31 Acrylamide Doses Producing No Signs of Adverse Effects 102
32 Effect of Acrylamide Analogs on the Development of Acrylamide 115
Neuropathy
33 Comparative Potency of Neurotoxic Analogs to Acrylamide Based on 115
Oral Exposures of Nine to Fourteen Days
34 Acrylamide Analogs Without Apparent Neurotoxic Activity to Rats 117
35 Phenobarbital Protection in Acrylamide-Treated Rats 121
36 Reactivity of Acrylamide and Its Analogs with Glutathione at 125
pH 7.3 and 37°C In Vitro
vii
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LIST OF FIGURES
Number
Page
1 Ultraviolet Absorption Spectrum of Acrylamide in Water 5
2 Vapor Pressure of Acrylamide 5
3 Reactions Involved in Commercial Production of Acrylamide and Selected 14
Analogs
4 Flowsheet for Sulfate Process for Acrylamide Production 23
5 Variations on the Sulfate Process for Acrylamide Manufacture 23
6 Catalytic Route to Acrylamide Eliminates Troublesome Byproducts and 24
Increases Product Yields
7 Catalytic Hydration Process for Acrylamide Production 26
8 Recommended Unloading and Storage Facility for 50% Aqueous Acrylamide 47
Solutions
9 Degradation of Acrylamide in River Water Supplemented with Nitrogen 56
and Phosphorus
10 Degradation of Acrylamide in Control and Inoculated Samples of River 57
Water
11 Histogram of Fiber Diameter 68
12 Blood Concentrations of Acrylamide and N-Methylolacrylamide After 70
Intravenous Injections to Rats
13 Excretion of II1+C] in Urine and Expiration of 14C02 After a Single 74
Dose of Il-14Cj Acrylamide
14 [il+C]Lysine Incorporation Into Tissue Proteins of Rats Dosed with 76
Acrylamide for 4 Weeks Expressed as Per Cent of Controls at Various
Times
15 Histograms Showing Distribution of Diameters of All Myelinated Fibers 106
in Posterior Tibial Nerves of Animals on the Following Diets: (see
text)
16 Histograms Showing Distribution of Diameters of Myelinated Fibers 106
in the Sural Nerves (Ankle) of One Control Baboon (Bab. 26) and
Three Baboons Intoxicated with Oral Doses of Acrylamide
17 Internodal Length and Fiber Diameter in Posterior Tibial Nerve of 107
(a) Normal Rats, (b) Rats AS and A4 on 300 ppm Acrylamide for Four
Months, Followed by Normal Diet for Five to Six Months
Viii
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Executive Summary
Of the acrylamide compounds reviewed, only acrylamide is produced in
sizable quantities; the 1973 estimate is 40 million pounds. For the most
part, acrylamides are consumed in the synthesis of commercial polyacrylamides.
The major uses of polyacrylamide are for waste water flocculants (40% of
production) and in the pulp and paper industry (20% of production); there
are a number of minor uses of polyacrylamides, such as adhesives and flooding
agents for petroleum recovery. Acrylamide monomer is marketed as a chemical
grout and soil stabilizer for use in dams, foundations, and tunnels (quantity
used is less than 5% of the total production).
The major source of acrylamide environmental contamination appears to be
from the release of residual acrylamide monomer from the polymers. British
effluent monitoring data support this contention, although even the highest
levels do not exceed 50 ppb. Contamination of media other than water does
not seem likely. Acrylamide is very water soluble and biodegradable, and
therefore, does not bioconcentrate.
From the current pattern of use and release, it does not appear that
widespread environmental contamination with acrylamide is likely; however,
there is some concern that local incidents of significant acrylamide con-
tamination could occur in aqueous systems including drinking water. A more
definitive study of the uses of polyacrylamide is needed to determine the
likelihood of such occurrences.
In considering its biological aspects, three possible adverse effects
from acrylamide are apparent: neurotoxicity, carcinogenicity, and toxicity
to aquatic organisms.
ix
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Acrylamide Is a neurotoxin and, as such, is a proven occupational hazard.
Certain acrylamide analogs are also neurotoxic and should be considered as
potential occupational hazards. However, repeated dosing studies with various
laboratory mammals indicate that there is a threshold concentration below
which the neurotoxic effects of acrylamide are not induced. Therefore, the
neurotoxicity hazard would seem to be of environmental concern primarily when
incidents of excessive acrylamide concentrations might occur in drinking
water.
The lack of information on carcinogenicity is a major impediment to a
more definite evaluation of acrylamide environmental hazard. While acrylamide
has not been specifically tested for carcinogenicity, it is able to bind and
possibly alkylate RNA and DNA and does alkylate protein, all three of which
are associated with chemical carcinogens. Therefore, carcinogenicity testing
of the commercially important acrylamides appears desirable.
The current limited information on fish toxicity indicates that ambient
levels as found in the British monitoring study should not affect these
aquatic organisms. Because acrylamide seems to biodegrade rapidly, the lack
of toxicity data on many aquatic organisms does not seem crucial. Again, how-
ever, the available data are not sufficient to fully assess the possible
effects on aquatic biota where incidental excessive concentrations of acrylamide
might occur.
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r Physical and Chemical Data
A. Structure and Properties
1. Chemical Structure
Acrylamide and its chemically related commercial products are
x,B unsaturated amides with the following structure:
0
II
R1R2C=C(R3)CNRLfR5
Of the several hundred acrylamide derivatives that have been prepared (MacWilliams,
1973), only the nine compounds listed in Table 1 (p. 3) appear to be produced in
commercial quantities (SRI, 1975). The parent compound, acrylamide (R^, R2, R3,
k^, and R5 = H), is, by far, the most significant commercial product, and the
quantity produced is almost totally consumed in the synthesis of polymers. The
other commercial products consist of one carbon-substituted derivative, methacryl-
amide (R3 = CH3), and seven N-substituted compounds.
Polyacrylamide is a nonionic linear polymer prepared by free
radical addition polymerization (Thomas, 1964):
n H2C = C
,H
'C - NH2
n
0
-CH2-C
0 NH2
Either linear or cross-linked polymers may be prepared from acrylamide and its
derivatives, with molecular weights on the order of 103 - 107, depending on
reaction conditions. Cross-linking via intra- or intermolecular imidization
produces structures such as
•CH2-CH-CH2-CH-
i i
H
and
-CH2-CH-CH2-CH-
N-H
' (X J>
0=C ^Cx
i i
-CH2-CH-CH2-CH-
n
and reduces the high water solubility of the linear polymer (Norris, 1967b).
-------
Polyamide formation (rather than polyacrylamide) is favored by
heating acrylamide with a strong base and gives poly-B-alanine (nylon 3) (Thomas,
1964):
CH2CH2C^N _
i
H n
Copolymerization with other vinyl polymers occurs readily and
is a means of producing polymers with a wide range of properties.
2. Physical Properties of Pure Material
Acrylamide is a white, crystalline solid noted for its high
solubility in water and other polar solvents; most other vinyl monomers are
liquids or gases with low water solubilities (Thomas, 1964). Table 1 summarizes
the physical properties of acrylamide and selected derivatives. Table 2 summa-
rizes the solubilities of these compounds in common solvents. Figure 1 shows the
UV spectrum of acrylamide, and Figure 2, the vapor pressure of the solid and molten
liquid.
The physical properties of polyacrylamides vary widely, depending
on the method of manufacture, the inclusion of copolymers, etc. Linear poly-
acrylamide is a white, odorless solid, soluble in water, and insoluble in methanol,
ethanol, acetone, and hexane. It is compatible with most natural and synthetic
water-soluble gums, dispersants, and surfactants (Swift, 1957). In very dilute
solutions, polyacrylamides of high molecular weight are efficient flocculants
which cause rapid agglomeration and sedimentation of finely divided solids in
suspension (Norris, 1967b). Solutions of polyacrylamides at least as high as
1% can be made in formamide, lactic acid, acrylic acid, and molten urea. At
85°C or less, the maximum possible concentration of polyacrylamide is less than
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-------
Figure 1. Ultraviolet Absorption Spectrum of Acrylamide in Water
(Anon., 1969) (Reprinted with permission from American
Cyanamid Company)
L.
120 130
Figure 2. Vapor Pressure of Molten Acrylamide (Anon., 1969)
(Reprinted with permission from American Cyanamid
Company)
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1% in acetic anhydride, nitroethane, dimethylformamide, dioxane, glycerol, acetoni-
trile, tetrahydrofuran, cresol, methyl ethyl ketone, pyrrolidone, triethanolamine,
and dibutyl phthalate (Norris, 1967b). The molecular weight of a polymer is
in part a function of the solvent in which the polymer forms; the less polar the
solvent, the lower the molecular weight of the polymer (Wagner, 1968).
The solvent medium for polymerization may be any of the following
(Bikales, 1973):
1) Water
2) Water and a water-miscible organic solvent
3) An emulsion of water and a solvent such as toluene
4) An organic liquid which is a solvent for the monomer
The greater the concentration of water miscible organic solvents, the less soluble
the polymer which is produced, and hence, the easier it is to recover the polymer
from the reaction medium. Recovery and drying of the pure polymer is, in fact, the
most difficult and expensive part of the manufacturing process (Anon., 1969). How-
ever, water miscible organic solvents seldom make up more than a small fraction of
the solvent medium, because the greater their concentration, the lower the molecular
weight of the polymer. Since the major industrial application of polyacrylamides
(flocculating agents) requires molecular weights to be as high as possible, water
is the most common polymerization medium, with organic solvents used as precipi-
tating and drying agents. Solvents are removed from the polymer by drum drying at
elevated temperatures. Temperature control is important, since relatively high
temperatures may have the effect of decreasing the molecular weight of the
polymer and causing some cross-linking via imidization (Bikales, 1973). The
overall manufacturing process must be optimized to obtain the desired require-
ments for a pure, dry, high molecular weight product, free of cross-linking.
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The concentration of the monomer is kept low during polymerization
to allow for adequate heat dissipation during the reaction. Also, high monomer
concentration and/or high reaction temperatures lead to cross-linking, with con-
sequent reduction of water solubility of the polymer (Thomas, 1964).
Free radical polymerization of acrylamide has been initiated by
a variety of catalysts which include redox systems (Thomas, 1964), azo compounds
(Cavell, 1962), peroxides (Dainton and Tordoff, 1957), X-rays and gamma-rays
(Collinson et al., 1957), and anodic oxidation at a platinum electrode (Kunugi
et_ a^. , 1972; Ogumi et_ aL. , 1974). The free radical mechanism of polymerization
has been studied extensively (Dainton and Tordoff, 1957). The polymer chain is
believed to go through several cycles of growth and rest before chain termination
over a relatively long period of time ranging from several seconds to several
minutes (Anon., 1969).
In addition to the previously-discussed factors affecting molecular
weight of the polymer (i.e., temperature of reaction medium, concentration of
monomer, etc.), the addition of specific amounts of 1-3 carbon aliphatic alcohols
to the reaction medium allows a reproducible method of regulating (lowering) the
weight average molecular weight of the polymer (Thomas, 1964).
The pH of the reaction medium also affects the nature of the
polymer product. At or below pH 2.5, imidization occurs, resulting in a cross-
linked, insoluble product (Anon., 1969). At pH 9 or higher, polymerization is
accompanied by hydrolysis of the amide groups (Bikales, 1970). The presence of
a strong base catalyzes polyamide formation (Breslow et_ a^., 1957), which is
particularly favored if an inhibitor for vinyl polymerization is also present
-------
(Thomas, 1964). The product formed under these conditions is poly-B-alanine
(nylon 3), whose physical properties are quite different from polyacrylamide.
Acrylamide monomer does not have to be in solution in order to
polymerize. When heated to its melting point, the pure solid may polymerize
quietly or violently accompanied by the evolution of a great deal of heat, resulting
in a highly cross-linked, insoluble gel. Polymerization in the solid state can
also be made to occur at ambient temperatures and without violence by exposing
acrylamidt to ionizing radiation (Thomas, 1964). After removal of the monomer
from the radiation source, polymerization continues for many months.
Polyacrylamide is nonionic. Polyelectrolytic character can be
introduced where required for specific applications. Anionic character is
introduced by partial hydrolysis of the amide groups by a strong base:
-CH2CH
n
Modification of the polymer is possible either after its formation or during
polymerization via the introduction of a suitable comonomer. Likewise, cationic
*
character may be introduced either via a comonomer or through a post-reaction
(Bikales, 1973).
Because ac.rylamide and its derivatives copolymerize with each
other and with many other polar vinyl monomers, a wide variety of materials can
be prepared via copolymerization. Solubility, softening temperature, viscosity,
and elastomeric nature are some properties of the polymers which can be predic-
tably modified by appropriate copolymer selection. A unique example of co-
polymerization in the recent literature involved gamma-ray induced graft copoly-
merization of acrylamide and acrylic acid to nylon 6 fabric (Trivedi et al., 1975).
-------
In the presence of a homopolymer inhibitor, mixtures of acrylamide and acrylic
acid were grafted to the fabric, considerably increasing its moisture retention
without significantly affecting dyeability or tensile properties. In addition,
the melting point of the grafted fabric was more than 100°C higher than that of
the ungrafted fabric (m.p., 215°C).
The chemistry of the derivatives of acrylamide is very similar
to that of the parent compound. Polymerization of methacrylamide, for example,
may be initiated in aqueous solution via an acidified bromate/thiourea free-
radical producing redox system (Misra and Gupta, 1973). In general, acrylamide
derivatives polymerize at a slower rate than acrylamide, and therefore, uncon-
trolled or spontaneous polymerization is less of a problem with the derivatives,
reducing the need for inhibitors during storage and shipment. N-Methylolacryla-
mide, supplied as a 60% aqueous solution, for example, is considered very stable
and is produced by at least one manufacturer without inhibitors (Proctor Chemical
Co., 1975).
Cross-linked polyacrylamide is a rigid gel, insoluble in water
and also impervious to the passage of water through it (Norris, 1967b). The
exact properties of the gel are controlled by conditions of polymerization and
the presence (or absence) of comonomers. American Cyanamid Company's chemical
grout AM-9, for example, consists of a mixture of acrylamide and N,N'-methylene-
bisacrylamide. An aqueous solution of the monomeric mixture and a catalyst
(g-dimethylaminopropionitrile and ammonium persulfate) are injected into soil
formations. In a period of time which depends on the relative concentrations
of the monomers and catalyst, polymerization takes place, sealing off the flow
of water in the soil and binding the soil particles together (Norris, 1967b).
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Molecular weights of polymers vary with preparation procedures
as well as with the nature of the monomer; high molecular weight polymers are in
general less soluble in water and have higher softening temperatures than low
molecular weight polymers. High molecular weight polymers of acrylamide itself
do form true solutions, but they are gels rather than fluids.
Substitution at the a-carbon of acrylamide tends to raise the
softening temperature of the polymer, whereas substitution on the nitrogen
tends to lower it. Branched alkyl groups as substituents tend to raise the
softening temperature over corresponding derivatives with n-alkyl groups
(Thomas, 1964).
Water solubility is retained through 3-carbon N-substituents.
Solubility in acetone and 1-3 carbon alcohols increases as N-alkyl substituents
increase to about 5 carbon atoms. Long alkyl chains confine solubility of the
acrylamide compound to hydrocarbons (Thomas, 1964).
3. Properties of Commercial Materials
Table 3 lists commercial specifications for solid and solution
acrylamide and selected acrylamide derivatives. The specifications in the table
emphasize physical rather than chemical properties.
The wide variety of polyacrylamides commercially available testi-
fies to the fact that manufacturers have considerable flexibility in designing
products and modifying them to meet specific applications. Hercules Chemical,
for example, produces under the trade name Hereofloc more than sixteen different
acrylamide polymers in liquid and powder form, for industrial waste water appli-
cations. Typical specifications for the powder products are listed in Table 3.
4. Principal Contaminants in Commercial Products
Acrylamide is prepared commercially by two processes. The conven-
tional "sulfate" process, which is rapidly declining in use, involves the hydration
10
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Table 3. Acrylamide and Commercial Specifications for Selected
Acrylamide Derivatives
(Prepared from Manufacturers' Product Data Sheets)
Acrvlamide
American Cyanamld
Vistron
Appearance
Assay, h
Water, %
Total iron as Fe, ppm
Water insolubles, %
Color of 20% solution, APHA
Butanol insolubles, %
White, crystalline solid or pellet
98.5 min.
0.8 max.
10.0 max.
0.02 max.
20 max.
0.2 max.
98.0 min.
0.7 max.
10.0 max.
20 max.
0.5 max.
Acrvlamide. 50% aq.
American Cyanamid
Dow
Appearance
Assay, wt. %
4-7
Inhibitor Cu " ,
pH
Stability
Boiling point
Vapor press @25°
Specific Gravity
ppm solids basis
C
@25°C
Miscibility in water @25°C
Crystallization
point
Clear, colorless to pale yellow
solution
50±2
25-30
5.2-6.0
6 mo.
105. 5°C
19 torr
1.04
All proportions
12-13°C
Clear liquid with
yellow cast
50+2
30 max.
5.5-6.5
6 mo.
Clear liquid with
yellowish cast
50+2
5.0-6.5
99-104°C
1.04
8-13°C
Methacrylamide
White Chemical
Rohm , GmbH
Assay, %
Water, %
Methacrylic acid
Ash, %
Bulk density, lbs./ft3
98.4
1.0
Not detected
0.04
28.7
98 min.
1.5
0%
N-^-octylacrylamide
Proctor Chemical Company
Melting point, °C
Water, %
Acrylonitrile, %
Diisobutylenes, %
Tetraisobutylenes, %
Solubility in 57. isopropanol
N-Methylolacrylamide,
58-63
0.04
0.10
nil
0.10
Trace
Soluble
Proctor Chemical Company
Appearance
Assay, %
Color, APHA
PH
Formaldehyde, %
Polyacrylamide Powder (Hercofloc
Clear solution
60±2
100 max.
6.0-6.5
1.5-2.0
Hercules Chemical
Density, gm/ml
Particle size, %
Moisture, % (as packed)
pH (1% aq. sol.)
0.7
25-35 through 200 mesh
15
6.0 anionic, 8.5 cationic
11
-------
of acrylonitrile (2-propenenitrile) with sulfuric acid monohydrate to form acrylamide
sulfate. Various methods are used to separate the products (Carpenter and Davis,
1957). In a typical process, the sulfuric acid is neutralized with calcium oxide
or ammonia. Calcium (or ammonium) sulfate is precipitated by concentrating and
evaporating the solution under reduced pressure. The acrylamide is frequently
removed by crystallization, although extraction with benzene or methanol has
been reported (Bikales, 1970). Contaminants in the final product may include
small quantities of acrylamide sulfate, calcium (or ammonium) sulfate, poly-
acrylamide (particularly if a polymerization inhibitor was not present during
+2 +3
the hydrolysis), and/or traces of the inhibitor (such as Cu or Fe ) if one
was present.
A new commercial process involves the direct catalytic oxidation
of acrylonitrile to the amide (Anon., 1973). The catalyst is metallic copper
(Otsuka
-------
The principal contaminants of acrylamide polymers are the monomers.
Although the polymers are generally considered to be nontoxic, the monomers are not.
Polyacrylamides with which humans or their food will come in contact must have
less than 0.05% residual acrylamide monomer in them (FDA, 1972 a).
B. Chemistry
1. Reactions Involved in Production and Uses
Synthesis of acrylamide begins with propylene, ammonia, and
oxygen, which are reacted to form acrylonitrile. Acrylamide is produced from
acrylonitrile as described above. Figure 3 shows the principal chemical equa-
tions for the production of acrylamide and its commercially significant derivatives,
Methacrylamide is prepared in an analogous fashion to acrylamide
by the hydration of methacrylonitrile, and also via the decomposition of acetone
cyanohydrin with sulfuric acid to give methacrylamide sulfate, which is then
separated and purified by procedures similar to those used for acrylamide sul-
fate (Thomas, 1964).
N-Monosubstituted acrylamides having a secondary or tertiary alkyl
carbon attached to the nitrogen are prepared via the Ritter reaction in which
acrylonitrile combines with an olefin or alcohol in the presence of a strong
acid (Plaut and Ritter, 1951). The other N-alkyl and N,N-dialkyl acrylamides
are usually prepared by transamidation.
Acrylonitrile reacts with formaldehyde under acidic conditions
in the industrial preparation of N,N'-methylenebisacrylamide (Bikales, 1970),
Acrylamide and its monomer analogs are considered to be thermally
stable. The pure compounds are without unusual explosion or fire hazard when
stored at room temperature (25°C). After three weeks of storage at 50°C, acryl-
amide shows no evidence of polymerization. After 24 hours at 80°C (just below the
13
-------
Acrylamide Q
ii
Sulfate process a) CH2=CHCN + H2S04.H20 —~—•> CH2=CHCNH2.H2S04
0 0
» NHo "
b) CH2=CHCNH2-H2SOi4-t:!fid-* CH2=CHCNH2+(NH4)2S04*
0
Cu "
Catalytic process CH2=CHCN + H20 — *- CH2=CHCNH2
Methacrylamide
CH3
I
CH2=CCN + H2S04-H20
OH
1
CH3 — C-CN + H2SOU
CH3
CH3
I
CH2=CCONH2' H2SOtt
CH2=CCONH2 + (NH^) 230^4-
CH3
I NHo
CH2=CCONH2-H2SOit — -^-+
CH3
CH2=CCONH2
N-Methylolacrylamide _
CH2=CHCNH2 + HCHO
N,N'-Methylenebisacrylamide
...
"
CH2=CHCNCH2OH
0 0
2CH2=CHCN + HCHO ———* CH2=CHCNHCH2NHCCH=CH2
N-Isopropylacrylamide
N-_t-Octylacrylamide
N-_t-Butylacrylamide
^
U CQ
CH2=CHCN + CH2=CHCH3 2 H> CH2=CHCNHCH
|
CH2=CHCN
CH2=CHCN
^.^
I 3
CH3
CH3
CH3
0
Figure 3. Reactions Involved in Commercial Production of Acrylamide and
Selected Analogs
14
-------
melting point), pure samples do not polymerize significantly (Anon., 1969).
Above the melting point, however, acrylamide polymerizes spontaneously. The
reaction is exothermic with the evolution of considerable amounts of heat
(19.4 kcal/mole) (Anon., 1969). Contamination with suitable catalysts can also
cause spontaneous polymerization regardless of the temperature. Under circum-
stances in which high temperatures cannot be avoided (as in the manufacture of
acrylamide via the sulfate process, when the reaction medium is typically 90~100°C),
or when it appears desirable to further stabilize solutions of acrylamide at
moderate temperatures, polymerization inhibitors are employed. For example, to
ensure the long-term stability of the 50% aqueous solution of acrylamide sold by
+2
American Cyanamid Company and Dow Chemical under similar specifications, Cu is
added to the solution (25-30 ppm) , and it is kept saturated with oxygen by being
constantly purged with air during storage (American Cyanamid Co., 1974; Anon.,
1976 b). Runaway polymerization of solutions of this concentration would result
in rapid boiling and consequently the generation of high pressures in the storage
container.
Although stability data for acrylamide derivatives are not as
complete as for the parent compound, in the pure form their stability is expected
to be similar to that of acrylamide (Bikales, 1970). 2-Acrylamido-2-methylpro-
panesulfonic acid, for example, is stable at room temperature without the addition
of any inhibitors or stabilizers. A 25% aqueous solution of this material (with-
out stabilizer) shows evidence of polymerization after one month at room tempera-
ture and after one day at 50°C (Lubrizol Corp., 1974). N-Isobutoxymethylacrylamide,
a liquid at room temperature, is stable in storage under normal conditions and
shows no significant changes in viscosity or polymerization behavior after three
months storage at 48°C (Anon., 1976 a). All acrylamide derivatives, are, however,
subject to accelerated deterioration under conditions of prolonged exposure to heat,
15
-------
ultraviolet light, low pH, and other conditions favoring initiation of free
radical catalyzed polymerization. A case of smoke, crackling, and small flames
has been reported for four fiber drums containing N-methylolacrylamide (Coventry,
1965) . Very small quantities of contaminants are believed to have catalyzed this
reaction, and the material may have been stored at elevated temperatures. At
the present time, N-methylolacrylamide sold in the United States is offered only
in aqueous solutions.
Acrylamide readily polymerizes in the presence of free radicals
under a wide range of conditions. In a typical industrial process, a 10-30%
aqueous solution of acrylamide monomer in the presence of an appropriate catalyst
at approximately 30°C yields linear polyacrylamide with molecular weights greater
than 10,000,000. Recipes of this general description can be used to make products
from about 500,000 daltons to over 10 million daltons by adjusting temperature,
initiator, and monomer concentrations. Commercial polymers are frequently dried
directly from the aqueous gel form and reduced to flake for sale. The polymeri-
zation reaction is carried out under a blanket of nitrogen with the solution
purged with nitrogen to remove oxygen, a polymerization inhibitor (Anon., 1969).
The pure polymer, recovered by precipitation and drying, is a white solid, usually
in the form of beads, soluble in water, and insoluble in nonpolar solvents
(Bikales, 1970). Substituents on the a-carbon have a greater effect on slowing
the rate of polymerization than N-substituents.
2. Hydrolysis, Oxidation, and Photochemistry
Acid or base catalyzed hydrolysis of the amide groups of acryl-
amide to carboxyl groups yields acrylic acid or acrylate ion (Anon., 1969):
0 + H0C=CHCOOH + NH.+
fi n j» Z 4
H2C=CHCNH2
16
-------
Although polyacrylamide made in aqueous solutions is likely to have undergone
some hydrolysis (Thomas, 1964), relatively severe conditions are required to com-
pleLely hydrolyze solutions of acrylamide (see Table 4). In 0.5 N NaOH at 100°C,
90% of the acrylamide in a 10% solution is hydrolyzed within 12 minutes, but
in a 0.03 N NaOH solution at 50°C, only 19% of the acrylamide in a 10% solution
is hydrolyzed in 15.5 hours (Anon., 1969). The rate of hydrolysis of a 5%
acrylamide solution in 0.5 M H SO at 50°C is 0.9%/hour. Acid or alkali hydrolysis
of polyacrylamide yields the corresponding salt or free acid of polyacrylic acid.
Table 4. Rates of Acid and Base-Catalyzed Hydrolysis of Acrylamide
(Anon., 1969)
Initial
PH
12
12.3
12.52
0.70
0.00
-0.30
-0.70
NaOH
(Initial
Normality)
0.01
0.02
0.03
J
H2SOlf
(Molarity)
0.1
0.5
1.0
2.5
% Hyd
4 Hours
5.11
10.30
15.66
rolysis
15.5 Hours
6.57
13.35
18.94
% Hydrolysis/Hourb
0.3
0.9
2.1
4.5
110% Acrylamide solution at 50.8°C
D 5% Acrylamide solution at 50°C
17
-------
Acrylamide, its derivatives, and their polymers are stable to
air oxidation at ambient temperatures. Polyacrylamide and its solutions degrade
at elevated temperatures, but the tendency to degrade is not dependent on the
presence of an oxidizing atmosphere. Above 175°C, polyacrylamide undergoes
imidization, releasing NH . Above 300°C, hydrogen gas and carbon monoxide are
also released as degradation becomes more extensive (Anon., 1969).
Acrylamide absorbs light in the ultraviolet range from 200-280 nm
(see Figure 1, p. 5), which is below the cutoff point for radiation from the sun at the
surface of the earth. Acrylamide solutions in water do not polymerize on ex-
posure to UV light, but acrylamide and N,N'-methylenebisacrylamide mixtures may
be photopolymerized by visible light in the presence of a sensitizer or catalyst,
such as riboflavin, silver salts, and metal oxides or sulfides (Anon., 1969).
Hydrogen peroxide has been used to cause photosensitized polymerization of aqueous
solutions of acrylamide (Dainton and Tordoff, 1957). One goal of photopolymeri-
zation investigations is to eventually develop a practical non-silver photographic
process (Chaberek, 1965). This application of acrylamides is discussed further
in the section on uses.
3. Other Chemistry
Several excellent reviews of the chemistry of acrylamide monomers
are available (Bikales, 1970; Bikales and Kolodny, 1963; Anon., 1969). However,
the only other chemical reaction, besides those described above, which appears to
be relevant to environmental considerations is the bromination of acrylamide. The
resulting addition product is used for analytical purposes (see Analysis and
Monitoring, p. 48.).
18
-------
II. Environmental Exposure Factors
A. Production and Consumption
1. Quantity Produced
The total production capacity of acrylamide monomer in the
United States in 1974 is estimated to exceed 70 million pounds. The production
of this much acrylamide would take about the same quantity of acrylonitrile
starting material, which amounts to about 3% of the acrylonitrile produced in
1974 (Blackford, 1974). Annual production of acrylamide has been estimated to
be 15-20, 30, 32, and 40 million pounds in 1966, 1969, 1972, and 1973, respec-
tively (Blackford, 1974).
Production data for acrylamide derivatives are not available,
but it is believed that they are all produced in significantly smaller quanti-
ties than acrylamide. In addition, many derivatives of acrylamide not mentioned
in this report are undoubtedly produced in research quantities, but not in
amounts of commercial significance at the present time. Blackford (1974) re-
ported that diacetone acrylamide was produced in 10 million pounds per year,
but the manufacturer (Lubrizol) has indicated that the compound is no longer
produced.
In 1973, slightly less than 20 million pounds of polyacrylamide
were produced in this country (U.S. International Trade Commission, 1973) (see
Table 5). That is the latest year for which firm data are available. Because
of increased manufacturing capacity for acrylamide monomer since 1973, poly-
acrylamide production for 1974 could be as high as 40 million pounds.
19
-------
Table 5. Polyacrylamide Produced and Sold in the United States
(U.S. International Trade Commission, 1971-73)
Year
1971
1972
1973
Quantity
Produced (Ibs.)
8,391,000
19,106,000
19,996,000
Quantity
Sold
3,385,000
14,418,000
17,289,000
Value of
Quantity Sold ($)
3,369,000
12,377,000
13,744,000
Average Cost
per Pound ($)
1.00
0.86
0.80
2. Producers, Major Distributors and Importers, Sources of
Import, and Production Sites
Table 6 lists the current manufacturers of acrylamide monomer
and their capacities as of April, 1974, as well as projected capacities based
on announcements made in March, 1975, by the major producer, American Cyanamid
Company. Table 7 lists those manufacturers who are producing acrylamide deri-
vatives in commercially significant quantities. Most of the acrylamide monomer
(and derivatives) manufactured by these companies is not sold, but is consumed
internally by the acrylamide polymer manufacturers (see Table 8).
Table 6. Producers of Acrylamide Monomer
(Blackford, 1974)
Manufacturer
American Cyanamid Co.
Industrial Chemicals Div.
New Orleans (Fortier),
Louisiana
Vistron Corp.
(Subsidiary of Standard
Oil of Ohio)
Chemicals Department
Lima, Ohio
Dow Chemical Company USA
Midland, Michigan
Bio Rad Labs
Richmond, California
Capacities (million pounds)
as of 4/1/74 as of 7/74 as of l/77t as of 3/77t
40
15
15
50
15
15
80
90
*Data not available, but appears to be negligible fraction of the combined output
of all producers (SRI, 1975; Blackford, 1974).
^Projected growth announced by company (Anon., 1975b).
20
-------
Table 7. Producers of Acrylamide Derivatives
Manufacturer
Product
Source
Lubrizol Corporation
Bayport, Texas
White Chemical Sales, Inc.
Bayonne, New Jersey
Proctor Chemical Company
Subsidary of National
Starch and Chemical Co.,
Salisbury, North Carolina
American Cyanamid Company
Organic Chemicals Div.,
Bound Brook, New Jersey
Vistron Co.
2-Acrylamido-2-methyl-
propanesulfonic acid
Methacrylamide
N-_t^-Octylacrylamide
N-jt-Butylacrylamide
N-Methylolacrylamide
N,N'-Methylenebisacrylamide
N-Isopropylacrylamide
N-Isobutoxymethylacryl-
amide
N ,N'-Methylenebisacrylamide
*
*
*
SRI, 1975
SRI, 1975
A
U.S. International
Trade Commission,
1973
* Industrial sources
Table 8. Producers of Acrylamide Polymers
(SRI, 1975)
Manufacturer
Location
Major Uses
American Cyanamid Company
Industrial and Plastics
Division
Betz Laboratories, Inc.
Celanese Corporation
Celanese Coatings and
Specialty Chemicals,
Subsidiary of Celanese
Resins Division
Dow Chemical USA
Hercules, Incorporated
Coatings and Specialty
Products Division
Linden, New Jersey
Trevose, Pennsylvania
Charlotte, North Carolina
Water and waste treatment
Midland, Michigan
Hopewell, Virginia
Water and waste treatment
21
-------
In 1969, the United States imported a total of 11 million pounds
of various amides and imides, including some acrylamide from Japan. At the same
time, over 200 million pounds of these compounds were manufactured domestically.
The exact amount of imported acrylamide is not known, but it would appear to be
a small fraction of domestic production (U.S. Tariff Conmission, 1971).
3. Production Methods and Processes
Acrylonitrile is the major starting material required for all
industrial methods for the manufacture of acrylamide. Acetone cyanohydrin or
methacrylonitrile are used to produce methacrylamide.
Figure 4 shows the main steps involved in the sulfate (sulfuric
acid) process for the production of acrylamide, with ammonia used as the neutral-
izing agent. Figure 5 is a flow diagram of the sulfate process including alterna-
tives to ammonia neutralization which have or have had significant industrial use.
The starting materials, acrylonitrile, sulfuric acid, and water, are usually
mixed in equimolar quantities. Temperatures are typically kept around 100°C
for the hydrolysis reaction, but some processes use higher temperatures, up to
200°C (Sittig, 1965). The hydrolysis reaction is strongly exothermic, necessi-
tating temperature controls. Lower temperatures are generally preferred to
minimize hydrolysis of the product as well as to prevent premature polymerization.
It can be seen from the figures that isolation and purification of the acrylamide
product is a major part of the sulfate manufacturing process.
The sulfate process will probably not be the main manufacturing
process for acrylamide by the end of this decade. In 1971 the Dow Chemical
Company began producing acrylamide via a new catalytic process suitable for
directly hydrolyzing most organic nitriles to the corresponding amides (Anon., 1973)
22
-------
M,0
~™-i_^r-
figure 4. Flowsheet for Sulfate Process for Acrylamide Production (Bikales
and Kolodny, 1963) (Reprinted with permission from John Wiley & Sons, Inc.)
lime p
CH2 - CHtNH/.H/bO,
Acryljmide sulf.ile
CH, —CHCNM, ,
Figure 5. Variations on the Sulfate Process for Acrylamide Manufacture
(Thomas, 1964) (Reprinted with permission from John Wiley & Sons, Inc.)
23
-------
The catalyst consists of metallic copper and chromium oxide (Haberman and
Tefertiller, 1971), which after several hours use is regenerated by treatment
with a peroxide followed by reduction with hydrogen (Haberman, 1972). An out-
line of the process is shown in Figure 6. No waste stream is produced in this
process; there are no byproducts. The process offers high yields (98.5+%) of
acrylamide of high purity (99.5%) at a substantial fixed and variable cost
advantage over the sulfate process. In the middle of 1974, the major producer
of acrylamide monomer, American Cyanamid Company, completed a new plant at
Fortier, Louisiana, capable of producing 10 million pounds per year of acryla-
mide monomer (Anon., 1975 b). This plant also uses a new process said to be
free of pollution and byproducts because the acrylamide is made directly via
hydrolysis of acetonitrile over a catalyst (Blackford, 1974). At the same
time, the company announced plans to replace its 30 million pounds per year
sulfate facility at Linden, New Jersey, with a 60 million pounds per year
catalytic facility scheduled to go on stream in 1977 (Anon., 1975 c).
REGENERATION CYCLE
WATER STORAGE
ACRYLONITRILE
STORAGE
ACRYLONITRILE
AND H2O STRIPPER
AQUEOUS
ACRYLAMIDE
STORAGE
Figure 6. Catalytic Route to Acrylamide Eliminates Troublesome Byproducts and
Increases Product Yields CAnon., 1973)
24
-------
Figure 7 outlines the catalytic hydration process as developed
by Mitsui Toatsu Chemicals, Inc., of Japan. The acrylonitrile is converted to
acrylamide by a metallic copper catalyst mixed with the acrylonitrile and water.
The optimum temperature of the reaction is 70-120°C, about the same as the tem-
peratures typically used in the sulfate process. Unreacted acrylonitrile is
removed by evaporation and the catalyst is removed (for reuse) by filtration.
Very few by-products are said to form (Otsuka et_ aJ., 1975), so the aqueous
acrylamide solution can be marketed or used internally with no further treatment
or purification. Because the process is carefully controlled and the product is pro-
duced in a highly purified state, no polymerization inhibitors are added at any
time. The manufacturer claims that the 30-50% acrylamide solutions marketed are
stable and safe if stored in the original shipping containers and handled properly.
Table 9 compares product specifications for acrylamide produced by the catalytic
hydration process and the conventional sulfate process. The former process is
capable of producing a product of higher purity at lower cost (because there are
fewer steps), and the process is inherently by-product and pollution free.
Industrial methods for preparing other derivatives are discussed
in Section I-B-1, p. 13).
25
-------
Figure 7. Catalytic Hydration Process for Acrylamide Production
(Otsuka et al., 1975)
Table 9. Product Specifications
(Otsuka et.al., 1975)
Composition
Acrylamide %
Water %
(NH^SO,,
Iron and other %
Polymerization
inhibitor %
Sulfuric
Acid Method
99.0
0.5
0.5
Trace
Trace
Catalytic Hydration
Method
99.9 (excluding water)
30-50% aqu. solution
None
Trace
None
26
-------
4. Market Prices
Table 10 lists the current market prices for pure acrylamide
monomer and selected derivatives and polymers. The price per pound for acrylamide
(drum and tank quantities) decreased from 5l£ in 1962 to 34
-------
The price per pound of acrylamide sold in aqueous solutions is
lower than that for the solid, because selling it in solution obviates the need
for the costly processes of separating the acrylamide from the solution in which
it is formed and drying the solid. Since the monomer is usually polymerized in
aqueous solution, purchasing it in this form can save the buyer the trouble of
handling the solid (i.e., problems of dust, etc.). Shipping costs for the solu-
tion are higher than for the solid, however. The greatest savings are therefore
obtained when the point of consumption of the acrylamide is near the manufacturing
plant.
5. Market Trends
Acrylamide production is estimated to have increased from
approximately 30 million pounds in 1969 to 40 million in 1973 (Blackford, 1974),
and this increase is expected to continue. For the period 1973-78, it is esti-
mated that the average annual growth rate will be 8.5%, which will result in
the production of approximately 60 million pounds in 1978 (Blackford, 1974).
The major factors suggesting an expanding market for acrylamide are the use of
polyaerylamides in water and waste treatment, and the expanding use of polymers
in the oil industry to increase secondary yields (see Section II-B). The major
factors which may tend to decrease the use of acrylamide are its toxicity and
its potential as an environmental contaminant.
B. Uses
1. Major Uses
The major use of acrylamide and its derivatives is in the pro-
duction of polymers and copolymers for various purposes.
28
-------
Currently, the largest market for polyaerylamlde is in sewage and
waste water treatment, and this is estimated to have consumed 40% of the acrylamide
produced in 1973 (Blackford, 1974). Polyacrylamides have also been approved
for treatment of potable water by the USPHS Technical Advisory Committee on
Coagulant Aids for Water Treatment as of September 28, 1961 (Anon., 1962). The
amount of residual monomer allowed in such applications is 0.05% (Croll et al.,
1974). Polyacrylamides make good flocculants because they are capable of forming
electrostatic bonds with particles in a dispersed suspension (Morozumi, 1971).
The activating points of hydrogen bond or coordinate bond formation between the
suspended or dispersed particles and the polymer are the polar groups on the
polymer. Therefore, these groups must not participate in significant inter- or
intramolecular polymer hydrogen bonding. Polymer-polymer interaction is minimized
in several ways:
1) Partial hydrolysis of the polymer chain results in chain
extension which minimizes intramolecular association and maximizes cohesion of
the suspended particles (Morozumi, 1971).
2) The concentration of the polymer is kept low, typically
about 0.1%, in order to minimize intermolecular interaction (Morozumi, 1971).
3) The polymer dose can be lower if the molecular weight of
the polymer is high. Since low polymer dose reduces intermolecular interaction,
the molecular weights of the polymers are kept as high as possible (Anthony ejt
al., 1975). An undesirable side effect of increasing the molecular weight of the
polymer is that this decreases its solubility, but polyacrylamides are sufficiently
soluble in water so that solutions of the required concentrations (ca. 0.1% or less)
can be prepared from polymers ranging in average molecular weights from 10-20
million daltons.
29
-------
4) Linear polymers have fewer intramolecular interactions than
branched-chain polymers; therefore, linear polymers are more effective flocculants
(Anthony et_ al^. , 1975). The atoms in branched-chain polymers are closer together
than in linear polymers; hence they have more opportunity to interact. The
linearity of a polymer is a function of the conditions under which it was formed.
As a general rule, low monomer concentrations and low polymerization temperatures
favor linear polymerization, while high monomer concentrations and high temper-
atures during polymerization favor formation of branched chains (see Section I-A,
p. I)-
Acrylamide polymers are normally nonionic but can be produced
in cationic or anionic forms when comonomers are used or by post reaction with
appropriate reagents (see Section I-A-2, p. 8). Cationic copolymer flocculants
are used for organic suspensions, low pH solutions, metallurgical processes,
and as dewatering aids for concentrating slurries. Anionic copolymer flocculants
are used in neutral and alkaline environments as thickening aids for dilute
slurries (Floyd, 1975), and nonionic polymers find a wide and general flocculant
use, especially in mining (Morozumi, 1971). Selection of the proper flocculant
for a given application is an empirical process dependent upon the detailed
laboratory examination of many variables (Hercules Corp., 1974).
The pulp and paper industry uses polyacrylamides as strengtheners
and to aid in preventing fibers from being washed away (Moore, 1975). The resid-
ual acrylamide (and/or acrylamide derivative) content of paper and paperboard to
be used in contact with aqueous or fatty foods is regulated by the Food and Drug
Administration (FDA, 1974a) (see also Section I-A-4, p. 10). Pulp and paper
uses accounted for approximately 20% of acrylamide consumption in 1973 (Blackford,
1974). The main uses of polyacrylamides in the paper industry are based on its
flocculation activity and binding ability. Improved filler, pigment and fines
30
-------
retention and increased drainage rate are obtained by adding 20-60 Ibs of alum
per ton of fibre followed shortly by 1/4 - 1/2 Ib of dissolved polyacrylamide
per ton of fibre. The polymer is added to the fan pump or head box (MacWilliams,
1973).
2. Minor Uses
Besides the flocculant and pulp and paper applications, there are
a number of minor uses of polyacrylamides. These uses are listed in Table 11
along with the major applications.
Table 11. Uses of Polyacrylamide (Thomas, 1964; Anon., 1969;
MacWilliams, 1973)
Adhesives
Coal dust loss preventative
Coal flotation
Coating resins
Dental fillers
Drilling-fluid additives
Elastomer curing agent
Electrorefining improvement
Emulsion stabilizers
Flocculating agents for minerals, coal,
sewage, industrial wastes, etc.
Flooding agents for petroleum recovery
Grouts for dams, foundations, tunnels, etc.
Hair sprays
Ion-exchange polymers
Leather-treating agents
Molding resins to increase strength,
raise softening temperature, or
to serve as plasticizing components
Paper additives and resins for faster
draining, improved filler retention,
coating, sizing, wet and dry
strength improvements, etc.
Photographic films
Pigment-binding resins
Polyester laminating resins
Printing pastes
Propellant binders
Rodent repellants
Shaving creams
Soil stabilizers
Suspending agents
Textile resins for warp sizing, printing,
shrinkproofing, antistatic treatments,
binding nonwoven fabrics, improving
dye receptivity, increasing dimensional
stability of viscose rayon
Thickening agents
Tumor suppressants
Water clarifying, water-loss prevention
in cements, waterproofing of masonry
31
-------
Water soluble polymers, including polyacrylamides, are widely used
in the petroleum industry. The polymers are used as flocculants in water recir-
culation systems (Huebotter and Gray, 1965), and they are also used for controlling
the mobility of drilling fluids. One of the advantages of polyacrylamides in
this application is their high resistance to biological attack under conditions
prevailing in this application (MacWilliams et_ al_. , 1973). The main use of poly-
acrylamides in drilling fluids is in secondary oil recovery. Primary oil recovery
ceases when natural underground pressures are reduced to atmospheric pressure by
the removal of oil from rock or sand, which usually occurs after only 1/5 to 1/3
of the oil present has been removed. Secondary recovery may involve pumping water
down behind the oil to generate sufficient pressure to keep the oil flowing.
However, the masses of pumped water do not stay intact, but seeking the paths of
least resistance, tend to form narrow streams through the oil/rock matrix and
eventually emerge from the oil well along with the oil. Eventually the water/oil
ratio becomes so high (20:1) that further use of the well becomes uneconomical
(MacWilliams et al., 1973). The use of polyacrylamides (previously polymerized
material) in water flooding inhibits streaming of the flood water and allows re-
covery of 50-100% more oil than would be possible using water alone (MacWilliams
e_t^ a^l. , 1973). This is possible because of a phenonmenon known as the "resistance
effect" which is the apparent enhancement of the solution viscosity in porous
media 5-20 times over the viscosity of the bulk solution (MacWilliams, 1973).
One of the few direct marketable uses of acrylamide monomer is in
the production of chemical grouts and soil stabilizers for use in dams, founda-
tions, and tunnel construction. The action of these materials has been described
in Section I-A-2 (p. 9). In addition to American Cyanamid's AM-9 Chemical Grout,
Nalco Chemical Company (Adams, 1966) has patented a mixture of acrylamide and
methylenebisacrylamide in a slurry which is catalyzed in soil, sand, or clay to
32
-------
form a suitable cross-linked polymer, which stabilizes the soil matrix in which
it forms. Similar monomer mixtures have been reported for use in sealing water
leaks during underground construction (Miyazawa et al., 1973) and soil stabili-
zation (Miki, 1973). A review of chemical grout materials for soil stabilization
is available in the Japanese language (Higashimura, 1974). Industry sources
have suggested that this market for acrylamide does not exceed 5% of the total
production.
Acrylamide and its methylol derivative have been used in the
textile industry to impart certain desirable qualities to fabrics, such as a durable
press characteristic (Doshi and Varghese, 1971), which is obtained by grafting the
monomer to the cellulose structure of the fabric (Doshi and Varghese, 1973). Acryl-
amide has also been used for the preservation of interfibrillar hydrogen bonding
in never-dried cotton (again by grafting the monomer to the cellulose fibers),
which results in wet extensibility (ability to swell) several times that of un-
treated cotton (Williams et^ al., 1974).
Acrylamide undergoes photosensitized polymerization upon exposure to
visible light in the presence of certain dyes (Delzenne et^ aJL. , 1962), and this
phenomenon has led to the investigation of acrylamide (and other monomers) as
possible replacements for silver halide in certain photographic applications
(Chaberek, 1965; Anon., 1975d). Photopolymers have been successfully used in
holography (VanRenesse, 1972). In this application, photopolymers have an ad-
vantage over silver halides, because they do not need to be processed after ex-
posure in order to obtain the hologram. Mixtures of acrylamide and N,N'-methylene-
bisacrylamide are of particular interest. These comonomers are the basis of a dye-
sensitized system which has a longer photosensitive life than others investigated
(Sugawara et^ al. , 1975).
33
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Polyacrylamide gels are used for a supporting medium in zone elec-
trophoresis (Raymond and Weintraub, 1959). Electrophoresis in a gel of increasing
polyacrylamide concentration allows the estimation of molecular weights of proteins
(Margolis and Wrigley, 1975). In this relatively new technique, the porosity of
the gel is controlled by varying the amount of cross-linking in the polymer.
Cross-linking is a function of monomer concentration, and therefore, cross-
linking tends to increase with high monomer concentration.
N-Isobutoxymethylacrylamide and other N-(alkoxymethyl)acrylamide
derivatives have been used mainly as comonomers in the production of water in-
soluble protective coatings, fabric binders and finishing agents, elastomers,
adhesives, and photographic emulsions (Anon., 1976 a).
Acrylamide derivatives, especially N,N'-methylenebisacrylamide,
have been investigated as possible antitumor agents (Tomcufcik et^ al_., 1961).
3. Discontinued Uses
Acrylamide sulfate was formerly used as an intermediate in the
production of acrylic acid. This use was discontinued in 1972 when catalytic
oxidation of propylene was shown to be lower in cost, to take fewer steps, and
not to produce large quantities of by-product (ammonium sulfate) which had to be
recovered (Blackford, 1974).
Diacetone acrylamide (MacWilliams, 1973) was used in formulating
and molding low-pressure polyester decorative laminates, resulting in reduced
cost and simplicity and speed of production over high-pressure laminating systems
(Cech and Bretz, 1972). The only U.S. manufacturer of diacetone acrylamide,
Lubrizol Corp., discontinued production in late 1975.
4. Projected or Proposed Uses
The wide range of uses acrylamide has been put to since its
commercial production began in 1954 (Bikales and Kolodny, 1963) and the relatively
34
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short period of time it has been available in commercial quantities suggest
that there may be additional applications, as yet undiscovered, in which acryla-
mide will serve. As for those uses which are current, acrylamide will undoubtedly
remain important in sewage and waste water treatment in the future. Since many
domestic oil wells are no longer capable of primary production, the demand for
oil will probably make secondary recovery procedures (such as flooding) employing
polyacrylamides more economically favorable than in the past. This is likely to
be the area of greatest potential growth for acrylamide (Blackford, 1974).
5. Possible Alternatives to Uses
In the sewage and waste industry, polyacrylamides offer the
advantage of retaining their water solubility even when very high molecular
weight polymers are used. An equally effective substitute flocculant which is
also biodegradable would be an excellent alternative to the non-biodegradable
polyacrylamides. Such biodegradable flocculants were not noted in the literature
that was examined.
The drilling industry employs a number of polymers besides poly-
acrylamides, including polyamines, polyacrylate salts, carboxymethylcellulose,
hydroxyalkylcellulose, guar gum, and xanthum gum (MacWilliams et^ ol., 1973).
While each polymer has usually been introduced for a specific purpose, their pro-
perties overlap to some extent. For example, all except the polyamines have been
used in drilling applications. Therefore, if the use of polyacrylamide were dis-
continued in this field, substitutes are already available.
Polyacrylamides have been used in the applications listed in
Table 11 (p. 31) because of their solubility in water, polar functional groups,
low toxicity, and competitive cost. Similar results might be obtained in
these applications if other polymers having like features can be found. For
example, in applications involving low molecular weight polymers, polyacrylamides
35
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can be directly replaced by polymers of the methacrylic series with no substan-
tial change in functional characteristics (Thomas, 1964).
C. Environmental Contamination Potential
1. General
Acrylamide end products contact the environment almost exclusively
as polymers. However, a major exception is the use of acrylamide monomer in
chemical grouts for dams, foundations, tunnels, etc. Acrylamide polymers usually
contain some residual monomer which can escape into the environment at the point
of use of the polymer product. Other sources of the monomers in the environment
are from production, transportation, storage, polymerization, use, and disposal
of the monomers. The actual quantities lost from any of these sources is unknown.
However, the following sections will discuss the potential for such losses.
2. From Production
The environmental contamination potential from production depends
on the particular production process considered. With the sulfate process,
filters used in the separation steps are potential sources of environmental
contamination unless they are treated to remove the residual monomer in them
prior to being discarded. Likewise, solvents used for extraction and/or recrys-
tallization of the pure monomer will contain residual monomer and may be a potential
source of contamination if discarded rather than recirculated. The neutralization
by-product (such as ammonium sulfate from the sulfate process) is also a potential
source of trace amounts of the monomer.
While recrystallization is essential in the sulfate process in
order to obtain a product of satisfactory purity, this is not so in the catalytic
process. The acrylamide formed in the catalytic process may be eventually poly-
merized in the same aqueous solution in which it is formed, eliminating the processes
of separation, recrystallization, handling the pure powder, and dissolving it
36
-------
again in water. Unlike the sulfate process, the catalytic process does not gen-
erate any by-product. Thus, the catalytic process has inherently fewer potential
sources of environmental contamination (Otsuka ejt^ al., 1975).
Acrylamide and probably many of its derivatives are manufactured
in closed systems which are not likely to be sources of environmental contamin-
ation (other than as described above), except in the event of a leak in the
reaction vessel or pipes connected to it.
3. From Transport and Storage
Solid acrylamide is supplied in polyethylene-lined 5-ply bags
containing approximately 50 pounds of crystalline powder. This method of
packaging is not likely to lead to environmental contamination during shipping
and storage as long as the integrity of the bag is maintained and the transpor-
tation and storage environments are free of heat sources which might cause violent
spontaneous polymerization to occur.
Acrylamide solution (50% aqueous) is shipped in tank trucks built
of Type 304 or Type 316 stainless steel, or in 55 gallon polyethylene-lined drums.
Smaller volumes (1-5 gallons) are stored and shipped in molded polyethylene con-
tainers (American Cyanamid Co., 1974). Environmental contamination problems
could arise through leaks in pipes, pumps, or tanks. Because acrylamide solu-
tions must be constantly aerated while in storage to discourage polymerization
(oxygen inhibits polymerization), small amounts of acrylamide could conceivably
be removed from the tank with the air purge and thereby get into the atmosphere.
However, the low vapor pressure of acrylamide would suggest that these losses
are not very substantial.
37
-------
In summary, it appears that the only way substantial amounts of
acrylamide would be released to the environment during transport or storage would
be by spills. No spills of acrylamide have been documented.
4. From Use
The overall use patterns and facile biodegradability of acrylamides
would seem to preclude the likelihood of widespread environmental contamination.
Localized problems are more likely such as in manufacturing environments (see
Table 8, p. 21, for a list of producers and locations). In factories, there is
the possibility of dust from empty containers of solid acrylamide and spray from
solutions contaminating the surrounding air, floor, and walls of the building
and clothes of persons in the manufacturing area. The residual contents of
containers used to store and dilute solutions of acrylamide monomer, as well as
to polymerize the monomer, and the water used to wash the containers are also
sources of potential environmental contamination in the manufacturing facility.
Forty per cent of all polyacrylamides manufactured are used in
water treatment as aids in increasing sedimentation rates and also as sludge de-
watering agents. Residual monomer in the polymers would be likely to leach out
into the water and be present in the processed water, subject, of course, to prior
or consequential chemical or biological degradation. Should the processed water
reach end users prior to chemical or biological removal of the acrylamide, its
presence could present a hazard. There are no data as to how much acrylamide is
placed in the environment from this use, nor is a reliable quantitative estimate
easily established. At the concentrations at which polyacrylamides are typically
used in water processing (a few percent), the concentration of the residual monomer
in the water would be very low (roughly an order of magnitude less than the dis-
solved polymer). It is, therefore, expected that any residual monomer present
38
-------
in the polymer is not likely to precipitate out in the sludge, but would appear
in the processed water output. This is supported by the work of Croll et al.
(1974) who found that the acrylamide content present in two sewage sludge
samples that had been conditioned (sludge settling and filter pressing) con-
tained less than 0.1 yg/£. Croll and coworkers (1974) further examined seven sludge
samples to determine the acrylamide recovered in the effluent. The recovery
varied from 13 to 100% depending upon the sample and the sludge concentration
procedure (filter pressing, settling, or freezing). The recovered water from
the dewatering procedure may be returned to the water treatment process or
disposed of as an effluent (Croll e^t al., 1974), the latter being a source of
acrylamide release.
About 20% of all polyacrylamides manufactured are used in the
pulp and paper industry directly in paper manufacturing to impart certain de-
sirable physical characteristics to the fibres, as well as in waste water treat-
ment. In these uses, contamination of water could result from the leaching
of monomer in the polymer, exactly as in the use described in the previous
paragraph. Monitoring data have demonstrated the presence of acrylamide in
paper mill effluents (Croll et^ al. , 1974).
As in the above two uses, the potential contamination of the
environment with acrylamide in oil well secondary recovery flooding techniques
also involves the possibility of residual monomer in the polymer leaching into
the immediate vicinity of the well, which, in this case, might possibly involve
migration into groundwater supplies if prior chemical or biological degradation
did not take place. The likely increased use of polyacrylamides in oil produc-
tion increases the risk of contaminating the surrounding areas and possibly local
aquifers.
39
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Chemical grouts containing acrylamide monomer (less than 5% of
the total acrylamide production) are applied in such a way that the monomer has
direct contact with soil. Any residual monomer that has not polymerized during
the soil stabilization step in dams, tunnels, etc., could leach into the sur-
rounding soil and eventually into water. Such an incident has been reported
by Igisu ejt^ al. (1975) where acrylamide was used as a chemical grout near a
family well. Also, these grouts present an occupational hazard to the per-
sonnel using the material. This is the major use in a non-manufacturing en-
vironment which could give rise to serious, although restricted, acrylamide
poisoning incidents in humans.
In summary, the major usage source of environmental contamin-
ation potential of acrylamides is residual monomer in the polymers, especially
when they are used in food processing, waste water treatment, food container
manufacturing, pulp and paper processing, and other applications where residual
monomer may come into direct contact with water.
5. From Disposal
Potential disposal sources of acrylamide include the residues
in reaction vessels used for its manufacture, pipes used for transport of solu-
tions of the monomer, empty bags used for transport and storage of the solid, and
empty tanks, trucks, and drums used for transporting solutions of the monomer. The
acrylamide residues in these sources may be decontaminated by catalytic polymeriza-
tion (see Section II-D-3, p. 46) prior to discarding the containers or equip-
ment. Polymerization should take place before these items are rinsed with water
which flows directly into a sewer whose effluent is not treated to remove acrylamide.
The Dow Chemical Company recommends biological degradation as the procedure of
choice for detoxification of disposed acrylamide, whenever facilities for this
40
-------
type of disposal are available (Anon., 1976 b). Biodegradation is preferred
because of the risk that polymerization will not proceed to completion. When
chemical detoxication is necessary, the use of 20% sodium sulfite in excess is
recommended. This reagent reacts with acrylamide to form 3-sulfoacrylamide, a
compound of demonstrated low toxicity (MacWilliams, 1976).
Croll et al. (1974) studied the effectiveness of various water
treatment processes in the removal of acrylamide from samples of water from the
River Thames. Table 12 summaries the results of their study. Filtration methods
and the usual chlorination at pH ^ 8 were shown to have no practical effect on
the concentration of acrylamide. Thus, it appears that if acrylamides are re-
leased into waste waters while being used as flocculants, they will not be removed
by physical or chemical methods. Of the chemical techniques explored, the most
efficient and the safest is probably the treatment of the water samples with
3 mg/1 ozone. On the other hand, Croll et_ al. (1974) have demonstrated that
acrylamide is biodegraded, and therefore, if a biological process is used sub-
sequent to flocculant treatment, the amount of acrylamide released will probably
be very small.
Table 12. The Effect of Some Water Treatment Processes on 6 yg 1~ Acrylamide
(Croll et. al., 1974)
Treatment
KMnO^
KMnOit
MhO column
MnO column
Ozone
C12
C12
C12
Active carbon
Quantity
mg 1 l
1
1
3
10
10
10
8
PH
5.0
8.5
5.0
7.0
7.0
1.0
5.0
8.5
5.0
Contact time
00
4
4
0.1
0.1
0.5
4
4
4
0.5
% Acrylamide
removed
100
100
17
33
100
100
64
nil
13
41
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6. Potential Inadvertent Production of the Chemical in Other
Industrial Processes as a By-Product
Industrial processes, other than those involving direct pro-
duction of acrylamide and its derivatives, are not, in general, likely to produce
a vinyl-amide by-product because of the relative chemical reactivity of the monomer
and specialized conditions necessary for the formation of this type of compound.
The following reagents and conditions have been shown to result in the production
of acrylamide (MacWilliams, 1973) but are not known to be found in commercial
processes:
a) Acrylyl chloride and ammonia at low temperatures
b) Acrylic anhydride and ammonia
c) Acrylyl isocyanate and water
d) Acetylene and carbon monoxide in the presence of ammonium hydroxide
and iron and nickel carbonyls
e) Thermal decomposition of g-hydroxy, g-dialkylamino, or g-alkoxypropion-
amides in the presence of silica, calcium oxide, or other suitable
catalysts
f) Dehydrohalogenation of a g-halopropionamide in the presence of a
base
g) Pyrolysis of a-acetoxypropionamide
h) Neutralization and heating of ethylene cyanohydrin-sulfuric acid
adduct after reacting with ammonium sulfate or ammonia
7. Potential Inadvertent Production in the Environment
The major potential source of environmental contamination by
acrylamide is from its release into the environment after being produced else-
where. There is no evidence that acrylamide or its commercially significant
derivatives are, or are likely to be, directly produced in the environment. How-
ever, this does not preclude the possibility of the production of noncommercial
42
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derivatives. For example, acrylamide rapidly undergoes halogenation of its double
bond; this is in fact used as a means of quantitatively assaying the pure compound
(see Section II-E-1, p. 48). Since acrylamide passes through water treatment
plants employing chlorination (see Section II-C-5, p. 40), it is possible for the
acrylamide eventually to undergo halogenation in the chlorinated water to form
2,3-dichloropropionamide:
0 0
II , |J
CH2=CHCNH2 + C12 CH2CHCNH2
Cl Cl
Croll et_ al^. (1974) have demonstrated that, under acidic aqueous conditions,
sizable quantities of acrylamide are removed by chlorination.
D. Current Handling Practices and Control Technology
1. Special Handling in Use (American Cyanamid, 1974)
Acrylamide does require special handling for safe use and can cause
serious health problems if handled carelessly. Clean work clothing should be
worn daily, consisting of a head covering, long sleeves and pants, impervious
gloves of rubber or plastic, and rubber footwear. Spills of acrylamide solution
on clothing or the contamination of clothing with solid acrylamide requires imme-
diate removal of the affected clothing followed by laundering before reuse. Gloves
should be washed thoroughly before removal and discarded if contaminated on the
inside. Work clothing should never be worn home and workers should shower before
changing into fresh clothing.
The handling of acrylamide in ways that may create dust from the
solid or spray from solutions should be avoided, if possible. When dust or spray
is unavoidable, goggles and respirators should be worn (see Table 13).
43
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Table 13. Respirators Suitable For Work With Acrylamide (American Cyanamid, 1974)
Name
Model
Cartridge/Filter
Manufacturer
Glendale
A.O. Respirator
Wilson Respirator
GR-2021
R-5055
841CD
C-21/F-10
R55
41/R415
Glendale Optical Company, Inc.
130 Crossways Park Drive
Woodbury, New York 11797
American Optical Company
Southbury, Massachusetts 01550
Wilson Products
Division of Ray-0-Vac Co.
Reading, Pennsylvania 19605
Dust or spills on exposed skin require immediate flushing with
plenty of water. Food, beverages, tobacco, magazines, newspapers, and other
material that will be eaten or intimately handled should never be used in the
acrylamide work area. Before eating in a non-work area .workers should wash
their hands thoroughly. Spills should be promptly cleaned and the entire work
area decontaminated at least once a week. Empty containers should be isolated
and then buried in an approved landfill or incinerated. Drums may be reused if
washed up under carefully controlled conditions (Anon., 1976 b).
2. Methods of Transport and Storage
Solid acrylamide is shipped in multi-wall moisture-proof bags
containing approximately 50 pounds each, in lots of 24,000 pounds per truckload
or 30,000 pounds per carload (Vistron, 1975).
Acrylamide solution (50% aqueous) is shipped in tank trucks made
of either Type 304 or 316 stainless steel, lined tank cars, or in 55 gallon
drums consisting of a polyethylene insert (DOT-2SL Spec.) overpacked in a fiber
drum (DOT-21P Spec.). Smaller samples are shipped in 5 gallon blow-molded poly-
ethylene containers with 2" screw caps overpacked in a strong fiber box, and in
44
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one-gallon glass jugs with plastic screw caps and polyethylene liners. Each
jug is overwrapped with two 4 mil polyethylene bag liners, tied off, and in-
serted in a strong fiber drum. Adequate cushioning is required during trans-
portation for acrylamide solutions shipped in glass jugs (American Cyanamid,
1974). The Dow Chemical Company prefers the use of steel drums (DOT 37M) over
fibre drums for bulk shipments because of the greater resistance to accidental
holing by fork lift trucks. Also, Dow limits shipment of 50% aqueous acrylamide
in glass containers to specially packed pint bottles (Anon., 1976 b).
Drums, glass jugs, and polyethylene containers should not be
filled to more than 85% of capacity to allow for a supply of air sufficient to
inhibit polymerization. Storage temperatures should not exceed 100°F. Direct
sunlight must be avoided, as should any other significant heat source. In the
case of solutions, the storage temperature should not be allowed to fall below
60°F. American Cyanamid (1974) recommends that all solutions be dated and not
stored longer than six months before use.
Bulk storage tanks for acrylamide solutions should not be filled
to more than 75% of their capacity. Bulk tanks must have provision for continuous
air purging with approximately 1/2 cubic foot per minute per 1000 gallons capacity.
*
The air must be instrument grade (clean) and monitored for temperature and flow.
The pH of the solution should be monitored also, and adjusted if necessary to the
range 5.2 - 6.0 for optimum inhibitor effectiveness. All tanks and lines must
be insulated and temperature controlled with water. The storage tank should
be surrounded by a concrete dike capable of containing the entire volume of
the tank should it rupture. Provision must also be available for the rapid
addition of a polymerization inhibitor (such as copper sulfate pentahydrate,
4 pounds per 1000 gallons 50% acrylamide solution) and cold water, in the event
45
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that unexpected polymerization should commence. Also, a facility for rapid
mixing of the cold water, copper sulfate, and monomer solution should be
available. An example of a typical storage facility recommended by the Dow
Chemical Company is shown in Figure 8.
3. Disposal Methods
Rinse water containing acrylamide and surplus acrylamide solu-
tion must be treated prior to disposal in a sewer or landfill. The recommended
treatment (American Cyanamid, 1974) is to add to every 12.5 gallons of the waste
solution 0.4 pounds potassium or ammonium persulfate dissolved in a minimum amount
of water, followed by 0.2 pounds sodium bisulfite dissolved in a minimum amount
of water. After allowing two hours for polymerization to take place, the waste
solution may be disposed of in a sewer or landfill. An alternate method for
disposal is biodegradation, which is preferred by Dow Chemical where available
because of the risk of failing to chemically polymerize all of the monomer (see
Section II-C-5, p. 40).
4. Accident Procedures
In the event of accidental physical exposure to acrylamide, such
as contact of the solid or solution with the skin, the individual involved
should discontinue exposure as soon as possible, immediately irrigate the
affected area thoroughly with plenty of water, and seek the advice of a physician.
Speed of action in washing is important (American Cyanamid, 1973).
Persons dealing with accidental spills of solid or solutions of
acrylamide should protect themselves with proper dress and respirators (see
Section II-D-1, p. 43). Solid spills may be swept up and placed in a metal
container prior to incineration, although dust may be a problem. Liquid spills
should be covered with an absorbent material which can be swept up and placed in
46
-------
jlifllii 4=
-S «
S 2 !
c
2 o o
u C/l C»
2 o 5
00
00
47
-------
a suitable container for disposal by incineration. Residues on floors and
equipment should be treated with 3 gallons/sq. ft. 1.6% potassium persulfate
solution followed immediately by an equal volume of 1.6% sodium metabisulfite
solution. The mixture of catalysts, after standing for 30 minutes, may be
rinsed down a floor drain with generous quantities of water.
5. Current Controls and Technology Under Development
Although no definite data are available on this matter, it is
assumed that those who manufacture, transport, and use acrylamide are aware of
its hazards and use proper handling techniques in most cases. Monitoring tech-
niques for the determination of acrylamide in air have been developed by
American Cyanamid (1974) and Dow Chemical Company (1976). Presumably these are
in use in industrial environments.
E. Monitoring and Analysis
1. Analytical Methods
There are many chemical and instrumental techniques available
for the analysis of acrylamide. As may be expected, the suitability of each
varies with the particular application required. Analysis of the monomer for
purity, of the polymer and products made from the polymer for residual monomer,
of waterways for trace amounts of acrylamide, and of the blood or urine of workers
exposed to acrylamide are typical assay problems for this material. The dis-
cussion below includes current analytical techniques and their application to
these problems.
Acrylamide may be purified by sublimation of the solid under
reduced pressure, recrystallization from a solvent such as benzene, or via ion
exchange of aqueous solutions. The usual elemental procedures may then be used
to determine C, H, N, and 0. An infrared absorption spectrum and, if necessary,
48
-------
qualitative tests for unsaturation and the presence of the amide group confirm
the identification of the compound.
Several procedures may be used to determine the purity of acryla-
mide as the commercial product. Probably the most widely used is the "bromate-
bromide" method, which depends upon the ease with which acrylamide undergoes
addition reactions at the a,$ unsaturation as a result of the electron-withdrawing
character of the amide group. In this method, acrylamide reacts stoichiomet-
rically with excess bromine generated by an acidified bromate-bromide solution.
The unreacted bromine is then converted to bromide by the addition of excess
iodide, and the liberated iodine is back-titrated with standardized thiosulfate
using a starch indicator (Anon., 1969). A reagent blank must be run, since this
Pi Br2 ft
CH2=CHCNH2 *-»• BrH2C-CHCNH2
Br
is a difference method. The method works not only for acrylamide, but also for
N,N'-methylenebisacrylamide and methacrylamide, and, therefore, each of these
three compounds interferes with assays for the others. The method does not
work for N-isopropylacrylamide, N-methylolacrylamide, or diacetone acrylamide
(MacWilliams, 1973). Other interferences include acrylic acid, ethyl acrylate,
and other olefins. The precision of the method is about +0.3% (Norris, 1967 a).
The B.C. polarographic method is highly specific for acrylamide,
but has lower precision (+1%) than the preceding method (Norris, 1967 a). A
two electron reduction corresponding to the formation of propionamide occurs at
-1.90 volts vs. a saturated calomel electrode in 0.1 M tetramethylammonium
hydroxide in 30% ethanol-water solution (MacWilliams, 1973). Acrylonitrile
interferes with this technique (Norris, 1967 a), which is primarily a trace
method rather than a method meant for routine assay.
49
-------
Trace amounts of acrylamide in polyacrylamide can be detected to
less than 1 ppm via differential pulse polarography (Betso and McLean, 1976),
which is more sensitive than conventional D.C. polarography. Although ethyl
acetate interferes with this technique, acrylic acid and acrylonitrile do not.
Techniques which are less commonly used include morpholine
addition, for which a precision of 0.1% has been reported (other unsaturated
compounds interfere), and nonaqueous titration of acrylamide in nitromethane
with standard perchloric acid, for which a precision of 1% is estimated (other
compounds of comparable base strength interfere) (Norris, 1967 a).
A spectrophotometric technique, involving the reaction of
acrylamide with diazomethane to give a stable 2-pyrazoline, which produces an
intense color on reacting with 4-dimethylaminobenzaldehyde or 4-dimethylamino-
cinnamaldehyde, has been used to estimate acrylamide concentrations in urine
(Mattocks, 1968). The technique is linear over a range of 50-200 ug acrylamide
per milliliter of urine.
The Food and Drug Administration has set a maximum level of
0.05% (500 ppm) as an acceptably safe level for residual acrylamide monomer in
polyacrylamide used in processing beet and cane sugars (FDA, 1972 c) and in
paper goods in contact with food (FDA, 1974 a). The same standard is applied
to polymers used for clarification of potable water in England (Croll and
Simkins, 1972) and in this country (Spencer and Schaumburg, 1975). Methanol-
water (4:1) solution has been found to be an efficient quantitative extractant
for acrylamide monomer from polymers and copolymers (Croll, 1971). Flame
ionization gas chromatography has been used to analyze the polymer extracts
without further preparation. The sensitivity of the technique is 0.004%
acrylamide in polymer or 40 ppm. Acrylic acid does not interfere.
50
-------
American Cyanamid (1974) has used flame ionization gas chromato-
graphy in the determination of acrylamide in air. A minimum of 10 cubic feet of
air is sampled in a two hour period. The acrylamide is extracted with water
which is then diluted with methanol prior to injection into the gas chromato-
graph. No data are given on sensitivity, which would depend upon the actual
size of the sample used for the assay. The Dow Chemical Co. has also developed
a method for determination of trace amounts of acrylamide in air (Anon., 1976 d).
The acrylamide present in samples is retained in an aqueous solution. Inter-
ferences are removed with mixed-bed ion exchange resins and the acrylamide de-
termined via differential pulse polarography (electrochemical reduction of the
double bond). Five to 200 yg of acrylamide can be determined per ten m£ of
aqueous solution.
An electron capture gas chromatographic assay has been developed
which is much more sensitive (0.1 ppb) than flame ionization gas chromatography
(Croll and Simkins, 1972). This method was developed to detect acrylamide in
water levels down to 0.1 yg/1. The high sensitivity is achieved by bromination
of the acrylamide to a,3-dibromopropionamide which can easily be quantitatively
extracted from aqueous solutions with organic solvents. High volatility solvents
are selected so that the extract can be concentrated without losing the bro-
minated solute. Acrylamide itself is very difficult to extract from aqueous
solutions and tends to escape when such extracts are concentrated by evaporation.
Acrylamide monomer can be easily and quickly determined in samples
of pure aqueous solutions by means of measurement of the refractive index of
the solutions (Anon., 1976 c). The method offers 0.4% absolute reproducibility
(at 95% confidence) and is suitable for solutions ranging in concentrations from
5-50%.
51
-------
Differential thermal analysis, a qualitative technique, has been
used to characterize polyacrylamides used as flocculating and dispersing agents
(Concilio and Jahnke, 1972). Anionic, cationic, and neutral polymers could be
distinguished from each other and from polyacrylic acid with this technique, and
hydrolysis products of polyacrylamide could be identified. The concentrations
of polymers in the aqueous solutions studied were about 1%.
The analytical techniques described above are summarized in
Table 14.
52
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53
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2. Current Monitoring
In England, the acceptable concentration of 0.05% acrylamide
monomer in polyacrylamide being used for potable water treatment applies where
the average polymer dose to the water does not exceed 0.5 mg/1 (in the U.S.
1 mg/1 is the standard) (Croll et^ al., 1974). This corresponds to a highest
acceptable average level of acrylamide in potable water of 0.25 yg/1 and a
maximum short-term level of 0.5 yg/1. Croll and his coworkers (1974) monitored
industrial effluents and sludge conditioning works to determine if these levels
were being maintained. They also explored the biodegradation of acrylamide in
river water and sewage effluent, and the possibility that acrylamide might be
removable from water supplies by commonly employed processes, such as chlori-
nation, charcoal filtration, etc. (see Section II-C-5, p. 40 and III-A-1, p. 56).
The results of analyses of industrial effluents are summarized
in Table 15. All the plants that were monitored employed polyacrylamide or
acrylamide-acrylic acid copolymers as flocculating agents, and without exception,
all discharge acrylamide into the environment in amounts which far exceed the
maximum allowed levels for potable water. In the case of the clay pit, the
concentration of acrylamide in the receiving stream was 1.2 yg/1. Further
downstream at a waterworks intake the level dropped to 0.3 yg/1, which is
still above the average permissible level for drinking water.
54
-------
Table 15. Concentrations of Acrylamide in Some Industrial Effluents
(Croll, et. al., 1974)
Effluent
Coal mine A tailings lagoon
Coal mine B tailings lagoon
Coal mine C coal washing effluent lagoon
Coal mine/coking plant effluent
Paper mill A treated effluent
Paper mill B treated effluent
Clay pit
Acrylamide concentration
ug I"1
42
39
1.8
0.74
0.47
1.2
16
The conditioned sewage sludge at two sewage conditioning plants
which used polyacrylamide was found to contain acrylamide at levels below the
standard (^0.1 yg/1). The effluent emitted from these plants is further diluted
by a factor of at least 10:1 prior to discharge into waterways, and hence the
acrylamide monomer content resulting from the use of that particular polyacrylamide
flocculant is not expected to be a cause for concern in terms of exceeding the
drinking water standard.
In summary, only one British study of effluent and ambient
monitoring data for acrylamide compounds is available. No United States moni-
toring data were noted in the available literature.
55
-------
III. Health and Environmental Effects
A. Environmental Effects
1. Persistence
a. Biological Degradation, Organisms and Products
Relatively little is known about the environmental fate of
acrylamide and its derivatives. Cherry and coworkers (1956) have studied the
fate of acrylamide in natural water. Acrylamide (10 ppm) was added to filtered
river water which had been supplemented with inorganic nutrients - nitrogen and
phosphorus - to supply nutrients to the river microorganisms. The water was
aerated by bubbling air at a rate of about one bubble per second. COD analysis
at various intervals revealed a rapid loss of acrylamide from the water (Figure
9). When the river water was redosed with acrylamide, faster rates of degra-
dation were observed.
FORMULA CH.'CHCONH,
10 20 JO 4041
ELAPSED TIME (DAYS)
Figure 9. Degradation of Acrylamide in River Water Supplemented
with Nitrogen and Phosphorus (1 part P, and 7-10 parts N for
each 100 ppm of COD) (Cherry et a_l. , 1956)
(Reprinted with permission from Water Pollution Control Federation)
In the river die-away test carried out by Croll and co-
workers (1974), river water enriched with 8 ppb of acrylamide was incubated
aerobically in a beaker in sunlight. The method of analysis of acrylamide in-
volved bromination of acrylamide to a,g-dibromopropionamide which was extracted
56
-------
and analyzed by electron capture gas chromatography. The authors noted a
rapid loss of acrylamide from the river water after a lag period which ranged
from 50 - 220 hours. Redosing the river water with acrylamide, or seeding the
river water with the microorganisms acclimated to acrylamide, resulted in
faster rates of degradation with shorter lag periods (Figure 10). These results
coo
TIME (hr)
Figure 10. Degradation of Acrylamide in Control and Inoculated
Samples of River Water (Croll £t^ al. , 1974)
(Reprinted with permission from Pergamon Press Inc.)
A River water
B River water inoculated with acclimated culture
suggested that the loss of acrylamide was the result of microbial degradation
and that acclimation of the microorganisms prior to degradation was necessary.
This was confirmed by Cherry and coworkers (1956), who determined 5-day BOD with
10 ppm of acrylamide using a variety of different seeds. As shown in Table 16,
the seed material acclimated to acrylamide yielded a BOD equivalent to about
57
-------
Table 16. Standard 5-Day BOD Test with Acrylamide Using Different
Types of Seeds (Cherry e_t al. , 1956)
BOD
Type of Seed (Expressed as % of COD*)
(i) River microorganisms acclimated to acrylamide 75
(ii) River microorganisms acclimated to acrylonitrile 17
(iii) Sewage seed, unacclimated 13
* COD (ppm) = 1,300,000
75% of COD. On the other hand, when unacclimated seed or seed material which
had been acclimated to another substance (acrylonitrile) was used, the BOD was
only in the range of 13-17% of COD.
The susceptibility of acrylamide to rapid biological break-
down is also indicated from the studies of Edwards (1975b). In the tanks which
he used to expose goldfish to acrylamide, it was found that acrylamide decreased
very rapidly if weeds, algae, and microorganisms were present. However, when
the tanks were cleaned with permanganate and freed from weeds, the levels of
acrylamide remained fairly constant.
Croll and coworkers (1974) investigated the fate of acryla-
mide under sewage treatment conditions by analyzing the acrylamide levels in
the influent and effluent of a sewage works receiving trade effluent containing
acrylamide. The authors noted that the works caused a 75% reduction in acrylamide;
the levels decreased from 1.1 mg/£ to 0.28 mg/£ (treatment period unknown). Since
acrylamide is very water soluble, significant loss due to adsorption on the
sludge seems unlikely. Therefore, the loss may have been largely due to micro-
bial degradation. In an aqueous medium (composition not given) inoculated with
58
-------
5 m£ of settled sewage effluent per liter, a breakdown of acrylamide was also
observed, but after a lag period. The degradation was more rapid in closed
vessels than in open vessels (Table 17), suggesting that anaerobic conditions
were preferred for biodegradation.
Table 17. The Degradation of Acrylamide by Sewage Effluent
(Croll et al., 1974)
Period of experiment
(days)
0
5
9
12
16
Co
Aeratec
1
0.06
0.06
0.08
0.05
n. d.
ncentration of .
vessels
2
0.17
0.14
0.17
0.08
n. d.
acrylamide (mg ]
Closed \
1
0.08
0.08
n.d.
n.d.
L"1)
vessels
2
0.
0.
n.
n.
n.d. = Not detected
Although the carbon in acrylamide appears to be utilized
fairly rapidly by stream and sewage microorganisms, it is unclear if nitrogen
in the molecule can serve as the nitrogen source for growth. Hynes and
Pateman (1970) have reported that acrylamide could not serve as the sole nitrogen
source for the growth of the fungus Aspergillus nidulans. This was attributed
to the inability of acrylamide to induce the synthesis of acetamidase, an en-
zyme involved in amide-N utilization. The conclusion was based on the finding
that a regulatory mutant of A. nidulans, producing acetamide constitutively,
was able to grow on acrylamide as the nitrogen source.
59
-------
In summary, the available information suggests that
acrylamide will biodegrade in the environment. Microorganisms can utilize
the carbon in acrylamide for growth, but the fate of nitrogen in the molecule
is unclear. The environmental fate of the derivatives of acrylamide has not
been studied, and their behavior and fate in the environment is uncertain.
b. Chemical Degradation
Information on the alteration of acrylamide and its deriv-
atives by chemical processes (e.g., hydrolysis, oxidation, photolysis) has
been reviewed in Section I-B-2 (p. 16). Unfortunately, no experimental data
are available on the nonbiological alteration of acrylamide and its derivatives
under environmental conditions.
Acrylamide and its derivatives and polyacrylamide are
relatively stable under oxidative conditions at ambient temperatures. Poly-
acrylamide may be subjected to some hydrolysis in aqueous solution. Some photo-
sensitized polymerization is possible for certain acrylamide derivatives in
aqueous solution. Overall, it appears that chemical and photochemical reactions
will be of some importance in the environmental fate of acrylamide and its deriv-
atives and polyacrylamide, although any major modification of the molecule as
a consequence of these chemical reactions seems unlikely.
2. Environmental Transport
No experimental data are available concerning the environmental
transport of acrylamide and its derivatives. Environmental movement of chemicals
generally takes place via processes such as adsorption of colloidal substances,
volatilization, codistillation, leaching, etc., and is governed by such properties
of the compound as solubility in water, volatility, adsorptivity, etc. Acrylamide
60
-------
and most of its derivatives are so water soluble that they will probably be
leached through soils and will also migrate through soil and eventually make
their way to ground water. In aquatic systems, these compounds will be expected
to be contained in the overlaying water, and very little, if any, should reside
in the sediment or suspended matter. Therefore, they will be transported with
flowing water.
The vapor pressure of a chemical determines to a great extent
the possibility of the compound vaporizing into the atmosphere. The low vapor
pressure of acrylamide (e.g., 0.007 mm Hg at 25°C) and its derivatives suggests
that evaporation should not be appreciable. Chemicals from aquatic systems can
be lost by codistillation with water, a phenomenon which is dependent upon the
water solubility and vapor pressure of the compound. The high water solubility
of acrylamide and its extremely low vapor pressure suggest that appreciable quanti-
ties will not be lost to the atmosphere from water. This is supported from the
calculated half-life for acrylamide (~ 400 years) in a square meter of water
(calculated according to the approach of Mackay and Leinonen, 1975). It should
be kept in mind, however, that the equation derived by Mackay and Leinonen (1975)
is applicable to low solubility contaminants where water evaporation rate is
not appreciably affected by the presence of the contaminant. The equation has
been applied with acrylamide even though it is extremely water soluble, only to
obtain the order of magnitude of the losses via codistillation.
In summary, although no experimental data on environmental trans-
port of acrylamide and its derivatives are available, on the basis of the physical
properties, it can be predicted that these chemicals will have a fairly high
61
-------
mobility in aqueous and soil environments. It is unlikely, however, that they
will enter and be distributed through the atmosphere to a significant extent.
This conclusion assumes that acrylamide compounds are stable enough in the en-
vironment to permit time for transport; the information on biodegradation suggests
that this may not be the case.
3. Bioaccumulation and Biomagnification
No experimental data could be found in the literature concerning
bioaccumulation and biomagnification potential of acrylamide and its derivatives.
Kenaga (1972) has suggested that some of the characteristics of a molecule which
will affect its bioaccumulation are solubility, partition coefficient, and po-
larity. In view of the fact that a large number of the acrylamide compounds are
extremely water soluble, it is unlikely that they will bioaccumulate in food chain
organisms in significant quantities. Furthermore, in the case of acrylamide, it
is expected that it will be fairly rapidly attacked by microorganisms in the
X
environment and, consequently, may not come in contact with food chain organisms
at appreciable concentrations.
Metcalf and Lu (1973) have found that the ecological magnifi-
cation of several chemicals (concentration in organisms/concentration in water)
in their model aquatic ecosystem follows a straight line relationship with water
solubility. Their data show that for a log of the water solubility (ppb) > 7,
the ecological magnification becomes insignificant. For acrylamide and all of
its derivatives for which water solubilities are known, the log of the water
solubility (ppb) is > 7 (e.g., log HO sol. (ppb) is 9.33 and 7.47 for acrylamide
/
and N,N-methylenebisacrylamide, respectively). On the basis of the information
summarized above, it can be suggested that acrylamide and its derivatives will
not biomagnify in the food chain.
62
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B. Biological Effects
Acrylamide exerts its primary biological effect on the nervous system.
Man, other mammals, and certain non-mammalian vertebrates seem to respond in
about the same way. In acute intoxication, the central nervous system is most
severely affected. The major signs of acute exposures include ataxia, weakness,
tremors, and convulsions. In subacute and chronic intoxication, both the central
and peripheral nervous systems are affected, with the clinical effects of the
peripheral nervous system damage being the most prominent. In such exposures,
tremors and convulsions are usually absent. The major features of prolonged
intoxication are ataxia and weakness, the latter first appearing distally in
the hindlimbs and later extending more proximally. In severe exposures,
weakness and paralysis of all four limbs may develop.
The acrylamide derivatives have been much less extensively studied
than acrylamide. These compounds appear to be considerably less toxic than
acrylamide, and only a few N-substituted acrylamides seem to have chronic
toxicological properties similar to those of acrylamide. Little information
is available on the acute toxicity of these compounds.
1. Toxicity and Clinical Studies in Man
a. Occupational Studies
Human intoxication from industrial exposure to acrylamide
has been recognized for over twenty years (Golz, 1955). Although the last pub-
lished report of human poisoning appeared in 1972 from France (Cavigneaux and
Cabasson, 1972), Spencer and Schaumburg (1974a) indicate that cases are still
appearing in the United States.
The general picture of acrylamide intoxication in man is
not dissimilar to that seen in laboratory mammals (see Section III-B-2, p. 85).
63
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The common signs of acrylamide poisoning in man are limb fatigue, unsteady
walking, general impairment of limbs, skin peeling on the hands, and excessive
sweating. In addition, eye irritation, sensory impairment, dizziness, slurred
speech, gastrointestinal disturbances, and muscle pain may develop. However,
evaluations of cases of industrial intoxication are complicated by the inability
to precisely define the degree of exposure. Thus, because many clinically docu-
mented cases may involve both acute and chronic exposures, the latency period
and nature of the symptoms vary markedly.
Six cases of acrylamide neuropathy have been reported from
England (Garland and Patterson, 1967). The common clinical characteristics and
some other relevant details from these exposures are summarized in Table 18.
Table 18. Main Signs and Symptoms of Occupational Acrylamide
Intoxication in Six Cases in England
(Garland and Patterson, 1967)
Age in years
Exposure in weeks
Hands peeling
Increased sweating of
feet and hands
Fatigue, lethargy, and
drowsiness
Muscle weakness
Muscle pain
Abnormal skin sensa-
tions
Sensory loss
Absent reflexes
Romberg's sign positive
Case 1
19
6
X
X
X
X
X
X
X
X
Case 2
23
12
X
X
X
X
X
X
X
Case 3
30
12
X
X
X
X
X
Case 4
56
8
X
X
X
X
X
X
X
X
Case 5
59
60
X
X
X
X
X
X
X
Case 6
57
4
X
X
X
X
X
X
X
64
-------
In that no cases of acrylamide intoxication were found in factories where
dermal contact was minimized, Garland and Patterson (1967) state that excessive
dermal contact rather than inhalation was the major route of exposure in these
cases. Muscular weakness and loss of reflexes are common to all of these ex-
posures and are also typical of subacute mammalian intoxication. Some degree
of sensory impairment is also common to all of the above occupational intoxica-
tions. In Case 4, sensory loss was so severe that the individual felt no pain
when his fingers were being burnt by a cigarette. Such severe sensory loss
is uncommon even in severe intoxication of other mammals, although sensory
nerve damage has been demonstrated in pathological and electrophysiological
findings. In Case 1, severe ataxia appeared without marked sensory impairment.
Cases 1, 4, and 6 also show signs of central nervous system
(CNS) effects common in acute mammalian intoxication. In Case 6, CNS involve-
ment is suggested by the presence of truncal ataxia. Case 1 had general body
tremors which are also associated primarily with acute intoxication. Both
Cases 1 and 4 exhibited slurring of speech, which might be indicative of
midbrain or cranial nerve damage. [As detailed in Section III-B-2-c, p. 78,
the midbrain may be a primary target of acrylamide in the acute poisoning of
mammals.] However, Case 4, which had both severe sensory loss and signs of
acute intoxication, also developed urinary incontinence during recovery similar
to that seen in chronically exposed mammals.
Because of the appearance of both peripheral and central
nervous system effects described above, Garland and Patterson (1967) postulated
that acrylamide caused both peripheral neuropathy and midbrain lesions in man. In
Japan, Fujita and coworkers (1960) proposed a similar dual effect based on the
symptoms found in ten cases of industrial exposure to acrylamide. More recently,
65
-------
Takahashi and coworkers (1971) have described 15 cases of neuropathy in Japan.
The major symptoms of these cases are similar to those described above and are
summarized in Table 19.
Table 19. Symptoms of Acrylamide Intoxication in Fifteen Cases of
Industrial Exposures from Japan
(Takahashi £t al. , 1971)
Duration
of Fatigue of Unsteadiness G.I. Hand
No. Age jiandling Numbness Lower Limbs of Walking Myalgia Dizziness Tiredness Upset Peeling
1 28
J 28
3 32
4 27
5 27
6 22
7 26
8 20
9 21
10 18
11 18
12 18
13 18
14 27
15 22
G.I. = gastro-intestinal
Again, both peripheral effects - numbness, lower limb fatigue, and muscular
pain -as well as probable CNS effects - unsteadiness of walking and dizziness -
are apparent.
The remaining clinical reports of acrylamide intoxication in
man are similar to those detailed above. Auld and Bedwell (1967) reported a
single case from Canada which primarily involved dermal exposure. Leg weakness
was noted seven weeks after exposure began. In subsequent weeks, a stumbling
gait had developed as well as weakness and impaired use of the hands. Only
after two and a half months did dermal symptoms develop. These included blue-
ness, coldness, and profuse sweating of the arms and legs which was attributed
66
-------
to sympathetic overactivity. Contact was discontinued by hospitalization after
14 weeks. Apparently, full recovery occurred after an additional 14 weeks.
The six cases described from France (Cavigneaux and Cabasson,
1972; Graveleau et^ al. , 1970; Morviller, 1969) also present no remarkable char-
acteristics. Cavigneaux and Cabasson O-972) emphasize that skin lesions do not
always serve as an early warning of acrylamide exposure. This is evident in the
report of Auld and Bedwell (1967), as well as in results shown in Tables 18 and 19.
Morviller (1969) indicated that acrylonitrile rather than acrylamide might be the
neuropathic agent in four cases where exposure to both chemicals occurred. How-
ever, Barnes (1970) has indicated that acrylonitrile is not neurotoxic to rats
(see Section III-B-2-d-iv, p. 111).
In all cases in which details are available, the neuropathic
effects of acrylamide in man are reversible when contact is discontinued. How-
ever, one individual who developed severe acrylamide neuropathy displayed imperfect
recovery with evidence of spastic ataxia and sensory loss suggestive of damage to
long ascending and descending spinal cord tracts (Schaumburg and Spencer, 1976).
b. Neurophysiology and Pathology of Occupational Exposures
Both Fullerton (1969) and Takahashi and coworkers (1971)
have described functional and structural changes in humans after occupational
intoxication with acrylamide. Fullerton (1969) examined three of the cases
described by Garland and Patterson (1967) [cases 1, 4, and 5 - see Table 18].
Both pathological and electrophysiological measurements conformed to detailed
data on acrylamide neuropathy in experimental mammals. Electrophysiological
measurements indicated that the distal portions of the nerves were more severely
affected than proximal portions and sensory fibers were more severely affected
than motor fibers. Fiber diameter distribution measurements indicated that
large diameter fibers are most susceptible to acrylamide intoxication (see
Figure 11).
67
-------
1000
800
600
400
. 200
E
? °
5 1000 - b
1
"- 800
600
400
200
0
Control
under 60 years
I.
I
C.H.
2 4 6 8 10 12 14 16
Fibre diameter (p.)
Figure 11. Histogram of Fiber Diameter. a=control histogram for eight sural
nerves calculated from data of 0'Sullivan and Swallow (1968);
b=acrylamide patient C.H.
Nearly identical patterns of nerve fiber damage have been noted in baboons
(Hopkins, 1970 - see Figure 16, p. 106). A general decrease in internodal length
relative to fiber diameter indicated that regeneration was occurring (see p. 107).
A marked dispersion of muscle response to nerve stimulation further indicated a
"dying back" neuropathy typical of chronic acrylamide exposure in other mammals.
Little effect was seen on nerve conduction velocity, although decreased conduc-
tion velocity is common in severely intoxicated mammals (Fullerton, 1969 and 1970).
Similar results have been noted by Takahashi and coworkers
(1971). While nerve conduction velocity remained normal in most patients, action
potentials of both median and tibial nerves were greatly reduced. In addition,
three of the fifteen patients had abnormal electroencephalograph (EEC) recordings
indicative of central nervous system involvement.
68
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c. Other Human Studies
Igisu and coworkers (1975) have described five cases of
central and peripheral nervous system intoxication which occurred in a family
using water from a well contaminated with 400 ppm acrylamide. All five in-
dividuals developed signs of neurological disturbance within one week after
acrylamide had been used in chemical grouting at a site 2.5 meters from the
family well. Early signs of intoxication were characteristic of CNS damage
and included severe truncal ataxia, mental confusion, and hallucinations.
After exposure was terminated, CNS effects markedly diminished within about
one week. However, after or during CNS recovery, signs of peripheral nervous
system intoxication - numbness of the limbs, absence of ankle jerks, or re-
duction of sensory conduction velocity of the sural nerve - developed in three
individuals. By four months after exposure, all individuals appeared normal.
Acrylamide derivatives have not been cited in published cases of human intoxica-
tion.
2. Effects on Non-Human Mammals
a. Absorption, Distribution, and Elimination
No information is available on the absorption kinetics of
acrylamide or acrylamide analogues. In that acrylamide is toxic to rats, mice,
dogs, cats, and guinea pigs by oral, dermal, or inhalational exposures (Hamblin,
1956; see also Section III-B-2-c, p. 78 and d, p. 85), absorption by these routes
may be presumed (Anon., 1969; Auld and Bedwell, 1967). Fassett (1963) states
that N,N-dimethylacrylamide, but not N-isopropylacrylamide, is readily absorbed
through the skin by guinea pigs. However, this statement is based on observations
of toxicological responses and not on actual monitoring of acrylamide absorption.
Once in the blood stream, levels of free acrylamide and
free N-methylolacrylamide decrease rapidly. This is illustrated in Figure 12,
69
-------
Time after dosing, hr.
Figure 12. Blood Concentrations of Acrylamide (•) and N-Methylolacrylamide
(o) After Intravenous Injections to Rats (Edwards, 1975a)
In this figure, the bars represent standard errors and the
number of rats is given in parentheses.
70
-------
which gives blood levels of free acrylamide and free N-methylolacrylamide in
rats after intravenous injections of 100 mg/kg acrylamide and 140 rag/kg N-
methylolacrylamide. The calculated blood half-lives for free acrylamide and
N-methylolacrylamide are 1.90 and 1.55 hours, respectively. By extrapolating
these curves back to zero time, dilution volumes approximate that of total body
water for both compounds in the unbound form.
Twenty-four hours after identical doses to rats, Hashimoto
and Aldridge (1970) demonstrated that most of the label from [l-ll*C] acrylamide
and [l-^C] methylolacrylamide is protein bound (see Table 20). Although the
labeled material was not identified, the available information summarized in
the following section suggests that extensive metabolism of these compounds to
carbon dioxide does not occur. Consequently, the distribution of labeled material
probably represents the parent compounds or slightly modified metabolites.
The patterns of binding and tissue distribution are similar
for both acrylamide and N-methylolacrylamide. Going from one to four days after
dosing, levels in all tissue except blood decline. During all periods measured,
blood contains the highest levels of labeled material, primarily bound to protein.
The increase of label in blood during the first four days after dosing suggests
that both of these compounds have a high affinity for blood cells. In vitro
studies consistent with this interpretation are summarized in Section III-B-7-b
(p. 124). After blood, the next highest levels of both compounds are found in
the liver and kidney. No extremely high affinity is apparent in nerve tissue.
However, Ando and Hashimoto (1972) have shown that the distal half of the sciatic
nerve accumulates 2.4 times as much ll+C-acrylamide as the proximal half and four
times as much as the brain. This distribution could be a factor in the more severe
pathological changes usually noted in the distal portions of nerve fiber in acryla-
mide intoxication (see Section III-B-2-d-ii, p. 103).
71
-------
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In addition to general tissue binding, Hashimoto and
Aldridge (1970) have also demonstrated that small amounts of label appear in
the DNA and RNA fractions of rat brain and liver twenty-four hours after intra-
venous administration of 100 mg/kg of acrylamide (see Table 21). However, because
the nucleic acid fractions were not pure, the significance of this low level of
activity is questionable. Based on the data in Table 20, 0.5-2.0% protein con-
tamination could account for the observed activity. Although the investigators
did not specify the levels of protein contamination, they state that the observed
activity indicates "an extremely low level of incorporation."
Table 21. [ll+Cj in Nucleic Acids Isolated from Rat Brain and Liver After a
Single Dose of {1-J1+CJ Acrylamide to Rats (Hashimoto and Aldridge,
1970)
nmoles/mg
Brain
RNA
DNA
RNA
0.0075
0.018
0.023
Liver /
DNA 0.016
The elimination of acrylamide after a single intravenous
injection (100 mg/kg) is initially rapid. As indicated in Figure 13, urinary
elimination is predominant with 40% excreted after one day, 60% after three days,
but very little additional urinary elimination between three and sixteen days
after dosing. The urinary metabolites were not identified. Expiration of
labeled C02 accounts for only about 6% of the total dose, with most appearing
73
-------
after the first eight hours. Spencer and Schaumburg (1974a) have summarized
unpublished reports indicating that rats excrete 40-65% of labeled acrylamide
after one day and 60-85% after 3-4 days. However, based on the information
in Figure 13, approximately 30% of the original dose is not excreted by rats by
two weeks after dosing (Hashimoto and Aldridge, 1970).
S
•8
•5
8
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S
Time, doy
-------
b. Metabolism
The metabolism of acrylamide has not been extensively in-
vestigated. The presence of 11+C02 after injections of [1-11+C] acrylamide,
accounting for 6% of the total dose after eight hours, clearly indicates that an
enzymatic apparatus for the degradation of acrylamide is present in rats (see
Figure 13, p. 74; Hashimoto and Aldridge, 1970). The rapid decrease in such deg-
radation after eight hours may be due to extensive binding of acrylamide to
various tissue components.
As indicated above, the nature of acrylamide urinary metab-
olites has not been determined. However, Edwards (1975a) has demonstrated that
both acrylamide and N-methylolacrylamide are conjugated with glutathione prior
to biliary elimination. Two to four hours after intraperitoneal injections of
acrylamide (100 mg/kg) or N-methylolacrylamide to rats, liver glutathione levels
are lowered to 36% of normal and remain depressed for twenty-four hours. Simi-
larly, Hashimoto and Aldridge (1970) have shown that acrylamide and N-methylol-
acrylamide decrease levels of nonprotein sulfhydryls in the brain, spinal cord,
and liver of rats. Thus, glutathione conjugation of acrylamide may be a detoxi-
cation reaction in nervous tissue. The reactivity of acrylamide and its analogues
with glutathione and other sulfhydryls is discussed in Section III-B-7-e (p. 124 ).
Because acrylamide analogs are apparently much less toxic
than acrylamide itself, the conversion of these analogs to acrylamide is a
potentially important metabolic reaction. However, Edwards (1974, 1975a) has
found little indication that such reactions occur to a significant extent. Less
than 9% of N-methylolacrylamide is converted to acrylamide in rats. No evidence
was found indicating that either N-methylacrylamide or N,N-diethylacrylamide is
converted to acrylamide (Edwards, 1974, 1975a).
75
-------
The mechanism for the predominant neurological effects of
acrylamide and various acrylamide analogues has not been determined. No enzymes
have been identified as targets of acrylamide activity. Oral doses of 0.3 - 3
mg/kg/day over a one year period do not affect blood cholinesterase activity
in cats (McCollister et al., 1964). Acrylamide given orally to rats at 400 PPm
for 20 days has no effect on oxygen consumption of brain slices (Hashimoto and
Aldridge, 1970). As indicated in Section III-B-7 (p. 123), acrylamide does not
seem to interfere with mitochondrial activities including oxidative phosphorylation.
However, acrylamide has been shown to alter patterns of amino acid and nucleic
acid incorporation and may affect the axonal flow of proteins.
The effect of acrylamide on amino acid incorporation into
nervous tissue has been studied by Hashimoto and Ando (1973) and Asbury and co-
workers (1973). Rats fed acrylamide at 500 ppm for four weeks evidenced altered
incorporation patterns of both 11+C-lysine and 35S-methionine in spinal cord and
sciatic nerve tissue but not in brain cortex or liver (see Figure 14 for lysine
patterns).
a Spinal cord.lower
b Sciatic nerve
c Spinal cord.middle
d Spinal cord.upper
e Brain cortex
f Liver
c 100
Acrylomids 500 ppm
Time, week
Figure 14 [luC]Lysine Incorporation Into Tissue Proteins of Rats Dosed
with Acrylamide for 4 Weeks Expressed as Per Cent of Controls
at Various Times (Hashimoto and Ando, 1973) (Reprinted with
permission from Pergamon Press Inc.)
76
-------
In spinal cord tissue, both lysine and methionine incorporation remained normal
during the first three weeks of exposure. Between four and six weeks after initial
exposure, incorporation of both amino acids increased to nearly 100% above normal,
but by the eigth week (fourth week of recovery), the incorporation had a tendency
to return to normal. The lower portions of the spinal cord showed the greater
increase for both amino acids. In the sciatic nerve, methionine incorporation
followed the same pattern, remaining normal for the first three weeks and then in
creasing by about 80% in the sixth week. The pattern for lysine was similar except
that incorporation during the first three weeks of exposure was depressed to about
80% of control levels (see Figure 14). Autoradiographic studies indicated that in-
creased lysine incorporation occurred primarily in the anterior horn cells of
the spinal cord and the Schwann cells of the sciatic nerve. Clinically, mild
signs of intoxication (hind limb weakness) appeared after two weeks, paralysis
after four weeks, and recovery from paralysis by five to six weeks. Consequently,
the above patterns of amino acid incorporation were attributed to regeneration
of damaged nerve tissue (Hashimoto and Ando, 1973). In mice given 250 ppm in
water, Asbury and coworkers (1973) noted a 40% decrease in the incorporation
3
of H -leucine into the perikarya of the anterior horn cells of the lumbar spinal
cord. This decrease initially occurred seven days after the beginning of ex-
posure, preceding the onset of clinical and pathological signs by one week. No
attempt was made to monitor amino acid incorporation during recovery.
Increased nucleic acid incorporation has also been noted
in the sciatic nerve of animals during acrylamide intoxication. In mice given
3
acrylamide at 250 ppm for 4,5 days, increased H-thymidine incorporation into
the Schwann cells along the sciatic nerve coincided with the onset of clinical
77
-------
symptoms after about 23 days. Labeling peaked after 30 days and fell rapidly
after acrylamide exposure was terminated. The labeling patterns observed cor-
related better with the duration of acrylamide exposure than with the degree of
histological damage. In rats given acrylamide orally for two weeks [dose not
3
specified] , an increase in H-uridine was also noted along the sciatic nerve
(Ando and Hashimoto, 1971).
An impairment of anterograde axonal transport of materials
(axonal flow) has been suggested as a possible mechanism for the neuropathic
effects of acrylamide. Pleasure and coworkers (Pleasure et^ £LL. , 1969; Pleasure
3
and Engel, 1970) used the movement of H-leucine along the axons to measure
slow axonal flow (1-2 mm/day). In most cats showing clinical signs of acrylamide
intoxication after daily doses of 20 mg/kg, axonal flow in both the dorsal (sensory)
and ventral (motor) root ganglia was greatly suppressed. Consistent with toxico-
logical data (see Section III-B-2-d, p. 105 ), sensory flow seemed somewhat more
affected than motor flow. However, in two cats with acrylamide intoxication, no
depression of axonal flow was seen. Bradley and Williams (1973) measured both
slow and fast (several hundred mm/day) axonal flow in acrylamide-intoxicated cats
and found no evidence of diminished slow waves. The crest but not the fronts
of fast waves was reduced. Because the degree of histological damage did not
correspond to the magnitude of flow reduction, Bradley and Williams (1973) con-
cluded that impairment of axonal flow is not a major factor in the development
of acrylamide neuropathy.
c. Acute Toxicity
(i) Acrylamide
Studies on the acute toxicity of acrylamide to various
mammals are summarized in Table 22. McCollister and coworkers (1964) have estimated
78
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the oral LD for rats, guinea pigs, and rabbits at 150-180 mg/kg. This estimate
is similar to the observed oral LD 's for rats (203 mg/kg; Fullerton and Barnes,
1966) and mice (170 mg/kg; Hamblin, 1956). Although information on other routes
of exposure for these mammals is sparse, the intraperitoneal LD of 120 mg/kg
for rats (Druckrey £t^ al. , 1953) indicates that this route may be somewhat more
toxic than oral administration. Conversely, dermal exposure was fatal to a
rabbit at about four times the oral lethal dose (McCollister e_t _al., 1964). While
LD estimates are not available for cats or monkeys, the data summarized in
Table 22 suggest a lethal range similar to that of the other mammals tested. In
most fatal exposures, death occurs 1-3 days after dosing. Hamblin (1956) states
that mice experienced delayed death but does not specify the period of delay.
The signs of acrylamide intoxication show marked simi-
larity. At oral doses below the lethal range, neurotoxicity is relatively mild.
Fullerton and Barnes (1966) noted only fine tremors in rats at 100 mg/kg. At
126 mg/kg, McCollister and coworkers (1964) noted lethargy, a slight weight loss,
but no tremors in rats; only a very slight weight loss in guinea pigs; and tremors
as well as pupil dilation in rabbits. Cats given intraperitoneal injections of
50 mg/kg/day for 2 days exhibited both tremors and ataxia (Kuperman, 1958).
Sussman et^ ai_. (unpublished) noted loss of functional activity of mesenteric
pacinian corpuscles, a type of peripheral sensory receptor, after 1-2 days in
cats receiving only 10-20 mg/kg of acrylamide subcutaneously.
At higher doses approximating the LD , the primary
signs of acrylamide intoxication are characteristic of central nervous system
stimulation. Kuperman (1958) outlines the general sequence of responses in cats
given intraperitoneal injections of acrylamide at 75-1000 mg/kg: ataxia, tremors,
weakness, vomiting, defecation, mass sympathetic stimulation, behavioral changes
suggestive of hallucinations, and periodic clonic-tonic convulsions prior to death.
80
-------
Ataxia, labored respiration, and convulsions have also been noted in fatally ex--
posed mice (Hamblin, 1956) and rats (Druckrey jat al., 1953). In addition, Druckrey
and coworkers (1953) noted behavioral changes in rats which were described as
resembling fright or excitement. A rather atypical response has been observed
in one monkey given intraperitoneal injections of 100 mg/kg acrylamide on two
successive days. Prior to death, at one day after the last injection, the animal
had no sense of balance but was able to use its muscles for crawling. No con-
vulsions were noted (McCollister &t_ al. , 1964). The direct cause of death, at
least in the lower mammals, has been attributed to respiratory failure associated
with laryngeal spasm and obstruction (Riker, 1954) or acute pulmonary obstruction
(Druckrey et_ al. , 1953).
The time course of acute acrylamide exposure is charac-
terized by a minimum latent period between dosing and the onset of adverse effects
as well as apparent complete recovery in animals surviving even severe intoxica-
tion. Kuperman (1958) noted an inverse relationship between the magnitude of
the dose and the length of the latent period. In cats given intravenous injec-
tions of acrylamide, the doses and respective latent periods were as follows:
75 mg/kg, 7-12 hours; 1000 mg/kg, 1 hour; and 5,000 mg/kg, 15 minutes. Recovery
from acrylamide intoxication has been described by several investigators. Rats
which survive doses near the LD show fine tremors but recover completely after
about two days (Fullerton and Barnes, 1966). Hamblin (1956), while not specifying
the period to complete recovery, notes that rats surviving doses above the LD
experienced peripheral motor weakness. A cat receiving a single intraperitoneal
injection of 100 mg/kg acrylamide exhibited severe symptoms after 24 hours but
survived, having only slight unstableness after two weeks (McCollister et al.,
81
-------
1964). At the same dose [route not specified], Spencer and Schaumburg (1974b)
report that cats recover completely two days after dosing.
The histopathological effects of acrylamide poisoning
in a monkey receiving intraperitoneal injections of 100 mg/kg on two consecutive
days included congestion of the lungs, congestion of the kidneys with degener-
ation of the convoluted tubular epithelium and glomeruli, as well as necrosis
and fatty degeneration of the liver. The brain and spinal cord of cats receiving
100 mg/kg acrylamide intraperitoneally were normal (McCollister et_ _al. , 1964).
Similarly, in rats receiving doses of acrylamide near the LD , no macroscopic
lesions were found in the peripheral nerves, although fine fatty infiltration
of the liver was noted. This latter effect is not seen in chronic poisoning
(Fullerton and Barnes, 1966). Druckrey and coworkers (1953) note that fatal
acrylamide intoxication resulted in abnormally rapid carcass rigidity which per-
sisted for about as long as normal rigor mortis.
The mechanism of acute acrylamide intoxication has
received relatively little attention. Kuperman (1958) has performed various
surgical procedures on the central nervous system of cats in an attempt to define
acrylamide's site of action. Doses of 500 mg/kg to decerebellate and decorticate
cats induced ataxia, tremors, sympathetic nervous system stimulation, and con-
vulsions typical of the response of surgically unaltered cats. Supracollicular
decerebrate cats (brain stem intact), at doses of 400-700 mg/kg acrylamide, also
experienced moderate convulsions but no signs of sympathetic stimulation. At
the same dose levels, infracollicular decerebrate cats (brain stem transected)
showed only brief periods of abrupt muscular contraction (myoclonus). Spinal
(T-12 or L-l) cats, at doses of 500 mg/kg acrylamide, evidenced only spasmodic
movements of the knee (patellar clonus). Electroencephalographs of intact cats
82
-------
revealed that acrylamide-induced convulsions were associated with sustained
high-voltage and hypersynchronous electrocortical activity. Generally, EEC
seizure patterns in decerebrate cats were less prolonged and lacked high-voltage
hypersynchrony. Thus, typical acrylamide convulsions and severe EEC seizures
require an intact brain stem (Kuperman, 1958).
Apart from its neurotoxic effects, acrylamide has been
tested for both skin and eye irritation. A 10% aqueous solution applied repeatedlv
to rabbits elicited no response in intact skin, and only transient erythema and
edema in abraded skin. A 10% aqueous solution applied to the eyes of rabbits
produced slight pain and conjunctival irritation, with complete recovery after
24 hours. A 40% solution applied to the eye without washing produced conjunc-
tival irritation and significant corneal injury. Complete recovery from corneal
damage occurred after 24 hours, while conjunctival damage healed slowly (McCollister
et_ al. , 1964) .
(ii) Substituted Acrylamides
All of the acrylamides thus far examined are less toxic
in acute exposures than acrylamide itself. Table 23 summarizes the available
information on the acute toxicity of substituted acrylamides. For the most part,
these studies were conducted to approximate dose levels for subacute or chronic
neurotoxicity, and thus, few details are available on the acute responses. Lethal
doses of both methacrylamide and N-methylolmethacrylamide cause damage to the
central nervous system of rats, rabbits, and mice (Strizhak, 1967). In addition,
methacrylamide applied to rabbit skin - 1 g moist solid over 12 sq. cm. for 4 hours -
resulted in minor primary irritation (Rohm and Haas, 1955). Oral doses of N,N-
dimethylacrylamide caused secretions around the mouth and eyes as well as convulsions
83
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in rats. Dermal applications of 0.5 mH/kg were lethal to guinea pigs. Diacetone
acrylamide is also reported to be nonirritating to the eyes and skin (experimental
animal not specified) (Lubrizol Corp., no date a, b). Further details on the acute
toxicity of these compounds are not available.
Based on the rather limited data presented in Table 23,
no clear pattern is evident in the acute toxicity of the substituted acrylamides.
a-Methyl substitution of acrylamide to form methacrylamide results in markedly
decreased toxicity. As in oral acrylamide exposures, mice seem more susceptible
than rats to methacrylamide, with the difference in susceptibility apparently
enhanced by the a-methyl group. However, a-methyl substitution seems to have no
apparent effect on the acute toxicity of N-methylolacrylamide as compared to N-
methylolmethacrylamide. While most of the N-substituted acrylamides are far
less toxic than acrylamide, N,N'-methylenebisacrylamide is about equitoxic with
acrylamide on a molar basis. In that N,N'-methylenebisacrylamide does not cause
peripheral neuropathy on chronic exposure (see Section III-B-2-d-iv, p.116), its
high toxicity relative to other N-alkyl acrylamides is probably not attributable
to metabolic acrylamide formation.
d. Subacute and Chronic Toxicity
Unlike acute exposures which primarily affect the central nervous
system, repeated exposures to acrylamide and a few acrylamide derivatives damage
the peripheral as well as the central nervous system. While the nature of peri-
pheral nerve damage has been well characterized, the full extent and locus of central
nervous system damage are unclear. Typically, neurotoxic exposures initially
cause bilateral weakness, which appears first in the hind limbs and may progress to the
85
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fore limbs. In more severe exposures, the clinical picture may include ataxia,
paralysis of all four limbs, and other signs of neurological disturbance, as well as
secondary toxic effects such as weight loss. These clinical signs are accompanied
by concurrent degeneration of vulnerable peripheral and central nerve fiber path-
ways. Degeneration characteristically commences in the distal regions and slowly
ascends the affected nerve fibers, sparing the nerve cell bodies. Consequently,
this pathological process is often referred to as the "dying-back process" or
"dying-back polyneuropathy" (Cavanagh, 1964). Spencer and Schaumburg (1976, 1977)
use the term "central-peripheral distal axonopathy" to emphasize the concurrent
central and peripheral nervous system damage to the distal axons in chronic acryla-
mide intoxication. Electrophysiologically, decreased neural conduction velocity
and amplitude also accompany gross signs of acrylamide neurotoxicity. Acrylamide
neuropathy has recently been reviewed by Spencer and Schaumburg (1974a and b, 1975).
Along with acrylamide, other chemicals which produce similar
peripheral neurological disturbances and central-peripheral distal axonopathy
include: triorthocresyl phosphate, some alkyl phosphates, lead, arsenic, methyl
mercury salts, thallium, certain organophosphates, isoniazid, nitrofurantoin,
trichloroethylene, tetrachloroethane, methyl n-butyl ketone, and 2,5-hexanedione
(Cavanagh, 1964, 1973; McLeod, 1971; Thomas, 1970; Barnes, 1969a and b; Spencer
and Schaumburg, 1976). In addition, peripheral neuropathies are also associated
with hypoglycemia, uremia, porphyria, deficiences of either vitamin B.. „ or thiamine,
and rheumatoid arthritis (McLeod, 1971; Dyck et^ a±. , 1975).
(i) Acrylamide - Gross Toxic Effects and Dose-Response
Relationships
General Characteristics
Repeated doses of acrylamide have been shown to induce
neurotoxic signs in mice, rats, guinea pigs, cats, dogs, baboons, and monkeys.
Some acrylamide exposures producing early signs of acrylamide neuropathy in rats,
cats, dogs, baboons, and monkeys are summarized in Table 24. Only continuous
86
-------
Table 24. Acrylamide Doses Producing Early Signs of Peripheral Neuropathy in
Various Mammals
Organism
Route
Dose, Schedule
Days to
Initial Effect
(Number Cumulative
of Doses) Dose (mg/kg)
Reference
RATS
(adult)
CATS
DOGS
PRIMATES
Oral
i.p.
i.p.
i.p.
Oral
i.p.
Oral
i.p.
Oral
i.p.
Oral
i.p.
Oral
i.p.
i.p.
s. c.
Oral
in chow
Oral
in water
i. v.
Oral
Oral
Oral
Oral
in fruit
Oral
in fruit
Oral
in fruit
Oral
in water
100 mg/kg, 2 doses /week
100 mg/kg, 1 dose/week
100 mg/kg, 1 dose/2 weeks
75 mg/kg, 1 dose/day
50 mg/kg, 3 doses /week
50 mg/kg, 1 dose/day *
*
40 mg/kg/day
40 mg/kg, 1 dose/day
*
30 mg/kg/day
30 mg/kg, 1 dose/day
25 mg/kg, 5 doses /week
25 mg/kg, 1 dose /day
*
9 mg/kg/day
50 mg/kg, 1 dose/day
20 mg/kg, 1 dose/day
20 mg/kg, 1 dose/day
10 mg/kg, 1 dose/day
10 mg/kg, 1 dose/day
3 mg/kg, 5 doses/week
3 mg/kg, 1 dose/day
1 mg/kg, 5 doses /week
15 mg/kg, 1 dose/day
10 rag/kg, 1 dose/day
5 mg/kg, 1 dose/day
20 mg/kg, 1 dose/day
15 mg/kg, 1 dose/day
10 mg/kg, 1 dose /day
10 mg/kg, 49 doses /69 days
21(6)
42(6)
210(15)
4.6
-18(7-8)
6.4
14
6.7
21
10.7
28(20)
16.8
+
56
2(2)
14-21
5
13-16
17-22
68
70+163
-180
2l"
28-35*
21*
16
42
56-97
48
600
600
1500
345
350-400
320
560
268
630
321
500
420
504
100
280-420
100
130-160
170-220
144
210+489
-130
315
280-350
105
320
630
560-970
-340
Fullerton and Barnes,
1966
Kaplan and Murphy, 1972
Suzuki and Pfaff, 1973
Kaplan and Murphy, 1972
McCollister et al. ,
1964
Kaplan et al. , 1973
McCollister et al. ,
1964
Kaplan et al. , 1973
Fullerton and Barnes,
1966
Kaplan and Murphy, 1972
McCollister et al. ,
1964
Kuperman, 1958
Leswing and Ribelin,
1969
Schaumburg ejt al. , 1974
Schaumburg et al. , 1974
Prineas, 1969
McCollister et al. ,
1964
Schaumburg et al. , 1974
Hamblin, 1956
Thomann e_t al. , 1974
Hamblin, 1956
Thomann et al. , 1974
Hopkins, 1970
Hopkins, 1970
Hopkins, 1970
McCollister et al. ,
1964
Acrylamide mixed with food. Dose in mg/kg estimated by McCollister and coworkers, 1964.
Effect noted in only 1/20 exposed animals.
Signs of intoxication probably appeared earlier than noted. See text, p. 96.
Signs of intoxication based on electrorod measurements. See text, p. 89.
87
-------
feeding exposures are available on mice. These are discussed below. Information
on acrylamide-induced neuropathy in guinea pigs is unpublished and has not been
available for this review (see Spencer and Schaumburg, 1974b).
In early studies on acrylamide neuropathy, Kuperman
(1957, 1958) noted that the gross toxic effects of acrylamide are related directJy
to the cumulative dose and are independent of the magnitude of the daily dose.
This pattern will be referred to as Kuperman's generalization and is illustrated
in Table 25.
Table 25. Development of Ataxia After Repeated Intraperitoneal Injections of
Acrylamide to Cats (Kuperman, 1958)
Daily Dose
mg/kg
1
2
5
10
15
25
40
50
No. Cats
5
7
3
8
5
11
6
3
*
Cumulative Dose
mg/kg
101 + 30
132 + 24
78 + 5
126 + 29
102 + 10
102 + 20
73 + 21
100 + 0
Time
days
125 + 26
91 + 18
22+3
19 + 6
9+11
6+2
3+1
2 + 0
*
Mean + per cent S.D.
Kuperman (1958) demonstrated that the onset of ataxia occurred after a mean dose
of 102 mg/kg, and deviations from this mean approximated a normal distribution.
As indicated in Table 24, subsequent exposures tend to support this relationship
if dose schedules are comparable and the total exposure period is not protracted.
However, as periods between dosing increase with subsequent increases in exposure
88
-------
periods, the relationship of toxic effect to total cumulative dose becomes less
substantial. The results of Fullerton and Barnes (1966), summarized at the top
of Table 24, show that rats tolerated 2.5 times the cumulative dose of acryla-
tride (as 100 mg/kg/dose) when administered once every 14 days as opposed to
closings once weekly or twice weekly. This apparent deviation from Kuperman's
generalization, however, was attributed to the increased sensitivity of the
older rats on the one dose/14 days schedule, rather than to an unusually delayed
cumulative effect (see p. 99).
Kuperman (1957, 1958) also stated that the route of
administration affects neither the dose required to produce a given effect nor
the latent period of the effect. Based on the exposures summarized in Table 24
as well as the more detailed dose response data presented below, this generali-
zation is also substantially correct. The apparent decreased cumulative dose,
with intraperitoneal as opposed to oral administration, necessary to cause initial
effects in rats at doses of 25, 30, and 40 mg/kg is an artifact of the technique
used to determine the onset of effects. Fullerton and Barnes (1966) and McCollister
and coworkers (1964), using oral administration, defined the onset of neurological
effects as observable hind limb weakness. In the intraperitoneal exposures, how-
ever, Kaplan and coworkers (Kaplan and Murphy, 1972; Kaplan et aJL , 1973) used an
electrorod to determine the onset of effects. This device measures the ability
of a rat to maintain balance on a horizontal wooden rod while the rod is being
rotated along the horizontal axis. In that the electrorod technique may be a
more sensitive index of early neurological damage, the cumulative doses necessary
to cause initial effects when measured by this technique should be lower than
89
-------
cumulative doses causing signs of hind limb weakness (Kaplan and Murphy, 1972;
Kaplan et al., 1973). Thus, Kuperman's generalization that the cumulative dose
is the overriding factor in the development of early signs of neurotoxicity in
repeated exposures to acrylamide over periods of a few days to a few months seems
valid. Exceptions to this generalization, involving prolonged exposures to sub-
neurotoxic levels of acrylamide, are discussed at the end of this section (see
p. 105).
Given Kuperman's generalization, Table 24 indicates
that cats are more susceptible to acrylamide neuropathy than rats or primates.
In most exposures, cats develop early signs of neuropathy after cumulative doses
of 100-300 mg/kg acrylamide. For primates and rats, 300-600 mg/kg acrylamide
is required to produce comparable effects. The cumulative doses (105-350 mg/kg)
described for dogs in Table 24 resulted in a complex of clinical signs (Hamblin,
1956; Thomann et^ ji]L., 1974; see also below, p. 96), indicating that initial effects
e.g., simple ataxia or hind limb weakness - appeared at lower cumulative dose
levels. This suggests that dogs are at least as sensitive as cats. As indicated
previously, comparable repeated dose data are not available for mice. In con-
tinuous feeding studies, acrylamide at 250 ppm in water caused clinical signs
including hind limb scissoring in mice after 14-21 days (Asbury et al., 1973;
Bradley and Asbury, 1970). Comparable exposures of rats to 300 ppm acrylamide
resulted in hind limb weakness after 20-28 days (Hamblin, 1956; Hopkins and
Lambert, 1972; McCollister ejt _al. , 1964; Tsujihata e_t _al. , 1974). This suggests
that mice may be somewhat more susceptible than rats to acrylamide in continuous
feeding exposures. However, because mice generally tend to consume more food
per unit body weight than rats (e.g., Hoeltge Inc., 1973), the total cumulative
90
-------
doses required to produce clinical signs in these two mammals probably do not
differ markedly. Therefore, based on the available data, the susceptibility of
mammals to acrylamide neuropathy seems to be: cats - dogs > mice - rats and
primates. However, given the variability evident in Table 24, this order should
be seen only as a general trend. The actual differences in susceptibility between
these groups of mammals are not substantial, and exceptions are readily apparent.
For instance, at oral doses of 20 mg/kg/day, cats developed early signs of neuro-
pathy after 14-21 days [280-420 mg/kg] (Leswing and Ribelin, 1969). On the same
dose schedule, Hopkins (1970) noted hind limb weakness in a baboon after 16 days
[320 mg/kg].
Clinical Signs of Intoxication
The gross signs of acrylamide intoxication have been
most extensively described for rats. While hind limb weakness is most often
cited as the first sign of repeated acrylamide exposure, growth inhibition and/
or proprioceptive impairment may precede or coincide with the onset of hind
limb debility. In rats given intraperitoneal injections of 50 mg/kg/day, slight
weight loss was noted after 2-4 days. The weight of the exposed animals remained
about 10% below control animals throughout the exposure period. During the
fourth through sixth days of exposure, decreased proprioception was indicated
by progressively increasing failures on the electrorod apparatus. Actual signs
of ataxia were not evident until the seventh day of exposure [350 mg cumulative
dose] (Kaplan and Murphy, 1972). Using the same route and dose schedule, Suzuki
and Pfaff (1973) noted that both decreased weight gain and slight hind limb
weakness appeared after five injections to young rats. On oral administration,
only growth retardation was seen at 100 ppm for 42 days while both growth re-
tardation and hind limb weakness appeared at 300 ppm for 28 days (Hamblin, 1956).
91
-------
Loss of proprioception appeared concurrently with hind limb weakness after oral
administrations of 9 mg/kg/day for 90 days and 30 mg/kg/day for 21 days. Response
to painful stimuli, however, was not impaired (McCollister et_ al_. , 1964). As
exposure proceeds, hind limb weakness becomes progressively more severe. On oral
exposures of 200-300 ppm over periods of 5-27 weeks, ataxia, hind limb splay,
dragging of hind limbs while attempting to walk, and flaccid hind limb weakness
develop (Tsujihata et^ _al. , 1974; Morgan-Hughes e_t al. , 1974). More severe ex-
posures are generally fatal to at least some animals. At concentrations of 300-
400 ppm over 24-42 weeks, most rats died after developing complete loss of hind-
quarter control. Extreme protrusion of the penis was also noted in male rats
(McCollister et al., 1964). Fore limb weakness has appeared in some rats after
the development of hind limb paralysis (Hamblin, 1956; Suzuki and Pfaff, 1973;
Tsujihata ejt _aJL. , 1974). In addition to severe weakness of the extremities, pro-
longed acrylamide intoxication commonly involves gross distention of the bladder
(Fullerton and Barnes, 1966; McCollister e^t al., 1964; Suzuki and Pfaff, 1973)
and reduced weight gain (Hamblin, 1956; Tsujihata et^ al.. , 1974). In severely
poisoned male rats, degeneration of the testicular tubules has also been noted
(McCollister et^jil. , 1974).
A summary of these effects showing approximate dose-
response relationships is given in Table 26. Given the variety of dosing
schedules, routes of administration, and different experimental techniques used
in these studies, the results are remarkably consistent. Growth retardation
and proprioceptive impairments are evident after cumulative doses of 100-200 mg.
Observable signs of hind limb weakness appear in rats after cumulative doses of
250-630 mg. At approximately twice this dose (600-12600 mg), signs of severe
92
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intoxication are elicited. Where comparable dose schedules are used [e.g., 30 mg/
kg/day, McCollister et^ ai. , 1956; 50 mg/kg/day, Kaplan and Murphy, 1972, and
Fullerton and Barnes, 1966], the ratio of cumulative dose producing hind limb
weakness to lethal cumulative dose is 2:1. The only dose-response relationship
that markedly deviates from Kuperman's generalization is the 9 mg/kg/day for
90 days exposure reported by McCollister and coworkers (1964). As discussed
below (see p.101), this deviation probably is attributable to an increase in
the ability of animals to tolerate large cumulative doses of acrylamide when the
chemical is administered in small daily amounts over prolonged periods. [This
should not be confused with the increased susceptibility of animals due to age
when large doses are administered over extended periods with long intervals be-
tween doses - see p. 99].
Similar extensive dose-response data are not available
for the other mammals tested. However, the general progress of prolonged acryla-
mide intoxication in cats has been described in detail by a variety of investi-
gators. The description given by Kuperman (1958) encompasses most of the signs
noted by subsequent investigators. Hind limb weakness and ataxia followed by
dysmetria are early signs of intoxication. The usual sequence of major signs
in chronic intoxication is ataxia, hind limb weakness, dysmetria, progressive
weakness of the voluntary muscles, hind limb drag, inability to move about,
quadraparesis, and death (Hamblin, 1956; Prineas, 1969). While walking, cats
often exhibit fore limb crossing with truncal sway and wide based gait
(Schaumburg et^ _al., 1974). Kuperman (1958) described tremors of the head and
muscles which occurred when cats were stationary, as well as irregular tremors
in the limbs which occurred during movement. Head tremors have also been described
94
-------
by Schaumburg and coworkers (1974), and a slight (unspecified) effect on head
movements has been noted by Prineas (1969). Although hind limb drag can occur
during severe intoxication (Leswing and Ribelin, 1969) , proximal muscle strength
in the hind limbs is not markedly affected even during hind limb drag (Sumner and
Asbury, 1975). Foot drop, toe splay, and loss of tendon reflexes are also com-
monly noted in severe intoxication (Prineas, 1969; Schaumburg et a]L_., 1974; Sumner
and Asbury, 1975). Hoarse cries in advanced intoxication have been noted by both
Prineas (1969) and Leswing and Ribelin (1969), suggestive of involvement of the
laryngeal nerves [see p. 104 for pathological data]. As in rats, response to pain
is not impaired even during extreme intoxication (Pleasure et al., 1969; Prineas,
1969; Leswing and Ribelin, 1969). Only Prineas (1969) describes loss of weight
as well as fur loss in cats.
A summary of the available dose-response relationships
in cats is given in Table 27. As in the rat exposures, an approximate 2:1
relationship is apparent in the ratio of cumulative doses required to produce
mild as opposed to severe effects.
Table 27. Effects of Repeated Acrylamide Exposure
on Cats
Effect
Hud
Kind limb weakness or ataxia
Moderate - Severe
Moderate - severe hind limb ataxia
Gross incoordination of all limbs
Foot drop, lack of tendon reflexes, hoarse
voice, some loss oi weight and fur
Distal muscle weakness and foot drop
Fxtreme hind limb ataxia, moderate fore limb
ataxia
Lack of control in all limbs , unable to
stand
Decreased control of all limbs, barely able
to walk
Dose Schedule; , Route
see Table 24
20 mg/kg/day
10 mg/kg/day
20
3
10
10
10
3
10
10
10
3
10
10
10
20
x 14-21 days, , oral
x 21-34
mg/kg X 10-60 tlo-.es/U-42 days, oral
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
mg/kg/day
X 5 days/week x 68 days
x 5 day^/week x 26 days
x 17-22 days,, s.c.
X 13-15 days, l.p.
x 70 + 163 days
x 38-44 days, s.c.
x 24-36 days , s.c.
x 40 days
x 7 months
x 47-67 dav,
x 5 days/week h 52 days, oral
x 28 days
x 15 days
Cumulative
Dose (mg/kg)
102
280-420
210-340
200-600
144
200
170-220
130-150
210-489
380-440
240-360
400
-630
470-670
170
280
300
Reference
Kuperman, 1958
Leswing and Ribelin, 1969
Sumner and Asbury, 1975
Bradlev and Williams, 1973
McCollister et al.
Prineas, 1969
Si haumburg et al . ,
Sumner and Asbury ,
Prineas, 1969
Prineas, 1969
Schaumburg et al. ,
Sumner and Asbury ,
McCollistfr et al.
Schaumburg et al.,
, 1964
1974
1975
1974
1975
, 1964
1974
95
-------
Mice have seldom been used as experimental mammals in
acrylamide neuropathy. Based on the available information, the quantitative signs
of intoxication are similar to cats. When administered acrylamide in the drinking
water at 250 ppm for 25 days, all mice developed hind limb weakness which included
hind limb dragging in some animals. By 35 days, a hoarse squeak and some loss
of weight and fur were evident (Bradley and Asbury, 1970).
The clinical picture in dogs 'is somewhat less clear.
At oral doses of 10 mg/kg/day for 28-35 days, Hamblin (1956) noted hind limb
weakness, ataxia, and general signs of hindquarter incoordination. More recently,
however, oral doses of 5 mg/kg/day for 60 days have been shown to result in not
only ataxia and weakness of the jaw muscles but also sedation. At 15 mg/kg/day
for 22 days, normal hind limb effects were also accompanied by mydriasis, sali-
vation, hypnosis, labored respiration, and convulsions. Because the dogs in the
latter exposure group were shown to have suppurative lobular pneumonia, the above
atypical effects cannot be directly attributed to acrylamide (Thomann et al., 1974)
The effects of acrylamide poisoning in primates have
been studied using baboons (Hopkins, 1970; Hopkins and Gilliat, 1967; Hopkins and
Gilliat, 1971) and monkeys (Leswing and Ribelin, 1969; McCollister £t al. , 1964).
Generally, these mammals show signs of intoxication typical of the other mammals
studied. Initially, ataxia and weakness of the hindquarters appear. Subsequently,
weakness develops in the fore limbs and facial muscles (see Table 28). In addition,
both baboons and monkeys experience difficulty in holding food during advanced
intoxication (Leswing and Ribelin, 1969; Hopkins, 1970). Baboons show some signs
of sensory impairment in that they sometimes behaved as if they were unaware that
food had been dropped. However, they remained sensitive to pinprick. In addition,
96
-------
baboons lost 17-45% of body weight and tendon reflexes were abolished during
prolonged exposures (Hopkins, 1970). Leswing and Ribelin (1969) inferred man-
dibular nerve involvement in severely poisoned monkeys which were unable to chew.
Table 28 summarizes the dose-response information from
primate exposures. While the cumulative doses necessary to produce mild effects
in primates do not differ radically from those of rats, the ratio of severe to
mild cumulative doses is somewhat less in primates (-1.1 - 1.75).
Table 28. Effects of Repeated Acrylamide Exposure on Primates
Cumulative
Effect Dose Schedule, Route Dose (mg/kg) Reference
Mild
Hind limb weakness 20 mg/kg/day x 16 days, oral 320 Hopkins,, 1970
15 mg/kg/day x 42 days, oral 630 "
10 mg/kg/day x 56-97 days, oral 560-970 " "
10 mg/kg/day x 49 doses/69 days x -340 McCollister e_t_ al. , 1964
48 days, oral
Severe
Extreme hind limb 10 mg/kg/day x 49 doses/69 days x 490 McCollister e_t al. , 1964
weakness 69 days, oral
Severe hind limb 20 mg/kg/day x 28 days, oral 560 Hopkins, 1970
weakness with fore 15 mg/kg/day x 73 days, oral 1095 " "
limb weakness 10 mg/kg/day x 61-147 days, oral 610-1470 " "
In rats, mice, and cats, several investigators have
noted periods during exposure in which gross signs of toxicity did not increase
with increasing cumulative dose. In rats, Suzuki and Pfaff (1973) noted that
young rats on a dosing schedule of 50 mg/kg (i.p.) x 3 doses/week x 30 days
began to show recovery after 28 days in spite of continued injections. In
oral administrations of 300 ppm x 125 days [estimated total dose of 1890 mg],
rats developed severe hind limb weakness with moderate fore limb weakness after
56 days [840 mg]. Although several animals died after 56 days, the general signs
of neurotoxicity did not increase (Hopkins and Lambert, 1972). In similar
exposures to 250 ppm x 45 days to mice, Bradley and Asbury (1970) noted no
97
-------
increase in the severity of hind limb involvement after 35 days. Neither
frank fore limb weakness nor death were seen in the total exposure period. A
definite plateau response is also described by McCollister and coworkers (1964)
for two cats on oral doses of 3 mg/kg/day x 5 days/week x 367 days. After day
68 (144 mg/kg) , definite hind limb weakness had developed in both cats. How-
ever, by the end of the exposure period (cumulative dose of 771 mg/kg) , no
further decrease in hindquarter weakness was seen. The significance of these
observations is questionable. Nevertheless, they do suggest that the onset of
signs of severe acrylamide intoxication, unlike those of initial intoxication,
are not directly dependent on total cumulative dose.
Recovery
In all mammals tested, even severe acrylamide intoxi-
cation is apparently reversible. Recovery from gross signs of intoxication is
accompanied by the repair of structural damage and a return to normal nerve con-
duction velocity (see Sections ii, p. 103 and iii, p. 109 below). Table 29 partially
summarizes recovery data in mammals .
Table 29. Recovery Periods In Mammals After Severe Acrylamide Intoxication
*
Days to
Duration of Total Cumulative Recovery After
Organism Exposure (Days) Dose (mg/kg) Last Day of Dosing Reference
Rats
Cats
Dogs
Primates
- 21
- 38
~ 56
~ 63
- 24
- 42
- 63
-240
-392
52
22
29
69
94
600
700
800
800
960
1260
1300
2400
2800
370
330
380
490
1410
21
28
(21)
24
55
57
-60
-150
-180
53
30
63
54
364
Fullerton and Barnes , 1966
It M
M II
Suzuki and Pfaff, 1973
McCollister et al. , 1964
it ti
Suzuki and DePaul, 1971
Fullerton and Barnes , 1966
it it
McCollister et al. , 1964
Thomann et al. , 1974
Hopkins, 1970
McCollister et al. , 1964
Hopkins, 1970
Recovery defined as decrease or absence of clinical signs of
intoxication;
Parentheses ( ) indicate partial recovery
93
-------
The period to recovery, at least in rats, correlates closely with the total
cumulative dose rather than the period of dosing or magnitude of the daily dose
used. In rats, Kaplan and Murphy (1972) have associated recovery with increased
sciatic nerve g-glucuronidase activity. Rats given intraperitoneal injections of
50 mg/kg/day x 8 days exhibited decreased electrorod performance. After 30 days,
a 340% increase above control activity was noted for this enzyme, which coincided
with a return to normal electrorod performance. However, rats with elevated $-
glucuronidase activity were significantly more susceptible to reexposure. A
return to normal susceptibility required about 90 days, at which time g-glucur-
onidase activity was normal (Kaplan and Murphy, 1972).
Similar patterns are evident for other mammals, although
the relationship of recovery to enzyme levels has not been studied. In cats,
the period to recovery is directly related to the severity of intoxication. In
the 53 day recovery period summarized in Table 29, the cats were unable to stand
at the end of the exposure period (McCollister et al., 1964). In exposures in-
volving only moderate to severe hind limb weakness, 31-36 days were required for
complete recovery (Schaumburg et^ aL. , 1973). At the other extreme, cats kept
severely intoxicated for prolonged periods did not recover fully even after
several months (Leswing and Ribelin, 1969). The recovery data on primates in
Table 29 suggest that these mammals recover more slowly than rats, even though
primates and rats are about equally susceptible to acrylamide intoxication in
terms of the cumulative dose required to produce hind limb weakness.
Influence of Age and Sex
The influence of age in the development of acrylamide
neuropathy has been determined only in rats. For the most part, young animals
99
-------
are able to tolerate higher cumulative doses of acrylamide before signs of
neurological damage appear. At intraperitoneal doses of 100 mg/kg/week x 4
weeks, Fullerton and Barnes (1966) found that groups of rats 5 and 8 weeks old
developed mild symptoms, while 26 week old rats evidenced severe symptoms. Rats
52 weeks old were able to tolerate only three doses before the onset of severe
symptoms. Similar age-response effects have been noted by Kaplan and Murphy
(1972) in rats between 5 and 14 weeks old given intraperitoneal injections of
50 mg/kg/day. Table 30 summarizes this data with onset of effect and recovery
defined as failure and reestablishment of normal electrorod performance.
Table 30. The Effect of Age on the Onset of and Recovery from Acrylamide
Intoxication in Rats
(Data from Kaplan and Murphy, 1972)
Age of Rats* Onset of Effects Recovery Period
(Weeks) (Days + SE) (Days + SE)
5
7
11
14
7.3 + 0.22
6.4 + 0.22
5.5 + 0.20
5.3 + 0.19
19.2 + 0.40
15.6 + 0.50
13.8 + 0.66
14.8 + 0.48
* Doses of 50 mg/kg/day, intraperitoneal; groups of 12 rats used.
The 5 week old rats were significantly more resistant than 11 and 14 week old
rats to the onset of acrylamide intoxication (p < 0.01) but required a signifi-
cantly greater period to recover than any of the older rats (p < 0.01). This
increased recovery period in younger rats is probably attributable to the greater
cumulative dose required to produce overt signs of toxicity rather than to impaired
recovery processes in the younger animals. The increased ability of the younger
rats to tolerate higher cumulative doses may be related to increased liver
100
-------
microsomal enzyme levels (Kaplan and Murphy, 1972; Kaplan «rt ad., 1973). Only
one study has shown greater susceptibility in younger rats. Using one-day old
suckling rats, Suzuki and Pfaff (1973) noted the onset of adverse neurological
effects after 5-6 doses of 50 mg/kg x 3 doses/week. Adult rats on the same
dosing schedule evidenced initial signs of toxicity after 7-8 doses. These in-
vestigators attributed the increased susceptibility of very young rats to incom-
plete development of the barrier system of the peripheral nerves. The possibility
that decreased levels of liver drug-metabolizing enzymes in very young rats might
also be a factor in increased sensitivity was not explored. In any event, some
one-day old rats, but no adult rats, showed signs of recovery during the six
week exposure period. This would seem to suggest that the increased suscepti-
bility is limited to very young rats (Suzuki and Pfaff, 1973).
Although no detailed studies are available, Fullerton
and Barnes (1966) indicated that sex does not influence the response of rats to
chronic acrylamide intoxication.
No Apparent Adverse Effect Levels
Table 31 summarizes acrylamide exposures which have no
apparent adverse effects on mammals. At sufficiently low daily dose levels over
prolonged periods of administration, mammals are not adversely affected by cumu-
lative doses of acrylamide which are neurotoxic over shorter periods of adminis-
tration. This can be illustrated by comparing mildly toxic exposures (Table 24,
p. 87) to exposures producing no signs of toxicity (Table 31, p. 102). For rats,
cumulative doses of 1323-2079 mg/kg given orally over six-month periods caused
no signs of limb impairment. Less than this cumulative dose (560-630 mg/kg) given
101
-------
Table 31. Acrylamide Doses Producing No Signs of Adverse Effects
Duration of Cumulative
Exposure in Days Dose
(Number of Doses)
Reference
CATS
PRIMATES
dial
Oral
Oral
Oral
Oral
Oral
Oral
Oral
Oral
Oral
Oral
Oral
3 mg/kg/day
10 mg/kg/day
10 mg/kg/day
7 mg/kg/day*
11 mg/kg/day*
40 ppm
0. 3 mg/kg/day
1.0 mg/kg/day
1 mg/kg/day
5 mg/kg/day
8 mg/kg/day
1 mg/kg/day
3 mg/kg/day
90
70.. (55)
116 (116)
189
189
730
365 (-260)
367(257)
-133
- 35
- 28
363(255)
363(255)
270
550
1160
1323
2079
-2900
(see text)
-78
257
133
175
224
255
765
McCollister et al. , 1964
Fullerton and Barnes, 1966
" "
McCollister et al. , 1964
11
Dow Chemical, no date
McCollister et al. , 1964
Hamblin, 1956
tr M
McCollister et al . , 1964
Acrylamide mixed with food. Dose in rag/kg estimated by McCollister and coworkers, 1964.
Duration not specified. Minimum estimate of duration assumes 1 dose/day.
over periods of 2-3 weeks, however, resulted in obvious signs of hind limb weak-
ness (McCollister et_ &L. , 1964). A similar, though less marked, comparison can
be made for the results of Fullerton and Barnes (1966). Weil and McCollister
(1963) summarized a study by Dow Chemical (no date) indicating that 40 ppm acryl-
amide in food had no effect on rats over a two-year period. Based on the conver-
sion factors given by McCollister and coworkers (1964), this would be equivalent
to a daily dose of 4 mg/kg and a total cumulative dose of about 2900 mg/kg. This
is about six times the cumulative dose shown to have neurotoxic effects when ad-
ministered over a period of about one month. Based on the results of Hamblin
(1956) and McCollister and coworkers (1964) in Tables 24 and 31, similar re-
lationships between duration of exposure and the effects of comparable cumulative
doses are also apparent with cats, primates, and - to a lesser extent - dogs.
102
-------
(ii) Acrylamide - Structural Changes
Acrylamide intoxication is accompanied by various
morphological signs of nerve tissue deterioration. In the peripheral nerves,
axonal degeneration with demyelination has been observed in mice (Bradley and
Asbury, 1970), rats (Fullerton and Barnes, 1966; Suzuki and Pfaff, 1973), cats
(Leswing and Ribelin, 1969; Prineas, 1969; Schaumberg et^ al. , 1974), dogs
(Thomann et_ aL , 1974), baboons (Hopkins, 1970), and monkeys (Leswing and Ribelin,
1969). To date, axonal degeneration has been demonstrated only in myelinated
fibers. Schaumberg and coworkers (1974) have found no evidence of unmyelinated
axon degeneration in cats.
By light microscopy, the first sign of morphological
deterioration appears to be nodal or paranodal axonal swelling - i.e., swelling
at or near the nodes of Ranvier (Hopkins, 1970; Prineas, 1969; Schaumburg et al.,
1974; Spencer and Schaumburg, 1974b). Electronmicroscopic examinations have
characterized these swellings as masses of neurofilaments, various dense bodies,
and either enlarged or degenerating mitochondria (Prineas, 1969; Schaumburg et al.,
1974; Suzuki and Pfaff, 1973). After initial swelling, the myelin sheath retracts
paranodally along the axon. Subsequent to myelin retraction, actual axonal degen-
eration occurs and may be accompanied by myelin fragmentation (Hopkins, 1970;
Prineas, 1969; Schaumburg et_ ai., 1974). Extensive myelin breakdown, as opposed
to retraction, occurs only after axonal degeneration (Fullerton and Barnes, 1966).
This may in part account for the wide variety of myelin involvement - which may
range from severe (e.g., Bradley and Asbury, 1970; Leswing and Ribelin, 1969) to
minimal (e.g., Hopkins, 1970) - in animals with comparable clinical signs of
acrylamide intoxication.
103
-------
Damage to the peripheral nerves is invariably more
severe distally than proximally. Paralleling the clinical signs of intoxication,
hind limb nerves seem to be the most severely affected. In rats, nerve fiber
degeneration is first seen in the plantar sensory nerves of the hindfeet and
branches of the tibial nerves supplying the calf muscles (Spencer and Schaumburg,
1977). Fullerton and Barnes (1966) noted marked decreases in fiber density in
the sural and posterior tibial nerves in the species, but only a moderate de-
crease in density in the sciatic nerve. Similar patterns of increasing damage
progressing distally along the hind limb nerves have been noted in mice, cats,
dogs, and primates (Bradley and Asbury, 1970; Hopkins, 1970; Leswing and Ribelin,
1969; Prineas, 1969; Schaumburg et^ al. , 1974; Suzuki and Pfaff, 1973; Thomann e_t al. ,
1974). However, the extent of hind limb nerve damage may vary in different species
showing comparable signs of intoxication. In severely poisoned mice, Bradley and
Asbury (1970) noted myelin breakdown in over 50% of the fibers of the sciatic
nerve. In cats with equally severe clinical signs, only a minority of fibers in
the tibial nerve evidenced morphological damage (Prineas, 1969). Fore limb nerves
also undergo axonal degeneration, but generally to a lesser degree than the hind
limbs. In rats showing moderate to severe hind limb damage, axonal degeneration
was seen in the median and ulnar nerves of the fore limb. In only one rat did
the extent of median nerve damage approximate that seen in the sciatic nerve of
the thigh (Fullerton and Barnes, 1966). In both monkeys and cats, fore limb
nerve damage was consistently less severe than hind limb damage (Leswing and
Ribelin, 1969). In addition to nerve damage of the limbs, Hopkins (1970) noted
axonal degeneration of the recurrent laryngeal nerve. As with the limb nerves,
damage was more severe distally.
Although distal to proximal degradation is the overall
pattern of acrylamide neuropathy, both Hopkins (1970) and Prineas (1969) have
104
-------
noted that, in a given area along a single nerve trunk, damage to the various
nerve fibers may differ markedly. This implies that certain nerve fibers are
more susceptible than others. Consistent with these findings, Schaumburg and
coworkers (1974) have demonstrated that Pacinian corpuscles (sensory nerve ter-
minals) are somewhat more rapidly affected than distal primary sensory fibers of
muscle spindle. Further, both of these sensory terminals are affected much more
rapidly than neuromuscular junctions. However, neuromuscular junctions have been
shown to undergo marked degeneration in acrylamide poisoning (Prineas, 1969;
Tsujihata et al., 197A). This damage and consequent muscle denervation probably
account for the muscular atrophy noted in many instances of acrylamide intoxi-
cation (Fullerton and Barnes, 1966; Leswing and Ribelin, 1969; Prineas, 1969;
Morgan-Hughes and coworkers, 1974). The sensitivity of nerve fibers to acryl-
amide is somewhat dependent on fiber diameter, but the precise relationship of
diameter to sensitivity may be species specific. In the tibial nerves of normal
rats, Fullerton and Barnes (1966) noted a unimodal distribution of diameter with
the peak at 8-9 y and a range of 2-14 y. In severely poisoned rats, the 8-9 y
peak was eliminated suggesting that these medium-sized fibers are most severely
affected (see Figure 15). In baboons - which normally show a bimodal distribu-
tion with peaks at 3 y and 11 y and a minimum at 7 y - larger diameter fibers
(10-16 y) show the most pronounced dose-related decrease after acrylamide ex-
posure, while medium-sized fibers stay the same or increase (Hopkins, 1970) [see
Figure 16]. Although comparable data are not available for other species, Schaumburg
and coworkers (1974) have noted that large diameter fibers are affected first in
cats. Recent electrophysiological studies in dogs (see next section) also suggest
that large fiber diameter axons are the most rapidly affected (Sumner and Asbury,
1975).
105
-------
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Figure 15. Histograms Showing Distribution
of Diameters of All Myelinated Fibers in
Posterior Tibial Nerves of Animals on the
Following Diets: (a) and (b) healthy adult
rats; (c) 400 ppm acrylamide for two months;
(d) 300 ppm acrylamide for four months; (e)
200 ppm acrylamide for six months; (f) 300
ppm acrylamide for four months, followed by
normal diet for six months.
(Fullerton and Barnes, 1966)
Figure 16. Histograms Showing Distri-
bution of Diameters of Myelinated Fibers
in the Sural Nerves (Ankle) of One Centre
Baboon (Bab. 26) and Three Baboons Intox:
cated with Oral Doses of Acrylamide as
Follows: Bab. 23, 10 mg/kg/day x 89 days
19 days recovery; Bab. 19, 10 mg/kg/day 3
137 days +17 days recovery; Bab. 25,
10 mg/kg/day x 10 days.
(Hopkins, 1970)
106
-------
Recovery from acrylamide intoxication is followed by
peripheral nerve tissue regeneration. Such regeneration has also been reported
to accompany intoxication (Suzuki and Pfaff, 1973). Increases in the number of
small diameter fibers, as well as a general decrease in internodal length (distance
between adjacent nodes of Ranvier) for fibers of a given diameter, have been used
as indices of regeneration (see Fullerton et_ al^. , 1965). Rats, fed 300 ppm
acrylamide for four months and allowed to recover for six months, no longer evi-
denced clinical signs of adverse effects. As previously discussed, this exposure
caused an elimination of the normal 8-9 u peak in nerve fiber diameter. After
the recovery period, this peak was still absent, but a large peak appeared in
the 3-4 u diameter range. Further, a marked decrease in internodal length was
apparent in fibers of 4-8 y (Fullerton and Barnes, 1966, see Figure 17).
1-4
12
1-0
e
e
f 08
% 0-6
0
c
-------
Similar patterns have been noted in baboons allowed to recover for a few months
after severe intoxication. After two years, fiber density returned to normal,
but fiber diameter was only two-thirds of preexposure values (Hopkins, 1970).
Several investigators have found no, or very little,
indication of central nervous system damage from subacute or chronic acrylamide
intoxication (Bradley and Asbury, 1970; Hamblin, 1956; Leswing and Ribelin, 1969;
McCollister et^ _al. , 1964; Thomann et^ ai. , 1974). However, Prineas (1969) as well
as Ghetti and coworkers (1973) have found pathological changes in both the spinal
cord and brain of cats with chronic acrylamide intoxication. Prineas (1969) has
noted degeneration in the ventral and lateral columns of the spinal cord and in
the dorsal spinocerebellar tract of the medulla. Ultrastructurally, these changes
are accompanied by accumulations of neurofilaments, mitochondria, and other dense
bodies similar to those seen in the peripheral nerves. These observations have
been confirmed by Ghetti and coworkers (1973), who have also noted similar patho-
logical changes in the cerebellar vermis. These changes correspond to distal
axonal degeneration of long descending and ascending spinal cord tracts, analogous
to the pathological picture seen in the peripheral nervous system (Spencer and
Schaumburg, 1976).
A less direct indication of central nervous system in-
volvement is cited by Hopkins (1970), who found that in one baboon which lost
the use of all four limbs, morphological damage to the peripheral nerves was
minimal. In conjunction with the electrophysiological finding detailed below
(see p. no)» Hopkins (1970) concluded that at least some central nervous system
damage had occurred.
Damage to other tissues has not been seen in acrylamide
intoxication. Fullerton and Barnes (1966) noted no abnormalities of the kidney,
spleen, pancreas, suprarenal, and lungs in rats with severe neurological signs.
In one year feedings to monkeys at 0.3-3.0 mg/kg/day, kidneys and liver appeared
normal (McCollister &t_ al. , 1964).
108
-------
(iii) Acrylamide - Functional Changes
Prolonged acrylamide intoxication has been shown to
cause decreased conduction velocity and amplitude of peripheral nerve and
muscle fiber, as well as increases in refractory period and chronaxy. As in
morphological changes, unmyelinated fibers are unaffected (Hopkins and Lambert,
1972). Although conduction velocity has been most frequently used in electro-
physiological studies of acrylamide neuropathy, it is a poor indicator of early
pathological changes (Thomann e_t aJ_. , 1974). Even after the onset of mild ataxia,
nerve conduction velocities are not significantly changed (Fullerton and Barnes,
1966; Leswing and Ribelin, 1969; Thomann e_t _al. , 1974). Lowndes and Baker (1976)
have demonstrated that decreased conduction velocities in motor nerves are pre-
ceded by functional changes at the level of the nerve terminal. Sumner and Asbury
(1974a) have also shown that acrylamide causes a functional block of nerve terminals
of muscle stretch afferents. However, in severe exposures, decreased conduction
velocities can be used as an index of intoxication. In rats showing severe hind
limb debility, conduction velocity of motor fibers supplying the hind limb de-
creased to 80% of the control value. Similar decreases have been noted in hind
limb nerves of dogs (70% of control value, Thomann et_ aL., 1974), cats (72%,
Leswing and Ribelin, 1969), baboons (51-70%, Hopkins and Gilliatt, 1967 and 1971),
and monkeys (78%, Leswing and Ribelin, 1969). Consistent with clinical and patho-
logical findings, hind limb nerves are more severely affected than fore limb
nerves (Hopkins and Gilliatt, 1971; Leswing and Ribelin, 1969).
The relatively mild decrease in conduction velocity -
80% of control - noted by Fullerton and Barnes CL966) suggested that fast nerve
fibers were preferentially attacked. This would be consistent with pathological
findings which indicate that large diameter nerve fibers are the first to under-
go degeneration. Sumner and Asbury (1975), using single fiber preparations of
cat muscle stretch receptors, have recently demonstrated that fast conducting
109
-------
fibers (Group I, 72-126 m/sec) are more severely affected than slow conducting
fibers (Group II, 24-72 m/sec). Further supporting pathological findings,
Sumner and Asbury (1974b, 1975) have shown that sensory (A-alpha) fibers are
markedly more susceptible to acrylamide than motor (A-delta) fibers. The in-
creased susceptibility of sensory over motor neurons has also been demonstrated
in the median nerve of baboons (Hopkins and Gilliatt, 1971).
In recovery, a lag period has been noted between dis-
continuation of acrylamide and return of normal electrophysiological measurements,
In the saphenous nerve of dogs, both refractory period and chronaxy increased
during the first ten days of recovery. By day 30 of recovery, nerve conduction
and chronaxy had returned to normal, although refractory periods were still ab-
normally long (Thomann et al., 1974). Similar lags lasting for several weeks
have been noted in the recovery of cats, monkeys, and baboons (Leswing and
Ribelin, 1969; Hopkins and Gilliatt, 1971). In cats recovering from severe in-
toxication, conduction velocities were still depressed after 2-3 months (Leswing
and Ribelin, 1969). Normal conduction velocities returned in rats 5-9 months
after exposure (Fullerton and Barnes, 1966). Similar to onset patterns, fore
limb and motor nerves recover more quickly than hind limb and sensory nerves,
respectively (Hopkins and Gilliatt, 1971).
Some electrophysiological studies imply central nervous
system involvement. Based on asynchronous high-frequency EEG patterns of chron-
ically intoxicated cats, Kuperman (1958) suggested brain stem damage. Hopkins
(1970) also suggested central nervous system involvement in a baboon that became
tetraplegic after oral doses of acrylamide at 20 mg/kg/day for 29 days. The
110
-------
median and anterior tibial nerves of this animal showed no decrease in con-
duction velocity, and the amplitude of the muscle action potential was normal.
In view of the atypical pathological changes noted previously (see p. 1Q8)»
Hopkins (1970) concluded that peripheral nervous system effects could not
account for the limb disability. Similar conclusions have recently been proposed
by Kuperman and Sunbhanich (1972). These investigators report that decreases in
amplitude and conduction velocity of A-alpha fibers did not worsen with progres-
sively worsening clinical signs. Further, the neurophysiological effects cor-
related with the magnitude of the daily dose, whereas the clinical signs of
toxicity correlated with the cumulative dose.
(iv) Acrylamide Analogs
Of the acrylamide analogs thus far tested, none
approaches acrylamide in neurotoxic potency and most appear to be inactive.
However, at least three acrylamide analogs have neurotoxic properties similar
or identical to those of acrylamide, and two additional analogs seem to exert
neurological effects. Those with acrylamide-like activity are:
H .0
I //
N-methylacrylamide, CH =C-CX
H 0
I //
N-methylolacrylamide, CH =C-C H
H 0
N,N-diethylacrylamide CH =C-C\ CH CH
2 N^ J
XCH CH
111
-------
Analogs with neurological effects not yet completely defined are:
H 0
N-isopropylacrylamide, CH =C-C .H
.CH
3
^CH
3
H 0
N,N-dime thy lacrylamide CH =C-C .CH
N
CH3
Barnes (1970) and Edwards (1975b) have studied the
effects of the first three acrylamide-like neurotoxins. Conflicting experi-
mental results have been obtained on the neurotoxicity of N-methylolacrylamide.
Using male Porton rats of approximately 200 g in weight, Edwards (1975b) found
that a daily dose in chow at levels of 1800 ppm (27 mg/rat/day or 135 mg/kg/day)
for one week followed by 900 ppm (18.6 mg/rat/day or 93 mg/kg/day) for four weeks
produced slight ataxia (cumulative dose approximately 3543 mg/kg, 35 day exposure)
N
Over the next two weeks, exposure to 900 ppm in diet plus four intraperitoneal
injections at 50 mg/kg produced moderate ataxia (approximate cumulative dose of
5045 mg/kg, 49 day exposure). The clinical symptoms were identical to those of
acrylamide. Barnes (1970) has noted only fine tremors in rats given seven oral
doses of N-methylolacrylamide at 100 mg/kg followed by doses of 200 mg/kg on
days 23 and 24 (cumulative dose 1100 mg/kg, 24 day exposure). However, rats
given N-methylolacrylamide in the diet at levels of 400 ppm x 14 weeks, followed
by 800 ppm x 7 weeks, followed by (1600 ppm x 6 weeks, did develop signs of hind
limb weakness. The results wereisomewhat equivocal because acrylamide contamin-
ation could not be ruled out. Using purified N-methylolacrylamide, Hashimoto and
112
-------
Aldridge (1970) were unable to detect signs of neurotoxicity in rats fed 1400 ppm
x 1 week followed by 700 ppm for seven weeks (estimated cumulative dose of 4500-
5400 mg/kg) . However, such exposure to N-methylolacrylamide did increase the sen-
sitivity of rats to acrylamide injections. Similar increases in sensitivity to
acrylamide from preexposure to N-methylolacrylamide have been noted by Edwards
(1975b) who suggests that the effect is additive rather than synergistic. Edwards
(1975b) concludes that the failure of Hashimoto and Aldridge (1970) to induce
neuropathic signs with the hydroxy-derivative was due to the low concentrations
used. However, the cumulative doses administered in these two studies do not
differ markedly.
Both Edwards (1975b) and Barnes (1970) have found N-
methylacrylamide neurotoxic to rats. At 980 ppm in chow (approximate intake of
19 mg/rat/day or 95 mg/kg/day) , slight hind limb disability was produced after
4-5 weeks [cumulative dose approximately 2660-3325 mg/kg over 28-35 days]. After
7-8 weeks, moderate disability was noted [approximate cumulative dose of 4655-5320
V
I
mg/kg over 49-56 days] (Edwards, 1975b). In the dosing schedule outlined below,
Barnes (1970) also noted clinical signs similar to mild acrylamide intoxication
in rats:
400 ppm x 10 weeks, oral
followed by 800 ppm x 3 weeks, oral
followed by 100 mg/kg x 7 doses in 14 days, oral
followed by 50 mg/kg x 10 doses, oral X^ w£ek iod
followed by 100 mg/kg x 11 doses, ^
Edwards (1975b) has shown that N,N-diethylacrylamide
produces signs in rats similar to those of acrylamide. Levels of 800 ppm in
chow (approximate intake of 19 mg/rat/day or 95 mg/kg/day) had no effect after
10 weeks [approximate cumulative dose of 6650 mg/kg in 70 days]. 'However,
113
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continued exposure on a diet of 1600 ppm (39 mg/rat/day or 195 mg/kg/day) resulted
in slight ataxia after two additional weeks [approximate cumulative dose of 9380
mg/kg in 84 days]. Slight ataxia was also produced after 8-10 weeks in chow con-
taining 980 ppm N,N-diethylacrylamide (23 mg/rat/day or 115 mg/kg/day; approximate
cumulative dose of 6440-8050 mg/kg in 56-70 days). Exposure at the same level for
three additional weeks followed by two intraperitoneal injections of 90 mg/kg in
the next week led to moderate disability within 2-4 days [approximate cumulative
dose of 10,645 mg/kg in 91 days] (Edwards, 1975b). However, Barnes (1970) found
ao neurotoxic or other adverse effects in rats on the following dose schedule:
400 ppm x 10 weeks, oral
800 ppm x 3 weeks, oral
100 mg/kg x 7 doses over the next two weeks
This failure to note neuropathy is probably attributable to the lower cumulative
dose in this exposure. Barnes (1970) regrettably does not supply estimates of
food consumption. If the possibly tenuous assumption is made that rats in these
two studies consumed about the same amount of food, the total cumulative dose
in rats exposed by Barnes (1970) would equal 5775 mg/kg over 105 days. At a
higher cumulative dose level (6650 mg/kg, see above), Edwards (1975b) also notes
no signs of neuropathy. Thus, the results of these two studies may not be con-
tradictory. As with the other acrylamide-like neurotoxins, N,N-diethylacrylamide
enhanced acrylamide toxicity. Data on the degree of enhancement of acrylamide
toxicity for all three compounds are summarized in Table 32. Thus, three N-
substituted acrylamide derivatives - N-methylacrylamide, N-methylolacrylamide and
N,N-diethylacrylamide - seem to have neuropathic activity similar to acrylamide
and have an additive effect with acrylamide on the development of neuropathy
(Edwards, 1975b).
114
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Table 32. Effect of Acrylamide Analogs on the Development of Acrylamide
Neuropathy
(Edwards, 1975b)
No. of
Weeks on
Special
Concentration Diet
m diet Before
(ppm) AL' i v 1 ami de 1
N-Met-hv lolacr> lanu de
\,N- Uielii) Uicry l
V- "It. I iw 1 ac i v i amide
1800 for 1 wk
then 900
800
980
980
1
1
J
3
Slight Slight Moderate
Slight
Slight Moderate Moderate
Symptoms After Number of Doses of AcryLanude Shown
2345 67
Slight Slight Mode rat i
Slight Moderate Moderate
Slight Slight Moderate Moderate Moderate
Rat", were fed throughout the experiment on a diet of A1B powder containing test compounds at the concentrations
.,1, >vr, Intraperitoneal doses of acrylamide (50 nig/kg) were given twice a week (compounds 1, 2, 3, and 8) or three
i ,nies a week (compounds 4, 9, and 10) beginning one or three weeks after commencing the special diet. Control rats
h'u'i.g no addition to the diet became ataxic after the same total number of doses of acrylamide, whether these are
given two or three times a week. The number of doses required to produce slight or moderate ataxia is taken as the
number ot doses to produce these symptoms in at least 50% of the rats.
Edwards (1975b) has compared the neurotoxic potencies
of these acrylamide derivatives to acrylamide using equitoxic doses. This com-
parison, summarized in Table 33, indicates that N-methylolacrylamide is more
potent than N-methylacrylamide.
Table 33. Comparative Potency of Neurotoxic Analogs to Acrylamide
Based on Oral Exposures of Nine to Fourteen Days
(Edwards, 1975b)
N-Methylolacrylamide N-Methylacrylamide N,N-Diethylacrylamide
Dose of analogue
Equivalent dose of
acrylamide
Approximate potency
based on equipotent
doses
(Acrylamide = 1)
35
7-10
. 30
91
10
,13
134
3
.04
115
-------
However, in the longer exposures described previously, N-methylacrylamide induced
early signs of neuropathy in 28-35 days with cumulative doses of 2660-3325 mg/kg,
while N-methylolacrylamide produced slight ataxia only after 35 days with a cumu-
lative dose of 3543 mg/kg. Thus, the relative potencies of these two acrylamides on
subacute exposure is not clear.
Unpublished studies summarized by Fassett (1963) seem
to suggest that both N,N-dimethylacrylamide and N-isopropylacrylamide may also
have neurological effects. A total dose of 840 mg/kg given intraperitoneally to
cats over an 18 day period produced paralysis of hindquarters and head tremors.
Although hind limb involvement is suggestive of acrylamide intoxication, no
period of ataxia or simple hind limb weakness is described. Similarly, a cum-
ulative dose of 540 mg/kg N,N-dimethylacrylamide given intraperitoneally to cats
over about a two week period resulted in weight loss, tremors, slight spasticity,
and difficulty in walking. However, the typical signs of acrylamide intoxication
were absent. Nevertheless, these latter two compounds seem suspicious, both be-
cause the neurological signs are not greatly dissimilar to those of acrylamide
and because these compounds are structurally quite similar to N-substituted acryl-
amide analogs with acrylamide-like neurotoxicity.
Five additional acrylamides are apparently not neurotoxic
at the dose levels tested. Available details of these exposures are summarized in
Table 34. Methylenebisacrylamide at levels of 1800 ppm in chow caused weight loss
and signs of poor general health in rats. At this level, food intake was reduced,
and the rats consumed only about 115 mg/kg/day (23 mg/rat) of the acrylamide. When
the concentration was lowered to 900 ppm in chow, food consumption rose, weight
116
-------
stabilized, and the total daily intake of the chemical was 105 mg/kg (21 rag/rat).
In a different exposure series, rats given 50 mg/kg/day x 5 days/week x 3 weeks
showed no neurotoxic signs but did not gain weight (Edwards, 1975b).
Table 34. Acrylamide Analogs Without Apparent Neurotoxic Activity to Rats
Approximate
Cumulative
Compound* Dose Schedule, Route Dose (mg/kg) Reference
Methacrylamide 50 mg/kg x 10 doses/11 days, oral 1500 Barnes, 1970
then 100 mg/kg x 10 doses/14 days, oral
Methylenebisacrylamide** 115 mg/kg/day x 1 week, oral 8155 Edwards, 1975b
then 105 mg/kg/day x 10 weeks, oral
N ,N-Pent.ame thyleneblsacry lamide 170 mg/kg/day x 6 weeks, oral 7140 Edwards, 1975b
N-tert-butylacrylamide no details available — Fassett, 1963
N-tert-octylacrylamide no details available — Fassett, 1963
* No adverse effects unless otherwise noted
** See text for adverse effects
A number of additional chemicals structurally related
to acrylamide have shown no apparent neurotoxic or other adverse effects on sub-
acute or oral exposure to rats. These include sodium acrylate, acrylonitrile,
crotonamide, senecioic acid amide, allyl acetamide (Barnes, 1970), methyl methacry-
late , ethyl crotonate, N-bis-acrylamido-acetic acid, 3,3'-iminodipropionamide,
and 5-3-propionamido-glutathione (Edwards, 1975b).
e. Sensitization, Repeated Doses
Although many of the acrylamides are skin irritants to both
laboratory mammals and man (see Sections III-B-2-c, p. 78 , and III-B-1-a, p. 63),
sensitization has not been reported. Fassett (1963) indicates that N,N-dimethyl-
acrylamide is not a skin sensitizer in guinea pigs. Specific studies on sensi-
tization for the other acrylamides have not been encountered.
117
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f. Teratogenicity
Edwards (1976) administered acrylamide to pregnant rats
at dietary levels of 200 ppm and 400 ppm from the day of mating until partur-
ition. Although the pregnant rats evidenced signs of acrylamide intoxication,
the offspring had no macroscopic skeletal or organ abnormalities attributable
to acrylamide exposure. Similarly, the offspring of pregnant rats given single
intraveneous injections of acrylamide at 100 mg/kg on day 9 of gestation had
no macroscopic or microscopic abnormalities in the brain, spinal cord, or
sciatic nerve. No signs of nervous system damage were seen in any of the
offspring even though transplacental transport of acrylamide was demonstrated.
g. Mutagenicity
No studies encountered.
h. Carcinogenicity
Tests specifically designed to determine the carcinogenic
potential of the acrylamides have not been conducted. Although no tumors have
been noted in chronic exposure studies described previously (see p. 108 , last
paragraph), detailed pathological examinations have been confined primarily to
nerve tissue.
The possible relationship between the alkylating ability
of acrylamide and potential carcinogenicity has not been discussed in the
literature. As described in Section III-B-2-a (p. 73), very small quantities
14
of C-labeled RNA and DNA are evident in rat brain and liver 24 hours after
14
exposure to C-labeled acrylamide. However, the levels of apparent incorporation
14
into DNA were exaggerated by unspecified levels of C-labeled protein contam-
ination. In addition to this questionable binding of acrylamide to nucleic
118
-------
acids, acrylamide is extensively bound to protein and has been shown to alkylate
with protein sulfhydryl groups (see p. 126 ). Although the mechanism of chemical
carcinogenesis is not known, the ability to alkylate nucleic acids is a property
common to many carcinogens (Clayson, 1975; Roberts, 1975). The degree of car-
cinogen binding to DNA is often very slight. For instance, 10 hours after
intraperitoneal injections of urethan at 668 mg/kg to mice, the extent of
3
binding to liver DNA is 9.3 x 10 moles nucleotides/mole urethan. Similarly,
120 hours after intraperitoneal injections of ethionine at 4.2 mg/kg to rats,
the extent of binding to liver DNA is 2.7 x 10 moles nucleotides/mole ethionine
(Sarma et^ _al_., 1975). In terms of nmoles carcinogen/mg DNA, the levels of
-1 -4
incorporation of urethan and ethionine are about 3 x 10 and 1 x 10 , respec-
tively. The apparent level of acrylamide incorporation into rat liver DNA after
_2
24 hours was 1.6 x 10 nmoles acrylamide/mg (p. 73). Although alkylation of
protein is a much less valuable index of carcinogenic potency (Sarma e_t al. , 1975) ,
it has proved useful in some experimental systems (Clayson, 1975; Heidelberger
1973). For example, in studies on the binding of various compounds to ligandin,
a binding protein in rat liver, Litwack and coworkers (1971) found that the car-
cinogens tested differed from other compounds in that they formed covalent bonds
with sulfur of cysteinyl groups. As indicated above, acrylamide forms covalent
bonds with some protein sulfhydryl groups. While this type of data can in no
way be construed as direct evidence of acrylamide carcinogenicity, it does suggest
the need for further testing.
Acrylamide and certain acrylamide derivatives have been sug-
gested as antitumor agents. Acrylamide has been shown to suppress the development
of adenocarcinomas in dogs (Tsou et a!L. , 1967) and sarcomas in mice (Kozlov and
Dobrin, 1966). The inhibition of plant tumors is discussed in Section III-B-5,
119
-------
p. 123. N, N'-methylenebisacrylamide has also been found to inhibit the develop-
ment of transplanted mouse tumors (Tomcufcik et^ al. , 1961). The mechanism of
this tumor inhibition is not known. However, some antitumor agents are themselves
alkylating agents (Stock, 1975). Consequently, many antitumor agents have sig-
nificant carcinogenic activity (Harris, 1976).
i. Behavioral Effects
A number of investigators have noted behavioral changes in
laboratory animals during acrylamide intoxication. However, such changes seem to
have been tangential to the interests of these investigators and have not been
described in great detail. In acutely poisoned rats (120 mg/kg, intraperitoneally) ,
fright and excitement were noted prior to the onset of ataxia and convulsions
(Druckrey e^t_ ali. , 1953). A variety of behavior effects described as "ranging from
the development of fearful apprehension to viciousness" were seen in cats after
subacute intoxication with acrylamide, while "behavior suggestive of hallucinations"
was noted in acute exposures (Kuperman, 1958). After 35 days exposure to 250 ppm
acrylamide in drinking water, mice with severe hind limb effects "appeared jittery"
(Bradley and Asbury, 1970).
No permanent behavioral effects have been described in
animals showing clinical signs of recovery from acrylamide intoxication.
j. Possible Synergisms and Other Drug Interactions
A number of factors have been examined for effects on acryl-
amide neuropathy. Hashimoto and Ando (1971) have found that administration of
methionine reduces the neurotoxic potency of acrylamide. Kaplan and coworkers
(1973) indicate that pyridoxine and thiamine deficient rats and rats injected with
cortisol show no increased sensitivity to acrylamide. However, induction of
microsomal enzymes with DDT or phenobarbital results in a markedly greater in-
crease in the total cumulative dose necessary to cause electrorod failure. The
effect of phenobarbital protection is illustrated in Table 35.
120
-------
Table 35, Phenobarbital Protection in Acrylamide-Treated Rats (Kaplan et^ al., 1973)
Mean Day For
Aery i amide
(mg/kg/day)
30
40
40
60
f nenooaroitai
(50 mg/kg/day)
10.
6.
+ 12.
+ 6.
Onset
7 + 0
7 + 0
3 + 0
0 + 0
.36
.33
.47
.40
Recovery
23.4 + 0.69
18.0 + 0.57
28.1 + 0.67
17.6 + 0.63
(mg/kg)
390
360
600
480
Phenobarbital started 5 days before and continued simultaneously with acrylamide.
Corresponding increases in recovery time with increased
cumulative dose was seen in the 40 mg/kg/day dose group. As described above,
similar prolonged recovery patterns were also noted in young rats tolerating
high cumulative doses (Kaplan and Murphy, 1972). Edwards (1975a), however,
has found that neither DDT nor phenobarbitone affects the onset of neuropathic
effects in rats on diets containing 500 ppm acrylamide. Further, doses of
vitamin A (5000 lUm/kg) and vitamin E (52 lUm/kg) did not affect the response
of rats to intraperitoneal injections of acrylamide [50 mg/kg x twice weekly].
As discussed in Section III-B-2-d-iv (p. 115 ), various
neurotoxic acrylamide analogues have additive, but not synergistic, effects
when administered with acrylamide.
k. Field Studies
None encountered.
3. Effects on Other Vertebrates
Acrylamide given orally at doses of 50 mg/kg/dose three times
a week caused ataxia and weakness in nine adult Star Cross hens after four to
nine doses. Clinical signs of toxicity were not reflected in histological damage
121
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to the peripheral nerves. In hens with severe ataxia, light microscopic examina-
tion of the sciatic, peroneal, and brachial nerves revealed only slight axonal
degeneration. Central nervous system damage included some degeneration of the
cervical spinocerebellar tracts and the medulla. Brain esterase activity was not
inhibited in one ataxic hen when measured twenty-four hours after the last dose.
Four severely ataxic hens showed complete clinical recovery after two to three
months (Edwards, 1975b).
Male frogs (Rana temporaria) are also adversely affected by
acrylamide but did not develop signs of neuropathy. Three of five animals died
after three injections of 50 yg/g (50 mg/kg) into the dorsal sac. Two of three
frogs died after a two-hour immersion in a 2% (v/v) aqueous solution of acrylamide.
However, survivors from both of these exposures showed no adverse effects (Edwards,
1975b).
In static exposures of fathead minnows to acrylamide, 96-hour
LC _ 5Q _ values were 89, 124, and 173 ppm, respectively (Dow Chemical, 1976).
Goldfish tolerated a continuous 30-day exposure to acrylamide in water at 50 ppm
without signs of intoxication. Exposure to 100 ppm, however, was lethal in five
to seven days. No signs of neuropathy were noted in sublethal exposures (Edwards,
1975b). Similarly, blackhead minnows survive for over two weeks in acrylamide
concentrations of 60 ppm but show marked mortality at concentrations of 1000 ppm
(Renn, 1956).
Tadpoles can absorb acrylamide from aqueous solutions with labeled
material being bound to the brain, nerves, and other organs (Tarusov et al., 1966a
and b).
4. Effects on Invertebrates
No studies encountered.
122
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5. Effects on Plants
Although no studies have been encountered on the toxicity of
acrylamide to plants, Ismailova (1966) indicates that acrylamide at concentra-
tions of 0.1, 0.5, and 1.0% inhibits the development of Pseudomonas tumefaciens-
induced tumors in plants. Acrylamide has similar activity on some mammalian
tumors (see Section III-B-2-h, p. 119).
6. Effect on Microorganisms
No detailed study has been reported concerning the effect of
acrylamide and its derivatives on microorganisms. Cherry et_ al_. (1956), by
microscopic examination of river water which had been treated with 10 ppm
acrylamide, found that the biota which developed in the water was mixed and
healthy. When acrylamide was added with acrylonitrile, they noted a selective
enrichment of a type of "spined" cell. It appears likely that these cells in-
creased in number by virtue of their ability to tolerate and/or degrade the test
compounds.
7• JLn Vitro and Biochemical Studies
a. Effects on Isolated Organs
Incubation of rat brain stem cortex slices with 10 mM
acrylamide has no effect on oxygen consumption or on the final concentrations
of pyruvate and lactate (Hashimoto and Aldridge, 1970).
b. Effect on Cell Cultures (Non-Microbial)
Spencer et al. (1976) utilized organotypic spinal cord-
peripheral nerve-spinal ganglion-striated muscle combination tissue cultures to
study the neurotoxic effects of acrylamide in vitro. Acute fiber breakdown
was noted after one week of exposure to 100 yg/ml of nutrient fluid and no
effect was noted after six weeks of exposure to 1 yg/ml. Twenty-five yg/ml
123
-------
produced neurotoxic effects in sensory axons after two to three weeks and distal
axonal degeneration by twelve weeks. Scattered demyelination was also a pro-
nounced feature.
Kuperman (1957) has shown that acrylamide, but not acrylamide
analogs, will harden whole human blood at acrylamide concentrations of 300-600 g/&.
Kojima and coworkers (1971) have shown that acrylamide and a number of other
vinyl monomers will undergo graft copolymerization with whole blood.
c. Effect on Isolated Organelles and Cell Homogenates
Hashimoto and Aldridge (1970) indicate that acrylamide at
10 mM concentration does not inhibit oxidative phosphorylation in rat liver mito-
chondria.
d. Effects on Purified Enzymes and Isolated Enzyme Systems
No studies encountered.
e. Effects on Nucleic Acids and Proteins
As indicated previously (see Section III-B-2-b, p. 75),
acrylamide and N-methylolacrylamide undergo glutathione conjugation and lower
non-protein sulfhydryls in rat brain, spinal cord, and liver. Hashimoto and
Aldridge (1970) have determined the reactivity of these two acrylamides and a
number of related compounds with glutathione in vitro. The results are summarized
in Table 36. The reactivity of these compounds with glutathione does not cor-
relate to their neurotoxicity. Acrylamide and N-methylolacrylamide are equally
reactive with glutathione. This has also been noted by Edwards (1975a). However,
acrylamide is at least three times more potent a neurotoxin than N-methylol-
acrylamide. Similarly, neither acrylonitrile (more reactive) nor sodium acrylate
(less reactive) axe neurotoxic.
124
-------
Table 36. Reactivity of Acrylamide and Its Analogs with Glutathione at pH 7.3
and 37°C In Vitro (Hashimoto and Aldridge, 1970)
Compounds 1-mole min
Acrylonitrile
n qi
Acrylamide U'^-L
N-Methylolacrylamide 0.91
N,N'-Methylenebisacrylamide °-5^
Ethyl Crotonate °-2^
N-Methylacrylamide 0.058
0.058
N,N-Diethylacrylamide
Sodium Acrylate 0.035
Methacrylamide 0.014
Similar to Kupennan's (1957) observation on solidification
of whole blood by acrylamide (p. 124), Druckrey and coworkers (1953) found that
acrylamide causes a number of different protein solutions to solidify. This
may have been due to polymerization of the acrylamide. The order of reactivity
for different proteins was: fibrinogen > gamma globulin » human serum > serum
albumin. Gavins and Friedman (1967a) have demonstrated that acrylamide alkylates
with the sulfhydryl groups of bovine serum albumin and wheat gluten. However,
the reactivity of acrylamide is less than that of either acrylate or acrylonitrile
(see also Gavins and Friedman, 1976b). The order of reactivity is different
125
-------
than noted by Hashimoto and Aldridge (1970) for jLn vitro conjugation with gluta-
thione. In addition, Hashimoto and Aldridge (1970) have found that four moles
of acrylamide bind to one mole of hemoglobin, implying that binding occurs at
the four active sulfhydryl groups.
No jn vitro studies have been conducted on the alkylation of
acrylamide to nucleic acids. As indicated previously (see Section III-B-2-a,
14
p. 73), small amounts of label from 11- C]acrylamide appear in both the RNA
and DNA fractions of rat brain and liver one day after dosing.
126
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IV. Regulations and Standards
A. Current Regulation
1. Food, Drug, and Pesticide Authorities
The Food and Drug Administration (FDA) has approved the use
of acrylamide and certain acrylamide derivatives in polymeric formulations
intended for contact with food. Sodium polyacrylate-aerylamide resin may be
used to control organic and mineral scale in beet and cane sugar juice or
liquor, so long as residual acrylamide monomer levels do not exceed 0.05% (FDA,
1972c). Acrylamide along with styrene may be used in preparations of N-
[(dimethylamino)methyl]aerylamide as dry strength agents for paper or paper-
board intended for food contact. This formulation may not exceed 1% by weight
of the finished paper product and acrylamide monomer may not exceed 0.2% by
weight of the formulation (FDA, 1974a). Modified polyacrylamide - residual
monomer content unspecified - is permitted in paper or paperboard intended for
contact with dry food when used as dry strength or pigment retention aids (FDA,
1972a). Acrylamide and ethylene may be copolymerized with vinyl chloride for
use in coatings on food contact surfaces. No more than 3.5% by weight of total
polymer units may be derived from acrylamide (FDA, 1974b).
Homopolymers and copolymers of N,N-methylenebisacrylamide or N-
methylolacrylamide may be used in food packaging adhesives. Residual monomer
levels are not specified (FDA, 1965). A reaction product of N-(l,l-dimethyl-
3-oxybutyl)acrylamide and formaldehyde may be used in levels up to 1% as com-
ponents of polyvinyl acetate latex coatings for paper and paperboard intended
for use in contact with food (FDA, 1972b).
The USPHS has approved polyacrylamides for potable water treat-
ment with the provision that the dose of polymer does not exceed 1 ppm and that
the polymer contains not more than 0.05% monomer (MacWilliams, 1976).
127
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2. OSHA
The Occupational Safety and Health Administration (OSHA, 1975)
is currently developing a criteria document on acrylamide. Present standards
3
are identical to the TLV, allowing 0.3 mg/m in workroom air (OSHA, 1974).
3. Other Federal, State, and County Regulations
None encountered.
4. Foreign Countries
In England, levels of acrylamide in water clarified using poly-
aery lamide have been established. Polyacrylamide may contain up to 0.05% acryl-
amide monomer. The maximum concentration of acrylamide monomer in clarified
water may not exeed 0.5 yg/liter, and the maximum average concentration may not
exceed 0.25 yg/liter (Housing and Local Government Ministry, 1969).
In Russia, the suggested maximum permissible concentration of
methacrylamide and N-methylolmethacrylamide in potable water is 0.1 mg/liter
(Strizhak, 1967).
B. Consensus and Similar Standards
1. TLV
The American Conference of Governmental Industrial Hygienists
(ACGIH, 1974) have recommended 0.3 mg/m (0.1 ppm) as the TLV for acrylamide in
workroom air. This standard is based on the daily exposure limit recommended by
McCollister and coworkers (1964) - see Section 3 below.
2. Public Exposure Limits
None encountered.
3. Other
McCollister and coworkers (1964) have recommended that daily
128
-------
levels of acrylamlde exposure to humans should not exceed 0.05 rag/kg in the
workplace and should not exceed 0.0005 rag/kg to the general population. This
recommendation is based on subacute and chronic testing of various laboratory
mammals (see Section III-B-2-c, d, p. 78, 85).
Spencer and Schaumburg (1975) have recommended periodic examina-
tions of workers exposed to acrylamide and are currently developing an assay
for the early detection of acrylamide intoxication based on polymer sensitivity.
129
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V. Summary and Conclusions
There are nine acrylamide compounds that are produced in commercial quantities.
However, acrylamide itself is by far the most important in terms of production
volume. In 1973, the annual production of acrylamide was estimated at 40 million
pounds. It is believed that the derivatives are all produced in significantly
smaller quantities than acrylamide.
The major use of acrylamide and its derivatives is in the production of
polymers and copolymers for a variety of applications. Linear polyacrylamides
are used because of their solubility in water, polar functional groups, low
toxicity, and competitive cost. The largest market for polyacrylamides (~ 40%)
is as a flocculant in sewage and waste water treatment. They are also approved
for treatment of potable water, but the residual monomer in the polymer must
be below 0.05%. Another major application (~ 20%) is in the pulp and paper in-
dustry as a strengthener and to aid in preventing fibers from being washed away.
Minor applications for polyacrylamides include drilling fluid additive, secondary
oil recovery agent (a fast growing application), chemical grouts and soil stabi-
lizers (one of the few applications in which acrylamide monomer is polymerized
in situ), adhesives, coal flotation and coal dust loss prevention, textile
treatments, printing paste, photographic applications, etc.
Losses to the environment from production, transport, and storage of
acrylamide are considered to be minor. The major source of acrylamide monomer
loss to the environment appears to be from the use of polyacrylamide products
which contain residual acrylamide monomer. In addition to losses of acrylamide
from polyacrylamide, another source of contamination is the direct use of acryla-
mide monomer to soil as chemical grouts and soil stabilizers for dams, foundations,
tunnels, etc. Although no United States monitoring information is available,
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this loss of residual monomer is supported by British monitoring data where
concentrations as high as 42 yg/£ (ppb) were detected in effluents from coal
mines and preparation plants, paper mills, and clay pits. In the case of the
clay pit, the concentration of acrylamide in the receiving stream was 1.2 yg/&,
and further downstream at a waterworks intake the level dropped to 0.3 yg/Jl,
which is still above the average permissible level for drinking water (0.25 yg/Jl).
The concentration of acrylamide in conditioned sewage sludge at two sewage con-
ditioning plants which used polyacrylamide was well below 0.1 yg/£. The residual
monomer in polyacrylamide used for potable water treatment is regulated, but any
improper uses of polyacrylamide with uncontrolled monomer residual in potable
water treatment could result in substantial exposure to humans.
A number of studies indicate that acrylamide will biodegrade in the environ-
ment as well as under biological sewage treatment conditions. Acclimation of
the microorganisms appears to be necessary. The importance of non-biological
alterations of acrylamide in the environment is unknown.
The high water solubility and low vapor pressure of acrylamide suggest
that acrylamide released to the environment will reside in aquatic systems.
The calculated evaporation half-life from water is ~ 400 years. The high
water solubility also suggests that bioconcentration should not be an important
process with acrylamide.
Based on these patterns of use, release, and environmental fate, as well
as the known biological effects of acrylamide and acrylamide analogs, three
areas of potential environmental concern are apparent: neurotoxicity, carcino-
genicity, and toxicity to aquatic organisms.
Of the commercially important acrylamide compounds, acrylamide itself
has the greatest neurotoxic potency. However, the dose-response patterns for
131
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neurotoxicity have been relatively well-defined in a number of mammals, and
these patterns indicate that prolonged exposure to probable environmental con-
centrations would not produce apparent neurotoxic effects. On acute exposures,
acrylamide primarily affects the central nervous system (CNS) and characteris-
tically causes ataxia, weakness, tremors, and convulsions. Single oral or intra-
peritoneal doses of 100-200 mg/kg cause severe CNS effects and are often fatal
to laboratory mammals 1-3 days after dosing. The acute effects of substituted
acrylamides have not been studied in great detail. Acute oral LD values for
these compounds range from about 300 mg/kg to over 1000 mg/kg.
Repeated exposure to acrylamide and some acrylamide derivatives causes a
clinical peripheral neuropathy which is associated pathologically with a central
and peripheral distal axonopathy. Characteristic symptoms of chronic intoxica-
tion include ataxia, bilateral weakness of the hind limbs which may progress
to limb paralysis, and loss of proprioception. In addition, sensory impairment,
bladder distention, weight loss, vocal changes, and various other secondary
effects have been noted in some experimental mammals. Clinical signs of neuro-
logical impairment are associated with consistent histological and physiological
changes, including axonal degeneration with demyelination and decreased nerve
conduction velocity. Even in cases of severe intoxication, clinical, histological,
and physiological signs of damage seem to be reversible.
The dose necessary to cause early signs of neurological damage over exposure
periods of up to about six months seems to be dependent primarily on the cumu-
lative dose rather than the dose schedule or route. For acrylamide, the total
effective cumulative dose is in the range of 300-600 mg/kg. As in acute exposure,
the acrylamide analogs are markedly less potent. Acrylamide-like neuropathy
132
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has been demonstrated by only three of these analogs: N-methylolacrylamide,
N-methylacrylamide, and N,N-diethylacrylamide. While potency estimates vary
somewhat among the available studies, the two monosubstituted acrylamides are
probably no more than 30% as potent as acrylamide, while N,N-diethylacrylamide
is only about 5% as potent. Two additional acrylamides, N,N-dimethylacrylamide
and N-isopropylacrylamide, also have neurotoxic effects, but these effects have
not been described in detail.
The chronic neurotoxicity of acrylamide and some acrylamide derivatives
is without doubt a cause for concern in occupational exposures. Cases of acryla-
mide-induced neuropathy in workers have been well-documented and the signs of
neuropathy in humans generally resemble those seen in laboratory mammals. How-
ever, the relationship between the extent of exposure and the specific neuro-
logical signs that develop is unclear. Mammalian studies suggest that prolonged
exposures to low daily doses of acrylamide do not produce signs of neurotoxicity
even when cumulative doses exceed the neurotoxic threshold of shorter exposure
periods. Given that the peripheral neuropathic effects of acrylamide are
apparently reversible, the daily exposure limit of 0.05 mg/kg/day in the work-
place and 0.0005 mg/kg/day in the general population recommended by McCollister
and coworkers (1964) and adopted by AGC1H (1974) and OSHA (1974) does not seem
unreasonable. With the extremely low levels of acrylamide that can be expected
in the environment, widespread neurotoxic effects due to acrylamide contamina-
tion seem unlikely. However, the possibility of human neuropathy resulting from
local incidents of acrylamide contamination cannot be disregarded.
The carcinogenic potential of the acrylamides does seem to be a legitimate
area of environmental concern. The carcinogenicity of the acrylamides has not
133
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14
been studied directly. However, the appearance of C-labeled RNA and DNA after
exposure to [1- C]acrylamide and the ability of acrylamide to alkylate with pro-
tein would seem to indicate that carcinogenicity screening studies should be per-
formed on acrylamide and some of its commercially important analogs before a
definitive assessment of environmental hazard can be made.
The information on the toxicity of acrylamide to life forms other than
mammals is not extensive. While the available information does not indicate a
remarkably high toxicity to hens, frogs, or fish, additional information on
aquatic biota might be desirable in order to assess potential local contamination.
Thus, the potential of a widespread environmental hazard associated with the
commercial use of acrylamide or polyacrylamide products does not seem very high.
Most of the acrylamide is polymerized to a stable resin. Dilute concentrations
of residual acrylamide monomer are leached out of the polymer in many of the aqueous
applications of polyacrylamide. However, the concentrations are low and acrylamide
is biodegradable; it probably does not bioconcentrate; and its neurotoxic effects
are largely reversible and appear to have a threshold concentration above likely
environmental concentrations. Nevertheless, there may be some instances where
the concentration of acrylamide emitted from polyacrylamide use could result in
excessive concentrations of acrylamide in water, with possible adverse effects
on aquatic ecosystems and/or human health. It would therefore seem appropriate
to examine the various applications of polyacrylamide (including direct appli-
cation of acrylamide monomer to soil) more intensively to determine which of
these applications could result in such incidents, the precipating factors, and
viable procedures to preclude such occurrences. Some selective monitoring should
be part of any assessment.
134
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TECHNICAL REPORT DATA
(Please read Inunctions on the reverse before completing/
RFPORT NO
EPA-560/2-76-008
3. RECIPIENT'S ACCESSION-NO.
4 TITLE AND SUBTITLE
Investigation of Selected Potential Environmental
Contaminants: Acrylamides
5. REPORT DATE
August 1976
6. PERFORMING ORGANIZATION CODE
7 AUTHORIS)
Leslie N. Davis, Patrick R. Durkin, Philip H. Howard,
Jitendra Saxena
8. PERFORMING ORGANIZATION REPORT NO
TR 76-507
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Center for Chemical Hazard Assessment
Syracuse Research Corp.
Merrill Lane
Syracuse, New York 13210
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
EPA 68-01-3127
2 SPONSORING AGENCY NAME AND ADDRESS
Office of Toxic Substances
U.S. Environmental Protection Agency
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
15 SUPPLEMENTARY NOTES
16. ABSTRACT
This report reviews the potential environmental hazard from the commercial use
of acrylamide and its derivatives. For the most part, acrylamides are used in the
production of polyacrylamides, which are used as flocculants in sewage and wastewater
treatment (~ 40%) and as a strengthener in the pulp and paper industry (~ 20%). Water
leaching of the monomer from the polymer has been demonstrated by effluent monitoring,
but the monomer has been demonstrated to be biodegradable. Acrylamide causes peri-
pheral neuropathic effects and is, therefore, of occupational concern. Its other
toxicological properties are not well defined. From the available information,
acrylamides do not appear to be widespread contaminants but local incidences of
contamination may occur.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
acrylamide
toxicology
peripheral neuropathy
flocculants
methacrylamlde
b.IDENTIFIERS/OPEN ENDED TERMS
o. COSATI Held/Group
18 DISTRIBUTION STATEMENT
Document is available to the public through
the National Technical Information Service,
Springfield, Virginia 22151
19. SECURITY CLASS (This Report)
21. NO. OF PAGtS
147
20. SECURITY CLASS (This page)
22. PRICE
E.PA Form 2220-1 (9-73)
148
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