POLYETHYLEMINE AND ETHYLENIMINE
EXPLANATION
Polyethylenimine is an immobilizing agent used in the production
of enzyme preparations for food processing. The substance is also used
in food packaging materials. Polyethylenime is produced by the acid-
catalyzed homopolymerization of ethylenimine. The polymerized material
is cross-linked with ethylene dichloride to give the 40,000 to 60,000
molecular-weight substance utilized in enzyme immobilization.
POLYETHYLEMINE
EXPLANATION
This substance has not been previously evaluated by the Joint
FAO/WHO Expert Committee on Food Additives.
BIOLOGICAL DATA
Biochemical aspects
No information available.
Toxicological studies
Special studies on mutagenicity
Two different forms of polyethylenimine were evaluated for
mutagenic activity in the presence or absence of an Archlor-induced
rat liver activation system. The indicator organisms used were
Salmonella typhimurium strains TA1535, TA1537, TA1538, TA98, and
TA100. A sample of polyethylenimine obtained prior to cross-linking
with ethylene dichloride was mutagenic to strains TA1535 and TA100
both in the presence and absence of the activation system. The sample
contained measurable amounts of ethylenimine which likely caused the
mutagenic activity (Mortelmans & Shepherd, 1980).
An ethylene dichloride cross-linked sample, the form utilized in
enzyme immobilization (Corcat P-600), did not contain measurable
amounts of ethylenimine and was not mutagenic in any of the tester
strains in the presence or absence of the activation system. At
concentrations of up to 5000 micrograms/plate, 2 other forms of
polyethylenimine, Corcat P-12 and Corcat P-18, were not mutagenic
under the same test conditions (Mortelmans & Miron, 1981).
Polyethylenimine (P-1000) having a molecular weight of 70,000 was
tested for mutagenicity with or without metabolic activation (source
of the activating system not specified) using Salmonella typhimurium
strains TA1535, TA1537, TA1538, TA98, and TA100 and E. coli strain
wp2 uvrA. No mutagenic activity was found when concentrations of up to
5000 micrograms/plate were tested (Kajiwara et al., 1984).
Acute toxicity
LD50
Species Route (mg/kg b.w.) Reference
Mouse oral 2,800 BASF, 1959
Mouse oral 8,000 Kobe University,
1974
Mouse i.p. 40 BASF, 1959
Rat oral (gavage Rushbrook &
in corn oil) Jorgenson, 1981
Male 7550(a)
Female 7500(a)
Both sexes oral 2286(b)
Male 2286(c)
Female 1991(c)
Rat gavage (aqueous 2000 Norris, 1973
solution)
Rat oral 3,000 BASF, 1959
Rat i.p. 70 mg/kg BASF, 1959
Rabbit oral 2,000 (no BASF, 1959
injury)
Rabbit i.v. 4 (lethal BASF, 1959
dose)
Cat i.v. 10 (lethal BASF, 1959
dose)
(a) Polyethylenimine type Corcat 600 (type used in enzyme
immobilization)
(b) Polyethylenimine type Corcat P-12
(c) Polyethylenimine type Corcat P-18
It was not possible to determine the lethal oral dose of
polyethylenimine in dogs and cats because of vomiting. Cats vomited
within 30 minutes of receiving 100-500 mg/kg, so only a small amount
of the material remained in the stomach. Doses of 100 mg/kg caused
vomiting in dogs. In cases where vomiting did not occur, no adverse
effects were reported (BASF, 1959).
In guinea-pigs, a single oral dose of 600 mg/kg was lethal to
6/10 animals and a dose of 800 mg/kg was lethal to 2/10 animals (BASF,
1959).
Short-term studies
Rats
Groups of 40 male and 40 female white rats received 0, 0.25, 0.5,
or 1.0 g/kg b.w. of polyethylenimine in the diet for 8.5 months. No
compound-related effects were reported with respect to mortality, body
weight, feed consumption, clinical signs, haematology, urinalysis, or
absolute and relative organ weights. An elevation in blood alkaline
phosphatase levels was observed in high-dose male rats as compared to
the controls, but the values were within normal limits for the
performing laboratory. No treatment-related changes were observed in
gross and microscopic pathology studies carried out on 5 animals/sex/
dose (McCollister & Copeland, 1968a).
Dogs
Groups of 4 male and 4 female beagle dogs were fed 0, 0.25, 0.5,
or 1.0 g/kg b.w. polyethylenimine in the diet for 9 months. No
compound-related differences were noted with respect to haematology,
urinalysis, clinical chemistry, or bromsulfophthalein dye retention.
Group mean body-weight gains were reduced as compared to controls in
high-dose males and females. Relative liver and kidney weights were
increased in high-dose females and relative kidney weights were
slightly increased in high- and mid-dose males and mid-dose females.
The pathology report indicated that severe degenerative changes
occurred in the kidney proximal convoluted tubules in the high-dose
animals. The same lesion, but not as severe, was reported to occur in
all mid-dose and 5 of 8 low-dose animals. No lesions of the proximal
convoluted tubules were reported in control animals. All of the low-
dose females and one of the low-dose males were reported to have the
lesion to a "very slight" degree. Brown pigmentation of Kupffer's
cells in the liver was considered to be compound-related. In the high-
dose animals, it was present in 3 of 4 males at a moderate to very
slight degree and in 2 of 4 females at a marked to moderate extent. In
the mid-dose groups, 1 of 4 animals of each sex had the lesion present
at a grade of "very slight". The lesion was not present in controls of
either sex or low-dose males, but was present at a "very slight" grade
in 1 of 4 low-dose females. There did not appear to be any other
compound-related microscopic lesions (McCollister & Copeland, 1968b).
Rabbits
Rabbits were reported to tolerate several once-per-week oral
doses of 1.0 g/kg polyethylenimine for several weeks without
impairment of liver function. No injury to the liver or kidney was
noted in rabbits receiving 1.0 g/kg daily, but the report stated that
the rabbits tolerated a maximum of 6 doses. Daily doses of 0.5 g/kg
were reportedly tolerated without any injury; however, details of the
study were not provided (BASF, 1959).
Comments
Although not up to modern standards of toxicity testing, the
8.5-month rat study of free polyethylenimine did not reveal any
adverse effects. In the 9-month dog study, compound-related changes in
the kidney and liver were found. Since absorption and distribution
studies are not available to show if appreciable uptake of this high-
molecular-weight compound occurs, it is not clear what the mechanism
of action is for the liver and kidney lesions. Polyethylenimine free
of measurable levels of ethylenimine showed no mutagenic activity when
tested with or without metabolic activation using Salmonella
typhimurium strains.
EVALUATION
Estimate of acceptable daily intake for man
Polyethylenimine is considered to be a suitable substance for use
as an immobilizing agent in the production of immobilized enzymes (see
ethylenimine).
REFERENCES
BASF (1959). Preliminary report on the toxicity of PEI. Unpublished
report of Badische Analin & Soda Fabrik AG. Submitted to WHO by
UOP, Inc.
Kajiwara, Y., Oguru, S., & Takeyasu, K. (1984). Ames metabolic
activation test to assess the potential mutagenic effect of
polyethylenimine. Unpublished report of the Hita Research
Laboratories, Chemicals Inspection & Testing Institute. Submitted
to WHO by UOP, Inc.
Kobe University (1974). Acute toxicity of P-1000. Unpublished report
of Kobe University, Medical Faculty, Public Health Section.
Submitted to WHO by UOP, Inc.
McCollister, D.D. & Copeland, J.R. (1968a). Results of 8.5 month
dietary feeding studies of polyethylenimine in rats. Unpublished
report of the Dow Chemical Company. Submitted to WHO by Cordova
Chemical Company.
McCollister, D.D. & Copeland, J.R. (1968b). Results of 9 month dietary
feeding studies of polyethylenimine in Beagle hounds. Unpublished
report of the Dow Chemical Company. Submitted to WHO by Cordova
Chemical Company.
Mortelmans, K.E. & Miron, K.L. (1981). In vitro microbiological
mutagenicity assays of Cordova Chemical Company's compounds
Corcat P-12, Corcat P-18, and Corcat P-600. Unpublished report of
SRI International. Submitted to WHO by Cordova Chemical Company.
Mortelmans, K.E. & Shepherd, G.F. (1980). In vitro microbiological
mutagenicity assays of Cordova Chemical Company's compound PEI
prepolymer, Sample No. SWM D32-084-1. Unpublished report of SRI
International. Submitted to WHO by Cordova Chemical Company.
Norris, J.M. (1973). Acute toxicological properties of PEI-600.
Unpublished report of the Dow Chemical Company. Submitted to WHO
by UOP, Inc.
Rushbrook, C.J. & Jorgenson, T.A. (1981). Acute toxicity studies of
three Corcat compounds. Unpublished report of SRI International.
Submitted to WHO by Cordova Chemical Company.
ETHYLENIMINE
EXPLANATION
Ethylenimine has not been previously evaluated by the Joint
FAO/WHO Expert Committee on Food Additives. Trace amounts of
ethylenimine may potentially migrate into food from the presence of
small amounts of unreacted monomer present as a contaminant in
polyethylenimine.
BIOLOGICAL DATA
Biochemical aspects
Distribution
Five male rats (Dow-Wistar strain) were injected i.p. with 0.3 to
0.4 mg/kg b.w. of 14C-labelled ethylenimine and sacrificed after 24
or 96 hours. In both cases about 50% of the radioactivity was excreted
in the urine and small amounts were present in faeces and exhaled
air. A small amount of ethylenimine and a number of non-volatile
metabolites were present in the urine and both ethylenimine and CO2
were present in expired air. About 2.5% of the radioactivity was
present in the liver after 24 hours and about 1% after 96 hours.
Smaller amounts were present in many other tissues. The authors
concluded that the compound was generally distributed throughout the
rat before reaction with tissue components occurred (Wright & Rowe,
1967).
Excretion
Monoethanolamine and ethylenimine were excreted in the urine of
rats following introduction of ethylenimine into the stomach
(presumably by gavage). The urinary excretion of these 2 compounds
accounted for approximately 50% of the administered dose. The fraction
of the administered dose that was excreted in the urine was dose-
dependent. At a dose of 1/20 the LD50 (0.85 mg/kg according to the
authors) about 60% of the administered dose was excreted as
monoethanolamine and ethylenimine in the urine over a 6-day period;
50% of the dose was excreted in the first 24 hours (Sanotsky et al.,
1977).
Toxicological studies
Special studies on renal toxicity
Rats
Groups of 6 or 7 female Sprague-Dawley rats were given single
subcutaneous injections of 0.25, 0.5, 1.0, 1.25, 2.0, 4.0, 6.25, or
8.0 mg/kg of ethylenimine in water. Animals were sacrificed 4 days
after treatment. Renal papillary necrosis was observed at doses of
1.25 mg/kg ethylenimine and greater, whereas none occurred at
1.0 mg/kg and below (Axelson, 1978).
Rabbits
Renal medullary necrosis occurred in male and female New Zealand
strain rabbits injected i.v. with a single 0.005 ml/kg dose (about
5 mg/kg) ethylenimine as a 1% v/v solution in water (Davies 1969;
Davies, 1970).
Dogs
Groups of 4 male beagle dogs were given either a single i.v.
injection of 3 µl/kg (about 3 mg/kg) ethylenimine or an initial
injection of 0.6 µl/kg ethylenimine followed by a second injection of
1 µl/kg 3 days later. In the animals receiving 2 injections of
ethylenimine the tubules of the collecting ducts and loop of Henle
were dilated and inflamation was found in the renal pelvis. A small
number of dilated tubules were observed in the medulla, and dilation
of the distal convoluted tubules and collecting ducts of the cortex
were noted. Almost complete necrosis of the papilla was observed in
2 dogs that became moribund after receiving the single high dose
(3 µl/kg) of ethylenimine. Functional and clinical chemistry studies
showed that treatment was related to impairment of renal function,
proteinuria, and elevated excretion of urinary enzymes (Ellis et
al., 1973).
Special studies on carcinogenicity
Mice
A carcinogenesis study of ethylenimine was carried out using
2 strains of mice, (C57BL/6 × C3H/Anf)F1 (strain x) and
(C57BL/6 × C3H/AKR)F1 (strain y). Test animals were given the maximum
tolerated dose (MTD), 4.64 mg/kg, daily by gavage in a 0.5% gelatin
vehicle from day 7 through day 28 of age (the MTD for this study was
the maximal dose giving no mortality when administered daily for
19 consecutive days). Thereafter, the animals received the same
calculated daily dose of ethylenimine mixed in the feed. Groups of
18 animals/sex/strain were used. A number of other compounds were
tested in this study. All the animals receiving a particular compound
were placed in 1 of 4 rooms. Each room also contained an untreated
control group of 18 animals/sex/strain. There was also 1 additional
control group of 18 animals/sex/strain given a gelatin suspension
during the time when the compounds were administered by stomach tube.
Ethylenimine was actually employed as a positive control. There was at
least 1 positive control group in each room. Ethylenimine-treated
animals were on test for 77 or 78 weeks. The controls were on test for
78 to 89 weeks.
Data on mortality, body weight, food and water consumption,
haematology, clinical chemistry, and non-carcinogenic pathological
effects were not reported.
A list of the major organs examined microscopically was not
provided. The report stated that all major organs and grossly-visible
lesions were examined microscopically. However, the cranium was not
dissected. Thyroid glands were sectioned in only 1 of the 5 control
groups and not in the ethylenimine-treated animals. The tabulation of
tumours listed only the following categories: hepatomas, pulmonary
tumours, lymphomas, and total mice with tumours. The investigators
lumped all 5 negative control groups together for purposes of
comparison with positive controls and experimental compounds.
In the ethylenimine-treated animals there was a significant
increase in the relative risk for development of hepatomas, pulmonary
tumours, and total tumours. In strain x males given ethylenimine, the
incidence of hepatomas, pulmonary tumours, and lymphomas was 15/17,
15/17, and 0/17, respectively. Corresponding values for the control
strain x males were 8/79, 5/79, and 5/79. For strain x females given
ethylenimine, the incidence of the different tumours was 11/15, 15/15,
and 0/15, respectively, while the corresponding values for controls
were 3/92, 3/92, and 5/92. In strain y males given ethylenimine, the
incidence of hepatomas, pulmonary tumours, and lymphomas was 9/16,
12/16, and 0/16, respectively. Corresponding values for strain y male
controls were 5/90, 10/90, and 1/90. In strain y females given
ethylenimine, the respective tumour incidences were 2/11, 10/11, and
2/11; the corresponding values for strain y female controls were 1/82,
3/82, and 4/82. The actual dose of ethylenimine the animals received
from the diet in this study is unclear. The concentration of
ethylenimine in the feed was not measured and some material would
certainly have been lost by volatilization and reaction with dietary
constituents. An experiment, aimed at mimicking conditions of mixing
in the diet and storage of ethylenimine during the conduct of the
study, indicated loss of a considerable amount of the test substance
(Bionetics Research Labs, Inc., 1968; Green & Lowry, 1983; Innest
et al., 1969).
The same group of workers gave single s.c. injections of
4.64 mg/kg b.w. of ethylenimine to groups of 18 male and 18 female
mice of strains (C57Bl/6 × C3H/Anf)F1 and (C57BL/6 × C3H/AKR)F1. The
animals were then observed for 18 months. Tumours developed in 7 of
the males of the (C57Bl/6 × C3H/Anf)F1 strain - 2 lymphomas, 2
hepatomas, and 5 pulmonary tumours. In the (C57BL/6 × C3H/AKR)F1
strain, 6 of 18 males each developed a lung tumour. For males of both
strains the total number of tumours and the incidence of pulmonary
adenomas was significantly greater than in the controls (P < .01). In
the treated females, 1 animal of each strain developed a lung tumour.
The controls consisted of 9 separate groups lumped together for
purposes of comparison with a total of about 160 animals/sex/strain
(Bionetics Research Labs., Inc., 1968).
Fragmentary data are available from another study of ethylenimine
administered s.c. at doses of 0.4, 1.3, or 4.0 mg/kg at weekly
intervals for 48 weeks to 187 male and female C56BL × CBA mice. After
2 years, dosed animals had an increased incidence of sarcomas at the
injection site, tumours of the harderian gland and lung, and malignant
hepatomas (Linnik, 1980).
Rats
A series of ethylenimine derivatives was administered by s.c.
injection to groups of 6 male and 6 female albino rats. Ethylenimine
was injected twice weekly in an arachis oil vehicle. The dosing
regimen occurred over a 67-day period, with a total dose of 20 mg/kg
being administered. Sarcomas were found at the injection site in 5 of
6 males and 1 of the females. The tumours were discovered between 355
and 511 days after the beginning of dosing. The study was terminated
at 546 days after the beginning of dosing. No tumours were found at
locations remote from the point of injection. In controls injected
with arachis oil for the same duration as the ethylenimine group, 1 of
10 males developed an injection-site sarcoma at 568 days while 2
tumours developed at remote sites. None of 9 control females developed
sarcomas at the injection site; however, a fibroma was found in 1
animal at that site and tumours were found in 2 other animals at
remote sites.
In another experiment, groups of 6 males and 6 females were given
ethylenimine dissolved in water twice weekly by s.c. injection. A
total dose of 10 or 12 mg/kg was given to males and females,
respectively, over a 59-day period (dosed 5 days/week). The animals
were observed up to 540 days; 2 sarcomas were observed at the
injection site in females and none in males, while a transitional cell
carcinoma of the kidney was seen in 1 male. Concurrent control groups
injected with a carbowax-300 vehicle had no injection-site sarcomas
(Walpole et al., 1954).
Special studies on mutagenicity
Sex-linked recessive lethals and translocations were reported in
a study in which day-old male Drosophila were treated with an i.p.
injection of 0.4 µl of a 10-2 M solution of ethylenimine and
subsequently mated. The authors stated that the compound was
radiomimetic in producing chromosomal abnormalities - translocations
were nearly as frequent as sex-linked lethals - but resembled some
chemical mutagens, such as mustards, in producing delayed lethals and
translocations which appeared in the F2 generation from F1 parents
that appeared normal (Alexander & Glanges, 1965).
Other studies have also found that ethylenimine induces recessive
lethals and translocations in Drosophila (Lim & Snyder, 1968;
Alexander, 1967).
Ethylenimine was mutagenic in Salmonella typhimurium strains
TA1535 and TA100 without metabolic activation (McCann et al., 1975).
The compound was also reported to be mutagenic in spot tests on
Neurospora crassa strain N-23 (reverted by base pair mutagens), but
not by strain N-24 (reverted by frame shift mutagens) (Ong, 1978),
Severe inhibition of replicon initiation and blocked-chain
elongation occurred when 5 × 10-4 M ethylenimine was added to
cultured HeLa 53 cells (Painter, 1978).
Injection of 1 mg/kg ethylenimine (i.p.) into male mice resulted
in about a 2/3 reduction in incorporation of 3H-thymidine into
testicular DNA as compared to control animals (Seiler, 1977).
Lymphocyte cultures from 10 workers exposed to workroom
ambient-air concentrations of 0.5 ppm ethylenimine reportedly did not
show an increase in chromosomal aberrations (Gaeth & Thiess, 1972).
The effect of incubation with ethylenimine was studied in
cultures of WI-38 cells and in leukocytes from an adult male
volunteer. A concentration of 10-2 M ethylenimine was cytotoxic to
the WI-38 cells. Concentrations of 10-3 and 10-4 M were associated
with chromatid breaks, gaps, and exchanges. Radiolabel studies with
leukocyte cultures incubated with 10-4 M ethylenimine also showed
gaps, exchanges, and breaks, occurring primarily in the S-period of
the cell cycle (Chang & Elequin, 1967).
Acute toxicity
LD50
Species Route (mg/kg b.w.) Reference
Rat oral 17 Santoski et al.,
1977
Rat oral 15 NIOSH, 1977
Rat i.p. 3.8 NIOSH, 1977
Short-term studies
No information available.
Long-term studies
No information available.
Comments
Ethylenimine appeared to be carcinogenic when administered orally
to 2 strains of mice. Both sexes were affected, with the liver and
lung being the major target organs. When administered s.c. to rats and
mice, the compound appared to be associated with sarcomas at the
injection site as well as at other locations. Ethylenimine was found
to be mutagenic in Neurospora, Salmonella, and Drosophila, and
chromosomal aberrations occurred in cultured mammalian cells exposed
to the compound.
Use of the oral feeding study in mice for risk analysis is
complicated because of the one-dose design of the experiment,
questions about the actual dose of ethylenimine received by the
animals, the appearance of tumours at 2 sites, and the very high
tumour incidence. While clearly indicating that ethylenimine is
carcinogenic, the mouse study is not up to modern standards of
toxicity testing. Carcinogenicity studies by the oral route are
available only in the mouse. Reproduction and teratology studies are
not available.
EVALUATION
Level causing no toxicological effect
Ethylenimine has been determined to be carcinogenic in mice. A
"no-effect" level in experimental animals has not been established.
Estimate of acceptable daily intake for man
Acceptable on condition that human exposure to ethylenimine
as a result of its migrations into food from immobilized enzyme
preparations is reduced to the lowest level technically possible
(see polyethylenimine).
REFERENCES
Alexander, M.L. (1968). Mosaic mutations induced in Drosophila by
ethylenimine. Genetics, 56, 273-281.
Alexander, M.L. & Glanges, E. (1965). Genetic damage induced by
ethylenimine. Proc. Nat'l Acad. Sci., 53, 282-288.
Axelson, R.A. (1978). Experimental renal papillary necrosis in the
rat: the selective vulnerability of medullary structures to
injury. Virchows Arch. A. Path. Anat. and Histol., 381,
79-84.
Research Labs., Inc. (1968). Evaluation of carcinogenic, teratogenic,
and mutagenic activities of selected pesticides and industrial
chemicals. Volume I, Carcinogenic Study. Prepared for National
Cancer Institute. Available from National Technical Information
Service, U.S. Department of Commerce.
Chang, T. & Elequin, F.T. (1967). Induction of chromosome aberrations
in cultured human cells by ethylenimine and its relation to cell
cycle. Mut. Res., 4, 83-89.
Davies, D.J. (1969). The structural changes in the kidney and urinary
tract caused by ethylenimine (vinylamine). J. Path., 97,
695-703.
Davies, D.J. (1970). The early changes produced in the rabbit renal
medulla by ethylenimine: electron-microscope and circulatory
studies. J. Path., 101, 329-332.
Ellis, B.G., Price, R.G., & Topham, J.C. (1973). The effect of
papillary damage by ethylenimine on kidney function and some
urinary enzymes in the dog. Chem-Biol. Interact., 7, 131-141.
Gaeth, V.J. & Thiess, A.M. (1972). Chromosome studies on chemical
workers, Zentralbl. Arbeitsmed. Arbeitsschutz, 22, 357-362.
Green, D.R. & Lowry, J.R. (1983). Stability of ethylenimine in mouse
chow and 0.5% gel solution. Unpublished report of Cordova
Chemical Company. Submitted to the World Health Organization by
Cordova Chemical Company.
Innes, J.R.M., Ulland, B.M., Valerio, M.G., Petrucelli, L., Fishbein,
L., Hart, E.R., Pallota, A.J., Bates, R.R., Falk, H.L., Gart,
J.J., Klein, M., Mitchell, I., & Peters, J. (1969). Bioassay of
pesticides and industrial chemicals for tumorigenicity in mice: A
preliminary note. J. Nat. Cancer Inst., 42, 1101-1114.
Lim, J.K. & Snyder, L.A. (1968). The mutagenic effects of two mono
functional alkylating chemicals on mature spermatozoa of
Drosophila. Mutation Res., 6, 129-137.
Linnik, A.B. (1980). Study of the carcinogenic effect of ethylenimine
on F1(C57BL × CBA) mice. Eksp. Onkol., 2, 67-68.
McCann, J., Choi, E., Yamasaki, E., & Ames, B.N. (1975). Detection of
carcinogens as mutagens in the Salmonella/microsome test: Assay
of 300 chemicals. Proc. Nat'l Acad. Sci., 72, 5135-5139.
NIOSH (1977). Registry of toxic effects of chemical substances.
National Institute of Occupational Safety and Health, Washington,
DC, USA.
Ong, T. (1978). Use of the spot, plate and suspension test systems for
the detection of the mutagenicity of environmental agents and
chemical carcinogens in Neurospora crassa. Mutation Res.,
53, 297-308.
Painter, R.B. (1978). Inhibition of DNA replicon initiation by 4
nitroquinoline 1-oxide, adriamycin and ethylenimine. Cancer
Res., 38, 4445-4449.
Sanotosky, I.V., Muravieva, S.I., Zaeva, G.N., & Semiletkina, N.N.
(1977). Urinary excretion of ethylenimine and its metabolite,
monoethanolamine, under experimental conditions. Gig. Tr. Prof.
Zabol., p. 10-14.
Seiler, J.P. (1977). Inhibition of testicular DNA synthesis by
chemical mutagens and carcinogens. Preliminary results in the
validation of a novel short-term test. Mutation Res., 46,
305-310.
Walpole, A.L., Roberts, D.C., Rose, F.L., Hendry, J.A., & Homer, R.F.
(1954). Brit. J. Pharmacol., 9, 306-323.
Wright, G.J. & Rowe, V.K. (1967). Ethylenimine: Studies of the
distribution and metabolism in the rat using carbon-14.
Toxicol. Applied Pharmacol., 11, 575-584.
See Also:
Toxicological Abbreviations