August, 1988
ETHYLENE THIOUREA
Health Advisory
Office of Etinking Vtater
U.S. Environmental Protection Agency
I. INTRODUCTION
Ihe Health Advisory (HA) Proqram, sponsored by the Office of Ctinkinn
Water (OEW), provides information on the health effects, analytical method-
ology and treatment technology that would be useful in dealinq with the
contamination of drinking water. Health Advisories describe nonregulatory
concentrations of drinkinq water contaminants at which adverse health effects
would not be anticipated to occur over specific exposure durations. Health
Advisories contain a margin of safety to protect sensitive members of the
population.
Health Advisories serve as informal technical guidance to assist Federal,
State and local officials responsible for protecting public health when
emergency spills or contamination situations occur. They are not to be
construed as legally enforceable Federal standards. Ihe. HAs are subject to
change as new information becomes available.
Health Advisories are developed for one-day, ten-day, longer-term
(approximately 7 years, or 10% of an individual's lifetime) and lifetime
exposures based on data describing noncarcinogenic end points of toxicity.
For those substances that are kncwn or probable human carcinogens, accordinq
to the Agency classification scheme (Group A or B), Lifetime HAs are not
recommended. Ihe chemical concentration values for Group A or B carcinoaens
are correlated with carcinogenic risk estimates by employing a cancer potency
(unit risk) value together with assumptions for lifetime exposure and the
consumption of drinking water. The cancer unit risk is usually derived from
the linear multistage model with 95% upper confidence limits. This provides
a low-dose estimate of cancer risk to humans that is considered unlikely to
pose a carcinogenic risk in excess of the stated values. Excess cancer risk
estimates may also be calculated using the One-hit, Wsibull, Logit or ftrobit
models. There is no current understanding of the biological mechanisms
involved in cancer to suggest that any one of these models is able to predict
risk more accurately than another. Because each model is based on differina
assumptions, the estimates that are derived can differ by several orders of
magnitude.

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Ethylene Thiourea
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Ajqust, 1988
II. GENERAL INFORMATION AND PROPERTIES
Ethylene thiourea (ETU) is no longer used in canmerce but is a canmon
degradation product of the ethylene bisdithiocarbamate (EBDC) pesticides.
Although the toxicity of ETU may be similar to the toxic effects observed
with the EBDCs, the One-day, Ten-day, Longer-term and Lifetime HAs for ETU
should not necessarily be considered protective of exposure to individual
EBDCs at this time. The mechanisms of toxicity for these substances are
still under evaluation.
CAS No. 96-45-7
Structural Formula
H
2-Imidazolidinethione
Synonyms
° ETU
Uses
0 Degradation product of several EBDC pesticides.
Properties
Chemical Formula
Molecular Weight
Hiysical State (25°C)
Boiling Ibint
Melting Paint
Density
\fopor Pressure
Specific Gravity
Vfater Solubility (30°C)
Log Octanol/Water ifertition
C3H6N2S
102.2
Wiite crystals
203°
20 a/L
Coefficient
Taste Threshold
Odor Threshold
Occurrence
° ETU was not found in sampling performed at 264 ground water stations,
according to the STORET database (STORET, 1988).

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Environmental Fate
° Ethylene thiourea can be deqraded by photolysis (U.S. EPA, 1982).
# 14C-Ethylene thiourea was intermediately mobile (Rf 0.61) to very
mobile (Rf 1.00) in muck and sandy loam soils, respectively, as determined
by soil TLC (U.S. EPA, 1986a). Ajsorption was correlated to organic
matter. Following 6 days of.incubation in dry silty clay loam soil,
ETU residues were inmobile; however, ETU residues subjected to a
wet-dry cycle were slightly mobile (Rf 0.2).
° Levels of ETU (purity unspecified) declined at an unspecified rate in
sand, with a half-life of 1-6 days (U.S. EPA, 1986a). Concentrations
of ETU declined frcm 220 ppra at day 0 to 116 ppm by day 1 and 86 ppm
by day 6.
° Mancozeb has been shown to have a half-life of less than 1 day in
sterile voter before degrading to ETU (U.S. EPA, 1982). The ethylene
bisdithiocarbamates (EBDCs) are Generally unstable in the presence of
moisture and oxygen, and the EBDCS decompose rapidly in water as well
as in biological systems (U.S. EPA, 1982).
0 The EBDCs decompose rapidly in water. Mancozeb has been shown to have
a half-life of less than 1 day in sterile water before degradinq to
ETU (U.S. EPA, 1982).
° Riotolysis is a major degrading pathway for ETU (U.S. EPA, 1982).
III. PHARMACOKINETICS
Absorption
0 Allen et al. (1978) reported a very high rate of absorption of l^C-ETU
gastrically administered at 40 mg/kg to female rhesus monkeys and
female Sprague-E&wley rats. In both species, feces accounted for less
than 1.5% of the excreted radioactivity at 48 hours after administration.
° Absorption was also high in male Sprague-E&wley rats orally administered
14c-ETU at 4 mgAg» with 82.7% of the total administered dose detected
in the urine at 24 hours (Iverson et al., 1980).
Distribution
° Allen et al. (1978) reported that in rhesus monkeys administered
l^c-ETU at 40 mgAg by gastric intubation, total tissue distribution
at 48 hours was apnroximately 25% of the administered dose; apDroximately
half of that was concentrated in muscle, with measurable amounts
noted in blood, skin and liver. In Sorague-C&wley rats, however,
total tissue distribution was less than 1% of the administered dose.
° Except in the thyroid, ETU was not found to accumulate in rats qiven
an oral dose (amount not specified) (U.S. EPA, 1982). Up to 80% of the
absorbed dose was eliminated in the urine 24 hours after administration.

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Metabolism
0 Iverson et al. (1980) identified the 24-hour urinary metabolites of
l^c-ETU orally administered to male Sprague-Dawley rats at 4 mg/kq.
Imidazoline was present at 1.9% of the total recovered dose, imidazolone
at 4.9%, ethylene urea at 18.3% and unchanged ETU at 62.6%. In female
cats, intravenous (iv) administration of this dose resulted in uncharged
ETU present in the urine at only 28% of the total recovered dose, with
S-methyl ETU at 64.3% and ethylene urea at 3.5%.
0 One hundred percent of the ETU (dose not specified) fed to mice was
recovered rapidly (time not specified) with 50% recovered in the
urine (U.S. EPA, 1982). Of the urinary products, 52% was unchanqed
ETU, 12% was ethylene urea, and 37% were polar products.
0 All animals that have been tested appear to metabolize EBDCs rapidly.
ETU and ethylene bisdiisothiocyanato sulfide (EBIS) are the major
metabolites formed (U.S. EPA, 1982). Approximately 7% of an EBDC
dose is converted to CTU in vivo in the rat and 2% in the mouse
(Nelson, 1987; Jordan and Neal, 1979).
Excretion
° Allen et al. (1978) reported that 48 hours after qastric admini-
stration of l^C-ETU at 40 mgAg to rhesus monkeys, approximately 55%
of the administered dose was detected in the urine and 0.5% in the
feces. In Sprague-Dawley rats dosed identically, 82% was recovered
in the urine and 1.3% in the feces.
0 Iverson et al. (1980) reported that 82.7 and 80.6% of the total
radioactivity of a single 4-mq/kg dose of ^C-ETU was eliminated in the
24-hour urine of orally treated male Sprague-Dawley rats and iv-treated
female cats, respectively.
HEALTH EFFECTS
Humans
0 No suitable information was found in the available literature on the
health effects of ETU in humans.
Animals
Short-term Exposure
0 The acute oral LD50 for ETU is 1,832 mg/kg in rats (U.S. EPA, 1982).
0 Graham and Hansen (1972) measured ^lj uptake in male Osborne-Mendel
rats administered ETU (purity not stated) in the diet at 50, 100, 500
or 750 ppm for various time periods (e.g., 30, 60, 90 or 120 days).
Assuminq that 1 ppm in the diet of younger rats is equivalent to
approximately 0.1 mgAg/day (Lehman, 1959), these levels correspond

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August, 1988
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to doses of about 5, 10, 50 or 75 mg/kg/day. Four hours after the
injection of 131I, uptake was decreased significantly in rats that had
ingested ETU at 500 or 750 ppm for all time periods. At 24 hours after
131i injection, uptake was significantly decreased in rats that had
ingested 100, 500 or 750 ppm for all time periods. Histologically,
the thyroid glands of rats ingesting ETU at approximately 5.0 mg/kg,
the No-Cfciserved-Adverse-Effect Level (NDAEL) for this study, were not
different from these of control rats. There was slight hyperplasia
of the thyroid in rats given 100 ppm (10 mg/kg/day). At doses of 500
or 750 ppm (50 or 75 mg/kg/day), the thyroid had moderate to marked
hyperplasia.
° In an 8-day maximum tolerated dose (MTD) study by Plasterer et al.
(1985), dose levels of 0, 75, 150, 300, 600 and 1,200 mgAo ETU were
given by gavaqe to mice (10/group, sex not specified). Body weiqht
and mortality were evaluated. No significant effects were noted on
body weight at the end of the eighth day. Based on mortality, ETU was
considered moderately toxic by the authors. An MTD of 600 mgAd was
determined.
° In a study by Freudenthal et al. (1977), ETU (>95% pure) was fed
to rats (20/sex/group) in the diet at levels of 0, 1, 5, 25, 125 or
625 ppm for 30 days. Assuming that 1 ppm in the diet of a youno rat
is equivalent to 0.1 mgAg (Lehman, 1959), these levels correspond to
doses of about 0, 0.1, 0.5, 2.5, 12.5 or 62.5 mqAq* Thyroid function,
food consumption, body weight gain and histopathology were assessed
in the animals, tets in the 625-ppm qroups showed signs of toxicity
after 8 days of exposure. Hair loss, dry skin, increased salivation
and decreased food consumption and body weight gain were observed.
Other effects noted in the 625-ppm dose group were decreased iodine
uptake and percent triiodothyronine (T3) bound to thyrcglobulin.
Thyroid-stimulating hormone (TSH) was increased, and T3 and thyroxine
(T4) decreased in the 625-ppm dose group. Thyroid hyperplasia was also
noted in this group. Aiimals exposed to 125 ppm exhibited increased
TSH; decreased T4, and thyroid hyperplasia. Other thyroid parameters
were not affected. Based on the absence of adverse effects in rats
exposed to 25 ppm or less after 30 days, a NDAEL of 25 ppm (2.5 mg/kg)
was identified.
0 Arnold et al. (1983) shewed that the thyroid effects of ETU (purity
not stated) administered in the diet for 7 weeks to male and female
Sprague-Dawley rats were reversible vtfien ETU was removed from the
diet. Dose-related significant decreases in body weight and increases
in thyroid weight were observed in all treated animals, starting at
dose levels of 75 ppm (approximately 7.5 mgAg/day based on Lehman,
1959). This dose was identified as the lowest-Observed-Adverse-Effect
Level (LQAEL) for this study.
0 In a 60-day study, which was a continuation of the above study by
Freudenthal et al. (1977), 14/40 rats in the 625-ppm group died.
Thyroid hyperplasia and altered thyroid function were observed in
the two high-dose groups. Thyroid hyperplasia was also observed in
the 25-ppm group. This effect, however, was not observed in this

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dose group when exposure was continued to 90 days. Thus, the NOAEL
for this study is presumed to be 25 ppm, or 2.5 mgAg*
Dermal/Ocular Effects
0 No information was found in the above literature on the dermal/ocular
effects of ETU.
Long-term Exposure
0 Freudenthal et al. (1977) described alterations in thyroid function
and changes in thyroid morphology when Sprague-Dawley rats were
administered ETU (96.8% pure) in the diet at levels of 1 to 625 ppm
(approximately 0.1 to 62.5 mgAg/day based on Lehman, 1959) for up to
90 days. The NOAEL was reported to be 19.5 mg/kg/day at week 1 and
12.5 mgAg/day at week 12.
• Graham and Hansen (1972) measured 131I uptake in male Osborne-Mendel
rats administered ETU (purity not specified) in the diet at 50, 100,
500 or 750 ppm for up to 120 days. Assuming that 1 ppm in the diet
of older rats is equivalent to aoproximately 0.05 mg/kg/day (Lehman,
1959), these dosages are equivalent to approximately 2.5, 5, 25 and
37.5 mgAg/day. Four hours after the injection of radioactive iodine,
uptake was decreased significantly in rats ingesting ETU at 500 or
' 750 ppm (25 or 37.5 mgAg/day) for all feeding periods. At 24 hours
after 13*1 injection, uptake was significantly decreased in rats
ingesting the 100-, 500- and 750-ppm doses for all feeding periods.
Histologically, the thyroid glands of rats ingesting ETU at approximately
2.5 mg/kg, the NDAEL for this study, were not different fran those of
control rats. Ihere was slight hyperplasia of the thyroid in rats
given 100 ppm (5 mg/kg/day). At doses of 500 or 750 ppm (25 or 37. 5
mgAg/day), the thyroid had moderate to marked hyperplasia.
0 The thyroid appears to be the primary target organ for ETU toxicity
in longer-term exposure studies. (Sraham et al. (1973) measured
131i uptake in male and female Charles River rats fed ETU (purity
not specified) in the diet at 0, 5, 25, 125, 250 or 500 ppm for up to
12 months. Assuming that 1 ppm in the diet of older rats is equivalent
to approximately 0.05 mg/kg/day (Lehman, 1959), these levels corresTOnd
to doses of about 0.25, 1.25, 6.25, 12.5 or 25 mgAg/day. Adverse
effects were noted at 2, 6 and 12 months. At 12 months, significant
decreases in body weight and increases in thyroid weight were seen at
the 125-, 250- and 500-ppm levels. Ujptake of 13*1 was significantly
decreased in male rats after 12 months at 500 ppm, but was increased
in females. Microscopic examination of the thyroid revealed the
development of nodular hyperplasia at dose levels of 125 ppm and
higher. The NDAEL for thyroid effects in this study *as 25 pnm
(approximately 1.25 mgAg/day).
° Ulland et al. (1972) reported a dose-related increased incidence of
hyperplastic goiter in male and female rats fed ETU at 175 and 350 pnn
in their diet for 18 months (approximately 8.75 and 17.5 mg/kg/day,
based on Lehman, 1959). An increased incidence (significance not
specified) of simple goiter was also reported in all treatment groups.

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° In a 2-year study by Qraham et al. (1975)/ Charles River rats were
fed ETU (purity not specified) in the diet at 0, 5, 25, 125, 250 or
500 ppn (approximately 0.25, 1.25, 6.25, 12.5 or 25 mg/kg/day, based
on Lehman, 1959). Statistically significant (p <0.01) decreases in
body weight were observed in both sexes fed at 500 ppm. Increases
in thyroid-to-body weight ratios were apparent at 250 and 500 ppn
(p <0.01). Ihere was an increased iodine (131I) uptake at 5 ppm and
a decreased uptake at 500 ppm, as well as slight thyroid hyperplasia
at the 5- and 25-ppm dose levels (significance not stated). Based on
these results, a LOAEL for lifetime exposure of 5 ppm (0.25 mgAg/day)
was identified.
Reproductive Effects
0 Plasterer et al. (1985) administered ETU (purity not specified) by
gavage as a water slurry to CD-I mice at 600 mgAg/day on days 7 to
14 of gestation. At this dose level, maternal toxicity was not
observed but the reproductive index was significantly decreased
(p <0.05), indicating severe prenatal lethality.
0 New Zealand Wiite rabbits were dosed with ETU (100% pure) at 10, 20,
40 or 80 mgAg/day on days 7 to 20 of pregnancy (Khera, 1973).
Observed effects included an increase (p <0.05) in resorption sites
at 80 mq/kg. fb adverse effects on fetal weight or on the number of
viable fetuses per pregnancy were noted at any dose level, and no
signs of maternal toxicity were observed. Based on the results of
this study, a NOAEL of 80 mg/kg/day for maternal toxicity and a NOAEL
of 40 mg/kg/day for fetotoxicity were identified.
Developmental Effects
0 The ability of ETU to induce various adverse effects, including
teratogenicity and maternal toxicity, has been demonstrated by several
investigators using various animal models. Available data indicate
that rats are probably the most sensitive species.
0 Wiera (1973) orally administered ETU (100% pure) to Wistar rats at
daily doses of 5, 10, 20, 40 or 80 mg/kg fran 21 or 42 days before
conception to pregnancy day 15 and on days 6 to 15 or 7 to 20 of
pregnancy. Dose-dependent lesions of the fetal central nervous and
skeletal systems were produced, irrespective of the time at which ETU
was administered. Teratogenic effects seen at the two highest dose
levels included meningoencephalocele, meningorrhagia, meningorrhea,
hydrocephalus, obliterated neural canal, abnormal pelvic limb posture
with eguincvarus, micrognathia, oligodactyly* and absent, short or
kinky tail. less serious defects were seen at 20 mgAdf and at
10 mgAg there was only a retardation of parietal ossification and of
cerebellar Purkinje-cell migration. Retarded parietal ossification
was the only abnormality seen at 5 mq/kg (significance not stated),
its incidence being limited to small areas and to a few large litters.
Nd signs of maternal toxicity were observed in rats administered ETU
at 40 mgAg/day for 57 days (42 days preconception to day 15 of
gestation). Based on the results of this phase of the study, the

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NOAEL for nvaternal toxicity was 40 mq/kg/day, and the NOAEL for
developmental effects was 5 mgAg/day.
° In the same study (Khera, 1973) New Zealand White rabbits were dosed
with ETU at 10, 20, 40 or 80 mg/kg/day on days 7 to 20 of pregnancy.
Observed effects included a reduction in fetal brain:body weight
ratio at 10 and 80 mg/kg (p <0.01). Renal lesions, characterized by
degeneration of the proximal convoluted tubules, were noted micro-
scopically {dose level not specified), but there were no skeletal
abnormalities that were attributed by the authors to ETU. Ihe results
of this study are not useful for determining a NOAEL or DDAEL.
0 Ebse-related central nervous system (CNS) lesions in Wistar rat
fetuses were reported by ttiera and Iryphonas (1985). Ethylene thiourea
(>98% pure) was administered by gastric intubation at 0, 15 or 30 mg/kg
to dams on day 13 of pregnancy. Observed lesions at 30 mg/kq included
histopathologic^ changes of the CNS such as karyorrhexis in the
germinal layer of basal lamina extending frcm the thoracic spinal
cord to the telencephalon, and obliteration and duplication of the
central canal and disorganization of the germinal and mantle layers.
In the brain, the ventricular lining was fully denuded, neuroepithelial
cells were arranged in the form of rosettes and nerve cell proliferation
was disorganized. In the 15-roq/kg/day qroup, cellular necrosis was
less severe and consisted of small groups of cells dispersed in the
germinal layers of the neuraxis. tone of the dams treated with ETU
at any level in this study showed any overt signs of toxicity. Based
on the results of this study, the NOAEL for maternal toxicity was 30
mgAg and the LOAEL for developmental toxicity was 15 mg/kg.
° Sato et al. (1985) investigated the teratogenic effects of ETU (purity
not specified) on long-Evans rats exposed by gastric intubation to a
single dose of 80, 120 or 160 mg/kg on one day between days 11 and 19
of gestation. Fetal malformations were related to both the day of
administration and the dosage level. A short or absent tail was
noted, for exanple, in 100% of fetuses exposed to ETU on gestational
day 11 to 14. On day 11, a dose-dependent incidence of spina bifida
and myeloschisis with hind-brain crowding were observed. A high
incidence (48 to 87.5%, not dose-related) of macrocephaly with occipital
bossing was noted, with administration of ETU on day 12, and an almost
total incidence (96 to 100%} with administration on day 13. Other
abnormalities seen in this study were exencephaly, microcephaly and
hypognathia, and extremely high incidences (100% in many groups) of
hydroencephaly and hydrocephalus, especially associated with administration
days 14 through 19. Maternal toxicity was not addressed by the
authors. Ihe results of this study are not useful in determining
IDAELs or NDAELs for teratogenicity or maternal toxicity, but serve
instead as evidence of the kinds of developmental effects that a single
dose of ETU at 80 mgAg can induce teratogenic effects in rats.
° Khera and Iverson (1978) reported that there was no clear evidence of
teratogenicity in kittens whose mothers had been administered ETU
(purity not specified) at 5, 10, 30, 60 or 120 mgAg by gelatin capsule
for days 16 to 35 of gestation. However, fetuses from cats in a

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moribund state subsequent to ETU toxicosis (30 to 120 mq/kq dosage
groups) did show a high incidence (11/35) of malformations including
colobana, umbilical hernia, spina bifida and cleft palate. Maternal
toxicity and death were observed at dose levels of 10 mqAg and
abcwe, manifesting signs of toxicity that were delayed in onset and
characterized by progressive loss of body weight, ataxia, tremors and
hind-limb paralysis. In this study, the NDAEL for maternal toxicity
was identified as 5 mgAg/day and the NDAEL for developmental effects
was 10 mg/kg/day.
0 Chemoff et al. (1979) demonstrated the teratogenic effects of ETU
in Sprague-Dawley rats, CD-I mice and golden hamsters. The rats
were administered ETU (purity not specified) by gastric intubation
at 80 mg/kg/day on days 7 to 21 of gestation. Gross defects of the
skeletal system (micrognathia, micramelia, oligodactyly, kyphosis)
and the CNS (hydrocephalus, encephalocele), as well as cleft palate
were noted in a majority of fetuses at this dose level, tto clear
evidence of teratogenicity was seen in groups of rats administered
dose levels of 5 to 40 mgAg/day. Nd similar pattern of defects was
observed in CD-I mice dosed at 100 or 200 mgAg/day on days 7 to 16
of gestation or in golden hamsters dosed at 75, 150 or 300 mq/kg/day
on days 5 to 10 of gestation. Observations of maternal toxicity
included a marked decrease in the average weight qain of pregnant
rats dosed at 80 mg/kg/day (p <0.001). Nb significant effects were
observed in mice or hamsters. Based on the results of this study,
the NOAELs for maternal and developmental toxicity were 40 mg/kg/day
in the rat, 200 mg/kg/day in the mouse and 300 mq/kq/day in the
hamster.
0 Adverse developmental effects of orally administered ETU, including
teratogenicity and/or maternal toxicity, have been reported at 60,
100 and 240 mg/kg in rats (Khera, 1982; Teramoto et al., 1975; Ruddick
and Wiera, 1975) and at 400 and 1,600 to 2,400 mg/kg in mice (Teramoto
et al., 1980; Khera, 1984).
Mutagenicity
0 Seiler (1973) described ETU as exhibiting weak but significant
mutagenic activity in Salmonella typhimurium HIS G-46. A 2.5-fold
increase in mutation frequencies (p <0.001) was seen at intermediate
concentrations (100 or 1,000 ppm/plate), but at higher concentrations
(10,000 and 25,000 ppm) ETU was somewhat lethal to the test colonies
resulting in lower relative mutagenic indices (1.60 and 1.16,
respectively).
° Schupbach and Hurcmler (1977) reported that ETU induced mutations of
the base-pair substitution type in £3. typhimurium TA 1530 in vitro as
well as in a host-mediated assay. In the host-mediated assay, a
dcse of 6,000 mg/kg (LO5Q = 5,400 mg/kg) resulted in a sliqht but
significant increase of the reversion frequency by a factor of 2.37.
Results of a micronucleus test were negative after twofold oral
administrations of 700, 1,850 or 6,000 mq/kg to 9wiss albino mice;
it was concluded that ETU does not induce any chrcmoscmal anomalies

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in the bone marrow. Nd daninant-lethal effect was deserved after
single oral closes of 500, 1,000 or 3,500 mg/kg were qiven to male
mice.
Carcinogenicity
0 Qraham et al. (1975) reported that ETU was a follicular thyroid
carcinogen in male and female Charles River rats that were fed the
compound (purity not specified) for 2 years at dietary levels of
250 and 500 ppm (approximately 12.5 and 25 mg/kg/day based on
Lehman, 1959).
0 In a survey of several compounds for tumorigenicity, Innes et al.
(1969) reported that ETU (purity not stated) administered by diet to
two strains of specific pathoqen-free hybrid mice at a daily dosage
of 215 mg/kg/day for 18 months resulted in statistically significant
(p <0.01) increases in hepatomas (14/16 or 18/18 for males and 18/18
or 9/16 for females) and in total tumor incidence. Pulmonary tumors
and lymphomas were also investigated, but were not found to occur in
the ETU group. Ihe thyroid was not evaluated in this study. No
other dose level was tested.
0 Ebse-related incidences of follicular and papillary thyroid cancers
with pulmonary metastases and related lesions such as thyroid solid-
cell adenomas were reported in Charles River CD rats by Ulland et al.
(1972). Ethylene thiourea (97% pure) vas administered by diet for
18 months at 175 or 350 ppm folloed bv administration of a control
diet for 6 months. Assuming that 1 ppm in the diet of older rats is
equivalent to approximately 0.05 mq/kg/day (Lehman, 1959) these
levels correspond to doses of about 8.75 and 17.5 mg/kg/day. Ihe
first tumor was found after 68 weeks, and most were detected after
18 to 24 months vrfien the study was terminated. Ihe statistical
significance of the reported findings was not addressed.
V. QUANTIFICATION OF TOXIGOLOGICAL EFFECTS
Health Advisories (HAs) are generally determined for one-day, ten-day,
longer-term (up to 7 years) and lifetime exposures if adequate data are
available that identify a sensitive noncarcinogenic end point of toxicity.
Ihe HAs for noncarcinogenic toxicants are derived using the following formula:
HA = (N3AEL or IQAEL) x (BW) -	mg/L (	uq/L)
(UF) x ( I/day)
where:
NOAEL or IOAEL = No- or Lowest-Observed-Adverse-Effect Level
in mgAg bw/day.
BW = assumed body weight of a child (10 kg) or
an adult (70 kg).

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UF = uncertainty factor (10, 100, 1,000 or 10,000),
in accordance with EPA or NAS/ODW guidelines.
	L/day = assumed daily water consumption of a child
(1 L/day) or an adult (2 L/day).
One-day Health Advisory
Nd data located in the available literature were suitable for determination
of the One-day HA value. It is therefore recamended that the Ten-day HA
value for the 10-kg child (0.3 mq/L, calculated below) be used at this time
as a conservative estimate of the One-day HA value.
Ten-Day Health Advisory
The study by Freudenthal (1977) has been selected to serve as the basis
for determination of the Ten-day HA for a 10-kg child. ETU was fed to a
group of rats (20/sex/group) for up to 90 days at levels of 0, 1, 5, 25, 125
or 625 ppm (0, 0.1, 0.5, 2.5, 12.5 or 62.5 mg/kg/day assuming that 1 ppm in
the diet of a young rat equals 0.1 mq/kg/day, based on Lehman, 1959). Toxic
effects on thyroid function and morphology were observed after 30 days'
exposure to 125 pnm or greater. Nb adverse effects were noted in the 25-ppm
group (2.5 mg/kg). Developmental effects reported in other studies have been
reported in rats exposed in utero at 5 mq/kg (delayed parietal ossification)
(ttiera, 1973). The adversity ofthis effect is unclear. Wiera and Iverson
(1978) have reported maternal toxicity and death in cats exposed to 10 mq/kq.
Therefore, 2.5 mg/kg was selected as a conservative NDAEL for derivinq the
Ten-day HA.
Using the NDAEL of 2.5 mg/kg/day, the Ten-day HA for a 10-kg child is
calculated as follows:
Ten-day HA = (2.5 mqAq/day) (10 kg) = 0.25 mgA (300 uqA)
(100) (1 L/day)
vdiere:
2.5 mg/kg/day = NDAEL, based on absence of fetal or maternal toxicity
in rats exposed to ETU for 30 days.
10 kg = assumed body weight of a child.
100 = uncertainty factor, chosen in accordance with EPA
or NAS/ODW guidelines for use with a NDAEL from an
animal study.
1 L/day = assumed daily water consumption of a child.
Longer-term Health Advisory
Ihe study by Qraham et al. (1973) has been selected to serve as the
basis for determination of the Longer-term HA. In a 12-month study, 131j
uptake was measured in male and female Charles River rats fed ETU (purity not
specified) in the diet at 5, 25, 125, 250 or 500 ppm for 2, 6 or 12 months.

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August, 1988
Assuming that 1 ppm in the diet of older rats is eauivalent to approximately
0.05 mg/kg/day (Lehman, 1959), these levels correspond to doses of about
0.25, 1.25, 6.25, 12.5 or 25 mgAg/day.
Adverse effects were noted at all three test intervals. At 12 months,
significant decreases in body weight and increases in thyroid weight were
seen at the 125-, 250- and 500-pom levels. Ubtake of ^"ll y^g significantly
decreased in male rats after 12 months at 500 ppm but was increased in females.
Microscopic examination of the thyroids revealed the development of nodular
hyperplasia at dose levels of 125 ppm and higher. The NOAEL for thyroid
effects in this study was 25 ppm (approximately 1.25 mg/kg/day).
The Longer-term HA for a 10-kg child is calculated as follows:
Longer-term HA = (1*25 mg/kg/day) (10 kg) = 0.125 mg/L (100 ug/L)
(100) (1 L/day)
vrfiere:
1.25 mgAg/day = NOAEL, based on absence of thyroid effects in male
rats exposed to ETU in the diet for up to 12 months.
10 kg = assumed body weight of a child.
100 = uncertainty factor, chosen in accordance with EPA
or NAS/ODW guidelines for use with a NOAEL frcm an
animal study.
1	L/day = assumed water consumption by a 10-kg child.
The Longer-term HA for a 70-kg adult is calculated as follows:
Longer-term HA = 1.25 mgAg/day) (70 kg) = 0.44 mgA (400 ugA)
(100) (2 L/day)
where:
1.25 mg/kg/day = NOAEL, based on absence of thyroid effects in male
rats exposed to ETU in the diet for up to 12 months.
70 kg = assumed body weight of an adult.
100 = uncertainty factor, chosen in accordance with EPA
or NAS/ODW guidelines for use with a NOAEL frcm an
animal study.
2	l/day = assumed daily water consumption by an adult.
Lifetime Health Advisory
Ihe Lifetime HA represents that portion of an individual's total exposure
that is attributed to drinking water and is considered protective of noncar-
cinogenic adverse health effects over a lifetime exposure. The Lifetime ha

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August, 1988
is derived in a three-step process. Step 1 determines the Reference Ebse
(RfD), formerly called the Acceptable Daily Intake (ADI). The RfD is an esti-
mate of a daily exposure to the human population that is likely to be without
appreciable risk of deleterious effects over a lifetime, and is derived frcm
the NOAEL (or LOAEL), identified frcm a chronic (or subchronic) study, divided
by an uncertainty factor(s). From the RfD, a Drinking W&ter Bauivalent Level
(EWEL) can be determined (Step 2). A DWEL is a medium-specific (i.e., drinkinq
water) lifetime exposure level, assuming 100% exposure from that medium, at
vrfiich adverse, noncarcinogenic health effects would not be expected to occur.
The DWEL is derived from the multiplication of the RfD by the assumed body
weight of an adult and divided by the assumed daily water consumption of an
adult. Ihe Lifetime HA is determined in Step 3 by factoring in other sources
of exposure, the relative source contribution (RSC)., Ihe RSC frcm drinking
water is based on actual exposure data or, if data are not available, a
value of 20% is assumed. If the contaminant is classifed as a Qroup A or B
carcinogen, according to the Agency's classification scheme of carcinogenic
potential (U.S. EPA, 1986b), then caution should be exercised in assessinq
the risks associated with lifetime exposure to this chemical.
Ihe study by Qraham et al. (1975) was selected as the most appropriate
basis for the calculation of a EWEL. In this 2-year study (presumably a
continuation of the Qraham et al. (1973) study, Charles River rats were fed
ETU (purity not stated) in the diet at 5, 25, 125, 250 or 500 ppm (approxi-
nately 0.25, 1.25, 6.25, 12.5 or 25 mg/kg/day based on Lehman, 1959).
Statistically significant (p <0.01) decreases in body weight were observed
in both sexes fed at 500 ppm. Increases (p <0.01) in thyroid-to-body veiqht
ratios were apparent at 250 and 500 ppm. There was an increased iodine (*31I)
uptake at 5 and 125 ppm and a decreased uptake at 500 ppm as well as slight
thyroid hyperplasia at the 5- and 25-ppnt dose levels (statistical significance
not stated). Ihis effect is considered to be biologically significant.
Tumors were evident in animals in the 125-ppm group. Based on these results,
the LOAEL for lifetime exposure was identified as 5 ppm (approximately
0.25 mg/kg/day).
Using the D0AEL of 0.25 mq/kg/day, the EWEL is calculated as follows:
Step 1: Determination of the Reference Dose (RfD)
RfD = (0.25 mqAq/day) = 0.000025 mg/kg/day (0.03 ug/kq/day)
(1,000) (10)
where:
0.25 mg/kg/day = LOAEL, based on increased iodine intake as well as
thyroid hyperplasia in rats exposed to ETU in the
diet for 2 years.
1,000 = uncertainty factor, chosen in accordance with EPA
or NAS/ODW guidelines for use with a LOAEL from an
animal study.
10 = additional uncertainty factor to account for the
severity of effect and response at this dose level.

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August, 1988
-14-
Step 2: Determination of the Etinking water Equivalent Level (EWEL)
DWEL = (0.00003 mqAq/day) (70 kg) = 0.00105 mg/L (1 ugA)
(2 L/day)
vtfiere:
0.00003 mg/kg/day = RfD.
70 kg = assuned body weight of an adult.
2 L/day = assumed daily water consumption of an adult.
Step 3s Determination of the Lifetime Health Advisory
According to EPA's guidelines for assessment of carcinogenic risk
(U.S. EPA, 1986b), ETU is classified in Group B: Rrobable human carcinogen.
Therefore, a Lifetime Health Ajvisory is not recamended for ETU. The
estimated cancer risk level associated with lifetime exposure to ETU at
1 ug/L is approximately 4.3 x 10~®.
Evaluation of Carcinogenic Potential
0 Three studies that evaluated the carcinogenic potential of ETU were
identified. The results of these studies indicate that ETU is a-
thyroid carcinogen in rats (Gtaham et al., 1975; Ulland et al., 1972)
and increases the incidence of hepatomas as well as total tumor
incidence in mice (Innes et al., 1969).
0 Graham et al. (1975) reported ETU to be a thyroid carcinoqen in male
and female Oiarles River rats that were fed the compound (Duritv not
specified) for 2 years at dietary levels of 250 and 500 ppm (approxi-
mately 12.5 and 25 mg/kg/day in the diet of older rats based on
Lehman, 1959). At 125 ppm (approximately 6.3 mg/kg/day), ETU was a
thyroid oncogen.
° Dose-related incidences of follicular and papillary thyroid cancers
with pulmonary metastases and related lesions such as thyroid solid-
cell adenomas were reported in Charles River CD rats by Ulland et al.
(1972). Ethylene thiourea (97% pure) was administered in the diet
for 18 months at 175 and 350 ppm followed by administration of a
control diet for 6 months. Assuming that 1 ppm in the diet of older
rats is equivalent to approximately 0.05 mg/kg/day (Lehman, 1959),
these levels correspond to doses of about 8.75 and 17.5 mg/kg/6ay.
The first tumor was found after 68 weeks, and most were detected
after 18 to 24 months when the study was terminated. The statistical
significance of the reported findings was not addressed.
0 Innes et al. (1969) reported that ETU (purity not stated) administered
by diet to specific pathogen-free hybrid mice at a daily dosage of
215 mgAg/day for 18 months resulted in statistically significant
(p <0.01) increases in hepatomas and in total tumor incidence. No
other dose level was tested. (Pulmonary tumors and lymphomas vere
also investigated in this study.)

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Ethylene Thiourea
August, 1988
-15-
0 Applying the criteria described in EPA's final guidelines for assess-
ment of carcinogenic risk (U.S. EPA, 198(b), ETU may be classified in
Group B2: probable human carcinogen based on sufficient evidence
frcm animal studies.
° The EPA Carcinogen Assessment Group estimated a one-hit slope of
0.1428/tng/kg/day based on the Innes et al. (1969) study identifying
male mouse liver tumors as the sensitive sex/species end point (U.S.
EPA, 1979). An assumed consumption of 2 liters of water per day by a
70-kg adult over a lifetime results in drinking water concen-
trations of 4, 2.4 and 0.24 ug/L for 10~4, 10"* ancj io~6 cancer risk
levels, respectively.
0 Data are not available to estimate excess cancer risks using other
mathematical models.
VI. OTHER CRITERIA, GUIDANCE AND STANDARDS
0 No other data have been located for ETU.
VII. ANALYTICAL METHODS
0 Ethylene thiourea is analyzed by a nitrogen-phosphorus detector/qas
chromatographic method as described in Method #6 (U.S. EPA, 1988).
In this procedure the ETU sample is mixed with ammonium chloride and
potassium fluoride and passed through an exchange column (Extrelut).
Ihe ETU is then eluted with methylene chloride, concentrated for
exchange with ethyl acetate to a volume of 5 mL. The method describes
conditions vrtiich permit the separation and measurement of ETU by GC
with a nitrogen-phosphorus detector. This method has been validated
by a single laboratory. The estimated detection limit for ETU by
Method #6 is 5 ug/L.
VIII. TREATMENT TECHNOLOGIES
0 No data were found on the removal of ethylene thiourea frcm drinking
water by conventional treatment.
0 No data were found on the removal of ethylene thiourea frcm drinkinq
water by activated carbon adsorption. However, since ethylene thiourea
has a high solubility and is hydrophilic, treatment with activated
carbon probably would not be effective.
0 No data were found on the removal of ethylene thiourea frcm drinkinq
water by ion exchange. However, the structure of ethylene thiourea
indicates it is not ionic and thus probably would not be amenable to
ion exchange.
° No data were found on the removal of ethylene thiourea frcm drinking
water by aeration. Since vapor pressure data are unavailable, Henry's

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Ethylene Thiourea
August, 1988
-16-
Coefficient, and thus the effectiveness of aeration, cannot be
estimated. However, the high melting point and the high solubility
indicate that Henry's Coefficient would be low and that aeration or
air stripping probably would not be an effective form of treatment.

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Ethylene Thiourea
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August, 1988
REFERENCES
Allen, J.R., J.P. \fon Miller and J.L.	Seymour. 1978. Absorption, tissue
distribution and excretion of	ethylenethiourea by the Rhesus monkey
and rat. Res. Conm. Chem. E&th.	Iharmacol. 20:109-115.
Arnold, D.L., D.R. Krewski, D.B. Junkins , P.F. McGuire, C.A. Moodie and
I.C. Munro. 1983. Reversibility of ethylenethiourea-induced thyroid
lesions. Toxicol. Appl. Riarmacol. 67:264-273.
CHEMLAB. 1985. Ihe Chemical Information System, CIS, Inc. Baltimore, MD.
Chernoff, N., R.J. Kavlock, E.H. Rogers, B.D. Carver and S. Murray. 1979.
Rsrinatal toxicity of Maneb, ethylene thiourea, and ethylenebisthio-
cyanate sulfide in rodents. J. Toxicol. Environ. Health. 5:821-834.
Freudenthal, R.I., G. Kerchner, R. Etersing and R. Baron. 1977. Dietary
subacute toxicity of ethylene thiourea in the laboratory rat. J. Fnv.
Ifeth. Toxicol. 1:147-161.
Graham, S.L. and W.H. Hansen. 1972. Effects of short-term administration
of ethylene thiourea upon thyroid function of the rat. Bull. Environ.
Gontam. Toxicol. 7(1):19-25.
Graham, S.L., W.H. Hansen, K.J. Davis and'C.H. Barry. 1973. Effects of
one-year administration of ethylenethiourea upon the thyroid of the rat.
J. Agr. Food Chem. 21:324-329.
Graham, S.L., K.J. E&vis, W.H. Hansen and C.H. Graham. 1975. Effects of
prolonged ethylene thiourea ingestion on the thyroid of the rat. Food
Gosmet. Toxicol. 13:493-499.
Inrtes, J.R., B.M. Ulland, M.G. \felerio, L. Bstrucelli, L. Fishbein, E.R. Hart
and A.J. I&llotta. 1969. Bioassay of pesticides and industrial chemicals
for tumorigenicity in mice: A preliminary note. J. Natl. Cancer Inst.
42:1101-1114.
Iverson, F., K.S. Riera and S.L. Hierlihy. 1980. In vivo and in vitro
metabolism of ethylene thiourea in the rat and the cat. Toxicol. Appl.
Eharmacol. 52:16-21.
Jordan, L.W., and R.A. Neal. 1979. Examination of the in vivo metabolism of
maneb and zineb to ethylenethiorea (ETU) in mice. Bull. Environ. Contan.
Toxicol. 22:271-277.
Khera, K.S. 1973. Ethylene thiourea: teratogenicity study in rats and
rabbits. Teratology. 7:243-252.
Khera, K.S. 1982. Reduction of teratogenic effects of ethylenethiourea in
rats by interaction with sodium nitrite in vivo. Food Cosmet. Toxicol.
20:273-278.

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Ethylene Thiourea
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August, 1988
Khera, K.S. 1984. Ethylenethiourea-induced hindpaw deformities in mice and
effects of metabolic modifiers on their occurrence. J. Toxicol. Environ.
Health. 13:747-756.
Khera, K.S., and F. Iverson. 1978. Toxicity of ethylenethiourea in pregnant
cats. Teratology. 18:311-314.
Wiera, K.S., and L. Tryphonas. 1985. Nerve cell degeneration and progeny
survival following ethylenethiourea treatment during pregnancy in rats.
Neurol. Toxicol. 6:97-102.
Lehman, A.J. 1959. Appraisal of the safety of chemicals in foods, druqs and
pesticides. Published in the Assoc. of Food and Drug Officals of the U.S.
Meister, R., ed. 1983. Farm chemicals handbook. Willoughby, OH: Meister
Publishing Co.
Nelson, S.S. 1987. Bioconversion of mancozeb to ETU in rats. Rohm and Haas
Technical Report No. 31C-87-24. Submitted to EPA. MRID 40301101.
Plasterer, M.R., W.S. Bradshaw, G.M. Booth, M.W. Carter, R.L. Schuler and
B.D. Hardin. 1985. Developmental toxicity of nine selected compounds
following prenatal exposure in the mouse: Naphthalene, p-nitrophenol,
sodium selenite, dimethyl phthalate, ethylenethiourea, and four glycol
ether derivatives. J. Toxicol. Ehviron. Health. 15:25-38.
Ruddick, J.A. and K.S. Wiera. 1975. Ifettern of anomalies following single
oral doses of ethylenethiourea to pregnant rats. Teratology. 12:277-282.
Sato, K., N. Nakagata, C.F. Hung, M. Vfeda, T. Shimoji and S. Ishii. 1985.
Transplacental induction of myeloschisis associated with hindbrain
crowding and other malformations in the central nervous system in Long-
Evans rats. Oiild. Nerv. Syst. 1:137-144.
Schupbach, M. and H. Hummler. 1977. A comparative study on the mutagenicity
of ethylenethiourea in bacterial and mammalian test systems. Mit. Res.
56:111-120.
Seiler, J.P. 1973. Ethylenethiourea (ETU), a carcinogenic and mutaqenic
metabolite of ethylenebis-dithiocarbamate. Hit. Res. 26:189-191.
STORET. 1988. STORET Vfeter Quality File. Office of Vfeter. U.S. Environ-
mental Protection Agency (data file search conducted in May, 1988).
Teranoto, S., R. Saito and Y. Shirasu. 1980. Teratogenic effects of combined
administration of ethylenethiourea and nitrite in mice. Teratology.
21:71-78.
Ulland, B.M., J.H. Wteisburger, E.K. Wsisburger, J.M. Rice and R. Cypher. 1972.
Brief carmunication: Ihyroid cancer in rats from ethylene thiourea intake
J. Natl. Cancer Inst. 49:583-584.

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Ethylene Thiourea
August, 1988
-19-
U.S. EPA. 1979. U.S. Environmental Rrotection Agency. Ihe Carcinogen
Assessment Group's Risk Assessment on Ethylene Bisdithiocarbamate.
U.S. EPA. 1982. U.S. Environmental Protection Agency. Ethylene Bisdithio-
carbamate Pesticides. Etecision Ebcument. Final Resolution of Rebuttable
Presumption Against Registration. Office of Pesticide Programs.
U.S. EPA. 1986a. U.S. Environmental Protection Aqency. Final report.
Task 2: Envirorroental Fate and Exposure Assessment. June 10.
U.S. EPA. 1986b. U.S. Environmental Protection Aqency. Guidelines for
carcinogen risk assessment. Fed. Reg. 51(185):33992-34003. September 24.
U.S. EPA. 1988. U.S. Environmental Protection Agency. Method #6 - Determi-
nation of Ethylene Thiourea (ETU) in Ground v&ter by Gas Chromatography
with a Nitrogen-FhosDhorus Detector. Available fran U.S. EPA's Environ-
mental Monitoring and Support laboratory, Cincinnati, OH 45268.
Windholz, M., S. Budavari, R.F. Blumetti and E.S. Otterbein, eds. 1983. The
Merck Index, 10th ed. Rah way, N.J.: Merck and Co., Inc.

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