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Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Pre-Guideline and non GLP study, study is sufficiently documented and meets generally accepted scientific principles

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
Embryo- and Fetotoxicity of Inhaled Methyl Ethyl Ketone in Rats
Author:
Deacon MM et al.
Year:
1981
Bibliographic source:
Toxicology And Applied Pharmacology 59, 620-622
Reference Type:
study report
Title:
Unnamed
Year:
1979
Report date:
1979

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
GLP compliance:
no
Limit test:
no

Test material

Constituent 1
Chemical structure
Reference substance name:
Butanone
EC Number:
201-159-0
EC Name:
Butanone
Cas Number:
78-93-3
Molecular formula:
C4H8O
IUPAC Name:
butan-2-one
Details on test material:
- Name of test material (as cited in study report): methyl ethly ketone
- obtained from Exxon Chemical Company, Technology Department, 1600 E. Linden Ave., Linden, NJ 07036
- Analytical purity: > 99 %
- Impurities (identity and concentrations): sec butyl alcohol < 0.4 %., sec butyl ether 0.005 %
- Lot/batch No.: 36799
- Storage condition of test material: in a 55-gallon metal drum for approximately five months

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Spartan Research Animals, Haslett, Michigan
- Age at study initiation: adult animals
- Weight at study initiation: approx. 250 g

- Housing: individually in stainless steel, wire-bottom cages
- Diet (ad libitum): commercial laboratory chow (Ralston Purina Comp~ny, St. Louis, Missouri)
- Water (ad libitum, except in the exposure chambers): tap water


ENVIRONMENTAL CONDITIONS
- Temperature: 70 +/- 3 °F
- Humidity (%): 45 +/- 5 %
- Photoperiod (hrs dark / hrs light): 12

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Vehicle:
unchanged (no vehicle)
Details on exposure:
The inhalation exposures were conducted under dynamic airflow conditions in glass and stainless steel chambers with a volume of 0.16 m³.
The chamber atmosphere was generated by metering MEK at a calculated rate with a precision syringe pump into a vaporization flask and then into the airstream being drawn into the exposure chamber. Nominal concentrations were calculated as the ratio of the amount of MEK used to the total chamber airflow.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
The chamber concentrations were monitored 15 min/hr/chamber using a Miran I Variable Filter Infrared Analyzer at a wavelenght of 8.5 µm.
Details on mating procedure:
The animals were bred by the supplier; the day on which sperm were found in the vaginal smear was considered day zero of pregnancy. Within three days after breeding, the animals were transported to the Toxicology Research Laboratory
Duration of treatment / exposure:
days 6 through 15 of gestation
Frequency of treatment:
7 hours/day
Duration of test:
termination of the test on day 21 of gestation
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0, 400, 1000, 3000 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
0, 412±31, 1002±16, 3005±49 ppm
Basis:
analytical conc.
(time weighted ean ± SD)
No. of animals per sex per dose:
- 25 per dose exposed to MEK
- 35 (control animals exposed to filtered room air)
Control animals:
yes

Examinations

Maternal examinations:
Animals were observed daily throughout gestation for indications of toxicity from the test material. The body weights of bred rats were recorded on days 6, 7, 8, 9, 10, and 16 of gestation. In addition, maternal body weights and the weight of the maternal liver were recorded at the time of cesarean section, day 21 of gestation. Food and water consumption were measured during the entire experimental period at 3 day intervals
Ovaries and uterine content:
On day 21 of gestation, the bred rats were sacrificed by carbon dioxide inhalation. The uterine horns were exteriorized through a midline incision in the abdominal wall, and the number and position of live, dead, and resorbed fetuses were recorded. The uteri of apparently non-pregnant animals were stained with a 10 % solution of sodium sulfide and examined for evidence of early resorption sites ; this was done solely for the purpose of determining the pregnancy rate, not the incidence of resorptions.
Fetal examinations:
After being weighed, measured (crown-rump length) and sexed, all fetuses were examined for external alterations and cleft palate. One-third of the fetuses of each litter, selected by a table of random numbers, were examined immediately under a low power microscope for evidence of soft-tissue alterations ; the heads of these fetuses were placed in Bouin's solution and examined by the free-hand razor section technique of Wilson (1965). All of the pups in each litter were placed in 95 % ethanol, eviscerated, and cleared and stained with alizarin red-S for subsequent examination of skeletal alterations.
Statistics:
The frequency of alterations and resorptions among litters and the fetal population was evaluated by the Wilcoxon test as modified by Haseman and Hoel (1974). Other incidence data were analyzed statistically by the Fisher exact probability test (Siegel, 1956). Analyses of rotal body weights and body measurements, maternal weight ga1ns, and maternal liver weights and food and water consumption data ware made by an analysis of variance. Group means were compared to control values using Dunnett's test (Steel and Torrie, 1960). The level of significance chosen for all cases was p<0.05.
Indices:
see above
Historical control data:
no

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:yes. Remark: Slight maternal toxicity (temporarily decreased weight gain and increased water consumption)

Details on maternal toxic effects:
Exposure of bred rats to 400, 1000, or 3000 ppm of MEK for 7 hours per day had no significant effect on the dam's appearance or demeanor. Maternal body weights were significantly decreased on day 16 and a decrease in maternal body weight gain occurred on days 10 through 15 in rats exposed to 3000 ppm of MEK. No changes were observed in maternal liver weight, either absolute or relative. The food consumption of pregnant rats was not altered by inhalation of any dose level of MEK. Water consumption of rats exposed to the high dose level of MEK was significantly increased on days 15 through 17 of gestation. There was no effect on the number of dams which were pregnant or on the number of maternal deaths among any of the rats exposed to MEK. Inhalation of 400, 1000, or 3000 ppm MEK did not significantly affect the incidence of pregnancy, the average number of live fetuses per litter, or the incidence of resorptions in rats.

Effect levels (maternal animals)

Dose descriptor:
NOAEC
Effect level:
1 000 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
No external or soft-tissue alterations were observed among fetuses at any of the exposure levels at an incidence which was statistically significantly different from the control incidence. Two fetuses, one each at the control and at the 3000 ppm levels were observed to have multiple malformations which included acaudia, imperforate anus, short trunk, ectopic ovaries and multiple skeletal defects. Diaphragmatic hernia was observed in one controlfetus, and one fetus at 400 ppm was observed to have a rotated and adducted forepaw. Single fetuses at the 1000 and 3000 ppm exposure levels were observed to have the right carotid and right subclavian branching from the aorta with the innominate appearing to be missing. When considered collectively no significant increase in the incidence of major malformations in fetuses exposed to MEK was observed.

Examination of the skeletons revealed statistically significant changes in the incidence of several minor skeletal variants. The incidence of delayed ossification of interparietal bones of the skull was significantly decreased when compared to controls at the 3000 ppm exposure level. A significant increase in the incidence of extra lumbar ribs and in the occurrence of delayed ossification of cervical centra was also noted at this exposure level, but not at the two lower exposure levels. The single control and 3000 ppm exposed fetuses which exhibited acaudia, imperforate anus, shore trunk and ectopic ovary were observed to have multiple vertebral defects or multiple skeletal defects, respectively. Multiple vertebral defects, observed in the control fetus, included missing ribs, vertebra, and centra. Assymetric pelvis, missing ribs, vertebrae and centra, and fused ribs composed the multiple skeletal defects seen in the fetus exposed to 3000 ppm MEK. These malformations are seen at a low incidence among the control population and the low incidence of skeletal malformations seen in this study are not considered to be of toxicologic significance, when compared with historic control data.

Effect levels (fetuses)

open allclose all
Dose descriptor:
NOAEC
Effect level:
3 000 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: teratogenicity
Dose descriptor:
NOAEC
Effect level:
3 000 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: embryotoxicity
Dose descriptor:
NOAEC
Effect level:
1 000 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: fetotoxicity

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Any other information on results incl. tables

Incidence of fetal alterations among rats inhaling methyl ethyl ketone

 

 

Methyl Ethyl Ketone (ppm)a

 

 

 

 

0

400

1000

 

3000

 

 

 

 

 

 

 

 

No. fetuses examined / No. litters examined

 

 

 

 

 

 

External an skeletal examination

329/26

238/19

226/19

231/18

Soft tissue examination

111/26

80/19

78/19

79/18

Bones of the skull

218/26

157/19

148/19

150/18

 

 

 

 

 

 

 

No. of fetuses (litters) affected

 

 

 

 

 

 

External examination

 

 

 

 

Multiple defects

1 (1)b

0

0

1 (1)c

Rotated and adducted forepaw

0

1 (1)

0

0

Soft tissue examination

 

 

 

 

Innominate artery missing

0

0

1 (1)

1 (1)

Skeletal examination

 

 

 

 

Skull, delayed ossificationd

26 (14)

19 (10)

23 (8)

6 (4)e

Ribs, extrad

2(2)

0

0

7 (6)e

Cervical centra, delayed ossificationd

83 (22)

58 (15)

44 (16)

114 (18)e

 

 

 

 

 

Total major malformations

1 (1)

1 (1)

1 (1)

2 (2)

 

a : Rats inhaled 0, 400, 1000 or 3000 ppm of methyl ethyl ketone from days 6 to 15 of gestation.

b : This fetus exhibited: acaudia, impetforate anus, short trunk. ectopic ovary. diaphragmatic hernia. and multiple vertebral defects,

including missing ribs, vertebrae, and centra.

c: This fetus exhibited: acaudia, imperforate anus, short trunk, ectopic ovary and multiple skeletal defects including asymmetric pelvis, fused ribs, and missing ribs.

vertebrae, and centra.

d: This alteration was considered to be a skeletal variant and was not included in the calculation of the total malformed fetuses.

e: Significantly different from control value by a modified Wilcoxon test. p

Applicant's summary and conclusion

Executive summary:
In a developmental toxicity study (Deacon, 1981) similar to OECD Guideline 414, methyl ethyl ketone (99.6 %) was administered to female Sprague-Dawley rats by inhalation at dose levels of 0, 400, 1000 or 3000 ppm for 7 hours a day from days 6 through 15 of gestation. Slight maternal toxicity, as evidenced by temporarily decreased weight gain and increased water consumption, was observed among rats exposed to 3000 ppm MEK. No embryotoxic effects were noted. The only effect observed in fetuses was a slightly but statistically significantly increased incidence of two minor skeletal variants (extra ribs and delayed ossification cervical centra) among litters from animals exposed to 3000 ppm MEK. In summary, MEK did neither cause an embryotoxic nor a teratogenic response in rats at exposure levels up to concentration of 3000 ppm. Slight fetal toxicity and maternal toxicity was seen at this concentration. Thus, 1000 ppm represent the NOAEC for maternal toxicity and fetotoxcity and 3000 ppm the NOAEC for embryotoxicity and teratogenicity.