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Toxicological information

Repeated dose toxicity: oral

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Administrative data

Endpoint:
sub-chronic toxicity: oral
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
weight of evidence
Study period:
1990
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Well reported guideline study.

Data source

Referenceopen allclose all

Reference Type:
study report
Title:
Unnamed
Year:
2002
Reference Type:
study report
Title:
Unnamed
Year:
1990
Reference Type:
study report
Title:
Unnamed
Year:
1998

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity in Rodents)
Deviations:
not specified
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Details on test material:
EC Number 203-962-1
EC Name 2-(2-(2-methoxyethoxy)ethoxy)ethanol
CAS Number 112-35-6
Molecular formula C7H16O4
IUPAC Name 2-[2-(2-methoxyethoxy)ethoxy]ethanol
Trade names: TGME, triethylene glycol methyl ether, triethylene glycol monomethyl ether
Synonyms Ethanol, 2- 2-(2-methoxyethoxy)ethoxy -
Ethanol, 2-[2-(2-methoxyethoxy)ethoxy]-
Molecular formula C7H16O4
Molecular weight range 164.1995
SMILES notation COCCOCCOCCO
InChI InChI=1/C7H16O4/c1-9-4-5-11-7-6-10-3-2-8/h8H,2-7H2,1H3

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
Animals were uniquely identified by a toe clip procedure.

TEST ANIMALS
- Source: Charles River Breeding Laboratory Inc., Portage, MI.
- Age at study initiation: 8 weeks at first dose.
- Weight at study initiation: 291.3 - 339.7 g (males); 177.4 - 218.0 g (females)
- Housing: individually in stainless-steel cages mounted in a stainless-steel Maxi-Rack. During the period of motor activity testing they were housed in chamber C, a modified Relocatable Containment System® in room 164 of the CHF Building of BRRC. A layer of Deotized Animal Cage Board@ was kept under each cage and changed at least three times per week.
- Diet: Ground Purina Certified Rodent Chow #5002 was available ad libitum except during periods of motor activity testing.
- Water: ad libitum except during motor activity tests on days 1, 30, 60 and 90 after initiation of TGME treatment. Water was provided by Nalgene bottles.
ENVIRONMENTAL CONDITIONS
Room temperature and relative humidity were monitored continuously by a Cole-Parmer Hygrothermograph Seven-Day Continuous Recorder, Model #8368-00.
- Temperature: 66 – 77°F
- Humidity: 40 – 70%
- Photoperiod: 12 hour light/12 hour dark cycle. (0500 – 1700 light)
- Other: White noise levels in 164C were routinely maintained between 59 dBA and 63 dBA during motor activity testing sessions. White noise generated during the motor activity test sessions was monitored with a Realistic® Sound Level Meter, Model #33-1050 and a Varian strip chart recorder, Model #A25 or a Graphtec® Microservo SR6402 chart recorder. The sound level meter was calibrated daily with a GenRad® Sound-Level Calibrator, Model #GR1562.

IN-LIFE DATES: From: July 24, 1989 To: October 25, 1989

Administration / exposure

Route of administration:
oral: drinking water
Vehicle:
water
Details on oral exposure:
PREPARATION OF DOSING SOLUTIONS: The drinking water solutions were prepared by direct addition of TGME to tap water. A concentrated solution was prepared from which the dosing solutions were made to help facilitate distribution of the test material with a minimum of mixing.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Samples of the actual dosing solutions were taken and analyzed for TGME concentration (prior to being administered to the animals) during study Weeks 1 through 4. In subsequent weeks, the samples were stored refrigerated, and one sample from each preparation (concentrations being selected sequentially) were analyzed in Weeks 8 and 13 with one control.
Duration of treatment / exposure:
90 days.
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0, 0.42, 1.24, 4.3 TGME/kg/day (males); 0, 0.42, 1.29, 4.1 TGME/kg/day (females)
Basis:
actual ingested
Remarks:
Doses / Concentrations:
0, 0.4, 1.2, 4.0 mg/kg/day
Basis:
other: (Target doses)
No. of animals per sex per dose:
Each dosage group was randomly divided into two blocks. Block 1 and Block 2.
Block 1: 7 males/7 females (control and mid-dose); 8 males/8 females (low dose and high dose)
Block 2: 8 males/8 females (control and mid-dose); 7 males/7 females (low dose and high dose).
Control animals:
yes
Details on study design:
- Dose selection rationale: Doses were selected based on a 14-Day dose range-finding study conducted at Bushy Run Research Center (BRRC Project Report '52-606). Dose levels were chosen to produce toxicity or clear behavioral effects at the high dose and graded dose dependent effects in at least two of the doses tested including the high dose.
- Rationale for animal assignment: Animals were assigned to test groups based on body weight, by a computer generated non-stratified randomization procedure. Once rats were randomized into dosage groups, each dosage group was randomly divided into two blocks. Block 1 contained 7 male and 7 females from each of the control and mid-dose treatment groups and 8 males and 8 females from each of the low-dose and high-dose treatment groups. Block 2 contained 8 males and 8 females from each of the control and mid-dose treatment groups and 7 males and 7 females from each of the low-dose and high-dose treatment groups. The first day of exposure to test drinking water solutions was Monday, July 24, 1989 for Block 1 animals and Tuesday, July 25, 1989 for Block 2 animals. Rats not selected for the study were removed from the room.
Positive control:
no

Examinations

Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily
- Cage side observations checked included mortality.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Weekly

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION:
- Yes, weekly
WATER CONSUMPTION AND COMPOUND INTAKE: Yes
- Time schedule for examinations: Day 1 and weekly thereafter. Due to the size of the water bottles, it was necessary to collect full and empty water bottle weights twice a week, but these weights were combined and reported on a weekly interval basis.

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: weekly
- Battery of functions tested:
- (motor activity) Ten animals/sex/group were evaluated for neurobehavioural function using a functional observational battery prior to their first exposure, on the day after their first overnight exposure to TGME, and on the 8th, 15th, 30th, 60th, and 90th day after their first day of exposure to TGME.
Sacrifice and pathology:
GROSS PATHOLOGY: Yes, all animals scheduled for neuroanatomic pathology were given a complete gross necropsy examination, and the following additional tissues were saved: Lungs, liver, kidneys, testes/ovaries, spleen and adrenals.
HISTOPATHOLOGY: Yes, Forebrain (cross sections), center of the cerebrum (cross sections), center of the midbrain (cross sections), cerebellum and pons (cross sections), medulla oblongata (cross sections), spinal cord (cervical and lumbar; cross and longitudinal sections), dorsal root ganglia (longitudinal sections), dorsal and ventral root fibers (longitudinal sections), proximal sciatic nerve (cross and longitudinal sections below the knee), tibial nerve (cross and longitudinal sections below the knee).
Other examinations:
See also IUCLID 7.9.1 Neurotoxicity - BRRC (1990)
Statistics:
The accepted level of Type 1 error rate was set to an approximate overall value of 0.05 within separate test domains, but individual p values were reported without correction for multiple testing. To reduce the increased false positives associated with repeated significance testing, the correction procedure suggested by Mantel (1980) was used when testing for overall significance. Evaluations were divided into 8 domains; body weights, body weight gains, food consumption, water consumption, functional observational battery, motor activity, organ weights, and microscopic diagnosis. The critical level of significance was adjusted for each test domain by dividing the overall critical level of significance for the test domain (α = 0.05) by the square root of the number of significance tests within the test domain. These levels were subsequently rounded up to either 0.005 or 0.01. All statistical tests, except the frequency comparisons for pathology findings were performed using BMDP Statistical Software (Dixon, 1985 and 1988). The frequency data tests for pathology findings are described by Sokal et al. (1969).

The data for water consumption, food consumption, body weight, body weight gain, and organ weights were intercompared for the dose and control groups by use of Levene's test for homogeneity of variances, by analysis of variance, and by pooled variance t-tests. The t-tests were used, if the analysis of variance was significant, to delineate which groups differ from the control group. If Levene's test indicated heterogeneous variances, the groups were compared by an analysis of variance for unequal variances followed, if necessary, by separate variance t-tests.

Results and discussion

Results of examinations

Body weight and weight changes:
effects observed, treatment-related
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Water consumption and compound intake (if drinking water study):
effects observed, treatment-related
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
effects observed, treatment-related
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Details on results:
CLINICAL SIGNS AND MORTALITY
There were no treatment-related clinical signs of toxicity observed for males and females in this study. One female from the high-dose treatment group died on study day 37.

BODY WEIGHT AND WEIGHT GAIN
Statistically significant decreases in mean body weight and body weight gain were observed for males in the high-dose treatment group throughout the study. Body weight decrement for males in the high-dose treatment group became more pronounced as the study progressed and mean body weight was ultimately 123 grams less than the mean for the control group at the end of the study. Mean body weight and body weight gain for males in the mid dose treatment group also tended to be decreased (2 to 8%) compared to the mean for the control group. Statistically significant decreases in mean body weight gain were observed for females in the high-dose treatment group at several measurement periods. Decreases in body weight gain were observed as early as the Week 0 to 1 measurement period (9% decrease) and lasted throughout the study (22% decrease for the Week 0 to 13 measurement period). Apparent dose-related decreases in body weight gain were observed for females in the low-dose treatment group beginning at Week 5 (3 to 8%) and in the mid-dose treatment group for most of the study (6 to 13%). Small dose-related decreases in mean body weight were observed for females in all three treatment groups. These changes were not statistically different from the control group.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study)
Statistically significant decreases in mean food consumption were observed for males and females in the high-dose treatment group through most of the study. The decreases observed were generally in the range of 10 to 23% for males and 8 to 15% for females. In addition, a tendency for decreased mean food consumption for males in the mid-dose treatment group throughout the study (generally 3 to 4%) and an apparent dose-related decrease in mean food consumption for females in the low-dose (generally 4 to 7%) and mid dose (generally 7 to 10%) treatment groups were observed. Statistically significant changes for animals in the low-dose and mid-dose treatment groups were limited to Week 5 for females from the mid-dose treatment group.

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study)
Unexpectedly high values for water consumption were observed for males (approximately 60 grams/animal/day) and females (approximately 52 grams/animal/day) in all treatment groups (including controls) during the first week of the study. These are in contrast to pre-treatment water consumption measurements evaluated under similar conditions over a 4-day period of approximately 40 grams/animal/day for males and approximately 29
grams/animal/day for females. It is unclear what contribution spills made to the high values observed during study Week 1 since excessive spills were not observed. Mean water consumption values were lower for all groups during study Week 2 than in study Week 1 and water consumption remained relatively constant during the remainder of the study. There were no treatment-related alterations' in water consumption for males during this study. A treatment-related decrease in mean water consumption was observed for females in the high-dose treatment group throughout the study (generally 15% to 29%). These values were statistically significant only during study Week 4. A statistically significant increase in mean water consumption for males in the high-dose treatment group during study Week 13 was not considered to be biologically significant based on the lack of similar findings during the study.

ORGAN WEIGHTS
Dose-related increases in mean liver weight were observed for male animals in all three TGME treatment groups. Mean brain weight for perfused male animals and mean kidney weight for non-perfused male and female animals were statistically increased when expressed as percent of final body weight. Decreases in absolute brain or kidney weights were not observed and the findings for relative organ weight were considered to be a result of decreased body weight. Decreases in mean absolute testes weights were observed for the non-perfused males in the mid-dose (9%) and high-dose (19%) treatment groups (n=5males/group). These changes were not statistically significant. Size decrease was observed for a single male in the mid-dose treatment group (approximately 50% size decrease) at necropsy.

GROSS PATHOLOGY
Necropsy of the deceased female revealed size increase for kidneys and adrenals and diffuse color change of various tissues. A specific cause of death was not apparent. There were no gross or microscopic lesions found in the nervous system of any rats that were attributed to TGME ingestion.

HISTOPATHOLOGY: NON-NEOPLASTIC
Minimal or mild hepatocellular hypertrophy was observed for 10 females in the high-dose treatment group. Fibrous connective tissue was observed around a small number of the bile ducts (cholangiofibrosis) for 7 males in the high-dose treatment group. All lesions were of minimal severity and were not considered to be physiologically significant. Cholangiofibrosis was not observed for males in any other treatment group or for females. Vacuolization or hypertrophy (minimal or mild severity) were also observed in the livers of some males in the low-dose and mid-dose treatment groups and females in the high-dose treatment group. Hypertrophy can be considered a physiological adaptation due to large subchronic doses of the test material, which is likely to be metabolized by alcohol dehydrogenase and aldehyde oxidase in the liver.

Treatment-related degeneration and/or atrophy of seminiferous tubules were observed for most males in the high dose treatment group. The cell types affected in the tubules were spermatocytes and developing spermatids. Similar lesions were not observed for males in the low-dose or mid-dose treatment groups. At the Sponsor's request, testes from all males on the study were examined histologically. Significant seminiferous tubule degeneration and/or atrophy were observed in 12 of 15 males in the high dose treatment group. The target cells in the tubules appeared to be spermatocytes and developing spermatids. Treatment-related lesions were not observed in the low-dose and mid-dose groups. No other potential treatment-related alterations in organ weights, gross pathology, or histopathology were observed in this study.

Effect levels

open allclose all
Dose descriptor:
LOAEL
Effect level:
1 200 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: Food consumption, body weight gain, liver weights, testicular atrophy
Dose descriptor:
NOAEL
Effect level:
400 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male/female

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
Based on the results of this study, treatment of Sprague-Dawley rats with TGME via the drinking water for 13 weeks produces moderate toxicity at 4.0
g/kg/day and minimal to mild toxicity at 1.2 g/kg/day.
Executive summary:

In a guideline (OECD 408) and GLP study, exposure to the substance triethylene glycol methyl ether (TGME) in the drinking water of rats for 90 days resulted in decreases in mean food consumption, body weight, and body weight gain for males and females in the 4 g/kg/day treatment group and trends for decreased food consumption and body weight for males in the 1.2 g/kg/day treatment group. Water consumption tended to be decreased at each measurement period for females in the 4 g/kg/day treatment group. Small decreases in mean food consumption, body weight, and body weight gain were also apparent for females in the 1.2 g/kg/day treatment group. One female animal from the 4 g/kg/day treatment group died on study Day 37 without apparent cause. Dose-related increases in mean liver weight were observed for male animals in all three TGME treatment groups. Associated microscopic changes included hepatocellular cytoplasmic vacuolization and/or hepatocellular hypertrophy, for males in the 4 g/kg/day treatment group. Vacuolization or hypertrophy (minimal or mild severity) were also observed in the livers of some males in the 0.4 g/kg/day and 1.2 g/kg/day treatment groups and females in the 4 g/kg/day treatment group. Hypertrophy can be considered a physiological adaptation due to large subchronic doses of the test material, which is likely to be metabolized by alcohol dehydrogenase and aldehyde oxidase in the liver. Treatment-related degeneration and/or atrophy of seminiferous tubules were observed for most males in the 4 g/kg/day treatment group. The cell types affected in the tubules were spermatocytes and developing spermatids. Similar lesions were not observed for males in the 0.4 g/kg/day or 1.2 g/kg/day treatment groups. On the basis of these findings 1200 mg/kg bw/day l is considered to be a subchronic LOAEL for TGME and 400mg/kg bw/day a NOAEL under the conditions of this study.

The substance triethylene glycol butyl ether (TEGBE or 2 -(2 -(2 -butoxyethoxy)ethoxy)ethanol, the subject of this dossier) is expected to exhibit very similar toxicity due to its close structural similarity to TEGME. Comparable metabolism would occur. On a molecular weight scaled basis, the LOAEL would be 1507.6 mg/kgbw/day and the NOEL 502.5 mg/kgbw/day.