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Carcinogenicity

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Description of key information

No specific studies for dipropylene glycol methyl ether are available. Two inhalation studies with propylene glycol methyl ether in rats and mice are available for read-across to dipropylene glycol methyl ether. Both studies are reliable without restrictions as they were conducted under GLP and according to OECD guideline 453.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion
Endpoint conclusion:
no study available

Carcinogenicity: via inhalation route

Link to relevant study records
Reference
Endpoint:
carcinogenicity: inhalation
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
1992-1993
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP-study according to OECD guideline 453
Qualifier:
according to
Guideline:
OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)
GLP compliance:
yes (incl. certificate)
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River (Portage, MI)
- Age at study initiation: 6-8 weeks
- Weight at study initiation: 143 g (males); 117 g (females)
- Fasting period before study: none
- Housing: 2 per stainless steel wire-mesh cage
- Diet (e.g. ad libitum): ad libitum except during inhalation exposures
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 7days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2°C
- Humidity (%): 40-60%
- Air changes (per hr): 12/hr
- Photoperiod (hrs dark / hrs light): 12/12
Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Vehicle:
unchanged (no vehicle)
Details on exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 14.5 m3 chambers (2.4 m wide x 2.4 m high x 2.4 m deep with a pyramidal top)
- Source and rate of air:
- Method of conditioning air: the various concentrations of PGME were generated using a glass J-tube method. Liquid PGME was metered into a glass J-tube assembly through which a preheated stream of approximately 90 liters per minute of compressed air was passed to vaporize the test material. The compressed air was heated to the minimum extend necessary to facilitate complete vaporization of the test material (approximately 65°C for the 300 ppm chamber, 105°C for the 1000 ppm chamber and 120-160°C for the 3000 ppm chamber). The compressed air and PGME vapors were diluted and mixed with room temperature air to the desired concentration at a flow rate of 2900 liters per minute into whole-body inhalation chambers.

- Temperature, humidity, pressure in air chamber: 22 ± 2°C, 40-60%, the chambers were operated at a slight negative pressure relative to the surrounding area.
- Air flow rate: chamber airflows were maintained at approximately 2900 liters per minute
- Air change rate: 12 changes/hour

TEST ATMOSPHERE
- Brief description of analytical method used: infrared spectrophotometer
- Samples taken from breathing zone: yes
PGME concentrations were measured from the breathing zone of the animals inside the chambers two times per hour using a Miran 1A infrared spectrophotometer. Analytical concentrations were within 0.5% of nominal concentrations throughout the study.

Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Analytical concentration of PGME was measured in the breathing zone of the animals in each chamber twice per hour using a MIRAN 1A infrared spectrophotometer (Foxboro Analytical, Norwalk, CT) at a wavelength of 9.0 microns. The spectrophotometer was calibrated using standards having known PGME vapor concentration contained in approximately 90 liter SARAN film or Tedlar gas bags prior to the first exposure and approximately monthly thereafter. Calibration standards and their values were entered into the Camile Data acquisition and control System.
Duration of treatment / exposure:
2 years
Frequency of treatment:
6 hr/day, 5 days/wk
Post exposure period:
none
Remarks:
Doses / Concentrations:
3000 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
1000 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
300 ppm
Basis:
nominal conc.
No. of animals per sex per dose:
50
Control animals:
yes, concurrent no treatment
Details on study design:
- Dose selection rationale: the selection of the highest dose tested was based on results from previous subchronic studies in which sedation, hepatic enzyme induction and increased hepatic and renal (males) cellular proliferation were shown to occur. The lowere concentrations, which have been used in previous subchronic studies, were selected to define dose-response relationships, if necessary, and to establish a no-observable effect level (NOEL).
- Rationale for animal assignment (if not random): Randomized by weight

Additional groups of rats (groups B, C and D) were added specifically for the evaluation of hepatic and renal cellular proliferation, hepatic enzyme induction and to characterize the alpha2u-globulin-related renal lesions.

Group B:
Quantitative cell proliferation (liver and kidney). Groups of 20 rats per sex per exposure concentration were exposed to 0, 300, 1000 and 3000 ppm PGME. Subgroups of 5 rats/sex/exposure concentration were evaluated following 6 and 12 months of exposure. A subgroup of 10 rats/sex/exposure concentration was evaluated following 18 months of exposure (this latter group size was increased to compensate for expected increases in mortality by this age). Prior to the final week of exposure at each time interval, osmotic minipumps containing 5-bromo-2-deoxyuridine (BrdU) were implanted for nuclear labeling of hepatocytes and tubular cells in the renal cortex.

Group C:
Enzyme induction (liver). Groups of 20 rats/sex/exposure concentration were exposed to either 0 or 3000 ppm PGME. Subgroups of 5 rats per sex per exposure concentration were evaluated following 6 and 12 months of exposure. A subgroup of 10 rats/sex/exposure concentration were evaluated following 18 months of exposure to compensate for expected increases in mortality by this age. On the morning following the final exposure at each time interval, the livers were removed, weighed, frozen and microsomes prepared. Total cytochrome P450 (CYP) content and induction of specific CYP_dependent enzyme activities were determined.

Group D:
Protein droplet nephropathy. Groups of 10 male rats/exposure concentration were exposed to 0, 300, 1000 or 3000 ppm PGME. Subgroups of 5 rats/exposure concentration were evaluated following 6 and 12 months of exposure. On the morning following the final exposure at each time interval, each animal was perfused with fixative and the kidneys were removed, processed and evaluated by light microscopy for observations of cellular degeneration using special strains and immunohistochemical techniques to characterize the alpha2u-globulin nephropathy.
Positive control:
none
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily (Monday-Friday)
- Cage side observations: All animals were observed for overt signs of toxicity or demeanor. Particular attention was paid to signs of sedation or central nervous system depression during the first several weeks of exposure to PGME since these effects have been noted previously at the concentrations used in this study.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: prior to the start of the study and weekly thereafter.

BODY WEIGHT: Yes
- Time schedule for examinations: prior to initial exposue and at weekly intervals for the first 13 weeks and at approximately 4-week intervals thereafter.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No data

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations:prior to start of the study and prior to scheduled necrospy
- Dose groups that were examined: all animals from all dose groups except for the additional groups B, C and D.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: after 6, 12, 18 and 24 months of exposure to PGME
- Anaesthetic used for blood collection: Yes (methoxyflurane)
- Animals fasted: Yes (overnight)
- How many animals: 10 randomly preselected rats/sex/exposure concentration after 6-18 months of exposure & 20 rats/sex/exposure concentration after 24 months of exposure
- Parameters examined: hematocrit, hemoglobin concentrations, erythrocyte count, total leukocyte counts and platelet counts. Complete blood smear exminations included a differential leukocyte count of 100 cells and an assessment of erythrocyte, leukocyte and platelet morphology.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: after 6, 12, 18 and 24 months of exposure to PGME
- Animals fasted: Yes (overnight)
- How many animals: 10 randomly preselected rats/sex/exposure concentration after 6-18 months of exposure & 20 rats/sex/exposure concentration after 24 months of exposure
- Parameters examined: alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase and creatine phosphokinase activities as well as urea nitrogen concentration, creatinine, total protein, albumin, globulin, glucose, cholesterol, triglycerides, total bilirubin and electrolytes (Na, K, P, Cl and Ca)

URINALYSIS: Yes
- Time schedule for collection of urine:1 to 6 days prior to the 6-, 12-, 18- and 24-month blood collections.
- Metabolism cages used for collection of urine: No (spontaneous urination or manual compression of the urinary bladder.
- Animals fasted: No
- Parameters examined: semiquantitative estimate of pH, bilirubin, glucose, proteins, ketones, occult blood and urobilinogen. Color, appearance and specific gravity of urine was also determined for each sample and the presence or absence of microsediment in a pooled sample from each group was determined.
Sacrifice and pathology:
Gross Pathology:
Main Group A: All surviving animals were fasted overnight and necropsied after approximately 24 months of exposure. A similar procedure was followed for rats which died or were sacrificed in a moribund condition.
Group B: one week after minipumps were implanted, the animals were fasted overnight and necropsied. A complete gross pathologic examination was done on all animals. Moribund animals or animals found dead from this subgroup were necropsied and tissues saved for determination of cause of death.
Group C: all surviving animals were fasted overnight and necropsied after 6, 12 or 18 months of exposure. A complete gross pathologic examination was conducted on all animals.
Moribund animals or animals found dead from this subgroup were necropsied and tissues saved for determination of cause of death.
Group D: all surviving animals were fasted overnight and necropsied after 6 or 12 months of exposure. A complete gross pathologic examination was conducted on all animals.
Moribund animals or animals found dead from this subgroup were necropsied and tissues saved for determination of cause of death.

Histopathology:
Main Group A: a complete histopathologic evaluation was conducted on all control and 3000 ppm PGME exposure rats and from all rats that died or were sacrificed in a moribund condition during the course of the study.
Microscopic examination of tissues fro the low and middle exposure groups included the liver, kidneys, lungs, nasal tissues and all gross lesions.
Group B: Liver, kidney and duodenum (positive control tissue for cell division process and BrdU incorporation) from each animal were processed for histopathological and immunohistochemical analyses.
Group C: histologic evaluation was conducted on the livers of all animals.
Group D: histologic evaluation was conducted on the kidneys of all animals.
Other examinations:
none
Statistics:
See any other information on materials and methods.
Clinical signs:
effects observed, treatment-related
Mortality:
mortality observed, treatment-related
Body weight and weight changes:
effects observed, treatment-related
Food consumption and compound intake (if feeding study):
not specified
Food efficiency:
not specified
Water consumption and compound intake (if drinking water study):
not specified
Ophthalmological findings:
no effects observed
Haematological findings:
effects observed, treatment-related
Clinical biochemistry findings:
effects observed, treatment-related
Urinalysis findings:
no effects observed
Behaviour (functional findings):
not examined
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
Histopathological findings: neoplastic:
no effects observed
Details on results:
CLINICAL SIGNS AND MORTALITY
At 3000 ppm, the rats exhibited decreased activity, incoordination, and transient sedation during the first week of exposure. Subjects recovered 1-2 hours after removal from the chambers. These signs disappeared after the second week but returned after 12-18 months into the study. Mortality was unaffected until 18 months when males but not females showed higher mortality rates that were not ascribable to any particular cause

BODY WEIGHT AND WEIGHT GAIN
During the course of the study, body weights were decreased at the 3000 ppm exposure level. These decreases were not large but were statistically significant in female rats. Despite changes during the study, body weights were not statistically different from controls at terminal sacrifice. No histological changes accompanied these effects.

OPHTHALMOSCOPIC EXAMINATION
No treatment-related effects were observed in this study.

HAEMATOLOGY
There were no hematological effects in male and female rats that were attributable to PGME exposures.

CLINICAL CHEMISTRY
Several clinical chemistry parameters in male rats exposed to 3000 ppm PGME were altered at the 24 month sacrifice: creatinine increased 78% and urea nitrogen increased 100%. Serum alkaline phosphatase was increases as well and earlier, at 6 through 24 months at the 3000 ppm level, and at 1000 ppm, at 24 months in male rats. Changes in SGOT (AST) and SGPT (ALT), which could be associated with liver injury, were mildly and inconsistently increased in male rats during the first year of exposure at 3000 ppm but not after.

URINALYSIS
There were no treatment-related effects evident in urinalaysis data.

ORGAN WEIGHTS
Liver and kidney weights were increased at 3000 ppm in both sexes.

GROSS PATHOLOGY
A slight increase in the incidence of dark foci in the liver of male rats exposed to 1000 and 3000 ppm PGME for 2 years was correlated with the presence of alteredhepatocellular foci observed histologically. All other gross pathological observations and the occurrence of palpable mass were distributed across all groups, including controls, and were typical for rats of this age and strain.

HISTOPATHOLOGY: NON-NEOPLASTIC
Dark foci in the liver were grossly observable in male rats exposed to 1000 and 3000 ppm PGME after 24 months. These subjects also exhibited eosinophilic hepatocellular foci and cystic degeneration microscopically that was not reported in female rats. Male rats showed increased S-phase DNA synthesis when exposed to 3000 ppm PGME. This effect was not pronounced (reported in a separate, 2-week study), and was evident to a lesser extent in female rats. MFO activity was increased in the livers of rats exposed to 3000 ppm PGME.

In the kidney, histopathology revealed that male rats had a2µ-globulin nephropathy as is typical for this strain. The incidence and severity of this condition was increased in males exposed to 1000 and 3000 ppm PGME compared to controls.

HISTOPATHOLOGY: NEOPLASTIC (if applicable)
No increase in renal epithelial tumors was observed in rats.

OTHER FINDINGS
Hepatic cell proliferation: statistically sifgnificant increased labeling indices were observed in males exposed to 3000 ppm PGME at all time intervals.
Renal cell proliferation: no treatment related statistically significant effects on cell proliferation were observed in the kidneys.
Dose descriptor:
NOEL
Effect level:
300 ppm
Sex:
male/female
Basis for effect level:
other: overall effects
Remarks on result:
other: Effect type: toxicity (migrated information)
Dose descriptor:
NOEL
Effect level:
3 000 ppm
Sex:
male/female
Remarks on result:
other: Effect type: carcinogenicity (migrated information)
Conclusions:
Rats exhibited a NOAEL of 300 ppm based on altered hepatocellular foci in males. No carcinogenic effect as evidenced by any increase in tumor incidence, even in kidneys of the male rats, occurred from exposure to propylene glycol methyl ether (PGME) at any concentration.
Executive summary:

In a chronic toxicity/carcinogenicity study, Fischer rats (50/sex/exposure level) were exposed to vapor concentrations of propylene glycol methyl ether (PGME) at concentrations of 0, 300, 1000, or 3000 ppm 6 hr/day, 5 days/wk for 2 years. Over the course of the study, these subjects were evaluated for clinical signs and body weights. At the end of two years, survivors were subjected to clinical chemistry and hematological examinations, urinalyses, determination of body organ weights, and histopathological examination of a large number of tissues. 

In order to evaluate potential toxicity at interim time intervals during the exposure period, additional subjects were exposed to PGME vapors and subjected to routine and specialized toxicological tests at the times shown in the experimental design table below.
 Specialized tests at time intervals of 6, 12, 18 and 24 month included evaluation of 1) cell proliferation in liver and kidneys, 2) hepatic mixed function oxidase (MFO) activity, and 3) a2µ-globulin nephropathy.

Group A: routine study, Group B: cell proliferation in liver and kidneys, Group C: Hepatic MFO induction, Group D: a2µ-g nephropathy evaluation.

Atmospheres of PGME were generated by metering the test material into a glass J-tube assembly through which compressed, heated air was channeled.
 Evaporated PGME in the heated air was diluted with room temperature air to the desired concentration at a flow rate of 2900 liters per minute into whole-body inhalation chambers. Airflow in the chambers was maintained at a level that provided approximately 12 changes/hour and normal oxygen concentration. PGME concentrations were measured from the breathing zone of the animals inside the chambers two times per hour using a Miran 1A infrared spectrophotometer. Analytical concentrations were within 0.5% of nominal concentrations throughout the study.

At 3000 ppm, rats exhibited decreased activity, incoordination, and transient sedation during the first week of exposure. Subjects recovered 1-2 hours after removal from the chambers. These signs disappeared after the second week but returned after 12-18 months into the study. Mortality was unaffected until 18 months when males but not females showed higher mortality rates that were not ascribable to any particular cause.  During the course of the study, body weights were decreased at the 3000 ppm exposure level. These decreases were not large but were statistically significant in female rats. Despite changes during the study, body weights were not statistically different from controls at terminal sacrifice. 

In the chronic study, no hematology or urinalysis changes were evident.
 However, several clinical chemistry parameters in male rats exposed to 3000 ppm PGME were altered at the 24 month sacrifice: creatinine increased 78% and urea nitrogen increased 100%. Serum alkaline phosphatase was increases as well and earlier, at 6 through 24 months at the 3000 ppm level, and at 1000 ppm, at 24 months in male rats.  Changes in SGOT (AST) and SGPT (ALT), which could be associated with liver injury, were mildly and inconsistently increased in male rats during the first year of exposure at 3000 ppm but not after. No histological changes accompanied these effects. Liver and kidney weights were increased at 3000 ppm in both sexes.

Dark foci in the liver were grossly observable in male rats exposed to 1000 and 3000 ppm PGME after 24 months. These subjects also exhibited eosinophilic hepatocellular foci and cystic degeneration microscopically that was not reported in female rats.
 Male rats showed increased S-phase DNA synthesis when exposed to 3000 ppm PGME. This effect was not pronounced (reported in a separate, 2-week study), and was evident to a lesser extent in female rats. MFO activity was increased in the livers of rats exposed to 3000 ppm PGME. 

In the kidney, histopathology revealed that male rats had a2µ-globulin nephropathy as is typical for this strain.
 The incidence and severity of this condition was increased in males exposed to 1000 and 3000 ppm PGME compared to controls. No increase in renal epithelial tumors was observed in rats.

The major changes seen in this study were 1) decreased body weights, 2) liver effects including increased weight, increased MFO activity and increased cell proliferation primarily in males, 3) kidney effects of a2µ-globulin nephropathy typical of the Fischer 344 strain, and 4) slightly increased mortality occurring only after 18 months of exposure in males. Clinical chemistry parameters reflected and corroborated these effects. 

Rats exhibited a NOAEL of 300 ppm based on altered hepatocellular foci in males.

No carcinogenic effect as evidenced by any increase in tumor incidence, even in kidneys of the male rats, occurred from exposure to PGME at any concentration.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEC
18 184.05 mg/m³
Study duration:
chronic
Species:
rat
Quality of whole database:
Good (Klimisch 2)

Carcinogenicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Repeated exposure to dipropylene glycol methyl ether resulted in toxicity only at high exposure levels and usually consisted of increased organ weights without accompanying histopathology. In vitro genotoxicty studies are negative, indicating that dipropylene glycol methyl ether is not genotoxic. No carcinogenicity studies are available for dipropylene glycol methyl ether.The sole propylene glycol ether that has been subjected to chronic toxicity/carcinogenicity testing is propylene glycol methyl ether. Thus, the propylene glycol methyl ether study is used as a surrogate for dipropylene glycol methyl ether. Propylene glycol methyl ether, tested by inhalation in rats and mice at concentrations up to 3,000 ppm, caused very little chronic toxicity and caused no cancer. Further justification for the use of read across is contained in the category document attached at section 13.


Justification for selection of carcinogenicity via oral route endpoint:
There is an inhalation (most relevant route of exposure) carcinogenicity study available

Justification for selection of carcinogenicity via inhalation route endpoint:
Read across from PGME - GLP-study according to OECD guideline 453

Justification for selection of carcinogenicity via dermal route endpoint:
There is an inhalation (most relevant route of exposure) carcinogenicity study available

Justification for classification or non-classification

No carcinogenic effect as evidenced by any increase in tumor incidence occurred from exposure to propylene glycol methyl ether at any concentration in either species.