Registration Dossier

Administrative data

Description of key information

ORAL ROUTE RAT (reliable studies only reported.  Gavage unless stated otherwise)

- NOAEL<70mg/kg (90 day drinking water) (testes, thymus)

- BMDL10=15.4mg/kg (10 day) (creatine:creatinine ratio)

- NOAEL<50mg/kg (10 day) (thymus)

- NOAEL<50mg/kg (5 day) (testes, sperm)

- NOAEL<161mg/kg (21 day-drinking water) (thymus, immune system)

- NOAEL=50mg/kg (11 day) (sperm)

- NOAEL<100mg/kg (4 day) (testes, white blood cells)

ORAL ROUTE MOUSE

- NOAEL=295mg/kg (90 day - drinking water) (testes, spleen)

- NOAEL=125mg/kg (5 week) (testes, sperm)

DERMAL ROUTE (rat, all available studies reported)

- NOAEL (4 week) <100mg/kg (occluded); 100mg/kg (non-occluded.)  (Body weight gain)

- NOAEL (13 week) <1000mg/kg

- NOAEL (1 week) <625mg/kg (occluded); =1250mg/kg (non-occluded) (sperm count, testes-epididymides weight)

INHALATION (rat unless specified, reliability 1 or 2 studies only included.)

- NOAEC (90 day): female: 30ppm (body wt, clin chem.); male 100ppm (body wt, liver-testes wt, haematology)

- NOAEC (90 day, rabbit): female 30ppm (thymus wt, haematology); male: <30ppm (testes)

- NOAEC (2 wk): <100ppm (male and female) (WBC)

- NOAEC (2 wk, mouse): female 100ppm (thymus); male 300ppm (thymus-liver-testes wt)

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Dose descriptor:
BMDL10
15.6 mg/kg bw/day

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Dose descriptor:
LOAEC
95 mg/m³

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion
Dose descriptor:
LOAEL
100 mg/kg bw/day

Additional information

ORAL ROUTE

All of the available studies consistently indicate that the rat is more sensitive than the rabbit. In a well conducted drinking water study, rats were exposed to methoxyethanol at concentrations ranging from 750 -6000ppm for a period of 90 days. A NOAEL was not established in the study as the lowest dose tested, equivalent to 70 -71mg/kg produced adverse changes to the male testes (degeneration). At this dose, both sexes also showed a significant reduction in thymus weight, both relative and absolute. Bone marrow cellular depletion, splenic atrophy and/or capsular fibrosis and thymic atrophy were apparent in both sexes from doses of 135 -165mg/kg upwards.

A sub-acute study in male rats was designed to establish if creatinuria (a non-invasive biomarker) was maintained as a result of testicular damage.  Animals were dosed with methoxyethanol in drinking water up to nominal doses of 250mg/kg. The study established a NOAEL of 43mg/kg based on adverse testes histopathology and other gross effects at the next highest dose, but a NOAEL could not be established based on an elevated urinary creatine/creatinine ratio at the lowest dose tested (43mg/kg). Sufficient data is available in the paper to use the Benchmark dose approach to estimate a no effect level.  Using a continous power model and a BMD level of 10%, the BMD for no elevation of creatine:creatinine ratio is 15.6mg/kg. This study defines the lowest oral NOEC observed for methoxyethanol for available studies using oral treatment of rats

In a study designed to look at testicular recovery following exposure to methoxyethanol known to cause testicular toxicity, groups of rats were given daily doses of 50 -200mg/kg for 5 days and recovery followed over 8 weeks by sacrificing groups of dosed animals at weekly intervals. The study found adverse effects on the testes at all dose levels but were very mild in the lowest dose group and limited to deformed sperm between weeks 4 -7 with complete recovery by week 8. More severe and permanent changes were seen at doses of 100mg/kg and above.

Numerous other sub-acute studies are available that consistently support the above results. None of them establish LOAELs below 71mg/kg. These studies consistently report reduction in thymus weight in the absence of body weight effects and reversible effects on markers for immune system function. Adverse effects on white blood cell population are also reported as well as effects on testes and sperm production. For the latter, the most sensitive cells appear spermatocytes undergoing division in early pachytene with other spermatocyte stages less sensitive. All other testicular cell types do not appear to be significantly affected by methoxyethanol exposure. It is also noticeable that these effects are consistently reversible, even at moderate doses, certainly at doses well above those reported above.

In a well conducted drinking water study, mice were exposed to methoxyethanol at concentrations up to 10000ppm for a period of 90 days. A NOAEL was established in the study for males at the lowest dose tested of 2000ppm, equivalent to 295mg/kg, based on testicular degeneration and increased hematopoiesis in the spleen at the next dose tested. However, a NOAEL was not established for female mice, since adrenal gland hypertrophy and increased hematopoiesis in the spleen occurred at the lowest concentration administered (equivalent to 492mg/kg). In a study s designed to look at testicular recovery following exposure to methoxyethanol known to cause testicular toxicity, groups of rats were given daily doses of 50 -200mg/kg for 5 days and recovery followed over 8 weeks by sacrificing groups of dosed animals at weekly intervals. The study found adverse effects on the testes at all dose levels but were very mild in the lowest dose group and limited to deformed sperm between weeks 4 -7 with complete recovery by week 8. More severe and permanent changes were seen at doses of 100mg/kg and above.

Other species have been examined, with both hamster and guinea pig being susceptible to testicular toxicity as seen in rats and mice. Both species showed a sensitivity more similar to rats than mice.

DERMAL ROUTE

Limited data is available by the dermal route. A study examined the sub-acute percutaneous toxicity of methoxyethanol in rats. Animals were subjected to daily doses of 100 or 1000mg/kg under both occluded and non-occluded conditions for a period of 28 days. The only effect seen at the lower dose was reduced body weight gain and food intake under occluded conditions. At the higher dose, significant toxicity was observed with adverse effects body weight reduction, on the testes, haematology and the bone marrow. Only the first two were seen under non-occluded conditions.

The only other data is from studies which used much higher dose levels. These confirmed the effects on body and organ weights (testes, spleen) as well as on the blood (haematology) and that effects are more severe for exposure under occluded conditions, as would be expected for a volatile substance. A short term study that only examined male reproductive toxicity and used an exposure of 7 days, established a NOAEL under non-occluded conditions of 1250mg/kg.

INHALATION ROUTE

In a sub-chronic 13 week study, both male and female rats and rabbit were exposed by inhalation to methoxyethanol vapour in concentrations of 30, 100 and 300ppm. No rats died prior to scheduled sacrifice, but some rabbits in the 100 and 300 ppm exposure groups died or were sacrificed when moribund during the study. Body weights as well as thymus and testicular weights of rats and rabbits in the 300 ppm group were reduced as a result of the exposures. Hematologic changes occurred in rats and rabbits exposed to 300 ppm. Concentrations of total protein, albumin and globulins in serum of rats (but not rabbits) in the 300 ppm group were lower than for controls. Gross lesions in rats and rabbits exposed to 300 ppm included decreased size of thymus in both sexes, decreased abdominal fat, and small flaccid testes in males. In addition there was decreased lymphoid tissue in some rabbits, as well as a slight-to-moderate decrease in size of testes in 4 of 5 rabbits in the 100 ppm group and in 2 of 5 rabbits exposed to 30 ppm. Treatment-related microscopic lesions included degenerative changes in germinal epithelium of testes in all male rats and rabbits in the 300 ppm group, as well as in 3 of 5 rabbits in the 100 ppm group and 1 of 5 male rabbits in the 30 ppm group. The only effects attributed to exposure to 30 ppm methoxyethanol in this study were slight microscopic changes in testes of 1 of 5 male rabbits.

In a sub-acute inhalation toxicity study, male and female rats and mice were exposed to methoxyethanol vapour for 9 days over an 11 day period at concentrations up to 1000ppm. In rats at 1000ppm, adverse effects were seen on body weight gain, peripheral blood counts, bone marrow, testes and lymphoid tissue. Similar, albeit less marked, effects were seen at 300ppm, including thymus weight reduction and reduced red and white blood cell counts. The only significant change seen in the lowest 100ppm dose group was a reduction in white blood cell counts. Only a partial analysis was made in the mice. At 1000ppm, adverse effects were seen in both sexes on thymus and male testes. Female liver weight was also significantly reduced. The only significant change seen in the lowest 300ppm dose group was reduced thymus weight in females. The study confirmed the results from the oral studies that mice appear to be less sensitive than rats to the toxic effects of methoxyethanol.

In a sub-acute inhalation toxicity study, male rats were exposed to 300 ppm 2-methoxyethanol for 2 weeks. Exposed rats were killed after 10 days of exposure and 14, 42, or 84 days post-exposure (PE), respectively. The exposure caused marked testicular atrophy and affected all spermatogenic stages. Damaged seminiferous tubules were lined with regenerating pachytene spermatocytes at 14 days PE and with spermatocytes and round spermatids after 42 days PE. Most but not all testes in rats had normal morphology after 84 days PE.

In a study that was designed to provide a rapid assessment of the effect on some aspects of reproduction, male rats were exposed for 10 days to 100 and 300ppm of methoxyethanol. In the high exposure group, there was a reduction in testicular weight accompanied by semeniferous tubular atrophy along with significant reductions in white blood cell count, red blood cell count, hemoglobin concentration, hematocrit, and mean cell hemoglobin. There were no effects at 100 ppm.


Repeated dose toxicity: via oral route - systemic effects (target organ) urogenital: testes

Repeated dose toxicity: inhalation - systemic effects (target organ) urogenital: testes

Justification for classification or non-classification

Classification requirements for reproductive toxicity are not discussed here. See chapter 7.8.

CLASSIFICATION UNDER DIRECTIVE 67/548

For the oral route the lowest reported non-reproductive adverse effects from reliable and robust studies were in a 10 day immunotoxicity study in rats where significant thymus weight reduction was seen at 50mg/kg. Similar changes were reported at 71mg/kg (the lowest dose tested) in a 90 day study.

For the dermal route, the lowest reported effects from reliable and robust studies were in a 28 day study in rats where the changes were restricted to reduced body weight gain and food intake. This is not regarded as a 'severe lesion' that would warrant classification. More serious adverse effects were seen at the only other dose tested of 1000mg/kg (which could be 'equated' to a sub-chronic exposure of 333mg/l for classification and labelling purposes - division by 3 - if the default assessment factors for extrapolation of sub-acute and sub-chronic data to lifetime exposure are compared.)

For the inhalation route, the lowest reported adverse effect (non reproductive) was in a 9 day study where an exposure of 0.316mg/l produced adverse changes in white blood cells in rats. However, these results were not repeated in a follow on 90 day study where thymus weight reduction was seen at only seen at 0.95mg/l.

These results suggest that a classification of serious damage to health by prolonged exposure R48 by the oral route is warranted.

CLASSIFICATION UNDER REGULATION 1272/2008

Based on the considerations above, classification for specific organ toxicity by repeated exposure needs to be considered. Using the above data it is possible to conclude that a category STOT 2 classification would again be appropriate for only the oral route. The following phrase would be appropriate "May cause damage to organs (thymus) through prolonged or repeated exposure".