2-isopropoxyethanol

Toxicity to reproduction

Administrative data

Endpoint:

multi-generation reproductive toxicity

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
Please refer to the document shown as an attached justification which describes the hypothesis, target substances and analogue approach justification in detail.

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

multi-generation reproductive toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1988

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Remarks:

Well documented publication which meets basic scientific principles”. Full study report also available

Qualifier:

according to guideline

Guideline:

other: National Toxicology Programme Continuous Breeding Protocol

Deviations:

yes

Remarks:

, F1 tests were only carried out with the control and low dose groups

GLP compliance:

yes

Limit test:

no

Species:

mouse

Strain:

CD-1

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Kingston NY
- Age at study initiation: (P) x 11wks; (F1): 74+/-10 days
- Housing: by sex in solid bottom polypropylene or polycarbonate cages with stainless steel wire lids, then subsequently in breeding pairs. Ad-Sorb-Dri bedding used.
- Diet (ad libitum): NIH-07
- Water (ad libitum): tap
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-25
- Photoperiod (hrs dark / hrs light): 10/14

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Each dosing solution formulated directly. No loss of compound after 3 days at room temperature and only 0.9% after 21 days lost. Consequently, fresh solutions prepared every 2 weeks.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: 7-day pre-mating period and a 98-day cohabitation period.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analysis on days 1, 6, 10 and 14. All doses found to be within 97-104% of expected values.

Duration of treatment / exposure:

14 weeks

Frequency of treatment:

continuous

Details on study schedule:

At the completion of the continuous breeding phase, the F0 breeding pairs were separated and housed individually and exposure to 2-butoxyethanol continued. When the last litter was weaned from the continous breeding phase F0 males and females from the 1 % dose group were mated with male and female control animals in a one-week crossover mating study to determine any sex-related reproductive effects of 2-butoxyethanol.

Remarks:

Doses / Concentrations:
0 0.5, 1.0 or 2.0 %
Basis:
nominal in water

Remarks:

Doses / Concentrations:
0, 720, 1340 and 2050 mg/kg bw
Basis:
actual ingested

No. of animals per sex per dose:

20. 40 in control

Control animals:

other: Yes. Control males and females were also mated for comparative purposes.

Details on study design:

-The study itself consisted of three phases:
Phase 1 = continous breeding phase
Phase 2 = F0 males and females mated with control animals
Phase 3 = F1 males and females mated

Exposure to 2-butoxyethanol was discontinued during the one-week mating period and then reintroduced at 1 % dose level (estimated daily intake 1830 mg/kg bw). Control males and females were also mated for comparative purposes. The proportion of successful copulations from the breeding pairs was similar in all groups. However, the number of fertile females was significantly reduced in the group where treated females were mated with control males.

A final phase was conducted to assess the fertility and reproductive effects of 2-butoxyethanol in second generation (F1) pups. The pups selected were those born after the CBP and when the maternal animals were individually housed. As there were insufficient pups in the 1 and 2 % dose groups, only the pups from the 0.5 % dose group were used. The F1 generation pups were nursed, weaned and reared to sexual maturity. After weaning, the mice received 0.5 % 2-butoxyethanol in their drinking water (estimated daily intake 950 mg/kg bw). At 74 ± 10 days of age, the F1 animals from different litters were mated. The animals were necropsied after delivery.

Positive control:

No

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes

DETAILED CLINICAL OBSERVATIONS: Yes

BODY WEIGHT: Yes

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): Yes

Oestrous cyclicity (parental animals):

F0 Females Mated with Control Males
-When evaluated over the 7 day period prior to necropsy, proportionally more females (7/13) in the 1 % treated group than controls (9/38) had oestrus cycles longer than 7 days.

Sperm parameters (parental animals):

Parameters examined in P and F1 male parental generations

Litter observations:

Parameters examined in P and F1 generations

Postmortem examinations (parental animals):

Parameters examined in P and F1 generations

Postmortem examinations (offspring):

Parameters examined in F1 and F2 generations

Statistics:

Cochran-Armitage test for dose related trends in fertility. Chi-square test for differences in fertility among groups. Pairwise comparisons between dose groups and control using Fisher's exact test. Reproductive indices between groups compared using Kruskal-Wallis test and ordered differences using Jonckheere's test. Pairwise comparisons of treatment groups perfomed using Wilcoxon-Mann-Whitney U test. Pup number per litter corrected for when calculating average pup weight.

Reproductive indices:

The numbers of fertile pairs from the surviving pairs of the continuous breeding phase were 38/39, 19/19, 13/14 and 5/7 at 0, 0.5, 1.0 and 2.0 % dose levels, respectively.

Offspring viability indices:

no further information

Mortality:

mortality observed, treatment-related

Description (incidence):

-During the 98 day cohabitation period, deaths occurred in the female mice: 13/20 in the 2 % group, 6/20 in the 1 % dose group, 1/20 in the 0.5 % dose group and 1/40 in the control group. In the male mice, no deaths occurred.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

-The average body weights in the female 2 % dose group were consistently lower than the controls. Male groups experienced weight loss (1-2 % of initial body weight) in the two highest doses.
-At necropsy, male and female mice from the 1 % dose group had significantly lower body weights.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

-Reduced fluid consumption was observed at all dose levels in both sexes (22 %, 18 % and 36 % reduction relative to controls at 0.5 %, 1.0 % and 2.0 %, respectively after 14 weeks of dosing).

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

-In the only histopathological examination carried out on the treated females, no treatment related kidneys lesions were observed.

Histopathological findings: neoplastic:

not examined

Reproductive function: oestrous cycle:

no effects observed

Description (incidence and severity):

-In the 1% group no significant differences were observed between the control and treated animals for the average oestrous cycle length and frequency.
-No treatment-related changes in the oestrous cycle length and frequency were noted in the F1 generation.

Reproductive function: sperm measures:

no effects observed

Description (incidence and severity):

-In the 1% group no significant differences were observed between the control and treated animals for the weights of reproductive organs, sperm motility or morphology.
-No treatment-related changes in the weights of reproductive organs, sperm motility or morphology were noted in the F1 generation.

Reproductive performance:

effects observed, treatment-related

Description (incidence and severity):

-Significant reduction in reproductive performance occurred at 1 and 2 % dose levels as indicated by dose-related decrease in number of litters per fertile pair, litter sizes, pup viability and live pup weight.
-No significant fertility and reproductive effects were observed in the F1 animals as indicated by the proportions of successful copulation and fertile females, litter size, pup viability and live pup weights.

Dose descriptor:

NOAEL

Effect level:

720 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

mortality

body weight and weight gain

reproductive performance

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Relative liver and kidney weights were increased in the dose group receiving 2-butoxyethanol (0.5%)

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Description (incidence and severity):

On the P1 generation (low dose and control only tested) , there were no effects on mating and fertility indices or any other reproductive parameter.

Dose descriptor:

LOAEL

Effect level:

635 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

organ weights and organ / body weight ratios

Critical effects observed:

no

Lowest effective dose / conc.:

635 mg/kg bw/day (actual dose received)

System:

other: see organs

Organ:

kidney

liver

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

A small but significant reduction (by 3 %) of live F1 pup weight was also observed in the 0.5 % dose group without other significant reproductive effects but no effect was seen in the pups born to the F1 generation.

Sexual maturation:

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

720 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

There were no significant differences in F2 litter size, pups numbers or weights.

Dose descriptor:

NOAEL

Generation:

F2

Effect level:

> 720 mg/kg bw/day

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Remarks:

Observations limited by maternal toxicity

Reproductive effects observed:

not specified

The continuous breeding first generation study showed that treatment significantly affected fertility at the mid and high dose levels and marginally affected pup weight at the lowest level. The cross-breeding results suggest that the fertility effects were only due to effects on the female mice. In the cross-over study there were no effecting on mating index (number with copulatory plugs/number co-habited), however for females that co-habited with control males the fertility index (number fertile/number with copulatory plugs) ws significantly reduced compared to the controls and other cross-over group. Similarly, the number of live pups/litter of the 1% treated females/control males fell. These effects may have been an indirect consequence of the severe general systemic toxicity rather than a direct effect of 2-butoxyethanol on the reproductive organs.

The top dose exceeded the MTD in the first generation animals.

Conclusions:

In this study, effects were seen on fertility only at doses which were severely toxic to the animals (1340 and 2050 mg/kg bw/d). A NOAEL of 720 mg/kg bw/day can be identified for fertility effects by oral route in mice. Marginal pup weight reductions at this dose were not repeated in the second generation and therefore not regarded as a significant finding.

Executive summary:

In a continuous breeding study carried out to an NTP protocol, mice were exposed for a period of 14 weeks to the oral drinking water routes to 2 -butoxyethanol at doses from 720 to 2050mg/kg. Significant adverse reproductive effects were observed in the females at very high dose levels (1340 mg/kg and above) which also caused severe general toxicity, including death. At the lowest dose studied, the only adverse finding was a marginal statistically significant reduction in pup weight. However, since this reduction was only 3% compared to controls and was not repeated in the F1 generation, it was not considered a significant adverse finding.

No NOAEL or LOAEL can be determined for systemic parental toxicity because this kind of study is not designed to assess systemic toxicity although it is of note that there were effects (reduced fluid consumption) even at the lowest dosage of 720 mg/kg/day. Under the conditions of the study, the NOAEL for reproductive toxicity of 2-butoxyethanol (fertility) can be set as 720 mg/kg/day.

Cross-reference 2

Reason / purpose for cross-reference:

read-across source

Reference

Endpoint:

toxicity to reproduction

Remarks:

other: data from a sub-chronic toxicity study

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1993

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Well documented NTP publication which meets basic scientific principles.

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD repeat dose toxicity 409

Deviations:

not applicable

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Route of administration:

oral: drinking water

Vehicle:

water

Details on mating procedure:

not applicable

Duration of treatment / exposure:

13 Weeks

Frequency of treatment:

daily

Details on study schedule:

not applicable

Remarks:

Doses / Concentrations:
0, 750, 1500, 3000, 4500 or 6000 ppm
Basis:
other: These concentrations provided target dose levels of 0, 100, 150, 250, 400 or 650 mg/kg bw per day (US NTP, 1993).

Remarks:

Doses / Concentrations:
0, 69, 129, 281, 367, 452
Basis:
other: actual dose received in mg/kg/day (males)

Remarks:

Doses / Concentrations:
0, 82, 151, 304, 363, 470
Basis:
other: actual dose received in mg/kg/day (females)

No. of animals per sex per dose:

10 male and 10 female rats

Control animals:

yes, concurrent vehicle

Oestrous cyclicity (parental animals):

Vaginal cytology was assessed over the 7 days prior to sacrifice. With respect to oestrous cycle evaluations, normally cycling Fischer 344 females have 5-6 day oestrous cycles. While there were 10 females per dose group, 3-4 females per group had estrous cycles longer than 12 days or cycles that were unclear, including the control group. These animals were excluded from the analysis, meaning that only 6-7 females per group were evaluated. Furthermore, given the approximate times in the various stages of estrous (see table below from Zarrow et al., 1964), it appears that the control animals spent an excessive amount of time in estrus. Typically, estrus would comprise approximately 30% of the estrous cycle, rather than the 57.9% reported for the control females. Using Zarrow’s table, if one assumes 2 days for estrus and minimal durations for the other estrous stages, estrus would only comprise 44% of the cycle (2 days out of 4.5 days total estrous cycle). This value is well below the 57.9% reported in the control animals in the study. Vaginal smears were collected only once per day. With only 6-7 rats per group and stages of the cycle that are less than one day in duration, some phases could have gone undetected.

Method: Vaginal vaults were lavaged and the fluid and cells stained with toluidine blue. Relative numbers of leucocytes, nucleated epithelial cells and large squamous epithelial cells were determined and used to ascertain estrous cycle stage (eg. diestrous, proestrus, estrus and metestrus.)

Sperm parameters (parental animals):

Sperm morphology and motility were estimated from epididymal sperm samples taken at necropsy. The left epididymis was isolated and weighed. The tail of the cauda epididymis was then removed and weighed. Test yolk was applied to slides and a small incision made to distal border of epididymis tail. Sperm effluxing was dispersed in buffer on slide and numbers of motile/non-motile spermatazoa counted (5 views per slide.) After this evaluation, epididymis was minced in buffered saline and incubated before sperm density determined (microscopically with a haematometer.) To quantifiy spermatogenesis, testicular spermatid head count was determined by removing tunica albuginea and homogenising left testis in phosphte buffered saline. Homogenisation resistant spermatid nuclei were then counted as for sperm density.

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Reproductive function: oestrous cycle:

effects observed, treatment-related

Reproductive function: sperm measures:

effects observed, treatment-related

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
Terminal body weight was decreased by 9 and 14% in males given 4500 and 6000 ppm 2-butoxyethanol. In females, body weights were decreased by 14 and 22% at these concentrations.

REPRODUCTIVE FUNCTION: ESTROUS CYCLE (PARENTAL ANIMALS)
There were no significant differences from the control group in oestrous cycle length for treated females, although females treated at 4500 and 6000 ppm spent more time in dioestrous than the other groups. This correlates with the smaller uterine size, which was attributed to a secondary consequence of reduced body weight gain.

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS)
The only spermatozoal measurement that showed significant change relative to the control group was sperm concentration which was slightly decreased in all groups of treated males; however, this effect was not dose-related.

ORGAN WEIGHTS (PARENTAL ANIMALS)
There was no treatment effect on testis weights but there was a reduction in the size of the uterus in females at 4500 and 6000 ppm. There was aslo a decreae in the epididymal weights in the top two dose groups. However, changes in uterine and epididymal weights were considered by the authors to be secondary to the reduction in body weight gain rather than a direct effect of 2-butoxyethanol.

HISTOPATHOLOGY (PARENTAL ANIMALS)
In the rat, haematotoxicity was evident in males at doses of and above 3000 ppm and in all female groups.

Dose descriptor:

NOAEL

Effect level:

> 452 mg/kg bw/day (actual dose received)

Sex:

male

Basis for effect level:

other: sperm parameters

Dose descriptor:

NOAEL

Effect level:

> 470 mg/kg bw/day (actual dose received)

Sex:

female

Basis for effect level:

other: estrus cyclicity, vaginal cytology.

Reproductive effects observed:

not specified

Data on estrous cycling

Study parameters	0 ppm	3000 ppm	4500 ppm	6000 ppm
n	7	6	7	6
Necropsy body weight (g)^1	186 + 4	172 + 2	160 + 2	145 + 2
Estrous cycle length (days)	6.50 + 0.70	6.83 + 0.95	7.57 + 0.53	5.83 + 0.70
Estrous stages (% of cycle)
Diestrus	28.9	45.6	52.8	67.5
Proestrus	8.8	11.4	13.9	7.0
Estrus	57.9	38.6	20.4	17.5
Metestrus	4.4	4.4	13.0	7.9

¹ Based on n = 10.

Vaginal cytology during the estrous cycle of the rat¹

Time (days)	Stage	Vaginal smear
0.5-1	Proestrus (P)	Many rounded epithelial cells, few leukocytes
1-2	Estrus (E)	Cornified epithelial cells, no leukocytes
0.5-1	Metestrus (M)	Maximum number of leukocytes, often in clumps surrounding epithelial cells.  For our purposes this will be classified as part of Diestrus.
1.5-2	Diestrus (D)	Few epithelial cells; few to many leukocytes. Sometimes divided into Diestrus I and II

¹ Modified from Zarrow et al. (J Endocrinol, 30, 87 -95, 1964).

Conclusions:

No effects on sperm parameters or estrus cycle/vaginal cytology could be identified that were primarily as a result of treatment with 2-butoxyethanol.

Executive summary:

In a reliable 90 day repeat dose study using oral exposures via drinking water up to 450 -470mg/kg/day in male and female rats, a number of reproductive parameters were examined in the animals that survived to termination. In males, a decrease in epididymal weights was noticed but this was in proportion to overall reduced body weight. Sperm concentrations were also reduced by approximately 5 -10% in all dose groups but there was no dose response relationship evident. There were no effects on estrous length but some evidence that the two highest dose group animals spent more time in the diestrus stage. This correlated with the smaller uterine size, which was attributed to a secondary consequence of reduced body weight gain. In addition, the lack of effect on overall estrous cycle length and absence of histopathologic lesions suggest that the effects on estrous cycle length are unlikely to indicate a specific treatment-related reproductive effect. Thus, the effects on male and female rat reproductive endpoints are not considered to be indications of selective reproductive system toxicity.  The effects seen were minor in nature, not seen in males and only occurred in the presence of other significant systemic toxicity (i.e., decreased body weights, marked haematotoxicity).  In conclusion, the study does not indicate any primary effects on fertility that can be directly attributed to treatment.

Synopsis

NOAEL (sperm effects)>452mg/kg/day

NOAEL (oestrus cyclicity) >470mg/kg/day

Materials and methods

Test material

Test material information

Constituent 1

Reference substance name:

2-isopropoxyethanol

EC Number:

203-685-6

EC Name:

2-isopropoxyethanol

Cas Number:

109-59-1

Molecular formula:

C5H12O2

IUPAC Name:

Propan-2-ol

Details on test material:

- Name of test material (as cited in study report): ethylene glycol monoisopropyl ether

Results and discussion

Results: P0 (first parental generation)

Effect levels (P0)

Dose descriptor:

NOAEC

Effect level:

630 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

mortality

body weight and weight gain

reproductive performance

Target system / organ toxicity (P0)

Critical effects observed:

no

Results: F1 generation

Effect levels (F1)

Dose descriptor:

NOAEC

Generation:

F1

Effect level:

635 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

body weight and weight gain

Target system / organ toxicity (F1)

Critical effects observed:

no

Overall reproductive toxicity

Reproductive effects observed:

no