Diethyl ether

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Additional information

The clinical significance of elevated levels of abnormal spermatozoa caused by certain substances in the non-guideline study performed in male C57BL mice by Land (1981) is not clear. Nonetheless, in the case of diethyl ether, no increased numbers of abnormal spermatozoa above the control animals was observed, after 4h/day for 5 consecutive days exposure at concentrations of 3200, 16,000, or 32,000 ppm.

The single dose inhalation study in Wistar rats conducted by Arena (2002) is considered not to be reliable due to the uncontrolled manner of exposure to diethyl ether. It cannot be ruled out that the effects observed, including a reduction in wet weight of seminal vesicles, a significant reduction in spermatids and spermatozoa in males, and a 26% reduction in pregnancy rate compared to controls, are the result of hypoxia on the developing animal, either due to the anaesthesia itself, or physical displacement of oxygen from the "exposure chamber" by the heavier diethyl ether vapour. Similar effects on development and fertility but caused by other non-chemical stressors, were cited from the literature by the authors. Again, the significance of a positive result in such a study design, and its relevance to humans, has not been validated and is unclear.

Short description of key information:

According to REACH (REGULATION (EC) No 1907/2006), a two-generation reproductive toxicity study is required according to column 1 of Annex IX, if the 28-day or 90-day study indicates adverse effects on reproductive organs or tissues. Based on observations of increased relative weights of testes/epididymides in rats treated with diethyl ether by oral gavage for 90 days (U. S. EPA, 1997) and of an increased number of abnormal sperm in rats exposed to diisopropyl ether by inhalation for 90 days (Dalbey and Feuston, 1996), the registrant is proposing to read-across to a study to be performed using di-isopropyl ether according to OECD 416 (2-generation reprotoxicity study) resp. OECD 443 (extended one generation reproductive toxicity) whichever will be approved by ECHA.

Effects on developmental toxicity

Description of key information

430 ppm, NOAEC for rat, 6 hours/day on days 6 to 15 of gestation (Dalbey and Feuston)

73000 ppm, rat, 1 hour anaesthesia (Schwetz); no significant effects

65000 ppm, mouse, 1 hour anaesthesia (Schwetz); no significant effects

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The absence of developmental toxicity effects is confirmed by an OECD 414 study with rabbits (second species) in which also no developmental toxicity effects were observed in the high dose group (NOAEL = 200 mg/kg bw/d)

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Dose descriptor:

NOAEC

1 800 mg/m³

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

A key, non-GLP subchronic and developmental toxicity study of vaporized diisopropyl ether in rats was conducted equivalent to OECD Guideline 414 (Dalbey and Feuston 1996).

The registered substance, and the two read-across substances, DME and DIPE, all belong to the class of aliphatic ethers, each possessing two aliphatic alkyl groups connected by a single oxygen atom. Transition from DME to DEE and DIPE occurs with elongation of the aliphatic alkyl groups. DME possesses two methyl (C1) groups, DEE two ethyl (C2) groups and DIPE two isopropyl (C3) groups. These three mono-functional substances are considered to be members of a homologous series of aliphatic ethers, within which in general the properties of the individual homologues are expected to vary in a predictable manner, and in particular, the properties of DEE are expected to lie between those of the smaller DME and the larger DIPE. This expectation is supported by the known physicochemical properties.

Considering their structural similarities in sharing a common functional group, and given that their physicochemical properties follow a pattern, DME, DEE and DIPE can be considered as a “group”. As such, DME and DIPE are expected to be appropriate surrogates for DEE.

Sprague-Dawley rats were exposed to 0 (untreated), 0 (sham controls), 430, 3095, or 6745 ppm (0, 0, 1800, 12940, or 28200 mg/m³) of diisopropyl ether for 6 hours/day on Days 6 to 15 of gestation and were killed on gestation Day 20.

There were no treatment related changes in serum chemistry parameters, macroscopic examinations, or reproductive parameters (i.e. number of pregnant females, percent pre-implantation loss, percent resorptions, and litter sizes). Lacrimation and salivation were noted in a few DIPE-exposed females at the highest concentration during, or immediately following, exposures. The animals returned to normal appearance shortly after cessation of each daily exposure. In general, animals housed in chambers gained less weight and consumed less food during the exposure period than the untreated controls (statistically significant at 6745 ppm relative to both of the control groups). Statistically significant decrease in body weight gains were seen on gestation days 6 to 16 at all dose levels (compared to untreated controls for the low- and mid-dose groups and compared to both controls at the high-dose group). Statistically significant decrease was seen in food consumption on gestation days 6 to 16 at the mid- and high-dose groups (compared to untreated controls on gestation days 6 to 13 and compared to both control groups on gestation days 13 to 16).

Foetal body weight was not affected by exposure. Evaluations of foetal skeletons revealed a significant increase in rudimentary (small, discrete ossification) or short (less than one-half the length of the preceding rib) 14th ribs in foetuses exposed to DIPE at concentrations of 3095 and 6745 ppm. No other exposure-related findings were noted at the time of foetal evaluations. The study authors have stated that "the observed increase in the incidence of rudimentary 14th ribs does not appear to be indicative of an adverse effect on development" at the concentrations tested.

A NOAEC was not reported by the study authors. Review of the study data suggests that a NOAEC of 430 ppm can be derived for maternal toxicity based on the decrease in body weight gain and food consumption at higher concentrations, and a NOAEC of 430 ppm can be derived for foetal toxicity based on increases in rudimentary/short 14th ribs at higher concentrations (although the authors argue that this "variation" is not conclusive evidence of developmental toxicity).

 

The results of the study by Schwetz (1970) are based on a conference-proceedings abstract, from which only limited information is available. Pregnant Sprague-Dawley rats and Swiss-Webster mice were anesthetised for 1 hour, during early or late organogenesis, at 73000 ppm and 65000 ppm of 1,1’-dioxyethane, respectively. The animals were sacrificed one day prior to normal parturition; no significant effects were observed.

 

The available information on the inhalation study carried out by Garcia (1990) in Sprague-Dawley rats is too limited to make an evaluation.

 

The study design by Smith (1968), single-dose exposure at various concentrations of 1,1’-dioxyethane for 5 to 6 hours on day 1, 2, 3, or 4 of incubation for up to 18 days in white leghorn chicken embryos, has not been validated and the relevance of any potential findings to humans, even at more realistic concentrations, is not known. While teratogenic effects were observed, none were considered organ specific, apart from a prevalence of eye abnormalities. The results were considered to be normal for exposure close to the embryo's LD50. Exposures were in the range 90000 ppm to 300000 ppm for 5 to 6 hours.

 

With the exception of the Dalby and Feuston (1996) study, the concentrations used in the above experiments were not relevant for humans: all were in the explosive range for air-vapour mixtures, all were above the minimum alveolar concentration (i.e. anaesthesia would be induced), and all would cause maternal mortality.

 

Following a request by the European Competent Authority (ECHA) to perform developmental toxicity studies according to OECD Method 414 with rats and rabbits, such studies were performed and the results became available in 2019/2020 and are reported here:

In the study with rabbits, 92 mated female rabbits were assigned to four groups (G1: Sham control, G2: low dose, G3: mid dose and G4: high dose). The test item was administered at 80, 140 and 200 mg/kg/day along with the sham control from GD 6 to GD 28 by gavage.

All rabbits were observed for clinical signs, morbidity and mortality, body weight changes and food consumption. Caesarean section was performed for all the surviving rabbits on GD 29 and dams were examined for gross pathological changes. The uterus was removed by laparotomy, weighed and the contents were examined for number of implantation sites, early and late resorptions and number of foetuses. The number of corpora lutea in ovaries was counted. All the foetuses were sexed, weighed and examined for external malformations. All the live foetuses were examined for visceral and skeletal variations and malformations.

There were no mortalities, at any of the doses tested except for incidence of abortions.

There were treatment related clinical signs of drowsiness, vocalization, uncoordinated straggering gait at 140 and 200 mg/kg/day along with signs of hypernoea and curled up / often asleep posture at 200 mg/kg/day. These clinical signs were observed approximately 10 minutes post dose and all the rabbits recovered within 45 minutes to 1 hour post dose and were expected pharmacological related transient findings. Mean body weight, weight gain and food consumption were reduced at 140 and 200 mg/kg/day. The maternal and litter data parameters were unaffected up to the high dose of 200 mg/kg/day.

Foetal external, visceral and skeletal examination revealed no signs of teratogenicity up to the highest tested dose of 200 mg/kg/day.

In conclusion, based on the above finding, under the test conditions and doses employed in this study, it is concluded that No-Observed-Adverse-Effect Level (NOAEL) for maternal toxicity is 80 mg/kg/day due to decrease in body weight and food consumption at next higher doses of 140 and 200 mg/kg/day. Foetal developmental toxicity is 200 mg/kg/day as the litter parameters were unaffected by treatment and foetal external, visceral and skeletal examinations revealed no signs of teratogenicity in any of the tested dose levels up to 200 mg/kg/day.

In the study using rats a total of 96 Day 0 pregnant rats were randomly divided into different groups according to the study design as follows: Group G1 (Sham control, 24 animals): 0 mg/kg/day; Group G2 (Low dose, 24 animals): 250 mg/kg/day; Group G3 (Mid dose, 24 animals): 500 mg/kg/day; Group G4 (High dose, 24 animals): 1000 mg/kg/day.

The test item was administered orally (undiluted by gavage) to pregnant rats once daily from GD 5 to GD 19 at the dose levels of 250, 500 and 1000 mg/kg/day for low (G2), mid (G3) and high (G4) dose groups, respectively. Rats in the control (G1) group were sham treated.

The following parameters and end points were evaluated in this study: Clinical signs, body weights, body weight gains, food consumption, gross pathology, gravid uterine weights, intrauterine growth and survival, number of corpora lutea, foetus parameters (sex, weight and anogenital distance and external, visceral and skeletal observations). Approximately half of the foetuses from each litter were examined for visceral (soft tissue) malformations and the remaining half were evaluated for skeletal malformations. In addition, from each dam the thyroids were weighed and subjected to microscopic evaluation, and thyroid hormones were estimated from the blood collected at terminal sacrifice (GD20).

There were no mortalities or gross pathological changes in treated rats at any of the doses tested. At 1000 mg/kg/day, treatment-related expected pharmacological related transient clinical signs of drowsiness were observed approximately 10 minutes post dose and all the rats recovered within 45 minutes to 1 hour post dose. There was statistically significant decrease in mean maternal body weights gain (-26% and -19%) as compared to control animals during the treatment period (GD5 to GD20) and throughout the gestation period (GD0 to GD20) at 1000 mg/kg/day. The corrected body weight at 1000 mg/kg/day was also statistically significantly lower (-7%) compared to control animals. There was statistically significant reduction in feed consumption at 1000 mg/kg/day (up to 33%) as compared to control animals.

The maternal parameters comprising of uterine weight, number of corpora lutea, implantations and early and late resorptions, pre-and post-implantation loss were comparable to sham control group up to the high dose of 1000 mg/kg/day. Gross evaluation of placenta revealed no findings.

No treatment-related effects on litter parameters comprising of total number of foetuses, foetal weights, anogenital distance of male and female foetuses at all the doses tested were observed. The foetal external, visceral and skeletal examinations revealed no signs of teratogenicity or developmental toxicity up to 1000 mg/kg/day. Thyroid hormone profile (T3, T4 and TSH), thyroid gland weights and histopathology of thyroid gland were unaffected by treatment with diethyl ether up to the highest dose of 1000 mg/kg/day.

Based on the above findings, it is concluded that, the No Observed Adverse Effect Level (NOAEL) for maternal toxicity is 500 mg/kg/day due to test item related statistically significant reduction in mean maternal body weight and weight gain, corrected body weight gain and reduction in food consumption at 1000 mg/kg/day.

The NOAEL for foetal developmental toxicity and teratogenicity is 1000 mg/kg/day as foetal external, visceral and skeletal examinations revealed no signs of teratogenicity or developmental toxicity up to 1000 mg/kg/day.

Justification for classification or non-classification

Absence of developmental toxicity in rats and rabbits was shown in two independent OECD 414 studies. No developmental toxicity was observed in rats and rabbit, although maternal toxicity was observed at the high-dose levels in these studies. Thus, the substance is not subject for developmental toxicity classification. There is no information available concerning the affect to sexual function and fertility in adult males and females, as the corresponding study is still running. As a result, for the time being data is lacking for conclusive classification on reproductive toxicity according to Regulation (EC) No 1272/2008, Annex I section 3.7.