Diethyl oxalate

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

OECD TG 421 (GLP-conform) in rats: NOAEL for reproductive toxicity = 30 mg/kg bw/d (observed effects considered to be secondary to nephrotoxicity)

Effect on fertility: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

30 mg/kg bw/day

Species:

rat

Quality of whole database:

GLP and guideline study, whole database factor: 1.

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Diethyl oxalate was tested for reproduction/developmental toxicity using the Reproduction Developmental Toxicity Screening Test according to OECD Test Guideline 421 and GLP.

The test substance was administered daily to rats dissolved in olive oil using a stomach tube. Four groups of animals were included in the study, 3 treated groups (doses 30, 90, 270 mg/kg of body weight/day) and one control group (vehicle only). Each group consisted of 12 males and 12 females.

The treated groups were administered daily for the following periods: males and females - 2 weeks prior to the mating period and during the mating period; pregnant females - during pregnancy and till the 3rd day of lactation; males - after mating period- totally for 28 days; nonpregnant females (mated females without parturition) - for 25 days after the confirmed mating.

Administration of 270 mg/kg bw/d caused severe suffering and mortality (one female died, another was sacrificed in a moribund state). Severe suffering was characterized by severe oxalate nephrolithiasis (already with protein casts in tubules) accompanied by bad clinical status, reduced food consumption and reduced body weights leading to cachexia towards the end of the study. This demonstrates that the highest dose level exceeded by far the maximum dose which should have been tested according to OECD test guideline 421.

Oxalate nephrolithiasis (oxalate crystals and atrophy or necrosis of epithelium) accompanied by morphological changes of the kidney (enlargement and color changes) was also found in all male and female animals of the 90 mg/kg bw/d dose groups. Four males had also glomerulonephrosis. In this dose group, male body weights were reduced by 4.4% in comparison to control group animals from week 3 until study end. Body weight reduction was more pronounced in females (-11.7 % in comparison to control at study end).

The following changes in the male reproductive system were noted: degeneration of spermatids in two males, vacuolation of Sertoli-like cells in one male, changes in sperm motility and sperm morphology, slightly decreased absolute and relative prostate weight. These changes are considered secondary to the observed nephrotoxicity. No adverse effects on the female reproductive system were reported. The effects noted on reproduction parameters (two aborted females, increased post-implantation losses) are also considered as not directly substance related but secondary to the impaired health condition of the pregnant females due to the observed kidney toxicity. The decreased number of pups per dam (and as a consequence the reduced litter weight) and the decreased pup weight can also be ascribed to the poor health condition of the dams treated at 90 mg/kg bw/d. Malformations in pups were not observed.

 

The lowest dose level (30 mg/kg bw/d) did not cause adverse effects in parent males, females and pups. Consequently the NOAEL of 30 mg/kg bw/d can be derived for parental systemic and reproductive toxicity as well as for embryotoxicity and developmental toxicity.

 

Effects comparable to the ones seen in the above study with Diethyl oxalate at 90 mg/kg bw/d have been reported in a two-generation reproductive toxicity study in mice with Oxalic acid (Gulati et al., 1995, summarized in EMEA, 2003). This indicates that the toxicity of Diethyl oxalate is caused by its hydrolysis product Oxalic acid. With regard to classification and labeling, Oxalic acid is not classified for reproductive toxicity.

 

Gulati DK et al. (1985). Oxalic Acid: Reproduction and Fertility Assessment in CD-l Mice When Administered in Drinking Water (Revised September 1985); PB86-167053.

Effects on developmental toxicity

Description of key information

OECD TG 421 (GLP-conform) in rats: NOAEL for developmental toxicity = 30 mg/kg bw/d (observed effects considered to be secondary to nephrotoxicity)

OECD TG 414 (GLP-conform) in rabbits with the structural analogue oxalic acid (main metabolite of the target substance): NOAEL for maternal and embryo fetal toxicity = 450 mg/kg bw/d (no adverse effects observed)

Effect on developmental toxicity: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

30 mg/kg bw/day

Species:

rat

Quality of whole database:

GLP and guideline study, whole database factor: 1

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

OECD TG 421 - Reproductive / Developmental toxicity screening test in rats:

See above - Discussion for effects on fertility.

OECD TG 414 - Prenatal developmental toxicity study in rabbits:

In a GLP-conform prenatal developmental toxicity study according to OECD TG 414 Oxalic acid (CAS 6153-56-6; purity: 99.6 %; formulated in powder feed) was administered daily by diet to three treatment groups of 24 mated female New Zealand White rabbits per group from day 6 to day 29 of gestation at dose levels of 1000, 5000 and 10000 ppm. A control group comprised of 24 female rabbits was administered powder feed alone.

A dose range finding study was carried out before the main experiment to confirm the dose levels of the test item for the main study. Three groups (low, intermediate and high) consisting of 5 pregnant female rabbits each were treated daily from day 6 to day 29 of gestation at dose levels of 1000, 3000 and 10000 ppm.

In the dose range finding study, no effects were observed for mortality/viability, clinical signs, feed consumption, body weight, gross pathology and variations/malformations in fetuses subjected for external examination. Dose levels for main study were selected based on this dose range finding study results.

No mortality was observed in any of the treated animals throughout the scheduled treatment period.

No clinical signs were observed in any of the female animals treated at control (0 ppm), low (1000 ppm), intermediate (5000 ppm) and high dose (10000 ppm) groups.

No significant difference was observed in body weight, body weight gain (%) and feed consumption attributable to treatment in all treatment groups when compared with control group.

No treatment-related effects were observed in reproduction parameters such as corpora lutea count, early and late resorption and number of live and dead fetuses, pre-implantation loss, post-implantation loss as well as fetal sex ratio at any dose level. Litter weight and fetal body weight were significantly not different from the control group. The external and visceral variations observed were randomly distributed across the groups. Therefore, findings were considered as incidental findings and not test item-related. Type and distribution of variations noted during skeletal examination at all dose levels did not indicate any test item-related effects.

The oral (dietary) administration of Oxalic acid to pregnant New Zealand White rabbits from day 6 to day 29 of gestation at dose levels of 1000, 5000 and 10000 ppm resulted in no treatment-related maternal and embryo-fetal toxicity. Hence, the highest dose level employed, i.e. 10000 ppm (corresponding to 450 mg/kg bw/d) is the No Observed Adverse Effect Level (NOAEL) for maternal and embryo-fetal toxicity in New Zealand White rabbits under the conditions of this study.

There are no data for Diethyl oxalate from a teratogenicity study with a second species available to completely fulfil the reproductive toxicity data requirements set out in Annex X of Regulation (EC) No. 1907/2006. On the basis of the rapid hydrolysis of Diethyl oxalate to Oxalic acid, the result from the prenatal developmental toxicity study in rabbits with Oxalic acid can be transferred to Diethyl oxalate. Herein no adverse effects were observed up to and including the highest tested dose. The nephrotoxicity observed in rats, which led to the adverse reproductive and developmental effects, was not found in this rabbit study.

Justification for classification or non-classification

The available experimental test data are reliable and suitable for classification purposes under Regulation 1272/2008. As a result the substance is not considered to be classified for reproductive toxicity under Regulation (EC) No. 1272/2008, as amended for the tenth time in Regulation (EU) No 2017/776. The observed effects are considered to be secondary to the nephrotoxicity of the parental animals.

 

This is in agreement with the non-classification of Oxalic acid, the final metabolite of Diethyl oxalate which is regarded as responsible for the nephrotoxic effects.