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Description of key information

A NOAEL for subacute oral toxicity of 20 mg/kg bw/day was derived from a 28 day toxicity study in rats (according to OECD TG 407; GLP-conform) exposed to the test item.

A NOAL for chronic oral toxicity of ca. 63 mg/kg bw/day was derived from a 90 day toxicity study in rats (according to OECD TG 408; GLP-conform) exposed to the structural analogue oxalic acid (main metabolite of the target substance).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
20 mg/kg bw/day
Study duration:
subacute
Species:
rat
Quality of whole database:
GLP and guideline study
System:
urinary
Organ:
kidney

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

OECD 407: 28 Days repeated dose toxicity study in rats (oral)

The test substance was administered orally to Wistar rats daily for 28 days as suspension in olive oil using a stomach tube. The study included four main groups and two satellite groups of animals. Doses for the main study were 0, 20, 60, 180 mg/kg bw/day and were chosen on the basis of the results of a dose-range finding experiment. Each main group and satellite group consisted of 6 males and 6 females. The satellite groups contained one control group (vehicle only) and one treated group (180 mg/kg bw/day). After the sacrifice of the main group animals the satellite animals were observed for a 14 days period without treatment.

There were no unscheduled deaths during the test. No clinical signs of toxicity were observed. The functional observations (behavior, sensory reactivity, grip strength) evidenced no effect of the test substance. Kidney toxicity was identified as the primary and predominating adverse effect. It was characterized by dose dependent and irreversible oxalate nephrolithiasis in males and females of the mid and high dose group (mild and severe degree at mid and high dose, respectively). The kidney damage was accompanied by macroscopic changes in the kidney at 180 mg/kg bw/d and by significantly increased kidney weights in both sexes at 180 mg/kg bw/d and in females at 60 mg/kg bw/d. The observed findings did not reverse during the 14-d recovery period. The deposition of oxalate crystals in cortex, medulla and also freely in the renal pelvis was identified as mode of action. The remaining effects seen in the study (i.e. slight reversible body weight reduction, reduced food and increased water consumption, changes in some blood and clinical chemistry parameters, changes observed during urinalysis) are considered as secondary effects caused by the severe kidney damages.

No adverse effects were noted at the lowest dose level.

The value of NOAEL (No Observed Adverse Effect Level) for MALES and FEMALES was 20 mg/kg/day. The value was established on the basis of haematology, biochemistry and histopathological examination. The test substance had specific target organ toxicity effect on the kidneys.

The target organ effects can be ascribed to the main metabolite of Diethyloxalate (DEO), i.e. Oxalic acid (OA). For this substance identical renal effects and the same mode of action (deposition of oxalate crystals in kidney tissues) have been reported (EMRA, 2013).

Crystallization of oxalic acid is dependend on the concentration and since the plasma half-life of OA was determined to be about 2h bolus application of DEO has a significant impact on the effect and effect level of the resulting kidney toxicity.

OECD 408: 90 Days repeated dose toxicity study in rats (oral)

In a sub-chronic oral repeated dose toxicity study according to GLP and OECD TG 408 Oxalic acid (CAS 6153-56-6; purity: 99.6 %) was administered to Wistar rats (10 animals per sex and dose) through the diet for a period of 90 days. The reversibility of treatment related changes was assessed after a treatment-free 28-day recovery period.

Dose levels for the main study were selected based on a dose range finding study, were rats (4 animals per sex and dose) were treated with the test substance via the diet for a period of 28 days at doses of 1000, 5000 and 10000 ppm followed by a 14-days reversal period. In this 28-d dose range finder, histopathology revealed mineralization of Oxalic acid in the kidneys at dose levels of 10000 and 5000 ppm. Considering these observations, the dose of 1000 ppm was selected as high dose for the 90-day study.

As intermediate and low dose 500 ppm and 250 ppm were chosen, respectively.

No mortality as well as clinical signs were observed in any of the animal treated with test item at dose levels of 250, 500 and 1000 ppm throughout the experimental and recovery period.

Ophthalmological examination did not reveal any abnormalities in the control and high dose treated animals at the end of treatment period. During the 90 consecutive days of treatment period, the body weight (g), body weight gain (%) and food consumption in animals across all dose groups was found to be non-significant different when compared with control animals. Functional observation battery parameters did not show any treatment related significant changes in all treated groups. Changes observed in the haematological and clinical biochemistry parameters were marginal and could not be attributed to the test item administration as these values were considered as biological variation. As microscopically no test item-related changes were observed in the evaluated organs in all animals, observed changes in organ weights were considered as biological variation.

Since no adverse effects were observed at the highest tested dose, i.e. 1000 ppm, the same was selected as NOAEL. The value is equivalent to 63 mg/kg body weight (actual test item consumed by the animals).

There are no data on sub-chronic repeated dose toxicity of Diethyl oxalate available to completely fulfil the repeated dose 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 the Oxalic Acid the result from the sub-chronic repeated dose toxicity study with Oxalic acid can be transferred to Diethyl oxalate. Despite the fact that Oxalic acid did not cause any adverse effects up to and including an oral dose of 63 mg/kg bw/d for 90 consecutive days (for details see below), whereas the LOAEL for Diethyl oxalate (derived from the above described subacute repeated dose toxicity study) was 60 mg/kg bw/d, the results of the sub-chronic repeated dose toxicity study with Oxalic acid can be transferred to Diethyl oxalate. Based on this it is assumed, that the effect level for nephrotoxicity (caused by the deposition of oxalate crystals), which is considered as predominant adverse effect, does not decrease at a longer treatment period of the animals. Therefore, the NOAEL of the subacute repeated dose toxicity study with Diethyl oxalate is regarded as sufficient to cover a sub-chronic exposure duration as well.

Justification for classification or non-classification

The test substance caused nephrotoxicity in the 28-d oral gavage study in rats at 60 and 180 mg/kg bw/d. The findings represent significant toxic effects with relevance to human health. The available experimental test data are reliable and suitable for classification purposes under Regulation 1272/2008. Accordingly, the test substance is considered to be classified for repeated dose toxicity as STOT RE, category 2, H373 (target organ: kidney) under Regulation (EC) No 1272/2008 as ammended for the tenth time in Regulation (EU) No 2017/776.