1,1'-(ethane-1,2-diyl)bis[pentabromobenzene]

Toxicity to reproduction

Administrative data

Endpoint:

extended one-generation reproductive toxicity - with developmental neurotoxicity (Cohorts 1A, 1B without extension, 2A and 2B)

Type of information:

experimental study planned

Remarks:

A Tiered testing proposal is submitted in order to minimize the use of experimental animals

Justification for type of information:

TESTING PROPOSAL ON VERTEBRATE ANIMALS:
Extended one generation study in rats according to Annex X of REACH with cohorts 2A and B
[Please provide information for all of the points below. The information should be specific to the endpoint for which testing is proposed. Note that for testing proposals addressing testing on vertebrate animals under the REACH Regulation this document will be published on the ECHA website along with the third party consultation on the testing proposal(s).]

NON-CONFIDENTIAL NAME OF SUBSTANCE: 1,1'-(Ethane-1,2-diyl)bis[pentabromobenzene] (EBP),
CAS number: 84852-53-9
EC-number: 284-366-9
- Name of the substance on which testing is proposed to be carried out:
1,1'-(Ethane-1,2-diyl)bis[pentabromobenzene] (EBP)

CONSIDERATIONS THAT THE GENERAL ADAPTATION POSSIBILITIES OF ANNEX XI OF THE REACH REGULATION ARE NOT ADEQUATE TO GENERATE THE NECESSARY INFORMATION [please address all points below]:
- Available GLP studies
Available GLP studies include several repeated dose studies, including a 90-day oral gavage study with extended evaluation of the reproductive organs did not reveal any indications of a possible impairment of fertility up to the highest dose level of 1000 mg/kg bw tested. Developmental toxicity studies in rats and rabbits up to the limit dose likewise showed not adverse effect. However, a recent developmental neurotoxicity study, although also revealing a NOAEL of 1000 mg/kg bw and day in rats for most maternal and developmental endpoints including and extensive battery of behavioural tests, showed some changes in brain morphometrie parameters in male F1 rats only, that were considered ambiguous as the findings could also be related to the section and measuring methods applied. Toxicokinetic studies after single oral administration to rats did show that the substance is hardly absorbed in the gastro-intestinal tract and absorption by other routes is also considered very low. This finding was also confirmed in the recent fish feeding study showing very low uptake and rapid elimination after repeated exposure of fish.
- Available non-GLP studies
No relevant non-GLP studies covering the fertility endpoint were identified.
- Historical human data
There are no human data available concerning the fertility endpoint.
- (Q)SAR
No valid QSAR methods are available that cover the complicated endpoint of toxicity to reproduction. According to ECHA guidance R7.a. (2017) there is a large number of potential targets and mechanisms associated to reproductive toxicity, which on the basis of current knowledge, cannot normally be adequately covered by a battery of QSAR models. I addition there is no indication of a possible adverse effect on reproduction in the current database that could be addressed by targeted QSAR’s.
- In vitro methods
According to the ECHA guidance R7a, 2017 non-animal testing approaches do at present not provide information equivalent to the animal test and cannot be used alone for classification and labelling or risk assessment purposes. I addition there is no indication of a possible adverse effect on reproduction in the current database that could be addressed by targeted in vitro tests.
Furthermore any in vitro testing with EBP is hampered by its very low solubility in water and other solvents compatible with in vitro assays.
- Weight of evidence
The available GLP guideline studies did not show adverse effects after 90 day repeated oral dosing of up to 1000 mg/kg bw/day of EBP. Extended histopathology of the reproductive organs was performed in these studies and did not show any substance related adverse effects. Two developmental toxicity studies in rats and rabbits by oral gavage at the limit dose of 1000 mg/kg bw/day likewise did not show any adverse effect. In addition Toxicokinetic studies after single oral administration to rats did reveal a very low, almost negligible absorption from the gastrointestinal tract. This finding was also confirmed in the recent fish feeding study showing very low uptake and rapid elimination after repeated exposure of fish. Dermal absorption of EBP is not expected. Dermwin v1.43 estimates dermal absorption of 3.2E-15 mg/cm2-event using Fick's first law of diffusion or 5.6E-9 mg/cm2-event using equations contained in the program. This is consistent with the high molecular weight and negligible solubility of the substance.
From these data one could conclude that there is no concern for a possible adverse effects on reproduction.
Human exposure to the substance is limited, but can occur also through articles or dust from articles.
In any case a waiving on the grounds of negligible uptake and no effects at the limit dose in repeated dose studies seems not acceptable according to REACH Annex X for the EOGRT study and ECHA's information on manual verification at completeness check of Nov. 21, 2018.
In addition, a recent developmental neurotoxicity study, although also revealing a NOAEL of 1000 mg/kg bw and day in rats for most maternal and developmental endpoints including an extensive battery of behavioural tests, showed some changes in brain morphometrie parameters in male F1 rats only, that were considered ambiguous, as the findings could also be related to the section and measuring methods applied. Further testing as proposed, could help to clarify these findings and their relevance.
As the absorption of EBP is very slow, a kinetic study with repeated dosing at different dose levels including pregnant females could give additional information of possible absorption, conditions to reach steady state and distribution to the developing embryo/foetus after repeated exposure to the substance. Such a study would also be informative for chosing the dose levels for an EOGRT study
ECHA in a response to our original testing proposal responded, that such a preliminary study should not be part of a testing proposal, but as it involves vertebrate animal testing, we prefer to include it in the full proposal.
- Grouping and read-across
The substance has very unique physical chemical properties and structure that do not allow any meaningful read across to other related substances.
- Substance-tailored exposure driven testing [if applicable] : not applicable some exposure is expected (workplace and low exposure to some articles)
- Approaches in addition to above:
As indicated above, we propose to perform a toxicokinetic study after repeated exposure to 1000 mg/kg bw and lower exposure levels (e.g. 10 mg/kg bw) in pregnant rats in order to learn more about the absorption, distribution and elimination behaviour of the substance.
Should the low bioavailability be confirmed, an extended one generation study may not be needed due to a lack of systemic exposure.
Should this study on the other hand reveal a considerable higher uptake after repeated than after single exposure and availability to the offspring, an extended one generation study including a developmental neurotoxicity cohort is proposed as a second Tier.
The EOGRT study should be performed including 10 weeks of premating exposure, as the absorption of the substance is slow.
In addition because of the ambiguous findings in the developmental neurotoxicity study, we propose to include cohorts 2A and 2B in case the toxicokinetic study shows a distribution to the developing embryo to clarify possible effects in particular after a longer exposure duration.
The dose levels will also be chosen based on the existing 90-day study and the additional kinetic information. However, a dose-range finding study may still be needed depending on the results of the kinetic study.
- other reasons: not applicable
- Considerations that the specific adaptation possibilities of Annexes VI to X (and column 2 thereof) were not applicable:
As indicated above column 2 of Annex X does not give much room for adaptation options (non-animal testing) at this level for this endpoint. However, with our tiered testing proposal allowance of an adaptation in case of a negligible uptake after repeated exposure would in our opinion be an adequate adaptation.

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 443 (Extended One-Generation Reproductive Toxicity Study)

Version / remarks:

including cohorts for developmental neurotoxiciy (see justification) and provided the proposed kinetic study in the tiered testing proposal shows bioavailability after repeated exposure.

Justification for study design:

Available toxicokinetic data after single exposure to EBP suggest a very limited uptake of the substance and existing repeated dose toxicity studies up to the limit dose of 1000 mg/kg bw by the oral route did not suggest any adverse effect. In the 90-day study extended examination of the reproductive organs was included and also showed no test substance related adverse effect. Developmental toxicity studies in rats and rabbits up to the limit dose likewise showed not adverse effect. However a recent developmental neurotoxicity study, although also revealing a NOAEL of 1000 mg/gk bw and day in rats for most maternal and developmental enpoints including and extesnive battery of behavioural tests showed some findings on brain morphometrie parameters in male F1 rats only, that were considered ambigous as the findings could also be related to the section and measuring methods applied.
The registrants therfore propse a tiered testing approach starting with a repeated dose toxicokinetic study in pregnant rats to look for maternal and foetal blood levels following oral dosing.
Should the low bioavailability be confirmed,an extended one generation study might not be needed.
Should ths study on the other hand reveal a considerable higher uptake after repeated than after single exposure and availability to the offspring, an extended one generation study including developmental neurotoxicity cohorts (2A and 2B is proposed as a second Tier.
SPECIFICATION OF STUDY DESIGN FOR EXTENDED ONE-GENERATION REPRODUCTION TOXICITY STUDY WITH JUSTIFICATIONS [please address all points below]:

- Premating exposure duration for parental (P0) animals 10 weeks to ensure exposure and account for a slow absorption rate.
- Basis for dose level selection : repeated dose and DNT study: 100, 300, 1000 coudl be modified based on the results of the kineitc study.
- Inclusion/exclusion of extension of Cohort 1B: only if triggered by the results in F1 or the kinetic study
- Termination time for F2 : F2 inclusion only foreseen if triggered by the results in F1 or the kinetic study
- Inclusion/exclusion of developmental neurotoxicity Cohorts 2A and 2B iclusion as ambiquous result in the DNT study
- Inclusion/exclusion of developmental immunotoxicity Cohort 3 exclusiom of immunoxicity cohort as no indication from previous studies
- Route of administration : oral
- Other considerations, e.g. on choice of species: Rat

Test material

Test material information

Constituent 1

Reference substance name:

1,1'-(ethane-1,2-diyl)bis[pentabromobenzene]

EC Number:

284-366-9

EC Name:

1,1'-(ethane-1,2-diyl)bis[pentabromobenzene]

Cas Number:

84852-53-9

Molecular formula:

C14H4Br10

IUPAC Name:

1,2,3,4,5-pentabromo-6-[2-(2,3,4,5,6-pentabromophenyl)ethyl]benzene

Test material form:

solid

Specific details on test material used for the study:

For the kinetic test: radiolabeled material in the aromatic ring

Test animals

Species:

rat

Sex:

male/female

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Remarks:

could be changed based on the kineitc sudy

Results and discussion

Overall reproductive toxicity

Reproductive effects observed:

not specified