Cobalt sulphide

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

Study duration:

subchronic

Species:

rat

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Introductory remark – read-across

 

Read-across entails the use of relevant information from analogous substances (the ‘source’ information) to predict properties for the ‘target’ substance(s) under consideration. Substances whose physicochemical or toxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity may be considered as a category of substances. Structural similarity is a pre-requisite for any read-across approach under REACH (ECHA Read-Across Assessment Framework, 2015).

 

In accordance with Annex XI, 1.5 of the REACH regulation and the ECHA Guidance Read-Across Assessment Framework (ECHA, 2017), the similarities may be based on:

 

1) A common functional group (i.e. chemical similarity within the group);

2) Common precursors and/or likelihood of same breakdown products through physical and/or biological processes which result in structurally-similar degradation products (i.e. similarity through (bio) transformation); or

3) A constant pattern in the changing of the potency of the properties across the group (i.e. of physical-chemical and/or biological properties).

 

Due to the absence of substance specific information for the majority of substances within the cobalt category, the approach will read-across data from representative source substances to all other members of the read-across group.

 

Due to the route-specific toxicological properties of the cobalt category substances, several read-across groups are formed as shown in the table below:

 

	Route	Read-across group
Cobalt category	oral-systemic	bioavailable cobalt substances group
Cobalt category	oral-systemic	inorganic poorly soluble
Cobalt category	oral-systemic	poorly soluble in aqueous solutions with organic ligand
Cobalt category	inhalation-local	reactive
Cobalt category	inhalation-local	non-reactive

 

  Further details on the read-across approach for the dermal sensitisation, oral systemic effects and the inhalation local effects are given in in IUCLID section 13.2.

Cobalt sulfide is assigned to the read-across group oral-systemic: inorganic poorly soluble.

 

Effects on fertility

 

Tricobalt tetraoxide and cobalt sulfide are the source substances for the inorganic poorly soluble cobalt substances group based on the read-across approach as outlined in Appendix 1.1 in the CSR. Two inorganic poorly soluble cobalt substances, tricobalt tetraoxide and cobalt sulfide, have been tested for effects on fertility, resulting in an absence of effects on the reproductive organs of male and female animals up to the limit dose of 1000mg/kg bw/day.

 

In a sub-chronic repeated dose toxicity study, tricobalt tetraoxide was given male and female rats at doses of 0, 100, 300, 1000 mg/kg bw/day. A total of 10 males and 10 females per group were given the test items suspended in 0.5% hydroxypropyl methylcellulose gel orally via gavage once daily for 90 days. Additional 2 groups of 5 male and 5 female animals, dosed with 0, 1000 mg/kg bw/day were assigned as recovery animals, kept for 28 days after the treatment period without receiving the test item. Additional examinations were added to the study design:

 

(i) monitoring of the oestrus cycle pre-dose, during study conduct, at the end of test week 13 and at the end of the recovery period in all female animals

(ii) hormone level status (testosterone, progesterone, 17beta-estradiol) pre-dose, during study conduct, at the end of test week 13 and at the end of the recovery period in all animals

(iii) Detailed histopathologic examination on one testicle and one epididymis (with special emphasis on the qualitative stages of spermatogenesis and histopathology of interstitial testicular structure)

 

During the conduct of the study no deaths occurred and no test item-related changes in behaviour or external appearance were observed. At the high dose of 1000 mg Tricobalt tetraoxide/kg bw/day, a slightly reduced body weight by up to 10 %, body weight gain, and body weight at autopsy were observed. This is considered to be a test item-related effect. The female animals were only marginally affected by up to 5 %, lacking statistical significance.

 

No test-item related changes were observed during histopathological examination of the male and female reproductive organs. Histopathological examination performed on one testicle and one epididymis with special emphasis on the qualitative stages of spermatogenesis (proliferative, meiotic and spermiogenic phases) and histopathology of the interstitial testicular structure, did not reveal any test item-related effects. No test item-related difference was noted in the mean number of oestrous cycles for the female animals. No test item-related influence was noted on the serum levels of the hormones testosterone, progesterone, and 17 beta-estradiol in the male and female animals treated with 1000 mg tricobalt tetraoxide/kg bw/day compared to the control group during study conduct, at the end of the treatment period, and at the end of the recovery period.

 

The No-Observed-Effect-level (NOEL) for fertility/reproductive effects was 1000 mg tricobalt tetraoxide/kg bw/day by oral administration based on a complete absence of effects on reproductive organs, oestrus cycle, qualitative sperm staging and hormone levels.

 

 

In acombined repeated dose toxicity studies with the reproduction/developmental toxicity screening test (according to OECD 422 and under GLP), cobalt sulfide was administered orally to rats at dose levels of 100, 300 and 1000 mg/kg b.w./day during the pre-mating, mating and post-mating periods to parental males as well as during the pre-mating, mating, gestation and lactation periods until day 3 post-partum (or shortly thereafter) to parental female animals. None of the parental animals died prematurely. The only treatment-related finding, not regarded as adverse, was piloerection noted in few male or female rats from a dose level of 100 mg Cobalt sulfide/kg b.w./day onwards. Macroscopic inspection did not reveal any test item-related changes at necropsy. Histopathological inspection did not reveal any pathological changes. No test item-related influence was noted on the sperm staging or interstitial cell structure (qualitative examination). No test item-related influence was noted on mating behaviour, fertility, implantation, the gestation length or the birth index. No test item-related influence was noted at 100, 300 or 1000 mg Cobalt sulfide/ kg b.w./day on the growth and development of the offspring from conception until sacrifice on day 4 post-partum or shortly thereafter.

The NO(A)EL for effects on the F0-generation and reproductive toxicity was above 1000 mg/kg b.w./day, based on a complete absence of adverse effects.

 

Conclusion

 

There is a substantial data base on the effects of soluble cobalt compounds to organs of male reproduction. However, the studies in themselves do not show a clear dose-response relationship and beyond that suffer from several shortcomings in experimental design and reporting. Furthermore, none of the available studies represent state-of-the-art, guideline-compliant, extended one-generation reproduction toxicity studies or other relevant study designs, from which robust no-effect levels for human risk assessment could be derived as specifically required under the REACH regulation. For this reason, DNELs for reproductive toxicity cannot be established with adequate reliability. Moreover, the above mentioned studies have a primary focus on effects in males, whereas there are no adequate data which would allow a hazard or risk assessment for effects on female reproduction. Existing studies show a hazard for male reproductive organs at high doses of cobalt dichloride. These findings have led to an existing harmonised classification as Cat 1B (H360F) for the substances cobalt dichloride, cobalt sulfate, cobalt diacetate, cobalt carbonate and cobalt dinitrate as well as to a self-classification of all remaining members of the bioavailable cobalt substances group.

 

No data was identified for the inorganic poorly soluble substance group. The screening studies (according OECD 422) with tricobalt tetraoxide and cobalt sulfide and the additional investigations on fertility impairment in a 90-day RDT oral toxicity study (according to OECD 408) did not show any effect on male or female fertility impairment. The proposed testing for an extended one-generation reproductive toxicity study with cobalt sulfide represents a major element in a weight of evidence approach needed to address the endpoint reproductive toxicity for the inorganic poorly soluble substance group.

 

Due to an absence of adverse effects for the inorganic poorly soluble cobalt substances group in toxicity studies on fertility impairment, no DNEL for reproductive toxicity will be derived.

 

Effects on developmental toxicity

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

Study duration:

subacute

Species:

rat

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

Developmental toxicity

 

Tricobalt tetraoxide and cobalt sulfide are the source substances for the inorganic poorly soluble cobalt substances group based on the read-across approach as outlined in Appendix 1.1 in the CSR. Two inorganic poorly soluble cobalt substances, tricobalt tetraoxide and cobalt sulfide, have been tested for developmental toxicity, resulting in an absence of effects on the developing organism up to the limit dose of 1000mg/kg bw/day.

 

In a pre-natal developmental toxicity study (according to OECD 414 and under GLP), tricobalt tetraoxide was given to pregnant rats at doses of 0, 100, 300, 1000 mg/kg bw/day. A total of 25 females per group were given the test items suspended in 0.5% hydroxypropyl methylcellulose gel orally via gavage once daily from gestation day 6 until gestation day 19.

 

No test item-related premature death was noted in the control or in any of the test item treated groups. No changes in behaviour, the external appearance or the faeces were noted in the control group or in any of the test item treated groups. No test item-related changes in body weight in comparison to the control group were noted for the dams of all treatment groups. Body weight gain for the whole gestation period revealed no test item-related differences (control group: 59.7%, 100 mg/kg bw dose group: 61.8%, 300 mg/kg bw dose group: 59.1%; 1000 mg/kg bw dose group: 56.1%). Furthermore, the 3-day intervals of body weight change also revealed no test item-related changes.

 

Macroscopic inspection of the internal organs of the dams revealed no changes in the control and the test item-treated groups. No test item-related changes in the gravid uterus weight and the carcass weight in comparison to the control group were noted for the dams of all treatment groups. Furthermore, no test item-related changes in the absolute and the net (without uterus) body weight change in comparison to the control group were noted for the dams of all treatment groups (100, 300 or 1000 mg/kg bw/day) between gestation day 6 and 20.

The reproduction data of the dams revealed no test item-related differences for pre-implantation loss, post-implantation loss and resorptions/implantation site ratios between the dams of the control group and the dams treated with 100, 300 or 1000 mg/kg bw/day.

 

No dead foetuses were noted in the litters of the dams of the control group and in the litters of the dams treated with 100, 300 or 1000 mg/kg bw/day. No test item-related influence on the ratio of live male foetuses to live female foetuses were noted for all treatment groups. All values of the treatment groups were within the range of laboratory background data.

No test item-related differences of the placental or foetal weights were noted between the control group and the treatment groups.

No test item-related macroscopically visible malformations or variations were noted for the foetuses of the treatment groups during the external examination of the foetuses at laparotomy. The internal examination revealed no malformation or variations in the control or any of the treatment groups. Skeletal examination showed no test-item related malformations, variations or retardations in the control or any of the treatment groups. No test item-related malformations were noted during soft tissue examinations of the foetuses according to WILSON in any of the treatment groups. No test item-related differences for the incidences of the observed soft tissue variations were noted between the control group and the test item treated groups.

 

Under the test conditions of the pre-natal developmental toxicity study with tricobalt tetraoxide, the no-observed-adverse-effect level (NOAEL) was above 1000 mg Tricobalt tetraoxide/kg bw/day for the dams. No test item-related premature deaths, signs of clinical toxicity or findings at necropsy were noted. Body weight, food consumption and the haematological parameters were not influenced by the test item.

 

The no-observed-adverse effect level (NOAEL) for the foetal organism was above 1,000 mg Tricobalt tetraoxide/kg bw/day. No test item-related changes were noted for the number of resorptions and the foetal body weight. No dead foetuses, no test item-related malformations, variations or retardations were noted at any of the tested dose levels.

 

In acombined repeated dose toxicity studies with the reproduction/developmental toxicity screening test (according to OECD 422 and under GLP), cobalt sulfide was administered orally to rats at dose levels of 100, 300 and 1000 mg/kg b.w./day during the pre-mating, mating and post-mating periods to parental males as well as during the pre-mating, mating, gestation and lactation periods until day 3 post-partum (or shortly thereafter) to parental female animals. None of the parental animals died prematurely. The only treatment-related finding, not regarded as adverse, was piloerection noted in few male or female rats from a dose level of 100 mg Cobalt sulfide/kg b.w./day onwards. Macroscopic inspection did not reveal any test item-related changes at necropsy. Histopathological inspection did not reveal any pathological changes. No test item-related influence was noted on the sperm staging or interstitial cell structure (qualitative examination). No test item-related influence was noted on mating behaviour, fertility, implantation, the gestation length or the birth index. No test item-related influence was noted at 100, 300 or 1000 mg Cobalt sulfide/ kg b.w./day on the growth and development of the offspring from conception until sacrifice on day 4 post-partum or shortly thereafter.

 

The NO(A)EL for effects on the F0-generation and reproductive toxicity was above 1000 mg/kg b.w./day, based on a complete absence of adverse effects.

 

 

Conclusion

Due to an absence of adverse effects for developmental toxicity for the inorganic poorly soluble inorganic cobalt substances group in pre-natal developmental toxicity studies and reproductive toxicity screening tests, no DNEL for reproductive toxicity will be derived.

 

Since the two source substances of the inorganic poorly soluble cobalt substance group do not exert any developmental toxicity when administered via oral route up to the limit dose of 1000 mg/kg bw/day, further experimental testing for this endpoint is considered dispensable. A detailed justification for non-submission is presented in the IUCLID section 7.8.2 and in the CSR chapter 5.9.2 for the inorganic poorly soluble cobalt substance group members. In brief, the standard testing regime of Annexes VII-X may be adopted in case testing does not appear scientifically necessary. Specifically, a weight of evidence evaluation can be performed to demonstrate that evidence from several independent sources of information leading to the assumption/conclusion that a substance has or has not a particular dangerous property, while the information from each single source alone is regarded insufficient to support this notion. The registrant is of the opinion that sufficient weight of evidence is available to demonstrate an absence of pre-natal developmental toxicity in a second (non-rodent) species for the inorganic poorly soluble cobalt substance group and that testing on vertebrate animals shall be omitted.

 

In general, more and more scientific evidence is emerging that suggests that non-rodent species such as rabbits are not a priori more sensitive that rats with respect to developmental toxicity. However, particularly in the case of metals, the absence of metabolic conversion and similarities in toxicokinetic profiles render testing in a second, non-rodent species as questionable.

 

In the case of inorganic poorly soluble cobalt substances, the weight of evidence information demonstrates that tricobalt tetraoxide and cobalt sulfide are extremely poorly soluble in water, shows very low in vitro bioaccessibility over a whole range of surrogate biological media, is poorly bioavailable in vivo in several mammalian species (tricobalt tetraoxide) and is of low toxicological activity in

(i) a repeated dose toxicity study with reproductive toxicity screening with no adverse effects on reproductive organs or the developing foetus (cobalt sulfide) and,

(i) a sub-chronic repeated dose toxicity study via oral administration with no adverse effects on reproductive organs, hormone levels or the female cycle (tricobalt tetraoxide) and,

(ii) a pre-natal developmental toxicity study in rats, showing no adverse effects against the dams of the developing foetus (tricobalt tetraoxide).

 

Most importantly, highly reliable toxicokinetic investigations in five different species (baboons, guinea-pigs, rats, mice and hamsters) demonstrated no relevant species-differences in absorption and excretion of orally administered tricobalt tetraoxide. The low order of reproduction toxicity is manifested in an absence of concern in a developmental toxicity study in the rat and an absence of any adverse effects on organs of reproduction in any repeated dose toxicity studies reported to date. Detailed toxicokinetic investigations did not reveal any significant absorption and excretion differences between five species. Tricobalt tetraoxide showed very little gastrointestinal absorption.

 

Overall, the conduct of a developmental toxicity in a second species with a source substance of the inorganic poorly soluble cobalt substances read-across group cannot be expected to contribute any relevant information to the assessment of (otherwise negative) information on reproduction toxicity.

However, considering the equivocal findings in the pre-natal developmental toxicity study in rabbits with the bioavailable cobalt dichloride showing some evidence of developmental toxicity manifested as early resorptions. Consequently, a testing is proposed for the inorganic poorly soluble group with the source substance cobalt sulfide.

Justification for classification or non-classification

No proposal on classification and labelling for reproductive toxicity-fertility impairment can be made, due to lack of data.

The existing data for the inorganic poorly soluble cobalt substance group did not show any effect on male or female fertility impairment. The proposed testing for an extended one-generation reproductive toxicity study with the source substance cobalt sulfide represents a major element in a weight of evidence approach needed to address the endpoint reproductive toxicity for the inorganic poorly soluble substance group.

 

Due to an absence of adverse effects for developmental toxicity for the inorganic poorly soluble inorganic cobalt substances group in pre-natal developmental toxicity studies and reproductive toxicity screening tests, the classification criteria as developmental toxicant are not met, hence no classification is proposed.