Registration Dossier

Administrative data

Description of key information

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
Study duration:
subchronic
Species:
rat
Quality of whole database:
Key study available
System:
haematopoietic

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEC
Study duration:
chronic
Species:
other: human data

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

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

inorganic poorly soluble

poorly soluble in aqueous solutions with organic ligand

inhalation-local

reactive

non-reactive

 

Further details on the read-across approach are given in Appendix 1.1 of the CSR for the oral systemic effects and Appendix 1.2 of the CSR for the inhalation local effects.

 

Cobalt dinitrate is assigned to the read-across groups (i) oral-systemic:  bioavailable cobalt substances group and (ii) inhalation-local: reactive

Toxicological relevance of the non-common compound

The toxicological relevance of the non-common compound in cobalt dinitrate for oral-systemic toxicity is discussed in Appendix 1.1 of the CSR.

 

Human data - inhalation

 

Repeated dose toxicity - local effects

The comprehensive discussion of the available human data can be found at the beginning of chapter 5 of the CSR and in section 7.10 of the IUCLID.

 

The overall outcome was that, based on the findings of the epidemiological studies in workers by Swennen et al. (1993) and Verougstraete et al. (2004), Roto (1980) and Sauni et al. (2010) a cobalt concentration of 0.12 mg Co/m³ will be used as NOAEC for setting a DNEL (inhalation, chronic, local effects).

 

Repeated dose toxicity - systemic effects

An investigation on the effects of cobalt exposure in a Finnish cobalt plant in Kokkola on the cardiovascular system of workers was published by Linna et al. (2004). The cross-sectional study population comprised 203 male workers with at least one year of exposure to cobalt at the end of 1999. The average exposure time was 15.0 years with a mean cumulative exposure to cobalt of 0.40 mg-year (median 0.18 mg-year, range 0.02-2.52). The control group consisted of an age-stratified sample of 94 male workers in a zinc plant that had not been exposed to cobalt, arsenic or lead. The zinc exposure level was 0.1-0.2 mg/m³ for four fifths of the workers, and for one fifth it was about 1 mg/m³. No significant differences in the electrocardiography findings and conduction parameters, heart rate, blood pressure and laboratory tests (inter alia serum T4 and TSH levels) were found between the cobalt exposed and control workers. There were no significant differences between the exposed group and the control group in the prevalence of reported cardiovascular diseases, diabetes mellitus, or pulmonary diseases, except asthma, diagnosed by a physician. Echocardiography was performed on a subset of 122 cumulatively most exposed workers, of which 109 was analysed, and 60 controls with same age distribution, of which 57 were analysed. The average exposure time was 21.2 years with a mean exposure to cobalt of 0.58 mg-year (median 0.47 mg-year, range 0.03-2.52). The echocardiographic data were studied using a regression analysis and an analysis of covariance (ANCOVA). In the final analyses high and low exposure was determined on the basis of being above or below the median mg-years of cobalt exposure. Two of the echocardiography parameters measured was associated with cobalt exposure. In the higher exposure group the left ventricular isovolumic relaxation time (mean 53.3, 49.1, and 49.7 ms in the high exposure (>0.47 mg-year), low exposure (<0.47 mg-year), and control groups, respectively) and the deceleration time of the velocity of the early rapid filling wave (mean 194.3, 180.5, and 171.7 ms for those in the high exposure, low exposure, and control groups, respectively) were prolonged, indicating altered left ventricular relaxation and early filling. The clinical significance of these changes, however, remains to be evaluated. Minor increases in the left ventricular wall thickness concurred with these observations. No signs of systolic cardiac dysfunction were found. The ejection fraction, fractional shortening, and the left ventricular end diastolic diameter were similar in the exposed and control groups.

 

No clinically significant cardiac dysfunction, no evidence of polycythaemia and only equivocal indications of interferences with thyroid metabolism were observed in workers occupationally exposed to inorganic cobalt compounds. Therefore, it can be concluded that systemic effects following inhalation exposure are expected at higher dose levels compared to the dose levels for local effects. Thus, no DNEL(inhalation, systemic) will be derived for workers and the general population.

 

 

Animal data - inhalation

 

Repeated dose toxicity

 

Cobalt sulfate

In 13-week inhalation toxicity studies, groups of 10 F344 rats and 10 B6C3F1 mice of each sex were exposed to aerosols of cobalt sulfate heptahydrate at concentrations of 0, 0.3, 1.0, 3.0, 10 or 30 mg/m³ (0, 0.063, 0.21, 0.63, 2.1 or 6.3 mg Co/m³), 6 hours/day, 5 days/week (Bucher et al., 1990). The MMAD of the aerosol was in the range of 0.83 to 1.10 µm. Mean body weights of mice exposed to 30 mg/m³ were lower than those of the controls throughout the study, and two of 10 males in this group died before the end of the study. At the end of the studies, lung weights were generally increased in rats and mice exposed to 1 mg/m³ and higher. The above described exposure of rats and mice to aerosols of cobalt sulfate heptahydrate resulted primarily in necrotising injury to the respiratory tract. The larynx appeared to be the most sensitive tissue, showing squamous metaplasia lesions after exposure at concentrations as low as 0.3 mg/m³ cobalt sulfate heptahydrate (equivalent to 0.063 mg cobalt/m³). Rats developed chronic inflammation of the larynx at concentrations of 1 mg/m³ and more severe effects in the nose, larynx, and lung at higher concentrations. Mice exhibited acute inflammation of the nose at concentrations of 1 mg/m³ and more severe effects in the nose, larynx, and lung at higher exposures. A NOAEC for local effects in the respiratory was not reached in these studies, as lesions, particularly in the larynx, were observed at the lowest concentration of 0.3 mg/m³ cobalt sulfate thus representing a LOAEC.

 

Thyroid function as indicated by serum T3, T4, and thyrotropin concentrations did not appear to be consistently affected in rats. Polycythemia was seen at 10 and 30 mg/m³ for female rats and at concentrations of 3 mg/m³ for male rats. No consistent significant haematological effects were seen in mice. At 6.3 mg Co/m³, mice showed hyperplasia of the mediastinal lymph nodes.

 

Reproductive system effects were more prominent in mice than in rats.Decreases of testicular and epididymal weights and of sperm counts and increased numbers of abnormal sperm occurred in mice exposed to 30 mg/m³. The NOAEC for testicular weight decrease in mice is 10 mg/m³. Sperm motility was significantly reduced in mice at 0.63 mg Co/m³ (lower concentrations were not evaluated) and at higher concentrations. In female mice, the oestrous cycle was significantly longer in the highest dose group. However, it is unclear to what extent the changes of these reproductive parameters were associated with a decline in fertility because effects on fertility were not studied. No statistically significant effects on sperm motility, sperm counts, or the incidence of abnormal sperm were observed in F344 rats exposed under identical dosing conditions.

 

Shortcomings of the study: The study report presents data on the effect on the respiratory tract in mice and rats in all dose groups comprehensively, and therefore allows the derivation of a NOAEC/LOAEC for local effects. However, since only selected species and/or dose groups were chosen for (i) histopathological examination (and where presented, the severity of such lesions is not indicated), (ii) investigation of reproductive system data, (iii) serum and thyroid function values, neither target organs for systemic toxicity nor any dose-response relationship for systemic effects can be determined. The body weight and clinical data which are available for both species and dose groups allow only the establishment of a NOAEC for general toxicity, but do not address non-lethal organ toxicity of minimal or moderate severity.

 

In a subsequent combined chronic inhalation toxicity/carcinogenicity studies, groups of male and female F344/N rats and B6C3F1 mice were exposed to aerosols of cobalt sulfate hexahydrate at concentrations of 0, 0.3, 1.0, or 3.0 mg/m³ for 6 hours/day, 5 days/week for 105 weeks (Bucher et al.). The MMAD (µm) ± GSD of the aerosol was in the range from 1.4 ± 2.1 to 1.6 ± 2.2. The study represents a highly reliable study without restrictions (RL 1). The respiratory tract was the primary site of non-neoplastic lesions and neoplasms.

 

In rats, proteinosis, alveolar epithelial metaplasia, granulatomous alveolar inflammation, and interstitial fibrosis were observed in the lung of all exposed groups. The incidence of hyperplasia of the respiratory epithelium of the lateral wall of the nose and atrophy of the olfactory epithelium in all exposed groups was significantly greater than those in controls, and the severity of these lesions increased with increasing exposure concentration. Nasal lesions in mice were less severe than in rats, but olfactory epithelial atrophy was observed at 1.0 mg/m³. The incidence of squamous metaplasia of the epiglottis in all exposed groups of rats and mice was significantly increased, and the severity of this lesion increased in rats with higher concentrations as well.

 

Taken together, 2-year exposure of rats and mice to cobalt sulfate resulted in non-neoplastic lesions of the nose, larynx and lung at all concentrations studied. Taking into account the lack of a NOAEC in the concentration-response assessment of cobalt sulfate a benchmark dose (BMD) was calculated using the US EPA BMD software (Version 2.0) with the Gamma Model (Version 2.13). The numbers of alveolar/bronchiolar adenoma or carcinoma in the lung of rats and mice were selected as benchmark response. The 95% lower confidence limit of the BMD for a treatment-related increase in response of 10% was calculated (BMDL10). The lowest BMDL10 value was that for female rat tumours with 0.414 mg/m³ cobalt sulfate which is equivalent to a cobalt concentration of 0.093 mg/m³.

 

 

Cobalt metal

Groups of five male and five female core study rats were exposed to cobalt metal particulate aerosol by inhalation at concentrations of 0, 2.5, 5, 10, 20, or 40 mg/m³, 6 hours per day, 5 days per week for 16 days. Additional groups of five female rats were exposed to the same concentrations for 16 days for tissue burden studies. All rats exposed to 40 mg/m³ and all male and three female rats exposed to 20 mg/m³ died before the end of the study. Mean body weights of males exposed to 10 mg/m³ and of females exposed to 10 or 20 mg/m³ were significantly decreased. Females exposed to 20 mg/m³ lost weight during the study.

Exposure-related clinical findings included abnormal breathing, lethargy, and thinness in male rats exposed to 20 or 40 mg/m³, and in females exposed to 40 mg/m³. Dark lungs were observed at necropsy in all rats exposed to 40 mg/m³ and most rats exposed to 20 mg/m³ that died early.

Increased incidences of nonneoplastic lesions of the lung occurred in exposed male and female rats and included haemorrhage, acute inflammation, alveolar epithelium hyperplasia, histiocytic cellular infiltration of the alveolus, cytoplasmic vacuolization of bronchiolar epithelium, necrosis of the bronchiolar epithelium, and interstitial fibrosis of the alveolar epithelium. Increased incidences of nonneoplastic lesions of the nose occurred in exposed male and female rats and included olfactory epithelium necrosis, olfactory epithelium atrophy, respiratory epithelium necrosis, and respiratory epithelium squamous metaplasia. Tissue concentrations of cobalt increased with increasing exposure concentration in all tissues examined.

 

Groups of 10 male and 10 female core study rats were exposed to particulate aerosols of cobalt metal by inhalation at concentrations of 0, 0.625, 1.25, 2.5, or 5 mg/m³, 6 hours per day, 5 days per week for 14 weeks. Additional groups of 10 male rats (clinical pathology study) were exposed to the same concentrations for 14 weeks. All male and female rats survived to the end of the study. Final mean body weights of males and females exposed to 5 mg/m³ were significantly less than those of the chamber controls, and the mean body weight gain of 5 mg/m³ males was significantly less than that of the chamber controls. At necropsy, pale foci were noted in the lungs of most exposed male and female rats. In male rats, exposure concentration-related increases in the haemoglobin concentration, erythrocyte count, haematocrit value, and manual packed cell volume occurred in the 2.5 and 5 mg/m³ groups on days 3 and 23 and in all exposed groups by week 14; at week 14, female rats also had increases in these parameters. Exposure concentration-related decreases in cholesterol concentrations were observed at all three time points in male and female rats. While this change was not always observed in the lower exposure groups, decreases were consistently observed in the 2.5 and 5 mg/m³ groups of both sexes on day 23 and at week 14. In addition, glucose concentration was decreased in males exposed to 1.25 mg/m³ or greater at week 14.

In the lung, chronic active inflammation and alveolar proteinosis occurred in all exposed males and females, and bronchiole epithelium hyperplasia occurred in all males and females exposed to 1.25 mg/m³ or greater. In the nose, incidences of olfactory epithelium degeneration and respiratory epithelium hyperplasia were significantly increased in males and females exposed to 2.5 or 5 mg/m³. The incidences of olfactory epithelium hyperplasia were significantly increased in 2.5 and 5 mg/m³ males and in 5 mg/m³ females. Significantly increased incidences of turbinate atrophy occurred in 2.5 mg/m³ females and 5 mg/m³ males and females. Tissue concentrations of cobalt increased with increasing exposure concentration in all tissues examined.,

 

Groups of five male and five female mice were exposed to cobalt metal particulate aerosol by inhalation at concentrations of 0, 2.5, 5, 10, 20, or 40 mg/m³, 6 hours per day, 5 days per week for 17 days. Three male and three female mice exposed to 40 mg/m³ died before the end of the study. Final mean body weights were significantly decreased in male and female mice exposed to 20 or 40 mg/m³, and mean body weight gains of 20 and 40 mg/m³ males and all exposed groups of females were significantly less than those of the chamber controls. Females exposed to 20 mg/m³ and males and females exposed to 40 mg/m³ lost weight during the study. Exposure-related clinical findings included abnormal breathing, lethargy, and thinness in male mice exposed to 20 or 40 mg/m³ and females exposed to 10 mg/m³ or greater. At necropsy, tan lungs were observed in most males and females exposed to 20 or 40 mg/m³. Lung weights of both sexes exposed to 10 mg/m³ or greater were significantly greater than those of the chamber controls. Liver weights of exposed male and female mice were significantly less than those of the chamber controls (except relative weight at 40 mg/m³). Increased incidences of nonneoplastic lesions of the lung occurred in exposed male and female mice and included alveolar histiocytic cellular infiltration, cytoplasmic vacuolization of the bronchiolar epithelium, alveolar/bronchiolar epithelium karyomegaly, interstitial fibrosis, and acute inflammation. Increased incidences of nonneoplastic lesions of the nose occurred in exposed groups of male and female mice and included acute inflammation, olfactory epithelium atrophy, olfactory epithelium necrosis, cytoplasmic vacuolization of the respiratory epithelium, and squamous metaplasia of the respiratory epithelium. Tissue concentrations of cobalt increased with increasing exposure concentration in all tissues examined.

 

Groups of 10 male and 10 female core study mice were exposed to particulate aerosols of cobalt metal by inhalation at concentrations of 0, 0.625, 1.25, 2.5, 5, or 10 mg/m³, 6 hours per day, 5 days per week for 14 weeks. One 2.5 mg/m³ female mouse was accidentally killed during the first week of the study; all other mice survived to the end of the study. The mean body weights of males and females exposed to 10 mg/m³ were significantly less than those of the chamber controls. Abnormal breathing was noted in approximately 50% of males and females exposed to 10 mg/m³. At necropsy, tan lungs were noted in mice exposed to 5 or 10 mg/m³. Lung weights of males exposed to 2.5 mg/m³ or greater and females exposed to 5 or 10 mg/m³ were significantly greater than those of the chamber controls. Liver weights of males exposed to 10 mg/m³ and females exposed to 2.5 mg/m³ or greater were significantly less than those of the chamber controls. Kidney weights of males and females exposed to 5 or 10 mg/m³ were significantly less than those of the chamber controls. Testes weights of males exposed to 5 or 10 mg/m³ were significantly less than those of the chamber controls.

In the lung, alveolar histiocytic cellular infiltration and bronchiole epithelium cytoplasmic vacuolization occurred in the lung of all exposed male and female mice. Bronchiole epithelium hyperplasia occurred in all mice exposed to 2.5 mg/m³ or greater. Alveolar proteinosis and alveolar/bronchiolar epithelium karyomegaly occurred in all males and females exposed to 5 or 10 mg/m³. The incidences of haemorrhage were significantly increased in 5 mg/m³ females and in 5 and 10 mg/m³ males. In the nose, the incidences of olfactory epithelium degeneration were significantly increased in males and females exposed to 1.25 mg/m³ or greater. Incidences of respiratory epithelium degeneration were significantly increased in males exposed to 1.25 mg/m³ or greater and females exposed to 2.5 mg/m³ or greater. Incidences of respiratory epithelium squamous metaplasia were significantly increased in males and females exposed to 2.5 mg/m³ or greater, and incidences of turbinate atrophy and chronic active inflammation were significantly increased in the 5 and 10 mg/m³ groups of males and females. The incidences of squamous metaplasia were significantly increased in the larynx of all exposed groups of males and females. Tissue concentrations of cobalt increased with increasing exposure concentration in all tissues examined.

 

Several studies were identified which do not fulfil the relevance, reliability and adequacy criteria as foreseen by the ECHA Guidance on information requirements. The most prominent deficiencies are: single dose studies, targeted studies examining isolated organ systems, incomplete or unclear description of the experimental procedures, several shortcomings in execution and reporting (e.g. test item insufficiently described, animal strain, age, weight or source not reported, dosing unclear, exposure period unclear or too short). The studies are discussed below in brief for information purposes only (further information is provided in the SIDS (IUCLID)).

·        Miniature swine were exposed to an inhalation of pure cobalt metal powder concentrations of 0.1 and 1.0 mg/m³ (Kerfoot, 1973 and 1975). Early detection of pulmonary disease is apparent from the pulmonary function tests showing a mark decrease in lung compliance, and from electron microscopy showing an increase in the amount of septal collagen.

·        A group of sensitised and non-sensitised guinea pigs were exposed by inhalation to 2.4 mg/m³ cobalt dichloride for six hours a day for two weeks. For the sensitised group, much more lavage liquid was retained in the lungs than in the other groups, and the percentage of neutrophils and eosinophils tended to be higher than in the non-sensitised exposed group.

·        In a publication series by one working group (Johansson, 1980, 1983, 1984, 1986, 1987, 1991, 1992, Berghem, 1987, Johansson and Camner, 1986, Camner and Johansson, 1992), male rabbits were exposed for 4-16 weeks to cobalt dichloride and concentrations of 0.5-2.0 mg/m³. Exposed animals had hyperplasia of type II cells in the lung with small nodules formed, interstitial inflammation, and increased number and activity of alveolar macrophages.

 

Conclusions - inhalation

 

In human epidemiological studies following prolonged inhalation exposure, no clinically significant cardiac dysfunction due to cobalt exposure was found. Also no further adverse systemic effects were reported in humans. Therefore, it can be concluded that systemic effects following inhalation exposure are expected at higher dose levels compared to the dose levels for local effects. Thus, a DNEL for systemic effects will not be derived based on these data.

 

Human epidemiological data will be used for the hazard assessment of repeated dose toxicity via inhalation, non-neoplastic lesions. Changes in lung function were the predominant findings in the studies by Swennen et al. (1993) and Verougstraete et al. (2004), Roto (1980) and Sauni et al. (2010). A cobalt concentration of 0.12 mg Co/m³ will be used as NOAEC for the setting of a DNEL (inhalation, local, chronic).

 

Although two carcinogenicity studies with cobalt metal and cobalt sulfate are available, the cobalt metal study will not be considered for risk assessment purposes. The dose descriptor derived from this study (NOAEC: 1.25mg Co/m³) is above the BMDL10 derived from the carcinogenicity study with cobalt sulfate. Following the chronic inhalation exposure of cobalt sulfate in rats and mice, the 95% lower confidence limit of the BMD for a treatment-related increase in response of 10% was calculated (BMDL10), in which the numbers of alveolar/bronchiolar adenoma or carcinoma in the lung of rats and mice were selected as benchmark response (BMDL10: 92.7µg Co/m³). Since the carcinogenic mode of action is identical for both substances, both studies could be used for risk assessment purposes interchangeably. However, the point of departure derived from the cobalt sulfate study is ensuring a higher level of protection for humans, as it provides a significantly lower point of departure and a subsequent lower DNEL value for workers and consumers.

 

Animal data- oral

 

Repeated dose toxicity

Based on the read-across approach presented in Appendix 1.1 of the CSR the substances of the bioavailable cobalt substances are grouped and assessed for their hazardous properties using information from the source substance cobalt dichloride and supporting evidence form cobalt metal and cobalt acetylacetonate.The source substances cobalt dichloride and cobalt metal, have been tested for repeated dose toxicity, resulting in comparable effect levels (28-day NOAEL CoCl2: 2.5mg Co/kg bw/day; 90-day NOAEL CoCl2: 0.74 mg Co/kg bw/day; 28-day NOAEL Co metal: 30 mg Co/kg bw/day). In all studies, the effect levels were based on similar findings, predominantly body weight effects and haematological findings. Further details on the findings are presented below.

 

 

In the sub-chronic repeated dose toxicity study, cobalt dichloride was given male and female rats at doses of 0, 3, 10, 30 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, 30 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. The body weight of the male animals treated with 10 mg Cobalt dichloride hexahydrate/kg b.w./day and the body weight of the male and female animals treated with 30 mg Cobalt dichloride hexahydrate/kg b.w./day were slightly reduced. Body weight gain and body weight at autopsy changed accordingly. No test item-related influence was observed on the food and drinking water consumption, biochemical parameters, urinary parameters, the eyes and optic region at any of the tested dose levels. Observational screening and functional tests did not reveal any test item-related neurological effects. No test item-related macroscopic changes in organs or tissues were noted at necropsy. The histopathological examination of the high-dosed animals did not reveal any test item-related morphological lesions. At the end of the 4-week recovery period (restricted to the high dose group), the body weight in the previously high-dosed animals were within the range of the control group, indicating a complete recovery. Repeated oral treatment of male and female rats with 10 or 30 mg Cobalt dichloride /kg b.w./day led to a few test item-related changes in haematological parameters in comparison to the control animals. In particular, slightly increased values were noted for red blood cell-related parameters as the haemoglobin content, the number of erythrocytes, the haematocrit value, the mean corpuscular volume and the mean corpuscular haemoglobin. The number of reticulocytes and platelets was decreased and the thromboplastin time and activated partial thromboplastin time were increased. In general, the male animals were affected to a higher degree than the females. Correspondingly, the microscopic evaluation revealed test item-related changes in the bone marrow (erythroid hyperplasia) of the femur. There was a significant and test item-related increase for erythroid hyperplasia in the bone marrow of the male and female animals treated with 30 mg Cobalt dichloride /kg b.w./day compared to the controls: 7 of 10 animals for both sexes in the high dose group versus 0 of 10 in controls. 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 influence on the ovaries, oviducts, uterus (incl. cervix) and vagina were noted. 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 Cobalt dichloride/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. All changes previously observed in haematological and biochemical parameters and at histological examination after repeated treatment with 30 mg Cobalt dichloride/kg b.w./day had subsided after 4 weeks of recovery. Under the test conditions of this 90-day repeated dose toxicity study with Cobalt dichloride, the No-Observed-Adverse-Effect-Level (NOAEL) for systemic effects was 3 mg cobalt dichloride/kg bw/day by oral administration based on findings related to the haematopoiesis and reduced body weight and body weight gain at the mid and high dose group. The No-Observed-Effect-level (NOEL) for fertility/reproductive effects was above 30 mg cobalt dichloride/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 a 28-days repeated dose toxicity study with reprotox screening (according to OECD 422 and under GLP), cobalt metal powder was administered orally to rats at dose levels of 30, 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. Piloerection, reduced motility, soft faeces/diarrhoea and reduced food consumption were noted - in relation to the dose - from a dose level of 100 mg Cobalt Powder/kg b.w./day onwards. In addition, reductions of body weight were noted from 300 mg Co-balt Powder/kg b.w./day onwards. Premature deaths occurred in five female rats at 100 mg Cobalt Powder/kg b.w./day and eight female rats at 300 mg Cobalt Powder/kg b.w./day. Treatment with 1000 mg Cobalt Powder/kg b.w./day caused the premature death of nine of ten males and all ten females. Macroscopic inspection revealed changes of the gastro-intestinal tract - mainly in the prematurely deceased animals - from a dose level of 100 mg Cobalt Powder/kg b.w./day onwards and adrenal changes and pulmonal lesions at 1000 mg Cobalt Pow-der/kg b.w./day. Histopathological inspection did not reveal any pathological changes. No histopathological correlate could be found for the macroscopic lesions noted at necropsy. No test item-related influence was noted on the sperm staging or interstitial cell structure (qualitative examination). The NO(A)EL for systemic effects was 30 mg/kg b.w./day, based on mortality, clinical signs of toxicity, effects on food consumption and macroscopic pathological changes observed at and above 100 mg Cobalt Powder/ kg b.w./day and reduced body weight at and above 300 mg Cobalt Powder/kg b.w./day.

 

In a 28-day repeated dose toxicity study, rats were given oral doses of cobalt acetylacetonate of 0, 15, 50, 150 mg/kg bw/day. In the 50 mg/kg/day dose group, males displayed lower mean body weight gains and a lower food consumption. Additionally, haemoglobin concentration was increased in males of this dose group. Whereas in the 150 mg/kg/day dose group, males and females both displayed reduced body weight gain, lower food consumption (except females had a higher food consumption during weeks 2 and 3) and an increase in some blood parameters (red blood cell count, haemoglobin, haematocrit). Lastly, ptyalism was observed in 4 of 5 females treated at 150 mg/kg/day. One of these females also had soft feces for 7 days during week 2. Under the conditions of this study, the no observed adverse effect level (NOAEL) for males was determined to be 15 mg/kg/day (equivalent to 3.05 mg cobalt/kg/day) based on clinical signs, body weight and weight gain, food consumption, and haematology. The NOAEL for females was determined to be 50 mg/kg/day (equivalent to 10.6 mg cobalt/kg/day) based on haematological findings.

 

The NOAEL for systemic effects derived from the sub-chronic study with cobalt dichloride is used as point of departure for the derivation of DNEL (oral, systemic effects) for the general population. Based on the DNEL for cobalt dichloride of, all further DNELs for the substances in this group will be calculated taking into account the cobalt mass fraction of total molecular mass of the respective substance. Details on the substance specific derivation of DNELs-oral, systemic for the general population are given in the report, which can be found as attachment to the endpoint summary in section 7 of the IUCLID.

 

In addition to the above, several other (published) studies on bioavailable cobalt substances were identified which however do not fulfil the relevance, reliability and adequacy criteria as foreseen by the ECHA Guidance for information requirements. The most prominent deficiencies are: single dose studies, targeted studies examining isolated organ systems, incomplete or unclear description of the experimental procedures, several shortcomings in execution and reporting (e.g. test item insufficiently described, animal strain, age, weight or source not reported, dosing unclear, route of administration unclear, exposure period unclear or too short). Therefore, these studies are discussed below only briefly for information purposes (further information is provided in the IUCLID).

·        In a 30-day study, male and female rats were fed an iron-sufficient diet mixed with cobalt dichloride at 5 doses (10-300 ppm). A NOAEL of 50ppm was identified based on thymus weight difference (Chetty, 1979).

·        In a 90-day drinking water study male rats were given cobalt dichloride at 500 ppm (Domingo, 1984). Treated animals showed a reduced body weight gain and development of polycythaemia. It is unclear whether reduced water consumption was caused by impaired palatability of the cobalt dichloride supplemented drinking water. No NOAEL/LOAEL for systemic toxicity could be established.

·        Female rats given cobalt dichloride during GD 6-15 showed signs of maternal toxicity by reduced body weight gain, decreased food consumption, haematological changes. A NOAEL of 50 mg/kg bw/day was established (Paternain, 1988).

·        Cobalt sulfate administered to pregnant mice, rabbits and rats at doses of 20, 100, 200 mg/kg bw/day produced dose-dependent maternal toxicity (Szakmáry, 2001). No NOAEL/LOAEL for maternal toxicity could be established.

·        In short term and subchronic studies on cobalt dichloride in rats, polycythaemia and increased haemoglobin were induced at doses of 0.5 mg Co/kg bw/day and above (Stanley et al., 1947; Murdock, 1959; Krasovskii and Fridlyand, 1971).

·        Male rats were dosed with 100, 200 and 400 ppm of cobalt chloride hexahydrate in drinking water for at least 12 weeks (Pedigo, 1988).

·        Thyroid necrosis was observed in mice dosed by the oral route for 15 to 45 days with cobalt chloride at 400 ppm (Shrivastava et al., 1996).

·        In rats given cobalt sulfate in the diet for 24 weeks at 40 mg/kg bw/day, cardiac enzyme activity and mitrochondrial ATP production were significantly reduced. The hearts of treated animals were isolated and were found to have left ventricular hypertrophy and impaired ventricular function (Haga et al., 1996; Clyne et al., 2001). In contrast, the same working group did not find any myocardial dysfunction in male rats administered cobalt sulfate for 8 weeks (Pehrsson, 1991).

·        Rats treated with cobalt sulfate at 26 mg Co/kg/bw per day for 8 weeks or cobalt chloride at 50 mg/kg bw/day for 3 weeks had cardiac degeneration (Grice et al., 1969; Morvai et al., 1993).

·        Guinea pigs given cobalt sulfate at 20 mg Co/kg bw per day for 5 weeks had abnormal EKGs, increased heart weight, and cardiac lesions (Mohiuddin et al., 1970).

·        In a study series of one working group, the authors investigated the influence of cobalt dichloride on male rats via oral route for 57-98 days at varying single doses. Testicular atrophy, degeneration and necrosis, induction of polycythaemia were reported. The authors concluded that observed testicular degeneration was not a primary response to cobalt, but instead suggested that the testes become hypoxic due to both a blockage of veins and arteries by red blood cells as well as changes in permeability caused by a thickening of basal lamina and basement membranes (Corrier, 1985, Nation, 1983, Bourg, 1985, Mollenhauer, 1985).

·        In an additional study series the authors investigated the potential toxicity of cobalt dichloride in male and female mice and rats. Cobalt dichloride was administered via the oral route in varying concentrations for 7-60 days. They reported changes in blood parameters, increase in oxidative stress markers and changes in hepatic, cardiac as well as renal enzyme expression/activity (Zaksas (2013), Akinrinde (2016), Ajibade (2017), Akinrinde (2016b), Awoyemi (2016)).

 

 

Repeated dose toxicity: dermal

The submission of a repeated dose toxicity study via dermal route is considered unjustified, since:

 

(a) Lung function impairment is the predominant finding in human epidemiological data by Swennen et al. (1993) and Verougstraete et al. (2004), Roto (1980) and Sauni et al. (2010), whereas no significant systemic toxicity due to prolonged inhalation exposure towards cobalt substances was found. It can be concluded that systemic effects following inhalation exposure are expected at higher dose levels compared to the dose levels for local effects. In order to be protective against local effects after repeated dose toxicity via inhalation, the human NOAEC derived from the above mentioned human epidemiological data will be used to derive a DNEL for all cobalt substances. Consequently, the inhalation route is considered as the route of exposure showing the highest concern for which safety levels for workers and consumers are to be implemented

 

(b) In total 22 out of 26 cobalt substances prepared by the Cobalt REACH Consortium (CoRC) are legally and/or self-classified for dermal sensitisation properties. The risk management measures for such substances foresee to minimise dermal exposure to as low as reasonably achievable. Protective gloves according to EN 374 have to be worn at all workplaces unless any exposure to the substance can be excluded when taking into account the nature of the conducted process, applied exposure prevention measures and physical appearance of the substance of concern in the specific type of application (e.g. protecting from splashes by containment of emission source).

 

(c) Based on the physico-chemical properties of all inorganic cobalt substances and results of a dermal absorption study with a cobalt salt of high in vitro bioaccessibility in artificial sweat suggest a potential for a negligible rate of absorption through the skin. A dermal absorption rate of 0.38% for the low exposure scenarios (ca 31.9μg Co/cm² loading) and 1.08% for the high exposure scenarios (ca 319μg Co/cm² loading) was determined. These values also account for part of the material associated with the stratum corneum and the test was conducted with a highly water soluble form of Cobalt in an aqueous solution. Thus, these values are considered to represent a conservative estimate.

In conclusion, the dermal absorption of cobalt has been shown to be low in a guideline-conform in-vitro percutaneous absorption study conducted under GLP with the highly soluble substance cobalt dichloride (Roper, 2010). This renders percutaneous uptake a negligible route of entry into the body, which is why this route is not further considered in risk characterisation

 

Conclusions - oral

 

The substances of the bioavailable cobalt substances group exert adverse findings in test animals, such as

(i) reduced body weight and body weight gain

(ii) induction of adverse gastro-intestinal effects upon macroscopic inspection, manifested as soft faeces/diarrhoea in mid-dose animals and reddened intestines, caecum or stomach in high-dose and above

(iii) microscopically visible induction of erythroid hyperplasia in the bone marrow after sub-chronic exposure with correlating changes in haematological parameters, such as increased values in red blood cell parameters (haemoglobin content, the number of erythrocytes, the haematocrit value, the mean corpuscular volume and the mean corpuscular haemoglobin).

These findings were seen in a sub-chronic oral study in rats with cobalt dichloride and in a sub-acute oral study in rats with cobalt metal.

 

For risk assessment purposes, a read-across is applied by using the cobalt equivalent NOAEL derived from the sub-chronic oral study with cobalt dichloride (i.e. 3 mg CoCl2 6H20/kg bw/day or 0.744 mg cobalt/kg bw/day) for the calculation of substance-specific DNEL (oral, systemic, long-term) for all members of the bioavailable cobalt substances group.

 Details on the substance specific derivation of DNELs-oral, systemic for the general population are given in the report, which can be found as attachment to the endpoint summary in section 7 of the IUCLID.

 

 

 

Statement on the preferential use of human data in risk assessments for human health

 

(I) In almost 20 years of practical conduct of risk assessments under the “Existing Substances Regulation (793/93), human data has been given preference over animal studies. This is documented in the Technical Guidance Document in chapter 3.1 as follows: „Generally human data will only be available for existing substances. If both animal data and human data are available, as a general rule, well reported relevant human data for any given endpoint is to be given preference for the risk assessment.“ (ECB, 2003).

 

(II) Similarly, the US Environmental Protection Agency (EPA) in their guidance have stated that they look to human data whenever possible in completing human risk assessments: "If adequate human studies (confirmed for validity and applicability) exist, these studies are given first priority in the dose-response assessment, and animal toxicity studies are used as supportive evidence" (EPA, 1989). Often, such data can be obtained from epidemiological studies, which do not involve the intentional dosing of research participants, but rather evaluate the effects of exposures that have occurred in an occupational setting or because of the peculiarities of a specific geographical setting. Regardless of the origins of such human data, risk assessments based on human data have the advantage of avoiding the problems inherent in interspecies extrapolation" (EPA, 1993). In the same document, EPA also states: “The default assumptions that are of particular relevance to the issues raised by third-party intentional human dosing studies are those that bridge gaps between animal results and estimates of effects in humans. In the context of FIFRA, for example, EPA has routinely divided the calculated "safe" dose for animals by a factor of 10, to account for the possibility that humans are more sensitive to the substance being tested than are the animal species. Third-party submitters of human dosing studies have been particularly interested in modifying this default assumption by introducing data obtained directly from human studies.”

 

(III) When addressing the relevance and use of human data, ECHA guidance specifies the requirements for such studies as follows in section B.4.3.3 (human data) of their guidance, for the following four types of human data (ECHA, 2008):

 

Analytical epidemiology studies on exposed populations (case-control, cohort and cross-sectional studies) are useful for identifying a relationship between human exposure and effects and may provide the best data for risk assessment.

 

Descriptive or correlation epidemiology studies are useful for identifying areas for further research but are not very useful for risk assessment since they often can only identify patterns or trends but cannot ascertain the causal agent or degree of human exposure.

 

Case reports may demonstrate effects which cannot be observed in experimental animals. Thorough assessment of the reliability and relevance of case reports is needed because they often lack critical information on e.g. substance purity, human exposure, and effects.

 

Controlled studies in human volunteers are acceptable in very rare cases. Testing with human volunteers is strongly discouraged but when good quality data are already available, they should be used as appropriate in well justified cases.

 

In the case of cobalt and cobalt substances, the human studies that were used for the derivation of DNELs were assessed for their reliability and relevance, and were found to be of acceptable quality for the purpose envisaged.

 

(IV) Finally, the use of human data in risk assessment largely avoids a need for the application of assessment or extrapolation factors to account for differences in toxicokinetics, toxicodynamics, metabolic capacity and species sensitivity.

 

 

References

ECB (2003) Technical Guidance Document on Risk Assessment in support of Commission Directive 93/67/EEC on Risk Assessment for new notified substances, Commission Regulation (EC) No 1488/94 on Risk Assessment for existing substances, Directive 98/8/EC of the European Parliament and of the Council concerning the placing of biocidal products on the market, Part I, EUR 20418 EN/1

 

ECHA (2008) Guidance on information requirements and chemical safety assessment, Guidance on information requirements and chemical safety assessment, Part B: Hazard Assessment, European Chemicals Agency, 2008

 

EPA (1989) Risk Assessment Guidance for Superfund, Vol. 1: Human Evaluation Manual, EPA/540-1-89/002, US Environmental Protection Agency. available at:www.epa.gov/cgi-bin/claritgw?op-Display&document=clserv:OSWER:1175;&rank=4&template=epa

 

EPA (1993) Reference Dose (RfD): Description and Use in Health Risk Assessments, § 1.3.2.2.1, US Environmental Protection Agency, background document, available at:www.epa.gov/IRIS/rfd.htm.

 

IGHRC (2006) Guidelines on route-to-route extrapolation of toxicity data when assessing health risks of chemicals. The Interdepartmental Group on Health Risks from Chemicals, http://www.silsoe.cranfield.ac.uk /ieh/ighrc/ighrc.htm

Justification for classification or non-classification