Aluminum cobalt oxide

Endpoint summary

Description of key information

Read-across with cobalt compounds:
LOAEC (rat): 0.114 mg Co2+/m³ 
LOAEC (mouse): 0.114 mg Co2+/m³
Read-across with aluminium compounds:
There was only limited evidence for systemic toxicity (NOAELS: 200 - 3225 mg/kg bw/day based on various aluminium compounds).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Additional information

There are no data available on repeated dose toxicity for cobalt aluminium oxide. However, there are reliable data for various cobalt and aluminium compounds considered suitable for read-across using the analogue approach. For identifying hazardous properties of cobalt aluminium oxide, the existing forms of the target substance at very acidic and physiological pH conditions are relevant for the assessment of human health effects. As cobalt aluminium oxide is a metal-organic salt, which is insoluble in water at pH 6, it is probable that the target substance has also a low degree of solubility at the physiological pH of 7.4. At acidic pH conditions, however, the study of Stopford et al. (2003) showed that water-insoluble cobalt compounds release cobalt ions. Thus, it can be assumed that cobalt aluminium oxide dissociates at acidic pH in the human body resulting in bioavailable cobalt and aluminate ions. Due to the fact that the toxicological effects of cobalt aluminium oxide are mainly caused by exposure to the cobalt ion, the use of data on soluble cobalt compounds is justified for toxicological endpoints as a worst case scenario. In addition, various aluminium compounds are used within the read-across approach. For further details, please refer to the analogue justification attached in section 13 of the technical dossier.

 

Cobalt compounds

In a 13-week inhalation study, groups of mice and rats were exposed to cobalt(II)sulfate heptahydrate aerosols at concentrations of 0.3, 1, 3, 10 and 30 mg/m³ (calculated as anhydrous salt and equivalent to 0.114, 0.38, 1.14, 3.8 and 11.4 mg Co2+/m³, respectively) for 6 hours/day and 5 days/week (Bucher, 1991). All rats, all female mice, and all but 2 male mice exposed at the top concentration survived to the end of the studies (10 animals per group). Rats and mice exposed to 11.4 mg Co2+/m³ lost weight during the first exposure week and then gained weight at the same rate as controls. Lung weights were increased over those of controls in rats exposed at concentrations as low as 0.114 mg Co2+/m³ and in mice exposed to 3.8 mg Co2+/m³ or more. Polycythemia was observed in rats exposed to the test substance but not in mice. Cobalt content in the urine of rats increased with increasing atmospheric cobalt exposure. Both in rats and mice, lesions seen in the respiratory tract included degeneration of the olfactory epithelium, squamous metaplasia of the respiratory epithelium, and inflammation in the nose, inflammation, necrosis, squamous metaplasia, ulcers (rats), and inflammatory polyps (rats) of the larynx, squamous metaplasia of the trachea (mice); and histiocytic infiltrates, bronchiolar regeneration, peribronchiolar and septal fibrosis, and epithelial hyperplasia in the alveoli of the lung. The most sensitive tissue was the larynx, with squamous metaplasia observed in rats and mice at the lowest exposure concentration of 0.114 mg Co2+/m³. Thus, no NOAEC could be determined, neither in rats nor in mice.

 

Aluminium compounds

Oral:

A GLP study from Beekuijzen (2007) was performed in accordance with OECD 422 and adds to the weight of evidence for the absence of reproductive/breeding, mating impairment and early postnatal developmental effects due to short-term exposure to high doses of aluminium chloride (basic). No mortality or clinical signs of intoxication were observed in male and female Wistar rats due to treatment with Al chloride basic at dose levels of 40, 200, and 1000 mg/kg body weight. Treatment with Al chloride basic by oral gavage revealed paternal toxicity (irritation effect on glandular stomach mucosa, local effect) at 1000 mg/kg in both the male and female Wistar rats. Based on findings observed macroscopically (red foci or thickening of the grandular mucosa of the stomach) and supported by microscopic examination, the maternal/parental No Observed Adverse Effect Level (NOAEL) for local toxic effects on stomach was established at 200 mg/kg and LOAEL – at level 1000 mg/kg, for both males and females.

Several statistically significant changes in clinical biochemistry parameters were observed at 1000 mg/kg suggesting a possible impact on the blood system (decreased Hb level in males, MCHC in both Al treated males and females), on the liver (decreased total protein and albumin in blood serum) and possibly the kidney functions (increase potassium level) at this dose. Decreased Hb levels were observed in two other doses in males but no dose response relationship was observed. Lack of relevant baseline values for the observed clinical data limit the interpretation of the results. The authors consider the and clinical biochemistry and haematology changes observed at 1000 mg/kg to be of slight nature and generally within the range expected for rats of this age and strain. Because any morphological correlates were absent, these changes were considered not indicative of organ dysfunction and not of toxicological significance.

 

Male Sprague-Dawley rats were exposed to aluminium-compounds with diet (Hicks et al., 1987). The animals were randomly assigned to five groups, 25 animals in each. The groups were receiving 1) basal diet (control), 2) aluminium hydroxide (302 mg Al/kg body weight), 3) KASAL -the basic form of sodium aluminium phosphate containing ≈6% of Al (141 mg Al/kg body weight), 4) KASAL II - the basic form of sodium aluminium phosphate containing ≈13% of Al (67 mg Al/kg body weight) and 5) KASAL II (288 mg Al/kg body weight). The treatment continued for 28 days, during which the animals were observed twice daily for their behaviour, signs of toxicity, and mortality. General physical examinations, body weight and food consumption measurements were performed weekly. After 28 days of treatment, 15 animals from each group were killed. Blood was collected from 5 rats of each group for blood cell counts, haemoglobin concentration, hematocrit and serum chemistry measurements. These rats were subjected to gross necropsy and histopathological examination. Femurs from 10 rats were taken for possible aluminium analysis; femurs from 5 rats were analyzed for Al concentrations. Five rats were allowed to recover for 2 months and five rats – for 5 months after termination of the treatment. During these recovery periods, the rats received the basal diet and were observed daily; body weight and food consumption were measured monthly. Femurs were collected at autopsy from these rats for aluminium analysis. During the entire experimental period, no mortality was reported and no treatment-related clinical signs were observed. All clinical observations were characteristic of male Sprague-Dawley rats of relevant age. There were no significant group differences in body weight, food and water consumption and haematological parameters. A mild (2-4%) but significant increase in serum sodium level was observed in all treated group compared to the control group. However, all the increased sodium levels were within the range of historical control for rats of the same age in the laboratory. A significant 16% increase in absolute kidney weight was reported in the group of rats receiving KASAL II at 67 mg Al/kg b.w. This increase appeared to be not treatment-related because no such increase was seen in the group of animals treated with this substance at 288 mg Al/kg b.w. There were no other significant group differences in organ weights. All lesions seen at microscopic examination were “those normally expected for young adult male Sprague-Dawley rats.” No lesions suggestive of a treatment-related effect were seen. Aluminium concentrations in all femur samples from all groups were <1 ppm and most were below the limit of detection or quantification. The distribution of samples in which Al was not detectable, was detectable but not quantifiable or was quantifiable, was similar in all the groups. It should be noted that this comparison was based on small numbers of samples from each group. Al was quantifiable in all 5 samples from animals treated with Al(OH)₃, in 2 samples from the control animals and in none of the samples from animals treated with KASAL or KASAL II.The results of this study provide no evidence for significant deposition of Al in the bone and for toxicity of Al hydroxide or basic food grade sodium aluminium phosphate (KASAL and KASAL II) during 28-day dietary administration at daily doses up to ≈300 mg Al/kg body weight. 

Aluminium citrate was administered to ten female Sprague Dawley rats with drinking water at a concentration of 80 mmol/L for 8 months (Vittori et al., 1999). Eight female rats that received drinking water without added aluminium citrate were used as controls. Blood was collected at the end of the treatment. After blood collection, the animals were sacrificed, femoral bone marrow was removed and smears were prepared. The remaining bone marrow cells were conditioned for in vitro clonal assays of haematopoietic progenitors (late colony-forming unit-erythroid, CFU-E) and in vitro cellular iron uptake. Livers, kidneys, spleens, brains and the remaining femora were removed and prepared for subsequent analysis for Al content. Haemoglobin, hematocrit, reticulocyte counts, circulating haptoglobin, plasma iron and aluminium, free haemoglobin in plasma and total iron-binding capacity were determined. Morphology of erythrocytes and erythropoietic cells in peripheral blood films were studied under light and electronic microscopes. Plasma iron concentration and total iron-binding capacity were not different in the control and the Al treated rats, indicating that the Al treated animals were not depleted of iron. There were no significant group differences in blood urea concentration, which suggests that kidney function was not altered by Al administration. Significantly lower haematocrit and blood Hb concentration were observed in the Al treated rats than in the control rats. Significantly higher reticulocyte count, abnormal erythrocyte morphology, a significant inhibition of CFU-E growth and a significant reduction of ⁵⁹Fe uptake in the bone marrow were reported in the Al treated rats. Plasma haptoglobin concentration was significantly lower in the Al treated animals than in the control animals. This and the presence of abnormal erythrocytes in the Al treated rats are indicative of intravascular haemolysis. Scanning electron microscopy combined with EDAX detected Al inside circulating erythrocytes with abnormal shape from animals in the Al treated group. Al concentrations in the bone, spleen, liver, kidney and plasma were significantly higher in the Al treated group than in the control group. No significant group difference in brain Al concentrations was seen. There was no correlation between plasma Al concentrations and Al levels in the organs or any other biochemical data. The results of this study suggest that Al affects erythropoiesis in rats with normal renal function.

A recent combined one-year developmental and chronic neurotoxicity study with Al-citrate (ToxTest, 2010) may be of interest for the evaluation of the neurotoxicity of Aluminium hydroxide, taking into consideration the tenfold lower bioavailability of Al-hydroxide compared to Al-citrate and excluding effects that can likely be related to the salt rather than the cation. The study was conducted according to OECD TG 426 and GLP, and the exposure covered the period from gestation day 6, lactation and up to 1 year of age of the offspring. Pregnant Sprague-Dawley dams (n=20 per group) were administered aqueous solutions  via drinking water of  3225 mg/Al citrate/ kg bw/day (300 mg Al/kg bw/day); 1075 mg/Al citrate/kg bw/day (100 mg Al/kg bw/day); 322.5 mg/Al citrate/kg bw/day (30 mg Al/kg bw/day). The highest dose was a saturated solution of Al-citrate. Two control groups received either a sodium citrate solution (citrate control with 27.2 g/L, equimolar in citrate to the high dose Al-citrate group) or plain water (control group). The Al citrate and Na-citrate were administered to dams ad libitum via drinking water from gestation day 6 until weaning of offspring. Litter sizes were normalized (4 males and 4 females) at postnatal day (PND) 4. Weaned offspring were dosed at the same levels as their dams. Dams were sacrificed at PND 23. At PND 4  1 male and 1 female pup of each litter  were allocated to 4 testing groups: D23-sacrifice group for pre-weaning observations and D23 neuropathology, D64, D120 and D365 postweaning groups for post weaning observations and neuropathology at the respective days of sacrifice. Endpoints and observations in the dams included water consumption, body weight, morbidity and mortality and a Functional Observational Battery (FOB) (GD 3 and 10, PND 3 and 10). Pups were examined daily for morbidity and mortality. Additional neurobehavioral tests were performed at specified intervals and included, T-maze, Morris water maze, auditory startle, and motor activity. Female pups were monitored from PND26 for vaginal opening, male pups from day 35 for preputial separation. Clinical chemical and haematological analysis was performed for each group on the day of scheduled sacrifice. Al-concentrations were determined in blood, brain, liver, kidney, bone and spinal cord tissues by inductively coupled plasma mass spectrometric analysis. Further metals such as iron, manganese, copper and zinc were also determined. The pathological investigation includes rain weight and neuropathology. Statistical analyses were performed using the SAS software release 9.1. Data collected on dams and pups were analysed separately. All analysis on pups was performed separately for each sex. Statistical significance was declared from P ≤ 0.05.

Results: Dams: Eight high dose dams developed diarrhoea. In the Na-citrate group one dam stopped nursing and the pups were euthanized. No significant differences between mean body weights of dosed animals compared to controls were observed during gestation and lactation. During gestation and lactation low and mid dose group animals consumed considerably more fluid than controls and high dose group animals. This is not considered treatment related as there was no dose response. In all animals the target dose was exceeded during lactation due to the physiologically increased fluid consumption.

Pups: During the pre-weaning phase weights of mean body weights of male and females in the sodium citrate and high dose group were significantly lower than the untreated controls. This suggests a citrate rather than Al-related effect. No differences between treated and control animals were observed in the FOB. No other clearly treatment related effects were observed pre-weaning.

F1-postweaning: General toxicity

No significant differences in body weights throughout the study were observed between low and mid-dose animals sodium-citrate and untreated controls. High dose males had significant lower body weights than controls by PND 84. These animals also had clinical signs. At necropsy urinary tract lesions were observed in the animals of the high dose group, most pronounced in the males, hydronephrosis, uretal dilatation, obstruction and/or presence of calculi. All high dose males were sacrificed on study day 98. The effect is probably due to Al-citrate calculi precipitating in the urinary tract at this high dose level. This effect is related to the citrate salt and cannot be attributed to the Al-ion. Female high dose animals showed similar urinary tract lesions, but with a lower incidence and severity. Urinary tract lesions were also observed in single mid dose males, but also in a few sodium citrate and control animals. Fluid consumption during the study was increased in the sodium citrate and Al-citrate groups (in particular high and mid dose) compared to controls. This is probably due to the high osmolarity of the dosing solutions. However, the consumed dose levels decreased in all dose groups during the study. In the beginning the target dose was considerably exceeded, while versus the end of the study it was considerably below the target dose.  According to the authors the assigned dose levels still remain valid.

Developmental landmarks:

In sodium citrate controls and high dose males and females the number of days to reach preputial separation or vaginal opening was longer than in untreated control animals. This may be related to the lower body weights in these animals at the respective time-point. As the sodium citrate group showed similar retardation this effect cannot be allocated to the aluminium cation.

Neurobehavioral testing

No consistent treatment related effects that could be related to Al-ion exposure were observed in the FOB. No treatment related effects on autonomic or sensimotoric function were observed in the study. A weak association between Al exposure and reduced home cage activity, a very weak association with excitability, some association with neuromuscular performance were reported but according to the authors this may also be related to group differences in body weight, and an association with physiological function and is thus not considered clearly treatment related. No treatment related effect on general motor behavior was observed. No clearly treatment related effect on auditory startle response was observed. There was no evidence of any treatment related effect on learning and memory in the Morris Water Maze test and no clearly treatment related effects in the T-maze test. Hind limb grip strength and to a lesser extend foot splay were reported to be reduced compared to controls in high and mid dose male and female animals, more pronounced in younger than in older  rats. However, the observed effects can be related to the lower body weights of the individual animals undergoing this test. No details on the individual findings and historical control data are available. It can therefore not be concluded with certainty that the observed neuromuscular effects are primary effects of the treatment and attributable to Al3+. The NOAEL was reported based on this effect as 30 mg Al/kg bw in a conservative approach.

Haematology: No clinically significant differences in hematology were observed at the investigation on day 23. In day 64 and 120 females and day 64 males the high dose group showed slight reduction in hematocrit (males only), mean hemoglobin and mean corpuscular cell volume. No such changes were observed in the 364 day group.

Clinical chemistry: while a number of borderline statistically significant changes were observed, such as globuline levels, alkaline phosphatase and glucose in the high dose group little or no biological significance is associated with them. Elevated creatinine and urea levels in Day 64 males are consistent with the renal toxicity observed in these animals.

Organ weights: Brain weights did not differ among the groups, with two exceptions in the day 64 group males brain weights were significantly lower than controls. In the 120 day female high dose group brain weights were also significantly lower than controls. These findings were not reproduced at the other sacrifice times. Brains to body weight ratios were not significantly different and the lower brain weights can be attributed to the body weight.

Pathology: The main pathology findings were the renal lesions with precipitates in the urinary tract and secondary lesions such as hydronephrosis and uretal dilatation   in particular in the high dose group males and to a lesser extend females. Fluid colonic content was also observed in some high dose animals, in particular males. According to the authors the test item clearly precipitated in the urinary tract causing stone formation and blockage and resulted in fluid colonic content. No other macroscopic effects were observed in other organs.

Histopathology: No treatment related histopahological effects were observed in the nervous system at any time point.

Aluminium concentrations in different organs were dose related. Tissue concentrations were highest in blood, and then in decreasing order brainstem, femur, spinal cord, cerebellum, liver cerebral cortex.

A conservative NOAEL of  322 mg Al-citrate/kg bw  corresponding to 30 mg Al/kg bw was derived from this study (with a bioavailability correction this would correspond to ca. 300 mg Al from Al(OH)3).

The most important effects were however related to a precipitation of the citrate in the kidneys and urinary tract and this effect is not related to the Al3+ ion.  The effects on grip strength and foor splay observed can also not be attributed unequivocally to Al-exposure as they may have been secondary to the general toxicity and body weight differences between treated and control animals undergoing this test.

 

Inhalation:

Gross et al. (1973) observed reversible alveolar proteinosis in rats, guinea pigs and hamsters exposed for 6 months to high levels (50 and 100 mg/m³) of either British pyro powder (0.18% grease), a US-source flake powder, or a US-source atomized powder (0% grease). The alveolar proteinosis was most severe in rats and an inflammatory response was observed only in rats. Progressive fibrosis was not observed in any of the animals despite the high doses. A companion experiment administering the same dusts in a single intratracheal instillation in rats showed clear fibrotic responses and focal accumulations of dust that progressed into collagenous foci. The results of Gross et al. (1973) indicate that the instillation route of administration can lead to artefactual effects not relevant to inhalation exposure and also that the presence of stearin did not lead to markedly different histopathological effects at the dose levels of aluminium metal powder administered.

Justification for classification or non-classification

Although the respiratory tract was damaged in rats and mice, soluble cobalt substances will not be classified for repeated dose toxicity since also carcinogenic effects in the respiratory tract were observed in a 2-year inhalation study (NTP, 1998, see carcinogenicity). Therefore, cobalt aluminium oxide is classified as carcinogenic (DSD: Carcinogenicity category 2; R49; CLP: Carcinogenicity category 1B; H350). According to CLP, there should be no double classification for the same effect, thus no classification for repeated dose toxicity.

Based on the analogue approach, the available data on repeated dose toxicity do not meet the criteria for classification according to Regulation (EC) 1272/2008 or Directive 67/548/EEC, and are therefore conclusive but not sufficient for classification.