Cobalt molybdate

Endpoint summary

Key value for chemical safety assessment

Skin sensitisation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

There are no data available on the skin sensitisation potential of cobalt molybdenum oxide. However, there are reliable data for soluble cobalt and molybdenum substances considered suitable for read-across using the analogue approach. For identifying hazardous properties of cobalt molybdenum oxide, the existing forms of cobalt molybdenum oxide at very acidic and physiological pH conditions are relevant for risk assessment of human health effects. Cobalt molybdenum oxide is a metal-organic salt, which is water soluble (~ 508 mg/L) and nearly completely dissociates in aqueous solutions. As it is expected that cobalt molybdenum oxide is capable of forming ions at very acidic and physiological pH conditions, cobalt cations and molybdate anions will be present and completely bioavailable, same as for other soluble cobalt and molybdenum compounds. Due to the existing cobalt and molybdate ions, data from other soluble cobalt and molybdenum substances are used in the derivation of toxicological endpoints for cobalt molybdenum oxide. For further details refer to the analogue justification.

 

Cobalt substances

Cobalt(II)chloride hexahydrate caused positive reactions in a modified guinea pig maximization test (GMPT) (Wahlberg and Boman, 1978). The test substance sensitised 100% of the test animals at the highest challenge dose (1% cobalt(II)chloride hexahydrate) tested 25 h after removal of the Finn chambers. The percutaneous absorption rate of the test substance through normal skin is obviously sufficient to induce contact allergy.

Ikarashi et al. (1992) showed a sensitising potential of cobalt(II)chloride hexahydrate in a local lymph node assay (LLNA) conducted similar to OECD 429. Repeated exposure to 5% of the test substance for three consecutive days induced an increase of LNC proliferative response in the draining lymph node of mice and resulted in a total stimulation index of 4.33.

In conclusion, reliable studies using different protocols, either GPMT or LLNA, demonstrated that cobalt(II)chloride hexahydrate is a skin sensitiser in guinea pigs and mice.

In humans, dermal exposures have been also observed to result in sensitisation reactions to soluble cobalt salts. Contact allergy was reported in 22 of 223 (9.9%) nurses who were tested with a patch test of 1% cobalt(II)chloride (Kiec-Swierczynska and Krecisz, 2000), as well as 16 of 79 (20.3%) of examined dentists (Kiec-Swierczynska and Krecisz, 2002). Numerous human data also showed that soluble cobalt(II)salts are skin sensitisers (Kanerva et al., 1988; Goh et al., 1986; Alomar et al., 1985).

 

Molybdenum substances

Guideline conform skin sensitisation studies (guinea pig maximisation tests) are available for sodium molybdate, ammonium dimolybdate and molybdenum trioxide (Allan, 1996).

The test substance concentrations selected for the main studies were based on the results of preliminary studies. In the main studies, 20 Dunkin-Hartley guinea pigs were intradermally and epicutaneously exposed to the molybdenum substances. 20 control animals were similarly treated, but with the vehicle (Alembicol D or water) only. Two weeks after the epidermal application, all animals were challenged either with two test substance concentrations applied to one flank (35% and 70% w/w molybdenum trioxide and disodium molybdate) or with one test concentration (45% w/w ammonium dimolybdate). Based on the clear absence of sensitising properties, the molybdenum substances were not considered to be skin sensitiser.

 

References not cited in the IUCLID:

Kiec-Swierczynska M and Krecisz B, 2002, Allergic contact dermatitis in dentists and dental nurses. Exogenous Dermatology. 1(1): 27-31

Kanerva L et al., 1988, Occcupational skin disease in Finland, International Archives of Occupational and Environmental Health, 60: 89-94

Goh et al., 1986, Occupational dermatitis in a prefabrication construction factory. Contact dermatitis, 15: 235-240

Alomar A et al., 1985, Occupational dermatosis from cutting oils. Contact dermatitis, 12: 129-138

Migrated from Short description of key information:
Read-across from soluble cobalt(II)salts: Cobalt(II)chloride hexahydrate was sensitising in the guinea pig maximization test as well as in the local lymph node assay. Numerous human data also showed that soluble cobalt(II)salts are skin sensitisers. Based on an analogue approach, cobalt molybdenum oxide is also expected to be a skin sensitiser.

Respiratory sensitisation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (sensitising)

Additional information:

There are no data available on the respiratory sensitisation potential of cobalt molybdenum oxide. However, there are reliable data for soluble cobalt and molybdenum substances considered suitable for read-across using the analogue approach. For identifying hazardous properties of cobalt molybdenum oxide, the existing forms of cobalt molybdenum oxide at very acidic and physiological pH conditions are relevant for risk assessment of human health effects. Cobalt molybdenum oxide is a metal-organic salt, which is water soluble (~ 508 mg/L) and nearly completely dissociates in aqueous solutions. As it is expected that cobalt molybdenum oxide is capable of forming ions at very acidic and physiological pH conditions, cobalt cations and molybdate anions will be present and completely bioavailable, same as for other soluble cobalt and molybdenum compounds.Due to the existing cobalt and molybdate ions, data from other soluble cobalt and molybdenum substances are used in the derivation of toxicological endpoints for cobalt molybdenum oxide. For further details refer to the analogue justification.

 

Cobalt substances

The available case reports revealed that soluble cobalt(II) salts are capable of inducing hypersensitive reactions in the respiratory tract after inhalation exposure. These hypersensitive reactions include e. g. respiratory irritation, bronchial asthma, wheezing and pneumonia.

Shirakawa et al. (1989) reported that inhalation of cobalt(II)chloride aerosols can provoke an asthmatic attack in sensitised individuals. Inhalation exposure to cobalt(II)salts among glass bangle workers resulted in decreases in ventilatory function relative to the control workers (Rastogi et al., 1991). In the cross-sectional study of Nemery et al. (1992), 194 workers (166 men and 28 women) in the diamond polishing industry were exposed to cobalt dusts. A significant increase in the prevalence of eye, nose, and throat irritation and reduced lung function compared to 59 unexposed control workers (46 men and 13 women) were observed. Cobalt exposure groups were defined based on air measurements at the time of the study, and exposure was confirmed by measurement of cobalt in urine. The duration of employment was not discussed. In another cross-sectional study, workers in a cobalt refinery who were exposed to cobalt metal, salts and oxides for up to 39 years at an average concentration of 0.125 mg Co/m3 had increased dyspnoea and wheezing, and decreased lung function compared to unexposed controls (Swennen et al., 1993). Linna et al (2003) also found that asthma symptoms were more prevalent in workers in a cobalt plant who were exposed to cobalt compounds. However, many of the epidemiological studies on inhalation exposure to cobalt have been conducted on workers in the hard metal industry where subjects are co-exposed to elemental cobalt and other substances such as tungsten carbide. It is difficult to assess the effects of cobalt alone from these studies as the toxicity of cobalt metal is increased in the presence of tungsten carbide, and it has been proposed that a mixture of cobalt and tungsten carbide behaves as a unique entity (IARC 2006).

 

Molybdenum substances

There are no data available on respiratory sensitization.

 

References not cited in the IUCLID:

Roto P, 1980, Asthma, symptoms of chronic bronchitis and ventilatory capacity among cobalt and zinc production workers. Scand J Work Environ Health 6: 1-49

Kusaka Y et al., 1996a, Epidemiological study of hard metal asthma. Occup Environ Med 53: 188-193

Kusaka Y et al., 1996b, Decreased ventilatory function in hard metal workers. Occup Environ Med 53: 194-199

Ruokonen EL et al., 1996, A fatal case of hard-metal disease. Scand J Work Environ Health 22: 62-65

IARC (International Agency for Research on Cancer). 2006. IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. Volume 86. Cobalt in hard metals and cobalt sulphate, gallium arsenide, indium phosphide and vanadium pentoxide.

Migrated from Short description of key information:
Case reports evidenced respiratory sensitisation reactions by soluble cobalt(II)salts in humans. Based on the analogue approach, cobalt molybdenum oxide is also expected to be a respiratory sensitiser.

Justification for classification or non-classification

Based on an analogue approach, the available data on skin sensitisation meet the criteria for classification as Category 1 (H317) according to Regulation (EC) 1272/2008 and as R43 according to Directive 67/548/EEC.

Based on an analogue approach, the available data on respiratory sensitisation meet the criteria for classification as Category 1 (H334) according to Regulation (EC) 1272/2008 and as R42 according to Directive 67/548/EEC.