International Agency for Research on Cancer (IARC) - Summaries & Evaluations

(Group 2B)

For definition of Groups, see Preamble Evaluation.

VOL.: 52 (1991) (p. 363)

: 7440-48-4

Cobalt-chromium alloy
: 11114-92-4

Nickel-based cobalt alloy
: 11068-91-0

Cobalt-chromium-nickel-tungsten alloy
: 12638-07-2

Cobalt-chromium-molybdenum alloy
: 12629-02-6

Cobalt[II] acetate
: 71-48-7

Cobalt[II] acetate tetrahydrate
: 6147-53-1

Cobalt[III] acetate
: 917-69-1

Cobalt[II] carbonate
: 513-79-1

Cobalt[II] carbonate hydroxide (1:1)
: 12069-68-0

Cobalt[II] carbonate hydroxide (2:3)
: 12602-23-2

Cobalt[II] carbonate hydroxide (2:3) monohydrate
: 51839-24-8

Cobalt[II] chloride
: 7646-79-9

Cobalt[II] chloride hexahydrate
: 7791-13-1

Cobalt[II] hydroxide
: 21041-93-0

Cobalt[III] hydroxide
: 1307-86-4

Cobalt[II] naphthenate
: 61789-51-3

Cobalt[II] nitrate
: 10141-05-6

Cobalt[II] nitrate hexahydrate
: 10026-22-9

Cobalt[II] molybdenum[VI] oxide
: 13762-14-6

Cobalt[II] oxide
: 1307-96-6

Cobalt[II,III] oxide
: 1308-06-1

Cobalt[III] oxide
: 1308-04-9

Cobalt[III] oxide monohydrate
: 12016-80-7

Cobalt[II] sulfate
: 10124-43-3

Cobalt sulfide
: 1317-42-6

Dicobalt octacarbonyl
: 10210-68-1

Tetracobalt dodecacarbonyl
: 17786-31-1

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Cobalt is widely distributed in the environment; it is the thirty-third most abundant element in the earth's crust. Cobalt is obtained primarily as a by-product of the mining and processing of copper and nickel ores and is a constituent of about 70 naturally occurring oxide, sulfide, arsenide and sulfoarsenide minerals. Cobalt is extracted from ore and concentrated by pyrometallurgical, hydrometallurgical and electrolytic processes alone or in combination. Refined metallic cobalt is available to the industrial market as cathodes and to a lesser extent as powders; oxides and other compounds are also available.

Cobalt compounds have been used as pigments in glass and ceramics in many countries for thousands of years. Since the beginning of the twentieth century, the major uses of cobalt have been in the production of metal alloys, such as superalloys and magnetic alloys, as well as high-strength steels and hard-metal cemented carbides. At the end of the 1980s, about one-third of the cobalt used was in the production of cobalt chemicals, which are used primarily as catalysts and pigments.

The main route of occupational exposure is via the respiratory tract by inhalation of dusts, fumes and mists containing cobalt. Exposures have been measured in hard-metal production, processing and use and in porcelain painting. Occupational exposure to cobalt is regulated in many countries.

Cobalt occurs in vegetables via uptake from soil, and vegetables account for the major part of human dietary intake of cobalt. Animal-derived foods, particularly liver, contain cobalt in the form of vitamin B12. Cobalt is also found in air, water and tobacco smoke. Human tissues and fluids normally contain low levels of cobalt, which may be increased as a result of occupational exposures. Cobalt concentrations in tissue, serum and urine can be increased in patients with implants made of cobalt-containing alloys.

Cobalt-containing particles have been detected in tissues immediately adjacent to such prostheses.

5.2 Experimental carcinogenicity data

Cobalt metal powder was tested in two experiments in rats by intramuscular injection and in one experiment by intrathoracic injection, producing sarcomas at the injection site.

A finely powdered cobalt-chromium-molybdenum alloy was tested in rats by intramuscular injection, producing sarcomas at the injection site. In two other experiments in rats, coarsely or finely ground cobalt-chromium-molybdenum alloy implanted in muscle or pellets of cobalt-chromium-molybdenum alloy implanted subcutaneously did not induce sarcomas. Implantation in the rat femur of three different cobalt-containing alloys, in the form of powder, rod or compacted wire, resulted in a few local sarcomas. In another experiment, intramuscular implantation of polished rods consisting of three different cobalt-containing alloys did not produce local sarcomas. In an experiment in guinea-pigs, intramuscular implantation of a cobalt-chromium-molybdenum alloy powder did not produce local tumours.

Intraperitoneal injection of a cobalt-chromium-aluminium spinel in rats produced a few local malignant tumours, and intratracheal instillation of this spinel in rats was associated with the occurrence of a few pulmonary squamous-cell carcinomas.

In two experiments in rats, intramuscular injection of cobalt[II] oxide powder produced sarcomas at the injection site. In an experiment in mice, intramuscular injection of cobalt oxide powder did not produce local tumours. Intratracheal instillation of cobalt oxide powder in rats was associated with a few benign and malignant pulmonary tumours. In a study limited by poor survival, hamsters administered a cobalt oxide dust by inhalation showed no increase in the incidence of pulmonary tumours. In two experiments in rats by subcutaneous and intraperitoneal injection, cobalt oxide powder produced local malignant tumours.

Cobalt[II] sulfide powder was tested in one study in rats by intramuscular injection, producing a high incidence of local sarcomas.

Cobalt[II] chloride was tested in one study in rats by repeated subcutaneous injection, producing many local and a few distant subcutaneous sarcomas.

Cobalt[II,III] oxide was tested in one experiment in hamsters to determine the effects of various particulates on carcinogenesis induced by N-nitrosodiethylamine. Intratracheal instillation of cobalt[II,III] oxide did not increase the incidence of pulmonary tumours over that in appropriate control groups.

Studies in mice and rabbits with cobalt naphthenate could not be evaluated.

In a screening test for lung adenomas by intraperitoneal injection, cobalt[III] acetate did not increase the incidence of lung tumours in strain A mice.

Interpretation of the available evidence for the carcinogenicity of cobalt in experimental animals was difficult because many of the reports failed to include sufficient details on results of statistical analyses, on survival and on control groups. Further, statistical analyses could not be performed by the Working Group in the absence of specific information on survival and on whether the neoplasms were fatal. Nevertheless, weight was given in the evaluation to the consistent occurrence of tumours at the site of administration and to the histological types of tumours observed.

5.3 Human carcinogenicity data

A number of single cases of malignant tumours, mostly sarcomas, have been reported at the site of orthopaedic implants containing cobalt. In one cohort study of people with a hip prosthesis, there was a significant increase in the incidence of lymphatic and haematopoietic malignancies, and significant deficits of breast and colorectal cancers. Overall cancer incidence was significantly lower than expected in the first 10 years after surgery, but significantly higher than expected after 10 or more years. No data were provided on the composition of the prostheses in this study.

Four cohort studies on the association between industrial exposure to cobalt and death from cancer were reviewed, two of which provided information for the evaluation. In a French electrochemical plant, there was a significant increase in the risk for lung cancer among workers in cobalt production, who were also exposed to nickel and arsenic, but not among workers in other departments of the factory. In a study in Sweden of hard-metal workers with documented exposure to cobalt-containing dusts, a significant increase in lung cancer risk was seen in persons exposed for more than 10 years whose exposure had begun more than 20 years previously.

Interpretation of the available evidence on the possible association between occupational exposure to cobalt and cancer in humans is made difficult by the fact that in three of the four studies there was concurrent exposure to other potentially carcinogenic substances, including forms of nickel and arsenic. In the Swedish study, there was concurrent exposure to other components of hard-metal dust.

5.4 Other relevant data

Occupational exposure to cobalt-containing dusts can cause fibrotic changes in the lung and can precipitate asthma. Cardiotoxic effects have been reported in exposed humans; in particular, cardiomyopathy can occur after prolonged oral intake.

Cobalt[II] chloride reduced fertility in male mice.

Cobalt[II] compounds had weak or no genetic effect in bacteria; some cobalt[III] complexes with heterocyclic ligands were active.

In single studies with an extensive range of eukaryotes, including animal and human cells in vitro, cobalt[II] compounds induced DNA damage, mutation, sister chromatid exchange and aneuploidy. Gene conversion and mutation in eukaryotes and DNA damage in human cells were observed in several studies. There was some evidence that these compounds can also induce aneuploidy in hamsters in vivo. In single studies, cobalt[II] sulfide induced DNA damage and transformation in cultured mammalian cells.

5.5 Evaluation

There is inadequate evidence for the carcinogenicity of cobalt and cobalt compounds in humans.

There is sufficient evidence for the carcinogenicity of cobalt metal powder in experimental animals.

There is limited evidence for the carcinogenicity of metal alloys containing cobalt, chromium and molybdenum in experimental animals.

There is sufficient evidence for the carcinogenicity of cobalt[II] oxide in experimental animals.

There is limited evidence for the carcinogenicity of cobalt[II] sulfide in experimental animals.

There is limited evidence for the carcinogenicity of cobalt[II] chloride in experimental animals.

There is inadequate evidence for the carcinogenicity of cobalt-aluminium-chromium spinel, cobalt[II,III] oxide, cobalt naphthenate and cobalt[III] acetate in experimental animals.

Overall evaluation

Cobalt and cobalt compounds are possibly carcinogenic to humans (Group 2B).

For definition of the italicized terms, see Preamble Evaluation.

Synonyms for Cobalt

Synonyms for Cobalt-chromium alloy

Synonyms for Nickel-based cobalt alloy

Synonyms for Cobalt-chromium-nickel-tungsten alloy

Synonyms for Cobalt-chromium-molybdenum alloy

Synonyms for Cobalt[II] acetate

Synonym for Cobalt[II] acetate tetrahydrate

Synonyms for Cobalt[III] acetate

Synonyms for Cobalt[II] carbonate

Synonyms for Cobalt[II] carbonate hydroxide (1:1)

Synonyms for Cobalt[II] carbonate hydroxide (2:3)

Synonyms for Cobalt[II] carbonate hydroxide (2:3) monohydrate

Synonyms for Cobalt[II] chloride

Synonyms for Cobalt[II] chloride hexahydrate

Synonyms for Cobalt[II] hydroxide

Synonyms for Cobalt[III] hydroxide

Synonyms for Cobalt[II] naphthenate

Synonyms for Cobalt[II] nitrate

Synonyms for Cobalt[II] nitrate hexahydrate

Synonyms for Cobalt[II] molybdenum[VI] oxide

Cobalt[II] oxide

Synonyms for Cobalt[II,III] oxide

Synonyms for Cobalt[III] oxide

Synonyms for Cobalt[III] oxide monohydrate

Synonyms for Cobalt[II] sulfate

Synonyms for Cobalt sulfide

Synonyms for Dicobalt octacarbonyl

Synonym for Tetracobalt dodecacarbonyl

Last updated: 17 November 1997

    See Also:
       Toxicological Abbreviations