Cobalt has a strong association with hard metal disease, a rare condition. In this article, Lisa Bushby discusses cobalt, how it is used, its health effects and how to control exposure.
Cobalt is a naturally-occurring transition metal element and the 33rd most abundant element. It has been found in a variety of media, including air, surface water, leachate from hazardous waste sites, groundwater, soil, and sediment.
59Co is the only stable isotope, which is a hard, bluish-white metal. While there are around 26 known radioactive isotopes, only 57Co and 60Co are commercially important.
Cobalt occurs in the 0, +2, and +3 valence states. Cobalt(II) is more stable than cobalt(III), which is a powerful oxidising agent that can oxidise water and liberate oxygen. At high temperatures, it is attacked by atmospheric oxygen and by water vapour where it oxidises to cobalt (II) oxide. Cobalt (II) oxide is an olive-green compound. Simple inorganic salts of cobalt are readibly soluble in water.
Cobalt and its compounds are used in many processes and products. For example, cobalt is primarily used for its magnetic properties, to make alloys with other metals and for jet engine and cutting tool production. It is also used as a pigment in glass, ceramics and paints as paint dryer, and as a catalyst for the petroleum industry and in batteries.
Hazards and classification
Cobalt has the Signal word “Danger” and the following pictogram assigned to it under the CLP Regulation:
It also has the following Hazard Statements.
H317 May cause and allergic skin reaction.
H334 May cause allergy or asthma symptoms or breathing difficulties if inhaled.
H413 May cause long lasting harmful effects to aquatic life.
Precautionary Statements associated with cobalt are as follows.
P261 Avoid breathing dust/fume/gas/mist/vapours/spray.
P280 Wear protective gloves.
Cobalt is listed in the Health and Safety Executive’s EH40 Workplace Exposure Limits document with a long-term exposure limit (8-hour time weighted average reference period) of 0.1 mg/m3. This limit must not be exceeded in the workplace.
Cobalt can enter the body through:
Inhalation of dusts or mists
skin contact with dust or solutions
handling food cobalt or its compounds are present on the skin.
Short-term effects can include vomiting and abdominal pain if cobalt salts are ingested.
Longer-term effects can include:
allergic reactions in the skin (allergic dermatitis) and respiratory tract (asthma)
inflammation and fibrosis of the lung as the result of a condition called “hard metal disease”, which can become irreversible and lead to early death
occasional instances of heart disease (cardiomyopathy)
a possible effect on thyroid function, with enlargement of the thyroid gland.
Even though the primary route of occupational exposure to cobalt is the respiratory tract, skin contact is also important because dermal exposures to hard metal and cobalt salts can result in significant systemic uptake. Sustained exposures can cause skin sensitisation, which may result in eruptions of contact dermatitis.
Hard metal disease
Hard metal disease is an interstitial lung disease (pulmonary fibrosis) that has a strong association with chronic exposure to the inhalation of cemented tungsten carbide dust and cobalt, as generated during the manufacture of high-speed drill or saw tips.
Although rare, exposure can cause lung disease with a typical histological pattern of giant cell interstitial pneumonia. There is also a potential hypersensitivity component to the disease with a case of diffuse panbronchiolitis reported in a worker exposed to tungsten carbide and cobalt.
The highest concentrations of cobalt are often found in waters containing high iron or manganese, although the concentration of total cobalt in freshwaters is generally low.
Higher concentrations are generally associated with industrialised or mining areas. The production of alloys and chemical compounds containing cobalt, sewage effluents, urban run-off and agricultural run-off are major sources of cobalt contamination.
Cobalt should not be allowed to enter drains and any discharge into the environment must be avoided.
The Control of Substances Hazardous to Health Regulations 2002 (COSHH) apply to cobalt, as with any hazardous substance.
Wherever it is reasonably practicable, exposure to substances that can cause occupational asthma should be prevented. Where this is not possible, the primary aim is to apply adequate standards of control to prevent workers from becoming sensitised. For substances that can cause occupational asthma, COSHH requires that exposure be reduced as low as is reasonably practicable. Activities giving rise to short-term peak concentrations should receive particular attention when risk management is being considered. Health surveillance is appropriate for all employees exposed or liable to be exposed to a substance which may cause occupational asthma and there should be appropriate consultation with an occupational health professional over the degree of risk and level of surveillance.
Those handling cobalt should ensure the following guidelines are followed:
any extraction equipment or other control measures must be used correctly.
any protective clothing and equipment provided should be used as it is intended. (Nitrile rubber gloves that meet the requirements of EN 374 are recommended for full and splash protection.)
use washing facilities provided.
any respirator should:
have a tight-fitting mask
be fit tested
be clean and in good working order
have the filter changed regularly
be stored in a clean/dry place, preferably a locker.
report defects in enclosures, extraction equipment or other control measures to the lab manager.
do not eat or drink in work areas where cobalt or cobalt compounds may be present.
The health of people exposed to cobalt and its compounds should be monitored by an occupational health professional. They will normally carry out an examination after an offer of employment and at regular intervals thereafter.
As cobalt is highly soluble, it is generally excreted in urine. Part of the examination will therefore usually involve testing a urine sample so the level of cobalt content can be measured.
Those exposed to cobalt should examine your skin regularly, looking for colour changes, rashes and skin damage.
If additional examination or tests are needed, occupational health professionals will be able to explain what these are and why they are necessary.
Managers should be prepare information, instruction and training for those handling cobalt on:
the risks to health from the use of cobalt and its compounds
the safe way of working, the reasons for it, and how to use equipment properly, eg extraction systems
the reasons for personal protective equipment and clothing, the jobs where they are needed, and how they should be used, stored and maintained
the results of any tests for cobalt levels in the air of the lab
the role of any health surveillance and arrangements for workers to get information about the results
any further requirements of COSHH.