In this feature article, Lisa Bushby discusses the uses and risks associated with cadmium and its compounds and offers some safe handling advice.
Cadmium is a naturally-occurring silver-white metal. It has a melting point of 321°C and a boiling point of 767°C. When heated above its melting point in air, cadmium oxide fumes are emitted, which are toxic.
Cadmium is most stable in its 2+ oxidation state, such as in cadmium chloride. Along with its compounds, cadmium is widely used in many processes and products including:
welding and soldering
production of iron, steel and cement
dyes, plastics and phosphate fertilisers
nickel-cadmium rechargeable batteries.
The reason for adding cadmium to an alloy will generally be to lower the melting point of the resulting material, but by far the highest percentage of cadmium produced worldwide is for nickel-cadmium rechargeable batteries, found in laptops, power tools, mobile phones, etc.
Risk to the environment and human health
Useful as it may be, the growing concern at the environmental risks and potential health hazards associated with exposure to cadmium must be taken into account. For example:
cadmium and its compounds are dangerous for the environment and very toxic to aquatic organisms
short-term exposure to cadmium oxide fumes may cause sore eyes, nose and throat, coughing, headache, dizziness and weakness, chills, fever, chest pains and breathlessness
ingestion may cause nausea, vomiting, abdominal pain and diarrhoea
long-term exposure to cadmium or cadmium compounds may cause damage to the kidneys and lungs, and some cadmium compounds have been shown to cause cancer in animals.
The CLP classification of cadmium includes the carcinogenic, mutagenic and toxic to reproduction (CMR) codes H350 Carc.1B, meaning it may cause cancer, H361 Repr. 2, meaning it is suspected of damaging fertility or the unborn child, and H341 Muta. 2, meaning it is suspected of causing genetic defects.
Further, cadmium is included in the Candidate List of substances of very high concern owing to its CMR properties and because of its adverse effects on kidney and bone tissues after prolonged exposure, which cause probable serious effects to human health. Producers or importers of articles have to notify the European Chemicals Agency if their article contains a substance on the Candidate List. This obligation applies if the substance is present in those articles in quantities totalling over one tonne per producer or importer per year and if the substance is present in those articles above a concentration of 0.1% (w/w).
Managing the risk of inhalation
The risk of workers inhaling fumes that contain cadmium and cadmium compounds should be controlled.
Owing to its carcinogenicity, where cadmium-free alternatives are not suitable, the requirements of regulation 7(3) of the Control of Substances Hazardous to Health Regulations 2002 must be followed, which include:
total enclosure of the process and handling systems as far as is reasonably practicable
local and general extract ventilation and the use of other processes and systems of work that minimise, suppress and contain fumes and dust, for example, use cadmium compounds in the form of damp pastes, and keep them damp during handling
minimising the number of people exposed and periods of exposure
prohibiting smoking, eating and drinking in contaminated areas
regularly cleaning work areas to minimise contamination
providing suitable washing and changing facilities
demarcating potentially contaminated areas and displaying suitable warning signs
safely storing, handling and disposing of materials
keeping containers closed when they are not being used and having them clearly labelled.
Extract ventilation systems must be examined and tested by a competent person at least once every 14 months and appropriate records must be kept. It is recommended that all engineering control measures in use also receive frequent visual inspections, at least weekly.
Preventative maintenance procedures should indicate which engineering control measures require servicing, the nature of the work to be carried out, by whom, and how any defects which are found will be rectified. Respiratory protective equipment should also be properly maintained and regularly examined, tested, cleaned and suitably stored when not in use. Filters will need replacing where appropriate in accordance with the conditions of use and suppliers’ instructions.
Where significant exposure to cadmium or its compounds can occur, monitoring may be required to ensure the effectiveness of control measures and establish that exposure levels are being kept within the legal limits and as low as is reasonably practicable. EH40: Workplace Exposure Limits outlines the various exposure limits of different cadmium compounds. Cadmium sulphide and cadmium sulphide pigments are subject to a long-term exposure limit (8-hour time weighted average reference period) of 0.025mg/m3. Cadmium oxide fume is also subject to a short-term exposure limit (15 minute reference period) of 0.05mg/m3. Cadmium sulphide and cadmium sulphide pigments (respirable dust as (as Cd)) is subject to a 0.03mg/m3 long-term exposure limit.
To determine the concentration of airborne cadmium and inorganic compounds of cadmium in air, the Health and Safety Executive in MDHS10/2 recommends a laboratory method using flame atomic absorption spectrometry or electrothermal atomic spectrometry that is suitable for sampling over periods in the 15 minute to 8 hour range.
Avoiding releases to the environment
Cadmium has been found to bioaccumulate in all levels of the food chain, and in the aquatic environment the toxicity of cadmium has been found to generally increase with reducing water hardness, reducing concentrations of dissolved organic matter and increasing solution pH. Care should therefore be taken in its handling and disposal to avoid any release to the environment.
Batteries containing cadmium should be recycled. A battery compliance scheme will collect waste batteries.
Spillages and decontamination run-off should be prevented from entering drains and watercourses. The Environment Agency should be informed of any substantial incidents.
Cadmium and Inorganic Compounds of Cadmium in Air: Laboratory Method Using Flame Atomic Absorption Spectrometry or Electrothermal Atomic Absorption Spectrometry (1994), HSE
Cadmium and You. Working with Cadmium: Are You At Risk? (2010), HSE. Available from the HSE website
Final Review of Scientific Information on Cadmium (2010), UNEP. Available from the UNEP website
Member State Committee Support Document for Identification of Cadmium as a Substance of Very High Concern (2013), ECHA. Available from the ECHA website.