Restricted substances-Cadmium
10 July 2008What is cadmium?
Cadmium is a transition metal which occurs naturally in the form of greenockite. It is rare and nearly always associated with sphalerite (a sulfide ore of zinc). Hence, cadmium is largely produced as a byproduct from the mining of zinc. The name of the element was derived from the Latin ‘cadmia' and the Greek ‘kadmeia,' both ancient names for calamine (zinc carbonate). Cadmium and several cadmium containing-compounds are known carcinogens and can induce many types of cancer.
Naturally occurring cadmium is composed of eight isotopes, of which two are known to be radioactive and three are completely stable. Cadmium is highly toxic and is an occupational hazard associated with industrial processes such as production of batteries, pigments, plastics and other synthetics. The toxicity issues Annually about 25,000 tons of cadmium is released into the environment. Half of this is released naturally into rivers through weathering rocks and some is released into the air because of forest fires and volcanoes. The rest, however, is due to manufacturing. Currently, according to HSE guidelines, it is recommended that 7 micrograms per kilogram of bodyweight per week is the maximum safe level of cadmium intake. Cadmium is a highly toxic metal and is mainly absorbed by humans through food. A greater exposure can occur with people who work in factories where cadmium is used and can be breathed in as dust. There are different degrees of toxicity depending on type and length of exposure. If ingested, it can firstly be transported by the blood to the liver and in turn to the kidneys. The cadmium accumulates in the kidneys, where it damages the filtering mechanisms and can result in severe kidney damage. If inhaled, it can severely affect the lungs. High levels may cause lung inflammation (pneumonitis) or fluid in the lungs (pulmonary oedema). If an individual is subjected to cadmium in these ways for a long time then they could develop kidney dysfunction, anaemia and lung conditions. Cadmium is relatively abundant in our everyday life through diet, fertilised soils and cigarette smoke. Being exposed to it in the workplace could also prove to be a significant health risk. Industrial uses Three quarters of the cadmium produced is used in the production of nickel-cadmium batteries. The rest of the stock is used for pigments, coatings and plating and as stabilisers for plastics. Cadmium freely forms various salts, the most common being cadmium sulfide which is used as a yellow pigment and another common one is cadmium selenide, used as a red pigment. Other uses of cadmium include:
- Electroplating, because cadmium has a high level of lubricity and easy solderability.
- A barrier against nuclear fission.
- Cadmium-containing compounds are used in black and white television phosphors and also in blue and green phosphors for colour television picture tubes.
- The pigments from the compounds of this metal achieve very vibrant colours and so are favoured by painters and other industries such as leather and textiles. The colours can get so potent that during production they have to be toned down before they are mixed with oils and binders. It is recommended that a barrier cream is used on the hands when handling these paints.
- To stabilise plastics such as pvc.