By Razak Hj. Lajis
The Sun, November 28, 1995
CADMIUM HAS LONG BEEN recognised as a toxic element. Naturally, it exists mainly as sulfide in zinc-containing mineral deposits. All soils and rocks, including coal and mineral fertilisers, have some cadmium in them. It is recovered as a by-product from smelting processes of these metals.
Cadmium can also be found in combination with other elements such as oxygen, chlorine and sulphur, leading to the formation of cadmium oxide, cadmium chloride and cadmium sulphate.
Cadmium is emitted during processes that utilise ores and during combustion of fossil fuels as well. It is also released into the atmosphere through certain manufacturing operations such as the preparation of fungicides and fertilisers.
Not surprisingly, those involved in these industries are exposed to cadmium. But the general population may also be at risk due to some environmental factors. These include cigarette smoke, certain food and even water.
The highest concentration of cadmium may appear in fish, shellfish and organs such as the liver and kidneys. Shellfish accumulate cadmium from the water which then attach them to cadmium-binding peptides.
Among the many metals, cadmium is one of the most readily absorbed and accumulated element in plants grown on contaminated soil. People may also be exposed by drinking contaminated water.
Cadmium is a highly toxic element. In addition to being a cytotoxic heavy metal, it is also known to be embryotoxic and has an extremely long biological half-life.
Studies have suggested that excessive cadmium salts have adverse effects on our health. Its absorption is enhanced by dietary deficiencies of calcium and iron. It is transported in the blood by red blood cells and large protein molecules. Most of the body burden (total amount of a chemical in the body at a given point of time) of cadmium is retained in the liver and kidneys.
| Compounds of cadmium | Industrial uses |
|---|---|
 Cadmium oxide Cadmium sulphide Cadmium sulphate Cadmium stearate Cadmium chloride |
used in batteries as an intermediate and catalyst in electroplating used as a pigment in paint used as an intermediate in electroplating used as a plastic stabiliser used in photography and in dyes |
Acute poisoning of cadmium usually results from the inhalation of cadmium dust and fumes, specially cadmium oxide. Such poisonings are relatively rare but dangerous. Its symptoms usually develop four to 12 hours after exposure and they are characterised by a metallic taste in mouth, cough, breathing difficulties and fever.
Exposure to high concentrations of cadmium by inhalation will cause severe damage to the lungs and subsequently, can lead to death. Prolonged inhalation of cadmium oxide can result in lung dysfunction and emphysema.
At present, one major public concern is the association between exceptionally high environmental exposure to cadmium and lung cancer. Early and recent studies provide consistent evidence that the risk of lung cancer is increased among workers exposed to cadmium.
Through chronic exposure, cadmium can accumulate in certain organs, particularly the kidneys. In Japan, kidney failure has been observed in individuals whose food and water intakes were affected by high levels of cadmium.
Low exposure, which generally occusr due to moderate occupational factors, mainly affect blood cadmium levels in the last two to three months of exposure. Cadmium concentrations in whole blood are affected by both recent exposure and body burden.
Blood cadmium levels in adults without excessive exposure are usually less than one microgram per litre (ug/litre). The body burden of cadmium in an average person is approximately 30mg.
Newborns have a much lower body content of cadmium - usually less than 1mg. Whole blood cadmium levels average 0.4 to 1 ug/litre in non-smoking, non-exposed adults. Its levels in smokers are normally higher, in the range of 1.4 to 4.5 ug/litre.
Although the target organ of cadmium toxicity is the kidney, other adverse effects may occur in the bones and stomach. This was observed in a syndrome known as "itai-itai" in Japan. It occurred as a result of consuming cadmium-contaminated rice and was characterised by severe bone pain and osteomalacia (softness of bones). Bone pain due to cadmium toxicity is common in the ribs, backbone and femur.
Stomach irritation leading to vomiting and diarrhoea are also often associated with the ingestion of high levels of cadmium in food and drinking water.
As mentioned earlier, the general population is also exposed to cadmium from breathing cigarette smoke. It is universally accepted that smoking during pregnancy results in decreased infant birth weight and birth defects. Cadmium is just one of the many harmful elements found in cigarette smoke that causes such damage.
Each cigarette smoked contributes approximately one to two microgram of cadmium to the body burden and about 10% of the cadmium in a cigarette is inhaled.
It has also been reported that the cadmium in cigarette smoke may decrease the transfer of zinc across the human placenta.
Cadmium may also have adverse effects because it competes with zinc for certain enzymatic pathways. This is worsened by the fact that more than 70 human enzyme systems depend on zinc for their functions.
Other studies conducted have shown that cadmium may cause harm to the reproductive system.
In experiments on animals, parenteral administration of cadmium salts has been reported to produce adverse effects on the testes, ovaries, placenta and embryo.
Administration of cadmium at doses affecting placental morphology or function can induce foetal anaemia, growth retardation, teratogenicity and embryonic and foetal death in experimental animals.
Protective measures must provide a critical assessment of health effects and potential risks to human health of environmental exposure to cadmium.
Major sources and routes of exposures must be identified and handled with relevant control and regulation. Regulatory bodies should come up with practical solutions and programmes to enable the public and health-related organisations to monitor the situation closely.
The writer is a pharmacist at National Poison Centre, Universiti Sains Malaysia, Penang.
