Cadmium is an accumulative poison and by the age of 50 a person will have around 20 mg of it in their body, mainly in their liver. If the level of cadmium in this vital organ exceeds 200 ppm it prevents reabsorption of proteins,
other poisonous elements glucose, and amino acids, and damages the filtering system, leading to kidney failure. Cadmium is on the list of the UN Environmental Programme's top ten most hazardous pollutants.
Cadmium can never be totally excluded from our diet: it is present in foods like liver, shell-fish, and rice. Some plants have an ability to absorb cadmium, such as lettuce, spinach, cabbage, and turnip, while the mushroom Amanita muscaria can absorb cadmium in large amounts. Plants growing on contaminated land, such as that around old zinc mines, can have high levels of the metal, and food that is grown on such soil should not be eaten. Even when such land is turned over to sheep grazing they too have been shown to accumulate cadmium in their kidneys and livers.
The human daily intake of cadmium may be as low as 10 ^g or as high as 100 ^g, but the average is probably less than 25. The World Health Organization recommends that the maximum safe daily intake should not exceed 70 ^g. The problem with cadmium is that this metal is chemically very similar to zinc which is needed for several enzymes in the body. Thankfully the human gut is able to keep out most of the cadmium that enters the stomach, but some slips past the defences and then it is trapped by the enzyme metallothionen. This is a protein that can bind to several cadmium atoms and transport them to the kidneys where in theory they are then ready to be excreted in the urine. Unfortunately cadmium binds so strongly to this enzyme that it tends to accumulate rather than be flushed away. The result is that a cadmium atom remains in the human body on average for around 30 years, and this is why there is so much concern about the effect of this metal on human health.
There have been several serious incidents of cadmium poisoning, and it has been known to kill within days. Inhaled cadmium oxide fumes are particularly dangerous, and this was how a team of construction workers was poisoned while working on the Severn Road Bridge in England in 1966. They used an oxyacetylene torch to remove steel bolts but were unaware that the bolts were galvanized with a thick layer of cadmium to prevent corrosion. The fumes that were given off poisoned them and the following day the men were all ill, experiencing breathing difficulties and coughing violently. One of them had to be taken to hospital, where he died a week later of acute cadmium poisoning. The others were also admitted for treatment but they survived.
Fuchu is a town of 45000 inhabitants situated on the Ashida River in
West Honshu and about 200 miles north-west of Tokyo. It was there that a curious disease appeared in the mid-1950s which the locals called Itai-Itai (loosely translated as 'Ouch-Ouch' on account of the sound its sufferers made every time they moved). The cause was the rice that the inhabitants were eating which was heavily contaminated with cadmium and this originated from the spoil heaps of the Kamioka mine owned by the Mitsui Company. The dietary intake of cadmium was around 600 ^g/person/day, and eventually around 5000 people were affected.
There have been instances where the high level of cadmium in a corpse has led to the arrest of the person suspected of giving it to the victim. This is what happened to 46-year-old John Creamer, a painter and carpenter who lived in Pinellas Park, near St Petersburg on the west coast of Florida. He took his 37-year-old wife Jayne to Orlando on St Valentine's Day in 2002, where they had a celebratory dinner. She died a few hours later. Forensic analysis showed that the level of cadmium in her blood was 12 times higher than normal. Creamer was arrested in December 2002 following accusations by Jayne's relatives that he had poisoned his wife. Indeed her sister said that Jayne had e-mailed her on the day she died, saying she thought her husband had slipped something into her gin. Analysis of Mrs Creamer's blood had found a high level of alcohol along with cadmium and the anti-depressant drug Xanax that she was taking. After Creamer's arrest the police found quantities of cadmium salts, although these may well have been legitimate paint pigments.*
In October 2003, the charges were dropped against Creamer and he was released from jail. And the reason? The previous month, the medical examiner, Dr Shashi Gore, who had originally ruled that Jayne had been poisoned with cadmium, had learned that analyses of cadmium blood levels could often give spuriously high readings. Gore had ordered more forensic tests to be carried out on Jayne's liver and kidneys, and those revealed normal levels of cadmium. Clearly there was no way that a successful prosecution could be brought.
An apparent 'outbreak' of cadmium poisoning appears to have afflicted Indiana County, Pennsylvania, following the death, which appeared to be due to a heart attack, of Thomas Repine, aged 61, in 2002. Some members of
* Cadmium yellow, which is cadmium sulphide (CdS), is one such pigment that was widely used for many years.
his family found his death to be suspicious and as a result of their enquiries his body was exhumed and a high level of cadmium was found in his blood. Other seemingly suspicious deaths in the locality were brought to the attention of the coroner after tests for cadmium on corpses also uncovered elevated levels of the metal, sometimes as high as 1000 ^g/litre of blood. (The US Environmental Protection Agency says the acceptable level is 5.) Whether a serial cadmium poisoner is at large remains to be seen, but it seems unlikely because there were no links between the various deaths, and environmental sources of the cadmium are now suspected.
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