Cadmium

Cadmium (Cd) is a heavy metal that is naturally found in the environment associated with zinc, copper and lead, therefore it is an inevitable by-product of mining activities relating to these metals.  It has many industrial applications, the reason for which its emission into the environment is rising due to the action of man (the burning of fossil fuels, metallurgy, the incineration of rubbish) and the use of phosphate-based and residual sludge-based fertilisers

This metal has no biological function in humans or animals but, although its absorption in the digestive system is low, it tends to accumulate in other parts of the body, primarily in the liver and kidneys, for a time estimated to be between 10 and 30 years. Cadmium is toxic to the kidneys, accumulating primarily in the proximal tubules, which possibly leads to kidney dysfunction. It can also cause demineralisation of the bones, either directly or indirectly as a result of kidney failure. After a prolonged and/or high exposure the tubular damage evolves in such a way as to produce a reduction of the glomerular filtration rate and can cause kidney failure, and in the long term, cancer. (The International Agency for the Research of Cancer (IARC) has classified cadmium as a category 1 agent (carcinogenic to humans) due to the existence of sufficient scientific evidence that supports this.      

The greatest source of human exposure to cadmium is foodstuffs, therefore it is considered to be a food risk. To keep the levels of cadmium in foods within acceptable levels for the consumer, bearing in mind its inevitable presence in the environment, Regulation 1881/2006 lays down the maximum contents admitted.

Given its potential to accumulate in the liver and kidneys in animals, the highest levels of cadmium found in foods are precisely in edible offal (kidney>liver>>other edible offal). High levels are also found in shellfish since in many cases the whole animal is consumed, including the offal, where the cadium is found. In products of vegetable origin, the highest levels are found in Swiss chard, cocoa, wild mushrooms and oilseed. As regards exposure, we would point out that the group of foods that provide most cadmium to the intake is that of cereals, not because they contain a high level, but cereals are an important part of our diet.  

In the case of crustaceans, the maximum content laid down in Regulation 1881/2006, which has been recently amended, applies to the white flesh of the appendix and the stomach, excepting crabs and crustaceans of a crab type (spider crab, crawfish, and so forth), to which the limit applicable only concerns the “white flesh of the appendix”. The presence of cadmium in these parts of crustaceans is considered to be “low”.

Nevertheless, in some European countries, among which is Spain, in addition to the “white” part, other parts of crustaceans, such as the head of prawns, king size prawns, Norway lobster, and so forth, are consumed and the body of crustaceans of the crab type, whose levels of cadmium are high, due to the fact that cadmium accumulates primarily in the hepatopancreas, which forms part of the digestive system of crustaceans and is located in the head.       

For this reason, the Directorate General for Health and Consumer Policy (DGSANCO) of the European Commission has published in its web site an  informative note on “Cadmium in crustaceans”, requesting the Member States in which a high level of this shellfish is completely consumed to make consumption recommendations due to the high content of this heavy metal in certain parts of the animal.              

In a control exercise conducted over 2009 and 2010 by the European Commission, it was brought to light that the levels found in the flesh of the inside of the shell of crustaceans of the crab type were very high and very variable. On average, the content of cadmium in this flesh was 8 mg/Kg as opposed to the level of 0.08 mg/Kg found in the white flesh of the appendix. The final content of cadmium that would be obtained on mixing the edible parts, both of the appendix and the head, would be 2.3 mg/Kg on average, which means some 30 times the content of the appendix. We would point out that the content of cadmium in the eggs of crustaceans, although it is greater than that found in the appendix, is not high (2.5 times).

The situation of the other crustaceans, such as prawns and the like, is not as extreme as in the case of crabs since the consumption of the head with respect to the stomach is less. The data available point to the fact that the intake of cadmium when the head is consumed is 4 times greater than the intake involved on consuming the stomach only.

Consumers of this type of product must be aware that the intake of these parts of the crustaceans may lead to an unacceptable exposure to cadmium, particularly when intake is habitual.

For further information please consult the scientific opinion on Cd in foods issued by the European Food Safety Authority (EFSA) in March 2009.

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