Prawns and other shellfish can absorb cadmium which can cause serious problems when digested. | Ultima Hora

The Spanish Food & Safety Agency, or AESAN is advising diners not to suck the heads of prawns, shrimps, crayfish and other crustaceans because of the risk of exposure to cadmium.

This silver-white metal is known to pollute the heads of shellfish and can cause irreversible damage to kidneys, lungs and bones.

Spaniards love nothing more than to suck the heads of shrimp and prawns, but the Organisation of Consumers and Users, or OCU, warns that the metal usually accumulates in the liver and kidneys and in less serious cases will cause severe diarrhoea or stomach pain, but says absorbing too much cadmium can be fatal.