However, the Spanish Food & Safety Agency, (AESAN) issued an advisory warning diners not to suck the heads of such shellfish because of the health risks associated with cadmium.
Concentrated levels of cadmium (Cd) a heavy metal associated with zinc, copper and lead, are found in the dark meat of shellfish such as prawns, crab and lobster but cannot be processed by humans and can cause problems in the liver and kidneys.
The metal accumulates in the human body over a period of between 10 and 30 years and has been classed a category 1 carcinogen by the International Agency for Research on Cancer (IARC).
It can cause renal problems or liver damage, demineralization of bones and in the worst case, cancer.
It is also present in high levels in the edible offal of animals such as kidneys and livers.
In prawns these organs are found in the ‘head’ part which is considered a delicacy by Spaniards and is pulled off and sucked on before the body is peeled and the white meat consumed.