Is it dangerous to suck the head of prawns for cadmium?

10 years ago the AESAN (Spanish Agency for Food Safety and Nutrition) recommended not to suck the head of prawns due to its Cadmium content. This year it has come to the fore again, but… what is the real risk from cadmium and a shrimp’s head?


Let’s start with one of the two elements: cadmium. What is the problem with cadmium? The main problem is that it is a heavy metal, and heavy metals are not very friendly to the health of living beings in general, and therefore, neither of humans. 

head of prawns for cadmium
head of prawns for cadmium

The cadmium can be a serious problem due to acute intoxication but also by exposure to long – term above the limits considered as the WHO safe classifies as a group I within the classification of carcinogens at the same level as snuff. But it can not only cause cancer but also serious kidney problems and loss of bone mass (osteoporosis, loss of bone density), leading to death.

Among the main sources of cadmium entry into humans is inhalation (essentially from tobacco smoke, and to a lesser extent from smoke from burning fossil fuels, incineration of garbage, emissions from mining operations …), for dermal contact and by ingestion (in contaminated food and / or water).

Currently, the limit set by the EFSA (European Food Safety Authority) is set at 2.5 micrograms per kilogram of weight per week, which is a fairly low limit. In this link you can find the maximum limits for cadmium in food.

In Europe, and in Spain in particular, we are very close to that tolerable weekly limit due to our dietary habits. 

Cadmium, being a heavy metal, is difficult for living beings to excrete and tends to accumulate in tissues: kidneys and liver are some of the places where we can find cadmium in living beings. Its excretion is usually carried out in small quantities through the urine, which is why it has a long biological life inside human beings, between 10 and 30 years.

Why is cadmium a concern in shrimp head?

Cadmium can be found in many different foods, terrestrial animal kidneys, meat, fish, vegetables, and even cocoa, but why are prawns a concern?

The prawn is a decapod crustacean belonging to the Dendrobranchiata suborder where shrimp and prawns are also located. Your digestive system is distributed throughout your body, but one of the main glands, the hepatopancreas, which performs the same functions as the liver and pancreas in mammals, is located in the cephalothorax, the head. It is the gland that we observe brown in color in prawns and prawns and, here comes the problem, it is capable of accumulating heavy metals. By stopping eating the head of the prawns, we greatly reduce the intake of this heavy metal.

All this concern is due to a  note  from 2011 where EFSA reported that the “brown meat” of crabs and similar crustaceans could have highly variable concentrations of cadmium that could contain up to 8 mg / kg (8000 micrograms / kilogram) of cadmium, while white meat only reaches 0.08 mg / kg (80 micrograms / kg). 

However, this is for crabs and the like where the “brown meat” is more abundant than in the case of prawns, and could be a problem in very specific areas.

In the rest of crustaceans such as prawns, prawns and the like,… the amount of cadmium is not so high since the abdomen / head ratio is lower than in the case of crabs. “The available data suggest that the intake of cadmium when the head is consumed is 4 times the intake that would be obtained by consuming only the abdomen.” (AECOSAN recommendation of April 2011).

If the amount in the appendices were 0.08 mg / kg, in the head we would find 0.32 mg / kg, or 320 micrograms per kilogram of head of shrimp ingested.

In Spain, given that due to cultural habits, the consumption of the head of prawns is common (and abundant on Christmas festivities), this note takes on some relevance, given that due to its high variation in concentration it is very difficult to control the weekly amount of ingested cadmium.

In the worst case, a 60 kg person could consume up to 0.15 milligrams (150 micrograms) of cadmium per week, so it would be necessary to consume 468 g of brown prawn meat per week to reach the maximum dose assuming its content was 0.32 mg / kg.

It must be borne in mind that not only prawns are the source of cadmium intake , but there are other foods involved where it is more difficult to avoid it, for example in mushrooms or shellfish, and of course, tobacco than within all the toxins it contains, it also contains cadmium. If you are a smoker, you should take special care since your blood cadmium content is more than three times higher than that of a non-smoker.

The consumption of crustaceans and prawns in large quantities is something sporadic that only occurs at a very specific time of the year, and from time to time in other celebrations, but given its cumulative nature, it may be appropriate that we rethink the suitability of sucking the heads of prawns.

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