Cadmium and lead in bivalves: importance for food safety

The National Institute of Nutrition and Seafood Research (NIFES) has analysed the content of cadmium and lead in scallops and horse mussels harvested in Norwegian waters. The results show levels above EU's maximum limits when analysing the digestive gland of the scallop and the kidney of the horse mussel.

Cadmium in the digestive gland from scallops

Shell feed by filtering seawater. During this process they may take up particles which contain contaminants. NIFES analysis indicates that scallops contain little lead. The quantity of lead (0.02 - 0.08 mg/kg) is well below EU's maximum limits of 1.5 mg/kg.

However, analysis showed that the cadmium content (3.7 - 8.4 mg/kg) exceeded EU's maximum limits if the entire shell content was measured, but that most of this was found in the digestive gland. If the shell content is measured after the removal of the digestive gland, the cadmium levels were below EU's maximum limits. The amount of cadmium in muscle and gonad (0.11-0.75 mg/kg) was below EU's maximum permitted level of 1 mg/kg. In Norway it is usually these parts that are used for consumption.

Illustration: An opened scallop with labelled organs. The digestive gland contains high levels of cadmium and should not be consumed. In Norway, it is the muscle and roe which is most commonly consumed. Photo: NIFES

Lead and cadmium in horse mussels

Horse mussels are less well known than scallops, and are often served as a delicacy. Most of the cadmium in the horse mussels analysed was in the kidneys and not in the digestive gland, as with the scallop. The levels of cadmium in the horse mussels varied from 0.35 to 1.5 mg/kg and the highest levels were found in the largest and oldest shells. If the kidneys are removed, the level of cadmium in these shells are also well under EU's maximum limits of 1.0 mg/kg.

The concentration of lead in the horse mussels sampled was between 1.4 and 6.6 mg/kg. More than 90% of the lead present in the horse mussel samples was found in the kidney. This organ is the only organ which is black in colour.

Illustration: Steamed and opened horse mussel. The black kidney should be removed before consuming the rest of the mussel. Photo: NIFES

Dietary advice

The Norwegian Food Safety Authority's has given a dietary advice for the consumption of scallops and horse mussels. The food authority recommends the removal of the dietary gland in scallops and the kidney in horse mussels before consumption.