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Flatøsters på brun trebakgrunn.
Foto: Eivind Senneset

The annual monitoring showed that one in four flat oysters had cadmium levels above the maximum level, but that Norwegian bivalve molluscs are otherwise in good condition.

NIFES has been commissioned by the Norwegian Food Safety Authority to examine Norwegian bivalve molluscs and mollusc locations for E. coli, Salmonella and various environmental toxins. The purpose of this monitoring is to be able to document that it is safe to eat Norwegian bivalves.

‘The monitoring showed that it is generally safe to eat the Norwegian bivalves that are offered on the market,’ says Arne Duinker, scientist at NIFES.

The levels are below the maximum limit for E. coli in 87 per cent of the mussel samples

For 2016 it was reported that 87 per cent of the 330 samples taken under the national control programme had values below the EU’s maximum level for E. coli. All the locations are tested for E. coli several times a year. NIFES has also analysed 130 samples received from the industry. In 85 per cent of these samples, the E. coli content was below the maximum level.

No Salmonella bacteria were found in any of the 46 samples. All the locations are tested for Salmonella once a year.

Areas where bivalve molluscs are produced are classified as class A and class B areas. In class A areas, the bivalves can be harvested from the sea and sold directly. These areas are almost free of exposure to intestinal bacteria. In the class B areas, there is moderate exposure to intestinal bacteria. Bivalves from these areas must therefore go through purification before they can be sold. All areas where bivalves are produced, whether they are classified in class A or class B, are checked annually.

Low levels of environmental toxins in mussels

With respect to environmental toxins, NIFES has analysed a total of 41 samples from 19 locations received from the Norwegian Food Safety Authority, to determine the levels of cadmium, mercury, dioxins and dioxin-like PCBs, and polyaromatic hydrocarbons (PAHs). NIFES has also analysed 13 samples received from the industry.

The concentrations of metals in mussels remained at the same levels as in previous years, and EU’s maximum levels were not exceeded for any of the heavy metals cadmium, mercury or lead. The concentrations of dioxins and dioxin-like PCBs, PCB6 and PBDE were also found to be low in the analysed mussel samples.

Cadmium in oysters and horse mussels

Regarding the European flat oysters, one in four samples showed cadmium levels above the EU’s maximum level. The levels of environmental toxins were otherwise low.

‘High cadmium levels in oysters occur naturally due to their physiology. Oysters prefer to bind the cadmium rather than to excrete it,’ Duinker explains.

That is why one should not eat too many oysters, but then large quantities of oysters are not generally part of people’s daily diet.

‘Oysters with slightly elevated cadmium levels can not be sold, but it is quite safe to eat one meal of these oysters per week,’ says the NIFES scientist.

In horse mussels, NIFES found cadmium levels above the maximum level in both samples that were analysed, and lead above the maximum limit in one of two samples. These substances are present in the kidney, however, and it is therefore recommended to remove the kidney before eating horse mussels.

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