NIFES has studied the content of undesirable substances in shellfish and crabs. The results for 2010 show that the contents of undesirable substances in shellfish are usually low and below current upper permitted limits. The microbiological quality of the shellfish was consistently high, and was better than the corresponding values in 2009.

On behalf of the Norwegian Food Safety Authority, NIFES performed microbiological studies of shellfish for the hygiene indicator organisms E. coli and  enterococci, as well as bacteria in the genus Salmonella. Chemical analyses for a number of undesirable chemical substances in shellfish and crabs were also carried out.

Microbiological quality

Shellfish can take up intestinal bacteria such as E. coli, enterococci and Salmonella if present in the water in which they are growing. Studying these organisms indicate whether there is sewage contamination at harvesting sites, which could pose a potential health hazard if the shellfish were consumed. Sites are classified in terms of microbiological quality and of whether the shellfish can be harvested for immediate consumption (A-zone) or whether they must either be resuspended in clean water or heat-treated before being sold (B- and C-zones).

The shellfish samples were collected in 2010 and comprised 391 pooled samples of mussels, 34 of oysters, four of scallops, three of cockles and four of periwinkles.

Ninety-two percent of the 436 samples analysed had an E. coli content that satisfied the requirements for classification as an A-zone. Enterococci were demonstrated in seven of 420 samples analysed, and in all cases the concentrations were low. Salmonella was not identified in any of the 94 samples analysed.

Content of chemical undesirable substances

Sixty-nine mussel samples were analysed for undesirable chemical substances, as were five samples of king scallops, four of oysters and 19 of crabs. None of the samples exceed the European Union and Norwegian upper permitted limits in shellfish for human consumption. The level of organic contaminants was relatively low in all the samples, although there was a clear effect of petroleum pollution in the sea around the County of Aust-Agder, eight or nine months after the “Full City” shipwreck.

Three of the 14 crabs sampled in the County of Nordland displayed concentrations of cadmium in claw-meat that exceeded the upper permitted limit of 0.5 mg/kg wet weight. Crab brown meat also contained relatively high cadmium concentrations that rose to as much as 19 mg/kg wet weight. The European Union and Norway have not set upper limits for undesirable substances in crab brown meat. The Norwegian Food Safety Authority has issued an advisory to the effect that women of child-bearing age and children should avoid eating brown meat of crab (

READ MORE: NIFES to survey environmental toxins in crabs

The monitoring programme

The aim of this part of the shellfish monitoring programme, which is carried out by NIFES on behalf of the Norwegian Food Safety Authority, is to demonstrate that shellfish harvested for human consumption do not come from areas that could be contaminated with micro-organisms which may cause disease, nor contain concentrations of undesirable substances beyond the permitted limits. The shellfish monitoring programme also monitors toxic algae, but that part of the programme is not performed by NIFES.


Filer til nedlasting • Skjellrapport 2010 mikrobiologi og fremmedstoff 05072011.pdf 4,1 mb

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