Undesirable Substances In Shellfish Is Low

The Fish Site
by The Fish Site
10 November 2010, at 12:00am

NORWAY - The National Institute of Nutrition and Seafood Research (NIFES) has examined the content of undesirable chemical substances and microorganisms in samples of bivalves, snails and crabs. The results for 2009 show that the shellfish were of good microbiological quality throughout and that the level of undesirables was generally low and not exceeding current regulatory limits.

The number of samples of other species than the blue mussel was very low in 2009 and there is a need for a more thorough knowledge of the presence of undesirables in several species, especially crab.

NIFES has in 2009, on behalf of the Norwegian Food Safety Authority (NFSA), carried out microbiological examinations of bivalves and snails for E.coli, enterococci and Salmonella. Chemical analyses were also carried out to determine the concentrations of copper, zinc, arsenic , selenium, silver, tin, lead, mercury and cadmium in bivalves and crabs, as well as DDT, PCB, dioxins, brominated flame retardants and PAH in shellfish.

Microbiological quality

Bivalve molluscs can absorb intestinal bacteria such as E.coli, enterococci and Salmonella if such bacteria are present in the water where the bivalves grow. Examination of these microorganisms can therefore reveal exposure to faecal pollution which could be a potential health risk. Mussel growing localities are classified on the basis of microbiological quality and whether shellfish can be harvested directly for consumption (A-locality) or must be reconditioned or heat treated before they can be sold (B- and C-locations).

Among a total of 400 samples analysed for E. coli, 82% had concentrations of E.coli which were below the limit for classification as an A-location, while there were no findings of Salmonella in any of the 58 samples which were examined.

The samples analysed were collected throughout 2009 and consisted of 369 pooled samples of blue mussels, 17 of great scallops, ten of European flat oysters, two of cockles and two of periwinkles.

Contents of undesirable chemical substances

In order to determine the presence of undesirable substances in blue mussels, a total of 59 samples were collected in 2009. In general, the analyses showed low concentrations of all of the different substances and the level was the same as in previous years. Six samples of muscle and gonad of scallops also showed low concentrations of undesirables.

Among the seven oyster samples analysed, two had cadmium concentrations which were equal to the regulatory limit, after allowing for the measurement uncertainty of the method (in the report the values are given without allowing for the measurement uncertainty). Historically, a number of oyster samples have had cadmium concentrations above the upper limit set by EU and Norway, and some oyster farmers have experienced harvesting bans for periods of time because of cadmium. The oyster samples showed low concentrations of all other undesirable substances that were analysed for.

The presence of metals in the edible crab was determined in two samples of claw meat and two samples of brown meat. The results showed the same levels as in 2007, with the exception of cadmium where the concentration was slightly higher in brown meat in 2009. Brown meat from crab can contain relatively high levels of cadmium and is exempt from the EU’s upper limit, while the NFSA advises pregnant and breast-feeding women not to eat brown meat from crab (

The claw meat contained only low concentrations of the undesirable substances analysed for. As our knowledge of the levels of undesirables in crab from different areas along the Norwegian coastline is insufficient, a larger number of crab samples have been analysed this year, and a separate, large-scale programme to identify the levels of undesirable substances in crab is being planned for 2011.

Surveillance programme

The purpose of the NFSA’s annual surveillance programme for shellfish is to ensure that bivalve molluscs which are harvested for consumption do not come from areas which are polluted by microorganisms which can cause disease or contain undesirable substances at levels above the regulatory limits. The programme also aims to provide more knowledge of the levels of undesirables in different species of bivalves, snails and crabs. The surveillance programme for shellfish also includes monitoring of algal toxins, but this part of the programme is not performed by NIFES.