Since 1999 the National Institute of Nutrition and Seafood
Research (NIFES) has annually (spring and autumn) analysed blue
mussels from around 50 locations along the Norwegian coast in order
to monitor the level of metals and other chemical components. The
analysis are related to the Norwegian Food Safety Authorities
The results show that blue mussels from some locations in the
Sogne Fjord and the Hardanger Fjord have had a high level of total
arsenic, especially in the spring. Total arsenic includes all the
different chemical forms of arsenic found in shellfish, both
organic and inorganic. It is the inorganic arsenic forms that are
toxic. In a food safety perspective, it is therefore important to
examine the amount of inorganic arsenic in blue mussels. NIFES
developed a new method in 2002 that can be used to measure the
inorganic arsenic in addition to the total arsenic.
- Data from the period 2002 to 2005 have occasionally shown
unusually high levels of inorganic arsenic in blue mussels from
these two fjords, says Kåre Julsham, Head of the Surveillance
Research Programme at NIFES.
- The observations are related to only a few locations.
Also, one location which has shown a high level of inorganic
arsenic one year has not necessarily shown a high content of
inorganic arsenic the next year. This makes it difficult to
identify the factors that cause the high level of inorganic
arsenic, but it is possible that the levels are connected to algal
blooms, says Julsham
The study is conducted in connection to the Norwegian Food
Safety Authority Surveillance programme on mussels, and analyses of
inorganic arsenic in blue mussels will continue with the same
frequency as previously.
Not of significance with respect to food safety
Although the concentrations of inorganic arsenic was high in the
Sogne Fjord and the Hardanger Fjord, the findings represent no
threat to food safety.
- If you weigh 70 kilos and eat 200 grams of blue mussels with
the highest content of inorganic arsenic every week of your life,
your provisional Tolerable Weekly Intake (PTWI) will be exceeded by
10 per cent. This is a very unlikely scenario, says Julshamn.
PTWI stands for Provisional Tolerable Weekly Intake. It
describes the amount of a substance that can be eaten every week
throughout a person`s life with no risk of negative health effects.
Eating more than the PTWI limit does not pose an immediate threat,
but the safety margin is reduced. Read more about PTWI below.
Concentrations of inorganic arsenic
In the Sogne Fjord the concentration of inorganic arsenic in
blue mussels varied between 0.002 to 3.9 mg per kilo of blue
mussel, depending on location. The corresponding concentration of
arsenic in mussels from the Hardanger Fjord varied from 0.001 to
5.8 mg per kilo. An inorganic arsenic content of 5.8 mg per kilo of
wet weight is among the highest that has been observed in marine
A high level of total arsenic involves an increased level of
The results showed that blue mussels with a high concentration
of total arsenic had a high proportion of inorganic arsenic, and
that this proportion increased when the concentration of total
arsenic was above a certain level. At the highest observed
concentration of total arsenic, the share of inorganic arsenic
accounted for as much as 42% of the total arsenic.
Arsenic in fish
Analyses of fish fillet show that inorganic arsenic account for
less than 1% of the total arsenic, and that most of the arsenic is
in the organic form of arsenobetain, which is essentially
Sloth, J. J. and Julshamn, K. Survey of Total and Inorganic Content
in Blue Mussels (Mytilus edulis L.) from Norwegian Fjords:
Revelation of Unusual High Levels of Inorganic Arsenic. 2008.
Journal of Agricultural and Food Chemistry. 56: 1269-1273.
Kåre Julshamn, Head
of Research, Surveillance, NIFES
Telephone: (+47) 99 48 77 01
What is arsenic and why do we measure it?
arsenic consists of organic and inorganic arsenic, both of which
are present in seafood in about 20 different chemical forms.
Seafood is the most common source of arsenic in our diet, and
mostly it is in the form of arsenobetaine, which is essentially
non-toxic. Arsenic is an element which occurs naturally in all rock
and sea water. It may be present in different organic
chemical compounds (such as arsenobetaine) and in different
inorganic chemical compounds (such as arsenite). Organic arsenic is
not considered to be a health risk, but inorganic arsenic is very
poisonous. Blue mussels can accumulate trace elements from the
surroundings. Monitoring of inorganic arsenic in seafood is
important in order to make a correct risk assessment.
What is PTWI?
PTWI stands for Provisional
Tolerable Weekly Intake. It describes the amount of a substance
that can be eaten every week throughout a person`s life with no
risk of negative health effects. Use of the word
”provisional” means that the assessment is temporary
and that it will be reconsidered when more data is available. An
assessment of this kind will always include a certain safety
margin. Consuming more than the PTWI limit does not pose an
immediate health risk, but the safety margin is reduced. EFSA (the
European Food Safety Authority ) is in the process of revising the
PTWI value for inorganic arsenic in foodstuffs and its conclusion
is expected by September 2009.