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Algal Toxins in Shellfish


Shellfish may be toxic.
Photo: Hege Hellberg.

Shellfish have become a popular delicacy and an important resource throughout the world in recent decades. Demand and production of shellfish are increasing, and food safety is an important consideration. Unfortunately, a number of episodes of human food poisoning have been recorded throughout history.

Knowledge of the existence of algal toxins in shellfish at certain times of the year has existed in certain cultures for centuries. Nowadays, shellfish sold commercially are tested, and the Norwegian Food Safety Authority provides advice on areas to avoid so as to prevent poisoning episodes.

What is an algal toxin and how do shellfish become toxic?
Shellfish, such as blue mussels, scallops and oysters, live by filtering plankton. Certain algae can produce or contain toxins. Shellfish can take up and concentrate the toxins during blooms of such algae. Marine algal toxins can occur in shellfish in all seasons, and the shellfish show no apparent ill effects from large amounts of toxin. The algal toxins do not affect the taste of the shellfish, and people therefore have no possibility of checking whether the shellfish are toxic on their own. The algal toxins are chemical compounds that are not destroyed by freezing or cooking.

What types of algal toxin do we have?
The algal toxins are divided into groups based on their effects

  • Paralytic shellfish toxins PST) cause paralysis
  • Diarrhetic shellfish toxins (DST) cause diarrhoea
  • Amnesic shellfish poisoning (AST) cause amnesia

In addition, there are three groups of compounds called azaspiracids, pectenotoxins, and yessotoxins.

What methods do we have for detecting algal toxins in shellfish?
All shellfish that are sold commercially must be tested for the presence of algal toxins, and internationally it is only the so-called mouse test that is recognised for determining whether shellfish don’t contain high concentrations of PST and DST.

Depending on which toxin is being tested, different types of extracts are made of the shellfish meat are injected into the stomach cavity of mice. To limit the use of mice, and to obtain more information about which toxins are present, a range of chemical and immunological methods for analysis of algal toxins have been developed in recent years.

It is hoped that, within a relatively short time, sufficiently good chemical and immunological methods will be developed that can replace the mouse test. Chemical methods for determining algal toxins involve HPLC or LC-MS analysis. For some of the toxins there are also ELISA methods.

Norway follows the EU’s regulatory framework for control of algal toxins in shellfish. The EU’s regulations are presented in: “Development of cost-effective tools for risk management and traceability systems for marine biotoxins in seafood”.

What is the Norwegian Veterinary Institute doing about algal toxins?
The Norwegian Veterinary Institute (NVI) has for many years worked with the problems associated with biotoxins such as mycotoxins and plant toxins and their occurrence in foodstuffs. Since 2000, the Norwegian Veterinary Institute has also been researching algal toxins in shellfish.

The Norwegian  Veterinary Institute’s activity is concentrated around three themes:

  • Development of new methodologies for detection of algal toxins
  • Identification of new algal toxins
  • Depuration of algal toxins from shellfish.

Contacts at the Norwegian Veterinary Institute
Chris. O Miles
Telephone: +47 23 21 62 32
E-mail: chris.miles@vetinst.no

Thomas Rundberget
Telephone: +47 23 21 62 31
E-mail: thomas.rundberget@vetinst.no

Ingunn Samdal
Telephone: +47 23 21 62 26
E-mail: ingunn.samdal@vetinst.no

Morten Sandvik
Telephone: +47 23 21 62 12
E-mail: morten.sandvik@vetinst.no