ScienceDaily (Mar. 3, 2009) — Trine-Lise Torgersen described in her doctorate new variants of diarrhoea-causing toxins in mussels, oysters and crabs. These variants are assumed to be less virulent than the forms of diarrhoea toxin we are already familiar with and were found in varying amounts in the different types of seafood examined.
For her doctoral thesis, Trine-Lise Torgersen looked at how toxins from algae are taken up and metabolised by mussels and oysters, and also by crabs that eat mussels. During an algal bloom in the ocean, toxins produced by the algae can be taken up by shellfish that filter seawater for food, and the result for the consumer can be diarrhoea, vomiting and nausea. Some of these algal toxins are already well-known.
Torgersen studied how mussels and oysters process some of these toxins, and found that more types of toxin are produced than we previously have been aware of. She also looked at how the toxins are taken up and metabolised by crabs that eat poisonous shellfish. The results indicate that a particularly complex pattern of toxins is formed in these species, and that the levels of modified diarrhoea toxins may be higher than the levels of the known forms, especially in oysters and crabs.
The current procedure for measuring algal toxins involves converting all of the variants back to the original molecule, and then measuring the total amount of original toxin. However, since the modified variants of the toxins can be assumed to be less virulent than the original forms, measuring all of the substances as if they were the original may overestimate the toxicity of the seafood. Therefore, when estimating the risk of food poisoning from shellfish, levels of variants of the original toxin in the various types of seafood should be considered.
In her thesis, Torgersen showed that oysters, mussels and crabs differ regarding the forms of diarrhoea toxin they contained, and also regarding how much of modified variant is present relative to the original toxin. In particular, crabs and oysters contained very little of the original substances and nearly all of the toxin had been converted to other forms. Torgersen therefore recommends that different types of seafood need to be considered individually when estimating the risks of food poisoning from seafood.