Temporal and spatial distribution of diarrhetic shellfish toxins in blue mussels, Mytilus edulis (L.), on the Swedish west coast, NE Atlantic, 1988-2005

Type: Report
Author: Bengt Karlson, Ann-Sofi Rehnstam-Holm, Lars-Ove Loo


The main goal of this report is to compile and present available data on algal toxins in blue mussels from the west coast of Sweden. The hazards associated with the consumption of mussels are mostly dependent on the occurrence and composition of toxic algae in the areas where shellfish are grown. Diarrhetic shellfish toxins (DST), i.e. okadaic acid (OA) and dinophysistoxin-1 (DTX-1) have occurred regularly in blue mussels (Mytilus edulis) at the Swedish west coast (i.e. Skagerrak) during the past years. A maximum residue limit of 160 μg.kg-1 mussel meat has been set by National Food Administration. The toxic incidences in the region has been linked to the occurrence of Dinophysis acuminata and D. acuta. In general there is seasonal variation of DST in mussels with low concentrations from March to August (<160 μg.kg-1 mussel meat) and high from October to December (>160 μg.kg-1 mussel meat). Peaks above the maximum residue limit have in some years also occurred in late June to late July. Rapid intoxication vs. slow detoxification of mussels is a common phenomenon, especially in autumn-winter. Temporal and regional differences are large. There is also a considerable variation in toxin levels between years. In 1994 almost 5000 μg DST.kg-1 mussel meat was detected. In 1997 mussel farmers experienced very low levels, i.e. only three samples above the restriction limit of DST. In autumn 1989 to spring 1990 and in early autumn 2000 to early 2001, high levels (about 200 to 2000 μg DTX.kg-1 mussel meat) were recorded during 26 weeks. The Koljö Fjord region had low levels of toxins until 1998, despite regular recordings of potentially DST producing algae in the area. Today mussels grown and harvested in this area have similar toxin levels to mussels from other fjords in the Skagerrak region. Measurements of other toxins than DST are few and are not included in the report