There is only limited information about the accumulation of algal toxins in aquatic organisms in the Baltic Sea. In this study we measured total cyanobacterial hepatotoxin levels in blue mussel (Mytilus edulis) and flounderi (Platichthys flesus) tissues. Flounder were caught with gillnets from the western Gulf of Finland during July and August 1999. Blue mussels were collected from an enclosure at 3 m depth and from an artificial reef (wreck, 25-35 m depth) in the western Gulf of Finland between June and September 1999. Flounder liver and muscle samples and soft tissues of mussels were analyzed for the cyanobacterial hepatotoxins (nodularin, NODLN and/or microcystins, MCs) using an enzyme-linked immunosorbent assay (ELISA). Results showed a time-dependent accumulation of hepatotoxins in flounder and mussels. In flounder, the maximum concentration 399 +/- 5 (sd) ng NODLN or MC/g dry weight (dw) was found in the liver of specimens caught on 21 August 1999. No hepatotoxins were detected in muscle samples. The maximum concentration of 2150 ng +/- 60 (sd) ng hepatotoxin/g dw was found in the mussel soft tissues collected on 20 August 1999. Temporal NODLN or MC trends indicated depuration of cyanobacterial hepatotoxin from mussels at surface level and an increase in NODLN or MC concentrations in those from the sea bed. These studies showed that despite the low cyanobacteria cell numbers the cyanobacterial hepatotoxins can accumulate in flounder and mussels. This may allow the further transfer of cyanobacterial hepatotoxins in the food web.
The brackish water cyanobacterium Nodularia spumigena regularly forms waterblooms in the Baltic Sea. Many N. spumigena strains can produce nodularin, a hepatotoxic penta-peptide, which has caused several animal poisonings in the Baltic Sea area. To improve our understanding of nodularin bioaccumulation in aquatic organisms this study measured nodularin in flounder and cod caught from the Baltic Sea. Flounders were collected from the western Gulf of Finland in July 1996, September 1997, and September 1998, and from the Gulf of Bothnia in August 1997 and September 1998. Flounders were also collected from the coastal areas of Sweden in the Baltic Proper during September 1998. Cod were caught from the southern Baltic Sea in August 1998. Livers and muscles of the 1997 fish were isolated, extracted, and analysed for nodularin using high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA) and protein phosphatase 1 (PP1) inhibition assay. Approximately 30-70 ng of nodularin/g dry weight (maximum value 140 ng/g) were found in the liver tissue samples by ELISA and PP1 inhibition. These concentrations were below the detection limit of HPLC. PP1 assay showed inhibition also in muscle samples, but this may due to other compounds present in the muscle extracts rather than NODLN or due to matrix interference. The recovery of nodularin from liver tissue with ELISA and PP1 assays was about 30%. Nodularin concentrations in samples are not corrected for recovery. Although the concentrations of nodularin found in this study are low further studies of nodularin are needed to assess possible bioaccumulation in brackish water food webs.
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