UPTAKE AND DEPURATION OF THE HEPTAPEPTIDE TOXIN MICROCYSTIN-LR IN MYTILUS-GALLOPROVINCIALIS

Mussels (Mytilus galloprovincialis Lamarck) were exposed to the toxic cyanobacterium Microcystis aeruginosa Kutz. emend Elkin for 16 days in order to study bioaccumulation of the cyclic heptapeptide toxin microcystin-LR. After this time period the animals were fed marine phytoplankton for 2 weeks and the amount of microcystin in the mussels was monitored again. During the exposure phase mussels attained a maximum of 10.5 mu g of toxin per g dry mussel weight at day 10. Microcystin was detectable after the second day of exposure. The percentage of toxin that was taken up relative to the total amount administered varied from 24.1% to 54.8%. When the mussels were fed marine phytoplankton there was a 50% decrease in the amount of detectable toxin in the mussels within 2 days. This was followed by a slight increase in toxin levels over 5 days with no microcystin-LR being detected at day 13. The major part of the toxin (96%) was found in the digestive gland + stomach while the gills, muscle, foot, and other organs combined had less than 4% of the total toxin. The results presented here show that cyanobacteria blooms present in estuaries where bivalves are growing naturally constitute a health hazard in that these organisms can retain microcystins and transfer them through the food chain.