BIOACCUMULATION AND CLEARANCE OF MICROCYSTINS FROM SALT-WATER, MUSSELS, MYTILUS-EDULIS, AND IN-VIVO EVIDENCE FOR COVALENTLY BOUND MICROCYSTINS IN MUSSEL TISSUES

Over a period of 3 days saltwater mussels, Mytilus edulis, were fed a cyanobacteria, Microcystis aeruginosa, that contained a high concentra tion of microcystins, The mussels were killed on a periodic basis over the course of 2 months, Mussels were also collected at two sites were high levels of microcystins in tissues had been noted. A strategy bas ed on the chemically unique nature of the C-20 beta-amino acid, -metho xy-2,6,8-trimethyl-10-phenyldeca-4,6-dienoic acid (Adda), portion of t he microcystins was used in conjunction with a protein phosphatase (PP ase) assay to analyse for both covalently bound microcystins and free microcystins in the mussel tissues, The mussel PPase assay results wer e compared with the Lemieux oxidation gas chromatography-mass spectrom etry (GCMS) analysis. Less than 0.1% of the total microcystin burden i n the mussel tissue was found to be extractable with MeOH. Thus, direc t evidence was provided for the existence of covalently bound microcys tins in mussel tissues in vivo. The mussels rapidly cleared the covale ntly bound microcystins when transferred to untreated seawater. Within 4 days the total microcystin burden dropped from a high of 336.9 (+/- 45.8) mu g/g wet tissue to 11.3 (+/- 2.6) mu g/g. After 4 days postex posure until completion of the experiment the total levels remained be low the detection limits of the GCMS method, The levels of free microc ystins, extracted with MeOH and detected by the PPase assay, fell from 204 ng/g wet tissue to a residual 14 ng/g over a 53 day postexposure period. Presumably the bound microcystin present in the mussel tissue exists as a covalent complex with the PP-1 and PP-2A enzymes. We concl ude that in any shellfish monitoring program it is the total tissue mi crocystin burden that needs to be considered. (C) 1997 Elsevier Scienc e Ltd.