METABOLISM OF ARSENIC COMPOUNDS BY THE BLUE MUSSEL MYTILUS-EDULIS AFTER ACCUMULATION FROM SEAWATER SPIKED WITH ARSENIC COMPOUNDS

Blue mussels (Mytilus edulis) were exposed to 100 mu g As dm(-3) in th e form of arsenite, arsenate, methylarsonic acid, dimethylarsinic acid , arsenobetaine, arsenocholine, trimethylarsine oxide, tetramethylarso nium iodide or dimethyl(2-hydroxyethyl)arsine oxide in seawater for 10 days. The seawater was renewed and spiked with the arsenic compounds daily. Analyses of water samples taken 24 h after spiking showed that arsenobetaine and arsenocholine had been converted to trimethylarsine oxide, whereas trimethylarsine oxide and tetramethylarsonium iodide we re unchanged. Arsenobetaine was accumulated by mussels most efficientl y, followed in efficiency by arsenocholine and tetramethylarsonium iod ide. None of the other arsenic compounds was significantly accumulated by the mussels. Extraction of mussel tissues with methanol revealed t hat control mussels contained arsenobetaine, a dimethyl-(5-ribosyl)ars ine oxide and an additional arsenic compound, possibly dimethylarsinic acid. Mussels exposed to arsenobetaine contained almost all their exp erimentally accumulated arsenic as arsenobetaine, and mussels exposed to tetramethylarsonium iodide contained it as the tetramethylarsonium compound. Mussels exposed to arsenocholine had arsenobetaine as the ma jor arsenic compound and glycerylphosphorylarsenocholine as a minor ar senic compound in their tissues. The results show that arsenobetaine a nd arsenocholine are efficiently accumulated from seawater by blue mus sels and that in both cases the accumulated arsenic is present in the tissues as arsenobetaine. Consequently arsenobetaine and/or arsenochol ine present at very low concentrations in seawater may be responsible for the presence of arsenobetaine in M. edulis and probably also among other marine animals. The quantity of arsenobetaine accumulated by th e mussels decreases with increasing concentrations of betaine. HPLC-IC P-MS was found to be very powerful for the investigation of the metabo lism of arsenic compounds in biological systems.