Mechanism of acute silver toxicity in marine invertebrates.

In freshwater crustaceans and in both freshwater and marine fish, the key mechanism of acute silver toxicity involves ionoregulatory impairment. An inhibition of the Na+ ,K+-ATPase located at the basolateral membrane of the gill epithelium seems to be the key site for silver toxicity. However, studies to determine if the same mechanism of toxicity is occurring in marine invertebrates, which also are ionoregulators, had not been done. Thus, the present study was carried out to determine acute silver effects on hemolymph osmo- and ionoregulation in three marine invertebrates: the shrimp Penaeus duorarum, the sea hare Aplysia californica, and the sea urchin Diadema antillarum. Animals were exposed to silver (1 or 10 microg/L), as silver nitrate, in seawater for 48 h. Results show that acute silver exposure did not affect hemolymph osmolality or ion concentration (Na+, Cl-, K+, Ca2+ and Mg2+) in the three species studied. However, silver induced significant changes in the water content in shrimp gill and sea hare gill and hepatopancreas. Silver also caused significant changes in Na+ ,K+-ATPase activity and in both total and intracellular ion (Cl-, Na+, K+, Mg2+, and Ca2+) concentrations in different tissues of the three species studied. Overall, these results show that the key mechanism of acute silver toxicity in marine invertebrates is not associated with an osmotic or ionoregulatory impairment at the hemolymph level, as observed in freshwater fish and crustaceans and in seawater fish. However, they indicate that acute waterborne silver induces significant changes in Na+ ,K(+)-ATPase activity and probably affects other mechanisms involved in water and ion transport at the cell membrane level, inducing impairments in water and ion regulation at the cellular level in different tissues of marine invertebrates. These results indicate the need to consider other "toxic sites" than gills in any future extension of the biotic ligand model (BLM) for seawater.