Do selenium and glutathione ( GSH ) detoxify mercury in marine invertebrates ? 11 . Effects on gill adenosine triphosphatase and related blood factors in an arcid clam Anadara granosa

Selenium, because of its affinity for SH/SS, thiol group, offers protection against or detoxifies mercury in marine vertebrates. This study explores the possibility of a similar effect for a marine invertebrate. Arcid blood clams Anadara granosa (L.) with erythrocytic haemoglob~n were exposed to sublethal concentrations of ~ g ' + (0.1 mg I-', as HgCI2), Se4+ (1.0 mg I' , SeO?) and reduced glutathione (GSH, 1.0 mg I' ) , either individually or in combination, for 96 to 144 h in vivo. Parameters studied included gill ATPase, haemoglobin (Hb), haemolymph, haematocrit, protein, free amino acids ( F M ) and plasma Na', K + , Ca+', Mg++ and osmolality. Hg reduced gill ATPase activity by at least 50 "/a Se alone and Hg + Se also inhlblted enzyme activity. No similar changes occurred on exposure to GSH alone. GSH in the presence of Hg, on the other hand, completely nullified the inhibitory effect of Hg In the clams transferred to GSH (for 72 h) after initial exposure to Hg (72 h) and vice versa, enzyme actlvity was inhibited by 45 O O compared to controls Haematocrit increased significantly in clams exposed to Hg alone and to Se alone, but exposure to GSH alone and GSH + Hg had no significant effect. Erythrocyte sedimentation rate (ESR) increased significantly in clams exposed to Se, but was lowered to varying degrees in all other experimental clams. Hb content and haemolymph protein levels in experimental groups did not change significantly compared to controls. Methaemoglobin increased significantly in all experimental groups, the maximum increase (ca 137 %) being in those exposed to Hg. Free amino acid (FAA) levels were appreciably raised in clams treated with Hg alone and Hg + Se. but exposure to Se alone and GSH alone had no significant effect. Plasma cations (Naf . K* and Caf +) showed significant changes following exposure to Hg. However, in clams exposed to Hg + Se only K' and Ca++ levels increased. Concentration of Mg++ in haemolymph of groups treated with Hg, Se and GSH remained practically unaltered, but in groups exposed to Hg + Se and Hg + GSH it increased appreciably. Plasma osmolality, however, was reduced in all experimental clams; the Io\vest being in clams exposed to Hg. Unlike ~ t s effects on marine vertebrates, Se failed to provide protection agalnst deleterious effects of Hg on the marine clams. GSH, on the other hand, nullified the impact of mercury and/or exerted its own effect.