Adults of the softshell clam M y a a r e n a r i a were c o n t i n u o u s l y subjected to a flowing raw seawater solution containing a m i x t u r e of salts of manganese, zinc, lead, nickel, copper, and cadmium. Final calculated concentrations, in ~g 1-I, of the toxicant solution were 7200 Mn, 2500 Zn, 70 Pb, 50 Ni, 50 Cu and I Cd; these conc e n t r a t i o n s a p p r o x i m a t e d highest m e a s u r e d levels w i t h i n surficial interstitial sediment waters from m i d -N a r r a g a n s e t t Bay, Rhode Island. M. arenaria were also subjected to a 20% solution, i.e., 1440 Mn, 500 Zn, 14 Pb, 10 Ni, 10 Cu, and 0.2 ~g 1 -I Cd. One study was c o n d u c t e d for 112 days in winter at 0 o to IO~ and another for 16 days in summer at 16 ~ to 22~
In the winter study, all clams exposed to a 1OO% solution died between the 4th and IOth week; soft parts of survivors at 6 weeks c o n t a i n e d about 19 times more Pb, 15 x m o r e Zn, 12 x m o r e Cu, 10 x more Mn, 3 x more Ni and 0.1 x more Cd than controls; r e l a t i v e l y m i n o r changes in w h o l e body elemental content of Ca, Cr, Fe, K, Mg, Na, Sr, and V were observed. Clams exposed to a 20% solution during winter survived the 112 day study; at that time these contained about 5 x m o r e Cu, 4 x more Mn, 3 x more Zn and about 2 x m o r e Pb than controls; c o m p a r a t i v e l y minor changes were observed in other elements examined. In the summer study, all M. arenaria subjected to the 1OO% solution died b e t w e e n 6 and 14 days; survivors from this group at 7 days c o n t a i n e d about 25 x m o r e Pb, 13 x more Cu, 11 x more Zn, 7 x more Mn, and 3 x more Ni than controls; other changes in elemental content were not as pronounced. M o r t a l i t y in the 20% group during summer was slightly higher than controls during the 16 day study; at 14 days survivors from this group contained about 12 x more Mn, 7 x m o r e Pb, 7 x more Zn, 4 x more Cu, and 3 x more Ni than controls. Survival and bioaccum u l a t i o n patterns were not altered through feeding a supplemental diet of algae. The s i g n i f i c a n c e of these findings are d i s c u s s e d in terms of potential environmental perturbations, e s p e c i a l l y local d r e d g i n g practices.
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A l t h o u g h there is a growing body of inf o r m a t i o n on the toxicity of heavy metals salts to e c o n o m i c a l l y important species of m a r i n e b i v a l v e m o l l u s c s (Eisler, 1973; Eisler and Wapner, 1975;Eisler, 1977), p u b l i s h e d i n f o r m a t i o n on b i o l o g ical effects of m i x t u r e s of m e t a l salts v e s t i g a t o r s concluded that behavior of the m i x t u r e was not n e c e s s a r i l y predictable on the basis of action of individual components. It is also noted that each of the p r e c e d i n g studies employed a m a x i m u m of three metals, chosen from a list comprising Cd, Cu, Hg, Pb, and Zn, with final c o n c e n t r a t i o n s of individual m e t a l s in the m i x t u r e having little reon this group under c o n t r o l l e d conditions lation to c o n c e n t r a t i o n s or ratios enis absent. Only limited data on this subject are avaiblable for other assemblages of aquatic taxa (