Abstract
Cadmium tansport in the plasma of Mytilus edulis L. displays attributes similar to those previously described for Mercenaria mercenaria (L.). The majority of Cr, Cu, Ni, and Zn is partitioned in the plasma rather than the hemocytes in both species, although differences in Fe and Mn are apparent. Mussels however contain twice the number of circulating hemocytes (2.1 Β± 0.8% of whole blood weight; n = 75 vs 1.2 Β± 0.3%; n = 70 for the quahog) and approximately three times more plasma protein than the quahog. Titration experiments using ionβspecific electrode (ISE) measurements and equilibrium dialysis (ED) experiments indicate that both species have a lowβaffinity, highβcapacity system for the internal transport of Cd. At low blood Cd concentrations (<8.9 ΞΌM) and short dialysis times (24 h), approximately 90% of the Cd in mussel plasma is bound to plasma proteins. At higher Cd concentrations and at longer dialysis times, the percentage of free Cd increases substantially. The Cd affinity was slightly lower in mussel plasma compared to the quahog (log~10~K = 2.6β3.9/M vs 3.7β4.3/M), and mussel plasma C~L~ values were appreciably lower (0.16β1.11 mmol/g protein) than those for the quahog (1.97β2.26 mmol/g protein). Both ISE and ED experiments on quahog plasma yielded similar estimates of K and C~L~.