Cadmium speciation and transport in the blood of the bivalve Mytilus edulis

Cadmium (Cd) speciation in the blood plasma of Mytilus edulis was investigated using the metal speciation model MINTEQA2. In the presence of inorganic ions alone, Cd–chloro complexes dominated the speciation (97% of total Cd), with 3% as Cd2+. Inclusion of a novel Cd-binding histidine-rich glycoprotein (HRG) purified from mussel blood plasma decreased the contribution of chloro-complexes to 11.9%, with 86.8% of the Cd bound to the HRG and 1.3% present as Cd2+. Cd transfer from the blood plasma to the kidneys in vivo was studied by injecting 109Cd (both with and without additional chelation) into mussels. Oxine and EDTA complexed a significant amount of blood-borne Cd (23.7% CdOxine; 57.1% CdEDTA). In the presence of each chelator, plasma retained significantly more Cd, although there was no significant difference in Cd uptake by tissues (kidney, gill-mantle, and remaining viscera).