Histidine--rich Glycoprotein in the Blood of the Bivalve Mytilus Edulis: Role in Cadmium Speciation and Cadmium Transfer to the Kidney

Cadmium transfer from M. edulis L. blood plasma to tissues was investigated in relation to its chemical speciation in the blood. 109Cd was injected into the posterior adductor muscle along with synthetic chelators oxine, ethylenediaminetetraacetic acid (EDTA) or cyclohexanediaminetetraacetic acid (CDTA). Chelator concentrations were chosen to bind up from 0 to 98.7% of the total blood Cd, based on speciation calculations using the geochemical speciation model MINTEQA2. Increases in synthetically chelated Cd were accompanied by linear decreases in the calculated percentages of Histidine-rich Glycoprotein (HRG)-bound Cd, and nonlinear decreases in Cd(2+) and Cd chloro-complexes. Cadmium uptake by the kidneys decreased with increasing percentage synthetic chelation, while uptake by other tissues was not affected by chelation. Results indicate that there is at least one mechanism of Cd uptake common to all M. edulis tissues, and an additional, more rapid uptake mechanism in the kidneys that is mediated by CdHRG.