Phosphatidylcholine vesicles harboring the lipophilic metal ion carrier A23187 in the bilayer and encapsulating ethylenediamine tetraproprionate (EDTP) selectively sequester Cu2+, Pb2+, and Cd2+ from dilute aqueous solution at neutral to acidic pH. At pH 7.0, individual metal ion uptake experiments reveal up to a 3-fold difference in permeability and capacity among the three metal ions, whereas at pH 5.5, up to similar to 290-fold difference in metal ion permeability and similar to 1300-fold difference in capacity is observed in favor of Cu2+ relative to Cd2+. The uptake profiles of metal-sorbing Vesicles at pH 7.0 essentially are unchanged in the presence of a 100-fold greater concentration of Mg2+ relative to the ions of interest. A decrease of about 10-35% in both permeability and capacity is observed at a 100-fold greater concentration of Ca2+. The selectivity behavior of these metal-sorbing vesicles is predictable based on intrinsic metal ion and proton affinity parameters of both the encapsulated chelator (EDTP) and the membrane-bound carrier (A23187), and on the composition of the aqueous and membrane environments.