Competitive binding of Pu and Am with bone mineral and novel chelating agents

Effective direct removal of actinides such as Pu and Am from bone in vivo has not been accomplished to date, even with the strong chelating agents CaNa3DTPA or ZnNa3DTPA. This study, using an established in vitro system, compared removal of Pu and Am bound to bone mineral by ZnNa3DTPA and 10 chelating agents designed specifically to sequester actinides, including Pu and Am. Ligands tested were tetra, hexa, and octadentate, with linear or branched backbones containing sulfocatechol [CAM(S)], hydroxycatechol [CAM(C)], hydroxipyridinone (1,2-HOPO, Me-3,2-HOPO), or hydroxamate functional groups. The wide range of Pu and Am removal exhibited by the test ligands generally agreed with their metal coordination and chemical properties. The most effective agents for Pu (100 µM concentration, 24-48 h contact) are all octadentate as follows: 3,4.3-LICAM(S) (54% unbound); 3,4.3-LICAM(C) (6.2%); 3,4.3-LI(1.2-HOPO) (3.8%); H(2.2)-(Me-3,2-HOPO) (2.2%) and DFO-(1,2-HOPO) (1.8%). The other ligands removed less than 1% of the bound Pu; and ZnNa3DTPA removed only 0.086%. The most effective ligands for Am removal (100 µM, 24-48 h contact) are as follows: octadentate H(2.2)-(Me-3,2-HOPO) (21% unbound); 3,4.3-LI(1,2-HOPO) (14.5%) and 3,4.3-LICAM(C) (5.9%); hexadentate TREN-(Me-3,2-HOPO) and TREN-(1,2-HOPO) (9.6%); and tetradentate 5-LIO(Me-3,2-HOPO) (5.2%). Am removal by ZnNa3DTPA was about 1.4%. Among the ligands presently considered for possible human use, only 3,4.3-LI(1,2-HOPO) removed potentially useful amounts of both Pu and Am from bone mineral.