Paper FUNCTIONAL SORBENTS FOR SELECTIVE CAPTURE OF PLUTONIUM, AMERICIUM, URANIUM, AND THORIUM IN BLOOD Wassana Yantasee,* Thanapon Sangvanich,† Jeffery A. Creim,† Kanda Pattamakomsan,† Robert J. Wiacek,† Glen E. Fryxell,† R. Shane Addleman,† and Charles Timchalk† INTRODUCTION Abstract—Self-assembled monolayer on mesoporous supports (SAMMSTM) are hybrid materials created from attachment of ACTINIDE ISOTOPES are components in nuclear explosives, organic moieties onto very high surface area mesoporous silica. and could be used in dirty bombs. Uranium is readily SAMMS with surface chemistries including three isomers of absorbed by the body, and currently there are no chelat- hydroxypyridinone, diphosphonic acid, acetamide phosphonic acid, glycinyl urea, and diethylenetriamine pentaacetate (DTPA) ing agents recommended for its removal from systemic analog were evaluated for chelation of actinides (239Pu, 241Am, circulation (Stradling and Taylor 2005). The diethylene- uranium, thorium) from blood. Direct blood decorporation using triamine pentaacetate (DTPA) recommended for thorium sorbents does not have the toxicity or renal challenges associated is still ineffective in animal studies at high doses (Stra- with traditional chelation therapy and may have potential appli- cations for critical exposure cases, reduction of nonspecific dose dling et al. 1991). Although DTPA has been reported to during actinide radiotherapy, and for sorbent hemoperfusion in be effective for plutonium and americium, emerging renal insufficient patients, whose kidneys clear radionuclides at a ligands that are significantly more effective for pluto- very slow rate. Sorption affinity (K ), sorption rate, selectivity, d nium and americium decorporation in animals have been and stability of SAMMS were measured in batch contact exper- iments. An isomer of hydroxypyridinone (3,4-HOPO) on reported (Stradling et al. 1993; Volf et al. 1996a and b). SAMMS demonstrated the highest affinity for all four actinides This work evaluates solid sorbents in search for from blood and plasma and greatly outperformed the DTPA better decorporating agents for actinides from blood than analog on SAMMS and commercial resins. In batch contact, a the currently used DTPA chelator. Actinides are hard fifty percent reduction of actinides in blood was achieved within minutes, and there was no evidence of protein fouling or material Lewis acids and are larger than most transition metals, leaching in blood after 24 h. The engineered form of SAMMS thus both ligands’ hardness/softness and synergy play a (bead format) was further evaluated in a 100-fold scaled-down role in designing effective and selective ligands for hemoperfusion device and showed no blood clotting after 2 h. A actinides. Herein, our focus is evaluating novel sorbents 0.2 g quantity of SAMMS could reduce 50 wt.% of 100 ppb ,uranium in 50 mL of plasma in 18 min and that of 500 dpm mL؊1 for actinide removal from complex biological matrices in 24 min. 3,4-HOPO-SAMMS has a long shelf-life in air and at such as blood and plasma, which contain lipids, proteins, room temperature for at least 8 y, indicating its feasibility for cells, electrolytes, and anions. The effective sorbents will stockpiling in preparedness for an emergency. The excellent potentially be used in hemoperfusion. In patients with efficacy and stability of SAMMS materials in complex biological matrices suggest that SAMMS can also be used as orally admin- renal insufficiency, free metals or metal-chelates (if istered drugs and for wound decontamination. By changing the chelating agent like DTPA is administrated) are cleared organic groups of SAMMS, they can be used not only for from the body at a much slower rate. For illustration, actinides but also for other radionuclides. By using the mixture of with normal renal function, the half-life of Gd is ϳ2h; these SAMMS materials, broad spectrum decorporation of ra- dionuclides is very feasible. with loss of renal function the half-life is prolonged Health Phys. 99(3):413–419; 2010 reaching extremes of 34 h in chronic kidney disease Key words: actinides; adsorption; radiological terrorism; uranium patients, during which time Gd may dissociate from the chelate via transmetallation process (Penfield and Reilly * Biomedical Engineering, Oregon Health & Science Univer- 2007). Delayed clearance of actinides leads to their sity, Portland, OR 97239; † Pacific Northwest National Laboratory, deposition in liver and bone, from which they are Richland, WA 99352. For correspondence contact: W. Yantasee, Biomedical Engineer- difficult to remove (Stradling and Taylor 2005). ing, Oregon Health & Science University, Portland, OR 97239, or Developed at the Pacific Northwest National Labo- email at [email protected]. ratory (PNNL) originally for environmental and nuclear (Manuscript accepted 4 December 2009) 0017-9078/10/0 waste cleanups, the self-assembled monolayers on meso- Copyright © 2010 Health Physics Society porous supports (SAMMSTM) materials offer extremely Ϫ DOI: 10.1097/HP.0b013e3181ce5f3e large surface area (up to 500 m2 g 1) and functionalities 413 414 Health Physics September 2010, Volume 99, Number 3 that have been fine-tuned to selectively capture heavy plasma purchased from Golden West Biologicals, Inc. metals (Feng et al. 1997; Yantasee et al. 2003), actinides (Temecula, CA). They were spiked with a known amount (Fryxell et al. 2005; Lin et al. 2005), lanthanides (Fryxell of uranium, 239Pu, or 241Am prior to batch sorption et al. 2004; Yantasee et al. 2005), radioiodine (Mattigod experiments. Am and Pu stocks were kept in acid (e.g., 239 241 et al. 2003), cesium (Lin et al. 2001), and oxometallate Pu in 2 M HNO3 and Am in 0.5 M HCl) for long anions (Fryxell et al. 1999). term stability. Before spiking to blood or plasma, the Pu Herein, SAMMS having organic moieties known to and Am stocks were diluted in 0.1 M citrate buffer to be effective at capturing actinides were evaluated for the avoid the precipitation of actinides while the pH was sorption of actinides from blood and plasma. SAMMS increased to ϳ7 using 1.0 M NaOH. Blood or plasma materials investigated include three isomers of hydroxy- contained either 0.1 M sodium citrate or 15 unit mLϪ1 of pyridinone, diphosphonic acid, acetamide phosphonic sodium heparin as anticoagulant. Only a small volume of Ϫ1 acid, glycinyl urea, and a DTPA analog. Understanding uranium and thorium stock (1,000 mg L in 1–2% HNO3) how these SAMMS materials behave in complex biolog- was spiked directly into blood or plasma to achieve the ical matrices would lead to many potential applications desired concentration, with no impact on matrix pH. Sea- such as blood decorporation using sorbent hemoperfu- water (used in a stability study) was obtained from the sion, orally administered sorbents for safe and long term Sequim Bay (WA) and was filtered with 0.45 ␮m cellulose treatment of radionuclide poisoning, and wound decon- acetate membranes prior to use. Its pH was adjusted to a tamination of radionuclides, all of which will advance the desired pH value with HNO3 or NaOH. field of health physics and protect health and safety of the public in events resulting in the release of radioactive materials. Batch contact Adsorption experiments were performed using the MATERIALS AND METHODS following conditions: 0.003 g of solid sorbent in 3 mL of Ϫ1 Ϫ1 Sorbent materials fluid (liquid per solid ratio, L S , of 1,000 mL g ), Synthesis and characterization of the SAMMS materi- shaken for2hat250rpmand37°C. Then the sorbent als have been described elsewhere, including SAMMS was removed using custom made filters (porous glass frit ϳ immobilized with three analogs of hydroxypyridinones having pore size of 8 micron), which allowed only (1,2-HOPO, 3,2-HOPO, and 3,4-HOPO) (Lin et al. 2005; fluid passing through but not sorbent. The metal content Yantasee et al. 2005), acetamide phosphonic acid (Ac- in the fluid before and after adding the sorbent was Phos), glycinyl-urea (Gly-Ur) (Fryxell et al. 2004, 2005), analyzed by an inductively coupled plasma-mass spectrom- diphosphonic acid (Di-Phos), and DTPA analog (Fig. 1). eter (ICP-MS, Agilent 7500ce, Agilent Technologies, Santa The Na-DTPA derivatized silica gel (Silia Bond Clara, CA) for uranium and thorium, by gamma counts for 241 TAAcONa) was obtained from SiliCycle® Inc. (Que- Am (Wallac Wizard 1480 Gamma counter, Perkin- bec City, Canada). Elmer, Waltham, MA), and by liquid scintillation counts for 239Pu (Wallac 1414 Liquid Scintillation Counter). All batch Test matrices experiments were performed in triplicates and the averaged For evaluation of SAMMS to be used in hemoper- values were reported. The use of commercially available fusion of uranium, 239Pu, and 241Am, batch contact human blood fell under the Institutional Review Board experiments were performed using human blood and (IRB) exempt classification. Fig. 1. Chemical structures of SAMMS having various organic groups. Functional sorbents ● W. YANTASEE ET AL. 415 Sorption rate cannot overcome the mass transport limitations, espe- Kinetics experiments were carried out similarly to cially when the analyte is very dilute (as in case of batch equilibrium experiments except that 0.03 g of radionuclide exposure). Ϫ sorbent was dispersed in a 30 mL volume (L S 1 of 1,000 Preliminary screening (which will be published Ϫ Ϫ mL g 1) of plasma containing 1,000 dpm mL 1 of 241Am, elsewhere) was carried out in pH-adjusted seawater since Ϫ 700 dpm mL 1 of 239Pu, or mixture of 100 ppb U/Th. this would allow us to evaluate the affinity of the various Kinetics of U removal was also performed in blood using ligands for the actinides in a high ionic strength matrix, Ϫ 0.06 g of sorbent and 30 mL of blood (L S 1 of 500 without the complications of competitive binding, pro- Ϫ mL g 1). The aliquots were removed at 1, 2, 5, 10, 30, tein fouling, etc. The second tier screening was per- 60 min, 2, 8, and 24 h, filtered through the custom formed in human blood and plasma since, in these made filters and subjected to ICP-MS analysis along biological fluids, sorption affinity (Kd) of radionuclides with the initial solution (zero time point).