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Journal of Environmental Radioactivity 100 (2009) 301–307

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Journal of Environmental Radioactivity

journal homepage: www.elsevier .com/locate/ jenvrad

Solid state speciation and potential bioavailability of depleted uraniumparticles from Kosovo and Kuwait

O.C. Lind a,*, B. Salbu a, L. Skipperud a, K. Janssens b, J. Jaroszewicz b, W. De Nolf b

a Isotope Laboratory, Department of Plant and Environmental Sciences, Norwegian University of Life Sciences, P.O. Box 5003, N-1432 Ås, Norwayb Department of Chemistry, University of Antwerp, Universiteitsplein 1, Antwerp, Belgium

a r t i c l e i n f o

Article history:Available online 11 February 2009

Keywords:Depleted uranium particlesMicro-XANESMicro-XRDSolubility

* Corresponding author. Tel.: þ47 64965545; fax: þE-mail address: ole-christian.lind@umb.no (O.C. Li

0265-931X/$ – see front matter � 2009 Elsevier Ltd.doi:10.1016/j.jenvrad.2008.12.018

a b s t r a c t

A combination of synchrotron radiation based X-ray microscopic techniques (m-XRF, m-XANES, m-XRD)applied on single depleted uranium (DU) particles and semi-bulk leaching experiments has beenemployed to link the potential bioavailability of DU particles to site-specific particle characteristics. Theoxidation states and crystallographic forms of U in DU particles have been determined for individualparticles isolated from selected samples collected at different sites in Kosovo and Kuwait that werecontaminated by DU ammunition during the 1999 Balkan conflict and the 1991 Gulf war. Furthermore,small soil or sand samples heavily contaminated with DU particles were subjected to simulatedgastrointestinal fluid (0.16 M HCl) extractions. Characteristics of DU particles in Kosovo soils collected in2000 and in Kuwait soils collected in 2002 varied significantly depending on the release scenario and tosome extent on weathering conditions. Oxidized U (þ6) was determined in large, fragile and brightyellow DU particles released during fire at a DU ammunition storage facility and crystalline phases suchas schoepite (UO3$2.25H2O), dehydrated schoepite (UO3$0.75H2O) and metaschoepite (UO3$2.0H2O)were identified. As expected, these DU particles were rapidly dissolved in 0.16 M HCl (84 � 3% extractedafter 2 h) indicating a high degree of potential mobility and bioavailability. In contrast, the 2 h extractionof samples contaminated with DU particles originating either from corrosion of unspent DU penetratorsor from impacted DU ammunition appeared to be much slower (20–30%) as uranium was less oxidized(þ4 to þ6). Crystalline phases such as UO2, UC and metallic U or U–Ti alloy were determined in impactedDU particles from Kosovo and Kuwait, while the UO2,34 phase, only determined in particles from Kosovo,could reflect a more corrosive environment. Although the results are based on a limited number of DUparticles, they indicate that the structure and extractability of DU particles released from similar sources(metallic U penetrators) will depend on the release scenarios (fire, impact) and to some extent envi-ronmental conditions. However, most of the DU particles (73–96%) in all investigated samples weredissolved in 0.16 M HCl after one week indicating that a majority of the DU material is bioaccessible.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Large amounts of depleted uranium (DU), a waste product of Uenrichment, have been applied as armour-piercing ammunition,due to the high density, hardness of the metal and pyrophoricproperties. Several reports have been published on DU contami-nation due to DU penetrators use during war time in Kosovo(Danesi et al., 2003a,b; Salbu et al., 2003), Serbia–Montenegro(McLaughlin et al., 2003), Bosnia and Herzegovina (UNEP, 2003),Kuwait (Salbu et al., 2005) and Iraq (Gerdes et al., 2004). At all sitesa part of the DU contamination was identified as DU particles

47 64967006.nd).

All rights reserved.

except in Iraq where no information on particles appears to beavailable. Large amounts of DU ammunition have also contami-nated military proving grounds and their surroundings (Sowderet al., 1999).

Following the impact of metallic DU penetrators on a hard targetsuch as tanks, a cloud of DU dust that ignites spontaneously iscreated (The Royal Society, 2001). It appears to be generallyaccepted that UO2 and U3O8 are produced upon oxidation ofmetallic DU at the high temperatures created during impact (TheRoyal Society, 2001). However, U4O9, U3O7 and UO3 have also beenreported from DU penetrator tests (Chazel et al., 2003). Fragmentsand particles are also formed as unspent DU penetrators depositedin the field will corrode over time due to oxidation of the metal(Buck et al., 2004; Johnson et al., 2004; Mellini and Riccobono,2005; Salbu et al., 2005). In the environment, U metal can also

O.C. Lind et al. / Journal of Environmental Radioactivity 100 (2009) 301–307302

experience passivation where an oxide, hydroxide or salt coatingcan protect against further corrosion. Corrosion, weathering andremobilization of uranium from DU solid phases will depend onenvironmental factors such as pH, concentration of interactingagents, redox conditions and microbial activities. Following inha-lation or ingestion of DU particles, the amount of DU that istransferred into blood and distributed to tissues and organs willlargely depend on particle weathering rates and solubility both inthe respiratory system as well as in the GI tract. Particle weatheringrates are related to particle characteristics such as specific surfacearea, size distribution, elemental composition, U oxidation statesand crystallographic structure. To estimate the potential bioavail-ability of radioactive particles however, biotests would be mostuseful. Alternatively, simulated gastrointestinal fluid (e.g. 0.16 MHCl) extractions have frequently been used to mimic potentialuptake from particles (Crocker et al., 1966; Hamel et al., 1998;White et al., 1968).

Salbu et al. (2003, 2005) have previously reported that charac-teristics of DU particles in Kosovo soils contaminated during theBalkan conflict and in sand from Kuwait contaminated during theGulf war varied significantly depending on the DU release scenario.In the present work an attempt is made to link new and previouslyobtained information on particle characteristics to the potentialbioavailability of DU particles, utilizing simulated gastrointestinalfluid (0.16 M HCl) extractions of heavily contaminated soil or sandsamples.

A combination of scanning electron microscopy with X-raymicroanalysis (SEM-XRMA) and synchrotron radiation based micro-scopic X-ray fluorescence (m-SRXRF), synchrotron radiation basedmicroscopic X-ray absorption near edge spectroscopy (m-XANES) andsynchrotron radiation based microscopic X-ray diffraction (m-SRXRD)applied on single depleted uranium (DU) particles has been utilised tocharacterize the DU particles.

2. Materials and methods

2.1. Samples and pre-treatment

In 1999, the International Atomic Energy Agency (IAEA) as part of an UN missionto Kosovo, collected soil samples contaminated with DU (Danesi et al., 2003b). In2002, the IAEA organised a field mission to collect samples at selected sites inKuwait, where DU ammunition had been used (IAEA, 2003). Soil and sand samplescollected at target sites at Ceja Mountain (a former Serbian army and anti-aircraftposition) in south west Kosovo and at Al Doha, Manageesh and Um Al Kwaty inKuwait, were air dried. The Kosovo samples were sieved into two fractions,a ‘‘coarse’’ fraction (>3 mm) and a ‘‘fine’’ fraction (<3 mm), which were madeavailable to UMB (Danesi et al., 2003b). Kuwaiti dried soil and sand samples aswell as swipe samples (tissues) from inside impacted tanks were also madeavailable to UMB for the characterization of particles without further treatment(Salbu et al., 2005).

2.2. SEM and ESEM with XRMA

Despite the low radioactivity of DU, particles containing DU were easily iden-tified and isolated using SEM (Lind, 2006; Salbu et al., 2003, 2005). Soils were fixedonto carbon double-faced sticky tape mounted on Al stubs and subjected to scan-ning electron microscopy (SEM) using a JEOL JSM 840 instrument interfaced withX-ray micro-analyser (ISIS 300, Oxford Instruments) and using a Zeiss EVO 50variable pressure Environmental Scanning Electron Microscope (ESEM). The U wasidentified in backscattered electron imaging mode (BEI-mode) and DU particleswere further localised and characterised using X-ray micro-analyser (XRMA) prior tosynchrotron radiation based X-ray microscopic experiments. In some cases, large DUparticles with a bright yellow appearance could also be identified and separatedfrom soil working under a light microscope.

2.3. Synchrotron radiation X-ray microscopic techniques

The DU particles were subjected to synchrotron radiation X-ray microscopictechniques (m-XRF, m-XANES and m-XRD) using the Beamline L, HamburgerSynchrotron Labor (HASYLAB) and the ID18F Beamline at European SynchrotronRadiation Facility (ESRF).

2.3.1. m-XRD experimentsMicro-XRF spectra and m-XRD diffraction patterns were recorded simulta-

neously from the same location on the DU particles using a scanning micro-XRF/XRDset-up at HASYLAB. This set-up was also utilised to obtain m-XRF/m-XRD maps (2D)and line scans of the particles. A focused monochromatic X-ray microbeam of 10–15 mm diameter, having a divergence of w4 mrad was used for the investigations.This beam was obtained by employing a 200 period Mo/Si multilayer mono-chromator with mean layer thickness of 2.98 nm for energy band selection (DE/E¼ 1%) and a single-bounce elliptical capillary for beam focussing (Falkenberg et al.,2004). A 1K Bruker CCD camera positioned behind the sample, was used for col-lecting diffraction patterns in transmission mode, along with a Si(Li) detector,positioned at 90� relative to the primary X-ray beam, for simultaneous detection ofthe XRF signals. The HASYLAB XRD set-up was calibrated with Silicon powder (NISTSRM 640c).

Micro-X-ray fluorescence spectra and micro-X-ray powder diffraction patternshave also been recorded from individual DU particles in a similar way at ESRF (Salbuet al., 2005). During these experiments, the monochromator was tuned to 28 keV,a compound refractive lens focused the monochromatic beam and a PhotonicsScience X-ray diffraction camera was used to record the diffracted Debye rings.Measurements included point measurements (5 � 10 mm, single XRF spectrum andm-XRD image collected during typically 10–100 s) and line scans (horizontal orvertical lateral movement of the particle through the primary beam with incrementof typically 2–5 mm and the collection of an XRF spectrum and/or m-XRD image at allpositions along the line). The XRD set-up at ESRF was calibrated using reflectionsfrom UO2 in the samples. XRD data from ESRF (Salbu et al., 2005) have been rean-alyzed utilizing new software.

2.3.2. m-XANES experimentsParticles characterised by SEM with XRMA were subjected to m-XANES analysis

using the X-ray microscopic facility at beamline L, HASYLAB, Hamburg (Salbu et al.,2003, 2005). Using m-XANES, information on the oxidation state of U in DU particleswas obtained by tuning the monochromatic, focused (20 � 20 mm beam usinga polycapillary lens) X-ray beam over the U LIII absorption edge (17.163 keV), whilekeeping the beam position on individual DU particles. The flux at the beam spot onthe sample was about 109 photons per second at 17.1 keV. The incident and trans-mitted beam intensity (I0, I) were measured by ionisation chambers, while the U LIII

fluorescence intensity was recorded by means of a HPGe detector having an activearea of 30 mm2 mounted at 90� relative to the incoming beam and 30 mm fromthe sample. The HPGe detector was well collimated (2 mm diameter pinhole). Them-XANES spectra were collected at 1 eV increments over a 300 eV energy range(extending from about 80 eV below and 220 eV above the U LIII edge). Based on well-defined U oxidation state standards (UO2, Institute of Energy Technology, Kjeller;U3O8, Institute of Energy Technology, Kjeller; UO2Ac2$2H2O p.a., Riedel-De Haen AG,Seelze-Hannover; UO2(NO3)2$6H2O p.a., Merck, Darmstadt) the m-XANES spectrawere recorded and the inflection point energies for the oxidation states of Uestablished. The m-XANES profile shapes and energy shifts (inflection point energies)of U in DU particles were compared with those of the standards. For non-stoichio-metric U oxides, linear regression was employed to determine the oxidation state(Proost, 2005). For Kuwaiti samples, the m-XANES analyses were backed up bycrystallographic structure analysis using m-XRD (Salbu et al., 2005).

2.4. Leaching experiments

For leaching experiments, about 0.04 g soil (contaminated with 4000 mg DU/kgsoil following impact with tank; Ceja Mountains, Kosovo), 0.5 g sand (collected inthe vicinity of the site of the DU ammunition storage fire; Al Doha, Kuwait) and 2 gsand (collected from below a corroded DU penetrator; Manageesh, Kuwait) ofsamples known to be contaminated with DU particles were transferred to centrifugetubes and extracted with 20 mL of simulated human gastrointestinal (GI) tract fluid(0.16 M HCl secretion of the digestive tract (White et al., 1968)) for 2, 24 and 168 h.An incubation time of 2 h was selected as being representative of a residence time inthe stomach, while 24 h incubation mimics the transit times through the intestines(Darley et al., 2003). By continuing the extraction for one week (168 h), informationon the long term potential mobility of U could be obtained. The supernatant wasseparated from the solid by high-speed centrifugation (10 000 rpm), followed byfiltration (Blue band paper filter) prior to ICP-MS measurements.

2.5. ICP-MS

Extracts, filters and residual material were analysed with respect to 235U and238U by means of ICP-MS (ELAN 6000). Extracts were taken to dryness twice withconcentrated nitric acid. Residual material and filter papers were combined, ashed,boiled in Aqua Regia for 3 h, filtered and taken to dryness. Finally, all the DU con-taining samples were dissolved and further diluted in 0.1 M HNO3 prior to ICP-MSanalyses. No chemical separations were needed and intensities of 235U and 238Uwere recorded (usually 3 replicate sample introductions per sample) for each of theextracts obtained. The sum of the intensities of the extracts amounted to 100%.

Table 1Characteristics of DU particles investigated in the present work.

Source and event Particleno.

Average U oxidationstate

Crystallographicstructure

DU impact, Kosovo 67 n.m. UO2, UO2,34, UC69 n.m. UO2, UC, metallic U70 þ4.0 � 0.5 UO2, UO2,34

71 þ4.0 � 0.5 UO2, UO2,34, UC72 n.m. UO2, UO2,34, UC74 n.m. UO2, metallic U

DU impact, Kuwait 80 þ4.7 � 0.5a UO2, UC81 n.m. UO2, UC82 þ4.4 � 0.5a UO2, UC, Fe2U

DU ammunition storage fire,Kuwait

84 þ6 UO3$2.0H2O,UO3$0.8H2O

85 þ6 UO3$2.0H2O,UO3$0.8H2O

89 þ6 Only spots in XRD90 þ6 UO3$2.25H2O,

UO3$2.0H2O91 þ6 UO3$2.25H2O,

UO3$2.0H2O92 þ6 UO3$2.0H2O

DU corrosion, Kuwait 94 þ6a Only spots in XRD95 þ4.6 � 0.5a Only spots in XRD

a Proost (2005).

O.C. Lind et al. / Journal of Environmental Radioactivity 100 (2009) 301–307 303

3. Results and discussion

All soil and sand samples contained a series of DU particles,varying in size, oxidation states and structure. In samples con-taining impacted DU, most particles were in the respiratory sizefraction. Thus, resuspension and subsequent inhalation isa pathway of concern. The 235U/238U isotope ratios determined byICP-MS were rather constant at approximately 0.002 and thepresence of Ti in Kosovo DU particles was confirmed by XRMA andm-XRF (Salbu et al., 2003, 2005). The 236U/238U ratios in individualDU particles from Kuwait (10�1, 10�2) and bulk samples fromCeja Mountains, Kosovo (10�2), reflected that these DU penetra-tors originated from reprocessed fuel (Danesi et al., 2003a;Salbu et al., 2005).

3.1. Characterization of DU particles

3.1.1. Kosovo DU particlesDetailed studies of the Kosovo samples demonstrated the pres-

ence of hot spots where hundreds of thousands of particles werepresent in a few milligrams of DU contaminated soils (Danesi et al.,2003). The particle distribution study showed that most of the DUparticles were smaller than 5 mm, and that more than 50% were lessthan 1.5 mm. This is in line with other studies, which show that thesize distributions (activity median aerodynamic diameters, AMAD,mm) for particles produced during a DU penetrator impact witha tank are characterised by fine particles (AMAD values from 0.8 to7.5 mm) and heterogeneous distributions (The Royal Society, 2001).

Based on m-XANES (Salbu et al., 2003, 2005), most of the DUparticles originating from combat use of DU ammunition was oxi-dised (Table 1). The XANES spectra corresponded with those of UO2

(oxidation state þ4.0 � 0.5) and U3O8 (oxidation state 5.3 � 0.5)standards, and using linear regression mixtures of these oxideswere identified in individual DU particles. Results from recentscanning m-XRF and m-XRD experiments confirmed that U in theparticles was present as oxides. The XRD diffractograms collectedfrom local spots on individual DU particles collected from under-neath an impacted penetrator jacket in the Ceja Mountainsresembled most closely those of uraninite (UO2, 41-1422) andUO2,34 (75-0456), while U3O8 Bragg reflections were not observedin XRD. Furthermore, metallic forms of U and/or U–Ti as well as UC(73-1709) were identified (Table 1; Fig. 1). The exact crystallinestructure of metallic U (e.g., a-uranium or U–Ti alloy) could not bededuced.

3.1.2. Kuwait DU particlesThe DU particles ranged from submicrons to several hundred

micrometers in diameter in the Kuwaiti samples; small-sizedparticles from impacted penetrators (swipe from inside hit tank)and from corroded penetrators (soil underneath penetrator), whilelarger and more fragile particles were associated with the DUammunition storage fire. Based on m-XANES and preliminary m-XRDanalysis at ESRF (Salbu et al., 2003, 2005), most of the DU particlesoriginating from combat use of DU ammunition and those releasedduring the ammunition storage fire were oxidised (Table 1). Forsmall DU particles from impacted penetrators, the XANES spectracorresponded with those of UO2 (oxidation state þ4.0 � 0.5) andU3O8 (oxidation state 5.3 � 0.5) standards, as well as a mixtures ofthese oxides. Preliminary m-XRD data confirmed to a certain extentthe XANES data, but problems associated with the identification ofphases and comparison with the XRD literature database wereidentified.

Although only 2 of the DU particles isolated from soil beneatha corroded penetrator were subject to XANES analysis, the resultsindicate that corroded DU may be present as a mixture of species

(Table 1). The average oxidation state of particle no. 95 corre-sponded to oxidation stateþ4.6, while the spectra of particle no. 94coincided with the uranyl standards (i.e. þ6). The latter result issupported by the fact that particles with bright yellow colourindicative of uranyl compounds were easily identified in soilsamples from this site both by us as well as the IAEA (IAEA, 2003).Mellini and Riccobono (2005) have reported corroded U on DUpenetrators to be present as black uraninite (UO2) and a yellowmaterial which they infer to be schoepite. Unfortunately, thediffraction patterns of these samples exhibited only spots (no rings)thus precluding the possibility of solving their crystallographicstructure.

Results from recent scanning m-XRF and m-XRD experiments andfrom re-examination of previously collected XRD data using theICDD PDF-2 library showed that U in the DU particles from Kuwaitwas present as oxides, carbide and metallic forms. Uranium in DUparticles from impacted penetrators (swipes) was present as UO2,U metal and UC (Table 1), similar to impacted DU from Kosovo.However, the UO2,34 phase observed for DU in Kosovo could notbe observed. Furthermore, diffractograms for one of these particlesindicated the presence of Fe2U. The presence of alloyedFe–U particles of varying composition has previously beenobserved during DU ammunition testing, and the presence of Fein DU particles from Kuwait probably reflects the violent interac-tion between penetrators and tanks at impact (Patrick andCornette, 1978).

According to the XANES spectra, U in the large, bright yellow DUparticles released during the ammunition storage fire and subse-quently collected from sand was oxidized to þ5 or þ6 (Salbu et al.,2005). The oxidation state þ6 was confirmed by recent XRD data,showing that uranium in the large, bright yellow DU particles(Figs. 2 and 3) was present as crystalline schoepite (S, UO3$2.25H2O,86-1383), dehydrated schoepite (DS, UO3$0.75H2O, 10-0309) andmetaschoepite (MS, UO3$2.0H2O, 43-0364).

These minerals are important reservoirs of mobile U(VI) in theenvironment originating from weathering of U minerals such asuraninite (Finch et al., 1992) and corrosion of anthropogenic Usolids such as DU material (i.e. U metal and U oxides) and spentnuclear fuel such as UO2 (Buck et al., 2004; Sowder et al., 1999).

Fig. 2. Electron micrograph of particle no. 92 collected from sand at Al Doha, Kuwait.The XRD data from local spots on the particle matches those of schoepite in the ICDDPDF-2 database.

Fig. 1. Diffraction patterns from DU particles and corresponding ICDD PDF-2 database entries.

O.C. Lind et al. / Journal of Environmental Radioactivity 100 (2009) 301–307304

Schoepite has previously been observed in U contaminated sites inFernald Environment Management Site (Buck et al., 1996; Morriset al., 1996), Oak Ridge National Laboratory (Roh et al., 2000), andKosovo (Mellini and Riccobono, 2005). The DU penetrators degraderelatively fast in the environment due to the chemical reactivity ofU metal under oxidizing conditions promoting surface formationof UO2 (Riba et al., 2005). Furthermore, oxidation to U oxides ofvariable stoichiometry (e.g. U4O9, U3O7 and U3O8) up to UO3 withhexavalent U occurs under dry conditions (Allen et al., 1982; Allenand Tempest, 1986). The UO3 readily hydrates to form S and similarphases (UO3$nH2O). Under ambient temperatures and in air, Sslowly transforms to more stable MS and these minerals arecommonly found intergrown in crystals (Finch et al., 1998). Am-XRF/m-XRD line scan of particle #85 (Fig. 4) revealed that S andDS coexist in the particle indicating that to some extent dehydra-tion of S to DS has taken place as described by Finch et al. (1992).

Finch et al. (1998) have reported that crystals of S may alsospontaneously alter to a mixture of MS and DS. Under acidicconditions UO3$xH2O will dissolve according to the reaction:

UO3$xH2OD2HD [ UO 2D2 Dð1DxÞH2O (1)

The literature log ksp of this reaction reported for pH 2.8–9.0vary between 4.70 and 6.33 (Giammar and Hering, 2004) asa function of the degree of crystallinity, particle size, electrolyteconcentration, pH range, and atmosphere as pointed out by Ribaet al. (2005). Their experiments show a fast initial (1 h) MS disso-lution rate followed by fluctuations in concentrations of dissolved Ubefore equilibrium is attained after 3000 h. Given the strong pHdependence of the reaction (Eq. (1)), the low pH (pH 0.8) extractionreagent (0.16 M HCl) utilised in this work is expected to dissolvethese secondary minerals very efficiently (Fig. 5).

Table 1 summarizes the present knowledge on the DU particlecharacteristics, and illustrates that the characteristics of DU

particles originating from either penetrator impact or corrosion arerather different from those originating from the DU ammunitionstorage fire.

3.1.3. Leaching of DUExperiments carried out on soil/sand samples from Kosovo and

Kuwait known to be contaminated with DU particles showed thatthe solubility of U from DU particles in simulated GI tract fluidvaried significantly depending on the release scenario (Fig. 2). Sinceno chemical separations were needed, the uncertainties associatedwith measuring aliquots of the extracts should be well within the

Fig. 3. Grain of sand partly covered with bright yellow depleted U originating from the ammunition storage fire in Al Doha, Kuwait. (Left) Scanning electron micrograph recorded inBEI-mode. (Right) Light microscopy image of the same particle.

Fig. 4. Relative phase intensity distribution of schoepite and dehydrated schoepitealong a line across particle no. 85.

Fig. 5. Cumulative extraction (%) of U from DU particle contaminated samplescollected at selected locations in Kuwait and Kosovo using simulated gastrointestinalfluid (0.16 M HCl) at room temperature.

O.C. Lind et al. / Journal of Environmental Radioactivity 100 (2009) 301–307 305

precision (w20%, n ¼ 3) of the method. Application of ICP-MS todetermine the amount of U in extracts allowed the simultaneousmonitoring of the natural U contribution in the obtained fractions.The 235U/238U atom ratio for all fractions varied around 0.002within the reproducibility of the method (% relative standarddeviation <9). Thus, the amount of natural U in the samples wasnegligible.

The hexavalent DU in schoepite, metaschoepite and dehydratedschoepite in sand samples contaminated with particles originatingfrom the fire in the ammunition storage facility (Kuwait fire), wasrapidly dissolved in 0.16 M HCl (84 � 3% of total amount extractedafter 2 h of contact, n ¼ 3). Thus, these particles as well as otherpotential DU species in the samples such as carbonates exhibita high degree of potential mobility and bioavailability, assumingthat an incubation time of 2 h is representative of the residencetime of particles in the stomach. In contrast, the initial extraction ofDU, originating from the corrosion of ‘unspent’ DU penetrators(Kuwait below penetrator, n ¼ 1) or collected below an impacted(impact with tank) DU penetrator (Kosovo impact, n ¼ 1), wasmuch slower. After 2 h, 24 � 4% of the depleted U was extractedfrom sand samples contaminated with DU particles (UO2, UO2,34,UC and metallic U) originating from the corrosion of unspent DUpenetrators in Kuwait. The relatively low extraction indicates thatthe share of hexavalent U (as observed using XANES, see above) inthe sample should be rather small. A similar result was obtained forKosovo soil collected beneath a penetrator jacket (25� 5%). The DUparticles collected on swipes from inside impacted tanks in Kuwaitcontaining UO2, UO2,34, UC and possibly Fe2U could be expected todissolve equally slow. Tetravalent forms of U are sparingly solublewith measured solubility products (ksp) of 10�53.44 for UO2 (am)(Rai et al., 1997) and ranging from 10�57.6 (Bruno et al., 1986) to10�60.2 (Rai et al., 2003) for UO2 (c). Furthermore, dissolutionexperiments with different solutions indicate that UO2 will dissolvemuch slower than U(VI) particles in acidic solutions (Kashparovet al., 2000). Thus, the release scenario and subsequent weatheringof DU influence the particle characteristics and subsequently theinitial dissolution of DU. However, most (73–96%) of the DU speciesin all the contaminated soils from Kosovo and Kuwait was appar-ently dissolved after one week indicating a high degree of potentialmobility.

Our results can be compared with data reported by Gerstmannet al. (2008). They found that w75% of greenish-yellow corrosionproducts scraped off from fragments of DU penetrators collected inKosovo dissolved in simulated gastric juice after 2 h, i.e. similar to

Fig. 6. Summary of the results obtained in the present work. *No crystalline powder diffraction signals were observed, only spots.

O.C. Lind et al. / Journal of Environmental Radioactivity 100 (2009) 301–307306

but somewhat lower than our results for schoepite particles. Thisseems reasonable because greenish-yellow corrosion products onDU penetrators collected in Kosovo have previously been investi-gated by Mellini and Riccobono (2005), who suggested that thematerial was schoepite. Our results show that both the solid statespeciation and leaching behaviour of the DU particles originatingfrom the ammunition storage fire differ considerably compared toparticles formed as a result of impact or corrosion of DU pene-trators. The differences between particles originating from impactand those formed as a result of corrosion, however, are less obvious.The size distribution of DU particles from impact tends to besmaller, while DU in particles from corrosion tends to be moreoxidised as observed in XANES and in light microscope (yellowcolour) indicating the presence of uranyl ions, whereas no signalsindicating uranyl ions were observed in particles from impact.However, the leaching behaviour turned out to be very similar forthese types of particles.

The present results show the importance of the source term andthe release scenario associated with a nuclear event for the speci-ation of U and for the potential uptake in man and biota. As theparticle weathering rate is expected to be higher for U(VI) andUO2þx (x > 0) than for UO2, the presence of respirable S, MS and DSas well as UO2þx (x > 0) and their corresponding weathering ratesand the subsequent remobilization of U should be included inenvironmental impact assessments of areas contaminated with DUand in health implication assessments arising from the use of thistype of ammunition.

It should be emphasized that the present leaching experimentsinvolve the extraction from ‘‘semi-bulk’’ samples and not isolatedDU particles. The results include not only either full or partialdissolution of particle matrices but also dissolution of pH-sensitivephases (e.g. carbonates) as well as desorption of reversibly boundfractions from soil or sediment surfaces. The samples had beensubjected to natural weathering prior to the experiments anda certain fraction of DU will probably be present as physico-chemical forms (e.g. reversibly sorbed and pH-sensitive) morereadily available for extraction than the original particulate mate-rial. Carbonates of actinides, such as observed by Wolf et al. (1997)for instance, are dissolved in the 0.16 M HCl solvent. Furthermore,the size distribution of the DU particles in the investigated samples,which is known to be a key property with respect to solubility, isnot fully characterised. However, the present results clearly indi-cate that although the sources are similar (DU penetrators), therelease scenarios are of key importance; DU particles releasedduring the fire in an ammunition storage facility fire are moreoxidized and more bioaccessible than DU particles originating fromimpact or corrosion (Fig. 6).

4. Conclusions

To conclude, the present results show the importance of thesource term and the release scenario associated with a nuclearevent for the speciation of uranium and possibly other actinidesand for the potential uptake in man and biota. Furthermore,information on site-specific particle characteristics obtained bysolid state speciation techniques has been linked to extractionkinetics and bioavailability of U originating from different sourceterms and release scenarios. Thus, the results from this DU particlestudy should be of generic value for radioecological studiesinvolving U chemistry. The study also illustrates that the combi-nation of advanced solid state speciation techniques and relevantextraction schemes provides a powerful tool for environmentalimpact assessments in areas contaminated with radioactiveparticles.

Acknowledgements

We gratefully acknowledge the support provided by theEuropean Commission (contract no. IHP-Contract HPRI-CT-1999-00040), IAEA (CRP, ‘‘Characterization of radioactive particles’’)and the Norwegian Research Council (project no. 141479/720). Theauthors are indebted to Tove Loftaas, UMB/IPM for extraction work.

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