Isotopic investigation of the colloidal mobility of depleted uranium in a podzolic soil

Chemosphere 103 (2014) 343–348

Contents lists available at ScienceDirect

Chemosphere

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

Isotopic investigation of the colloidal mobility of depleted uraniumin a podzolic soil

0045-6535/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.chemosphere.2013.12.033

⇑ Corresponding author. Tel.: +33 559 407 671; fax: +33 559 407 674.E-mail address: gaetane.lespes@univ-pau.fr (G. Lespes).

S. Harguindeguy a,b, P. Crançon b, F. Pointurier b, M. Potin-Gautier a, G. Lespes a,⇑a Université de Pau et des Pays de l’Adour, Laboratoire de Chimie Analytique Bio-Inorganique et Environnement, IPREM-UMR 5254 Pau, Franceb CEA, DAM, DIF, F-91297 Arpajon, France

h i g h l i g h t s

�We investigated the colloidal transport of uranium in a contaminated site.� We clearly shows the importance of colloids in uranium mobilization and migration.� Mobilization of anthropogenic uranium is enhanced compared to native uranium.� Smaller colloids are likely to dominate for the sorption of anthropogenic uranium.� Native natural uranium is mainly associated with coarser fractions.

a r t i c l e i n f o

Article history:Received 3 October 2013Received in revised form 30 November 2013Accepted 11 December 2013Available online 31 December 2013

Keywords:Depleted uraniumColloidsMobilityBatch experimentsLeachingUltrafiltration

a b s t r a c t

The mobility and colloidal migration of uranium were investigated in a soil where limited amounts ofanthropogenic uranium (depleted in the 235U isotope) were deposited, adding to the naturally occurringuranium. The colloidal fraction was assumed to correspond to the operational fraction between 10 kDaand 1.2 lm after (ultra)filtration. Experimental leaching tests indicate that approximately 8–15% of ura-nium is desorbed from the soil. Significant enrichment of the leachate in the depleted uranium (DU) con-tent indicates that uranium from recent anthropogenic DU deposit is weakly bound to soil aggregates andmore mobile than geologically occurring natural uranium (NU). Moreover, 80% of uranium in leachateswas located in the colloidal fractions. Nevertheless, the percentage of DU in the colloidal and dissolvedfractions suggests that NU is mainly associated with the non-mobile coarser fractions of the soil. A fieldinvestigation revealed that the calculated percentages of DU in soil and groundwater samples result inthe enhanced mobility of uranium downstream from the deposit area. Colloidal uranium representsbetween 10% and 32% of uranium in surface water and between 68% and 90% of uranium in groundwaterwhere physicochemical parameters are similar to those of the leachates. Finally, as observed in batchleaching tests, the colloidal fractions of groundwater contain slightly less DU than the dissolved fraction,indicating that DU is primarily associated with macromolecules in dissolved fraction.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Uranium is a natural trace element present in the environmentand can be introduced by human activities, including agriculture,uranium mining, nuclear industry or military applications(Garnier-Laplace et al., 2001). Natural uranium (NU) is primarilycomposed of three isotopes, namely 234U, 235U and 238U, withwell-known relative abundances (Table 1). 236U, produced throughneutron capture by 235U, occurs as a minor isotope(236U/238U < 10�8%). Types of depleted uranium (DU) are distin-guishable by their isotopic and trace element compositions as sig-natures of their ‘‘nuclear history’’ (Hamilton, 2001). Of these types,

two are used in shielding, armor-piercing munitions, or for diversecivilian and military purposes: (i) Non-reprocessed Depleted Ura-nium (NDU), a waste product remaining after extraction of the fis-sile isotope 235U from natural uranium during enrichmentprocesses, and (ii) Reprocessed Depleted Uranium (RDU), a wasteproduct remaining after reprocessing of nuclear fuel from varioustypes of reactors using either natural or enriched uranium as anenergy source (Hamilton, 2001; Trueman et al., 2004). Like 236Uis produced during nuclear fission, RDU contains therefore 236Uin detectable quantity. This allows to identify RDU as a componentof a commercially available standard solution of uranium (Richteret al., 1999b), making 236U a convenient tracer for laboratory col-umn and batch experiments mixing natural uranium and DUsources. The typical isotopic compositions for uranium in NDUand RDU are presented in Table 1.

Table 1Typical relative mass abundances, mk

i , for uranium isotopes in natural uranium and in natural and reprocessed depleted uranium (DU) sources issued from the nuclear fuel cycle.

Isotope k 234U/238U (mass.%) 235U/238U (mass.%) 236U/238U(mass.%) Referencem234

i m235i m236

i

Uranium type iNatural U 0.0055 0.72 10�8–10�10 (Buchholz et al., 2007; Zhao et al., 1994;

Richter et al., 1999a)Non-reprocessed DU(NDU) 0.001 0.2 <10�3 (Bleise et al., 2003; Oliver et al., 2008b;

Richter et al., 1999b; Trueman et al., 2004)Reprocessed DU(RDU) 0.001 0.2–0.3 >2.10�3 (Richter et al., 1999b; Danesi et al., 2003; Jia et al., 2006)

344 S. Harguindeguy et al. / Chemosphere 103 (2014) 343–348

Fractionation of uranium isotopes exists in natural environ-ments in relation to low-temperature hydrothermal redox pro-cesses, as observed in marine environments, uranium ores orspeleothems. The anaerobic reduction of some soluble U (VI) spe-cies into insoluble U (IV) species in anoxic to euxinic (sulphidic)conditions is likely to induce fractionation of heavy U isotopes inprecipitates, leading to 235U/238U variations below 10�5 (Weyeret al., 2008; Brennecka et al., 2010). This indicates that natural frac-tionation of U isotopes is negligible in comparison with the differ-ences in isotopic composition of NU, NDU and RDU. Therefore, theisotopic composition of uranium is a powerful tool for radiologicalsurvey and impact assessment after DU contamination in soil orplants (Sansone et al., 2001; UNEP, 2001).

Many studies have examined the properties, use, health effectsand mobility of DU (Bleise et al., 2003; Briner, 2010; Handley-Sid-hu et al., 2010; Graham et al., 2011). However, the role of colloidsin the mobility of uranium in the environment is not completelyunderstood. The reduced mobility of uranium in soils and ground-water is mainly observed when the system is at thermodynamicequilibrium or under steady-state flow (Barnett et al., 2000; Donat,2010). Sorption onto mineral surfaces is then implicated as medi-ating this reduced mobility. However, it is now recognized that col-loids act as vehicles for a rapid and long-range migration ofuranium in subsurface and groundwaters (Artinger et al., 2002; Mi-bus et al., 2007). The presence of colloids in the environment war-rants their consideration in the study of uranium mobility.Inorganic colloids can play a major role in colloidal transportprocesses (Jackson et al., 2005; Claveranne-Lamolère, 2010). More-over, the colloidal organic complexes can enhance uranium migra-tion (Ranville et al., 2007; Graham et al., 2008; Crançon et al., 2010;Bryan et al., 2012). Additionally, humic substances can be adsorbedonto soil nanominerals, forming organic coatings that are likely tochange their charge and reactivity toward uranium (Murphy et al.,1992; Labonne-Wall et al., 1997; Shen, 1999). However, interac-tions between uranium and colloids are site-specific, and the pro-portions of total uranium associated with colloids ranges from 0%to 100% (Bednar et al., 2007; Arnold et al., 2011). Moreover, theproportion of remobilized uranium may be increased in soil orinterstitial waters when changes arise in flow velocity or waterchemistry. For example, a drop in ionic strength may lead to a par-tial reversibility of the sorption reactions or limited remobilizationof the uranium bound to colloids (Gabriel, 1998; Crançon et al.,2010). Therefore, the acquisition of data under controlled condi-tions is important to further understand the fate of uranium inenvironmental media.

The aim of this study was to determine the role of the colloidalphase on the mobilization and mobility of uranium in a podzolicsoil. Site investigations were conducted in a soil where limitedamounts of DU were deposited, adding to the naturally occurringuranium. To examine the mobilization processes for uranium insoil, laboratory batch leaching experiments were conducted usinga common isotopic uranium spiking method, which is fast and easyto conduct with controlled and repeatable experimental conditions.

In addition, on-site mobility of uranium was assessed from ground-water and surface water sampling and uranium isotope analysis.

2. Materials and methods

2.1. Field work

The study site is located in the wetlands of Landes Gascony,France. Pyrotechnic experiments in the context of military activi-ties using DU have led to metallic deposits on the surface of a pod-zolic soil situated on poorly mineralized fluvio-eolian sands. Thesedeposits were then continuously exposed to weathering. The stud-ied soil area overlies a surficial and shallow sandy aquifer. Themain chemical and mineralogical properties of the soil and aquiferwere previously reported (Crançon and van der Lee, 2003). The soil(taken outside of the DU-deposition area) exhibited a low NU con-tent (typically lower than 1 mg kg�1, which is typical of the NUbackground concentration for this region) and strong spatial andvertical homogeneity, except in spodic horizons where the ura-nium content can reach approximately 4 mg kg�1 (Crançon et al.,2010). The regional geochemical background in subsurface andgroundwaters is characterized by very low uranium concentra-tions, typically lower than 0.1 lg L�1. These values are among thelowest found in natural waters (Reimann and Caritat, 1998).Fig. 1 depicts a map of the site and sampling points.

The DU content in soil decreases sharply with depth. An artificialpond (point M) is located close to a drain crossing the DU-depositionarea from east to west (Fig. 1). The pond and the drain are suppliedby the drainage of soils and a shallow aquifer. The drain may beoccasionally fed by the pond water at the specific junction location.

Surface and subsurface water samples were collected from theDU-deposition area in ponds, drains and boreholes during a highflow period. 2 L of water were collected for each sample in squarebottle 1 L HDPE, and stored at 2 �C until analysis. Pond water sam-ples (point M) were collected in the immediate surroundings of theDU-deposition area. Drain water samples were collected upstream(point A), in the DU-deposition area (point C) and downstream(point E) of the site. Groundwater was sampled upstream (bore-hole P2, standing for geochemical background and also acting asa control site) and in the immediate surroundings (borehole P0)of the DU-deposition area at about 30 cm depth. Boreholesdesigned for site monitoring are approximately 15 years old.

O horizons are quite inexistent in the soils from the studies site.Soil samples were collected in the DU-deposition area (Fig. 1) inhorizon E (the most superficial soil horizon) at around 40 cmdepth. For that, a 1-m deep vertical trench was dug. Soil sampleswere stored at a temperature of 5 �C in plastic bags.

2.2. Sample analysis

For sample filtration, regenerated cellulose filters with a 1.2-lmcut off from Millipore (Bedford, MA, USA) were used as separationbetween particular and colloidal fraction. Ultrafiltration was

Fig. 1. Map of the study site and location of water samples.

S. Harguindeguy et al. / Chemosphere 103 (2014) 343–348 345

performed to separate the colloidal and dissolved phases using 10-kDa cellulose triacetate filters (Sartorius Stedim Biotech, Germany).A soft frontal filtration was used, and only the filtrates were consid-ered for analysis. The isotopic composition and total concentrationof uranium were determined by quadrupole-based inductivelycoupled plasma-mass spectrometry (ICP-MS) (Series X, Thermo-Scientific, Bremen, Germany). Mass bias effects were correctedusing standard bracketing with NBS U005 and IRMM184 as isotopicstandards (Pointurier et al., 2008). All samples were treated accord-ing to the following uranium purification method before ICP-MSanalysis: Samples were spiked with 233U and then evaporated todryness. 233U used is an isotopic reference material IRMM-057 ofvery high isotopic purity (mass fractions of impurities are:233U/U = 99.96314(14), 234U/U = 0.03537(14), 235U/U = 0.0004158(29), 236U/U = 0.00000440(14), 238U/U = 0.0016065(21))-alluncertainties are expanded with a coverage factor of 2. Thensamples were recovered with concentrated HCl, and the uraniumwas extracted on a purification column (AG1X8 resin) that waspreviously washed and conditioned with HCl solutions. Then, theuranium fraction was evaporated to dryness and recovered in2 wt.% HNO3.

The precision achieved on isotopic ratios was 2xRSD (relativestandard deviation), with RSD equal to 1% and 10% for 235U/238Uand 236U/238U respectively. Each analysis was duplicated.

2.3. Batch experiments

Batch experiments were conducted on soil material from hori-zon E after drying and sieving at 2 mm. Horizon E was studied

because it is the uppermost horizon of the soil, where surficialDU deposit lays. Experiments were systematically triplicated.Based on the methods of Claveranne-Lamolere et al. (2011), 10 gof sieved soil sample was mixed with 100 mL of synthetic rainwa-ter (liquid/solid ratio equal to 10). To reliably assess the mobiliza-tion phenomena, a raw soil subsample was spiked with syntheticRDU, which was used as a tracer. A 6 mg L�1 uranyl nitrate solution(SCP Science, Plasma Cal) was added to the soil with a liquid/solidratio of 1. The mixture was incubated for 7 d and centrifuged at4500 rpm for 30 min to remove the solution (Le Cointe, 2011).

2.4. Soil digestion in mineral acids

According to Tolu et al. (2011), the total soil uranium concentra-tion was determined after dissolution in a closed microwave sys-tem (Ethos touch control, Milestone GmbH, Shelton, USA).Approximately 0.2 g of soil was digested with an acid mixture con-taining 5 mL HNO3 (65%, Atlantic labo, Bruges, Belgium), 5 mL H2O2

(30%, Atlantic labo, Bruges, Belgium) and 2 mL HF (60%, Atlanticlabo, Bruges, Belgium). All acids used were of high purity.

2.5. Isotopic composition of uranium and source mixing calculation

In soils containing NU and DU, the isotopic composition of ura-nium was used to highlight the sources of the mixing andmigration processes (Oliver et al., 2006; Buchholz et al., 2007).DU isotopic composition was considered, taking into account that(i) NDU is characterized by low 235U/238U, 234U/238U and236U/238U mass ratios typically lower than 0.2%, 0.001% and

Table 2Concentrations of uranium and percentages of total uranium and depleted uranium insoil and the colloidal and dissolved leachate fractions.

Unspiked soil Spiked soil

Total soil[U] (mg kg�1) 0.98 ± 0.01 6.4 ± 0.1fDU (%) 25 ± 2 85 ± 6

Total leachate[U] (lg L�1) 8.9 ± 0.2 94 ± 1Uleached/Utotal soil (%) 8.1 ± 0.4 15 ± 1fDU (%) 85 ± 6 96 ± 7

Colloidal fraction (1.2 lm–10 kDa)Ucolloidal/Uleached (%) 80 ± 2 89 ± 2fDU (%) 85 ± 6 96 ± 7

Dissolved fraction (<10 kDa)Udissolved/Uleached (%) 20 ± 1 11 ± 1fDU (%) 100 ± 6 98 ± 8

346 S. Harguindeguy et al. / Chemosphere 103 (2014) 343–348

0.001%, respectively, and (ii) RDU is characterized by 235U/238U and234U/238U mass ratios typically lower than 0.3% and 0.001%, respec-tively, and by a significant proportion of 236U. Therefore, the rela-tive DU concentration, fDU, calculated from mass balance ofuranium isotopes, can give information on the presence of non-natural uranium in an environmental sample (Bleise et al., 2003;Oliver et al., 2008a). Thus, the uranium migration processes in acontaminated soil can be traced (Graham et al., 2011).

In complex systems, where natural uranium and n sources ofDU coexist such as NDU and RDU, the mass ratio between anyisotopes of uranium, kU, out of 238U can be written as follows:

kU238U

� �¼

kUNat þ kU1 þ kU2 þ � � þkUn238UNat þ 238U1 þ 238U2 þ � � þ238Un

¼kUNat þ

Pni¼1

kUi

kUNat þPn

i¼1238Ui

ð1Þ

fDU in the sample is the sum of all contributions of individual DUsources to the global isotopic composition of uranium:

f DU ¼Xn

i¼1

Ui

UNat þPn

i¼1Ui

� �ð2Þ

Ui is the total mass of uranium from a single DU source, i, in thesample.

In addition, the relative abundance of any isotope, kU, out of thetotal quantity of uranium in each individual source, i, is:

kUi ¼mki � Ui ð3Þ

Typical relative mass abundances, mki , for uranium isotopes in

NU, NDU and RDU are presented in Table 1.The combination of equations 1, 2 and 3 gives the expression of

the mass ratio of any uranium isotope, kU, out of the dominant iso-tope 238U as a function of the relative abundances of isotope kU inany sources of DU present in the system, mk

i . Hence, a system of kequations with n principal variables fDUi and k parameters kU/238Uis obtained:

kU238U

� �m238

Nat 1�Xn

i¼1

f DUi

!þXn

i¼1

m238i � f DUi

" #

¼ mkNat 1�

Xn

i¼1

f DUi

!þXn

i¼1

mki � f DUi

" #ð4Þ

This equation can be easily solved when the number of consid-ered isotopes is equal to the number of DU sources (i.e., k = n),neglecting high-powered, cross-over terms. For the study site,the system is ternary, constituted by a mixing of NU, NDU andRDU. Eq. (4) can be solved considering 238U, 235U and 236U andthe isotopic compositions of NDU and RDU, such as those pre-sented in Table 1. The corresponding expression of fDU obtained is:

f DU ¼�0:273 238U

238Uþ 0:00198þ 10:40 236U238U

0:000494 236U238Uþ 0:00156 236U

238Uþ 0:00153ð5Þ

Eq. (5) was used for the calculation of fDU under percentagesand for the estimation of DU content in soil, water samples andleachates. The term ‘‘DU’’ is used later onto qualify the general pol-luted source of the area study (i.e. a combination of NDU and RDU).

Moreover, soil surficial layers and aquifer conditions (low-tem-perature, suboxic to anoxic) from Landes Gascony typical of thissite can be close to those that are likely to induce fractionationof heavy U isotopes in precipitates. However, the variations of235U/238U resulting from fractionation are likely to be orders ofmagnitudes below variations in uranium isotopic composition in-duced by the mixing of NU with various sources of DU. Therefore,

in this study, the isotopic composition of uranium dominantlyhighlights the migration processes of DU through soil towardgroundwaters.

3. Results and discussion

The role of the colloidal phase in the mobilization and migrationof uranium in soil was investigated through two complementarysteps. The mobilization of uranium was examined by batch soilleaching experiments, conducted under controlled conditionsinvolving specific isotopic composition, while the transport ofuranium was investigated using results from the site survey.

3.1. Uranium mobilization

The first set of experiments (raw unspiked soil) was conductedon the bulk soil obtained from the DU-deposition area. A secondset of experiments (spiked soil subsample) was conducted on araw soil subsample, which was previously spiked with uraniumof a specific isotopic composition before the leaching. The resultsare presented in Table 2.

After digestion in mineral acids, the bulk surface soil sampledfrom the DU marked area exhibited 25% DU content. From thebatch experiments conducted on raw soil, 8% of the total uraniummass initially present in the soil was leached. Mobilization of ura-nium is thus quite limited, confirming the low reversibility of ura-nium adsorption onto soil materials. This observation is consistentwith previous studies conducted using the same soil (Crançonet al., 2010). Another observation is that the DU content in theleachate (85%) is higher than the DU content in bulk soil (25%). LikeNU is mainly situated in clayey and organic aggregates rather thanin the silica matrix of the sand grains, it has been shown that itsdistribution is mediated by finer granulometric fractions (Crançonand van der Lee, 2003). Therefore, fractionation between NU from asilica matrix and DU from organo-clayey aggregates should not ac-count for the observed increasing DU content in the leachate in thepresent study. These data suggest a larger remobilization of DUfrom deposits initially sorbed onto soil materials as opposed toNU of geological origin.

From batch experiments carried out with spiked soil subsam-ples, a strong uranium immobilization also occurred, despite thisuranium was expected to be easily mobilized. Indeed, only 15%of this uranium was released during batch experiment leaching.The results obtained here could be explained by a weak associationbetween DU from the spike and the soil materials, suggesting thatthe strength and the reversibility of uranium retention on organo-clayey aggregates are different depending on the origin of uranium

S. Harguindeguy et al. / Chemosphere 103 (2014) 343–348 347

and/or soil organo-clayey aggregate structure and maturity.Therefore, a unique mechanism could not address the global sorp-tion/desorption processes for uranium in soil. Similar observationswere made for the DU association with labile complexes that en-hance uranium mobility in soils from Southern Serbia (Radenkovicet al., 2008).Approximately 80% of the uranium leached duringbatch experiments was in colloidal form (10 kDa–1.2 lm), while20% was in the dissolved phase (<10 kDa) (Table 2). These resultsare in agreement with observations conducted on a clay-loam soil(Oliver et al., 2008a; Graham et al., 2011) indicating that at least90% of the mobilized uranium was associated with colloids. Theseresults highlight the importance of the colloidal fraction in themobilization of uranium. In addition, the percentages of DU werecalculated in the colloidal and dissolved fractions of the leachates(Table 2). It appears that DU predominates in both fractions, as ob-served for the mobilization of uranium from soil during leachingtests. Additionally, all of these results suggest that NU is mainlyassociated with the non-mobile coarser fractions of the soil. TheDU percentage in the colloidal fraction is slightly less than in thedissolved fraction, suggesting that macromolecules in dissolvedfraction can be dominantly responsible for the complexation ofDU in the soil leachate. Graham et al. (2011) obtained similarresults in a clayey-loamy soil.

3.2. Uranium migration

The uranium mobility assessment for the field is based on mea-surements in surface and groundwaters of the total uranium con-centration in the aqueous phase, including colloidal anddissolved phases, and the corresponding DU content (fDU) in thetotal, colloidal and dissolved fractions (Table 3).

In the soils from the DU-deposition area, the bulk total U con-centration and DU content are susceptible to local variation be-cause of the nugget effect related to the scattering of pellets (i.e.when a strong variability of soil U content is observed, due to theheterogeneous distribution of uranium pellets at the soil’s surface)(Crançon et al., 2010). Therefore, the observation of fDU varying ingroundwater from <8% (in P2) to 74% (in P0) together with totalaqueous concentrations of <0.1–0.29 lg L�1 is not surprising be-cause the heterogeneity of DU deposits in soil would not be ex-pected to lead to a homogeneous uranium plume in the shallowaquifer. These concentrations are just above the regional baselinefor uranium in groundwater (0.01–0.05 lg L�1), suggesting a lim-ited enhanced mobility from soils (Crançon et al., 2010). However,water sampling occurred during a high-flow period, indicating thathigher concentrations could be expected during low-flow condi-tions as observed in a previous study reporting maximum concen-trations up to 150 lg L�1 (Crançon et al., 2010). An apparent

Table 3Uranium concentrations, percentages and DU percentages in surface and groundwaters in

Surface water

Geochemical background Drainwaters Pondw

A C E

Total aqueous[U] (lg L�1) 0.06 ± 0.04 0.20 ± 0.01 0.76 ± 0.01 0.66 ±fDU (%) <8a 19 93 88Colloidal fraction (1.2 lm–10 kDa)Ucolloidal (%) – 10 ± 2 15 ± 1 17 ± 1fDU (%) 17 86 100Dissolved fraction (<10 kDa)Udissolved (%) – 90 ± 2 85 ± 1 83 ± 1fDU (%) 16 89 86

a Maximum value of geochemical background fDU derived from detection limits on u

contradiction arises when considering both the low uraniumconcentration and the high DU content observed in P0: uraniumtransfer from soil to the aquifer is assumed to be limited in bulkquantity but produces a strong enrichment of DU. This findingdemonstrates that an assessment based on the criteria of totalaqueous uranium concentrations alone may not account for a cor-rect estimation of the importance of DU mobilization through soil.

In groundwater, the percentage of uranium in the colloidal frac-tion is significant (68% and 90% in borehole P0 and P2, respec-tively); therefore, colloid-bound uranium dominates thedistribution of uranium in groundwater. These results are in agree-ment with observations from the soil leaching experiments where80–89% of uranium in leachate was present in the colloidalfraction.

In drain waters, total aqueous concentrations for uranium andDU increase when crossing the DU-deposition area and then de-crease downstream (Table 3). The highest uranium concentrationsand the highest DU content are found in or near the pond located inthe DU-deposition area (point M).

Isotopic composition and total uranium concentration indicatethat almost 100% of uranium in pond water is of anthropogenicorigin.

In the surface waters (Table 3), the percentage of colloidal ura-nium is generally lower (between 10% and 32%) than in groundwa-ter, which is consistent with the results obtained fromgroundwater and soil leaching tests that indicate a leading roleof colloids in the migration of uranium through soil and aquifers.In drain waters, the percentage of colloidal uranium continuouslyincreases downstream from point A toward point E. This increasecan be attributed to the contribution of groundwaters to the com-position of drain waters. Indeed, these waters contain 5 times morecolloidal uranium than drain waters, and this contribution is con-tinuous throughout the drain, as showed by a complementaryhydrological monitoring. In addition, no important change in Eh(around 300 mV), pH (from 6 to 7), and conductivity (around150 lS cm�1) was observed from point A to point C.

The surface water DU content does not exhibit differences be-tween total, colloidal and dissolved fractions, in contrast togroundwater where the colloidal fraction contains less DU thanthe dissolved fraction (Table 3). This observation is similar to re-sults found in leaching tests where DU is mainly associated withsmall-sized colloids as opposed to NU that mainly associates withcoarser fractions.

4. Conclusion

The mobilization and migration of uranium were investigatedin a podzolic soil where limited amounts of DU were deposited.

the total aqueous phase and in the colloidal and dissolved fractions.

Groundwaters

aters Geochemical background P0 P2

M

0.01 8.1 ± 0.1 0.06 ± 0.03 0.19 ± 0.004 0.29 ± 0.0198 <8a 74 <8

32 ± 1 – 68 ± 2 90 ± 2100 74 5

68 ± 1 – 32 ± 2 10 ± 292 83 12

ranium isotope characterization by ICP-MS on low uranium concentration waters.

348 S. Harguindeguy et al. / Chemosphere 103 (2014) 343–348

Batch lixiviation experiments indicate that approximately 8–15%of uranium is desorbed from the soil, with approximately 80% ofuranium associated with the colloidal fraction in soil leachates.Moreover, the DU fractionation between the soil and leachate con-tributes evidence for an enhanced mobilization of ‘‘anthropogenic’’uranium (more than ‘‘native’’ uranium).

Field monitoring indicates a vertical migration of DU throughsoil, followed by a lateral transport in ground and then surfacewaters. Colloidal transport of uranium ranges from significant insurface waters to dominant in groundwaters. These results are inagreement with those obtained in batch-leaching experiments.

Furthermore, macromolecules in dissolved fractions are likelyto dominate for DU, although native uranium is mainly associatedwith coarser fractions

This study clearly highlights the role of colloids in uraniummigration. Nevertheless, a sound comprehension of the structureof uranium-bonding colloids is still needed. A thorough study onthe characterization of leachates and water colloids is in progress.

Acknowledgements

Funding for this research was provided by the Atomic EnergyCommission (CEA) within the frame of the Environment Project.Moreover, the authors thank François Renard (DEA/DAM) for hiscareful review of the fDU calculation; Amélie Hubert and Anne-Claire Pottin (CEA/DAM) for isotopic measurement support; andMarie-Hélène Tailleur and Nathalie Bouillard (CEA/DAM) for theirhelp in field investigations.

References

Arnold, T., Baumann, N., Krawczyk-Bärsch, E., Brockmann, S., Zimmermann, U., Jenk,U., Weiß, S., 2011. Identification of the uranium speciation in an undergroundacid mine drainage environment. Geochimica et Cosmochimica Acta 75, 2200–2212.

Artinger, R., Rabung, T., Kim, J.I., Sachs, S., Schmeide, K., Heise, K.H., Bernhard, G.,Nitsche, H., 2002. Humic colloid-borne migration of uranium in sand columns. J.Contam. Hydrol. 58, 1–12.

Barnett, M.O., Jardine, P.M., Brooks, S.C., Selim, H.M., 2000. Adsorption and transportof uranium(VI) in subsurface media. Soil Sci. Soc. Am. J. 64, 908.

Bednar, A.J., Medina, V.F., Ulmer-Scholle, D.S., Frey, B.A., Johnson, B.L., Brostoff, W.N.,Larson, S.L., 2007. Effects of organic matter on the distribution of uranium in soiland plant matrices. Chemosphere 70, 237–247.

Bleise, A., Danesi, P.R., Burkart, W., 2003. Properties, use and health effects ofdepleted uranium (DU): a general overview. J Environ Radioact 64, 93–112.

Brennecka, G.A., Borg, L.E., Hutcheon, I.D., Sharp, M.A., Anbar, A.D., 2010. Naturalvariations in uranium isotope ratios of uranium ore concentrates:Understanding the 238U/235U fractionation mechanism. Earth Planet. Sci.Lett. 291, 228–233.

Briner, W., 2010. The Toxicity of Depleted Uranium. Int. J. Environ. Res. PublicHealth 7, 303–313.

Bryan, N.D., Abrahamsen, L., Evans, N., Warwick, P., Buckau, G., Weng, L., VanRiemsdijk, W.H., 2012. The effects of humic substances on the transport ofradionuclides: recent improvements in the prediction of behaviour and theunderstanding of mechanisms. Appl. Geochem. 27, 378–389.

Buchholz, B.A., Brown, T.A., Hamilton, T.F., Hutcheon, I., Marchetti, A., Martinelli, R.,Ramon, E., Tumey, S.J., Williams, R.W., 2007. Investigating uranium isotopicdistributions in environmental samples using AMS and MC-ICPMS. Nucl.Instrum. Method. Phys. Res. Sect. B: Beam Interact. Mater. Atom., 733–738.

Claveranne-Lamolère, C., 2010. Evaluation et caractérisation des interactionscolloïdes-actinides dans les sols par une approche multi-technique: exemplede l’uranium en milieu carbonaté. Université de Pau et des Pays de l’Adour.

Claveranne-Lamolere, C., Aupiais, J., Lespes, G., Frayret, J., Pili, E., Pointurier, F.,Potin-Gautier, M., 2011. Investigation of uranium-colloid interactions in soil bydual field-flow fractionation/capillary electrophoresis hyphenated withinductively coupled plasma-mass spectrometry. Talanta 85, 2504–2510.

Crançon, P., Pili, E., Charlet, L., 2010. Uranium facilitated transport by water-dispersible colloids in field and soil columns. Sci. Total Environ. 408, 2118–2128.

Crançon, P., van der Lee, J., 2003. Speciation and mobility of uranium(VI) in humic-containing soils. Radiochimica Acta 91, 673–679.

Danesi, P.R., Bleise, A., Burkart, W., Cabianca, T., Campbell, M.J., Makarewicz, M.,Moreno, J., Tuniz, C., Hotchkis, M., 2003. Isotopic composition and origin ofuranium and plutonium in selected soil samples collected in Kosovo. J. Environ.Radioactiv. 64, 121–131.

Donat, R., 2010. Adsorption and thermodynamics studies of U(VI) by compositeadsorbent in a batch system. Ionics 16, 741–749.

Gabriel, U., 1998. Transport reactif de l’uranyle; mode de fixation sur la silice et lagoethite; experiences en colonne et reacteur fermé; simulations. UniversitéJoseph Fourier Grenoble.

Garnier-Laplace, J., Colle, C., Morello, M., 2001. Fiche radionucléide: uraniumnaturel et environnement.

Graham, M.C., Oliver, I.W., Mackenzie, A.B., Ellam, R.M., Farmer, J.G., 2008. Anintegrated colloid fractionation approach applied to the characterisation ofporewater uranium-humic interactions at a depleted uranium contaminatedsite. Sci. Total Environ. 404, 207–217.

Graham, M.C., Oliver, I.W., MacKenzie, A.B., Ellam, R.M., Farmer, J.G., 2011.Mechanisms controlling lateral and vertical porewater migration of depleteduranium (DU) at two UK weapons testing sites. Sci. Total Environ. 409, 1854–1866.

Hamilton, E., 2001. Depleted uranium (DU): a holistic consideration of DU andrelated matters. Sci. Total Environ. 281, 5–21.

Handley-Sidhu, S., Keith-Roach, M.J., Lloyd, J.R., Vaughan, D.J., 2010. A review of theenvironmental corrosion, fate and bioavailability of munitions grade depleteduranium. Sci. Total Environ. 408, 5690–5700.

Jackson, B.P., Ranville, J.F., Bertsch, P.M., Sowder, A.G., 2005. Characterization ofcolloidal and humic-bound Ni and U in the ‘‘dissolved’’ fraction of contaminatedsediment extracts. Environ. Sci. Technol. 39, 2478–2485.

Jia, G., Belli, M., Sansone, U., Rosamilia, S., Gaudino, S., 2006. Concentration andcharacteristics of depleted uranium in biological and water samples collected inBosnia and Herzegovina. J. Environ. Radioact. 89, 172–187.

Labonne-Wall, N., Moulin, V., Vilarem, J.-P., 1997. Retention properties of humicsubstances onto amorphous silica : consequences for the sorption of cations.Radiochimica acta 79, 37–49.

Le Cointe, P., 2011. Impact des colloïdes sur le transport de l’Uranium appliqué à lanappe phréatique du Centre de Stockage FMA de l’Aube. Thèse de l’EcoleNationale Supérieure des Mines de Paris, Fontainebleau.

Mibus, J., Sachs, S., Pfingsten, W., Nebelung, C., Bernhard, G., 2007. Migration ofuranium(IV)/(VI) in the presence of humic acids in quartz sand: a laboratorycolumn study. J. Contam. Hydrol. 89, 199–217.

Murphy, E.M., Zachara, J.M., Smith, S.C., Phillips, J.L., 1992. The sorption of humicacids to mineral surfaces and their role in contaminant binding. Sci. TotalEnviron. 117–118, 413–423.

Oliver, I.W., Graham, M.C., Mackenzie, A.B., Ellam, R.M., Farmer, J.G., 2008a.Distribution and partitioning of depleted uranium (DU) in soils at weaponstest ranges - investigations combining the BCR extraction scheme and isotopicanalysis. Chemosphere 72, 932–939.

Oliver, I.W., Graham, M.C., MacKenzie, A.B., Ellam, R.M., Farmer, J.G., 2008b.Depleted uranium mobility across a weapons testing site: isotopic investigationof porewater, earthworms, and soils. Environ. Sci. Technol. 42, 9158–9164.

Oliver, I.W., Mackenzie, A.B., Ellam, R.M., Graham, M.C., Farmer, J.G., 2006.Determining the extent of depleted uranium contamination in soils at aweapons test site: An isotopic investigation. Geochimica et Cosmochimica Acta70, A457.

Pointurier, F., Hubert, A., Baglan, N., Hémet, P., 2008. Evaluation of a new generationquadrupole-based ICP-MS for uranium isotopic measurements inenvironmental samples. J. Radioanal. Nucl. Chem. 276, 505–511.

Radenkovic, M.B., Cupac, S.A., Joksic, J.D., Todorovic, D.J., 2008. Depleted uraniummobility and fractionation in contaminated soil (Southern Serbia). Environ. Sci.Pollut. Res. Int. 15, 61–67.

Ranville, J.F., Hendry, M.J., Reszat, T.N., Xie, Q., Honeyman, B.D., 2007. Quantifyinguranium complexation by groundwater dissolved organic carbon usingasymmetrical flow field-flow fractionation. J. Contam. Hydrol. 91, 233–246.

Reimann, C., Caritat, P. de, 1998. Chemical elements in the environment: factsheetsfor the geochemist and environmental scientist. Springer.

Richter, S., Alonso, A., De Bolle, W., Wellum, R., Taylor, P.D., 1999a. Isotopic‘‘fingerprints’’ for natural uranium ore samples. Int. J. Mass Spectrom. 193, 9–14.

Richter, S., Alonso, A., Wellum, R., Taylor, P.D.P., 1999b. The isotopic composition ofcommercially available uranium chemical reagents. J. Anal. At. Spectrom. 14,889–891.

Sansone, U., Danesi, P.R., Barbizzi, S., Belli, M., Campbell, M., Gaudino, S., Jia, G.,Ocone, R., Pati, A., Rosamilia, S., Stellato, L., 2001. Radioecological survey atselected sites hit by depleted uranium ammunitions during the 1999 Kosovoconflict. Sci. Total Environ. 281, 23–35.

Shen, Y.-H., 1999. Sorption of natural dissolved organic matter on soil.Chemosphere 38, 1505–1515.

Tolu, J., Le Hécho, I., Bueno, M., Thiry, Y., Potin-Gautier, M., 2011. Seleniumspeciation analysis at trace level in soils. Anal. Chim. Acta 684, 126–133.

Trueman, E.R., Black, S., Read, D., 2004. Characterisation of depleted uranium (DU)from an unfired CHARM-3 penetrator. Sci. Total Environ. 327, 337–340.

UNEP, 2001. Depleted uranium in Kosovo, post-conflict environmental assessment.United Nations Environment Program, Switzerland.

Weyer, S., Anbar, A.D., Gerdes, A., Gordon, G.W., Algeo, T.J., Boyle, E.A., 2008. Naturalfractionation of 238U/235U. Geochimica et Cosmochimica Acta 72, 345–359.

Zhao, X.-L., Nadeau, M.-J., Kilius, L., Litherland, A., 1994. The first detection ofnaturally-occurring 236U with accelerator mass spectrometry. Nucl. Instrum.Methods Phys. Res. Sect. B: Beam Interact. Mater. At., 249–253.