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Journal of Environmental Radioactivity 125 (2013) 74e80

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Journal of Environmental Radioactivity

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

Fate and transport of radiocesium, radiostrontium and radiocobalt onurban building materials

K. Maslova a, I. Stepina a, A. Konoplev a,*, V. Popov a, A. Gusarov a, F. Pankratov a, S.D. Lee b,N. Il’icheva a

aRPA “Typhoon”, Centre for Environmental Chemistry, Pobedy St. 4, Obninsk, Kaluga Region 249038, RussiabNational Homeland Security Research Center, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA

a r t i c l e i n f o

Article history:Received 15 January 2013Accepted 19 January 2013Available online 9 February 2013

Keywords:RadiocesiumRadiostrontiumRadiocobaltBuilding materialsDistribution coefficientPenetration

* Corresponding author. Tel.: þ7 48439 71896; fax:E-mail addresses: konoplev2002@mail.ru, konoplev

0265-931X/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jenvrad.2013.01.013

a b s t r a c t

Kinetics of 137Cs, 60Co and 85Sr sorption on powdered building materials in aqueous suspensions at 20 �Cfor interaction times of 1, 7, 14 and 28 days were studied. The 137Cs distribution coefficient (Kd) values forall building materials except limestone practically did not change during 28 days of sorption. The Kd

(85Sr) was several orders of magnitude lower than for 60Co. The highest values were observed for asphaltand granite. An effective method to study the radionuclide distribution in depth of building materialsusing layer-by-layer sanding was developed. Using the developed method, the 137Cs, 60Co and 85Srdistribution with depth of selected building materials at different air humidity, time and temperaturewas studied. Relative humidity (RH) was found to influence significantly the 85Sr depth distribution inthe case of granite (unlike 137Cs and 60Co). While 85Sr penetrated to 0.5 mm in depth of granite at RH 30%,at RH 87% the depth of 85Sr penetration to granite reached up to 7 mm.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

The previous experience from radiological accidents shows thatthere can be a hazard fromcontamination of the urban environmentby long-lived radionuclides such as radiocesium, radiostrontiumand radiocobalt. These radionuclides are also believed to be poten-tial agents that may be used in radiological dispersal devices in actsof terrorism. Basically there are two main ways of decreasing thecontaminatione natural attenuation and artificial decontamination(IAEA, 2006; Hille et al., 1988). The natural attenuation processes onurban materials include radioactive decay, run-off, short-termweathering and long-termweathering. Theseweathering processesgreatly depend on the meteorological conditions. A better under-standing of the interactions of radionuclideswith buildingmaterialsunder varied atmospheric conditions will help increase the effec-tiveness of artificial decontamination methods.

The objective of this study was to investigate the fate andtransport of water soluble radiocesium, radiostrontium and radio-cobalt in common urban building materials. For this purpose it isnecessary to determine the kinetics of radionuclide sorption onpowdered building materials in aqueous suspensions and the

þ7 48439 44204.@obninsk.com (A. Konoplev).

All rights reserved.

radioactive migration profile (penetration) into urban buildingmaterials at various times and under various environmental con-ditions (such as temperature and relative humidity (RH)).

The depth distribution of radionuclide in a porousmedium, suchas thebuildingmaterials,maybedescribedusing anequation for thediffusion into a homogenous semi-infinite medium (Hu and Wang,2003). The transport equation includes an effective diffusion coef-ficientwhich depends on the dimensionless retardation factor (R). Itaccounts for the interaction of the dissolved radionuclide with theporous medium and is calculated as R¼ 1þ(Kdrb)/q, where Kd is theequilibrium distribution coefficient; q is the volumetric water con-tent and rb is the bulk density. Hence, the radionuclide diffusion intobuilding material greatly depends on the sorption of the radio-nuclide (the higher the radionuclide distribution coefficient is, theslower the radionuclide diffusion).

The radionuclide sorption by building materials can be influ-enced by a number of factors. Firstly, it depends on a concentrationof cations competing with the radionuclide in the pore solution.The higher the concentration is, the lower the initial sorption ofradionuclide. Secondly, the radionuclide sorption can change overtime due to dissolution of the building material matrix which leadsto an increase in the concentration of dissolved competing cations.Considering the variability of physico-chemical properties ofbuilding materials, the time of establishing the sorption equilib-rium, for example for 137Cs, varies from 1 to 3 days to one month(Wang et al., 2009; Tsai et al., 2008; Park and Hahn, 1999; Lee et al.,

K. Maslova et al. / Journal of Environmental Radioactivity 125 (2013) 74e80 75

2008; Rudin et al., 2005; Real et al., 2002). The sorption charac-teristics are essential for modeling and understanding of radio-nuclide penetration into building materials.

The ability of building materials to bind radionuclides can bejudged by Kd values in the system “powdered building material-solution” obtained in batch experiments. Quantitatively, the Kdvalues will not be those occurring in the actual porous medium ofbuilding materials, nevertheless the proportion is assumed to bethe same as in case of the batch experiment with powdered ma-terials (Atkinson and Nickerson, 1988).

To study the radionuclide depth distribution two methods areusually used: sawing of a sample into layers of given thickness, andgrinding followed by determination of radionuclide content in theremovedmaterial (Atkinson and Nickerson,1988; Allard et al.,1985).One of the grindingmethods consists in grinding fairly large volumesof a sample in closedpolyethylenebagswith furtherdeterminationofradioactivity in the collected dust (Zlobenko et al., 2002). Using thismethod, however, can lead to contamination of the clean surface ofa sample and associated materials, which causes an error in deter-mining the radionuclide distribution profile. Therefore, it becamenecessary to develop a simple and effective method for determiningthe radionuclide depth distribution in building materials.

2. Materials and methods

2.1. Sample description and analytical methods

The radionuclides studied were three key long-lived radionu-clides 137Cs (Eg ¼ 662 keV), 60Co (Eg ¼ 1332 keV) and 85Sr(Eg ¼ 514 keV). 85Sr was used as analog of 90Sr because the firstradionuclide has a shorter half-life and is a gamma-emitter whichmakes its measurement easier and experiments safer.

Five different building materials were used in this study and thematerial information is described in Table 1. Test coupons[3 cm � 3 cm � 3 cm (W � L � H)] were prepared using a diamondsaw (1400 Brick Xtreme BX3 model 157721, MK Diamond Products,Inc. Torrance, CA) with distilled water as the lubrication fluid. Eachcoupon was inspected visually to find any defects, cracks, or stains.Coupons with any defects noticed during visual inspection werediscarded. Coupons were dried in an oven at 80 �C with slightnegative pressure (w25 cm Hg) for 24 h; coupon dimensions andweight were then recorded. Five sides of each coupon were sealedwith water-impermeable sealant (Stonelok� E3, Richard JamesSpecialty Chemicals Corp., Hastings-on-Hudson, NY). The top sur-face remained unsealed for deposition of the radioactive material.

Table 1Building material descriptions and sources.

Material Description Locality Source

Red brick Red, fine-grained Made fromNorth Carolinared Triassic clay

Triangle BrickCompany Durham,North Carolina

Limestone Light-gray, coarse-grained,w75% skeletal grains,remainder calcite cementand trace (1%) quartz,dolomite, pyrite, clay

South centralIndiana

Cathedral StoneProducts HanoverPark, Maryland

Granite Pink with dark banding,medium-coarse texture,biotite

Mount Airy,North Carolina

Triangle BrickCompany Durham,North Carolina

Concrete Cement with sandaggregate

Concrete premix(QUIKRETE�

Atlanta, GA)

Home DepotDurham, NorthCarolina

Asphalt Laboratory PressedAsphalt

N/A North CarolinaDepartment ofTransportation

The brick sample contained predominantly 44% quartz and 28%hematitewith trace quantity of carbonateminerals. Observations ofthe limestone thin section enabled classification of the rock asa fossiliferous carbonate grainstone. Fossil fragments were diverseand generally moderately well sorted with very little carbonatemud matrix. Grains were cemented with coarse calcite (rockcomposition was 98% calcite). The granite rock was a granodioritewith plagioclase feldspar predominant over potassium feldspar.Quartz with minor amounts of mafic minerals (hornblende andbiotite mica) comprised the balance of the sample. Quartz was thepredominant component of concrete with minor amounts of illiteclay (3%) and carbonate minerals (calcite, 5%; dolomite, 1%; siderite,2%). The asphalt consisted of 34.8% binder and 62.0% grains ofmultiple types including quartz and feldspar as well as sedimentaryand metamorphic rock fragments.

The procedure for preparing powdered samples includedcrushing the building material coupons to the pieces of 5e10 mmdiameter. These were ground in a porcelain mortar and threeparticle-size fractions were obtained by sieving: <0.125; 0.125e0.25; >0.25 mm.

The exchangeable (pHKCl) acidity was determined by knownprocedures (Gorbyleva et al., 2000). Organic carbon was deter-mined by the wet combustion method (GOST (State Standard)262113-91). The cation exchange capacity (CEC) was determinedby the BaCl2 method at pH 6.5 (GOST 17.4.4.01-84). Loss on ignition(LOI) was determined at 1000 �C. The porosity, particle and bulkdensity were determined by water saturation.

2.2. Determination of 137Cs, 85Sr, and 60Co distribution coefficientsfor building materials in aqueous suspensions

The methodology for determining the kinetics of radionuclidesorption by building materials based on the batch method was asfollows. The polycarbonate centrifuge tubes of 80 mL were filledwith 1 g of air-dried powdered building material sample (fraction<0.125 mm). To obtain a contact solution with the composition ofcations characteristic of building materials, 50 mL of deionizedwater was added to the centrifuge tubes and these suspensionswere shaken on the to-and-fro shaker for 1 h. Then radioactivesolution of 137Cs (w1mL, A0 ¼ 2.0e4.6 kBq), 85Sr (w1mL, A0 ¼ 1.7e2.4 kBq), or 60Co (from 1 up to 2.5 mL, A0 ¼ 4.1e8.8 kBq) was addedto the centrifuge tubes. The tubes were continuously shaken at20 � 1 �C. At regular times (after 1, 7, 14 and 28 days) thesamples were centrifuged for 30 min at 3000 r.p.m. Using anacetate cellulose membrane syringe filter Rotilabo� P819.1 (CarlRoth GmbH þ Co, Germany) with the pore diameter <0.45 mm,40 mL of the supernatant liquid was taken from each centrifugetube and transferred to the measuring vials (2 vials of 20 mL).The radionuclide activity concentration of the solution in vialswas measured with a gamma-counter Wizard 1480 (PerkinElmer/Wallac, Finland). The counter has a well-type detector(NaI(Tl), its height is 80 mm and diameter is 75 mm). The detectorassembly is surrounded by a minimum of 50 mm of lead shieldingabove and below. Normalization of the counter is made in a timeperiod of six months, unless the instrument gives a warning askingfor the normalization. Measurements included the dead time andbackground automatic corrections. Counting time was set to obtainrelative standard deviation <10%. Two replicates were done foreach building material under study. The instrument calibrationwasdone before each series of measurements using a standard ofknown activity. Kd was calculated as a ratio of sorbed radionuclidein the solid phase to its activity concentration in the liquid phase.The activity of the radionuclide in the solid phase was calculated asa difference in its activity in the solution before and after the batchexperiment.

Fig. 1. Sequence of steps for sanding building material (see text for explanation).

K. Maslova et al. / Journal of Environmental Radioactivity 125 (2013) 74e8076

2.3. Determination of radionuclide distribution in depth of buildingmaterials using layer-by-layer sanding

A total of 25 mL of radionuclide water solution (137Cs, 85Sr, or60Co) was applied to the top unsealed surface of the samples usingthe syringe MicroSprayer IA-1C (Penn-Century, Inc., Windmoor,PA USA). The applied activity varied from 51 to 255 Bq for 137Cs(the median value being 122 Bq), from 300 to 2230 Bq for 60Co (themedian value being 817 Bq), and from 170 to 3800 Bq for 85Sr (themedian value being 930 Bq). The samples were stored in desicca-tors at the air relative humidity (RH) 30% (with calcium chloride)and 87% (with barium chloride) for 1 and 28 days after radionuclideapplication to the surface. For determination of the radionuclidedepth distribution in the sample the sandpaper No 25 or 40 wasused. The sequence of building material sanding steps is shown inFig. 1 (Gusarov et al., 2011). The contaminated coupons wereground against a piece of sandpaper (3 cm � 10 cm), which wasthen rolled to fit into a sample holder. Next the sandpaper samplewas counted for radioactivity in gamma-counter Wizard 1480.

The thickness of the ground layer Dhn was calculated by theground layer mass which was calculated by the difference betweenthe sample mass prior to sanding (n � 1) and following sanding (n)based on the equation (1), the initial length andmass of the sample,assuming that the cross section area and sample density did notchange with height:

Dhn ¼ mn�1 �mn

M0$Ho; (1)

where mn�1 and mn were the mass of the sample prior to sandingand following sanding of layer n, g, M0 was the initial mass of thesample, g; H is the initial height of the sample, mm. After the ac-tivity of the layer An was measured with the gamma-counterWizard 1480, the experimental results were presented as a rela-tionship of the relative activity of radionuclide in the ground layerFn ¼ An/A0, where A0 is the applied activity of radionuclide, and theground material thickness hn:

FnDh�1n ¼ f ðhnÞ (2)

where hn ¼ Pn�1n¼1 Dhn þ Dhn=2:

Table 2Physico-chemical properties of building materials.

CEC, cmol(þ)/kg rOKCl Loss on ignition, % Organic

Concrete 6.4 � 0.5 12.5 11.26 � 0.01 0.36 �Granite 5.9 � 0.6 9.7 0.238 � 0.001 0.092 �Limestone 3.3 � 0.4 9.6 20.2 � 1.8 0.092 �Asphalt 8.8 � 0.4 9.5 5.78 � 0.08 2.9 �Brick 6.9 � 0.1 10.5 1.14 � 0.05 0.30 �

3. Results and discussion

3.1. Physico-chemical properties and mineral composition ofbuilding materials

Studied physico-chemical properties of the materials are shownin Table 2. The highest porosity was for brick and concrete (about20% of the material volume). The lowest porosity was characteristicof granite (about 1.5%). All of the building materials had alkaline pHrate (pHKCl changed from 9.5 to 12.5). The content of organic carbon(Corg) in the materials was low and varied from 0.092% (in graniteand limestone) to 2.9% in asphalt. The cation exchange capacity(CEC) of the samples varied from 3.3 cmol(þ)/kg (limestone) to8.8 cmol(þ)/kg (asphalt). The maximum loss on ignition (LOI) wasobserved in limestone e 20%, which might be caused by highcontent of carbonates.

3.2. Change in the distribution coefficient, Kd, with time ofradionuclides (137Cs, 85Sr, and 60Co) in building materials at 20 �C

Fig. 2 shows data on 137Cs sorption by building materials asa function of time. For concrete, limestone and brick the max-imum degree of 137Cs sorption was seen after 24 h of interaction,while for asphalt and granite it occurred after 7 days. The highestKd (137Cs) occurred for asphalt (in 28 days Kd (137Cs) was11,000 dm3/kg). For limestone, like asphalt, there was a significantincrease in Kd (137Cs) from 950 up to 1960 dm3/kg during28 days. For all other materials Kd did not vary noticeably overthe time 1e28 days. The highest value of Kd (137Cs) wasabout 3300 dm3/kg in granite, w1400 dm3/kg in brick, andw2000 dm3/kg in concrete. It should be noted that the activity ofthe solution in case of granite and asphalt was low. As a result the137Cs measurement error was high, which affected the standarddeviation values. In case of asphalt most likely a low densityorganic particles were not effectively separated by centrifugationand stayed in the solution to block the filter. Hence, the standarddeviation of the Kd values is significant.

Fig. 3 shows data on 60Co sorption by building materials asa function of time. As can be seen from Fig. 3a for concrete andgranite powders the 60Co sorption increases with time. The Kd(60Co) increased from 2000 to 5000 dm3/kg in granite, and from

C, % Porosity, % Particle density, g/cm3 Bulk density, g/cm3

0.03 20.3 � 0.9 2.10 � 0.11 1.68 � 0.060.004 1.5 � 0.5 2.44 � 0.13 2.41 � 0.140.004 15.3 � 2.4 2.52 � 0.06 2.13 � 0.000.3 2.2 � 1.0 2.39 � 0.06 2.34 � 0.080.08 20.28 � 0.25 2.53 � 0.01 2.02 � 0.00

0

4

8

12

16

0 6 12 18 24 30

Kd

x 10

3, d

m3

kg-1

t, day

Fig. 2. Change in the distribution coefficients Kd (137Cs) with time in building materialsat 20 �C: � e asphalt;O e granite; > e concrete; B e limestone; , e brick.

K. Maslova et al. / Journal of Environmental Radioactivity 125 (2013) 74e80 77

3000 to 4300 dm3/kg in concrete during 28 days. For brick the valueof Kd (60Co) slowly decreased with time (during 28 days the value ofKd (60Co) decreased from 1200 to 700 dm3/kg). For asphalt andlimestone (Fig. 3b) the time dependencies of Kd (60Co) were notpronounced. This may be associated with high variability of theexperimental results. The significant variation of the data could beexplained by low activity of 60Co in the solution. No relationshipwas revealed between the kinetics of concentrations of water sol-uble cations and changes in 60Co sorption by building materials. Itpoints to the prevalence of non-exchangeable sorption processesfor this radionuclide.

Fig. 4 shows the kinetics of 85Sr sorption by building materials.The sorption behavior of 85Sr differed from that of 60Co. For asphaltand granite a decrease in 85Sr sorption with time was observed.During 28 interaction days the value of Kd (85Sr) in asphaltdecreased from 104 to 60 dm3/kg and from 81 to 60 dm3/kg ingranite. This is probably because the 85Sr ion exchange in thesematerials is the leading process. As a consequence, the increase inthe concentration of water soluble calcium in the suspension so-lution with time brought about a decrease in 85Sr sorption in thesematerials. The 85Sr sorption in concrete during 28 days increasedapproximately by a factor of two as compared to 1 interaction day(from 18,900 to 39,800 dm3/kg). For brick and limestone the valueof Kd reached maximum during 7 days and did not change withtime later on.

Thus 85Sr and 60Co sorption by the building materials can bothincrease and decrease with time. For some building materials therewas no time dependence found for the radionuclide sorption by thebuilding materials. However, the sorption of 137Cs increased withtime for all building materials under study.

0 5 10 15 20 25 30

0

1

2

3

4

5

6

7

Kd

x 10

3 , dm

3 kg-1

t, day

ab

Fig. 3. Change in the distribution coefficients Kd (60Co) with time in building materials at

3.3. Depth distribution of radionuclides (137Cs, 85Sr and 60Co) inbuilding materials at 20 �C

Fig. 5 shows the dependences FnDhn on hn for different times ofradionuclide application (1 and 28 days) and for two RH values: 30%and 87%. The figures show only the distribution of radionuclides inthe top layer of building material in which the radionuclide isconcentrated. Almost no effect of time was observed for the radi-onuclide penetration into the materials.

As can be seen from Fig. 5a and b, 85Sr penetrated in the uppergranite layer over the distance of about 0.6 mm. Two granite layerscan be identified by the radionuclide depth distribution features:the upper-most layer 0.15 mm in which major changes in 85Srconcentrationwith depth occur and the so-called “tail” going to thedepth of about 0.6mm. There is some difference in the curves of thedependence FnDhn on hn for the upper 0.15 mm layer. In the upper-most layer, the relative concentration of 85Sr is almost three timeshigher at 30% RH than at 87% RH.

Data on the 137Cs depth distribution in asphalt as a function oftime and RH (Fig. 5ced) showed that 137Cs penetrated only in theupper asphalt layer over the distance of 0.4 mm. For different RHthe curves of the FnDhn dependences on hn were practically iden-tical. Thus, there was no difference in 137Cs penetration depths inasphalt at different RHs. As can be seen from Fig. 5eef, 60Copenetrated into brick over a short distance of about 1 mm. Fordifferent RHs the FnDhn dependences on hn were practically iden-tical. This suggests that RH does not influence the 60Co penetrationinto brick.

Based on the data presented in Fig. 5 it can be concluded that RHand the time of liquid aerosol contact with the surface of buildingmaterial during 1e28 days did not influence the profile and pen-etration depth for these radionuclides. The radionuclide profile andpenetration depth primarily depended on the type of buildingmaterial and degree of non-uniformity of the sample surface. Theuniform quality of the surface of the building material couponsdiffered after sawing, which can be seen visually. So, in some casesthe radionuclide distribution profiles differed significantly fromtypical distributions of these radionuclides for a given buildingmaterial.

For comparing the penetration ability of radionuclides, the up-per layer depth inwhich 90% of applied radionuclide (the sum of allmeasured activities over all grinded layers) is concentrated (h90%)can be used as a parameter. This parameter accounts for the depthto which decontamination should go in order to reduce con-tamination level on urban surfaces by 10 times. The h90% valueswere obtained based on experimental results. Table 3 presentsexperimental results on h90% for all building materials under studyat 1, 7, 14 and 28 days after radionuclide application on the surfaceand RH 30% and 87%.

0 5 10 15 20 25 30

0

4

8

12

16

20

Kd x

103 ,

dm3 k

g-1

t, day

20 �C: a: > e concrete;O e granite; , e brick. b: � e asphalt; B e limestone.

0 5 10 15 20 25 30

0

20

40

60

80

100

120

Kd ,

dm3 k

g-1

t, day

0 5 10 15 20 25 30

0

10

20

30

40

50

Kd ,

dm3 k

g-1

t, day

a b

Fig. 4. Change in the distribution coefficients Kd (85Sr) with time in building materials at 20 �C: a: � e asphalt;O e granite. b: B e limestone; , e brick; > e concrete.

K. Maslova et al. / Journal of Environmental Radioactivity 125 (2013) 74e8078

The 137Cs penetration depth h90% in asphalt varied from 0.1 to0.66 mm and practically did not depend on RH. The median valuesof h90% for asphalt at RH 30% and at RH 87% were 0.2 and 0.4 mm,respectively. In this case the median seems better to use, as

0.0 0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10

12

Fnh-1

, m

m-1

hn, mm

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0

2

4

6

8

10

12

14

Fnh-1

, m

m-1

hn, mm

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fnh-1

, m

m-1

hn, mm

RH 30%

RH 30%

RH 30%

a

c

e

Fig. 5. Radionuclide depth distribution in building materials at 20 �C as a function of intedistribution in granite; c, d e 137Cs depth distribution in asphalt; e, f e 60Co depth distribu

compared to an arithmetic mean, because of high variability of h90%which is explained by coupon surface roughness.

Similar behavior of 137Cs was observed for limestone: the me-dian value of h90% was 1.2 (30% RH)-1.4 (87% RH) mm, the spread

0.0 0.1 0.2 0.3 0.4 0.5 0.6

0

2

4

6

8

10

12

Fnh-1

, m

m-1

hn, mm

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

0

2

4

6

8

10

12

14

Fnh-1

, m

m-1

hn, mm

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

Fnh-1

, m

m-1

hn, mm

RH 87%

RH 87%

RH 87%

b

d

f

raction time and relative humidity (RH): (B e 1 day, : e 28 days) a, b e 85Sr depthtion in brick.

Table 3The upper layer depth of material, h90%, in which 90% of applied radionuclide occurs(mm), showing results for different material, contact time, relative humidity (RH)and replication.

t,days

Replicate 137Cs 60Co 85Sr

30% RH 87% RH 30% RH 87% RH 30% RH 87% RH

Asphalt1 1 0.10 0.32 0.31 0.18 0.19 1.72

2 0.20 0.15 0.12 0.20 0.15 0.207 1 0.20 0.46 0.25 0.25 0.25 0.53

2 0.19 0.36 0.41 0.41 0.53 1.1214 1 0.23 0.40 0.47 0.47 0.47 5.43

2 0.55 0.31 0.54 0.54 0.54 4.1228 1 0.24 0.66 0.12 0.16 0.16 1.96

2 0.44 0.57 1.08 0.32 0.32 10.24Limestone1 1 0.77 0.45 0.80 1.10 1.18 1.08

2 3.92 0.95 0.58 1.40 1.90 1.907 1 1.01 1.46 0.99 0.94 e e

2 1.93 1.91 0.74 0.29 e e

14 1 1.03 1.02 0.46 1.19 e e

2 0.78 1.59 0.66 0.67 e e

28 1 1.28 1.51 0.99 0.49 1.10 1.072 1.26 1.26 0.87 2.25 1.43 1.63

Granite1 1 0.11 1.12 4.47 5.01 5.64 7.22

2 3.07 2.93 4.05 5.46 4.45 6.227 1 0.13 0.22 e e 5.56 6.19

2 0.34 0.26 e e 6.69 7.0214 1 0.35 2.34 e e 6.44 6.74

2 0.24 4.63 e e 6.60 5.5028 1 0.33 0.61 3.49 5.59 7.91 6.91

2 0.41 3.97 4.16 4.13 5.64 5.84Concrete1 1 2.59 0.30 0.86 1.10 0.83 0.38

2 0.24 0.60 0.32 1.40 0.90 0.807 1 0.24 0.76 0.85 0.94 0.40 0.40

2 5.20 0.60 0.39 0.29 0.54 0.4614 1 0.24 0.60 0.84 1.19 0.46 0.45

2 0.28 0.37 1.65 0.67 0.50 0.6928 1 0.50 4.43 0.87 0.49 0.63 0.73

2 0.38 0.73 1.88 2.25 0.30 0.39Brick1 1 0.76 0.85 0.68 0.65 2.49 1.62

2 0.57 0.78 1.06 0.45 1.93 2.347 1 0.64 0.53 0.87 0.74 2.99 4.38

2 0.99 1.04 0.93 1.01 2.32 2.2614 1 0.56 0.68 0.50 0.64 1.95 3.01

2 1.14 0.81 0.45 1.22 1.47 4.1028 1 0.92 1.24 1.06 0.64 1.88 7.00

2 0.75 0.86 1.53 0.77 4.35 7.20

K. Maslova et al. / Journal of Environmental Radioactivity 125 (2013) 74e80 79

varied from 0.8 to 3.9 mm. For brick these values were 0.8 mm atRH 30% and 0.5e1.2 mm at RH 87%, for concrete e the medianvalues were 0.3 mm (30% RH) and 0.6 mm (87% RH), with thespread from 0.2 to 4.4 mm. For granite the median value of h90% atRH 30%was 0.34mm and 1.73mm at RH 87%. Thereby, with respectto the median values of h90% the building materials had thesequence (30% RHe87% RH): 0.2e0.4 mm for asphalt<0.3e0.6 mmfor concrete <0.8 mm (for both RH) for brick <1.2e1.4 mm forlimestone <0.3e1.7 mm for granite.

The 60Co penetration depth h90% in asphalt varied from 0.1 to1.1 mm and practically did not depend on RH. The median value ofh90% at 87% RH was 0.29 mm and at 30% RH e 0.36 mm. For lime-stone the median values of h90% varied from 0.8 (30% RH) to1.0 (87%RH) mm. For brick RH was not seen to influence h90% either. For RH30% this value was 0.9 mm, and 0.7 mm for RH 87%.

For all building materials the 85Sr penetration depth practicallydid not depend on RH. At the same time, there were significantdifferences between themedian values of h90% for different buildingmaterials. The median value of h90% for asphalt at RH 30% was0.29 mm, and this parameter changed from 0.1 to 0.5 mm. For RH

87% the h90% varied from 0.2 to 10.2 mm. Therefore, the medianvalue of h90% 1.8mmwasmost likely explained by a large number ofused asphalt samples with a disturbed sample surface. In concrete,h90% changed from 0.3 to 0.9 mm, from 1.4 to 7.2 mm in brick (themedian value h90% for 30% RH is 2.1 mm and for 87% RH e 3.6 mm),from 1.1 to 1.9 mm in limestone (the median value h90% is 1.3 mmfor both RHs). The deepest penetration of 85Sr was found forgranite. Given the variation in h90% from 4.5 to 7.9 mm, the medianh90% changed from 6.0 mm at RH 30% to 6.5 mm at RH 87%.

4. Conclusions

Radiocesium, radiostrontium and radiocobalt sorption onpowdered building materials was studied in aqueous suspensionsat 20 �C for the interaction times 1, 7, 14 and 28 days. The highestvalue of Kd (60Co) was seen for limestone. For other building ma-terials the Kd (60Co) values varied from 800 to 5000 dm3/kg. Itshould be noted that for all building materials except granite thevalues did not vary significantly with time (Kd (60Co) in graniteincreased by a factor of 3 during 28 days). The 85Sr distributioncoefficients were several orders of magnitude lower than the Kd for60Co. The highest values were observed for asphalt and granite. Forother materials the Kd (85Sr) values slowly changed with time anddid not exceed 40 dm3/kg. The 137Cs Kd values for all buildingmaterials except limestone practically did not change over 28 daysof sorption. The highest Kd (137Cs) occurred for asphalt (in 28 daysKd (137Cs) reached 11,000 dm3/kg). For all other materials thehighest values of Kd (137Cs) varied from 1500 to 4000 dm3/kg.

It can also be concluded thatwith a liquid aerosol of radionuclideapplied to building material surfaces, the radionuclide penetrationdepth to asphalt, on the average, was from 0.2 to 0.4 mm. Thispenetrationdepthdidnotdependon a radionuclide or RH, or timeofcontact of the radionuclide liquid aerosol with building materialsurface. For limestone the penetration depth did not depend oncontact time or RH. The h90% varied for all radionuclides from 0.8 to1.2 mm. For concrete, similarly, no major differences were seen inthebehavior of 137Cs and 85Sr. Themedianvalues ofh90% ranged from0.3 to 0.6mm.A significant dependence of the penetration depth fordifferent radionuclideswas seen for brick.While themedianh90% for85Sr changed from 2.1 to 3.6, for 137Cs and 60Co this value changedfrom 0.7 to 0.9 mm. The most pronounced differences in the pene-tration depths of the radionuclides were for granite. While for 85Srthe median values h90% were about 6.0e6.5 mm, for 137Cs this valuewas practically 5 times lower and equal to about 0.3e1.7 mm.

Acknowledgments

The work was funded by International Science and TechnologyCenter (ISTC Project #4007).

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