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Applied Radiation and Isotopes 65 (2007) 445–453

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Radioactivity levels of recent sediments in the Butrint Lagoon andthe adjacent coast of Albania

C. Tsabarisa,�, G. Eleftherioub, V. Kapsimalisa, C. Anagnostoua, R. Vlastoub,C. Durmishic, M. Kedhid, C.A. Kalfase

aHellenic Centre for Marine Research, Institute of Oceanography, P.O. Box 712, GR-19013 Anavyssos, GreecebNational Technical University of Athens, Department of Physics, Zografou Campus, Polythechnioupolis, GR-15780 Athens, Greece

cAlbanian Geological Survey, Sherbimi Gjeologijk Shqiptar, Rr. Kavajes 153, Tirana, AlbaniadInstitute of Nuclear Physics, P.O. Box 85, Tirana, Albania

eNational Centre for Scientific Research ‘‘Demokritos’’, Institute of Nuclear Physics, GR-15310 Agia Paraskevi, Greece

Received 3 August 2006; received in revised form 17 October 2006; accepted 22 November 2006

Abstract

Sediment samples have been collected in the Butrint area, located in the south-west Albania to determine the radioactivity levels of40K, 137Cs, 212Bi, 212Pb, 214Bi, 214Pb, 226Ra and 228Ac on the bed of the lagoon and adjacent sea, using direct counting gamma

spectroscopy. The concentration of 137Cs and 40K varied from 2.8 to 37.5 Bq/kg and from 266 to 675Bq/kg dry weight (dw), respectively

(central values). The average concentrations of 238U and 232Th daughter products varied from 8 to 27Bq/kg and from 13 to 40Bq/kg dw,

respectively. The measured 235U activity ranged from 0.7 to 2.5Bq/kg dw. Samples of different sedimentary properties, studied for the

radioactivity concentration, revealed an inversely proportional relation between grain size and a linear combination of measured specific

activities of 226Ra, 232Th (228Ac, 212Bi and 212Pb), 40K and 137Cs.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Radioactivity measurements; Coastal sediments; Butrint Lagoon; g-spectrometry

1. Introduction

The study of natural radioactivity in marine and coastalenvironments is of significant importance to better under-standing of oceanographic and sedimentological processes.That might lead to better management and protection ofthe marine resources (Matishov and Matishov, 2004).

The distribution of natural radionuclides in the seabedcan be used as a tracer for both sediments and dredgedspoils dispersal and accumulation mechanisms (Venemaand De Meijer, 2001). They also provide an estimation ofthe sedimentological composition of the seabed (Ligero etal., 2001). Usually, the activity concentration of radio-nuclides increases inversely with the grain size (He andWalling, 1996) and, in proportion, with the density of thesediment (Schulling et al., 1985; Ligero et al., 2001). The

e front matter r 2006 Elsevier Ltd. All rights reserved.

radiso.2006.11.006

ing author. Tel.: +3022910 76410; fax: +30 229107 6323.

ess: tsabaria@ath.hcmr.gr (C. Tsabaris).

U–Th radionuclides are associated with heavy minerals,whereas 40K is concentrated within clay minerals (Cho etal., 1996). In addition, other parameters such as miner-alogy, organic content, and geochemical composition couldplay an important role in the absorption of radioactiveelements in sediments.Until now, little information has been available as

regards the Albanian marine and coastal environmentconcerning the natural and artificial radioactivity indifferent compartments, such as sediments, waters andorganisms. The aim of this work was to provide apreliminary assessment of the level of man made andnaturally occurring radioactivity as well as environmentalinformation concerning the morphology of the floor of theButrint lagoon and the adjacent coast in the south-westernpart of Albania. From the measured activity concentra-tions of 137Cs and naturally occurring radioactive isotopes,such as 40K, 238U and 234Th daughter products, and on thebasis of an empirical model (Ligero et al., 2001),

ARTICLE IN PRESSC. Tsabaris et al. / Applied Radiation and Isotopes 65 (2007) 445–453446

sedimentological characteristics of the lagoon were de-duced.

2. The study area

The Butrint Lagoon is an elongated basin with anaverage length of 7 km and width of 3 km. The surface issome 1600 ha and the water depth reaches 21m. It joins theIonian Sea (eastern Mediterranean) through the naturalchannel of Vivari, which is 3.6-km long, 100-m wide and 5-m deep. The adjacent coastal area is characterized by thepresence of the Pavllo River, which has developed anextended Holocene delta.

The Lagoon is surrounded by the Vurgu Plain to thenorth, the Mile Mountain range to the east, the Vrina Plainto the south and the mountainous Ksamili Peninsula to thewest (Fig. 1). This area is a Pleistocene graben that belongsto the geotectonic zone of Ionian (external Albanides orHellenides) (Mec-o and Aliaj, 2000). Outcrops of evapo-rates occur as isolated hills in the alluvial plains of Vrinaand Vurgu. Middle Jurassic–Middle Cretaceous limestone

Fig. 1. Location map of the southwestern part of Albania showing the samplin

in the Ionian Sea.

constructs the Ksamili Peninsula and the southern part ofthe Mile Mountain, whilst Paleocene flysch occurs to thenortheast of the Lagoon.The climate is characterized by dry summers and mild

winters, whilst the average rain precipitation is approxi-mately 1.5m/yr. The Butrint Lagoon is characterized bylow tide amplitude (o0.30m) and the water regime istypical of coastal lagoons. Freshwater enters the Lagoonfrom the Bristica and Kalasa Rivers, located in thenorthern part, and the Pavllo River and the Bufi Lake,located in the southern part.Lagoon waters are characterized by mesotrophic condi-

tions, with some seasonal eutrophic peaks. The watercolumn is divided in two layers: (a) the upper layer, inwhich dissolved oxygen ranges from 0.009 kg/m3 near sea-level to zero at the depth of 7.5–8m; and (b) the lowerlayer, in which there is no oxygen. The absence of dissolvedoxygen in deeper waters is accompanied by the productionof H2S, with concentrations varying between 0.01 and0.035 kg/m3. The salinity fluctuates from 18 psu in winter to35 psu in summer; whilst water averaged temperature vary

g sites in the Butrint Lagoon, Vivari Channel and the adjacent coastal area

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from 14 1C in winter to 25 1C in summer. The organicmatter is about 0.002–0.01 kg/m3 (Pano et al., 1984; Peja etal., 1996).

Over the last 50 years, physical, geochemical andecological conditions of the lagoon have changed signifi-cantly due to human activities. As a result of wetlandreduction, a number of globally endangered species of birdhave been lost to the habitat. In addition, agricultural soils,waters and lagoon bottom sediments were enriched bypollutants, mainly due to the overuse of pesticides andfertilizers (Martin, 2002).

3. Materials and methods

3.1. Sample collection and preparation

A total of 15 surficial sediments (upper 2 cm layer) weretaken from: (a) the Butrint Lagoon (BUT_01, 03, 04, 05,06, 08, 10), which was considered as Region A; (b) theVivari Channel (BUT_09, 14, 17) that was designated asRegion B and (c) the adjacent Ionian coast (PAV_01, 02,04, 05), which was named as Region C (Fig. 1). A grabsampler and a box corer were used for the sampling ofsurficial sediments. The uppermost 2 cm of the sample weregathered and stored for grain size analysis and radio-activity measurements.

3.1.1. Grain size analysis

All samples were split into sand and mud fractions bywet sieving through a 63 mm mesh. The coarse-grainedsubsamples (d463 mm) were fractioned by dry sieving,

Table 1

Sample characteristics and the results of the grain size analysis

Sample name Density (Kg/m3) Folk (1974)

Sand Silt Clay Texture

(%) (%)

Region A (Butrint Lagoon)

BUT_01 787 1 54 45 Mud

BUT_06 694 1 52 47 Mud

BUT_10 530 1 54 45 Mud

BUT_03 795 1 55 45 Mud

BUT_07 801 1 56 43 Mud

BUT_04 841 6 53 42 Mud

BUT_08 625 3 62 35 Mud

BUT_05 821 7 55 38 Mud

Region B (Vivari Channel)

BUT_09 945 31 50 19 Sandy silt

BUT_14 979 62 30 8 Silty sand

BUT_17 860 61 30 9 Silty sand

Region C (Adjacent coast-Ionian Sea)

PAV_04 828 6 66 27 Silt

PAV_01 825 3 67 30 Silt

PAV_02 854 7 64 29 Silt

PAV_05 959 40 45 15 Sandy silt

The classification of sediment texture was based on two different approaches:

whilst the fine-grained subsamples were determined by agrain-size analyzer (Sedigraph Micromeritics 5000 ET).Textural characterization and grain-size statistics ofsamples were based on two different classifications: (a)the first classification followed in this study was the oneproposed by Folk (1974), which is widely used fromsedimentologists. According to this classification, sandfraction is composed by grains whose diameter varies from63 to 2000 mm, silt fraction consists of grains with dia-meter ranging between 4 and 63 mm, and clay fractionconstitutes very fine material, whose diameter is less than4 mm. The textural type of the sediment was classifiedaccording to the Folk’s triangular, where sand, silt and claytake up the three peaks of the diagram, (b) the Ligero’sclassification was also followed in order to compare ourdata with the results provided by Ligero et al. (2001) for theBay of Cadiz (see below). According to the Ligero’sapproach, grains with diameter raging from 63 to 2000 mm,from 16 to 63 mm and less than 16 mm comprise the sand,silt and clay fractions, respectively. Furthermore, sedimentis defined as: (i) mud if it contains more than 80% fine-grained material (silt and clay fractions); (ii) sandy mud ifthe sum of the silt and clay fraction varies between 50%and 80%; and (iii) sand or muddy sand when the sandfraction is above 50%. The results are summarized inTable 1.

Sample preparation for radioactivity measurements: Thesamples were firstly cleaned from algae, cockles and gritsand then the sandy and dreggy samples were placed inspecial fire resistant holders and were dried at 50 1C for twodays and then sieved.

Ligero et al. (2001) Mean size (10�6m)

Sand Silt Clay Texture

(%) (%) (%) (F) (G)

1 8 91 Mud Clay 5.3

1 8 91 Mud Clay 5.4

1 7 92 Mud Clay 5.6

1 10 89 Mud Clay 7.0

1 10 89 Mud Clay 7.0

6 19 76 Mud Clay 7.5

3 15 82 Mud Clay 7.9

7 9 84 Mud Clay 8.9

31 28 41 Muddy sand 45.2

62 19 19 Sand 68.4

61 19 19 Sand 68.7

6 26 67 Mud Clay 12.2

3 24 73 Mud Clay 13.5

7 30 63 Mud Clay 14.7

40 24 36 Muddy sand 55.4

(a) Folk (1974); and (b) Ligero et al. (2001).

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Fig. 2. Typical gamma ray spectra: (a) before; and (b) after background

subtraction of the sample BUT_06.

C. Tsabaris et al. / Applied Radiation and Isotopes 65 (2007) 445–453448

3.2. Measurement methodology

All measurements and the development of the dataanalysis software were carried out at the Institute ofNuclear Physics of the NCSR ‘‘Demokritos’’. Natural andartificial radionuclides in sediment were analyzed using an80% (nominal relative efficiency) HPGe (Canberra) n-typecoaxial detector with a resolution of 2.15 keV at 1.33MeV.A lead shield surrounded the detector in order to reducethe ambient gamma ray background. For the dataacquisition an ORTEC computerized MCA system (ADCand related software) was used.

The energy and efficiency calibration were performedusing a 152Eu(93%)+154Eu(7%) source that had beenprepared and calibrated at NCSR ‘‘Demokritos’’, specifi-cally for this type of measurements, in the following way: Asmall quantity of 152Eu+154Eu diluted liquid source(obtained originally from Amersham Co.) was put in a0.5ml syringe, placed at a distance of 25 cm from the faceof the HPGe detector and its activity measured. Then thecontents of the syringe were injected-dropped into an inertmaterial (talcum powder) that had been placed inside aplastic container (diameter 6.9 cm, depth 2 cm) identical tothe ones used for the subsequently measured sedimentsamples. The self absorption in the inert material couldapproximate that in the samples. The residue activityremaining in the syringe was then measured in order todetermine the activity actually injected-dropped into theinert material. Finally, this newly prepared source wasplaced in contact geometry in front of the detector and a4000 s spectrum was recorded. The source was rotated sothat the back face was in contact with the detector’s frontand a second spectrum was recorded. The difference in theintensities for the two spectra was less than 5%, thusensuring that the distribution of radioactivity in the inertmaterial was almost homogenous. After adding the twospectra and using the most intensive gamma ray peaks ofthe source, the absolute detection efficiency as a function ofthe energy was determined. The empirical function used forthe fit was of the type:

y ¼ Axb=C þ xd ,

where, y is the absolute efficiency, x is the gamma rayenergy and A, b, C, d are free parameters. The source’s152Eu activity at the calibration time was 6770790Bq.

The same geometry was used for all samples. In mostcases the measuring time was 24 h, while in the cases of verylow specific activity of a sample 48-h spectra were recorded.Every 5 days a 48-h background spectrum was recorded. Inorder to minimize any systematic errors, a phantom samplecontaining only inert material was used for the backgroundspectra, thus simulating the absorption of the ambientbackground radiations taking place in its passage throughthe samples.

The measured data were analyzed using the SPECTRGsoftware package (Kalfas and Tsoulou, 2003). A typicalspectrum of a sample from the studied region is depicted

before and after background subtraction (Fig. 2) andtypical analysis results are shown in Table 2. In the table,the analyzed gamma rays have been grouped for eachisotope and wherever there is more than one gamma ray,the mean specific activity is shown. Among the analyzedphotopeaks there were two cases of unresolved doublets,i.e. the 185.71+186.21 and the 241.00+241.91 keV. In thecase of the first doublet, the 185.71 keV belongs to 235U,while the 186.21 keV belongs to 226Ra. Assuming that 238Uand 226Ra are in secular equilibrium and using: (a) theknown relative abundance in nature of the two Uraniumisotopes (99.3% for 238U and 0.7% for 235U); and (b) thedecay branching in each case, one can readily calculate theexpected detected relative intensity of the two gammas(0.43 and 0.57 for the 185.71 keV and the 186.21 keV,respectively). An additional test is the comparison of thespecific activity of 226Ra estimated in the above way withthat of 214Pb and 214Bi, assuming that all three isotopes arein secular equilibrium. In the present case, the two methodsgave almost identical results.In the second doublet, the 241.00 keV belongs to 224Ra,

while the 241.91 keV belongs to 214Pb. Since the latter hasnine detectable gamma rays, ranging from 241.91 keV up to

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Table 2

Analysis results of a typical spectrum, extracted by the software SPECTRG (Kalfas and Tsoulou, 2003)

Results

Sample name: BUT_06 NET (BGR 23 January)

Started on 26 January 2005, elapsed live time: 84116 s

Weight: .04373 kg

Energy FWHM Net area error counts Isotope B/R Activity Absolute efficiency

(keV) (keV) (%) (Bq/kg)

1460.83 2.24 50597288 40K 10.67 674.61738.42 0.019107

661.66 1.70 37637247 137Cs 85.20 37.5072.52 0.032006

583.19 1.50 11257132 208Tl 30.36 29.0473.43 0.034749

727.33 1.77 286772 212Bi 6.64 38.8879.83 0.030093

238.63 1.31 38067255 212Pb 43.50 38.1972.52 0.062120

609.32 1.60 10207128 214Bi 46.10 17.8172.24 0.033771

1120.28 1.94 279768 214Bi 15.00 22.2775.42 0.022713

Mean value 18.4772.93

241.91 2.04 3707136 214Pb 7.46 21.9178.05 0.061577

295.17 1.32 8277128 214Pb 19.20 21.6373.36 0.054134

351.90 1.41 12467145 214Pb 37.10 18.9172.20 0.048285

Mean value 19.8373.00

241.00 2.04 4607136 224Ra 4.05 50.08714.86 0.061727

186.21 1.63 4307136 226Ra 3.51 45.96714.64 0.072545

338.42 1.37 8387124 228Ac 11.26 40.9375.95 0.049528

463.10 1.47 3227100 228Ac 4.50 48.25714.86 0.040379

911.16 1.80 7827112 228Ac 26.60 30.8774.34 0.025985

968.97 1.82 514788 228Ac 16.23 34.5375.95 0.024964

Mean value 34.9674.41

185.71 1.63 3187132 235U 57.20 2.0870.86 0.072659

C. Tsabaris et al. / Applied Radiation and Isotopes 65 (2007) 445–453 449

785.91 keV, one can analyze the rest eight photopeaks anduse their mean specific activity value to estimate thecontribution of the 241.91 keV to the doublet.

4. Results

Grain size analysis showed that the lagoon bed consistsof mud with very small mean size (5.3–8.9 mm), whereascoarse-grained surficial sediments, probably due to thepresence of very strong currents, were found in the VivariChannel. The marine part of the adjacent Ionian coast isinfluenced by the deltaic depositional processes of thePavllo River. The sand fraction is dominant near theshoreline and it decreases towards the open sea, where fine-grained sediment covers the seabed.

The results of the radioactivity analysis of the coastalsediments in southwest Albania are given in Table 3. Thedetected radionuclides are related to the naturally occur-ring isotopes like 40K, 238U series (226Ra, 214Pb and 214Bi),232Th series (228Ac, 212Bi, and 212Pb), 235U and the artificialradionuclide 137Cs. The measured gamma ray intensities,after isotope identification, have been transformed intospecific activities for each corresponding isotope and givenin Bq/kg dw. The overall total specific activity (in Bq/kg) ofall identifiable isotopes with the calculated uncertainties ispresented schematically for all sample sites in Fig. 3. It isseen to range from 380 to 420Bq/kg at the Vivari Channel

(Region B), from 590 to 790Bq/kg in the coastal zone ofthe Ionian Sea (Region C) and from 810 to 900Bq/kgwithin the lagoon (Region A).The measured specific activity related to all the above-

mentioned nuclides is presented graphically in Figs. 4 and5. It is readily seen that the detected 214Pb and 214Bi specificactivities are in fair agreement with each other, within theiruncertainties, but slightly lower than the 226Ra values. Theactivity values reveal a consistent behavior with respect tothe mean grain size. In the case of BUT_05 sample theactivity is higher than expected, probably due to contam-ination from fertilizers carried by the rivers. In mostsamples the secular equilibrium condition is conserved,especially between 214Pb and 214Bi for the 238U series aswell as between 228Ac, 212Bi and 212Pb for the 232Th series.Secular equilibrium of the 238U series like 238U-226Ra-222Rn-214Pb-214Bi, is a reasonable assumption consider-ing the long half-life of the parent nucleus 238U and thetime scale since the rock formation on Earth (Eisenbud andGesell, 1997). However, 222Rn is a noble gas and its escapemainly after sample collection and processing reduces theactivities of 214Pb and 214Bi by about 10–20%, altering thesecular equilibrium of the series. Concerning the series of232Th the maximum divergence of the activity of the threechain products (228Ac, 212Pb, 212Bi) from the mean activityvalue is less than 17%. Moreover, in the Butrint lagoon theaveraged activity values exhibit a consistent behavior with

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Table 3

Mean specific activity of 137Cs, 40K, 238U series (226Ra, 214Pb, 214Bi), 235U and 232Th series (228Ac, 212Bi, 212Pb), and radiometric sediment characterization

(factors F and G), based on the empirical model of Ligero et al. (2001)

Sample name 137Cs 40K Activity (Bq/kg) F G

238U series 235U 232Th series

226Ra 214Pb 214Bi 228Ac 212Bi 212Pb

Region A (Butrint Lagoon)

BUT_01 29.672.0 635.8733.9 25.675.5 20.572.5 19.372.5 2.370.4 35.873.7 38.578.1 35.972.2 21.8 (mud) 9.4 (clay)

BUT_06 37.572.5 674.6738.4 22.476.8 19.873.0 18.572.9 2.570.3 35.874.4 38.979.8 38.272.5 26.9 (mud) 12.1 (clay)

BUT_10 23.372.2 633.5741.3 22.377.2 17.972.5 18.173.8 1.470.3 38.075.9 34.1711. 39.573.0 18.3 (mud) 7.4 (clay)

BUT_03 27.072.0 631.1734.5 18.872.7 21.072.6 15.972.0 1.070.1 36.773.0 34.979.8 36.172.4 20.6 (mud) 8.5 (clay)

BUT_07 28.772.0 626.6733.5 20.375.0 17.973.0 15.272.5 1.270.2 38.177.2 40.078.9 35.772.2 22.0 (mud) 9.1 (clay)

BUT_04 16.171.4 659.7734.1 20.372.9 19.772.2 13.872.0 1.470.1 31.372.7 38.977.7 31.372.1 12.1 (mud) 5.2 (clay)

BUT_08 18.271.3 504.4724.1 13.973.5 15.771.4 13.871.4 1.070.2 23.272.2 25.976.6 26.271.5 12.1 (mud) 5.1 (clay)

BUT_05 23.471.7 637.5733.2 23.377.5 18.172.5 17.872.6 2.070.3 26.672.6 25.578.7 25.571.9 15.6 (mud) 7.4 (clay)

Region B (Vivari Channel)

BUT_09 6.970.9 315.5721.2 13.072.9 11.471.1 7.971.2 0.670.1 16.671.7 13.774.9 15.871.3 3.6 (sand)

BUT_14 2.870.4 266.0713.9 14.573.2 12.771.2 11.771.1 0.970.2 13.171.2 14.273.7 13.170.9 0.2 (sand)

BUT_17 4.870.8 275.7721.4 14.274.0 9.271.8 14.272.7 0.770.2 16.072.4 13.373.2 14.272.7 2.1 (sand)

Region C (Adjacent coast-Ionian Sea)

PAV_04 9.971.1 544.1730.1 19.077.9 18.672.2 16.072.0 0.770.5 23.772.4 23.777.1 27.971.9 6.5 (muddy sand) 2.6 (clay)

PAV_01 10.871.2 557.9730.7 26.674.9 19.872.7 18.072.4 1.470.2 30.873.1 34.579.3 30.972.1 8.4 (muddy sand) 3.0 (clay)

PAV_02 11.470.9 578.2723.1 24.374.8 19.271.5 18.371.9 2.070.2 28.572.0 40.176.8 31.171.5 8.3 (muddy sand) 3.3 (clay)

PAV_05 7.670.6 449.7718.2 22.072.8 16.471.4 13.771.5 1.170.1 20.771.7 26.274.4 23.871.1 4.4 (muddy sand)

Fig. 3. The total activity of the samples within the three regions (Butrint Lagoon, Vivari Channel and Ionian Sea). The measured data are plotted with the

increase of the mean size of the sediments for each region. The mean size is drawn as points connected with solid line to guide the eye.

C. Tsabaris et al. / Applied Radiation and Isotopes 65 (2007) 445–453450

the mean grain size. The measured values of the 235Uspecific activity ranged from 0.7 to 2.5 Bq/kg (dry weight)and this is roughly 15 times lower as compared with thevalues obtained for the 238U series. Similarly, the BUT_05sample exhibits the same behavior as 238U measuredactivities.

The results for 40K and 137Cs are presented in Fig. 5. 40Kprovides, on the average, more than 75% of the totalactivity. The sediment samples of Region A contain an

average 40K specific activity of 650Bq/kg; those of RegionB contain 290Bq/kg, while in Region C the averaged valueof 40K is 550Bq/kg. The maximum value of 137Cs inRegion A is 37.5 Bq/kg dw and is located at the BUT_06sample site corresponding to the deepest part of the lagoon.In the same group, the lowest value (16Bq/kg) was ob-served in the BUT_04 sample collected in the shallow-est waters. The average value of 137Cs in Region B is4.5 Bq/kg, while in Region C is 9 Bq/kg.

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Fig. 4. The 235U, 238U and 232Th series activity for the three regions. The

measured data are plotted with the increase of the mean size of the

sediments and are connected by lines for each region to guide the eye.

Fig. 5. The activity of 137Cs and 40K for the three regions. The measured

data are plotted with the increase of the mean size of the sediments and are

connected by lines for each region to guide the eye.

C. Tsabaris et al. / Applied Radiation and Isotopes 65 (2007) 445–453 451

5. Discussion

No data have appeared in the literature concerningradionuclide concentrations in the specific region understudy; therefore, no comparison is possible. The presenceof 137Cs in sediments of the study area was evident.However, its activity is lower than the values from thepre-Chernobyl period cited in literature for marinesediments from different regions of the world (IAEA,1973; Livingston et al., 1977). The 137Cs contents of thesampled sediments are compared with respect to sitelocation. The samples of the deepest part of the lagoonexhibit high concentration mainly due to the muddycharacter of the sediments along with the stationaryconditions in the bottom waters of the lagoon character-ized by higher values of salinity which favors the dissolvedphase of 137Cs (Peja et al., 1996). In addition, the samplesfrom the Ionian Sea (10Bq/kg) exhibit twice as much 137Cs

activity as compared to the sediments collected from theVivari Channel. This is attributed to the sandy content ofthe channel floor which implies low radionuclide retainingability (He and Walling, 1996) of seawater.The results show that the 40K activity values in the

Ionian Sea are in the range of 500–600Bq/kg. Levels �15%higher (600–650Bq/kg) were measured in the lagoon. Thiscan be attributed to the mineralogical composition ofbottom sediments and to high salinity values in the deeplayer throughout the year (Peja et al., 1996). Lower valuesappeared (200–300Bq/kg) in the Vivari channel due to thesandy content of the samples. This result is in agreementwith literature information for 40K activity in sand(Venema and De Meijer, 2001).The specific activities of the decay series products of 238U

and 232Th were averaged (weighted) in order to deduce themean specific activities of the parent nuclei. In the lagoon,as well as in the Ionian Sea, the average activityconcentration of 238U and 232Th series products exhibitsimilar values, while in the Vivari Channel the activity isreduced by a factor of the order of 2.

5.1. Correlations

The ratio (Th/U) of the averaged daughter concentra-tions of 232Th and 238U was calculated for all samples andthe values varied from 1 to 2. As a comparison index, the

ARTICLE IN PRESSC. Tsabaris et al. / Applied Radiation and Isotopes 65 (2007) 445–453452

observed average value of the ratio samples in the lagoon is1.2. It is moderately above the world’s average Th/U ratio,which is close to unity (Ibrahiem et al., 1995) and this canbe attributed to the mineralogy of the specific lagoon. Thecorresponding value in the Vivari Channel was approxi-mately 0.8 indicating higher pollution levels, possibleresulting from agricultural activities. The Th/U ratio is 1for the samples of the Pavllo River estuary, confirming theequilibrium conditions of sediments in the marine environ-ment (Venema and De Meijer, 2001).

Similarly, other correlations were studied. The resultsindicate that there is a positive correlation between 40K andaveraged activities of the daughter nuclei of 232Th as well asbetween 238U and 232Th. The results were linearly fitted andthe measured ratios along with the fitted values are plottedin Fig. 6. The concentrations of 40K and 232Th aresignificantly correlated ðR ¼ 0:91Þ, while the averagedmeasured activities between 238U and 232Th exhibit acorrelation factor R ¼ 0:66. The good proportionalitybetween 232Th and 40K concentrations may be attributedto the fact that thorium is a particularly insoluble elementin water.

Fig. 6. Correlation between activity concentrations of 238U and 40K

versus 232Th concentration. The lines represent values calculated by linear

fit.

5.2. Radiometric sediment characterization

The textural type of the Butrint seabed was indirectlydetermined by applying two empirical formulas developedfor the Bay of Cadiz in Spain by Ligero et al. (2001). Theseformulas were used in the present study since thesedimentary (textural) characteristics of the Bay of Cadiz(Ligero et al., 2001) and the coastal area of southwestAlbania are similar. In particular, the presently measuredspecific activity (A) of the radionuclides 226Ra, 232Th, 137Csand 40K was used to determine the relative proportions ofmud or sand fraction in sediments, via the first empiricalexpression (Ligero et al., 2001):

F ¼ �0:048ARa þ 0:24ATh þ 0:65ACs � 0:002AK � 3:6.

(1)

The concentration of 232Th was deduced from 228Ac,assuming secular equilibrium. Positive values of F corre-spond to mud sediments (mud fraction 480%), whilevalues lower than –1.5 designate sand and muddy sandsediments (sand fraction 450%). Values of F varying from0 to –1.5 indicate sandy muds (mud fraction rangesbetween 50% and 80%).In addition, the dependence of 40K and 137Cs activity is

examined in order to determine the predominance of siltand clay content within the fine-grained sediments (muds)by using the second empirical formula (Ligero et al., 2001):

G ¼ �3:6þ 0:0054AK þ 0:32ACs. (2)

Positive values of G correspond to clayey sediments andnegative values to silty sediments. The factors F and G werecalculated using the experimental radioactivity measure-ments and are given in Table 3.The highest values of F (12.1–26.9) occurred in the

Butrint Lagoon, where all surficial sediments can beclassified as muds. In the Vivari Channel, the factor F

took the lowest values (0.2–3.6), indicating the predomi-nance of sand. Intermediate values, predicted for thesediments of adjacent Ionian seabed, could be related tothe relative abundances of the mud and sand fractions. Theresults in the lagoon were compared to measurements ofthe grain size of the sample and were found to be in a verygood agreement (Tables 1 and 3). In the case of theadjacent Ionian coast (PAV_01, 02, 04), the model predictsa coarser character (muddy sand) compared to theexperimental data (mud).Factor G, ranging between 2.6 and 12.1, indicates that

clay content (o16 mm) is dominant in all muddy samples ofthe lagoon and the Ionian seabed. This estimationcoincides with the results of the grain size analysis, whichconfirms the dominance of clay fraction over silt.Although the model successfully predicts sediment type

(mud, muddy sand or sand), the relationship betweenfactor F and the mean size, exhibit a nonlinear dependence.In Fig. 7 the F factor values are plotted with respect to thegrain size of the sediments. Although there is a lack ofexperimental data in the range 15–45 mm, the general

ARTICLE IN PRESS

Fig. 7. Relation between model prediction and mean size of sediments.

C. Tsabaris et al. / Applied Radiation and Isotopes 65 (2007) 445–453 453

behavior of the experimental points can be represented by apower function shown as solid line in Fig. 7. Furthermeasurements in regions with grain sizes in this range arenecessary in order to investigate the F factor forintermediate mean size values not covered in this work.In conclusion, a refined model for the mean size predictionhas to be developed. This refined model has to take intoaccount additionally the mineralogical and geochemicalcomposition of sediments, which are strongly related tosome radionuclides, such as 137Cs, 40K, 232Th and 226Ra(Matishov and Matishov, 2004).

In general, the model in its present form seems to workadequately in the Butrint lagoon, although the backgroundradioactivity level is higher than that in the Bay of Cadiz,for which it had been originally developed. However,further experimental work in a wide range of geographicalregions in the world coasts might justify the globalapplicability of the model.

6. Conclusions

New data on the activity concentration of anthropogenicand naturally occurring radionuclides in sediment samplescollected from the Butrint lagoon were presented anddiscussed. The adsorption of radioactive elements has astrong dependence on the nature of sediment and decreasesfrom fine- to coarse-grained materials.

Concerning secular equilibrium, 214Pb and 214Bi of the238U daughter isotopes as well as 212Pb and 228Ac from the232Th series were found in equilibrium. Besides, the 137Csactivity is smaller than the values quoted for the pre-Chernobyl period for different regions of the world. Thedeepest part of the lagoon provides the highest concentra-tion due to the muddy content and to the stationaryconditions of the specific lagoon at the deeper layer. Whencomparing sandy cases, the sandy fraction of the sediments

in the Vivari Channel have lower 137Cs concentrationcompared to that in the Ionian Sea; the observed specificactivities in the two cases differ by almost a factor of two.An enhanced level of 40K was measured in the lagoon dueto muddy content of the sediments, to the minerals of thespecific environment and to the high salinity values in thedeep water layer throughout the year. The average activityconcentration of the 238U and 232Th series products in thelagoon, as well as in the Ionian Sea exhibits similar values,while lower values by a factor of 2 are measured in theVivari Channel.The radiometric characterization of the seabed is an

efficient tool for geological studies. The applied empiricalmodel by Ligero et al. (2001), predicts successfully thecontent of the sediment in the Butrint Lagoon. The modelpredictions are validated by geological study for the grain-size analysis in the lagoon samples.

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