Local Enhancement of 210Po Atmospheric Flux at a Sitein İzmir, Turkey

Işık Filizok & Aysun Uğur & Banu Özden

Received: 29 March 2013 /Accepted: 21 November 2013 /Published online: 18 December 2013# Springer Science+Business Media Dordrecht 2013

Abstract The annual atmospheric deposition rates of210Po and 210Pb were determined in İzmir, Turkey. Thesamples were collected from 18 November 2008 to 17November 2009. The annual 210Po deposition flux wasdetermined as 44.1±3.0Bq m−2 year−1, while 210Pb fluxwas calculated as 73.1±4.4 Bq m−2 year−1 using bulkcollectors. The monthly deposition fluxes of 210Po and210Pb were correlated with the amount of precipitation.The activity concentrations of the samples were found tovary between 5.7±1.1 and 167.1±7.5 mBq L−1, with anaverage value of 41.2±1.9 mBq L−1 for 210Po; andbetween 5.3±0.6 and 265.7±10.8 mBq L−1, with anaverage value of 67.3±2.7 mBq L−1 for 210Pb. Theactivity ratios of 210Po/210Pb in the samples ranged from0.16 to 3.39, with an average value of 0.80. During thecourse of the study, 210Po enhancement from both nat-ural and anthropogenic sources was observed.

Keywords Atmospheric depositional flux . 210Po .210Pb . 210Po enhancement

1 Introduction

Nuclear techniques andmeasurement methods are wide-ly used for environmental monitoring and research

using natural and artificial radionuclides as indicatorsfor atmospheric, terrestrial, and marine transport pro-cesses (IAEA 2004). It is important to understand theorigins and sources of these radionuclides and theirinteractions within the ecosystem around them. Thethree main sources of the radionuclides found in theatmosphere are radon isotopes and their progeny, cos-mogenic radionuclides and anthropogenic radionuclides(Froehlich 2010). 210Po and 210Pb are two importantdecay products of radon.

Polonium is a radioactive element that occurs natu-rally and has 38 isotopes and isomers (Lide 2010).Ecologically, the most important polonium isotope is210Po with a half-life of 138 days. It can enter the humanbody through eating and drinking of contaminated food,breathing contaminated air, or through a wound(UNSCEAR 2000; Shaw 2007). According to the reportof UNSCEAR (1988), 210Po contributes significantly tothe natural internal dose through consuming food.Therefore, it is important to determine any possibleenhancements of this radionuclide in the environment.

210Pb (t1/2=22.3 years) is a naturally occurring radio-nuclide that originates predominantly from 222Rn ema-nation from the ground. It has been used as a tracer toquantify several atmospheric processes including sourcetracking and transport time scales of air masses, thestability and vertical movement of air masses, removalrate constants, and residence times of aerosols, chemicalbehavior of analog species, washout ratios and deposi-tion velocities of aerosols; and soil erosion, sedimenta-tion, and biogeochemistry (Shaw 2007; Baskaran 2011).

210Po and 210Pb are removed from the atmosphere byradioactive decay, wet deposition by precipitation, anddry deposition by impaction, diffusion, and

Water Air Soil Pollut (2014) 225:1823DOI 10.1007/s11270-013-1823-7

I. Filizok (*) :A. Uğur : B. ÖzdenInstitute of Nuclear Sciences, Ege University,35100 Bornova, İzmir, Turkeye-mail: ifilizok@gmail.com

B. ÖzdenInstitute of Physics, University of Tartu,51014 Tartu, Estonia

sedimentation (McNeary and Baskaran 2003;Papastefanou 2008). Their flux from the atmosphere tothe earth's surface can be determined by using eitherman-made or natural collectors (Turekian et al. 1977).Man-made collectors are more appropriate for under-standing the sources and pathways of these radionu-clides, while natural collectors have more applicationsin chronological studies.

In this study, we report on the total depositionalfluxes and activity concentrations of 210Po and 210Pbfor İzmir. The results are compared with results from anearlier sampling campaign from this same site given byUğur et al. (2011).

2 Material and Methods

A bulk collector was deployed at the roof of the Instituteof Nuclear Sciences, Ege University, İzmir (38° 27′ 26″N, 27° 13′ 40″ E) between 18 November 2008 and 17November 2009. İzmir is the third most populous prov-ince of Turkey with a population of approximately fourmillion.

In the sampling period, the total number of rainy daysis 125 days. The sampling intervals were changed due tofrequency of precipitation. The same sampling systemand radiochemical procedure to determine the specificactivities of the samples is used given by Uğur et al.(2011). In brief, Mediterranean climate is characterizedby warm to hot, dry summers and mild to cool, wetwinters. Most of the precipitation falls during the wintermonths. Sometimes it is not seen a significant precipi-tation event for several months. The samples were col-lected by a precipitation collector which consists of aplastic funnel connected via a plastic tube with polyeth-ylene bottle. Then the samples were prepared for alphaspectroscopy analysis, because the 210Pb-specific con-centrations were determined using the radioactive equi-librium between 210Pb and 210Po by alpha spectrometry.After collection, the samples were brought to the labo-ratory, and 3 mL HNO3 was added to the samples. Afterwaiting for the radioactive equilibrium between 210Pband 210Po, for analysis, 1 mL 0.2 M KMnO4 was addedto the sample which was brought to pH=9 with conedammonia. After addition of 1.5 mL 0.3 M MnCl2,polonium and lead coprecipitated with manganese diox-ide were dissolved with 100 mL 1 % H2O2 solution in1.2 M HCl, and the new solution was evaporated todryness. Next, the dry residue was dissolved in 50 mL

8 M HNO3 (Skwarzec 1997). Polonium had been spon-taneously plated onto a copper disc for 6 h in 0.5 M HClin the presence of ascorbic acid to reduce Fe3+ to Fe2+.In order to find the optimum conditions for plating 210Poon discs, the standard technique was used, which wasmodified by Flynn (1968). Specific alpha activities weremeasured by Ortec Octete Plus spectrometry system.The results were corrected for radioactive decay fromthe collection time to counting time. 209Po (4.88 MeValpha emission, t1/2=103 years) was used as the internaltracer. After the first deposition of 210Po, the residual0.5 M HCl was kept for 1 year to allow 210Po ingrowthfrom the 210Pb contained in the solution to search sup-ported 210Pb in the samples. The samples were replated,and the 210Po activities were determined. The seconddeposition provided information on the 210Pb content ofthe samples and hence on the extent to which the initial210Po was supported by its grandparent.

3 Results and Discussion

3.1 The 210Po and 210Pb Activity Concentrationsin the Samples

The sample collection intervals and the activity concen-trations of 210Po and 210Pb for samples are given inFig. 1. The total amount of precipitation is 1,121.9 mmfor the samples collected between 18 November 2008and 17 November 2009 as shown in Fig. 2. For the2000–2003 period, the average annual precipitationamount was 645 mm (Uğur et al. 2011). The averageannual precipitation amount for İzmir is 687.5 mm forthe period of 1970–2010. The amount of precipitationin the sampling period is thereupon approximately60 % higher than 40-year average. However, theprecipitation pattern in the sampling period is inaccordance with long-term average, and theamount of precipitation is high in winter and lowin summer.

The 210Po concentrations in samples were found tovary between 5.7±1.1 and 167.1±7.5 mBq L−1, with anaverage value of 41.2±1.9 mBq L−1. There is not asignificant correlation between the 210Po activity con-centration and the amount of rainfall (P>0.05). In anearlier study conducted by the researchers for the samesampling area from November 2001 to April 2003, the210Po activity concentrations in rainwater have beenfound in the range of 2±0.4–35±3 mBq L−1, with an

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average value of 8±0.5 mBq L−1 (Uğur et al. 2011).McNeary and Baskaran (2007) have measured the 210Poactivity concentrations in rainwater samples for Detroit,MI from September 1999 to March 2001. The re-searchers found the 210Po activity concentrations

between 2.4 and 126 mBq L−1, with an average valueof 23.0 mBq L−1.

The 210Pb concentrations in samples were found tovary between 5.3±0.6 and 265.7±10.8 mBq L−1, withan average value of 67.3±2.7 mBq L−1. There is not a

Fig. 1 The sample collection intervals and the activity concentrations of 210Po and 210Pb of the samples collected between 18 November2008 and 17 November 2009

Fig. 2 The amount of precipitation between 18 November 2008 and 17 November 2009

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significant correlation between the 210Pb activity con-centration and the amount of rainfall (P>0.05). The210Pb activity concentrations in rainwater have beenfound in the range of 9±1–198±6 mBq L−1, with anaverage value of 51±0.5 mBq L−1 for the area betweenJanuary 2000 and December 2003 (Uğur et al. 2011).

The 210Pb activity concentrations depend on a num-ber of factors, including the history of the air mass andthe particular characteristics of the storm, such as theintensity and the duration of the event or the height ofcloud cover for a single precipitation event (Turekianet al. 1977). The concentrations are also controlled bythe geographical position and the meteorological condi-tions of a sampling site. Therefore, 210Pb activity con-centrations may change both spatially and temporally.Duenas et al. (2011) have analyzed the radiometriccomposition of bulk deposition samples at a site inMalaga, Spain, from January 2005 to December 2009.Duenas et al. (2011) found the 210Pb activity concentra-tions between 50 and 1,320mBq L−1, with an average of410 mBq L−1. Ali et al. (2011) have investigated atmo-spheric 210Pb in precipitation samples in Murree andIslamabad, Pakistan. The 210Pb activity concentrationsare found to vary between 2 and 87 mBq L−1, with anaverage value of 30 mBq L−1 for Murree. For Islama-bad, the mean specific concentration value of 210Pb isdetermined as 123 mBq L−1. Rastogi and Sarin (2008)have found that the activity concentrations of 210Pb ofthe rain samples for Ahmedabad, India, were between 3and 367 mBq L−1, with a volume-weighted mean valueof 74 mBq L−1.

3.2 The Annual Depositional 210Po and 210Pb Fluxesof the Samples

In Fig. 3, the amount of depositional fluxes for thecollection intervals are given for the sampling period.The total annual 210Po and 210Pb atmospheric fluxeswe r e c a l c u l a t e d a s 44 . 1 ± 3 . 0 a nd 73 . 1 ±4.4 Bq m−2 year−1, respectively. The annual 210Po and210Pb fluxes given in the literature for other sites and/orsampling periods are shown in Table 1. The annuallyhigh 210Po deposition flux suggests that there is an inputof unsupported 210Po to the atmosphere during the sam-pling period. The possible sources of the unsupported210Po have been discussed in the next section in detail.

Baskaran (2011) stated that the atmospheric deposi-tional flux is strongly correlated with the amounts ofprecipitation for many sampling sites; however, there

are other places where such correlation was not ob-served. It is found that the monthly depositional fluxesof both 210Po and 210Pb were correlated with precipita-tion (r=0.92, P<0.01 for 210Po; r=0.79, P<0.01 for210Pb).

Baskaran and Swarzenski (2007) have investigatedthe depositional fluxes of 7Be and 210Pb in St. Peters-burg, FL, by using 20 bulk deposition samples collectedbetween July 2003 and July 2004. The researchersobserved that the depositional flux of 210Pb varied by afactor of 40 and concluded that the relatively largevariation in the depositional flux of 210Pb at that studysite is likely due to variations in the source of air masses.Similarly, Sanders et al. (2011) have measured the totalatmospheric deposition flux of 210Pb at a coastal site inNiteroi, Rio de Janeiro, Brazil. The researchers foundthe total 210Pb deposition flux as 153 Bq m−2 year−1 forthe period from June 2006 to May 2007 and reportedthat the 210Pb fallout rates in the study indicate a fluctu-ating origin of air masses, between continent and ocean.Duenas et al. (2011) found the total annual depositionf l u x o f 2 1 0 P b v a r i e d b e tw e e n 6 4 . 9 a n d1 6 0 . 8 B q m − 2 y e a r − 1 , w i t h a n a v e r a g e120 Bq m−2 year−1 for Malaga.

3.3 The Activity Ratios of 210Po/210Pb in the Samples

The activity ratios of 210Po/210Pb in the samples rangedfrom 0.16 to 3.39, with an average value of 0.80. In ourearlier study, the 210Po/210Pb activity ratio ranged from0.03 to 1.09 (Uğur et al. 2011). The elevated 210Po/210Pbactivity ratio with a value of 1.09 was observed inNovember 2002. In 2002, the average 210Po/210Pb ac-tivity ratio was 0.45. However, in the current study,elevated values (>1) were found in various months.Generally, the abnormally high 210Po/210Pb activity ra-tio can be associated with a complex array of variables,including the geographical proximity to the source, me-teorological conditions, dust storms, coal-burning pow-er plants, forest fires, plant exudates, phosphate fertilizerproduction, cement production, volcanic eruptions, seaspray generated from wind-driven 210Po-rich surfacemicro layer in the summer stratified surface water, theredeposition of the bio-volatile 210Po emitted from sur-face seawater (Moore et al. 1976; Su and Huh 2002;Tateda and Iwao 2008).

Considering the above factors, for our study, it seemsthat two of them are in effect primarily. The first factor islikely to be the concrete, cement, mining, and fine

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gravel plants, and quarries increase in number with timenear the sampling site. Generally, the 210Po/210Pb activ-ity ratios determined for this study for the 2008–2009period are higher than those determined for the 2001–2003 period given by Uğur et al. (2011). Between theperiod of the end of first sampling campaign (December2003) to the beginning of second sampling campaign(November 2008), two concrete plants began operationwith a total capacity of 240 m3/h; while one cementfactory company increased its production capacity by

more than 25 %. Additionally, one mining company hasstarted its operations in 2007. Therefore, it seems thatthe increased activities of these facilities contribute tothe enhanced levels of 210Po for the sampling period.The second factor should be the forest fire that occurredat the summer of 2009 within 7 km from the samplingsite. An area of approximately 200 ha was affected fromthe fire. After the fire, the 210Po/210Pb activity ratio wasalways higher than 1, except one sampling period with avalue of 0.97. Similarly, Tateda and Iwao (2008)

Fig. 3 The amount of depositional fluxes for the collection intervals

Table 1 The annual 210Po and 210Pb fluxes given in the literature for other sites and/or sampling periods

Site Period 210Po flux(Bq m−2 year−1)

210Pb flux(Bq m−2 year−1)

Average 210Po/210Pbratios

Source

Akajima, Japan 1997/1998 58.4 78.5 0.78 Tateda and Iwao (2008)

Tsuyazaki, Japan 1997/1998 21.9 197 0.18 Tateda and Iwao (2008)

Odawa Bay, Japan 1997/1998 13.0 73.3 0.33 Tateda and Iwao (2008)

Detroit, USA 1999/2001 18.1 240 0.03 McNeary and Baskaran (2003, 2007)

İzmir, Turkey 2000 – 77 – Uğur et al. (2011)İzmir, Turkey 2001 – 63 – Uğur et al. (2011)İzmir, Turkey 2002 – 27 0.45 Uğur et al. (2011)İzmir, Turkey 2003 – 26 – Uğur et al. (2011)İzmir, Turkey 2008/2009 44.1 73.1 0.80 This work

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determined elevated 210Po values for a subtropical Jap-anese island, Akajima. The researchers indicated thatwhile winter elevation of 210Po deposition at the islandis likely from the wind-driven regolith dust, summerelevation of 210Po deposition may be due to 210Po-richsea spray, the bio-volatile 210Po, and an Indonesianforest fire that affected the sampling site.

4 Conclusion

The total depositional fluxes of 210Po and 210Pb aredetermined at a sampling site in İzmir for a year (18November 2008–17November 2009). The annual 210Poflux was determined as 44.1±3.0 Bq m−2 year−1. The210Po activity concentrations ranged from 5.7±1.1 to167.1±7.5 mBq L−1, with an average value of 41.2±1.9 mBq L−1. The annual 210Pb flux was found as 73.1±4.4 Bq m−2 year−1. The 210Pb activity concentrationsranged from 5.3±0.6 to 265.7±10.8 mBq L−1, with anaverage value of 67.3±2.7 mBq L−1. In the study, the210Po/210Pb activity ratios varied between 0.16 and 3.39.It is known that 210Po can be elevated by naturally and/or anthropogenically in the environment, and it isthought that the elevated levels of 210Po of this studyare due to both natural and anthropogenic sources.However, it is difficult to model and distinguish thefactors that contribute to the 210Po enhancement. There-fore, more direct measurements of 210Po and 210Pb foratmospheric deposition should be done to constitute amore extensive database globally. In addition, asBaskaran (2011) stated for the time being, some of210Po and 210Pb to the atmosphere are eliminated ordiminished (such as nuclear weapons, leaded gasoline);we can quantify other sources and pathways of 210Po(such as plant exudates, fertilizers, forest fires, volcanicactivity, etc.) better.

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