Inflow of 210Po from the Odra River Catchment Area to the Baltic Sea+

Chem. Anal. (Warsaw), 53, 809 (2008)

by Bogdan Skwarzec and Agnieszka Tuszkowska

University of Gdañsk, Faculty of Chemistry, Chair of Analytical Chemistry ul. Sobieskiego 18/19, 80-952 Gdañsk, Poland

Keywords: Polonium; 210Po; Odra River; Catchment area; Poland

In this study the activity of polonium 210Po in the Odra River water samples, collected from October 2003 to July 2004 has been was determined using alfa spectrometry. In autumn the highest concentration of 210Po was found in the Odra River water at Gozdowice (1.64 ± 0.08 Bq m–3) and in the Nysa £u¿ycka River (5.21 ± 0.19 Bq m–3). In contrary, the lowest concentrations were determined in water from the Barycz and the Bystrzyca Rivers (1.09 ± 0.07 and 1.09 ± 0.06 Bq m–3, respectively). During winter season, in turn, the highest concentration of 210Po was observed in the Odra River water collected at Cha³upki (3.64 ± 0.03 Bq m–3) and S³ubice (3.62 ± 0.03 Bq m–3), and the lowest in the Noteæ River (1.00 ± 0.06 Bq dm–3). In spring the highest concentration was in the Odra at S³ubice (3.32 ± 0.04 Bq m–3) and in the Nysa K³odzka River (4.04 ± 0.03 Bq m–3), and the lowest in the Barycz River (1.10 ± 0.05 Bq m–3) and the Odra at G³ogów (1.04 ± 0.06 Bq m–3). In summer the highest 210Po concentration was observed in Odra River at Widuchowa (1.79 ± 0.04 Bq m–3) and in the Nysa K³odzka River (2.00 ± 0.05 Bq m–3), and the lowest in the Odra at Gozdowice (1.10 ± 0.05 Bq m–3) and in the Barycz River (0.60 ± 0.09 Bq m–3). The highest quantity of polonium 210Po was transported to the Baltic Sea in spring, and the lowest in winter. It was calculated that the southern Baltic Sea, especially the Pomera- nian Bay with the Szczecin Lagoon, receives 14.76 GBq 210Po annually. Among the Odra tributaries the highest surface runoff of 210Po was observed in autumn (up to 88 kBq km–2 quarter–1 for the Nysa £u¿ycka drainage area), and the lowest in summer (1 kBq km–2 quarter–1 for the Barycz drainage area).

Celem pracy by³o oznaczenie stê¿enia polonu (210Po) w próbach wody rzecznej pobranych wzd³u¿ g³ównego nurtu Odry oraz jej najwa¿niejszych dop³ywów, a nastêpnie okreœlenie wielkoœci sp³ywu 210Po z dorzecza Odry poprzez Zalew Szczeciñski do Morza Ba³tyckiego. Stosuj¹c spektrometriê promieniowania alfa zmierzono aktywnoœæ oraz obliczono stê¿enie 210Po w próbkach wody rzecznej pobranej z dorzecza Odry od paŸdziernika 2003 do lipca 2004. W okresie jesiennym najwiêksze stê¿enie 210Po stwierdzono w wodzie odrzanej

* Corresponding author. E-mail: [email protected]; Fax: (058) 523 53 38 + Dedicated to Professor Rajmund Dybczyñski on the occasion of his 75th birthday. 810 B. Skwarzec and A. Tuszkowska

pochodz¹cej z Gozdowic (1.64 ± 0.08 Bq m–3) oraz w wodzie z Nysy £u¿yckiej (5.21 ± 0.19 Bq m–3), najmniejsze w wodzie Baryczy i Bystrzycy (1.09 ± 0.03 i 1.09 ± 0.14 Bq m–3). Z kolei w okresie zimowym najwiêksze stê¿enie 210Po stwierdzono w wodzie odrzanej pobranej w Cha³upkach (3.64 ± 0.03 Bq m–3) i S³ubicach (3.62 ± 0.03 Bq m–3), najmniejsze zaœ w wodzie pochodz¹cej z Noteci (1.00 ± 0.06 Bq m–3). W okresie wiosennym najwiêksze stê¿enie 210Po stwierdzono w wodzie odrzanej ze S³ubic (3.32 ± 0.04 Bq m–3) oraz Nysy K³odzkiej (4.04 ± 0,03 Bq m–3), najmniejsze natomiast z Baryczy (1.10 ± 0.05 Bq m–3) oraz w G³ogowie (1.04 ± 0.06 Bq m–3). W okresie letnim najwiêksze stê¿enie 210Po zaobserwowano w wodzie z Widuchowej (1.79 ± 0.04 Bq m–3) oraz wodach z Nysy K³odzkiej (2.00 ± 0.05 Bq m–3), najmniejsze zaœ w wodzie odrzanej z Gozdowic (1,10 ± 0,05 Bq m–3) a tak¿e w wodach rzecznych Baryczy (0.60 ± 0.09 Bq m–3). W ci¹gu roku wodami Odry poprzez Zalew Szczeciñski wp³ywa do Morza Ba³tyckiego 14.76 GBq 210Po. Spoœród dop³ywów Odry najwiêksze sp³ywy powierzchniowe polonu 210Po zaobserwowano w okresie jesiennym (do 88 kBq.km–2 kwarta³–1 dla zlewni Nysy £u¿yckiej), najmniejsze natomiast w letnim (1 kBq km–2 kwarta³–1 dla zlewni Baryczy).

Some natural radionuclides of the 238U series (226Ra, 210Pb and 210Po) and the 232Th series (228Ra) are considered to be important either for their toxicological significance or their special accumulation behavior in the environment. The natural alpha emitter, 210 Po (T1/2 = 138.4 days), is of radioecological interest for the number of reasons, mainly because of its large contribution (90%) to the natural radiation dose received by many particularly aquatic organisms [1, 2]. Natural concentration of polonium in the environment can be enhanced due to the human activity (industrial processes such as sintering of ores in steelworks, burning of coal in coal-fired power stations, production and use of agricultural fertilizers, and domestic and industrial sewage) [3]. 210Po and 210Pb occur widely in the environment and constitute important compo- nents of the natural background radiation. Their presence in the terrestrial environment arises from 222Rn, which is a noble gas produced via alpha decay of 226Ra. The half-life of 222Rn (3.82 days) is sufficiently long to allow the isotope to diffuse from the soil to the atmosphere, where it decays finally to radioactive 210Pb and 210Po. These radionuclides are no longer in gaseous form, therefore return back to the Earth’s surface by both dry and wet deposition [4]. In an aquatic environment, polonium exists both in dissolved state and connected to the suspended matter. Its discharge into the coastal sea takes place mainly by a transport of sediment, whereas its discharge in a liquid form can account only for one third of the activities entering the estuary. In the estuary, residence time of dissolved 210Pb and 210Po was estimated to be 18 and 30 days, respectively [5]. Constant deposition of 210Po on large impoundments could lead to higher radioactivity buildup than in running waters carrying radioactivity away [1]. The main area, where polonium is retained, is aqueous environment. 210Po is accumulated there by marine plants and animals. The Odra and the Wis³a Rivers are two main sources of radionuclides and trace elements for the southern Baltic Sea [6, 2]. Inflow of 210Po from the Odra River catchment area to the Baltic Sea 811

Power industry based on the coal mining is the main source of waste and by-products with the increased content of radionuclides. In the coal mining industry, the mass of waste materials amounts to 50 mln tons p.a. For example, in power plants, the area covered with fly ash and sludge piles increases each year by several square kilometers. Underground coal mines in Poland often contain natural radioactive istotopes, mainly 226Ra and 228Ra. About 40% of their total amount stays underground as radioactive deposits but the rest is released daily into the rivers along with other mine effluents from coal mines [7, 8]. There has been little research in Poland with the aim to estimate the level of radionuclide concentration in Polish rivers. Our knowledge in this subject is still too small to estimate the amount of radionuclides transported from the Odra drainage to the Baltic Sea. The area of the Odra River watershed is 118 861 km2, whereof 106 050 km2 belongs to the Polish territory and represents 89.2% of the Odra catchment area. The length of the Odra is 854.3 km. Average elevation is 160 m and the larger part of the drainage area is located on the elevation between 100 and 300 m [9, 10]. Annually, the Odra River transports to the Szczecin Lagoon about 10.3 mln m3 of water with different fluvial material, including salt with considerable amount of natural radionuclides from the uranium series (238U, 234U, 226Ra, 210Pb, 210Po) [11]. Over 95% of the water supply in Poland originates from the atmospheric precipitation. The total runoff from all Poland territory to the Baltic Sea is approximately 60 000 m3 p.a., 34% of which are discharged by the Oder River [12]. Introduction of phosphate fertilizers to the soil (on average 19.7 kg ha–1 in 2003–2004 [10]) has a large influence on polonium concentration level. In Poland the plough ground area covered in 2004 about 16.3 mln ha, what constitutes 52.2% of the total country area [10, 13]. The aim of this work was to determine concentration of 210Po in the Oder River catchment area and to estimate its amount transported to the Baltic Sea.

EXPERIMENTAL

The sampling sites of surface water at the Oder River are presented in Figure 1. River water samples (volume about 60 dm3) were collected seasonally (every three months) from October 2003 to July 2004 down the main river bed of the Oder River (at 5 sites) and in the mouth of 8 main tributaries. Unfiltered water samples were subjected to the radiochemical procedure to determine concentration of polonium immediately after their collection and delivery to the laboratory. Before radiochemical treatment, water samples were 209 acidified with 65% HNO3 and ca 56 mBq of Po were added to each sample as a yield tracer. Polonium was co-precipitated with manganese dioxide and electrodeposited for 4 h on a silver disc at 90°C after mineralization with 65% HNO3 [6, 14]. 812 B. Skwarzec and A. Tuszkowska

Figure 1. Sampling sites of water. Odra – main river-bed: 1. Cha³upki, 6. G³ogów, 9. S³ubice, 12. Gozdowie, 13. Widuchowa; Tributaries: 2. Ma³a Panew – Turawa, 3. Nysa K³odzka – Skorogoszcz, 4. Bystrzyca – Jarno³tów, 5. Barycz – Osetno, 7. Bóbr – ¯agañ, 8. Nysa £u¿ycka – Gubin, 10. Warta – Gorzów Wielkopolski, 11. Noteæ – Goszczanowiec

Activity of 210Po was measured applying alpha spectrometry and using a Genie 2000 software package with surface barrier silicon detectors (PIPS) of 300 mm2 active surface area and 30–38% efficiency (Canberra– Packard, USA). Minimum Detectable Activity (MDA) was calculated as 0.1 mBq. Polonium samples were measured for 1–2 days and their activities were recalculated on the day of electrodeposition. Accuracy and precision of the radiochemical method were verified using IAEA reference materials (IAEA–384 and IAEA–414). The obtained results did not differ from the certified values by more than 8%. Chemical yield of polonium varied from 60% to 95%. The determined concentrations of polonium in river water samples and the corresponding standard deviations (SD) are shown in Table 1.

Table 1. Average concentration of 210Po in waters of the Oder and its tributaries

(Continuation on the next page) Inflow of 210Po from the Odra River catchment area to the Baltic Sea 813

Table 1. (Continuation)

RESULTS AND DISCUSSION

Concentrations of polonium 210Po in water samples from the Odra River and its tributaries are given in Table 1. In autumn, the highest concentration of 210Po was measured in the Odra at Gozdowice (1.64 ± 0.08 Bq m–3), and the lowest – at Widuchowa (1.25 ± 0.08 Bq m–3). Among the Odra tributaries in this period, the highest 210Po concentration was observed in the Nysa £u¿ycka River (5.21 ± 0.19 Bq m–3), and the lowest in the Barycz and the Bystrzyca Rivers (1.09 ± 0.07 Bq m–3 and 1.09 ± 0.06 Bq m–3, respectively). In winter, the concentration of 210Po in the Odra and its tributaries was higher than in autumn (Tab. 1). The highest amount of 210Po was determined in the Odra at Cha³upki (3.64 ± 0.03 Bq m–3) and S³ubice (3.62 ± 0.03 Bq m–3), and the lowest – at Widuchowa (1.13 ± 0.05 Bq m–3). Some variations in polonium concentration in the winter season were observed. 210Po concen- 814 B. Skwarzec and A. Tuszkowska tration ranged from 1.00 ± 0.06 Bq m–3 in the Noteæ River up to 7.83 ± 0.02 Bq m–3 in the Bystrzyca River. In spring, the highest amount of 210Po in the Odra River was observed at S³ubice (3.32 ± 0.04 Bq m–3) and the lowest at G³ogów (1.04 ± 0.06 Bq m–3). Among the tributaries of the Odra, the highest activity of 210Po was observed in the Nysa K³odzka (4.04 ± 0.03 Bq m–3) and the lowest in the mouths of the Barycz (1.10 ± 0.05 Bq m–3). In summer, the variations in polonium concentration in water samples were smaller (from 1.10 ± 0.05 Bq m–3 at Gozdowice to 1.79 ± 0.04 Bq m–3 at Widuchowa). Larger variations were found in the mouths of the Odra tributaries (from 0.60 ± 0.09 Bq m–3 in water from the Barycz River to 2.00±0.05 Bq.m-3 in the Nysa K³odzka River). The highest annual average concentration of polonium in the Odra was observed in water samples collected at S³ubice (2.39 ± 0.05 Bq m–3) and the lowest – at G³ogów (1.46 ± 0.06 Bq m–3). Among the Odra tributaries the highest activity of 210Po was found in water from the Nysa £u¿ycka (3.64 ± 0.07 Bq m–3) and the lowest in the water from the mouths of the Barycz River (1.02 ± 0.06 Bq m–3). The average 210Po concentration observed in the water from the Odra and its tributaries was higher than in the water from the southern Baltic Sea (0.59 Bq m–3). Based on the average seasonal and annual water flow of the Odra River and in the mouths of its tributaries, the seasonal and annual flow of polonium from the Odra drainage (Tab. 2) was calculated. The highest value of the seasonal flow of 210Po in the Odra and its tributaries was localized near the Szczecin Lagoon (Gozdowice – from 2.17 GBq quarter–1 in summer to 4.84 GBq quarter-1 in spring). The annual flow of polonium in this place was 14.8 GBq year–1. Therefore, both Odra and Vistula rivers are the most important sources of polonium in the southern Baltic Sea.

Table 2. Seasonal and average annual water flow of the Odra and its tributaries

(Continuation on the next page) Inflow of 210Po from the Odra River catchment area to the Baltic Sea 815

Table 2. (Continuation)

Among the Odra tributaries, the Warta River is characterized by the high runoff (from 0.96 GBq quarter–1 in autumn to 2.51 GBq quarter–1 in spring). The data in Table 3 show that seasonal inflow of polonium with the Odra water is the highest in spring. In this period, polonium eluted from the soil, contained in water from the melting snow and from dry and wet atmospheric precipitation is transported from the drainage area to the Baltic Sea. According to Carvalho, 210Po flowing through the estuary is exported to the coastal sea in a form bound to bottom sediments and suspended matter rather than in the soluble phase [5]. 816 B. Skwarzec and A. Tuszkowska

Table 3. Seasonal and annual runoff of 210Po from the Odra drainage Inflow of 210Po from the Odra River catchment area to the Baltic Sea 817

Table 4. Inflow of 210Po to the Baltic Sea

Processing of phosphate rock during production of phosphoric acid and, subse- quently, phosphate fertilizer is the important reason of enhanced natural radioactivity. Usually, phosphate rocks contain radionuclides of the uranium series of radioactivity ranging from 1300 to 1500 Bq kg–1 238U [15–17]. For example: Portuguese phosphogypsum contains 586 Bq kg–1 210Po [18]. Enhanced concentration of radionuclides constitutes an important problem of soil and groundwater pollution [19]. Ca 87–94% of 226Ra and 2–26% of uranium initially present in the phosphate rock can be still found in phosphogypsum (depending on the origin of the phosphate rock) [20]. In waste water from phosphoric acid production one can found the radionuclides connected firstly with phosphogipsum. This is a result of radionuclide leaching with acidic water (pH 1.6–2.0) in the following order: U > Po > Ra [20]. Therefore, in the neighborhood of phosphate fertilizers plants concentration of polonium in soil usually exceeded 285 mBq kg–1 in dry mass. The content of 210Po is also correlated with the concentration of 238U [21]. Knowing the concentration of 210Po and the surface area of the Odra tributaries, the surface runoff of polonium per unit area was calculated (Tab. 5 and Fig. 2). The data show that the inflow of 210Po is the highest in spring. Especially in mountain tributaries, such as the Nysa K³odzka and the Bystrzyca, the highest surface runoff was observed (Nysa K³odzka – 78 kBq km–2 quarter–1, Bystrzyca – 72 kBq km–2 quarter–1). The low-lying rivers contain polonium eluted from soil, which is strongly accumulated by the aquatic plants and animals. The amount of polonium in surface waters is related to the sampling site and hydrochemical parameters of water [1, 22]. During combustion some radionuclides are emitted to the atmosphere as a gas and radioactive dust, the others stay concentrated in ash [11, 24]. When coal is burned, radioelements become concentrated in the residual ash. For example, coal contains 20 Bq kg–1 210Po and 20 Bq kg–1 238U, however, in the fly ash the concentrations are 1700 Bq kg–1 for 210Po and 200 Bq kg–1 for 238U [25]. 818 B. Skwarzec and A. Tuszkowska

Table 5. Seasonal and annual surface runoff of 210Po from the Odra tributaries drainage

Figure 2. Average annual runoff of 210Po from the Odra tributaries drainage [kBq km–2 year–1] Inflow of 210Po from the Odra River catchment area to the Baltic Sea 819

CONCLUSIONS

The highest concentration of polonium in water samples from the Odra River and its tributaries was observed in spring, and the lowest in summer. The increased concentrations were observed in autumn. The largest amounts of 210Po were transported to the southern Baltic Sea in spring (4.82 GBq quarter–1), and the smallest in winter (2.23 GBq quarter–1). Annually, the Odra River supplies the Baltic Sea waters with 14.76 GBq 210Po through the Szczecin Lagoon and the Pomeranian Bay. The highest runoff of polonium, calculated on the basis of the known area of the Odra tributaries, was observed in winter (from 3 kBq km–2 quarter–1 for the Barycz drainage to 78 kBq km–2 quarter–1 for the Nysa £u¿ycka drainage), and the lowest in summer (from 1 kBq km–2 quarter–1 for the Barycz drainage to 39 kBq km–2 quarter–1 for the Nysa K³odzka drainage). The enhanced concentration of polonium in the Odra River and its tributaries is the result of the use of phosphate fertilizers in agriculture, discharge of saline coal mine waters, meltdown of snow, and enhanced dry and wet precipitation, which causes strong elution of radionuclides from soil and leaching of the materials from the river bed. In the Odra River drainage area the increasing amount of 210Po transported with water from the autumn to the summer season towards the estuary was observed.

Acknowledgements

The financial support of this work by the Ministry of Sciences and Higher Education, grant number: N N204 1590 33; and DS-8210-4-0086-8 is gratefully acknowledged.

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Received February 2008 Revised May 2008 Accepted July 2008