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Variations of 210Po and 210Pb concentration in mussels (Mytilus galloprovincialis) from Didim and Izmir Bay (Turkish coast of Aegean Sea)
Marine Pollution Bulletin 68 (2013) 152–156
Contents lists available at SciVerse ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Variations of 210Po and 210Pb concentration in mussels (Mytilus galloprovincialis) from Didim and Izmir Bay (Turkish coast of Aegean Sea) S. Aközcan a,⇑, A. Ug˘ur Görgün b a b
Kirklareli University, Faculty of Science and Literature, Department of Physics, Campus of Kavakli, Kirklareli, Turkey _ Ege University, Institute of Nuclear Sciences, Bornova, Izmir, Turkey
a r t i c l e
i n f o
Keywords: 210 Po 210 Pb Mussel Aegean Sea
a b s t r a c t In this study, the activity concentrations of 210Po and 210Pb were determined in mussels (Mytilus galloprovincialis) collected from Didim and Izmir Bay (Turkish coast of Aegean Sea) during the period of April 2006–March 2007. The concentrations activity of 210Po were determined spectroscopically through its 5.30 MeV alpha particle emission, using 209Po as an internal tracer. The 210Pb activity concentrations were determined from the ingrowth of 210Po, assuming zero initial 210Po activity. The results of 210Po and 210Pb activity concentrations were found to vary between 34 ± 9 and 1855 ± 98 Bq kg1 dry weight and ND (lower than limit of detection) – 64 ± 6 Bq kg1 dry weight, respectively. 210Po/210Pb ratio ranged between 1.00 and 106.87. The highest 210Po activities were found in mussels collected from Didim. Ó 2012 Elsevier Ltd. All rights reserved.
210 Po and 210Pb are the radionuclides within the 238U decay series with half lives of 138.4 days and 22.2 years, respectively. The main source of 210Po in the atmosphere is due to 222Rn emanating from the ground and its subsequent decay in the atmosphere. This process results in 210Po deposition on earth surface through fall out and rain (Mishra et al., 2009). 210Po is a hazardous element both chemically and radiologically. The radiotoxicity of 210Po is connected with the fact that it emits alpha particles with a relatively high energy of about 5.3 MeV (Stewart et al., 2008). It is known that the 210Po accumulated on marine organisms is generally derived from the food chain (Khan and Wesley, 2012; Carvalho and Fowler, 1994). Therefore the major contributor to radiation dose received by humans is from 210Po in sea food such as fish, crustacea and mollucs (Dahlgaard, 1996; Wildgust et al., 2000). 210 Pb is a beta emitter and also it is the second highest radiotoxic radionuclide in 238U decay chain, it decays into 210Bi, which further decays into 210Po (Štrok and Smodiš, 2011). 210 Po and 210Pb enter the aquatic environments mainly through the global fallout of aerosols and gases, released from the earth’s crustal material. In addition, the substances released due to activities related to the industrial waste such as mining, processing of phosphates and derivatives and oil industries are the other important pathways of these radionuclides (Germain et al., 1995; Camplin et al., 1996; McDonald et al., 1996; Carvalho, 1997; Godoy et al., 2008; Carvalho et al., 2010; Štrok and Smodiš, 2011). Mussels have been the main organism as pollution bioindicator for marine environmental monitoring of radioactive and
⇑ Corresponding author. Tel.: +90 2882461740. E-mail address: [email protected] (S. Aközcan). 0025-326X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2012.11.044
non-radioactive pollutants in coastal environments around the world. Besides, they are commonly used for pollution monitoring due to their sedentary filter feeding habits and ease of sampling. In particular, Mytilus galloprovincialis, a very common mussel, has been used as a sentinel organism for pollution monitoring because it is abundantly present along Turkish coast of the Aegean Sea. (Ryan et al., 1999; Carvalho et al., 2010, 2011). Since marine pollution levels tend to increase worldwide, the control strategies and routine monitoring are required. This paper reports the 210Po and 210Pb radioactivity concentrations in soft tissues of mussels collected periodically from a coastal and a gulf site. The biological and environmental parameters are also presented in order to assess the seasonal undulation and interdistrictal variation of radionuclide concentrations in mussels. Sampling for the determinations of 210Po and 210Pb in mussel (M. galloprovincialis) were done from the Izmir Bay and Didim in the coast of Aegean Sea between the April 2006 and March 2007. The sampling stations are presented in Fig. 1. The locations of the study areas are 37°250 N–27°260 E for Didim and 38°220 N– 26°460 E for Izmir Bay. Izmir Bay located at the west Anatolia is one of the great natural bays of the eastern Aegean Sea. It has been divided into three sections; Inner, Central and Outer Bays. Generally, the sections of the Bay are distinguished from one another by their different depth characteristics. The main urban conurbation around the bay is the Izmir city. Izmir is an important industrial and commercial center and a cultural location. The streams and small domestic discharge outlets flow to the Izmir Bay. The main industries in the region include food processing, beverage manufacturing and bottling, textile
S. Aközcan, A. Ug˘ur Görgün / Marine Pollution Bulletin 68 (2013) 152–156
153
Fig. 1. Map of sampling locations.
industries, oil, soap and paint production, metal and timber processing, chemical industries, paper and pulp factories (Küçüksezgin et al., 2006). Didim is a peninsula surrounded by the provincial limits of Mug˘la and the Akbük in the east, the Aegean Sea in the south west and the Bafa Lake and the Meander river in the north. Tourism is the main source of income for the area, particularly in summer. The region has been affected by Yatag˘an, Yeniköy and Kemerköy coal-fired power plants since 1982. The mussels were sampled at two stations (Didim and Izmir Bay) indicated in Fig. 1. After collection, the mussel samples were directly transferred to the laboratory and the shells were cleaned with a nylon brush, and were classified according to their size (1–4, 4–6, >6 cm). For each group, the soft tissues and shells of the mussels were separated and carefully rinsed with abundant distilled water in order to eliminate any sediment residues and other impurities. The soft parts, including interstitial fluid, were extracted from each sample and weighed. After dried to constant weight at 80 °C. They were grounded, passed through a 2 mm mesh, homogenized. These samples were processed for their determine 210Po and 210Pb content by alpha-counting following chemical purification and electroplating. After adding a standard addition of 209Po tracer, each sample was completely dissolved with HCl and HNO3. Polonium was spontaneously plated onto a copper disks of 2 cm in diameter in 0.5 M HCl in the presence of ascorbic acid to reduce Fe+3 to Fe+2(3) (Flynn, 1968). Measurements of 210Po were realized through its 5.30 MeV alpha particle, using 209Po (4.88 MeV alpha emission, t1/2 = 109 a) as the internal tracer. 209 Po tracer was added to determine the radiochemical recovery of the analysis and to calculate 210Po specific activity. (Wildgust et al., 2000). Measurements of alpha activities was performed using a Tennelec silicon surface-barrier detector (400 mm2 active area, 300 lm depletion depth) for which the efficiency is 29% using determined
226
Ra source. After the first deposition of 210Po, the residual solution was kept for 6 months to allow 210Po ingrowth from the 210 Pb present in the solution to determine the supported 210Pb in the samples. Bateman equations were used to obtain 210Pb activity from measured 210Po activity (Khan and Wesley, 2011). The activity concentration of 210Pb was calculated by measuring the activity of 210Po, using the following formula given below: The rate of decrease of 210Pb is given by:
dN0 ¼ k0 N0 dt
ð1Þ
where N0 and N1 are the number of 210Pb and 210Po nucleus and k0 and k1 the decay constants of 210Pb and 210Po. The rate of change of 210 Po is given by:
dN1 ¼ k0 N0 k1 N1 dt and activity of
ð2Þ
210
Pb.
dN0;0 k1 k0 dNa k0 t ek1 t 1 ¼ ½e dt k1 dt
ð3Þ
The activity concentrations of 210Po in mussel samples was found to vary between 34 ± 9 and 1855 ± 98 Bq kg1 (dry weight) for two stations. The values measured are presented in Figs. 2 and 3. The levels of 210Po concentrations in mussels from Izmir Bay for all seasons compared to those from Didim were found to be relatively low. The highest 210Po activity was found in the soft tissues of mussels with 1–4 cm shells length collected from Didim. The lowest activities were determined in the samples from Izmir Bay. As seen from Fig. 2, the highest activities were observed during the winter period and the lowest values during the summer period in Didim. Connan et al. (2007) have suggested that mussels bioaccumulate less 210Po during the warm period than the cold period. This finding can be attributed either or both to biological parameters e.g.
S. Aközcan, A. Ug˘ur Görgün / Marine Pollution Bulletin 68 (2013) 152–156
154
Fig. 2. Concentrations of
Fig. 3. Concentrations of
210
Po (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Didim.
210
Po (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Izmir Bay.
spawning time or environmental ones such as river outflow and agricultural activities. It is well known that the biological parameters play the main role in the bioaccumulation of polonium (Connan et al., 2007; Wildgust et al., 1998). In this study, the
Fig. 4. (a) Mean concentrations of 210Po (Bq kg1 dw) in all size classes of mussels (Mytilus galloprovincialis) sampled seasonally from each station, and (b) average seasonally rainfall in each station.
maximum seasonal 210Po activities determined in winter for Didim station as shown Fig. 4a. The possible source for the enhanced 210Po especially in Didim could be due to the discharge from Büyük Menderes river. Büyük Menderes river flows into Didim station by carrying fertilized agricultural soil. Likewise, Ug˘ur et al. (2006) studied variations of 210Po and 210Pb concentrations in mussels from Turkish coast of the Aegean Sea. They determined that the highest activities were observed during the winter period in mussels collected from Didim. Therefore, they have reported that the highest 210Po values in mussel were due to the discharge from Büyük Menderes river. Wildgust et al. (1998) reported that rainfall results in the introduction of 210Po into the sea from atmosphere. According to Turkish State Meteorological Service, the rain report for Didim and Izmir Meteorology which is shown in Fig. 4b supports our activity profiles during the 2006–2007. In this study a positive corelation was found between 210Po specific activity and rainfall (ANOVA, p < 0.05). Mussels profound ecological effects on marine environments. In particular, filter feeders, such as mussels, can be major consumers of phytoplancton (Elliotta et al., 2008). Wildgust et al. (1998) stated that high concentrations of 210Po were probably related to phytoplancton bloom. Likewise, Nybakken (1993) indicated that phtoplancton blooms generally occur during the spring and autumn in temperate regions. Our results in mussel samples collected from Izmir Bay are similar to those reported by Nybakken (1993). The results of this study were compared with the mean 210Po levels reported in a study conducted in Black Sea mussels (Güngör et al., 2006) This could be due to the fact that Aegean region is highly industrialized and there exist many large cities and also there are intense agricultural activities with dense use of fertilizer (Ug˘ur et al., 2006). The concentration of 210Pb in mussels (M. galloprovincialis) varies between ND (not detected) and 64 ± 6 Bq kg1 (dry weight). The values measured are presented in Figs. 5 and 6. The sampling
S. Aközcan, A. Ug˘ur Görgün / Marine Pollution Bulletin 68 (2013) 152–156
Fig. 5. Concentrations of
Fig. 6. Concentrations of
210
210
Pb (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Didim.
Pb (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Izmir Bay.
stations (Didim and Izmir Bay) are under the influence of Mediterranean climate. Therefore, especially high 210Pb concentrations in mussels in winter could be linked to high atmospheric deposition of 210Pb during this season (Ug˘ur et al., 2011). Table 1 present the measured 210Po and 210Pb activity concentrations in mussels compared with already reported values obtained from different regions of the world. Since the 210Po/210Pb activity ratio project the chemical properties of both radionuclides, it was also investigated. In our study the 210 Po/210Pb ratio in mussel samples varied between 1.00 and 106.87 with a mean value of 21.22, thus, 210Po data presented here is slightly affected by the decay of 210Pb. It is known that 210Po has considerably higher than 210Pb in marine organisms and the majority of 210Po in the mussel species comes from the environment, but not from the ingrowth of 210Pb, due to 210Po and 210Pb associate with particles in the marine with preferential adsorption on organic particles for 210Po and on fine inorganic particles for 210 Pb (Cherry and Heyraud, 1981; Charmasson et al., 2011; Tateta et al., 2003; Ug˘ur et al., 2011). Existing data in the literature for 210 Po/210Pb ratios are variable. The 210Po/210Pb ratio in total soft
Table 1 Comparison of
210
Po and
210
155
tissues of mussels collected from two different regions of Turkey (coastal of western Anatolia) are 3.1 and 25 showing a clear excess of 210Po relative to 210Pb (Ug˘ur et al. 2002). McDonald et al. (1986) reported that concentrations of 210Po and 210Pb varied from 428 ± 27 to 459 ± 18 Bq kg1(dry weight) and from 10.8 ± 1.4 to 13.9 ± 2.0 Bq kg1 (dry weight), respectively. In the same study, 210 Po/210Pb ratios were determined to vary from 33.5 to 41 for mussel samples collected from Monaco. As with 210Po, there were significant differences in 210Pb activity concentrations in the samples depending on the stations (p < 0.05). Also there were significant differences in 210Po and 210Pb concentrations in mussel samples with regard to the seasonal change (ANOVA, p < 0.05). 210 Po and 210Pb concentrations were measured in mussels (M. gallaoprovincialis) of Izmir Bay and Didim (Turkish coast of Aegean Sea). The results obtained in this study showed that 210Po levels in mussels collected along the Turkish coast were found in the range from (34 ± 9) Bq kg1 to (1855 ± 98) Bq kg1 dry weight while activity concentrations of 210Pb were between (ND) and (64 ± 6) Bq kg1 dry weight. The highest 210Po activity concentrations
Pb activity concentrations (Bq kg1) in mussels collected from different regions of the world.
Study area
210
Monaco United Kingdom Irish coast Aegean Sea (Turkish coast) Portugal Portugal Mid-Atlantic Ridge Adriatic coast Aegean Sea (Turkish coast)
428 ± 27–459 ± 18 104 ± 2–3124 ± 0.18 23 ± 15–468 ± 32 52 ± 6–1344 ± 108 518 ± 13–2254 ± 54 460 ± 128–1470 ± 291 72.4 ± 9–318.1 ± 27.7 22.1 ± 2.5–207 ± 21(fw) 34 ± 9–1855 ± 98
Po (Bq kg1)
210
Pb (Bq kg1)
11 ± 1–14 ± 2 2.8 ± 0.5–284 ± 14 4 ± 3–25 ± 2 6 ± 2–167 ± 10 21.5 ± 0.52–258.8 ± 10.5 23 ± 3–96 ± 7 3.5 ± 2.1–34.4 ± 5.2 2.8 ± 1.4–9.3 ± 0.7 ND–64 ± 6
References McDonald et al. (1986) McDonald et al. (1996) Ryan et al. (1999) Ug˘ur et al. (2002) Carvalho et al. (2010) Carvalho et al. (2011) Charmasson et al. (2011) Rozmaric et al. (2012) This work
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S. Aközcan, A. Ug˘ur Görgün / Marine Pollution Bulletin 68 (2013) 152–156
were observed in the mussel samples collected during the winter period from the Didim station. Izmir Bay station exhibited the lowest 210Po activities in mussels. The results were compared with those from other Mediterranean countries and were found to be in good agreement. The concentration of 210Po in the mussels has found to be higher than that of 210Pb. The mussel M. gallaoprovincialis has been identified to accumulate higher 210Po confirming that they could serve as an indicator organism of radionuclide pollutant in the environment. Acknowledgements This research work is supported by grants from Ege University Institute of Nuclear Sciences Contract No. 2006/NBE/001. References Camplin, W.C., Baxter, A.J., Round, G.D., 1996. The radiological impact of discharges of natural radionuclides from a phosphate plant in the United Kingdom. Environ. Int. 22, 259–270. Carvalho, F.P., Fowler, S.W., 1994. A double tracer technique to determine the relative importance of water and food as source of 210Po to marine prawns and fish. Mar. Ecol. Prog. Ser. 103, 251–264. Carvalho, F.P., 1997. Distribution, cycling and mean residence time of 226Ra, 210Pb and 210Po in the Targus estuary. Sci. Total Environ. 196, 151–161. Carvalho, F.P., Joao, M.O., Alberto, G., Battle, J.V., 2010. Allometric relationships of 210 Po and 210Pb and their application to environmental monitoring. Mar. Pollut. Bull. 60, 1734–1742. Carvalho, F.P., Joao, M.O., Alberto, G., 2011. Factor affecting 210Po and 210Pb activity concentrations in mussels and implications for environmental bio-monitoring programmes. J. Environ. Radioact. 102, 128–137. Charmasson, S., Faouder, A., Loyen, J., Cosson, R.P., Sarradin, P.M., 2011. 210Po and 210 Pb in the tissues of the deep-sea hydrothermal vent mussel Bathymodiolus azoricus from the Menez Gwen field (Mid-Atlantic Ridge). Sci. Total Environ. 409, 771–777. Cherry, R.D., Heyraud, M., 1981. Polonium-210 content of marine shrimp: variation with biological and environmental factors. Mar. Biol. 65, 165–175. Connan, O., Germain, P., Solier, L., Gouret, G., 2007. Variations of 210Po and 210Pb in various marine oragnisms from Western English Channel: contribution of 210Po to the radiation doses. J. Environ. Radioact. 97, 168–188. Dahlgaard, H., 1996. Polonium-210 in mussel and fish from Baltic-North Sea Estuary. J. Environ. Radioact. 32 (1–2), 91–96. Elliotta, P., Aldridgea, D.C., Moggridgeb, G.D., 2008. Zebra mussel filtration and its potential uses in industrial water treatment. Water Res. 42, 1664–1674. Flynn, W.W., 1968. The determination of low levels of polonium-210 in environmental materials. Anal. Chim. Acta 43, 221–227. Germain, P., Leclerc, G., Simon, S., 1995. Transfer of polonium-210 into Mytilus edulis (L.) and Fucus vesiculosus (L.) from the Baie de Seine (Channel coast of France). Sci. Total Environ. 164, 109–123.
Godoy, J.M., Oliveira, M.S., Almeida, C.E.B., Carvalho, Z.L., Silva, E.R., Fernandes, F.C., Pitanga, F.L., Danelon, O.M., 2008. 210Po concentration in Perna perna mussels: looking for radiation effects. J. Environ. Radioact. 99, 631–640. Güngör, N., Güngör, E., Göktepe, G., Köksal, G., 2006. 210Po in fish, algae, mussel and beach sediment samples collected along the Turkish coast of the Black Sea. Radioact. Environ. 8, 265–271. Khan, M.F., Wesley, S.G., 2011. Assessment of health safety from ingestion of natural radionuclides in seafoods from a tropical coast, India. Mar. Pollut. Bull. 62, 399– 404. Khan, M.F., Wesley, S.G., 2012. Radionuclide monitoring in molluscs inhabiting intertidal region near a nuclear installation, Gulf of Mannar. India Mar. Pollut. Bull. 64, 436–444. Küçüksezgin, F., Kontas, A., Altay, O., Uluturhan, E., Darılmaz, E., 2006. Assessment of marine pollution in Izmir Bay: nutrient, heavy metal and total hydrocarbon concentrations. Environ. Int. 32, 41–51. McDonald, P., Fowler, S.W., Heyraud, M., Baxter, M.S., 1986. Polonium-210 in mussels and its implications for environmental alphaautoradiography. J. Environ. Radioact. 3, 293–303. McDonald, P., Baxter, M.S., Scott, E.M., 1996. Technological enhancement of natural radionuclides in the marine environment. J. Environ. Radioact. 32 (1–2), 67–90. Mishra, S., Bhalke, S., Pandit, G.G., Puranik, V.D., 2009. Estimation of 210Po and its risk to human beings due to consumption of marine species at Mumbai, India. Chemosphere 76, 402–406. Nybakken, J.W., 1993. Marine Biology: An Ecological Approach, third ed. Harper Collins College Publishers, New York, NY. Rozmaric, M., Rogic, M., Benedic, L., Strok, M., Barisic, D., Ivsic, A. G., 2012. 210Po and 210 Pb activity concentrations in Mytilus galloprovincialis from Croatian Adriatic coast with the related dose assessment to the coastal, population. Chemosphere 87, 1295–1300. Ryan, T.P., Dowdall, A.M., McGarry, A.T., Pollard, D., Cunningham, J.D., 1999. 210 Po in Mytilus edulis in the Irish marine environment. J. Environ. Radioact. 43, 325– 342. Stewart, G.M., Fowler, S.W., Fisher, N.S., 2008. The bioaccumulation of U- and Th series radionuclides in marine organisms. Radioactiv. Environ. 13, 269– 305. Štrok, M., Smodiš, B., 2011. Levels of 210Po and 210Pb in fish and molluscs in Slovenia and the related dose assessment to the population. Chemosphere 82, 970–976. Tateta, Y., Carvalho, F.P., Fowler, S.W., Miquel, J.C., 2003. Fractionation of 210 Po and 210 Pb in coastal waters of the NW Mediterranean continental margin. Continental Shelf Res. 23 (3–4), 295–316. Ug˘ur, A., Gungor, Y., Bassari, A., 2002. Trace metals and 210 Po (210Pb) concentrations in mussels (Mytilus galloprovincialis) consumed in western Anatolia. Appl. Radiact. Isot. 57, 565–571. Ug˘ur, A., Yener, G., Topcuog˘lu, S., Sunlu, U., Akozcan, S., Ozden, B., 2006. 210 Po in mussels (Mytilus galloprovincialis) and sediments along the Turkish coast of the Aegean Sea. Radioact. Environ. 8, 272–280. Ug˘ur, A., Ozden, B., Filizok, I., 2011. Spatial and temporal variability of 210Po and 210 Pb in mussels (Mytilus galloprovincialis) at the Turkish coast of the Aegean Sea. Chemosphere 83, 1102–1107. Wildgust, M.A., McDonald, P., White, K.N., 1998. Temporal changes of 210Po in temperate coastal waters. Sci. Total Environ. 214, 1–10. Wildgust, M.A., McDonald, P., White, K.N., 2000. Assimilation of 210Po by the mussel Mytilus edulis from the alga Isochrysis galbana. Mar. Biol. 136, 49–53.
Contents lists available at SciVerse ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Variations of 210Po and 210Pb concentration in mussels (Mytilus galloprovincialis) from Didim and Izmir Bay (Turkish coast of Aegean Sea) S. Aközcan a,⇑, A. Ug˘ur Görgün b a b
Kirklareli University, Faculty of Science and Literature, Department of Physics, Campus of Kavakli, Kirklareli, Turkey _ Ege University, Institute of Nuclear Sciences, Bornova, Izmir, Turkey
a r t i c l e
i n f o
Keywords: 210 Po 210 Pb Mussel Aegean Sea
a b s t r a c t In this study, the activity concentrations of 210Po and 210Pb were determined in mussels (Mytilus galloprovincialis) collected from Didim and Izmir Bay (Turkish coast of Aegean Sea) during the period of April 2006–March 2007. The concentrations activity of 210Po were determined spectroscopically through its 5.30 MeV alpha particle emission, using 209Po as an internal tracer. The 210Pb activity concentrations were determined from the ingrowth of 210Po, assuming zero initial 210Po activity. The results of 210Po and 210Pb activity concentrations were found to vary between 34 ± 9 and 1855 ± 98 Bq kg1 dry weight and ND (lower than limit of detection) – 64 ± 6 Bq kg1 dry weight, respectively. 210Po/210Pb ratio ranged between 1.00 and 106.87. The highest 210Po activities were found in mussels collected from Didim. Ó 2012 Elsevier Ltd. All rights reserved.
210 Po and 210Pb are the radionuclides within the 238U decay series with half lives of 138.4 days and 22.2 years, respectively. The main source of 210Po in the atmosphere is due to 222Rn emanating from the ground and its subsequent decay in the atmosphere. This process results in 210Po deposition on earth surface through fall out and rain (Mishra et al., 2009). 210Po is a hazardous element both chemically and radiologically. The radiotoxicity of 210Po is connected with the fact that it emits alpha particles with a relatively high energy of about 5.3 MeV (Stewart et al., 2008). It is known that the 210Po accumulated on marine organisms is generally derived from the food chain (Khan and Wesley, 2012; Carvalho and Fowler, 1994). Therefore the major contributor to radiation dose received by humans is from 210Po in sea food such as fish, crustacea and mollucs (Dahlgaard, 1996; Wildgust et al., 2000). 210 Pb is a beta emitter and also it is the second highest radiotoxic radionuclide in 238U decay chain, it decays into 210Bi, which further decays into 210Po (Štrok and Smodiš, 2011). 210 Po and 210Pb enter the aquatic environments mainly through the global fallout of aerosols and gases, released from the earth’s crustal material. In addition, the substances released due to activities related to the industrial waste such as mining, processing of phosphates and derivatives and oil industries are the other important pathways of these radionuclides (Germain et al., 1995; Camplin et al., 1996; McDonald et al., 1996; Carvalho, 1997; Godoy et al., 2008; Carvalho et al., 2010; Štrok and Smodiš, 2011). Mussels have been the main organism as pollution bioindicator for marine environmental monitoring of radioactive and
⇑ Corresponding author. Tel.: +90 2882461740. E-mail address: [email protected] (S. Aközcan). 0025-326X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2012.11.044
non-radioactive pollutants in coastal environments around the world. Besides, they are commonly used for pollution monitoring due to their sedentary filter feeding habits and ease of sampling. In particular, Mytilus galloprovincialis, a very common mussel, has been used as a sentinel organism for pollution monitoring because it is abundantly present along Turkish coast of the Aegean Sea. (Ryan et al., 1999; Carvalho et al., 2010, 2011). Since marine pollution levels tend to increase worldwide, the control strategies and routine monitoring are required. This paper reports the 210Po and 210Pb radioactivity concentrations in soft tissues of mussels collected periodically from a coastal and a gulf site. The biological and environmental parameters are also presented in order to assess the seasonal undulation and interdistrictal variation of radionuclide concentrations in mussels. Sampling for the determinations of 210Po and 210Pb in mussel (M. galloprovincialis) were done from the Izmir Bay and Didim in the coast of Aegean Sea between the April 2006 and March 2007. The sampling stations are presented in Fig. 1. The locations of the study areas are 37°250 N–27°260 E for Didim and 38°220 N– 26°460 E for Izmir Bay. Izmir Bay located at the west Anatolia is one of the great natural bays of the eastern Aegean Sea. It has been divided into three sections; Inner, Central and Outer Bays. Generally, the sections of the Bay are distinguished from one another by their different depth characteristics. The main urban conurbation around the bay is the Izmir city. Izmir is an important industrial and commercial center and a cultural location. The streams and small domestic discharge outlets flow to the Izmir Bay. The main industries in the region include food processing, beverage manufacturing and bottling, textile
S. Aközcan, A. Ug˘ur Görgün / Marine Pollution Bulletin 68 (2013) 152–156
153
Fig. 1. Map of sampling locations.
industries, oil, soap and paint production, metal and timber processing, chemical industries, paper and pulp factories (Küçüksezgin et al., 2006). Didim is a peninsula surrounded by the provincial limits of Mug˘la and the Akbük in the east, the Aegean Sea in the south west and the Bafa Lake and the Meander river in the north. Tourism is the main source of income for the area, particularly in summer. The region has been affected by Yatag˘an, Yeniköy and Kemerköy coal-fired power plants since 1982. The mussels were sampled at two stations (Didim and Izmir Bay) indicated in Fig. 1. After collection, the mussel samples were directly transferred to the laboratory and the shells were cleaned with a nylon brush, and were classified according to their size (1–4, 4–6, >6 cm). For each group, the soft tissues and shells of the mussels were separated and carefully rinsed with abundant distilled water in order to eliminate any sediment residues and other impurities. The soft parts, including interstitial fluid, were extracted from each sample and weighed. After dried to constant weight at 80 °C. They were grounded, passed through a 2 mm mesh, homogenized. These samples were processed for their determine 210Po and 210Pb content by alpha-counting following chemical purification and electroplating. After adding a standard addition of 209Po tracer, each sample was completely dissolved with HCl and HNO3. Polonium was spontaneously plated onto a copper disks of 2 cm in diameter in 0.5 M HCl in the presence of ascorbic acid to reduce Fe+3 to Fe+2(3) (Flynn, 1968). Measurements of 210Po were realized through its 5.30 MeV alpha particle, using 209Po (4.88 MeV alpha emission, t1/2 = 109 a) as the internal tracer. 209 Po tracer was added to determine the radiochemical recovery of the analysis and to calculate 210Po specific activity. (Wildgust et al., 2000). Measurements of alpha activities was performed using a Tennelec silicon surface-barrier detector (400 mm2 active area, 300 lm depletion depth) for which the efficiency is 29% using determined
226
Ra source. After the first deposition of 210Po, the residual solution was kept for 6 months to allow 210Po ingrowth from the 210 Pb present in the solution to determine the supported 210Pb in the samples. Bateman equations were used to obtain 210Pb activity from measured 210Po activity (Khan and Wesley, 2011). The activity concentration of 210Pb was calculated by measuring the activity of 210Po, using the following formula given below: The rate of decrease of 210Pb is given by:
dN0 ¼ k0 N0 dt
ð1Þ
where N0 and N1 are the number of 210Pb and 210Po nucleus and k0 and k1 the decay constants of 210Pb and 210Po. The rate of change of 210 Po is given by:
dN1 ¼ k0 N0 k1 N1 dt and activity of
ð2Þ
210
Pb.
dN0;0 k1 k0 dNa k0 t ek1 t 1 ¼ ½e dt k1 dt
ð3Þ
The activity concentrations of 210Po in mussel samples was found to vary between 34 ± 9 and 1855 ± 98 Bq kg1 (dry weight) for two stations. The values measured are presented in Figs. 2 and 3. The levels of 210Po concentrations in mussels from Izmir Bay for all seasons compared to those from Didim were found to be relatively low. The highest 210Po activity was found in the soft tissues of mussels with 1–4 cm shells length collected from Didim. The lowest activities were determined in the samples from Izmir Bay. As seen from Fig. 2, the highest activities were observed during the winter period and the lowest values during the summer period in Didim. Connan et al. (2007) have suggested that mussels bioaccumulate less 210Po during the warm period than the cold period. This finding can be attributed either or both to biological parameters e.g.
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154
Fig. 2. Concentrations of
Fig. 3. Concentrations of
210
Po (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Didim.
210
Po (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Izmir Bay.
spawning time or environmental ones such as river outflow and agricultural activities. It is well known that the biological parameters play the main role in the bioaccumulation of polonium (Connan et al., 2007; Wildgust et al., 1998). In this study, the
Fig. 4. (a) Mean concentrations of 210Po (Bq kg1 dw) in all size classes of mussels (Mytilus galloprovincialis) sampled seasonally from each station, and (b) average seasonally rainfall in each station.
maximum seasonal 210Po activities determined in winter for Didim station as shown Fig. 4a. The possible source for the enhanced 210Po especially in Didim could be due to the discharge from Büyük Menderes river. Büyük Menderes river flows into Didim station by carrying fertilized agricultural soil. Likewise, Ug˘ur et al. (2006) studied variations of 210Po and 210Pb concentrations in mussels from Turkish coast of the Aegean Sea. They determined that the highest activities were observed during the winter period in mussels collected from Didim. Therefore, they have reported that the highest 210Po values in mussel were due to the discharge from Büyük Menderes river. Wildgust et al. (1998) reported that rainfall results in the introduction of 210Po into the sea from atmosphere. According to Turkish State Meteorological Service, the rain report for Didim and Izmir Meteorology which is shown in Fig. 4b supports our activity profiles during the 2006–2007. In this study a positive corelation was found between 210Po specific activity and rainfall (ANOVA, p < 0.05). Mussels profound ecological effects on marine environments. In particular, filter feeders, such as mussels, can be major consumers of phytoplancton (Elliotta et al., 2008). Wildgust et al. (1998) stated that high concentrations of 210Po were probably related to phytoplancton bloom. Likewise, Nybakken (1993) indicated that phtoplancton blooms generally occur during the spring and autumn in temperate regions. Our results in mussel samples collected from Izmir Bay are similar to those reported by Nybakken (1993). The results of this study were compared with the mean 210Po levels reported in a study conducted in Black Sea mussels (Güngör et al., 2006) This could be due to the fact that Aegean region is highly industrialized and there exist many large cities and also there are intense agricultural activities with dense use of fertilizer (Ug˘ur et al., 2006). The concentration of 210Pb in mussels (M. galloprovincialis) varies between ND (not detected) and 64 ± 6 Bq kg1 (dry weight). The values measured are presented in Figs. 5 and 6. The sampling
S. Aközcan, A. Ug˘ur Görgün / Marine Pollution Bulletin 68 (2013) 152–156
Fig. 5. Concentrations of
Fig. 6. Concentrations of
210
210
Pb (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Didim.
Pb (Bq kg1 dw) in three different size-groups of mussels (Mytilus galloprovincialis) sampled monthly from Izmir Bay.
stations (Didim and Izmir Bay) are under the influence of Mediterranean climate. Therefore, especially high 210Pb concentrations in mussels in winter could be linked to high atmospheric deposition of 210Pb during this season (Ug˘ur et al., 2011). Table 1 present the measured 210Po and 210Pb activity concentrations in mussels compared with already reported values obtained from different regions of the world. Since the 210Po/210Pb activity ratio project the chemical properties of both radionuclides, it was also investigated. In our study the 210 Po/210Pb ratio in mussel samples varied between 1.00 and 106.87 with a mean value of 21.22, thus, 210Po data presented here is slightly affected by the decay of 210Pb. It is known that 210Po has considerably higher than 210Pb in marine organisms and the majority of 210Po in the mussel species comes from the environment, but not from the ingrowth of 210Pb, due to 210Po and 210Pb associate with particles in the marine with preferential adsorption on organic particles for 210Po and on fine inorganic particles for 210 Pb (Cherry and Heyraud, 1981; Charmasson et al., 2011; Tateta et al., 2003; Ug˘ur et al., 2011). Existing data in the literature for 210 Po/210Pb ratios are variable. The 210Po/210Pb ratio in total soft
Table 1 Comparison of
210
Po and
210
155
tissues of mussels collected from two different regions of Turkey (coastal of western Anatolia) are 3.1 and 25 showing a clear excess of 210Po relative to 210Pb (Ug˘ur et al. 2002). McDonald et al. (1986) reported that concentrations of 210Po and 210Pb varied from 428 ± 27 to 459 ± 18 Bq kg1(dry weight) and from 10.8 ± 1.4 to 13.9 ± 2.0 Bq kg1 (dry weight), respectively. In the same study, 210 Po/210Pb ratios were determined to vary from 33.5 to 41 for mussel samples collected from Monaco. As with 210Po, there were significant differences in 210Pb activity concentrations in the samples depending on the stations (p < 0.05). Also there were significant differences in 210Po and 210Pb concentrations in mussel samples with regard to the seasonal change (ANOVA, p < 0.05). 210 Po and 210Pb concentrations were measured in mussels (M. gallaoprovincialis) of Izmir Bay and Didim (Turkish coast of Aegean Sea). The results obtained in this study showed that 210Po levels in mussels collected along the Turkish coast were found in the range from (34 ± 9) Bq kg1 to (1855 ± 98) Bq kg1 dry weight while activity concentrations of 210Pb were between (ND) and (64 ± 6) Bq kg1 dry weight. The highest 210Po activity concentrations
Pb activity concentrations (Bq kg1) in mussels collected from different regions of the world.
Study area
210
Monaco United Kingdom Irish coast Aegean Sea (Turkish coast) Portugal Portugal Mid-Atlantic Ridge Adriatic coast Aegean Sea (Turkish coast)
428 ± 27–459 ± 18 104 ± 2–3124 ± 0.18 23 ± 15–468 ± 32 52 ± 6–1344 ± 108 518 ± 13–2254 ± 54 460 ± 128–1470 ± 291 72.4 ± 9–318.1 ± 27.7 22.1 ± 2.5–207 ± 21(fw) 34 ± 9–1855 ± 98
Po (Bq kg1)
210
Pb (Bq kg1)
11 ± 1–14 ± 2 2.8 ± 0.5–284 ± 14 4 ± 3–25 ± 2 6 ± 2–167 ± 10 21.5 ± 0.52–258.8 ± 10.5 23 ± 3–96 ± 7 3.5 ± 2.1–34.4 ± 5.2 2.8 ± 1.4–9.3 ± 0.7 ND–64 ± 6
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