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Activity levels of 210Po and 210Pb in some fish species of the Izmir Bay (Aegean Sea)
Marine Pollution Bulletin 66 (2013) 234–238
Contents lists available at SciVerse ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Edited by Bruce J. Richardson The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only those papers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to ‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 60, 1–2).
Activity levels of 210Po and 210Pb in some fish species of the Izmir Bay (Aegean Sea) S. Aközcan a,⇑, A. Ug˘ur b a b
Kirklareli University, Department of Physics, Campus of Kavakli, Kirklareli, Kavakli, Turkey Ege University, Institute of Nuclear Sciences, 35100 Izmir, Turkey
a r t i c l e
i n f o
Keywords: Fish 210 Po 210 Pb Aegean Sea
a b s t r a c t Concentrations of 210Po and 210Pb were determined in the edible muscle tissue of twelve species of marine fish collected from Izmir Bay in the Aegean Sea Region of Turkey during the 2006–2007. 210Po activity concentrations in fish samples were found to vary from ND to 400 ± 9 Bq kg1 dry weight and 210Pb activity concentrations were found to vary from ND to 15 ± 3 Bq kg1 dry weight. The highest dose contribution due to 210Po to humans was found to be 8.908 lSv y1. Ó 2012 Elsevier Ltd. All rights reserved.
210
Po and 210Pb are members of 238U decay series. The natural radionuclides 210Po and 210Pb are well known to be particlereactive in the marine environment. 210Po in water column is preferentially absorbed by plankton and is abundant in their organic detrital particles, while 210Pb is adsorptive to fine inorganic particles in sea water. Therefore, these two radionuclides are regarded as good tracers for fine organic and inorganic particles in marine waters (Tateda et al., 2003). In additonal they are both reactive elements, their half lives are adapted to the study of marine biogeochemical processes and (Radakovitch et al., 1997). 210Pb is a beta emitter with a half-life of 22.2 years and decays into 210Bi, which further decays into 210Po with a half-life of 138.4 days (Browne et al., 1986; ENSDF, 2006; Magill et al., 2006; Štrok, and Smodiš, 2011). The main source of the 210Po and 210Pb is the 222Rn emanation, which is released from the earth’s crust to the atmosphere. 210 Po attaches itself further electrostatically to aerosol particles and are transported returns to earth’s surface to soil, plant and aquatic environments by dry deposition and wash out (Mishra et al., 2009; Mat Çatal et al., 2012). 210Pb is a particle reactive natural radionuclide and quickly absorbs to settling particulate mat-
⇑ Corresponding author. Tel.: +90 5057980659. 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.2012.10.003
ter. Regionally, 210Po and 210Pb activities may be influenced by industrial waste coming from mining, processing of phosphates and derivatives (Germain et al., 1995; McDonald et al., 1996; Connan et al., 2007). A large contribution to the radiation dose received by humans comes from 210Po, 210Pb and 210Bi radionuclides accumulated in body (Carvalho, 1995; Al-Masri et al., 2000). In particulary, in marine environment these radionuclides are known to be strongly accumulated by marine organisms and transferred to man with ingested food (Carvalho and Fowler, 1994; Carvalho, 1995, 2011). Altough, because the majority of studies on intake of 210Po and 210Pb are based on analyses of sea food, a widespread conclusion has been the existence of a 210Po:210Pb ratio lower than or near to unity in the human food (Carvalho, 1995; Dahlgaard, 1996; Aarkrog et al., 1997; Al-Masri et al., 2000). 210Po especially, provides a major contribution (90%) to the natural radiation dose from alpha emitting radionuclides to most marine organisms (Mishra et al., 2009; Cherry and Shannon, 1974; Stepnowski and Skwarzec, 2000; Wildgust et al., 2000). According to literature data the dose due to ingestion of 210Po was about 7% of the natural internal radiation dose. Also about 18% of the average internal dose of the population is due to ingestion of 210Po along with its precursor 210Pb (Bulman et al., 1995; Din, 2011). In the marine environment, fish is the final chain of aquatic food web and an important food source for the people of the world. The
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238
235
Fig. 1. The map of the study area.
uptake mechanism of these radionuclides by fish reflects biological variables such as feeding habits and location. Izmir Bay population consumes relatively large quantities of sea food. Therefore, the objectives of this study are to (i) present activity concentration data of 210Po and 210Pb in different species of fishes, (ii) estimate the committed effective dose to humans from Po-210 contained in fish consumed by inhabitants in Izmir Bay. In order to obtain a representative sample 12 fish species were collected from 2006 to 2007 at Izmir Bay, monthly (Fig. 1). The species were Sardine (Sardina plichardus), Grey mullet (Mugil cephalus), Bogue (Boops bopps), Seabass (Dicentrarchus labrax), Atlantic mackerel (Scomber scombrus), Two-banded bream (Diplodus vulgaris), Twaite shad (Alosa fallax), Salema (Sarpa salpa), Picarel (Spicara smaris), Red mullet (Mullus barbatus), Horse mackerel (Trachurus trachurus) and Gilt-head sea bream (Sparus aurata). Izmir Bay (western Turkey) is one of the largest natural bays in the eastern Aegean Sea in the eastern Mediterranean. The bay has been divided into three parts: inner, middle and outer according to the physical characteristics of the different water masses. The main urban conurbation around the bay is the Izmir Metropolitan Municipality. Izmir is an important industrial and commercial centre and a cultural focal point. Besides untreated wastewaters originating from the increasing population and substantial industrial development, intensive harbour activities in the bay and agriculture in the surrounding areas have exerted considerable pollution loads particularly to the inner Izmir Bay (Bizsel and Uslu, 2000; Küçüksezgin et al., 2006). The samples were washed first with seawater and then with distilled water. The fishes were separated into viscera and hard tissues. The 210Po and 210Pb concentrations were determined in the edible muscle tissue of different fish species. The edible muscle tissues were weighed and oven dried to a constant dry weight (dw) at 80 °C. The samples were ground and passed through a 2 mm mesh sieve followed by homogenisation. After the addition of a standardized amount of 209Po (4.88 MeV alpha emission, t1/2 = 109 year) tracer, each sample was completely dissolved with HCl and HNO3. Polonium was spontaneously plated onto copper discs (Flynn, 1968).
210
Po levels were measured via 5.30 MeV alpha particle emission rates using a high-resolution alpha spectrometer equipped with Passivated Implanted Planar Silicon (PIPS) detector (Canberra 7401). Typical resolution was 30 keV (full-width at half-maximum (FWHM)) for a 450 mm2 area detector. After the first deposition of 210 Po, the residual 0.5 M HCl was kept for about one year to allow 210 Po in-growth from the 210Pb contained in the sample solution. The samples were re-plated and the 210Po activities were determined. The second deposition provided information on the 210Pb content of the samples and thus indicated the extent to which the initial 210Po was supported by its grandparent species. Well known Bateman equations were used to obtain 210Pb activity from measured 210Po activity. 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 is the number of 210Pb nuclei and k0 the decay constant of 210 Pb. The rate of change of 210Po is given by:
dN0 ¼ k0 N0 k1 N1 dt
ð2Þ
where N1 is the number of 210Po nuclei and k1 the decay constant of 210 Po. Just after the deposition of 210Po, t0 = 0,
N0 ¼ N0;0
ð3Þ
N1 ¼ 0
ð4Þ
From Eq. (1) and initial condition (3) the number of given as follows:
N0 ¼ N0;0 ek0 t
210
Pb nuclei is
ð5Þ
Combining Eqs. (2) and (5) and initial condition (4) the number of 210 Po nuclei is given as follows:
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238
236 Table 1 Mean activity concentrations of
210
Po and
210
Pb (Bq kg1 dry wt.) and weight ratio in fish samples. The uncertainties represent 1 sigma standard deviations.
Fish species
Feeding habitat
Type of feding
Weight ratio dry/wet
210
210
Sardine (n = 360) (Sardina plichardus) Grey mullet (n = 44) (Mugil cephalus) Bogue (n = 72) (Boops bopps) Seabass (n = 48) (Dicentrarchus labrax) Atlantic mackerel (n = 92) (Scomber scombrus) Two–banded bream (n = 9) (Diplodus vulgaris) Twaite shad (n = 27) (Alosa fallax) Salema (n = 8) (Sarpa salpa) Picarel (n = 24) (Spicara smaris) Red mullet (n = 18) (Mullus barbatus) Horse mackerel (n = 90) (Trachurus trachurus)
P D&P P&D D&P P D P D&P P D
Carnivores (planktivor) Omnivores (planktivor) Carnivores (planktivor) Carnivores (piscivor) Carnivores (planktivor) Carnivores Carnivores (planktivor) Omnivores Carnivores (planktivor) Carnivores
0.29 0.25 0.26 0.27 0.28 0.23 0.27 0.24 0.23 0.26
91.3 ± 3.8 3.0 ± 0.2 12.5 ± 1.3 3.0 ± 0.3 23.2 ± 2.0 ND 46.7 ± 1.0 ND 14.0 ± 2.5 60.0 ± 3.0
4.7 ± 1.8 2.0 ± 0.9 2.8 ± 1.4 NDa 2.1 ± 1.1 4.0 ± 1.0 1.0 ± 0.7 NDa NDa NDa
19.43 1.5 4.46 – 11.05 – 46.7 – – –
P D
Carnivores (planktivor) Carnivores
0.26 0.32
18.6 ± 2.0 ND
1.3 ± 0.9 2.0 ± 1.0
14.31 –
0.23–0.32
ND–91.3
ND–4.7
1.50–46.70
Gilt–head sea bream (n = 48) (Sparus aurata) Range
Po (Bq kg1)
Pb (Bq kg1)
210
Po/210Pb
P: pelagic, D: demersal. a ND = not detected.
Table 2 210 Po and
a
N1 ¼
210
Pb concentrations in fish from different regions of the world.
Country
210
Portugal Japan America Poland Syria Sudan India Slovenia Turkey
0.2–11 0.6–2.6 0.4–153.3 0.9–5 0.27–27.48 0.25–6.42 1.2–92.3 0.039–35 a ND–100
210
Po (Bq kg1 w.w.)
– 0.04–0.54 0.1–7 – 0.05–0.38 – 1.1–14.8 0.13–0.82 a ND–3.75
References Carvalho, 1988 Yamamoto et al., 1994 Noshkin et al., 1994 Skwarzec (1997) Al-Masri et al. (2000) Hassona et al. (2008) Khan and Wesley (2011) Štrok and Smodiš (2011) This work
ND = not detected.
k0 N0;0 k1 k0
ð6Þ
By measuring the decay rate of 210Po, (dNa/dt) = k1N1 at a certain time t and using Eq. (1) at t = 0, Eq. (6) can be written as: and activity of 210Pb (Khan and Wesley, 2011).
dN0;0 k1 k0 dNa k0 t ek1 t 1 ¼ ½e dt k1 dt
ð7Þ
Lower limit of detection (LLD) was calculated using the Currie definition (Currie, 1968), using the following formula : 1
LLD ¼
Pb (Bq kg1 w.w.)
2:71 þ 4:65B2 et
where B is the background counts, e is the counting efficiency and t, counting time. The concentration of 210Po in a small number of samples was below the detection limit, but most of the 210Po activity levels were above this value (0.0003 Bq). Counting period was adjusted to obtain relative standard error of approximately 5%. Final activity calculations were attained to include the appropriate corrections for blanks and also for collection date. The recovery rates of standardized tracer for the fish samples varied from 70% to 90%. The alpha spectrometry system was calibrated with certified reference material, IAEA-437 (mussel). The average 210Po and 210Pb concentrations in samples and weight ratios are given in Table 1. 210Po and 210Pb concentrations in fish species collected from different regions of the world also given Table 2. 210 Po and 210Pb concentration in fish samples range from ND (not detected) to 400 ± 9 Bq kg1 dry wt. and ND (not detected) to 15 ± 3 Bq kg1 dry wt., respectively, with an average value of
7.72 ± 1.34 Bq kg1 dry wt. for 210Po and 1.66 ± 0.73 Bq kg1 dry wt. for 210Pb. The highest concentration of 210Po was measured in the sardine samples collected in autumn. The highest mean 210Po concentrations in fishes were found in sardine followed by, red mullet, twaite shad atlantic mackerel and horse mackerel. Besides, measured activities in these species feed on planktons are much higher than the average values. Strok and Smodis stated that the pelagic environment and plankton feeding contribute significantly to the 210 Po accumulation. And also, they are reported the larger is the animal, the lower is the 210Po activity concentration (Štrok and Smodiš, 2011). This is due to the slower metabolism of the larger, older and heavier animals. In this study, generally mean 210Po activity concentrations in small species like sardine (91.3 Bq kg1) and red mullet (60 Bq kg1) are higher than other larger species like Gilt-head sea bream (ND). It is because the small pelagic plankton feeding fish like sardine (Sardine plichardus) tend to accumulate more 210Po. However, low 210 Po concentrations were detected in other carnivorous fish, like the gilt-head sea bream and two-banded bream (Mat Çatal et al., 2012). Wildgust et al. indicated that 210Po behaves in a similar manner to other trace metals, seasonal changes arising from phytoplankton blooms, physico-chemical parameters and biological variables (Wildgust et al., 1998). They indicated that phytoplankton blooms generally occur during the spring and autumn in temperate regions. Our results in samples collected from Izmir Bay are similar to those given by Wildgust et al. In additional, Wildgust et al. reported that rain results in the introduction of 210Po into the sea. 210Po and 210Pb return to the earth as dry fallout or are washed out in rain. Ug˘ur et al. studied on the activity concentrations of 210Po and 210Pb in rainwater samples in Izmir. They measured that the activity concentrations of 210Po and 210Pb in rainwater vary considerably according to seasonal transport of
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238 Table 3 Minimum, mean and maximum values of
210
Po and
237
210
Pb in fish samples.
Radionuclides
Fish species
Minimum
Mean
Maximum
210
Po
Sardine (Sardina plichardus) Grey mullet (Mugil cephalus) Bogue (Boops bopps) Seabass (Dicentrarchus labrax) Atlantic mackerel (Scomber scombrus) Two-banded bream (Diplodus vulgaris) Twaite shad (Alosa fallax) Salema (Sarpa salpa) Picarel (Spicara smaris) Red mullet (Mullus barbatus) Horse mackerel (Trachurus trachurus) Gilt-head sea bream (Sparus aurata)
14 ND ND ND ND ND ND ND 10 ND ND ND
54.5 6.5 12 4.5 25 ND 23 ND 14 30 19.5 ND
400 24 27 9 42 ND 117 ND 18 60 31 ND
210
Pb
Sardine (Sardina plichardus) Grey mullet (Mugil cephalus) Bogue (Boops bopps) Seabass (Dicentrarchus labrax) Atlantic mackerel (Scomber scombrus) Two-banded bream (Diplodus vulgaris) Twaite shad (Alosa fallax) Salema (Sarpa salpa) Picarel (Spicara smaris) Red mullet (Mullus barbatus) Horse mackerel (Trachurus trachurus) Gilt-head sea bream (Sparus aurata)
ND ND ND ND ND ND ND ND ND ND ND ND
4.5 2 3 ND 2.5 2 1.5 ND ND ND 1.5 1.5
15 7 7 ND 5 4 3 ND ND ND 3 5
ND = not detected.
Table 4 Annual dose due to consumption of different fish species contaminated by Fish species Sardine (Sardina plichardus) Grey mullet (Mugil cephalus) Bogue (Boops bopps) Seabass (Dicentrarchus labrax) Atlantic mackerel (Scomber scombrus) Two-banded bream (Diplodus vulgaris) Twaite shad (Alosa fallax) Salema (Sarpa salpa) Picarel (Spicara smaris) Red mullet (Mullus barbatus) Horse mackerel (Trachurus trachurus) Gilt–head sea bream (Sparus aurata)
210
Po.
Dose (lSv y1) 8.908 0.044 0.343 0.008 0.093 – 0.287 – 0.044 0.389 0.252 –
the radionuclides. As indicated by Ug˘ur et al. whether dry or wet deposition is dominating removal process depends on the climate (Ug˘ur et al., 2011). However, according to Turkish State Meteorological Service, the rain report Izmir Meteorology supports concentrations of 210Po during the 2006–2007. In study correlation was found between 210Po specific activity and rainfall. In comparison with other regions, Suriyanara et al. studied concentrations of 210Po and 210Pb in various marine organisms (soft tissues) from the Point Calimere Coast (Palk Strait), India and determined the higher results than ours. They investigated 210Pb concentration in the muscle of fish ranged from 1.8 Bq/kg in C. dorab to 49.7 Bq/kg in Synaptura commersoniana (Suriyanarayanan et al., 2008). In another study, the concentration of 210Po in 23 different marine fish from Sudan ranges 0.25–6.42 (carnivores), 0.7–5 (omnivores) and 1.5–3.8 (herbivores) Bq/kg fresh weight. And also the highest value of 210Po concentration (6.42 Bq/kg ww.) was observed in Scomberomorus commersoni (Hassona et al., 2008). Similarly, Al-Masri et al. studied concentrations of 210Po and 210Pb in the edible muscle tissue of 36 species of marine fish and seven species of fresh water fish collected from Syrian local markets and determined that the concentrations in the edible tissue of sea fish (especially in Sardinella samples) are higher than in fresh water fish (Al-Masri et al., 2000). In this study, generally mean 210Po activity
concentrations in sardine are higher than in the other species as shown in Table 1. Minimum, mean and maximum values of 210Po and 210Pb in fish samples are given in Table 3. The 210Po/210Pb activity ratio is much higher than unity in all analysed fish samples. The total range varied from 1.5 in the species Mugil cephalus upto 46.70 in Alosa fallax. The 210Po/210Pb activity ratios reflect the chemical properties of both radionuclides (Stepnowski and Skwarzec, 2000). According to many researches the majority of the 210Po accumulated by marine organisms is unsupported (Mat Çatal et al., 2012). In additional, activity ratio may also be due to the metabolism of the particular tissue and feeding pattern and can be attributed to concentrations of 210Po and 210Pb (Shannon and Cherry, 1967; Carvalho and Fowler, 1993; Germain et al., 1995; Al-Masri et al., 2000; Khan and Wesley, 2011). 210 Po activity levels are higher than 210Pb activity levels. It is known that 210Po has a much higher affinity for organic matter than 210Pb in marine organisms. Furthermore, it is pointed out that such long storage of the samples after 210Po platting, the loss of analysed material in the platting for determination of 210Pb may occur in processes such as: adsorption on the walls of vessel, micro precipitation, hydrolysis and colloid formation etc. Fish play a significant role in the transfer of radionuclides to humans. Twelve of the most abundant fish varieties in the Izmir Bay (Aegean Sea) ecosystem were collected; dose due to 210Po from the fish species calculated are given in Table 4. The calculated dose rates increase depending on the activity concentrations of 210Po and the consumption ratio of the fish. For the calculation of dose due to 210Po from the fish species is summarized in the following formula (IAEA, 1995):
DPo ðfishÞ ¼ C b F c F h F e Df 4:3 107 where DPo is the collective committed effective dose of 210Po via consumption of fish from intake during 2010. The unit of collective committed effective dose is [man Sv]. The coefficients Cb and Fc denote activity concentration of 210Po in the edible part of the fish samples (Bq kg1 ww) and the catch calculated from Turkish Statistical Institute (TURKSTAT) statistics (kg y1), respectively. Fh, is the fraction of the catch that is used for regional human consumption
238
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238
and Fe, is the fraction that is actually eaten and Df, is the delay factor between the catch and consumption time. 4.3 107, is the factor used for adult members of the public, the recommended dose conversion coefficient (Mat Çatal et al., 2012). The calculated combined annual effective ingestion dose for human due to 210Po from the consumption of marine fishes collected from Izmir Bay is range from 0.044 to 8.908 lSv y1. It is clear that the highest dose value (8.908 lSv y1) was observed for S. Plichardus. These values are relatively low in comparison with other literature results. The annual effective ingestion dose due to 210Po in marine fish in Izmir Bay (Aegean Sea) (0.044–8.908 lSv y1, Table 4) is lower than this found in FAO (Food and Agricultural Organisation) fishing areas (5.1–9.1 lSv y1) (Aarkrog et al., 1997), Slovenia (0.07 and 32 lSv y1) (Štrok and Smodiš, 2011) and India (19.44 lSv y1) (Mishra et al., 2009). However, compared to Syria (0.75 lSv y1) (Al-Masri et al., 2000) the annual effective ingestion dose due to 210Po in marine fish in Izmir Bay (Aegean Sea) is much higher. And also, differences between the calculated results are attributed to a different dose coefficient was used by some investigators. Acknowledgements This research work is supported by Grants from Ege University Institute of Nuclear Sciences Contract No. 2006/NBE/001. References Aarkrog, A., Baxter, M.S., Bettencourt, A.O., Bojanowski, R., Bologa, A., Charmasson, S., Cunha, I., Delfanti, R., Duran, E., Holm, E., Jeffree, R., Livingston, H.D., Mahapanyawong, S., Nies, H., Osvath, I., Pingyu, L., Povinec, P.P., Sanchez, A., Smith, J.N., Swift, D., 1997. A comparison of doses from 137Cs and 210Po in marine food, a major international study. J. Environ. Radioactiv. 34 (1), 69–90. Al-Masri, M.S., Mamish, S., Budeir, Y., Nashwati, A., 2000. 210Po and 210Pb concentrations in fish consumed in Syria. J. Environ. Radioactiv. 49, 345–352. Bizsel, N., Uslu, O., 2000. Phosphate, nitrogen and iron enrichment in the polluted Izmir Bay, Aegean Sea. Mar. Environ. Res. 49, 101–122. Browne, E., Firestone, R.B., Shirley, V.S., 1986. Table of Radioactive Isotopes. John Wiley & Sons, New York. Bulman, R.A., Ewers, L.W., Matsumoto, K., 1995. Investigations of the potential bioavailability of 210Po in some foodstuffs. Sci. Total Environ. 173 (174), 151– 158. Carvalho, F.P., 1988. 210Po in marine organisms: a wide range of natural radiation dose domains. Radiat. Prot. Dosim. 24, 113–117. Carvalho, F.P., Fowler, S.W., 1993. An experimental study on the bioaccumulation and turnover of polonium-210 and lead-210 in marine shrimp. Mar. Ecol. Program Ser. 102, 125–133. Carvalho, F.P., Fowler, S.W., 1994. A double-tracer technique to determine the relative importance of water and food as sources of polonium-210 to marine prawns and fish. Mar. Ecol. Program Ser. 103, 251–264. Carvalho, F.P., 1995. 210Po and 210Pb intake by the Portuguese population: the contribution of seafood in the dietary intake of 210Po and 210Pb. Health Phys. 69 (4), 469–480. Carvalho, F.P., 2011. Polonium (210Po) and lead (210Pb) in marine organisms and their transfer in marine food chains. J. Environ. Radioactiv. 102, 462– 472.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. Radioactiv. 97, 168–188. Cherry, R.D., Shannon, L.V., 1974. The alpha radioactivity of marine organisms. Atom. Energy Rev. 12, 3–45. Currie, L.A., 1968. Limits for qualitative detection and quantitative determination. Anal. Chem. 40 (3), 586–593. Dahlgaard, H., 1996. Polonium-210 in mussel and fish from Baltic-North Sea Estuary. J. Environ. Radioactiv. 32 (1–2), 91–96. Din, K.S., 2011. Determination of 210Po in various foodstuffs and its annual effective dose to inhabitants of Qena City. Egypt. Science of the Total Environment 409, 5301–5304. ENSDF, Evaluated Nuclear Structure Data File,
Contents lists available at SciVerse ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Baseline
Edited by Bruce J. Richardson The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only those papers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to ‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 60, 1–2).
Activity levels of 210Po and 210Pb in some fish species of the Izmir Bay (Aegean Sea) S. Aközcan a,⇑, A. Ug˘ur b a b
Kirklareli University, Department of Physics, Campus of Kavakli, Kirklareli, Kavakli, Turkey Ege University, Institute of Nuclear Sciences, 35100 Izmir, Turkey
a r t i c l e
i n f o
Keywords: Fish 210 Po 210 Pb Aegean Sea
a b s t r a c t Concentrations of 210Po and 210Pb were determined in the edible muscle tissue of twelve species of marine fish collected from Izmir Bay in the Aegean Sea Region of Turkey during the 2006–2007. 210Po activity concentrations in fish samples were found to vary from ND to 400 ± 9 Bq kg1 dry weight and 210Pb activity concentrations were found to vary from ND to 15 ± 3 Bq kg1 dry weight. The highest dose contribution due to 210Po to humans was found to be 8.908 lSv y1. Ó 2012 Elsevier Ltd. All rights reserved.
210
Po and 210Pb are members of 238U decay series. The natural radionuclides 210Po and 210Pb are well known to be particlereactive in the marine environment. 210Po in water column is preferentially absorbed by plankton and is abundant in their organic detrital particles, while 210Pb is adsorptive to fine inorganic particles in sea water. Therefore, these two radionuclides are regarded as good tracers for fine organic and inorganic particles in marine waters (Tateda et al., 2003). In additonal they are both reactive elements, their half lives are adapted to the study of marine biogeochemical processes and (Radakovitch et al., 1997). 210Pb is a beta emitter with a half-life of 22.2 years and decays into 210Bi, which further decays into 210Po with a half-life of 138.4 days (Browne et al., 1986; ENSDF, 2006; Magill et al., 2006; Štrok, and Smodiš, 2011). The main source of the 210Po and 210Pb is the 222Rn emanation, which is released from the earth’s crust to the atmosphere. 210 Po attaches itself further electrostatically to aerosol particles and are transported returns to earth’s surface to soil, plant and aquatic environments by dry deposition and wash out (Mishra et al., 2009; Mat Çatal et al., 2012). 210Pb is a particle reactive natural radionuclide and quickly absorbs to settling particulate mat-
⇑ Corresponding author. Tel.: +90 5057980659. 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.2012.10.003
ter. Regionally, 210Po and 210Pb activities may be influenced by industrial waste coming from mining, processing of phosphates and derivatives (Germain et al., 1995; McDonald et al., 1996; Connan et al., 2007). A large contribution to the radiation dose received by humans comes from 210Po, 210Pb and 210Bi radionuclides accumulated in body (Carvalho, 1995; Al-Masri et al., 2000). In particulary, in marine environment these radionuclides are known to be strongly accumulated by marine organisms and transferred to man with ingested food (Carvalho and Fowler, 1994; Carvalho, 1995, 2011). Altough, because the majority of studies on intake of 210Po and 210Pb are based on analyses of sea food, a widespread conclusion has been the existence of a 210Po:210Pb ratio lower than or near to unity in the human food (Carvalho, 1995; Dahlgaard, 1996; Aarkrog et al., 1997; Al-Masri et al., 2000). 210Po especially, provides a major contribution (90%) to the natural radiation dose from alpha emitting radionuclides to most marine organisms (Mishra et al., 2009; Cherry and Shannon, 1974; Stepnowski and Skwarzec, 2000; Wildgust et al., 2000). According to literature data the dose due to ingestion of 210Po was about 7% of the natural internal radiation dose. Also about 18% of the average internal dose of the population is due to ingestion of 210Po along with its precursor 210Pb (Bulman et al., 1995; Din, 2011). In the marine environment, fish is the final chain of aquatic food web and an important food source for the people of the world. The
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238
235
Fig. 1. The map of the study area.
uptake mechanism of these radionuclides by fish reflects biological variables such as feeding habits and location. Izmir Bay population consumes relatively large quantities of sea food. Therefore, the objectives of this study are to (i) present activity concentration data of 210Po and 210Pb in different species of fishes, (ii) estimate the committed effective dose to humans from Po-210 contained in fish consumed by inhabitants in Izmir Bay. In order to obtain a representative sample 12 fish species were collected from 2006 to 2007 at Izmir Bay, monthly (Fig. 1). The species were Sardine (Sardina plichardus), Grey mullet (Mugil cephalus), Bogue (Boops bopps), Seabass (Dicentrarchus labrax), Atlantic mackerel (Scomber scombrus), Two-banded bream (Diplodus vulgaris), Twaite shad (Alosa fallax), Salema (Sarpa salpa), Picarel (Spicara smaris), Red mullet (Mullus barbatus), Horse mackerel (Trachurus trachurus) and Gilt-head sea bream (Sparus aurata). Izmir Bay (western Turkey) is one of the largest natural bays in the eastern Aegean Sea in the eastern Mediterranean. The bay has been divided into three parts: inner, middle and outer according to the physical characteristics of the different water masses. The main urban conurbation around the bay is the Izmir Metropolitan Municipality. Izmir is an important industrial and commercial centre and a cultural focal point. Besides untreated wastewaters originating from the increasing population and substantial industrial development, intensive harbour activities in the bay and agriculture in the surrounding areas have exerted considerable pollution loads particularly to the inner Izmir Bay (Bizsel and Uslu, 2000; Küçüksezgin et al., 2006). The samples were washed first with seawater and then with distilled water. The fishes were separated into viscera and hard tissues. The 210Po and 210Pb concentrations were determined in the edible muscle tissue of different fish species. The edible muscle tissues were weighed and oven dried to a constant dry weight (dw) at 80 °C. The samples were ground and passed through a 2 mm mesh sieve followed by homogenisation. After the addition of a standardized amount of 209Po (4.88 MeV alpha emission, t1/2 = 109 year) tracer, each sample was completely dissolved with HCl and HNO3. Polonium was spontaneously plated onto copper discs (Flynn, 1968).
210
Po levels were measured via 5.30 MeV alpha particle emission rates using a high-resolution alpha spectrometer equipped with Passivated Implanted Planar Silicon (PIPS) detector (Canberra 7401). Typical resolution was 30 keV (full-width at half-maximum (FWHM)) for a 450 mm2 area detector. After the first deposition of 210 Po, the residual 0.5 M HCl was kept for about one year to allow 210 Po in-growth from the 210Pb contained in the sample solution. The samples were re-plated and the 210Po activities were determined. The second deposition provided information on the 210Pb content of the samples and thus indicated the extent to which the initial 210Po was supported by its grandparent species. Well known Bateman equations were used to obtain 210Pb activity from measured 210Po activity. 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 is the number of 210Pb nuclei and k0 the decay constant of 210 Pb. The rate of change of 210Po is given by:
dN0 ¼ k0 N0 k1 N1 dt
ð2Þ
where N1 is the number of 210Po nuclei and k1 the decay constant of 210 Po. Just after the deposition of 210Po, t0 = 0,
N0 ¼ N0;0
ð3Þ
N1 ¼ 0
ð4Þ
From Eq. (1) and initial condition (3) the number of given as follows:
N0 ¼ N0;0 ek0 t
210
Pb nuclei is
ð5Þ
Combining Eqs. (2) and (5) and initial condition (4) the number of 210 Po nuclei is given as follows:
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238
236 Table 1 Mean activity concentrations of
210
Po and
210
Pb (Bq kg1 dry wt.) and weight ratio in fish samples. The uncertainties represent 1 sigma standard deviations.
Fish species
Feeding habitat
Type of feding
Weight ratio dry/wet
210
210
Sardine (n = 360) (Sardina plichardus) Grey mullet (n = 44) (Mugil cephalus) Bogue (n = 72) (Boops bopps) Seabass (n = 48) (Dicentrarchus labrax) Atlantic mackerel (n = 92) (Scomber scombrus) Two–banded bream (n = 9) (Diplodus vulgaris) Twaite shad (n = 27) (Alosa fallax) Salema (n = 8) (Sarpa salpa) Picarel (n = 24) (Spicara smaris) Red mullet (n = 18) (Mullus barbatus) Horse mackerel (n = 90) (Trachurus trachurus)
P D&P P&D D&P P D P D&P P D
Carnivores (planktivor) Omnivores (planktivor) Carnivores (planktivor) Carnivores (piscivor) Carnivores (planktivor) Carnivores Carnivores (planktivor) Omnivores Carnivores (planktivor) Carnivores
0.29 0.25 0.26 0.27 0.28 0.23 0.27 0.24 0.23 0.26
91.3 ± 3.8 3.0 ± 0.2 12.5 ± 1.3 3.0 ± 0.3 23.2 ± 2.0 ND 46.7 ± 1.0 ND 14.0 ± 2.5 60.0 ± 3.0
4.7 ± 1.8 2.0 ± 0.9 2.8 ± 1.4 NDa 2.1 ± 1.1 4.0 ± 1.0 1.0 ± 0.7 NDa NDa NDa
19.43 1.5 4.46 – 11.05 – 46.7 – – –
P D
Carnivores (planktivor) Carnivores
0.26 0.32
18.6 ± 2.0 ND
1.3 ± 0.9 2.0 ± 1.0
14.31 –
0.23–0.32
ND–91.3
ND–4.7
1.50–46.70
Gilt–head sea bream (n = 48) (Sparus aurata) Range
Po (Bq kg1)
Pb (Bq kg1)
210
Po/210Pb
P: pelagic, D: demersal. a ND = not detected.
Table 2 210 Po and
a
N1 ¼
210
Pb concentrations in fish from different regions of the world.
Country
210
Portugal Japan America Poland Syria Sudan India Slovenia Turkey
0.2–11 0.6–2.6 0.4–153.3 0.9–5 0.27–27.48 0.25–6.42 1.2–92.3 0.039–35 a ND–100
210
Po (Bq kg1 w.w.)
– 0.04–0.54 0.1–7 – 0.05–0.38 – 1.1–14.8 0.13–0.82 a ND–3.75
References Carvalho, 1988 Yamamoto et al., 1994 Noshkin et al., 1994 Skwarzec (1997) Al-Masri et al. (2000) Hassona et al. (2008) Khan and Wesley (2011) Štrok and Smodiš (2011) This work
ND = not detected.
k0 N0;0 k1 k0
ð6Þ
By measuring the decay rate of 210Po, (dNa/dt) = k1N1 at a certain time t and using Eq. (1) at t = 0, Eq. (6) can be written as: and activity of 210Pb (Khan and Wesley, 2011).
dN0;0 k1 k0 dNa k0 t ek1 t 1 ¼ ½e dt k1 dt
ð7Þ
Lower limit of detection (LLD) was calculated using the Currie definition (Currie, 1968), using the following formula : 1
LLD ¼
Pb (Bq kg1 w.w.)
2:71 þ 4:65B2 et
where B is the background counts, e is the counting efficiency and t, counting time. The concentration of 210Po in a small number of samples was below the detection limit, but most of the 210Po activity levels were above this value (0.0003 Bq). Counting period was adjusted to obtain relative standard error of approximately 5%. Final activity calculations were attained to include the appropriate corrections for blanks and also for collection date. The recovery rates of standardized tracer for the fish samples varied from 70% to 90%. The alpha spectrometry system was calibrated with certified reference material, IAEA-437 (mussel). The average 210Po and 210Pb concentrations in samples and weight ratios are given in Table 1. 210Po and 210Pb concentrations in fish species collected from different regions of the world also given Table 2. 210 Po and 210Pb concentration in fish samples range from ND (not detected) to 400 ± 9 Bq kg1 dry wt. and ND (not detected) to 15 ± 3 Bq kg1 dry wt., respectively, with an average value of
7.72 ± 1.34 Bq kg1 dry wt. for 210Po and 1.66 ± 0.73 Bq kg1 dry wt. for 210Pb. The highest concentration of 210Po was measured in the sardine samples collected in autumn. The highest mean 210Po concentrations in fishes were found in sardine followed by, red mullet, twaite shad atlantic mackerel and horse mackerel. Besides, measured activities in these species feed on planktons are much higher than the average values. Strok and Smodis stated that the pelagic environment and plankton feeding contribute significantly to the 210 Po accumulation. And also, they are reported the larger is the animal, the lower is the 210Po activity concentration (Štrok and Smodiš, 2011). This is due to the slower metabolism of the larger, older and heavier animals. In this study, generally mean 210Po activity concentrations in small species like sardine (91.3 Bq kg1) and red mullet (60 Bq kg1) are higher than other larger species like Gilt-head sea bream (ND). It is because the small pelagic plankton feeding fish like sardine (Sardine plichardus) tend to accumulate more 210Po. However, low 210 Po concentrations were detected in other carnivorous fish, like the gilt-head sea bream and two-banded bream (Mat Çatal et al., 2012). Wildgust et al. indicated that 210Po behaves in a similar manner to other trace metals, seasonal changes arising from phytoplankton blooms, physico-chemical parameters and biological variables (Wildgust et al., 1998). They indicated that phytoplankton blooms generally occur during the spring and autumn in temperate regions. Our results in samples collected from Izmir Bay are similar to those given by Wildgust et al. In additional, Wildgust et al. reported that rain results in the introduction of 210Po into the sea. 210Po and 210Pb return to the earth as dry fallout or are washed out in rain. Ug˘ur et al. studied on the activity concentrations of 210Po and 210Pb in rainwater samples in Izmir. They measured that the activity concentrations of 210Po and 210Pb in rainwater vary considerably according to seasonal transport of
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238 Table 3 Minimum, mean and maximum values of
210
Po and
237
210
Pb in fish samples.
Radionuclides
Fish species
Minimum
Mean
Maximum
210
Po
Sardine (Sardina plichardus) Grey mullet (Mugil cephalus) Bogue (Boops bopps) Seabass (Dicentrarchus labrax) Atlantic mackerel (Scomber scombrus) Two-banded bream (Diplodus vulgaris) Twaite shad (Alosa fallax) Salema (Sarpa salpa) Picarel (Spicara smaris) Red mullet (Mullus barbatus) Horse mackerel (Trachurus trachurus) Gilt-head sea bream (Sparus aurata)
14 ND ND ND ND ND ND ND 10 ND ND ND
54.5 6.5 12 4.5 25 ND 23 ND 14 30 19.5 ND
400 24 27 9 42 ND 117 ND 18 60 31 ND
210
Pb
Sardine (Sardina plichardus) Grey mullet (Mugil cephalus) Bogue (Boops bopps) Seabass (Dicentrarchus labrax) Atlantic mackerel (Scomber scombrus) Two-banded bream (Diplodus vulgaris) Twaite shad (Alosa fallax) Salema (Sarpa salpa) Picarel (Spicara smaris) Red mullet (Mullus barbatus) Horse mackerel (Trachurus trachurus) Gilt-head sea bream (Sparus aurata)
ND ND ND ND ND ND ND ND ND ND ND ND
4.5 2 3 ND 2.5 2 1.5 ND ND ND 1.5 1.5
15 7 7 ND 5 4 3 ND ND ND 3 5
ND = not detected.
Table 4 Annual dose due to consumption of different fish species contaminated by Fish species Sardine (Sardina plichardus) Grey mullet (Mugil cephalus) Bogue (Boops bopps) Seabass (Dicentrarchus labrax) Atlantic mackerel (Scomber scombrus) Two-banded bream (Diplodus vulgaris) Twaite shad (Alosa fallax) Salema (Sarpa salpa) Picarel (Spicara smaris) Red mullet (Mullus barbatus) Horse mackerel (Trachurus trachurus) Gilt–head sea bream (Sparus aurata)
210
Po.
Dose (lSv y1) 8.908 0.044 0.343 0.008 0.093 – 0.287 – 0.044 0.389 0.252 –
the radionuclides. As indicated by Ug˘ur et al. whether dry or wet deposition is dominating removal process depends on the climate (Ug˘ur et al., 2011). However, according to Turkish State Meteorological Service, the rain report Izmir Meteorology supports concentrations of 210Po during the 2006–2007. In study correlation was found between 210Po specific activity and rainfall. In comparison with other regions, Suriyanara et al. studied concentrations of 210Po and 210Pb in various marine organisms (soft tissues) from the Point Calimere Coast (Palk Strait), India and determined the higher results than ours. They investigated 210Pb concentration in the muscle of fish ranged from 1.8 Bq/kg in C. dorab to 49.7 Bq/kg in Synaptura commersoniana (Suriyanarayanan et al., 2008). In another study, the concentration of 210Po in 23 different marine fish from Sudan ranges 0.25–6.42 (carnivores), 0.7–5 (omnivores) and 1.5–3.8 (herbivores) Bq/kg fresh weight. And also the highest value of 210Po concentration (6.42 Bq/kg ww.) was observed in Scomberomorus commersoni (Hassona et al., 2008). Similarly, Al-Masri et al. studied concentrations of 210Po and 210Pb in the edible muscle tissue of 36 species of marine fish and seven species of fresh water fish collected from Syrian local markets and determined that the concentrations in the edible tissue of sea fish (especially in Sardinella samples) are higher than in fresh water fish (Al-Masri et al., 2000). In this study, generally mean 210Po activity
concentrations in sardine are higher than in the other species as shown in Table 1. Minimum, mean and maximum values of 210Po and 210Pb in fish samples are given in Table 3. The 210Po/210Pb activity ratio is much higher than unity in all analysed fish samples. The total range varied from 1.5 in the species Mugil cephalus upto 46.70 in Alosa fallax. The 210Po/210Pb activity ratios reflect the chemical properties of both radionuclides (Stepnowski and Skwarzec, 2000). According to many researches the majority of the 210Po accumulated by marine organisms is unsupported (Mat Çatal et al., 2012). In additional, activity ratio may also be due to the metabolism of the particular tissue and feeding pattern and can be attributed to concentrations of 210Po and 210Pb (Shannon and Cherry, 1967; Carvalho and Fowler, 1993; Germain et al., 1995; Al-Masri et al., 2000; Khan and Wesley, 2011). 210 Po activity levels are higher than 210Pb activity levels. It is known that 210Po has a much higher affinity for organic matter than 210Pb in marine organisms. Furthermore, it is pointed out that such long storage of the samples after 210Po platting, the loss of analysed material in the platting for determination of 210Pb may occur in processes such as: adsorption on the walls of vessel, micro precipitation, hydrolysis and colloid formation etc. Fish play a significant role in the transfer of radionuclides to humans. Twelve of the most abundant fish varieties in the Izmir Bay (Aegean Sea) ecosystem were collected; dose due to 210Po from the fish species calculated are given in Table 4. The calculated dose rates increase depending on the activity concentrations of 210Po and the consumption ratio of the fish. For the calculation of dose due to 210Po from the fish species is summarized in the following formula (IAEA, 1995):
DPo ðfishÞ ¼ C b F c F h F e Df 4:3 107 where DPo is the collective committed effective dose of 210Po via consumption of fish from intake during 2010. The unit of collective committed effective dose is [man Sv]. The coefficients Cb and Fc denote activity concentration of 210Po in the edible part of the fish samples (Bq kg1 ww) and the catch calculated from Turkish Statistical Institute (TURKSTAT) statistics (kg y1), respectively. Fh, is the fraction of the catch that is used for regional human consumption
238
S. Aközcan, A. Ug˘ur / Marine Pollution Bulletin 66 (2013) 234–238
and Fe, is the fraction that is actually eaten and Df, is the delay factor between the catch and consumption time. 4.3 107, is the factor used for adult members of the public, the recommended dose conversion coefficient (Mat Çatal et al., 2012). The calculated combined annual effective ingestion dose for human due to 210Po from the consumption of marine fishes collected from Izmir Bay is range from 0.044 to 8.908 lSv y1. It is clear that the highest dose value (8.908 lSv y1) was observed for S. Plichardus. These values are relatively low in comparison with other literature results. The annual effective ingestion dose due to 210Po in marine fish in Izmir Bay (Aegean Sea) (0.044–8.908 lSv y1, Table 4) is lower than this found in FAO (Food and Agricultural Organisation) fishing areas (5.1–9.1 lSv y1) (Aarkrog et al., 1997), Slovenia (0.07 and 32 lSv y1) (Štrok and Smodiš, 2011) and India (19.44 lSv y1) (Mishra et al., 2009). However, compared to Syria (0.75 lSv y1) (Al-Masri et al., 2000) the annual effective ingestion dose due to 210Po in marine fish in Izmir Bay (Aegean Sea) is much higher. And also, differences between the calculated results are attributed to a different dose coefficient was used by some investigators. Acknowledgements This research work is supported by Grants from Ege University Institute of Nuclear Sciences Contract No. 2006/NBE/001. References Aarkrog, A., Baxter, M.S., Bettencourt, A.O., Bojanowski, R., Bologa, A., Charmasson, S., Cunha, I., Delfanti, R., Duran, E., Holm, E., Jeffree, R., Livingston, H.D., Mahapanyawong, S., Nies, H., Osvath, I., Pingyu, L., Povinec, P.P., Sanchez, A., Smith, J.N., Swift, D., 1997. A comparison of doses from 137Cs and 210Po in marine food, a major international study. J. Environ. Radioactiv. 34 (1), 69–90. Al-Masri, M.S., Mamish, S., Budeir, Y., Nashwati, A., 2000. 210Po and 210Pb concentrations in fish consumed in Syria. J. Environ. Radioactiv. 49, 345–352. Bizsel, N., Uslu, O., 2000. Phosphate, nitrogen and iron enrichment in the polluted Izmir Bay, Aegean Sea. Mar. Environ. Res. 49, 101–122. Browne, E., Firestone, R.B., Shirley, V.S., 1986. Table of Radioactive Isotopes. John Wiley & Sons, New York. Bulman, R.A., Ewers, L.W., Matsumoto, K., 1995. Investigations of the potential bioavailability of 210Po in some foodstuffs. Sci. Total Environ. 173 (174), 151– 158. Carvalho, F.P., 1988. 210Po in marine organisms: a wide range of natural radiation dose domains. Radiat. Prot. Dosim. 24, 113–117. Carvalho, F.P., Fowler, S.W., 1993. An experimental study on the bioaccumulation and turnover of polonium-210 and lead-210 in marine shrimp. Mar. Ecol. Program Ser. 102, 125–133. Carvalho, F.P., Fowler, S.W., 1994. A double-tracer technique to determine the relative importance of water and food as sources of polonium-210 to marine prawns and fish. Mar. Ecol. Program Ser. 103, 251–264. Carvalho, F.P., 1995. 210Po and 210Pb intake by the Portuguese population: the contribution of seafood in the dietary intake of 210Po and 210Pb. Health Phys. 69 (4), 469–480. Carvalho, F.P., 2011. Polonium (210Po) and lead (210Pb) in marine organisms and their transfer in marine food chains. J. Environ. Radioactiv. 102, 462– 472.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. Radioactiv. 97, 168–188. Cherry, R.D., Shannon, L.V., 1974. The alpha radioactivity of marine organisms. Atom. Energy Rev. 12, 3–45. Currie, L.A., 1968. Limits for qualitative detection and quantitative determination. Anal. Chem. 40 (3), 586–593. Dahlgaard, H., 1996. Polonium-210 in mussel and fish from Baltic-North Sea Estuary. J. Environ. Radioactiv. 32 (1–2), 91–96. Din, K.S., 2011. Determination of 210Po in various foodstuffs and its annual effective dose to inhabitants of Qena City. Egypt. Science of the Total Environment 409, 5301–5304. ENSDF, Evaluated Nuclear Structure Data File,