Mussels (Mytilus galloprovincialis) as a bio-indicator species in radioactivity monitoring of Eastern Adriatic coastal waters

Journal of Environmental Radioactivity 144 (2015) 47e51

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Mussels (Mytilus galloprovincialis) as a bio-indicator species in radioactivity monitoring of Eastern Adriatic coastal waters Matea Krmpoti c*, Martina Ro zmari c 1, Delko Barisi c Rudjer Boskovic Institute, Bijenicka cesta 54, 10 000 Zagreb, Croatia

a r t i c l e i n f o

a b s t r a c t

Article history: Received 30 September 2014 Received in revised form 28 January 2015 Accepted 25 February 2015 Available online

Croatian Adriatic coastal waters are systematically monitored within the Mediterranean Mussel Watch Project using mussels (Mytilus galloprovincialis) as a bio-indicator species. The study includes determination of naturally occurring (7Be, 40K, 232Th, 226Ra and 238U), as well as anthropogenic 137Cs radionuclides. Activity concentrations in dry weight of mussels' soft tissue along the Croatian Adriatic coast are presented, with spatial and seasonal variations given and discussed. Samples were collected in spring and autumn for the period between 2009 and 2013. Radionuclides were determined by gamma-ray spectrometry. Activity concentrations of 7Be were the highest in spring periods, especially in the areas with significant fresh water discharges. Activity concentrations of 40K did not vary significantly with season or location. 137Cs activities were low, while 232Th, 226Ra and 238U activities were mostly below the detection limit of performed gamma-spectrometric measurement. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Radionuclides Mytilus galloprovincialis Adriatic Sea Gamma-spectrometry

1. Introduction Mediterranean Mussel Watch (MMW) is a program created by the Mediterranean Science Commission (CIESM) in 2002 with a purpose to record levels and trends of radioactivity in the coastal seawater environment using mussels Mytilus galloprovincialis as a bio-indicator species (CIESM, 2002). Over the years MMW extended to more than 20 Mediterranean and Black Sea countries for systematic determination of radionuclides, as well as the selected trace-contaminants, using standardized procedures and methods, thus creating a unique and reliable dataset of environmental pollution of these areas (Thebault et al., 2008). Mussels are sedentary, widely distributed marine organisms able to filter up to 80 L of seawater per day in optimal conditions (water temperature, food availability, reproductive cycle). High rates of accumulation of dissolved and particulate matter from seawater makes them a good bio-indicator species for environmental pollution studies (Alam et al., 1999; Ishikawa et al., 2004; Liang et al., 2004).

* Corresponding author. Tel.: þ385 1 4560 932; fax: þ385 1 4680 205. E-mail address: [email protected] (M. Krmpoti c). 1 Present address: Environment Laboratories, International Atomic Energy Agency, 4 Quai Antoine 1er, MC 98000, Monaco. http://dx.doi.org/10.1016/j.jenvrad.2015.02.027 0265-931X/© 2015 Elsevier Ltd. All rights reserved.

Laboratory for Radioecology systematically monitors Croatian Adriatic coastal waters as a part of the above mentioned MMW project (Orescanin et al., 2006; Ro zmari c et al., 2012). The study includes determination of naturally occurring 7Be, 40K, 232Th, 226Ra, 238 U and fallout 137Cs, which are omnipresent in seawater, entering the marine environment through the atmospheric deposition, winds, underground fresh water discharges and river flows. The project in Croatia started in 2003 covering the industrial areas of  Sibenik and Split in the Central Eastern Adriatic (Barisi c and Kniewald, 2004; Cuculi c et al., 2006). Special attention was given at the time to the Kastela Bay near Split where the factory Yugovinil (production of plastic masses and chemical products) used to be located and a large amount of uranium rich coal waste (slag and ash) was dumped into the sea (Mikac et al., 2006; Ores canin et al., 2005). Systematic radioactivity monitoring of the entire Croatian coast was introduced in 2009, expanding the initial study to locations in Istria in the north, Peljesac Peninsula area and Dubrovnik in the south. The research areas now include sites rich in natural mussel habitats, sites suitable for mussel cultivation for economic purposes, areas under the influence of heavy fresh water discharges and industrial areas with potential anthropogenic influence. In 2010 determination of naturally occurring 210Po and 210Pb was included in the study as well (Ro zmari c et al., 2012). These radionuclides are naturally present in the marine environment in low concentrations, and as a by-product of human activities (phosphate

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fertilizers, phosphoric acid industries, mining, etc.). Their higher levels may present a health hazard in marine coastal areas due to their high dose coefficients, easily resulting in elevated doses received by the local population (Aarkrog et al., 1997). Based on the research data published so far, the aim of the present study was as follows: i) to determine activity concentrations of naturally occurring (7Be, 40K, 232Th, 226Ra and 238U) and anthropogenic 137Cs radionuclides in dry mussel (M. galloprovincialis) soft tissue along the entire Croatian Adriatic coast, including not only critical points of anthropogenic influence but also areas known for intense mariculture; ii) to determine spatial and temporal variations of these radionuclides; iii) to provide baseline radioactivity levels of Croatian coastal environment which will be the starting point for further research of this area. Activity concentrations of 210Po and 210Pb are presented and discussed separately in our previous work (Ro zmari c et al., 2012, 2013), since the obtained data covered a shorter time period and was primarily oriented towards total annual effective doses received by coastal population due to mussel consumption. 2. Materials and methods 2.1. Sampling and sample preparation Mussels sampling was performed twice a year, in early spring and autumn periods, at 13 locations along the Croatian Adriatic coast presented in Fig. 1. The according descriptions of the sampling locations, their GPS coordinates and habitats are given in Table 2.

Mussels ranging between 3 and 5 cm in shell length were chosen at each location and approximately 5 kg of fresh mussels was pooled in one sample, as recommended by CIESM (CIESM, 2002). The shells were cleaned from any external material and opened using a microwave oven. The soft mussels' tissue, along with the interstitial fluids was removed from the shells and the composite sample was stored in a freezer upon arrival to the laboratory. All samples were dried at 80  C to constant weight and homogenized. Counting vessels (plastic containers of 125 cm3), suitable for gamma-spectrometric measurement (F ¼ 6 cm, h ¼ 4.7 cm), were filled with samples, hermetically sealed and stored for 4 weeks to allow ingrowth of gaseous 222Rn (T1/2 ¼ 3.8 days) and its short-lived decay products to equilibrate with the long-lived 226Ra precursor. 2.2. g-Spectrometric measurements Gamma-ray spectrometry was performed using a highresolution germanium detector (HPGe, Canberra, USA, with a relative efficiency of 25.4% and a resolution of 1.76 keV (FWHM) for the 1332.5 keV peak of 60Co), connected to 8192 channel analyzer (Meriden, USA). For energy calibration standard radionuclide point sources of 241Am, 60Co and 137Cs (Area CERCA LEA, France) were used. Efficiency calibration for the 125 cm3 sample geometry was made using standard mixed gamma radionuclide source in an appropriate matrix obtained from Eckert & Ziegler Analytics, USA. All the samples were counted in range between 80,000 (majority) and 300,000 s, and the obtained spectra processed in the

Fig. 1. Geographical locations of the mussels sampling sites at the Croatian Adriatic coast.

M. Krmpotic et al. / Journal of Environmental Radioactivity 144 (2015) 47e51 Table 1 Results of the ERA PT exercises for gamma-spectrometric measurements in biological samples (MRAD) in the period 2009e2013. Sample

Radionuclide (Bq/kg) 137 a

MRAD-10 2009

LRE Assigned valueb Acceptance limitsc

MRAD-12 2010

a b c

MRAD-14 2011

a b c

MRAD-17 2012

a b c

MRAD-18 2013

a b c

a b c

40

Cs

75.2 66.6 48.8e92.5 52.4 54.4 40.0e75.5 25.8 30.7 22.5e42.6 79.7 76.6 55.5e106.6 18.2 20.1 14.6e28.0

238

K

1111 1140 825e1617 1215 1291 929e1828 767 955 685e1351 1176 1095 792e1536 1010 1180 851e1658

U

72.3 74.7 52.5e94.4 58.6 63.3 44.4e79.9 72.9 95.8 67.3e121.0 154.5 158.4 105.8e201.3 78.4 90.3 60.3e114.7

LRE e Laboratory for Radioecology. Assigned value. Acceptance limits.

Canberra Genie 2000 software. The activities of 7Be were calculated using 477.56 keV-peak, 40K over 1460.75 keV-peak, 232Th from 911.1 keV-peak of its 228Ac progeny, 226Ra using 609.3 keV-peak of its 214Bi progeny, 238U via 235U at 186 keV-peak (after subtraction of the overlapping 226Ra peak, taking into account the 235U/238U ratio of 0.046) and 137Cs over 661.6 keV-peak. Quality control was performed internally by regular checking of gamma-spectrometric measurement stability (energy calibration, peaks' FWHM, efficiency curves and background) using control charts. On the other side, to assure external quality control of measurements and to provide reliable results, annual participation in international PT exercises organized by ERA, USA was performed. Obtained PT results for the period 2009e2013, presented in Table 1, were in the range of acceptable values given by the PT organizer.

3. Results and discussion The obtained results for activity concentrations of 7Be, 40K, Th, 226Ra, 238U and 137Cs in mussels M. galloprovincialis are presented in Tables 3 and 4 as average values for spring and autumn seasons (2009e2013), respectively, and their activity levels and trends are discussed herewith. 232

Table 2 GPS coordinates and types of sampling locations. Location

Sample identification

N

Lim Channel Rasa Bay Bakar Bay Martinska  Sibenik

D1 D2 D3 D4

45 45 45 43

Marina-Poljica Kastel Gomilica Giri ci c

D5 D6 D7

Vranjic Stobre c Bistrina Bay Mali Ston Dra ce Rijeka dubrova cka

E 08,2230 01,2180 18,4100 46,0560

43,2800 03,3880 32,3230 50,7220

Breeding site Breeding site Pier Breeding site

43 30,9000 43 32,6820 43 32,7550

16 09,4190 16 24,1300 16 24,3110

D8 D9

43 31,8940 43 30,0060

16 27,6520 16 31,5190

D10 D11 D12 D13

42 42 42 42

17 17 17 18

Breeding site Pier Harbour pontoons Pier Harbour pontoons Breeding site Breeding site Breeding site Harbour pier

52,3730 50,6500 55,0130 40,2440

13 14 14 15

Habitat

42,0800 42,6160 28,0890 07,5650

49

Activity concentration values of naturally occurring cosmogenic radionuclide 7Be in mussels' tissue were spread in a wide range, from 9.7 Bq/kg in autumn 2012 to 335 Bq/kg d.w. in spring 2009. Activities measured in early spring were regularly higher than those measured in early autumn for all locations. Activities below the detection limit of 0.1 Bq/kg d.w. were found only four times in autumn periods 2009e2011. These results were expected due to several facts: i) beryllium incorporates into cell membranes due to its biochemical behavior (Witschi and Aldridge, 1968); ii) the phytoplantkon bio-production in northern hemisphere (mussel food source) is higher in spring compared to the autumn season (Wildgust et al., 1998); iii) 7Be (T1/2 ¼ 53.4 days) enters the marine environment almost exclusively by atmospheric precipitation and/ or surface and groundwater discharges resulting in its considerably lower input to the marine environment during dry summer and early autumn seasons. Seasonal variations of 7Be activities in mussels' soft tissue were also comparable to those measured for 210 Po (Ro zmaric et al., 2013) due to similar 7Be and 210Po bioaccumulation processes and their input to the marine environment. Looking at individual locations along the coast, 7Be highest activities in spring were measured in Kastel Gomilica area (D6, D7) and in Bistrina Bay (D10). These locations are placed in almost entirely closed bays which are under strong influence of riverine and groundwater discharges, resulting in further input of 7Be to the marine environment. The lowest 7Be levels of the spring season were found in northern (D1 e D3; Lim Channel, Rasa Bay and Bakar Bay, respectively) and southern parts of the coast (D13 e Rijeka dubrovacka) where these factors of fresh water discharges are not as pronounced. Activities for the autumn period, on the other hand, did not differ significantly along the coast, but slightly higher values  could be found in Central Adriatic (D4 e D6; Martinska Sibenik,  Marina-Poljica and Kastel Gomilica, respectively) while slightly lower levels were again found in the south (D13 e Rijeka dubrova cka). Spatial variability of 7Be given as an annual average for the period 2009e2013 is presented in Fig. 2, showing the already mentioned activity peak for Central Adriatic (D6, D7 and D10; Kastel Gomilica, Giricic and Bistrina Bay, respectively). These results are not in full accordance with (previously mentioned) seasonally similar behavior to 210Po accumulation in mussels' tissue (Ro zmaric et al., 2013). Unlike 7Be, activity concentrations of the primordial 40K did not differ significantly either regarding the season or the location. Average annual levels of 40K for the period 2009e2013 are presented in Fig. 3. Activities for the spring season were in the range (198e389) Bq/kg d.w. with the average value of (287 ± 18) Bq/kg. The range for autumn was (188e377) Bq/kg d.w. with (295 ± 19) Bq/kg average value. This was also an expected result since the concentration of 40K in the seas and oceans is high and uniform (~12,500 Bq/m3) and consequently does not change in coastal seawaters even if stronger terrigenous effects take place. So it can be concluded that the concentration of this biogenic element, and its 40K isotope, is a reflection of the conditional state of mussels. Generally, measured activity concentrations of anthropogenic 137 Cs in mussels' tissue were low, in range from 0.3 Bq/kg to 1.1 Bq/ kg d.w. for all samples analyzed between 2009 and 2013. Measured activities were below the detection limit (<0.3 Bq/kg) during the whole 2009 and 2010 and in autumn 2013. The single exception was found in autumn 2009 in Bistrina Bay e a semi-enclosed bay where 137Cs activity concentration was 0.4 Bq/kg d.w. But it was detected eleven times in spring periods 2011e2013, ranging from 0.4 Bq/kg to 0.9 Bq/kg d.w. (Table 3): once in Rasa Bay (D2), Bakar  Bay (D3), Martinska Sibenik (D4), Kastel Gomilica (D6), Mali Ston (D11) and Rijeka dubrovacka (D13), and twice in Stobre c (D9) and Dra ce (D12). For the autumn periods of 2011 and 2012 its presence was detected twelve times at all locations except in Lim Channel

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Table 3 Average activity concentrations (Bq/kg d.w.) of the selected radionuclides in mussels (Mytilus galloprovincialis) measured in spring seasons 2009e2013. Location

Fa

7

40

D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13

5.232 5.463 5.412 5.038 5.364 5.062 4.880 5.354 5.599 5.439 5.353 6.030 5.744

21.0 ± 10.3b 31.4 ± 8.0 28.6 ± 12.5 40.1 ± 19.2 72.7 ± 42.5 101.6 ± 93.6 179.1 ± 120.3 69.1 ± 38.9 53.5 ± 13.3 78.3 ± 45.9 50.8 ± 17.3 38.7 ± 21.0 27.9 ± 8.6

319 317 293 289 284 276 298 263 271 283 304 267 272

Range

4.128e7.760

11.4e335c (65)d

198e389 (65)

a b c d

Be

232

K ± ± ± ± ± ± ± ± ± ± ± ± ±

74 65 68 54 34 38 31 51 47 58 69 48 40

Th

226

Ra

238

U

137

Cs

<1.2 <2.0 <2.3 <2.6 <2.3 <2.3 <2.8 <2.8 <2.9 <2.5 <2.0 <2.6 <3.1

<1.5 <2.6 <2.5 <2.1 <2.6 <2.8 <5.8 <3.1 <3.8 <3.1 <2.8 <2.8 <3.3

<5.7 <9.1 <10.1 <8.8 <9.1 <9.2 <10.8 <11.3 <11.9 <10.6 <10.7 <9.9 <12.7

<0.3 <0.4 <0.3 <0.3 <0.3 <0.3 <0.3 <0.3 <0.5 <0.3 <0.4 <0.3 <0.4

1.3e4.7 (9)

0.5e8.5 (32)

4.5 (1)

0.4e0.9 (11)

Concentration factor, average value 2009e2013. Standard deviation. Range of activity concentrations detected above the detection limit of gamma-spectrometric measurement in spring periods 2009e2013. Number of samples in which specific radionuclide was detected (total number of samples for spring periods 2009e2013 was 65).

(D1), Kastel Gomilica (D6) and Giricic (D7), with activities ranging from 0.3 Bq/kg to 1.1 Bq/kg d.w. (Table 4). Looking at 137Cs occurrence along the Croatian coast it was nearly always found in almost entirely closed marine environments under the strong influence of riverine outflows and fresh water discharges. Its presence in mussels' tissue could be the consequence of its significant input through heavy rains/snow (prior to sampling periods) and/or Adriatic seawater currents due to Ionian and Aegean Seas. It is also important to emphasize that 137Cs activity concentrations in Adriatic seawater have not changed significantly in the last decade. 137Cs activity concentrations measured four times yearly at three depths (surface, 15 m and 30 m) nearly 20 km in front of the Po River mouth were mainly in the range (1.5e2.5) Bq/m3 of seawater (unpublished results of the internal laboratory data). Averages of five year activity concentrations of 232Th, 226Ra and 238 U in mussels' dry tissue were below the detection limits of performed gamma-spectrometric measurement for both spring and autumn seasons and for all locations. Ranges of individually detected activities of these radionuclides in all analyzed samples are presented in Tables 3 and 4 for spring and autumn seasons, respectively. Activities no higher than 6.9 Bq/kg (D9 e Stobre c), 8.5 Bq/kg (D7 e Giri cic) and 13.1 Bq/kg d.w. (D10 e Bistrina Bay), for 232 Th, 226Ra and 238U, respectively, were found.

Generally, all obtained results were in accordance with the values published in the literature (Fisenne et al., 1987; Thebault et al., 2008).

4. Conclusion Activity concentrations of naturally occurring radionuclides 7Be, K, 232Th, 226Ra, 238U and anthropogenic 137Cs were determined in mussels' dry soft tissue collected from Croatian coast of Adriatic Sea in the period 2009e2013. Activity concentrations of 7Be for all sampling locations were found in a wide range, from <0.1 Bq/kg to 335 Bq/kg d.w. Activities found in early spring were regularly higher than those measured in early autumn for all locations which can be attributed to its input to the marine environment almost exclusively by atmospheric precipitation (rain/snow) and fresh water from the inland. Activity concentrations of 40K did not differ significantly either regarding the season or the location. Average activities for spring and autumn were (287 ± 18) Bq/kg and (295 ± 19) Bq/kg d.w., respectively. This 40K behavior can be attributed to its high and uniform concentration in the oceans, which consequently does not change its levels in coastal seawaters. 40

Table 4 Average activity concentrations (Bq/kg d.w.) of the selected radionuclides in mussels (Mytilus galloprovincialis) measured in autumn seasons 2009e2013. Location

Fa

7

40

Be b

D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13

5.050 5.263 4.542 5.535 4.764 4.723 4.748 4.621 4.905 4.842 4.712 5.510 4.705

20.0 ± 19.9 ± 17.4 ± 40.0 ± 33.1 ± 31.1 ± 26.8 ± <12.8 28.5 ± 23.1 ± 17.9 ± 21.4 ± <8.7

Range

3.729e7.309

9.7e79.9c (61)d

a b c d

3.6 11.4 4.2 30.5 14.1 11.1 16.8 16.1 12.7 7.5 4.4

232

K

312 325 307 285 278 304 312 299 298 292 291 285 248

± ± ± ± ± ± ± ± ± ± ± ± ±

37 35 22 24 46 24 45 29 69 42 20 31 43

188e377 (65)

Th

226

Ra

238

U

137

Cs

<3.1 <3.1 <3.2 <4.0 <3.3 <2.8 <3.8 <2.8 <4.3 <2.9 <3.7 <3.5 <3.2

<2.4 <2.5 <2.6 <2.6 <3.8 <2.5 <2.4 <2.6 <2.9 <2.9 <2.9 <2.9 <2.7

<12.8 <13.0 <13.6 <13.2 <13.8 <13.1 <12.7 <13.5 <13.5 <13.1 <13.5 <14.3 <12.7

<0.3 <0.4 <0.4 <0.5 <0.5 <0.3 <0.3 <0.3 <0.5 <0.4 <0.4 <0.4 <0.4

2.3e6.9 (13)

2.0e5.7 (9)

13.1 (1)

0.3e1.1 (13)

Concentration factor, average value 2009e2013. Standard deviation. Range of activity concentrations detected above the detection limit of gamma-spectrometric measurement in autumn periods 2009e2013. Number of samples in which specific radionuclide was detected (total number of samples for autumn periods 2009e2013 was 65).

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number: 098-0982934-2713)”) and State Office for Radiological and Nuclear Safety, Croatia (contract: “Research and monitoring of ionizing radiation in the environment e marine indicator organisms”).

References

Fig. 2. Average annual activity concentrations of 7Be (Bq/kg d.w.) in mussels' soft tissue for each sampling location along the Croatian Adriatic coast (2009e2013), with relevant standard deviations of the measured results.

Fig. 3. Average annual activity concentrations of 40K (Bq/kg d.w.) in mussels' soft tissue for each sampling location along the Croatian Adriatic coast (2009e2013), with relevant standard deviations of the measured results.

Generally, measured activity concentrations of anthropogenic Cs in mussels' tissue were low and varied in range (<0.3e1.1) Bq/ kg d.w. for all locations. It was detected only once in the period 2009e2010, but 23 times in the period 2011e2013 due to significant input through heavy rains/snow (prior to sampling periods) and/or Adriatic seawater currents of the Ionian and Aegean Seas. Activity concentrations of 232Th, 226Ra and 238U in mussels' tissue were generally below the detection limits of performed gamma-spectrometric measurement. 137

Acknowledgments This work was financially supported by Ministry of Science, Education and Sports of the Republic of Croatia (project: “Radionuclides and trace elements in environmental systems (project

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