A comparison of 210Po accumulation in molluscs from the southern Baltic, the coast of Spitsbergen and Sasek Wielki Lake in Poland

*Corresponding author.E-mail address: [email protected] (P. Stepnowski)

Journal ofEnvironmental Radioactivity 49 (2000) 201}208

A comparison of 210Po accumulation in molluscsfrom the southern Baltic, the coast of Spitsbergen

and Sasek Wielki Lake in Poland

Piotr Stepnowski!,*, Bogdan Skwarzec"!Faculty of Chemistry, University of Gdan& sk, 80-952 Gdan& sk, ul. Sobieskiego 18/19, Poland

"Institute of Oceanology, Polish Academy of Sciences, 81-712 Sopot, ul. Powstan& co&w W-wy 55, Poland

Received 1 December 1998; received in revised form 15 July 1999; accepted 25 August 1999

Abstract

210Po was analysed in the tissues and organs of four di!erent species of molluscs originatingfrom the Gulf of GdanH sk and S"upsk Narrow (Mytilus trossulus, Mya arenaria), Southern coastof Spitsbergen (Chlamys islandicus), and Sasek Wielki Lake in north-east Poland (Anodontacygnea). The results show a great disproportion in the 210Po distribution within the molluscsexamined. The highest 210Po concentrations were found in the hepatopancreas of the Balticand freshwater species whereas for the polar molluscs the highest values were observed in gills.The 210Po/210Pb activity ratio was calculated exclusively for the Baltic bivalves. The value ofthe ratio greatly exceeds unity for all organs and tissues (except for the shell of Mya arenaria).The concentration factor CF for the total soft tissue of all the molluscs analysed varies in therange of 3600}72,000. ( 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Polonium-210; 210Po; Molluscs; Bivalves; Bioaccumulation; Concentration factor

1. Introduction

The largest contribution to the radiation dose received by marine fauna comes fromnaturally-occurring 210Po (Cherry & Shannon, 1974; Cherry & Heyraud, 1982;Carvalho, 1995). Polonium, 210Po (¹

1@2"138.4 d), belongs to the natural uranium

0265-931X/00/$ - see front matter ( 2000 Elsevier Science Ltd. All rights reserved.PII: S 0 2 6 5 - 9 3 1 X ( 9 9 ) 0 0 0 9 4 - 6

series starting from 238U, but its distribution in the environment depends to a largeextent on other radionuclides in the decay series, such as 226Ra and 210Pb. In themarine environment 210Po is largely produced from the decay of 210Pb depositedfrom the atmosphere (Turekian, Nozaki & Beninger, 1977). Furthermore, the concen-tration of 210Po can be locally enhanced by the impact of industrial releases, inparticular the discharges from factories that produce phosphoric acid used in themanufacture of phosphate fertiliser and that generate phosphatic gypsum wastes(Kostner, 1994; Germain, Leclerc & Simon, 1995).

The 210Po concentrations in marine organisms and their variations with selectedbiological factors and environmental #uctuations are well documented (Cherry& Shannon, 1974; Cherry, Heyraud & Higgo, 1983; Carvalho, 1988; Cherry& Heyraud, 1981,1988; Heyraud, Cherry & Dowdle, 1987; Skwarzec & Falkowski,1988; Germain et al., 1995; McDonald, Baxter & Fowler, 1993; Wildgust, McDonald& White, 1998). These studies have highlighted the exceptionally elevated 210Poconcentrations in organs such as the hepatopancreas of crustaceans and have re-ported on temporal variations of 210Po in marine invertebrates with regard to thewater column, food chain dynamics or physiological cycles. However, there has beena lack of data on accumulation of 210Po by freshwater molluscs. Additionally, data forarctic bivalves are very rare, especially for their 210Po organ and tissue distribution.The available studies on the accumulation of 210Po in Mytilus trossulus (formerMytilus edulis) originating from the Baltic Sea have reported only soft tissue 210Poconcentrations with no detailed data on organ and tissue distributions (Skwarzec& Falkowski, 1988; Dahlgaard, 1996).

This study examines and compares the accumulation and organ/tissue distributionsof 210Po in four di!erent species of molluscs originating from the Gulf of GdanH sk andS"upsk Narrow (Mytilus trossulus, Mya arenaria), the southern coast of Spitsbergen(Chlamys islandicus), and Sasek Wielki Lake in the north-east of Poland (Anodontacygnea). Furthermore, 210Pb analyses were made for the organs and tissues of Mytilustrossulus and for the second Baltic bivalve Mya arenaria, in order to calculate210Po/210Pb activity ratios. This paper also reports on the concentration factors(CFs) for all the organisms analysed, calculated on the basis of the content of 210Po indeepwater originating from the study regions.

2. Materials and methods

The specimens of Mytilus trossulus (n"73) were acquired by trawling in the Gulf ofGdanH sk and S"upsk Narrow (southern Baltic Sea) during the cruises of r/v `Oceaniaain May 1996 and 1997. The second Baltic species, Mya arenaria (n"23), was obtainedduring the 1996 cruise from the southern part of the Gulf of GdanH sk, in the vicinity ofthe mouth of the Vistula river. The locations of the sample collection sites areillustrated in Fig. 1. Freshwater molluscs (Anodonta cygnea) (n"18) were collected bydivers from Sasek Wielki Lake in north-east Poland (Fig. 1). Additionally, three deepwater samples were taken for 210Po analysis. Samples of the polar species Chlamysislandicus (n"24) together with two deep water samples were acquired o! the coast of

202 P. Stepnowski, B. Skwarzec / J. Environ. Radioactivity 49 (2000) 201}208

Fig. 1. Sampling location sites for Mytilus trossulus (1, 2, 3), Mya arenaria (4), Anodonta cygnea and lakewater samples (5).

southern Spitsbergen during the polar expedition of r/v `Oceaniaa in June 1997.Sample collection sites are presented in Fig. 2. After collection, the molluscs weredissected into the following parts: hepatopancreas, gills, muscles and shell. In addi-tion, residue and fat were isolated from Mya arenaria, byssal threads from Mytilustrossulus, and residue and foot from Anodonta cygnea. The biological material wasoven-dried at 603C for 2 d and then digested using concentrated nitric acid with 209Pospike added as a yield tracer. Water samples (10 dm3) were "ltered (0.45 lm Sartoriusmembrane "lter), acidi"ed with concentrated nitric acid to pH"1 and then cop-recipitated with manganese dioxide. The sample was centrifuged and the MnO

2precipitate dissolved with 100 cm3 of H

2O

2in 1.2 M HCl and evaporated to dryness,

following the Skwarzec method (1997). The dry residues of both biological and watersamples were then dissolved in 0.5 M HCl, and after adding about 50 mg of ascorbicacid (reduction of Fe3` to Fe2`) polonium was spontaneously deposited onto silverdiscs (Flynn, 1968). The activity of 210Po was determined by alpha-spectrometry usinga surface-barrier detector with an active surface of 300 mm2 (ORTEC, USA) placed ina vacuum chamber connected to a 1024 multichannel analyser (TENNELEC TC 256,USA).

The activity of the 210Pb was calculated indirectly by measuring 210Po, originatingfrom the radioactive decay of its grandparent 210Pb, after an in-growth time of sixmonths (Takizawa, Zhao, Yamamoto, Abe & Ueno, 1990).

3. Results and discussion

The results of determining the 210Po content in organs and tissues of the molluscsare listed in Tables 1 and 2. Additionally, values of the total soft tissue concentrationfactor (Tables 1 and 2) and 210Po/210Pb activity ratio (Table 1) are reported.

P. Stepnowski, B. Skwarzec / J. Environ. Radioactivity 49 (2000) 201}208 203

Fig. 2. Sampling location sites for Chlamys islandicus and deep seawater samples (6, 7).

For the purposes of CF calculations for the Spitsbergen and lake species, watersamples from the molluscs' collection sites were analysed for 210Po content which was0.20$0.02 and 0.24$0.02 mBq dm~3, respectively. For the CF calculations for theBaltic species, a mean 210Po concentration of 0.6 mBq dm~3 in southern Balticdeepwater was used, as reported by Skwarzec and Bojanowski (1988).

The distribution of 210Po in Mytilus trossulus varies greatly, with the highest valuesin hepatopancreas (1026 Bq kg~1 dry wt) and gills (232 Bq kg~1 dry wt). The 210Poconcentration in byssal threads and muscles are of the same order at 30 and56 Bq kg~1 (dry wt) respectively, while in shell the radionuclide content is notsigni"cant (0.9 Bq kg~1 dry wt). The concentration of 210Po in the hepatopancreas ofMytilus trossulus is about twice that reported by McDonald et al. (1993) for the sametissue from Mytilus edulis sampled from an area not in#uenced by anthropogenicsources of this radionuclide. The 210Po/210Pb activity ratio greatly exceeds unityin all tissues and organs of Mytilus trossulus. However, the highest ratio valuesof 68.4 and 41.8 for hepatopancreas and muscles, respectively, re#ect both relatively


Table 1The 210Po concentrations, 210Po/210Pb activity ratios, CFs and wet:dry ratios in Baltic molluscs: Mytilustrossulus and Mya arenaria (Bq kg~1 dry wt$1SD)

Organ, tissue Mytilus trossulus Mya arenaria

210Po 210Po/210Pb wet:dry 210Po 210Po/210Pb wet:dry

Hepatopancreas 1026.0$107.0 68.4 7.7 87.0$17.0 16.8 4.8Gills 232.0$10.0 21.0 16.9 29.2$4.1 16.7 5.3Muscle 56.5$8.4 41.8 22.2 4.9$0.3 3.7 5.0Shell 0.9$0.1 6.0 1.1 0.4$0.1 0.4 1.3Byssal threads! 30.0$1.7 1.4 4.5 * * *

Residue" * * 12.7$3.9 8.9 5.0Fat" * * 2.9$0.4 14.8 3.8Total soft tissue 271.7$27.6 48.3 18.5 10.1$1.7 8.6 4.6Concentrationfactor#

24,000 3600

!Mytilus only."Mya only.#Values for total soft tissue.

Table 2The 210Po concentrations, CFs and wet:dry ratios in molluscs: Chalmys islandicus from southern Spitsber-gen and Anodonta cygnea from Sasek Wielki Lake (Bq kg~1 dry wt$1SD)

Organ, tissue Chlamys islandicus Anodonta cygnea

210Po wet:dry 210Po wet:dry

Hepatopancreas 22.7$1.7 4.2 61.8$2.0 9.7Gills 117.6$13.5 7.8 7.0$0.5 12.2Muscles 89.1$6.7 5.6 6.0$0.2 10.0Shell BDL 1.2 0.1$0.004 1.0Residue! * * 36.0$14.0 126.7Foot! * * 25.8$2.5 6.2Total soft tissue 82.5$6.7 5.7 19.3$1.6 13.0Concentration factor" 72,000 6150

!Anodonta only."Values for total soft tissue.BDL * below detection limit.

high 210Po concentrations and relatively low 210Pb concentrations. The valueof CF for the total soft tissue of Mytilus trossulus was calculated to be 24,000 andis greater than the recommended factors for mollusca (10,000) for total soft parts(IAEA, 1985).


The 210Po concentrations in tissues and organs of Mya arenaria are much lowerin comparison with those observed in Mytilus trossulus, covering the rangefrom 0.4 Bq kg~1 (dry wt) in shell to 87.0 Bq kg~1 (dry wt) in hepatopancreas.The remaining tissues accumulate 210Po to a very small extent, but the calculated210Po/210Pb activity ratios are quite high, a "nding which may illustrate a ratheruniform and simultaneous bioconcentration process of 210Po and 210Pb bysouthern Baltic molluscs. It is unlikely that the di!erences between these twobivalves, in terms of 210Po concentration and concentration factor (one orderof magnitude), arise from the feeding process; both species, from the "libranchsuborder (Mytilus) and eulamellibranch suborder (Mya), feed through "ltrationusing their gills to capture food (Brusca & Brusca, 1990). However, the di!er-ences in accumulation ability between the two species of mollusc might be a!ectedby the environmental characteristics of the regions of origin. The Mytilus trossuluswere obtained from the Gulf of GdanH sk and S"upsk Narrow, regions with a highcontent of organic matter in the sediments, while the Mya arenaria originatedfrom sandy bottoms in the vicinity of fresh water in#ow from the mouth of theVistula River.

The 210Po accumulation in the organs and tissues of the freshwater speciesAnodonta cygnea exhibits similar levels as these for Mya arenaria. The radionuclideconcentrations fall in the range of 0.1-61.7 Bq kg~1 (dry wt). The low 210Po concen-tration in gills is notable (7.0 Bq kg~1 dry wt). This observation may exclude a role forthis organ in an active transport and retention of the radionuclide within theorganism. The CF calculated for the total soft parts of Anodonta cygnea is low andsimilar to that quanti"ed for Mya arenaria, a marine species of the same Eulamellib-ranch suborder which is a!ected by freshwater inputs.

When the data are compared with available information about radionuclide accu-mulation in bivalves, the 210Po content within the tissues and organs of the polarmollusc Chlamys islandicus exhibits unusual and unexpected distributions. The high-est 210Po concentrations were found in the gills and muscles of the organism at 117.6and 89.1 Bq kg~1 (dry wt) respectively. The 210Po content of the hepatopancreas(22.7 Bq kg~1 dry wt) is comparable to that in the same tissue of Mya arenariaand is the lowest measured concentration for the soft tissues of Chlamys islandicus.The 210Po concentration in the shell was below the detection limit of the analyticalmethod (0.33 mBq). The unexpectedly low 210Po content in the hepatopancreasof Chlamys islandicus might be caused by di!erences in environmental variables,such as low seawater temperature and a comparatively short period of phyto-plankton production (potentially the greatest source of 210Po) in the study region,two phenomena which are most likely to a!ect the uptake of 210Po by thisbivalve. One of the primary uptake routes of metals by molluscs is across thegill (Viarengo, 1989). Therefore, it is possible that, under conditions of very inten-sive feeding (samples of Chlamys islandicus were acquired &20 d after maximumdevelopment of the bloom in the study area), an elevation of radionuclide concentra-tion in gills might occur. The calculated CF for the total soft tissue of Chlamysislandicus equals 72,000, thus exceeding the IAEA (1985) recommended values formollusca.


Acknowledgements

Thanks are due to Prof. Jan Marcin We7 c"awski of the Institute of Oceanology ofthe Polish Academy of Sciences for making it possible for one of us to participate inthe Spitsbergen expedition in 1997. The "nancial support of this work from the PolishState Committee for Scienti"c Research (KBN) under Grant BW/800-5-0105-8 isgreatly acknowledged.

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A comparison of 210Po accumulation in molluscs from the southern Baltic, the coast of Spitsbergen and Sasek Wielki Lake in Poland