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40K, 137Cs, 90Sr, 238,239+240Pu and 241Am in mammals' skulls from owls' pellets and owl skeletons in Poland
Journal of Environmental Radioactivity 78 (2005) 93–103 www.elsevier.com/locate/jenvrad
40
K, 137Cs, 90Sr, 238,239C240Pu and 241Am in mammals’ skulls from owls’ pellets and owl skeletons in Poland
Pawe1 Gacaa, Jerzy W. Mietelskia,), Ignacy Kitowskib, Sylwia Grabowskaa, Ewa Tomankiewicza a
Henryk Niewodniczan´ski Institute of Nuclear Physics, Environmental Radioactivity Laboratory, E Radzikowskiego 152, 31 342 Krako´w, Poland b Maria Curie-Skldodowska University, Department of Nature Conservation, Lublin, Poland
Received 20 December 2002; received in revised form 23 December 2003; accepted 5 January 2004
Abstract Skulls of small mammals belonging to two species of rodents and three species of insectivores collected in Eastern Poland were the subject of the present investigation. The skulls were separated from owl pellets. Activities of 40K, 137Cs, 90Sr, 238,239C240Pu and 241Am were determined by means of gamma spectrometry as well as liquid scintillation spectrometry or alpha spectrometry along with relevant radiochemical procedures. A detailed description of the procedures is provided. The research was supplied with the analysis of three skeletons of owls. No measurable difference between the skulls of rodents and insectivorous animals with regard to activity of any of the examined radionuclides was found. No accumulation effect in the owl skeletons was detected. Though measured activities of 137Cs and 40K for the skulls were of the same magnitude as those found previously for large wild herbivorous animals from typical locations in Poland, those for 90Sr were even lower than previously determined. A big difference was found for activities of plutonium and americium isotopes. Their mean activities were higher by an order of magnitude when compared to the examined previously values. The maximum 239C240Pu activity was equal to 97:5 G 7:7mBq=kg, with 65% of it originating from global fallout. Relatively high content of transuranic elements found for rodents and insectivorous mammals seems to be unrelated to their feeding habits and should rather be
) Corresponding author. Tel.: C48-12-662-8458; fax: C48-12-6628-392. E-mail address: [email protected] (J.W. Mietelski). 0265-931X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2004.01.032
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attributed to the living conditions. It is suggested that small mammals, together with tiny soil particles present in mid-soil living tunnels, can inhale the transuranic elements. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: 40K; Radioecology
137
Cs;
90
Sr;
238
Pu;
239C240
Pu;
241
Am; Mammal bones; Owl pellets; Owl bones;
1. Introduction For many years the main objective of studies conducted in the field of environmental radioactivity was to assess the impact of radionuclides on man. Recently a new consideration has emerged, namely the concept of protection of the environment from ionising radiation (Strand et al., 2000; Brechignac et al., 2003). In this novel approach the importance of doses to non-human biota is stressed, which involves studying radionuclides in parts of the ecosystem not occupied by humans and in food-chains in which humans are not involved. It is widely known that small mammals constitute the major element of owls’ diet. Parts of their bones and pieces of fur which are not digested are frequently found in so called ‘owl pellets’. A relatively large collection of such material can be obtained from ornithologists and mammalogists. The material is relatively easy to collect in the vicinity of owl nests (Mikkola, 1983; Love et al., 2000), and therefore it is easily attributable to specific owl species. Usually pellets are collected to study the proportion in which different species of mammals contribute to the diet of raptors. Bones from owl pellets might differ slightly from the raw ones, since they were present in owls’ stomachs for some time and therefore could be, at least partially, digested. However, digestion of mammal prey is very low in owls when compared to diurnal raptors (Mikkola, 1983). Small bones are not present in such samples, and their main components are skulls, which greatly facilitates identification of species they belong to. The main aim of this investigation was to study the concentration of bone-seeking radionuclides like 90Sr, 238,239C240Pu and 241Am isotopes in skulls found in pellets and in skeletons of owls. Prior to that, as a complementary investigation, samples were analysed for the presence of gamma emitters such as 137 Cs and 40K.
2. Materials and methods Twenty-eight sets of mammal skull samples were initially formed from pellets collected in the south-east of Poland. Each set contained skulls of specific species, collected in one village in a particular year. The skulls of prey belonged to species of both insectivorous and rodent small mammals. Namely (Pucek, 1984), among the analyzed sets of insectivorous skulls were: 10 of common shrew (Sorex araneus), two of Pygmy shrew (Sorex minutus) and one of bicolored white-toothed shrew
P. Gaca et al. / J. Environ. Radioactivity 78 (2005) 93–103
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Fig. 1. Sampling area (encircled) in the vicinity of Zamos´ c´ town on the map of Poland. Sampling sites marked with dots.
(Crocidura leucodon), whereas two sets of striped field mouse (Apodemus agrarius) and 10 sets of common vole (Microtus arvalis) represented sets of rodent skulls. Twenty-two samples were attributed to the barn owl (Tyto alba), while the remaining six to tawny owl (Strix aluco). All the samples were collected between 1995 and 2001 in villages around Zamos´ c´ town in south-eastern Poland (approximately 23(40# E, 50(50# N), see Fig. 1. Supplementary analysis was performed on one skeleton of the barn owl (Tyto alba) and two skeletons of the little owl (Athene noctua). The dead owls were found in 2001 in the investigated area. More details on the samples are presented in Tables 1 and 2. Two samples of Pygmy shrew were combined into one to increase the amount of investigated material. For the same reason four other samples of Common shrew were combined into one set as well. The skulls were prepared for measurements to determine activity concentrations of gamma-emitters. Dried samples were weighed subsequently to being kept overnight at 105 (C. To obtain a standardized geometrical form of the samples,
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Table 1 Data on samples of skull separated from owl pellets from Eastern Poland Code
Site/village
Skulls of
Pellets attributed to:
Dry mass of skulls [g]
Year
S S S S S S S S S S S S S S S S S S S S S S S S S S S S
Rzeplin Poturzyn Rzeplin Plebanka qabunie Nowosio´1ki Uchanie Tarnawatka Majdan Szczepiatyn Magdalenka Wierzbica Machno´w Nowy Rzeplin Magdalenka Rzeplin Magdalenka Uchanie Tarnawatka qabunie Kornie Kos´ cieszyn Wierzbica Machno´w Nowy Plebanka Kornie Wierzbica qabunie
Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Apodemus agrarius Apodemus agrarius Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex minutus Sorex minutus Crocidura leucodon
Strix aluco Strix aluco Strix aluco Strix aluco Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Strix aluco Tyto alba Strix aluco Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba
103.2 100.1 40.2 26.4 154.4 43.7 63.5 96.9 50.4 26.0 61.0 17.9 18.1 7.2 7.3 20.6 6.9 27.0 28.9 101.4 24.8 3.1 11.8 10.5 7.2 2.1 1.0 39.8
1995 1996 2001 2001 1995 1995 1996 1996 1999 2000 2000 2000/2001 2001 2001 2000 1995 2000 1996 1996 1995 2000/2001 2000 2000/2001 2001 2000 2000/2001 2000/2001 1995
1 7 10 19 2 3 4 5 6 8 9 11 21 17 27 16 12 14 15 18 20 22a 23a 24a 28a 25b 26b 13 a b
Mixed together for gamma measurements as SS 1. Mixed together for gamma measurements as SS 2.
all were powdered after incineration in the oven at 400 (C. A relatively low temperature was set to prevent evaporation of radiocesium from the samples during their ashing. Gamma activities of the ashes were measured by means of low background gamma-ray spectrometry with a HPGe detector. Then the samples were re-incinerated at 600 (C and reweighed after being cooled down to room Table 2 Data on owl skeletons taken for analyses Code
Species
Dry mass [g]
Ash (600( C) mass [g]
X1 X2 X3
Barn owl (Tyto alba) Little owl (Athene noctua) Little owl (Athene noctua)
18.0 5.4 2.7
11.07 3.51a 1.53a
a
Not complete skeleton.
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temperature. The ash 600 (C to dry mass ratio for all the samples showed a narrow distribution ranging from 0.678 to 0.742, with the mean value of 0.707 and standard deviation equal to 0.016. An identical procedure was applied to skeletons of owls. Once the gamma spectrometric measurements were finished, the skulls were grouped into 13 samples with respect to both raptor and prey species. Grouping was necessary to obtain samples of sufficient mass to allow determination of the activities for such isotopes as Pu and Am, or at least 90Sr, well above their detection limits. Despite this, two samples still did not reach the required mass level. Therefore, a sample containing all the available skulls of Apodemus agrarius and another one of all the available skulls of Sorex minutus were combined into one. Table 3 presents details on the combined sets. For ashed samples from the sets of skulls of insectivores the average weight reached 40.6 g with standard deviation of 26.6 g, whereas for rodents the value was equal to 71.5 g with standard deviation of 28.4 g. The tracers, namely 85Sr, 236Pu or 242Pu, 148Gd, were added to the ashed samples which were subsequently exposed to hot etching with hydrochloric acid. The insoluble residue was first separated by centrifuging and then mineralized by addition of hot HF, HNO3 and HCl with admixture of H3BO3 (LaRosa et al., 1992), to be combined again with samples etched previously. The solutions were diluted with water with some oxalic acid added and their pH was balanced at 3 with the help of ammonia. The oxalates were precipitated (Mietelski et al., 2000) and centrifuged. Coprecipitated Pu, Am and rare earths elements were expected to be found in their sediments. The second precipitation was performed with pH stabilized at 6. This second fraction contained Sr isotopes (Mietelski et al., 2001a). The coprecipitated radionuclides were separated sequentially. From pH ¼ 3 fraction after destroying oxalates in the oven at 600 (C, Pu was separated from 8 M HNO3 on Dowex-1 anion exchange column (LaRosa et al., 1992; Mietelski and Wa˛s, 1995) and Am, together with rare earth elements, using Dowex-1 and methanol-acids solutions (Holm and Table 3 Data on combined samples taken for radiochemical procedures Code
Codes in Table 1
Skulls of:
Ash (600 (C) mass [g]
S1 S2 S 34 S7 S5 S 69 SS 3 SS 6 S 18 SS 4 SS 5 SS 2 S 13
S1 S2 S 3CS 4 S7 S5 S 6CS 9 S 8CS 10CS 21CS 19CS 11 S 27CS 17 S 18 S 16CS 14CS 15 S 12CSS 1CS 20 S 25CS 26 S 13
Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Apodemus agrarius Sorex araneus Sorex araneus Sorex araneus Sorex minutus Crocidura leucodon
71.6 110.4 75.2 70.3 66.4 79.0 89.6 10.2 71.8 53.6 57.9 2.4 28.0
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Ballestra, 1989). From pH ¼ 6 fraction Sr was separated from 8 M HNO3 on SrResin. (Mietelski and Gaca, 2002; Vajda et al., 1992). To prepare alpha spectrometric sources (Pu, AmCGd) NdF3 co-precipitation method (Sill, 1987) was applied. A Silena AlphaQuattro spectrometer with Canberra PIPS detectors was used to perform the measurements. The activity of 90Sr was determined with a liquid scintillation spectrometer Wallac 1414-003 Guardian and recovery of 85Sr was determined by means of gamma spectrometry with HPGe detector. Three skeletons of owls underwent the same treatment. The analysis of the samples, was accompanied by an analysis performed on a reference material, namely on soil samples IAEA 375 and IAEA Soil-6, as well as on blank samples spiked with tracers. For alpha-spectrometric measurements it is typical to give the activities of 239Pu and 240Pu as the sum of both isotopes, noted as 239C240Pu. Both radionuclides emit alpha particles of energy of about 5.15 MeV. Resolution of standard alpha spectrometers does not allow alpha particles originating from these decays to be distinguished. Another difficulty, which often occurs in such analyses, is the interference of 228Th with 238Pu or 241Am. Despite the fact that both 238Pu and 241 Am emit alpha particles of 5.50 MeV, it is not their separation that causes chemical problems. The problem lies in 228Th itself and its daughterd 224Ra. 228Th emits 5.45 MeV alpha particles, so it is of great importance to have clear, separated lines in the spectrum. For lines contributing to a spectrum in low count rates, it is hard to judge whether a single count at 5.45 MeV comes from a scattered alpha emitted by 241Am or whether it shall be attributed rather to full energy 228Th alpha. 224 Ra emits alpha particles of 5.69 MeV, and 228Th and 224Ra activities, both granddaughters of 228Ra (a beta emitter), are typical for bone samples and are usually two or three orders of magnitude higher than for Pu or Am isotopes. Therefore, even relatively tiny traces of 224Ra contribute to counts in 5.5 MeV 241Am (or 238Pu) peak region due to alpha particles losing their energy. The described problems affect 238Pu and 241Am measurements, increasing the detection limits above 1 mBq/kg, a standard for 239C240Pu in samples of 100 g recorded with a spectrum acquisition time of a week.
3. Results and discussion The statistical parameters of results are presented in Table 4. Distributions of activity for main radionuclides are presented in Fig. 2a–d. The majority of the results for 40K range between 20 and 35 Bq/kg. The average (G standard deviation) activity was equal to 26:3 G 18:0 Bq=kg and 28:4 G 19:5 Bq=kg for rodents and insectivores, respectively. For 137Cs almost all the results were below 5 Bq/kg, and the respective parameters reached 2:1 G 2:7 Bq=kg and 2:6 G 1:9 Bq=kg. Such results are consistent with our previous measurements for wild herbivorous animals (deer, roe-deer, elk, boar) from Poland (Mietelski et al., 2001b), for which the average activity (G standard deviation) of 40K in ashed bones
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Table 4 Chosen statistical parameters obtained for activity of analyzed radionuclides in ashed skulls of small mammals and on skeletons of owls. Data for potassium and cesium isotopes from all initial samples analyzed by gamma spectrometry, for remaining nuclide from combined sets of samples (see Materials and methods for details) Mammals Rodents
Parameter
40
137 K Cs [Bq/kgash] [Bq/kgash]
Mean 26.3 SD 18.0 Min !10 Max 75 G 10 Mean uncert 9.4 Insectivores Mean 28.4 SD 19.5 Min !14 Max 50 G 35 Mean uncert 15.5 Owls Min 39 G 21 Max 93 G 76 Mean uncert 56
2.1 2.7 !1.2 10:4 G 0:6 0.9 2.6 1.9 !0.9 5:1 G 1:3 1.8 !1.3 !7 3
90
Sr [Bq/kgash]
239C240
238 241 Pu Pu Am [mBq/kgash] [mBq/kgash] [mBq/kgash]
17.5 14.5 2:3 G 0:4 42:4 G 2:8 1.3 27.2 8.9 17:6 G 1:1 49:1 G 3:0 5.7 !5 19:6 G 1:6 2.7
17.7 35.4 0:5 G 0:2 97:5 G 7:7 2.0 9.6 7.5 !2.4 16:7 G 2:0 1.3 0:7 G 0:3 3:2 G 1:1 3
2.9 7.4 !0.4 19:6 G 3:2 2.1 1.3 2.1 !0.8 4:9 G 1:0 2.8 !1.3 !24 12
8.0 9.2 !1.2 22 G 4 4.1 9.7 7.5 !2.5 16 G 4 3.2 !8 !196 60
varied for different species from 17:6 G 26:2 (elk) to 29:7 G 25:2 (boar) Bq/kg; for 137 Cs activities ranged from 1:9 G 1:8 (deer) to 5:7 G 7:1 (boar). This similarity suggests that observed levels of activities for 40K are perhaps typical for mammals in general, and those for 137Cs are typical for wild mammals, which live in Eastern Poland. This activity of 40K corresponds to about 0.4%0 of stable K content in fresh bones, which is about three times less than the typical value for adult humans
Fig. 2. Activity distribution for 137Cs (a), 40K (b), 90Sr (c) and 239C240Pu (d) activity concentration in ashen bones of small mammals and owls.
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(Iyenger et al., 1978). This discrepancy might appear due to the high solubility of potassium, which could also be the reason for possible losses of K during sample pretreatment. The radiochemical procedure yielded, on average, recovery of tracers equal to (80:0 G 20:3)%, (16:8 G 6:3)%, and (28:3 G 18:2) for 242Pu, 148Gd and 85Sr, respectively. In three samples 90Sr activity dropped below the detection limit, most likely due to poor recovery of the isotope. A few samples activities for 241Am and 238 Pu, owing to interference of 228Th and 224Ra traces in the spectrum, did not exceed the detection limit. The maximum activity of plutonium isotopes (Table 4) was an order of magnitude higher than found previously for bigger animals (Mietelski et al., 2000). The maximum was found for the sample of Common vole skulls separated from Barn owl pellets coded as S5 . The maximum for 239C240Pu was equal to (97:5 G 7:7) mBq/ kg for ash weight, which corresponds to (66 G 5) mBq/kg of dry weight. The sample showed also the highest 238Pu and 241Am activities of 19:6 G 3:2 mBq/kg and 22 G 4 mBq/kg (ash), respectively. Unfortunately, the 90Sr fraction of this particular sample was accidentally lost in preparation. The sample originated from Tarnawatka village. A sample of insectivores skulls, found at the same location, was combined together with samples from Rzeplin and Uchanie into a set coded as SS 4. In sample SS 4, despite the fact that it may be diluted by relatively low concentration of the nuclides in the samples from other locations – for skulls of rodents from Rzeplin and Uchanie activities were lowdstill relatively high 239C240Pu, 241Am and 90Sr activities were detected (Table 4). The reasons for such a high transfer factor of radionuclides in the surroundings of Tarnawatka village have not been discovered yet. The terrain consists of peat and wet grassy meadows. For S 5 sample, the Chernobyl fraction of Pu activity, determined on the basis of the isotopic ratio between 238Pu and 239C240 Pu (Mietelski and Wa˛s, 1995), can be estimated to be 36 G 12%, which roughly corresponds to the maximum percentage of Chernobyl fraction of Pu in the area (Komosa, 1999a,b). Generally, the 238Pu to 239C240Pu activity ratios indicate that the global fallout is the main source of Pu contamination. The ratio between 239C240 Pu and 241Am activities for S 5 sample of 0:224 G 0:044 is somewhat lower than the global fallout ratio of about 0.3 (UNSCEAR, 1993) and significantly lower than the present Chernobyl ratio of about 1.5. Such ratio for Chernobyl fallout can be calculated including americium ingrown from 241Pu decay (Kudryashov et al., 2001). Our result suggests that americium is transferred or accumulated in bones perhaps less effectively than plutonium, possibly due to a shorter biological half-life time of Am. The average (arithmetic mean) values for Pu and Am activities (Table 4) were also far higher that found for bigger animals. Taking into consideration that no difference has been observed for small mammals of different feeding habits, the obtained result may suggest that transuranic elements could be not ingested but inhaled (Mietelski et al., 2003). The level of 90Sr in all kinds of bone ashes covered by the presented study (Table 4) was lower than the values found previously for large wild herbivorous mammals (Mietelski et al., 2001a), especially when compared with ones living in the areas of
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Table 5 Squared Pearson’s correlation factor values for activity of various radionuclides found in the small mammals skulls separated from owl’s pellets 40 40
K Cs 90 Sr
K
137
90
239C240
241
0.582 1
0.281 0.364 1
0.041 0.048 0.238 1
0.002 0.057 0.431 0.641 1
Cs
1
137
Sr
Pu
239C240
Pu
241
Am
Am
North-Eastern Poland where 90Sr is known to have been deposited in a form of hot particles from Chernobyl. Present results compared to the ones obtained for large mammals from the areas practically unaffected by Chernobyl-originated 90Sr, such as central Poland or Denmark (Strandberg and Strandgaard, 1995), lead to the same conclusion of the lower level of observed activities. Respective results from our previous study varied from 59 G 10 Bq/kg for deer, to 127 G 13 Bq/kg for roe-deer, while Danish results for roe-deer lay between 60 Bq/kg, and 140 Bq/kg, the present results range from 2:3 G 0:4 Bq/kg to 49:1 G 3:0 Bq/kg. The values for squared Pearson’s correlation factors between determined activities are presented in Table 5. Here, for the samples combined into larger sets to enable radiochemical analysis, radiocesium and potassium activities were calculated from averaged for given set values. Correlation was calculated only for non-zero values. A considerable correlation was found between activities of 241Am and 239C240Pu (R2 ¼ 0:641) and between 40K and 137Cs (R2 ¼ 0:582) for all skulls of owls’ pellet samples taken together, i.e. not separated into rodents and insectivores. For all investigated isotopes any noticeable difference between the skulls of rodents and insectivorous animals was found in terms of Mann–Whitney nonparametric test and t-test for mean values.
Table 6 Results (in Bq/kg) for analyzed reference materials (IAEA, 2000) Name of reference material IAEA IAEA IAEA IAEA IAEA IAEA IAEA IAEA IAEA
Soil Soil Soil Soil Soil Soil Soil Soil Soil
375 375 375 6 375 375 375 375 375
Nuclide
Mass [g]
Determined activity (corrected for reference date), D
Certified value, C
95% Confidence interval
Difference ðD CÞ=C [%]
137
75.4 75.4 5.2 10.0 5.2 5.2 12.8 12.8 12.8
5559 G 66 423 G 28 104 G 10 1:06 G 0:01 0:267 G 0:025 0:076 G 0:010 0:259 G 0:026 0:052 G 0:009 0:126 G 0:033
5280 424 108 1.04 0.30 0.071 0.30 0.071 0.13
5200 5360 417 432 101 114 0:96 1:11 0:26 0:34 0:056 0:085 0:26 0:34 0:056 0:085 0:11 0:15
C5.3 0.2 0.4 C2 11 C7 13.7 27 3.1
Cs K 90 Sr 40
239C240
Pu Pu
239C240 238
Pu
239C240
Pu
238
Pu 241 Am
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3.1. Quality assurance The results for quality assurance measurements of reference materials are presented in Table 6. Since the presented uncertainties are just the counting statistics, each at one sigma level, they must be underestimated. The last column contains the relative discrepancy between determined and certified values. The results suggest the occurrence of small systematic errors, which might have hindered accurate determination of activities. In the case of gamma emitters, the activity of 40K seems to be determined accurately, though systematic error of about 5% overestimation, might occur for 137Cs. In case of 90Sr and alpha emitters the values are more precise. Almost all results lie within a reliable 95% confidence intervals.
4. Conclusions No measurable difference in the activities of any of the examined radionuclides in skulls of rodents and insectivorous animals has been found. Skeletons of owls did not reveal an accumulation effect. Levels of 137Cs and 40K retained in the bones are very much alike for small mammals and large wild herbivorous animals from typical Polish locations, and for 90Sr is even lower. On the contrary plutonium and americium activities found for small animals are, on average, significantly higher than for large animals. As was discussed elsewhere those transuranic elements can be introduced into small mammals via inhalation.
Acknowledgements The authors are grateful to the Polish State Committee for Scientific Research for partially supporting this investigation with a grant No PG04 07520.
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Komosa, A., 1999b. River sediment contamination with plutonium isotopes and heavy metals in Lublin agglomeration. Polish Journal of Environmental Studies 8, 155–160. LaRosa, J.J., Cooper, E., Ghods-Esphahani, A., Jansta, V., Makarewicz, M., Shawky, S., Vajda, N., 1992. Radiochemical methods used by the IAEA’s Laboratories at Seibersdorf for the determination of 90Sr, 144 Ce and Pu radionuclides in the environment samples collected for the International Chernobyl Project. Journal of Environmental Radioactivity 17, 183–209. Love, R.A., Webbon, C., Glue, D.E., Harris, S., 2000. Changes in the food of British barn owls (Tyto alba) between 1974 and 1997. Mammal Rev 30, 107–129. Kudryashov, V., Mironov, V., Konoplya, E., 2001. The contamination of Belarus territory by transuranium elements. In: Frontasyeva, M., Perelygin, V.P., Vater, P. (Eds.), Proceedings of NATO Advanced Research Workshop on Man-Made Radionuclides and Heavy Metals Wastes in Environment, Dubna, Russia, 3–6 October 2000. Kluwer Academic Publishers, pp. 127–134 (NATO Science Series, IV Earth and Environmental Sciences, vol. 5). Mietelski, J.W., Wa˛s, B., 1995. Plutonium from Chernobyl in Poland. Appl Rad Isot 46, 1203–1211. Mietelski, J.W., Gaca, P., Jasin´ska, M., 2000. Plutonium and other alpha-emitters in bones of wild, herbivorous animals from north-eastern Poland. Appl Rad Isot 53 (1–2), 251–257. Mietelski, J.W., Gaca, P., Zagrodzki, P., Jasin´ska, M., Zalewski, M., Tomczak, M., Vajda, N., Dutkiewicz, E.M., 2001a. 90Sr and stable strontium in bones of wild, herbivorous animals from Poland. J Radioanal Nucl Chem 247, 363–370. Mietelski, J.W., Gaca, P., Tomczak, M., Zalewski, M., Dutkiewicz, E.M., Szeglowski, Z., Jasin´ska, M., Zagrodzki, P., Kozak, K., 2001b. Radionuclides in bones of wild, herbivorous animals from north-eastern Poland. In: Frontasyeva, M., Perelygin, V.P., Vater, P. (Eds.), Proceedings NATO Advanced Research Workshop on Man-Made Radionuclides and Heavy Metals Wastes in Environment, Dubna, Russia, 3–6 October 2000. Kluwer Academic Publishers, pp. 113–120 (NATO Science Series, IV Earth and Environmental Sciences, vol. 5). Mietelski, J.W., Gaca, P., 2002. Measurements of 90Sr and 241Pu in various matrix samples. In: Moebius, S., Noakes, J.E., Shoenhofer, F. (Eds.), Advances in Liquid Scintillation Spectrometry 2001. Proceedings of the LSC 2001 Conference, 7–11 May 2001, Karlsruhe, pp. 373–378 (Radiocarbon, Tuscon). Mietelski, J.W., Kitowski, I., Gaca, P., Tomankiewicz, E., 2003. Elevated plutonium and americium content in skulls of small mammals. Journal of Radioanalytical and Nuclear Chemistry 256 (3), 593–594. Mikkola, H., 1983. Owls of Europe. T&AD Poyser, Calton. Pucek, Z., 1984. Klucz do rozpoznania ssako´w Polski [Key to identification of Polish mammals]. PWN, Warsaw (in Polish). Sill, C.W., 1987. Precipitation of actinides as fluorides or hydroxides for high resolution alpha spectrometry. Nuclear Chem Waste Mgmt 7, 201–215. Strand, P., Brown, J.E., Larsson, C.-M., 2000. Framework for the protection of the environment from ionizing radiation. Radiation Protection Dosimetry 92 (1–3), 169–175. Strandberg, M., Strandgaard, H., 1995. 90Sr in antlers and bone of a Danish roe deer population. Journal of Environmental Radioactivity 27, 65–74. UNSCEAR, 1993. Ionizing radiation sources and biological effects. Raport to the General Assembly with annexes, UN Pub, New York. Vajda, N., Ghods-Esphahani, A., Cooper, E., Danesi, P.R., 1992. Determination of radiostrontium in soil samples using a crown ether. J Radioanal Nucl Chem 162 (2), 307–323.
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K, 137Cs, 90Sr, 238,239C240Pu and 241Am in mammals’ skulls from owls’ pellets and owl skeletons in Poland
Pawe1 Gacaa, Jerzy W. Mietelskia,), Ignacy Kitowskib, Sylwia Grabowskaa, Ewa Tomankiewicza a
Henryk Niewodniczan´ski Institute of Nuclear Physics, Environmental Radioactivity Laboratory, E Radzikowskiego 152, 31 342 Krako´w, Poland b Maria Curie-Skldodowska University, Department of Nature Conservation, Lublin, Poland
Received 20 December 2002; received in revised form 23 December 2003; accepted 5 January 2004
Abstract Skulls of small mammals belonging to two species of rodents and three species of insectivores collected in Eastern Poland were the subject of the present investigation. The skulls were separated from owl pellets. Activities of 40K, 137Cs, 90Sr, 238,239C240Pu and 241Am were determined by means of gamma spectrometry as well as liquid scintillation spectrometry or alpha spectrometry along with relevant radiochemical procedures. A detailed description of the procedures is provided. The research was supplied with the analysis of three skeletons of owls. No measurable difference between the skulls of rodents and insectivorous animals with regard to activity of any of the examined radionuclides was found. No accumulation effect in the owl skeletons was detected. Though measured activities of 137Cs and 40K for the skulls were of the same magnitude as those found previously for large wild herbivorous animals from typical locations in Poland, those for 90Sr were even lower than previously determined. A big difference was found for activities of plutonium and americium isotopes. Their mean activities were higher by an order of magnitude when compared to the examined previously values. The maximum 239C240Pu activity was equal to 97:5 G 7:7mBq=kg, with 65% of it originating from global fallout. Relatively high content of transuranic elements found for rodents and insectivorous mammals seems to be unrelated to their feeding habits and should rather be
) Corresponding author. Tel.: C48-12-662-8458; fax: C48-12-6628-392. E-mail address: [email protected] (J.W. Mietelski). 0265-931X/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2004.01.032
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attributed to the living conditions. It is suggested that small mammals, together with tiny soil particles present in mid-soil living tunnels, can inhale the transuranic elements. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: 40K; Radioecology
137
Cs;
90
Sr;
238
Pu;
239C240
Pu;
241
Am; Mammal bones; Owl pellets; Owl bones;
1. Introduction For many years the main objective of studies conducted in the field of environmental radioactivity was to assess the impact of radionuclides on man. Recently a new consideration has emerged, namely the concept of protection of the environment from ionising radiation (Strand et al., 2000; Brechignac et al., 2003). In this novel approach the importance of doses to non-human biota is stressed, which involves studying radionuclides in parts of the ecosystem not occupied by humans and in food-chains in which humans are not involved. It is widely known that small mammals constitute the major element of owls’ diet. Parts of their bones and pieces of fur which are not digested are frequently found in so called ‘owl pellets’. A relatively large collection of such material can be obtained from ornithologists and mammalogists. The material is relatively easy to collect in the vicinity of owl nests (Mikkola, 1983; Love et al., 2000), and therefore it is easily attributable to specific owl species. Usually pellets are collected to study the proportion in which different species of mammals contribute to the diet of raptors. Bones from owl pellets might differ slightly from the raw ones, since they were present in owls’ stomachs for some time and therefore could be, at least partially, digested. However, digestion of mammal prey is very low in owls when compared to diurnal raptors (Mikkola, 1983). Small bones are not present in such samples, and their main components are skulls, which greatly facilitates identification of species they belong to. The main aim of this investigation was to study the concentration of bone-seeking radionuclides like 90Sr, 238,239C240Pu and 241Am isotopes in skulls found in pellets and in skeletons of owls. Prior to that, as a complementary investigation, samples were analysed for the presence of gamma emitters such as 137 Cs and 40K.
2. Materials and methods Twenty-eight sets of mammal skull samples were initially formed from pellets collected in the south-east of Poland. Each set contained skulls of specific species, collected in one village in a particular year. The skulls of prey belonged to species of both insectivorous and rodent small mammals. Namely (Pucek, 1984), among the analyzed sets of insectivorous skulls were: 10 of common shrew (Sorex araneus), two of Pygmy shrew (Sorex minutus) and one of bicolored white-toothed shrew
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95
Fig. 1. Sampling area (encircled) in the vicinity of Zamos´ c´ town on the map of Poland. Sampling sites marked with dots.
(Crocidura leucodon), whereas two sets of striped field mouse (Apodemus agrarius) and 10 sets of common vole (Microtus arvalis) represented sets of rodent skulls. Twenty-two samples were attributed to the barn owl (Tyto alba), while the remaining six to tawny owl (Strix aluco). All the samples were collected between 1995 and 2001 in villages around Zamos´ c´ town in south-eastern Poland (approximately 23(40# E, 50(50# N), see Fig. 1. Supplementary analysis was performed on one skeleton of the barn owl (Tyto alba) and two skeletons of the little owl (Athene noctua). The dead owls were found in 2001 in the investigated area. More details on the samples are presented in Tables 1 and 2. Two samples of Pygmy shrew were combined into one to increase the amount of investigated material. For the same reason four other samples of Common shrew were combined into one set as well. The skulls were prepared for measurements to determine activity concentrations of gamma-emitters. Dried samples were weighed subsequently to being kept overnight at 105 (C. To obtain a standardized geometrical form of the samples,
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Table 1 Data on samples of skull separated from owl pellets from Eastern Poland Code
Site/village
Skulls of
Pellets attributed to:
Dry mass of skulls [g]
Year
S S S S S S S S S S S S S S S S S S S S S S S S S S S S
Rzeplin Poturzyn Rzeplin Plebanka qabunie Nowosio´1ki Uchanie Tarnawatka Majdan Szczepiatyn Magdalenka Wierzbica Machno´w Nowy Rzeplin Magdalenka Rzeplin Magdalenka Uchanie Tarnawatka qabunie Kornie Kos´ cieszyn Wierzbica Machno´w Nowy Plebanka Kornie Wierzbica qabunie
Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Apodemus agrarius Apodemus agrarius Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex araneus Sorex minutus Sorex minutus Crocidura leucodon
Strix aluco Strix aluco Strix aluco Strix aluco Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Strix aluco Tyto alba Strix aluco Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba Tyto alba
103.2 100.1 40.2 26.4 154.4 43.7 63.5 96.9 50.4 26.0 61.0 17.9 18.1 7.2 7.3 20.6 6.9 27.0 28.9 101.4 24.8 3.1 11.8 10.5 7.2 2.1 1.0 39.8
1995 1996 2001 2001 1995 1995 1996 1996 1999 2000 2000 2000/2001 2001 2001 2000 1995 2000 1996 1996 1995 2000/2001 2000 2000/2001 2001 2000 2000/2001 2000/2001 1995
1 7 10 19 2 3 4 5 6 8 9 11 21 17 27 16 12 14 15 18 20 22a 23a 24a 28a 25b 26b 13 a b
Mixed together for gamma measurements as SS 1. Mixed together for gamma measurements as SS 2.
all were powdered after incineration in the oven at 400 (C. A relatively low temperature was set to prevent evaporation of radiocesium from the samples during their ashing. Gamma activities of the ashes were measured by means of low background gamma-ray spectrometry with a HPGe detector. Then the samples were re-incinerated at 600 (C and reweighed after being cooled down to room Table 2 Data on owl skeletons taken for analyses Code
Species
Dry mass [g]
Ash (600( C) mass [g]
X1 X2 X3
Barn owl (Tyto alba) Little owl (Athene noctua) Little owl (Athene noctua)
18.0 5.4 2.7
11.07 3.51a 1.53a
a
Not complete skeleton.
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temperature. The ash 600 (C to dry mass ratio for all the samples showed a narrow distribution ranging from 0.678 to 0.742, with the mean value of 0.707 and standard deviation equal to 0.016. An identical procedure was applied to skeletons of owls. Once the gamma spectrometric measurements were finished, the skulls were grouped into 13 samples with respect to both raptor and prey species. Grouping was necessary to obtain samples of sufficient mass to allow determination of the activities for such isotopes as Pu and Am, or at least 90Sr, well above their detection limits. Despite this, two samples still did not reach the required mass level. Therefore, a sample containing all the available skulls of Apodemus agrarius and another one of all the available skulls of Sorex minutus were combined into one. Table 3 presents details on the combined sets. For ashed samples from the sets of skulls of insectivores the average weight reached 40.6 g with standard deviation of 26.6 g, whereas for rodents the value was equal to 71.5 g with standard deviation of 28.4 g. The tracers, namely 85Sr, 236Pu or 242Pu, 148Gd, were added to the ashed samples which were subsequently exposed to hot etching with hydrochloric acid. The insoluble residue was first separated by centrifuging and then mineralized by addition of hot HF, HNO3 and HCl with admixture of H3BO3 (LaRosa et al., 1992), to be combined again with samples etched previously. The solutions were diluted with water with some oxalic acid added and their pH was balanced at 3 with the help of ammonia. The oxalates were precipitated (Mietelski et al., 2000) and centrifuged. Coprecipitated Pu, Am and rare earths elements were expected to be found in their sediments. The second precipitation was performed with pH stabilized at 6. This second fraction contained Sr isotopes (Mietelski et al., 2001a). The coprecipitated radionuclides were separated sequentially. From pH ¼ 3 fraction after destroying oxalates in the oven at 600 (C, Pu was separated from 8 M HNO3 on Dowex-1 anion exchange column (LaRosa et al., 1992; Mietelski and Wa˛s, 1995) and Am, together with rare earth elements, using Dowex-1 and methanol-acids solutions (Holm and Table 3 Data on combined samples taken for radiochemical procedures Code
Codes in Table 1
Skulls of:
Ash (600 (C) mass [g]
S1 S2 S 34 S7 S5 S 69 SS 3 SS 6 S 18 SS 4 SS 5 SS 2 S 13
S1 S2 S 3CS 4 S7 S5 S 6CS 9 S 8CS 10CS 21CS 19CS 11 S 27CS 17 S 18 S 16CS 14CS 15 S 12CSS 1CS 20 S 25CS 26 S 13
Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Microtus arvalis Apodemus agrarius Sorex araneus Sorex araneus Sorex araneus Sorex minutus Crocidura leucodon
71.6 110.4 75.2 70.3 66.4 79.0 89.6 10.2 71.8 53.6 57.9 2.4 28.0
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Ballestra, 1989). From pH ¼ 6 fraction Sr was separated from 8 M HNO3 on SrResin. (Mietelski and Gaca, 2002; Vajda et al., 1992). To prepare alpha spectrometric sources (Pu, AmCGd) NdF3 co-precipitation method (Sill, 1987) was applied. A Silena AlphaQuattro spectrometer with Canberra PIPS detectors was used to perform the measurements. The activity of 90Sr was determined with a liquid scintillation spectrometer Wallac 1414-003 Guardian and recovery of 85Sr was determined by means of gamma spectrometry with HPGe detector. Three skeletons of owls underwent the same treatment. The analysis of the samples, was accompanied by an analysis performed on a reference material, namely on soil samples IAEA 375 and IAEA Soil-6, as well as on blank samples spiked with tracers. For alpha-spectrometric measurements it is typical to give the activities of 239Pu and 240Pu as the sum of both isotopes, noted as 239C240Pu. Both radionuclides emit alpha particles of energy of about 5.15 MeV. Resolution of standard alpha spectrometers does not allow alpha particles originating from these decays to be distinguished. Another difficulty, which often occurs in such analyses, is the interference of 228Th with 238Pu or 241Am. Despite the fact that both 238Pu and 241 Am emit alpha particles of 5.50 MeV, it is not their separation that causes chemical problems. The problem lies in 228Th itself and its daughterd 224Ra. 228Th emits 5.45 MeV alpha particles, so it is of great importance to have clear, separated lines in the spectrum. For lines contributing to a spectrum in low count rates, it is hard to judge whether a single count at 5.45 MeV comes from a scattered alpha emitted by 241Am or whether it shall be attributed rather to full energy 228Th alpha. 224 Ra emits alpha particles of 5.69 MeV, and 228Th and 224Ra activities, both granddaughters of 228Ra (a beta emitter), are typical for bone samples and are usually two or three orders of magnitude higher than for Pu or Am isotopes. Therefore, even relatively tiny traces of 224Ra contribute to counts in 5.5 MeV 241Am (or 238Pu) peak region due to alpha particles losing their energy. The described problems affect 238Pu and 241Am measurements, increasing the detection limits above 1 mBq/kg, a standard for 239C240Pu in samples of 100 g recorded with a spectrum acquisition time of a week.
3. Results and discussion The statistical parameters of results are presented in Table 4. Distributions of activity for main radionuclides are presented in Fig. 2a–d. The majority of the results for 40K range between 20 and 35 Bq/kg. The average (G standard deviation) activity was equal to 26:3 G 18:0 Bq=kg and 28:4 G 19:5 Bq=kg for rodents and insectivores, respectively. For 137Cs almost all the results were below 5 Bq/kg, and the respective parameters reached 2:1 G 2:7 Bq=kg and 2:6 G 1:9 Bq=kg. Such results are consistent with our previous measurements for wild herbivorous animals (deer, roe-deer, elk, boar) from Poland (Mietelski et al., 2001b), for which the average activity (G standard deviation) of 40K in ashed bones
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Table 4 Chosen statistical parameters obtained for activity of analyzed radionuclides in ashed skulls of small mammals and on skeletons of owls. Data for potassium and cesium isotopes from all initial samples analyzed by gamma spectrometry, for remaining nuclide from combined sets of samples (see Materials and methods for details) Mammals Rodents
Parameter
40
137 K Cs [Bq/kgash] [Bq/kgash]
Mean 26.3 SD 18.0 Min !10 Max 75 G 10 Mean uncert 9.4 Insectivores Mean 28.4 SD 19.5 Min !14 Max 50 G 35 Mean uncert 15.5 Owls Min 39 G 21 Max 93 G 76 Mean uncert 56
2.1 2.7 !1.2 10:4 G 0:6 0.9 2.6 1.9 !0.9 5:1 G 1:3 1.8 !1.3 !7 3
90
Sr [Bq/kgash]
239C240
238 241 Pu Pu Am [mBq/kgash] [mBq/kgash] [mBq/kgash]
17.5 14.5 2:3 G 0:4 42:4 G 2:8 1.3 27.2 8.9 17:6 G 1:1 49:1 G 3:0 5.7 !5 19:6 G 1:6 2.7
17.7 35.4 0:5 G 0:2 97:5 G 7:7 2.0 9.6 7.5 !2.4 16:7 G 2:0 1.3 0:7 G 0:3 3:2 G 1:1 3
2.9 7.4 !0.4 19:6 G 3:2 2.1 1.3 2.1 !0.8 4:9 G 1:0 2.8 !1.3 !24 12
8.0 9.2 !1.2 22 G 4 4.1 9.7 7.5 !2.5 16 G 4 3.2 !8 !196 60
varied for different species from 17:6 G 26:2 (elk) to 29:7 G 25:2 (boar) Bq/kg; for 137 Cs activities ranged from 1:9 G 1:8 (deer) to 5:7 G 7:1 (boar). This similarity suggests that observed levels of activities for 40K are perhaps typical for mammals in general, and those for 137Cs are typical for wild mammals, which live in Eastern Poland. This activity of 40K corresponds to about 0.4%0 of stable K content in fresh bones, which is about three times less than the typical value for adult humans
Fig. 2. Activity distribution for 137Cs (a), 40K (b), 90Sr (c) and 239C240Pu (d) activity concentration in ashen bones of small mammals and owls.
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(Iyenger et al., 1978). This discrepancy might appear due to the high solubility of potassium, which could also be the reason for possible losses of K during sample pretreatment. The radiochemical procedure yielded, on average, recovery of tracers equal to (80:0 G 20:3)%, (16:8 G 6:3)%, and (28:3 G 18:2) for 242Pu, 148Gd and 85Sr, respectively. In three samples 90Sr activity dropped below the detection limit, most likely due to poor recovery of the isotope. A few samples activities for 241Am and 238 Pu, owing to interference of 228Th and 224Ra traces in the spectrum, did not exceed the detection limit. The maximum activity of plutonium isotopes (Table 4) was an order of magnitude higher than found previously for bigger animals (Mietelski et al., 2000). The maximum was found for the sample of Common vole skulls separated from Barn owl pellets coded as S5 . The maximum for 239C240Pu was equal to (97:5 G 7:7) mBq/ kg for ash weight, which corresponds to (66 G 5) mBq/kg of dry weight. The sample showed also the highest 238Pu and 241Am activities of 19:6 G 3:2 mBq/kg and 22 G 4 mBq/kg (ash), respectively. Unfortunately, the 90Sr fraction of this particular sample was accidentally lost in preparation. The sample originated from Tarnawatka village. A sample of insectivores skulls, found at the same location, was combined together with samples from Rzeplin and Uchanie into a set coded as SS 4. In sample SS 4, despite the fact that it may be diluted by relatively low concentration of the nuclides in the samples from other locations – for skulls of rodents from Rzeplin and Uchanie activities were lowdstill relatively high 239C240Pu, 241Am and 90Sr activities were detected (Table 4). The reasons for such a high transfer factor of radionuclides in the surroundings of Tarnawatka village have not been discovered yet. The terrain consists of peat and wet grassy meadows. For S 5 sample, the Chernobyl fraction of Pu activity, determined on the basis of the isotopic ratio between 238Pu and 239C240 Pu (Mietelski and Wa˛s, 1995), can be estimated to be 36 G 12%, which roughly corresponds to the maximum percentage of Chernobyl fraction of Pu in the area (Komosa, 1999a,b). Generally, the 238Pu to 239C240Pu activity ratios indicate that the global fallout is the main source of Pu contamination. The ratio between 239C240 Pu and 241Am activities for S 5 sample of 0:224 G 0:044 is somewhat lower than the global fallout ratio of about 0.3 (UNSCEAR, 1993) and significantly lower than the present Chernobyl ratio of about 1.5. Such ratio for Chernobyl fallout can be calculated including americium ingrown from 241Pu decay (Kudryashov et al., 2001). Our result suggests that americium is transferred or accumulated in bones perhaps less effectively than plutonium, possibly due to a shorter biological half-life time of Am. The average (arithmetic mean) values for Pu and Am activities (Table 4) were also far higher that found for bigger animals. Taking into consideration that no difference has been observed for small mammals of different feeding habits, the obtained result may suggest that transuranic elements could be not ingested but inhaled (Mietelski et al., 2003). The level of 90Sr in all kinds of bone ashes covered by the presented study (Table 4) was lower than the values found previously for large wild herbivorous mammals (Mietelski et al., 2001a), especially when compared with ones living in the areas of
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Table 5 Squared Pearson’s correlation factor values for activity of various radionuclides found in the small mammals skulls separated from owl’s pellets 40 40
K Cs 90 Sr
K
137
90
239C240
241
0.582 1
0.281 0.364 1
0.041 0.048 0.238 1
0.002 0.057 0.431 0.641 1
Cs
1
137
Sr
Pu
239C240
Pu
241
Am
Am
North-Eastern Poland where 90Sr is known to have been deposited in a form of hot particles from Chernobyl. Present results compared to the ones obtained for large mammals from the areas practically unaffected by Chernobyl-originated 90Sr, such as central Poland or Denmark (Strandberg and Strandgaard, 1995), lead to the same conclusion of the lower level of observed activities. Respective results from our previous study varied from 59 G 10 Bq/kg for deer, to 127 G 13 Bq/kg for roe-deer, while Danish results for roe-deer lay between 60 Bq/kg, and 140 Bq/kg, the present results range from 2:3 G 0:4 Bq/kg to 49:1 G 3:0 Bq/kg. The values for squared Pearson’s correlation factors between determined activities are presented in Table 5. Here, for the samples combined into larger sets to enable radiochemical analysis, radiocesium and potassium activities were calculated from averaged for given set values. Correlation was calculated only for non-zero values. A considerable correlation was found between activities of 241Am and 239C240Pu (R2 ¼ 0:641) and between 40K and 137Cs (R2 ¼ 0:582) for all skulls of owls’ pellet samples taken together, i.e. not separated into rodents and insectivores. For all investigated isotopes any noticeable difference between the skulls of rodents and insectivorous animals was found in terms of Mann–Whitney nonparametric test and t-test for mean values.
Table 6 Results (in Bq/kg) for analyzed reference materials (IAEA, 2000) Name of reference material IAEA IAEA IAEA IAEA IAEA IAEA IAEA IAEA IAEA
Soil Soil Soil Soil Soil Soil Soil Soil Soil
375 375 375 6 375 375 375 375 375
Nuclide
Mass [g]
Determined activity (corrected for reference date), D
Certified value, C
95% Confidence interval
Difference ðD CÞ=C [%]
137
75.4 75.4 5.2 10.0 5.2 5.2 12.8 12.8 12.8
5559 G 66 423 G 28 104 G 10 1:06 G 0:01 0:267 G 0:025 0:076 G 0:010 0:259 G 0:026 0:052 G 0:009 0:126 G 0:033
5280 424 108 1.04 0.30 0.071 0.30 0.071 0.13
5200 5360 417 432 101 114 0:96 1:11 0:26 0:34 0:056 0:085 0:26 0:34 0:056 0:085 0:11 0:15
C5.3 0.2 0.4 C2 11 C7 13.7 27 3.1
Cs K 90 Sr 40
239C240
Pu Pu
239C240 238
Pu
239C240
Pu
238
Pu 241 Am
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3.1. Quality assurance The results for quality assurance measurements of reference materials are presented in Table 6. Since the presented uncertainties are just the counting statistics, each at one sigma level, they must be underestimated. The last column contains the relative discrepancy between determined and certified values. The results suggest the occurrence of small systematic errors, which might have hindered accurate determination of activities. In the case of gamma emitters, the activity of 40K seems to be determined accurately, though systematic error of about 5% overestimation, might occur for 137Cs. In case of 90Sr and alpha emitters the values are more precise. Almost all results lie within a reliable 95% confidence intervals.
4. Conclusions No measurable difference in the activities of any of the examined radionuclides in skulls of rodents and insectivorous animals has been found. Skeletons of owls did not reveal an accumulation effect. Levels of 137Cs and 40K retained in the bones are very much alike for small mammals and large wild herbivorous animals from typical Polish locations, and for 90Sr is even lower. On the contrary plutonium and americium activities found for small animals are, on average, significantly higher than for large animals. As was discussed elsewhere those transuranic elements can be introduced into small mammals via inhalation.
Acknowledgements The authors are grateful to the Polish State Committee for Scientific Research for partially supporting this investigation with a grant No PG04 07520.
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