Activity concentration measurements of selected radionuclides in seals from Canadian Arctic

Journal of Environmental Radioactivity 169-170 (2017) 48e55

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Activity concentration measurements of selected radionuclides in seals from Canadian Arctic Jing Chen a, *, Weihua Zhang a, Baki Sadi a, Xiaowa Wang b, Derek C.G. Muir b a b

Radiation Protection Bureau, Health Canada, 775 Brookfield Road, Ottawa, Canada Aquatic Contaminants Research Division, Environmental Canada, Burlington, Ontario, Canada

a r t i c l e i n f o

a b s t r a c t

Article history: Received 12 July 2016 Received in revised form 19 December 2016 Accepted 28 December 2016

The activity concentrations of naturally occurring radionuclides (such as 226Ra, 210Pb and 210Po) and long lived 137Cs were measured in a total of 119 tissue samples (43 blubber, 43 liver, and 33 muscle samples) from 40 ringed seals and 4 bearded seals collected in the Arviat area of Canada during the fall of 2014. Activity concentration of 210Po was measured in all seal liver and muscle samples individually. The average 210Po activity concentrations were 25 ± 7.6 Bq/kg fresh weight (fw) in muscle and 211 ± 58 Bq/kg fw in liver for ringed seals, and 20 ± 6.1 Bq/kg fw in muscle and 231 ± 150 Bq/kg fw in liver for bearded seals. Due to insufficient sample material for most samples collected, gamma counting for radioactive caesium and radiochemical analysis for 226Ra and 210Pb were performed for pooled samples. Activity concentrations of 210Pb and 226Ra were generally below detection limits. While 134Cs activity concentration was not detectable, 137Cs activity concentration was detected in muscle and liver samples. On average, the 137Cs activity concentrations were 0.25 ± 0.05 and 0.12 ± 0.04 Bq/kg fw in muscle and liver samples of ringed seals, and 0.11 ± 0.02 and 0.10 ± 0.03 Bq/kg fw in muscle and liver samples of bearded seals, respectively. Neither 210Po nor 137Cs were detected in the blubber samples. This study confirmed that 210Po is the dominant contributor to radiation doses resulting from seal consumption. Man-made contaminant 137Cs only contributes less than 0.01% of the total ingestion dose obtained from Arviat seals. Crown Copyright © 2016 Published by Elsevier Ltd. All rights reserved.

Keywords: Natural radionuclides Radioactive caesium Marine fish

1. Introduction The ringed seal (Pusa hispida) is a relatively small seal (normally less than 1.5 m in length and with an average weight of about 50e70 kg), that has an affinity for ice-covered waters, and inhabits the circumpolar Arctic and sub-Arctic regions. Ringed seals eat a wide variety of small prey such as mysids, shrimp, arctic cod and herring (Yurkowski et al., 2015; Young et al., 2010). The bearded seal (Erignathus barbatus) is a medium-sized seal. The average length of an adult bearded seal is 2.1 m. They can weigh more than 300 kg. Bearded seals are predominantly benthic feeders that eat shrimps, crabs, clams and welks, but will opportunistically prey on fish such as cod and sculpin (NOAA, 2016). Ringed seals, along with bearded seals, have long been a popular component of the “traditional food” diet of indigenous people of the Arctic (AMAP, 2002; 2010; Donaldson et al., 2010). Contaminants in Canadian arctic seals are routinely monitored as part of the Northern Contaminants

* Corresponding author. E-mail address: [email protected] (J. Chen). http://dx.doi.org/10.1016/j.jenvrad.2016.12.015 0265-931X/Crown Copyright © 2016 Published by Elsevier Ltd. All rights reserved.

Program (Braune et al., 2015; Cooper et al., 2000; Donaldson et al., 2010). Cooper et al. (2000) determined the activity concentrations of the long-lived radioactive contaminant 137Cs (physical half-life 30 years) in tissues (blubber, muscle, liver, and kidney) of ringed seals primarily from the Northern Alaska and concluded that activities were well below activity concentrations that would normally merit public health concern. In the environment, most naturally occurring radionuclides come from the uranium decay series. Among various radionuclides in the uranium decay series, 210Po, 210Pb and 226Ra are commonly found in various traditional foods in varying activity concentrations. Previous work has shown that caribou in the Canadian arctic have relatively high activity concentrations of naturally occurring 210 Pb and 210Po (Macdonald et al., 1996) and are the main contributors in traditional foods to human dietary exposure to radionuclides (Berti et al., 1998; AMAP, 2010). Several other studies have reported on radionuclide activity concentrations, including those of naturally occurring radionuclides, in arctic seals although not in the Canadian arctic (Dahlgarrd et al., 2004; Gwynn et al., 2005, 2006; Hamilton et al., 2008; Nielsen and Joensen, 2009; Solatie et al.,

J. Chen et al. / Journal of Environmental Radioactivity 169-170 (2017) 48e55

2005). The release of radioactivity from the Fukushima accident, including radiocaesium, has been of public concern in recent years (WHO, 2013; UNSCEAR, 2014). Increased exploitation of resources in the arctic, especially regarding the oil and gas industries and their development, is expected to enhance the risk of releasing naturally occurring radioactive material to the environment (AMAP, 2016). As part of Health Canada's study on background radiation activity concentrations in traditional foods in the Arctic, a total of 119 tissue samples (43 blubber, 43 liver, and 33 muscle samples) from 40 ringed seals and 4 bearded seals were collected in the Arviat area of Canada during the fall of 2014. In this study, activity concentrations of the naturally occurring radionuclides 226Ra, 210Pb and 210Po as well as radiocaesium were measured in the samples collected. To address public concerns for the safety of seal consumption, ingestion doses resulting from the measured activity concentrations in the different seal tissues were derived and the associated health risk was assessed. 2. Methods 2.1. Seal samples Seals were collected in 2014 in coastal western Hudson Bay near the community of Arviat as part of the aboriginal hunt and in collaboration with studies by scientists from the Department of Fisheries and Oceans Canada (DFO) on the habitat and diets of seals in the region (Chambellant et al., 2013; Young et al., 2015). Hunters were supplied with sampling kits and instructions in both English and Inuktitut. They recorded length, girth and weight of each animal and placed samples of liver, blubber and muscle, as well as the lower jaw for age determination, into small plastic bags. Sampling was done outdoors as part of the traditional processing of the animal for food. Samples were frozen within 1e2 h of collection and shipped to DFO laboratories in Winnipeg where they were stored at
35  C. Subsequently they were transferred to the Canada Centre for Inland Waters (Burlington, Ontario) for processing for contaminants. Seal aging using a lower canine tooth was conducted by Matson's Laboratory (Milltown, Montana). Muscle samples were sent to Wildlife Genetics International (Nelson, British Columbia) for gender confirmation using a DNA marker and to the University of Waterloo (Environmental Isotope Laboratory) for C and N stable isotope analysis. For the purpose of addressing radiological concerns about seal consumption, only the edible portion of a seal is of interest. Therefore, blubber, liver and muscle samples were prepared for radioactivity measurement at the Radiation Protection Bureau, Health Canada (Ottawa, Ontario). 2.2. Gamma counting To determine activity concentrations of radioactive caesium in seal samples, gamma counting was used. Homogenised samples of about 170 g were packed in PVC vials (60 mm in diameter and 55 mm in height), and then scanned for gamma emitting radionuclides by counting on a Compton suppressed gamma spectrometer (ORTEC) (Zhang et al., 2013). Briefly, the spectrometer consists of an n-type GMX high purity germanium (HPGe) coaxial primary detector, crystal diameter of 66.2 mm and length 69.0 mm, with a carbon fibre end cap and a guard detector consisting of a 900 x900 NaI(Tl) annulus with four photomultiplier tubes (PMT) and a 300 x300 NaI(Tl) plug with one PMT. The list-mode data-acquisition system for the spectrometer utilizes all-digital electronics, based on the X-Ray Instrumentation Associates (XIA LLC) Digital Gamma Finder (DGF)/Pixie-4 software and card package. The use of a list-mode data-acquisition technique

49

enabled simultaneous determination of 134Cs and 137Cs activity concentrations using a single measurement by coincidence and anticoincidence mode respectively. Certified mixed radionuclide standards were used to determine the respective counting efficiencies on the Compton spectrometer. A standard consisting of a Parkway jar containing a solid with a density of 1.15 g/cm3 simulating water (Eckert and Ziegler Analytics, SRS: 79535-411) was used for the calibrations. The detection limits for radioactive caesium (134Cs and 137Cs) depend on each individual sample, and are lower than a normal non-Compton suppressed gamma spectrometer approximately by a factor of 5. During gamma counting, naturally occurring 40K was also measured in addition to radioactive caesium and other gamma emitters in the samples. Due to insufficient sample material for most samples collected and time available for gamma counting, samples were pooled, although a few large samples were counted individually. A pooled sample is a mixture of several seal samples of the same tissue (blubber, liver or muscle) and the same sex (female, male or unknown) with approximate equal weight contribution from individual samples. For the 4 bearded seals, information on sex and total body weight were only partially available when received for radiological analysis. Therefore, tissue samples from bearded seals were pooled together for gamma counting. For ringed seals, at the time when samples were received for radiological analysis, there were 8 seal samples without sex information. They are AV2014-01, 03, 13, 16, 17, 22, 23 and 35. Liver and muscle samples from those 8 seals were then pooled together whenever not enough tissues available for gamma counting and they were marked as sexunknown. Other 32 ringed seal samples were sorted by total body weight for males and females, respectively. Liver and muscle samples for a given sex were then pooled together according to the order of total body weight, i.e. samples of heavier seals were pooled together. Table A in the appendix provides information and pooled sample IDs on which individual samples were pooled together. However, the sex information of the 8 ringed seals and one of the 4 bearded seals originally marked as sex-unknown became available after the radiological analysis being completed. 2.3. Radiochemical analysis Radiochemical analyses for 210Po, 210Pb and 226Ra were conducted by the radiochemical laboratory of the Saskatchewan Research Council (422 Downey Road, Saskatoon, Canada). The radioactivity concentration of 210Po was determined for seal samples individually. Briefly, 20 g of wet sample was acid digested in a microwave digestion system prior to counting by alpha spectrometry for 210Po, with 209Po added as a tracer to determine the chemical recovery for the method. Due to the short half-life of 138 days, measured 210Po activity concentrations were reported after decay correction, i.e. the activity concentration at the harvest date was reported by back calculation from the measured activity concentration for each sample analysed. Decay corrections were carried out assuming no contributions from supported 210Po. To determine 210Pb and 226Ra activity concentrations in fresh samples, a minimum of 200 g of wet sample was needed in order to maintain a similar detection limits for 210Pb as was the case for 210 Po. The samples were thermally dried. For 210Pb, ashed samples were digested with nitric and perchloric acids and held for 30 days to guarantee equilibrium between 210Pb and 210Bi. Lead-210 was determined indirectly by the precipitation and counting of its high energy beta emitting progeny, 210Bi. Bismuth was isolated by solvent extraction and subsequently precipitated as bismuth oxychloride. The precipitate was collected on a filter paper/disk

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assembly and beta counted in a low background counting system. Radium isotopes in the sample solution were separated by coprecipitation with lead sulfate. The precipitate was re-dissolved and the radium isotopes were separated from the other elements by co-precipitation with barium sulfate. The precipitate was filtered and then mounted on a plastic disk. It was then counted on an alpha spectrometer. The 226Ra alpha energy is distinct and the peak can be clearly identified. Because a minimum of 200 g of material was required, only pooled samples were sent to the SRC for the analyses of 210Pb and 226Ra, due primarily to insufficient sample material for most individual samples. Table B in the appendix provides information on which individual samples were pooled together for the analyses of 210Pb and 226Ra. Pooled samples in Table A were counted for gamma radiation first before being further pooled into even larger samples and sent to the radiochemical laboratory for 210Pb and 226Ra analysis. 3. Results and discussion Activity concentrations of measured radionuclides are given in Tables 1 and 2 for muscle and liver samples, respectively. Summary results for blubber samples are given in Table 3. Results for 210Po are the activity concentrations measured in individual samples. Majority of results for 226Ra, 210Pb, 137Cs and 40K are the activity concentrations measured in pooled samples. A result of a pooled sample represents the average activity concentration of those individual samples pooled together. For the

calculation of overall average from different pooled samples, the average value of a pooled sample is assigned to individual samples in the pool. 3.1. Results for naturally occurring radionuclides Polonium-210 was detected in all muscle and liver samples in varying activity concentrations. The average 210Po activity concentrations were 25 ± 7.6 Bq/kg fw (ranged from 13 to 45 Bq/kg fw) and 211 ± 58 Bq/kg fw (ranged from 112 to 297 Bq/kg fw) in the muscle and liver of ringed seals, respectively. No 210Po was detected in blubber samples of ringed seals. For bearded seals, the average 210 Po activity concentrations were 20 ± 6.1 Bq/kg fw (ranged from 12 to 26 Bq/kg fw) and 231 ± 150 Bq/kg fw (ranged from 102 to 396 Bq/kg fw) in muscle and liver, respectively. These results are comparable to previous reported data for seal species in the Arctic (Nielsen and Joensen, 2009; Solatie et al., 2005; Dahlgarrd et al., 2004; Hamilton et al., 2008). Generally, 210Pb and 226Ra were not detectable in seal muscle and liver samples with detection limits of approximately 0.09 and 0.04 Bq/kg for 210Pb and 226Ra, respectively. While 210Po was clearly detectable in all muscle and liver samples, its parent, 210Pb, was below the detection limit for almost all samples as given in Tables 1 and 2. Only a few muscle samples showed a210Pb activity concentration around the detection limit of 0.09 Bq/kg. This indicates that the 210Pb activity concentration in seal muscle and liver is significantly lower than 210Po. This provided supporting evidence that

Table 1 Measured activity concentrations of selected radionuclides in muscle samples of 40 ringed seals and 4 bearded seals. Sample ID Ringed seal AV2014-01 AV2014-02 AV2014-03 AV2014-04 AV2014-05 AV2014-06 AV2014-07 AV2014-09 AV2014-10 AV2014-11 AV2014-12 AV2014-13 AV2014-14 AV2014-15 AV2014-17 AV2014-18 AV2014-19 AV2014-20 AV2014-21 AV2014-22 AV2014-23 AV2014-24 AV2014-25 AV2014-30 AV2014-32 AV2014-36 AV2014-38 AV2014-39 AV2014-40 Bearded seal AV2014-43 AV2014-47 AV2014-49 AV2014-50

Sex

Total body weight (kg)

Po-210 Bq/kg fw

Pb-210 Bq/kg fw

Ra-226 Bq/kg fw

Cs-137 Bq/kg fw

F M F F F F M M M M M M F M M M M M F M M M M M M F F M F

27 45 44 32 60 36 33 70 69 54 66 51 44 68 69 70 46 44 24 36 44 26 78 63 55 21.5 23 66 63

24 22 17 33 27 22 25 19 22 13 15 19 32 27 13 29 23 25 19 30 39 d 22 26 18 27 34 d 45

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

2 2 2 2 2 2 2 2 2 1 1 2 2 2 1 3 2 2 2 3 2

<0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04

0.22 0.19 0.39 0.33 0.26 0.26 0.19 0.25 0.25 0.26 0.25 0.22 0.26 0.25 0.22 0.25 0.19 0.19 0.33 0.22 0.22 d 0.25 0.26 0.26 0.33 0.33 0.26 0.23

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.05 0.05 0.07 0.04 0.06 0.06 0.05 0.03 0.03 0.05 0.04 0.05 0.06 0.04 0.05 0.03 0.05 0.05 0.04 0.05 0.05

±3

<0.09 0.09 ± <0.09 <0.08 <0.08 <0.08 0.09 ± <0.09 <0.09 0.09 ± <0.09 <0.09 <0.08 <0.09 <0.09 <0.09 0.09 ± 0.09 ± <0.08 <0.09 <0.09 0.09 ± <0.09 0.09 ± 0.09 ± <0.08 <0.08 0.09 ± <0.08

± ± ± ± ±

2 2 2 3 2

± ± ± ± ± ± ±

F F F M

>100 >100 >100 >100

12 23 18 26

± ± ± ±

<0.1 <0.1 <0.1 <0.1

0.08 0.12 0.12 0.12

± ± ± ±

1 2 2 2

Note: “d” means that samples were not enough for certain analysis. No muscle samples from AV2014-08, -16, -26, -27, -28, -29, -31, -33, -34, -35, and -37. The uncertainties represent 1 sigma for 137Cs and 40K, and 2 sigma for 210Po, 210Pb and

226

Ra.

0.1

0.1

0.1

0.1 0.1

0.1 0.1 0.1

0.1

0.07 0.07 0.07 0.07

± ± ± ±

0.06 0.06 0.06 0.06

K-40 Bq/kg fw ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

3.8 3.9 3.8 4.1 4.6 4.6 3.9 3.7 3.7 3.6 3.9 3.8 4.6 3.9 3.8 3.7 3.9 3.9 4.1 3.8 3.8

0.03 0.05 0.05 0.04 0.04 0.05 0.04

64 65 58 71 74 74 65 68 68 60 64 64 74 64 64 68 65 65 71 64 64 d 68 60 60 71 71 60 63

± ± ± ± ± ± ±

3.7 3.6 3.6 4.1 4.1 3.6 3.7

0.02 0.02 0.02 0.02

76 78 78 78

± ± ± ±

4.0 4.2 4.2 4.2

J. Chen et al. / Journal of Environmental Radioactivity 169-170 (2017) 48e55

51

Table 2 Measured activity concentrations of selected radionuclides in liver samples of 40 ringed seals and 4 bearded seals. Sample ID Ringed seal AV2014-01 AV2014-02 AV2014-03 AV2014-04 AV2014-05 AV2014-06 AV2014-07 AV2014-08 AV2014-09 AV2014-10 AV2014-11 AV2014-12 AV2014-13 AV2014-14 AV2014-15 AV2014-16 AV2014-17 AV2014-18 AV2014-19 AV2014-20 AV2014-21 AV2014-22 AV2014-23 AV2014-24 AV2014-25 AV2014-26 AV2014-27 AV2014-28 AV2014-29 AV2014-30 AV2014-31 AV2014-32 AV2014-33 AV2014-34 AV2014-35 AV2014-36 AV2014-37 AV2014-38 AV2014-40 Bearded seal AV2014-47 AV2014-49 AV2014-50

Sex

Total body weight (kg)

Po-210 Bq/kg fw

F M F F F F M F M M M M M F M M M M M M F M M M M F F M M M M M F F F F F F F

27 45 44 32 60 36 33 31 70 69 54 66 51 44 68 66 69 70 46 44 24 36 44 26 78 22 26 71 81 63 23 55 28 22 22 21.5 26 23 63

246 199 132 281 196 215 264 198 264 264 155 147 163 155 294 d 297 294 165 202 137 275 277 d 196 d d d d 154 d 159 d 112 d 208 148 254 271

F F M

>100 >100 >100

Note: “d” means that samples were not enough for certain analysis. No liver samples from Av2014-39, -43. The uncertainties represent 1 sigma for 137Cs and 40K, and 2 sigma for

210

Pb-210 Bq/kg fw

Ra-226 Bq/kg fw

Cs-137 Bq/kg fw

10 9 20 20

<0.2 <0.1 <0.2 <0.2 <0.2 <0.2 <0.1 <0.2 <0.1 <0.1 <0.1 <0.1 <0.2 <0.2 <0.1 <0.2 <0.2 <0.1 <0.1 <0.1 <0.2 <0.2 <0.2 <0.1 <0.1 <0.2 <0.2 <0.1 <0.1 <0.1 <0.1 <0.1 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

<0.07 <0.06 <0.07 <0.1 <0.1 <0.1 <0.06 <0.1 <0.07 <0.07 <0.06 <0.07 <0.07 <0.1 <0.07 <0.07 <0.07 <0.07 <0.06 <0.06 <0.1 <0.07 <0.07 <0.06 <0.07 <0.1 <0.1 <0.07 <0.07 <0.06 <0.06 <0.06 <0.1 <0.1 <0.07 <0.1 <0.1 <0.1 <0.1

0.19 0.12 0.19 0.10 0.10 0.10 0.12 0.10 0.09 0.09 0.12 0.09 0.19 0.10 0.09 0.19 0.19 0.09 0.12 0.12 0.10 0.19 0.19 0.12 0.09 0.10 0.10 0.09 0.09 0.12 0.12 0.12 0.10 0.10 0.19 0.10 0.10 0.10 0.10

196 ± 10 102 ± 6 396 ± 20

<0.3 <0.3 <0.3

<0.2 <0.2 <0.2

0.10 ± 0.03 0.10 ± 0.03 0.10 ± 0.03

Po,

± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

20 10 8 20 10 10 20 10 20 20 10 9 10 9 20

± ± ± ± ± ± ±

20 20 10 9 8 20 10

± 10

± 10 ± 10 ±7 ± ± ± ±

210

Pb and

Table 3 Measured activity concentrations of selected radionuclides in blubber samples of ringed seals. Samples

Sex

Po-210 Bq/kg fw

Pb-210 Bq/kg fw

Ra-226 Bq/kg fw

Cs-137 Bq/kg fw

K-40 Bq/kg fw

Blubber Blubber

M F

d <0.9

d <0.2

d <0.05

<0.01 <0.01

10.4 ± 1.6 8.7 ± 1.5

Note: “d” means that the analysis was not performed. The uncertainties represent 1 sigma for 40K.

there is no or negligible contribution from supported 210Po as assumed for decay correction made to measured 210Po activity concentrations. These results are consistent with and comparable to findings in the literature as well (Nielsen and Joensen, 2009; Gwynn et al., 2006). Pooled blubber samples from ringed seals were analysed for naturally occurring radionuclides 210Po, 210Pb and 226Ra. As expected, their activity concentrations were not detectable in the blubber samples.

226

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.05 0.04 0.05 0.02 0.02 0.02 0.04 0.02 0.03 0.03 0.04 0.03 0.05 0.02 0.03 0.05 0.05 0.03 0.04 0.04 0.02 0.05 0.05 0.04 0.03 0.02 0.02 0.03 0.03 0.04 0.04 0.04 0.02 0.02 0.05 0.02 0.02 0.02 0.02

K-40 Bq/kg fw 65 60 65 64 64 64 60 64 53 53 60 53 65 64 53 65 65 53 60 60 64 65 65 60 53 64 64 53 53 60 60 60 64 64 65 64 64 64 64

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

4.0 3.7 4.0 4.0 4.0 4.0 3.7 4.0 3.4 3.4 3.7 3.4 4.0 4.0 3.4 4.0 4.0 3.4 3.7 3.7 4.0 4.0 4.0 3.7 3.4 4.0 4.0 3.4 3.4 3.7 3.7 3.7 4.0 4.0 4.0 4.0 4.0 4.0 4.0

55 ± 3.4 55 ± 3.4 55 ± 3.4

Ra.

The previous studies of freshwater fish in southern Canada (Chen et al., 2015, 2016) not only confirmed that 210Po is the main contributor to radiation dose resulting from fish consumption but also showed that small fish may be more capable of incorporating 210 Po into muscle. In the current study, the size dependency of 210Po was further evaluated with seal samples, i.e. relationships between body size (total body weight) and activity concentration of 210Po in muscle and liver samples were evaluated by linear regression. Whereas for bass and pike the 210Po activity concentrations decrease clearly with increasing body size (Chen et al., 2015, 2016), the 210Po activity concentration in the muscle samples seems to be independent of the total body weight (linear regression was not significant, F1,25 ¼ 1.11, p ¼ 0.3, R2 ¼ 0.0427). As well, 210Po activity concentration in the liver samples seems to be independent of the total body weight (linear regression was not significant, F1,28 ¼ 1.67, p ¼ 0.2, R2 ¼ 0.0564). With gamma counting, naturally occurring 40K was detected in all samples. The average activity concentrations of 40K were 66 ± 5, 61 ± 5 and 10 ± 2 Bq/kg fw for muscle, liver and blubber samples from ringed seals, respectively. For bearded seals, gamma counting

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was not performed with blubber samples. The 40K activity concentrations were 78 ± 1 Bq/kg fw in muscle and 55 ± 3 Bq/kg fw in liver of bearded seals. Activity concentrations of 40K in muscle were in the range of 33e127 Bq/kg fw reported in the literature (AMAP, 2010). 3.2. Results of radioactive caesium The gamma counting results of long-lived contaminant 137Cs are given in Tables 1e3 for muscle, liver and blubber samples, respectively. The average activity concentrations were 0.25 ± 0.05 Bq/kg fw for muscle, and 0.12 ± 0.04 Bq/kg fw for liver samples from ringed seals. While 137Cs activity concentrations in muscle were higher than measured in the liver of ringed seals, similar 137Cs activity concentrations were observed in muscle and liver samples from bearded seals; 0.11 ± 0.02 Bq/kg fw in muscle and 0.10 ± 0.03 Bq/kg fw in liver. Pooled blubber samples from ringed seals were gamma counted for 7 days. The 137Cs was not detectable in blubber samples at a detection limit of 0.01 Bq/kg. In all samples, 134Cs was below the detection limit (~0.01 Bq/kg). While 134Cs (an indicator of recent releases from the Fukushima accident of 2011) was not detectable, 137Cs was detected in muscle and liver samples of seals harvested in the Arviat area during the fall of 2014. This indicates that environmental 137Cs in this region results mainly from the fallout of atmospheric nuclear weapons tests in the 1950s and 1960s and major accidental releases such as from the Chernobyl accident in 1986 (AMAP, 2002; 2010; 2016). Due to its 30 year half-life, 137Cs has been intensively monitored globally, especially after atmospheric nuclear weapons tests and the Chernobyl accident (Cooper et al., 2000; Hamilton et al., 2008; AMAP, 2010; 2016). The highest concentration values of 137Cs (about 10 Bq/kg fw) were reported in the 1960s. There was a decreasing trend at the start of the monitoring period, but activity concentrations have since stabilized at around 0.1e1 Bq/kg fw. The activity concentrations of 137Cs in marine mammals are principally dependent on the activity concentrations within prey species and, therefore, differences in diet may account for some of the observed variation between species. Estimations of dietary composition of the different seal species suggests that ringed seals tend to consume a greater percentage of fish in their diet, whereas bearded seals consume mainly benthic invertebrates (Pauly et al., 1998). 3.3. Estimated radiation dose from seal consumption Ingestion doses were estimated for intakes of seal flesh and liver products where contaminant 137Cs and naturally occurring 210Po were present. An activity concentration of naturally occurring 40K is present in all samples analysed, as shown in Tables 1e3. Potassium is ingested with foods, including seal products, and is a critically important element for proper functioning of the human body. Because the potassium content of the body is under strict homeostatic control, the 40K content is constant and not influenced by variations in environmental activity concentrations. Therefore, the effect of 40K intake from seal consumption will not be considered in the following discussion on ingestion doses due to radioactivity in seal products. Since only 40K was detected in blubber samples, there is no need to assess radiation dose resulting from ingestion of blubber. In the calculation, average activity concentrations of 137Cs and 210 Po in the muscle and liver of ringed seals were used. With dose conversion coefficients for adults given in the ICRP Publication 119 (ICRP, 2013), the annual effective doses were derived for 137Cs and 210 Po from ingestion of seal flesh at various consumption rates up to 100 kg per year, as shown in Fig. 1. The annual effective doses were

calculated for ingestion of seal liver at various consumption rates up to 12 kg per year, as shown in Fig. 2. As shown in the Figures, ingestion doses from 137Cs in seal flesh and liver are several orders of magnitude lower than the doses from 210Po in the same product. The Canadian Department of Fisheries and Oceans (DFO) encourages the fullest possible commercial use of seals, including seal meat for human and animal consumption as well as seal oil (blubber), which is rich in Omega-3 fatty acid, widely believed to have numerous health benefits (DFO, 2013). A survey conducted by Statistics Canada (2007) showed that traditional food made up about half of the meat eaten in the northern communities. Based on food statistics given by Statistics Canada (2010), averaged from year 2000e2009, the Canadian consumption rate for red meat is 23 kg per year. Assuming half of the 23 kg of meat products (i.e. 11.5 kg) were replaced completely with seal meat in the northern communities, the resulting radiation dose would be 0.34 mSv (more than 99.99% from 210Po and less than 0.01% from 137Cs). The resulting 0.34 mSv dose is a small fraction of the worldwide average annual effective dose from exposure to natural background radiation (2.4 mSv per year) (UNSCEAR, 2000). Activity concentration of 210Po is much higher in liver than in muscle. If an individual would eat 11.5 kg of fresh seal liver per year, the resulting radiation dose would be 2.9 mSv, which is then comparable to the worldwide average dose from exposure to natural background radiation. As mentioned above, 210Po activity concentrations reported here are decay corrected to the activity concentrations at the harvest date. They represent 210Po activity concentrations in very fresh meat products from seals. However, the meat is often frozen for consumption at a later date. Due to its short half-life, the 210Po activity concentration in frozen seal products decreases quickly with the time stored in freezer. Seal products consumed several months after the hunting season will have significantly less 210Po activity concentration than the fresh products. Over the course of a hunting and non-hunting season, the actual ingestion doses from 210 Po in seal meat and liver are likely to be lower than indicated. In summary, when considering the radiation doses received by the general public resulting from seal consumption, naturally occurring radionuclides make a much greater contribution than anthropogenic radionuclides in fresh seal products. Comparing doses from anthropogenic 137Cs and naturally occurring 210Po, gives a ratio of 0.0001. This means that less than 0.01% of the total ingestion dose obtained from Arviat seals come from man-made 137 Cs (resulting mainly from nuclear weapon tests and major nuclear accidents). 4. Conclusions For the consumption of fresh harvested seal meat, this study confirmed that 210Po is the dominant contributor to ingestion doses from radionuclides measured here. Activity concentration of 210Po was measured in almost all liver and muscle samples of seals. Due to its short half-life, 210Po activity concentration in frozen seal products decreases quickly with the time stored in freezer. Over the course of a hunting and non-hunting season, the annual ingestion dose for seal meat is only a fraction of the worldwide average annual effective dose from exposure to natural background radiation. None of the seal samples analysed in this study contained any detectable activity concentrations of 134Cs. This indicates that 137Cs in seals studied has mainly resulted from the fallout of atmospheric nuclear weapons tests in the 1950s and 1960s and accidental releases such as from the Chernobyl accident in 1986 (AMAP, 2002; 2010, 2016). Ringed seals are distributed across the Arctic, and are the primary seal species harvested by the Inuit in Canada (DFO, 2011).

J. Chen et al. / Journal of Environmental Radioactivity 169-170 (2017) 48e55

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Fig. 1. Annual effective doses for adults resulting from consumption of seal flesh.

Fig. 2. Annual effective doses for adults resulting from consumption of seal liver.

Based on the observed activity concentrations of 137Cs in this study, there is no radiological health concern to consumers resulting from man-made 137Cs in seal meat. Although the radioactivity in the marine environment is generally decreasing in the past decades, there is a potential for

further and new sources of naturally occurring radionuclides in Arctic as a result of human activities, including the expansion of the oil and gas industry and the start of other activities, such as uranium mining and fracking (AMAP, 2016). Therefore, continued monitoring of contaminants in the arctic including the assessment

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J. Chen et al. / Journal of Environmental Radioactivity 169-170 (2017) 48e55

of the radiological impact from naturally occurring radionuclides is important to identify any potential changes in radiation health risk to consumers. Acknowledgement Collection of the seal samples in Arviat and analysis for stable isotopes, gender and age was funded as part of the Northern Contaminants Program (Aboriginal Affairs and Northern Development Canada). The authors thank Steve Ferguson and Brent Young (DFO, Winnipeg) for permission to use the seal samples from Arviat for analysis in this study. The authors would also like to thank Christopher Rinaldo (Co-op student at Health Canada) for his contribution during the processing and preparation of the seal samples for radioactivity measurements. Appendix. Information of sample pooling for gamma counting and radiochemical analysis of 210Pb and 226Ra. For the analyses of blubber samples, all blubber samples were pooled into two large samples for male and female, respectively. For liver and muscle samples, samples of limited mass were pooled together for gamma counting first. The sample pooling results are given in Table A. Further pooling was needed for muscle samples in order to perform radiochemical analysis for 210Pb and 226 Ra, as shown in Table B.

Table A Pooling of samples for gamma counting. Pooling ID

Gamma counting

Liver1 Liver2 Liver3 Liver4 Liver5 Muscle1 Muscle2 Muscle3 Muscle4 Muscle5 Muscle6 Muscle7 Muscle8

AV2014-02, 07, 11, 19, 20, 24, AV2014-09, 10, 12, 15, 18, 25, AV2014-04, 05, 06, 08, 14, 21, AV2014-01, 03, 13, 16, 17, 22, AV2014-47, 49 and 50 AV2014-02, 07, 19 and 20 AV2014-04, 21, 36 and 38 AV2014-05, 06 and 14 AV2014-09, 10, 18 and 25 AV2014-11, 30, 32 and 39 AV2014-12 and 15 AV2014-01, 13, 17, 22 and 23 AV2014-47, 49 and 50

Table B Pooling of samples for radiochemical analysis of

30, 31 and 32 28 and 29 26, 27, 33, 34, 36, 37, 38 and 40 23 and 35

210

Pb and

226

Ra. 210

Pooling ID

Radiochemical analysis for

Liver-A Liver-B Liver-C Liver-D Liver-E Muscle-A Muscle-B Muscle-C Muscle-D Muscle-E

Liver1 Liver2 Liver3 Liver4 Liver5 Muscle1, Muscle5 and AV2014-24 Muscle2, Muscle3 and AV2014-40 Muscle4 and Muscle6 Muscle7 and AV2014-03 Muscle8 and AV2014-43

Pb and

226

Ra

References Arctic Monitoring and Assessment Programme (AMAP), 2002. AMAP Assessment 1999: Radioactivity in the Arctic. Oslo. Arctic Monitoring and Assessment Programme (AMAP), 2010. AMAP Assessment 2009: Radioactivity in the Arctic. Oslo. Arctic Monitoring and Assessment Programme (AMAP), 2016. AMAP Assessment

2015: Radioactivity in the Arctic. Oslo. Berti, P.R., Chan, H.M., Receveur, O., Macdonald, C.R., Kuhnlein, H.V., 1998. Population exposure to radioactivity from consumption of caribou among the Dene/ Metis of Denendeh (western Northwest Territories, Canada). J. Expo. Anal. Environ. Epidemiol. 8 (2), 145e158. telat, J., Amyot, M., Brown, T., Clayden, M., Evans, M., Fisk, A., Braune, B., Che Gaden, A., Girard, C., Hare, A., Kirk, J., Lehnherr, I., Letcher, R., Loseto, L., Macdonald, R., Mann, E., McMeans, B., Muir, D., O'Driscoll, N., Poulain, A., Reimer, K., Stern, G., 2015. Mercury in the marine environment of the Canadian Arctic: review of recent findings. Sci. Total Environ. 509e510, 67e90. Chambellant, M., Stirling, I., Ferguson, S.H., 2013. Temporal variation in western Hudson Bay ringed seal Phoca hispida diet in relation to environment. Mar. Ecol. Prog. Ser. 481, 269e287. Chen, J., Zhang, W., Sadi, B., 2015. A report of radioactivity measurements of freshwater fish samples from the national capital region of Canada. J. Environ. Radioact. 144, 175e178. Chen, J., Rennie, M.D., Zhang, W., Sadi, B., St-Amant, N., 2016. A study on the levels of radioactivity in fish samples from the Experimental Lakes Area in Canada. J. Environ. Radioact. 153, 222e230. Cooper, L.W., Larsen, I.L., O'Hara, T.M., Dolvin, S., Woshner, V., Cota, G.F., 2000. Radionuclide contaminant burdens in Arctic Marine Mammals harvested during subsistence hunting. Arctic 53 (2), 174e182. Dahlgarrd, H., Eriksson, M., Nielsen, S.P., Joensen, H.P., 2004. Levels and trends of radioactive contaminants in the Greenland environment. Sci. Total Environ 331, 53e67. Donaldson, S.G., Van Oostdam, J., Tikhonov, C., Feeley, M., Armstrong, B., Ayotte, P.,  Boucher, O., Bowers, W., Chan, L., Dallaire, F., Dallaire, R., Dewailly, E., Edwards, J., Egeland, G.M., Fontaine, J., Furgal, C., Leech, T., Loring, E., Muckle, G., Nancarrow, T., Pereg, D., Plusquellec, P., Potyrala, M., Receveur, O., Shearer, R.G., 2010. Environmental contaminants and human health in the Canadian Arctic. Sci. Total Environ. 408 (22), 5165e5234. Fisheries and Oceans Canada (DFO), 2011. 2011e2015 Integrated Fisheries Management Plan for Atlantic Seals. Available at: http://www.dfo-mpo.gc.ca/fm-gp/ seal-phoque/reports-rapports/mgtplan-planges20112015/mgtplanplanges20112015-eng.htm#c2. Fisheries and Oceans Canada (DFO), 2013. Commercial Fisherieseconsumption. Statistics CanadadTable 002e0011. Available at: http://www.dfo-mpo.gc.ca/ stats/commercial/consumption-eng.htm. Gwynn, J., Anderson, M., Fuglei, E., Lind, B., Dowdall, M., Lydersen, C., Kovacs, K., 2005. Radionuclides in Marine and Terrestrial Mammals of Svalbard. Stralevern Rapport 2005. Norwegian Radiation Protection Authority, p. 7. Gwynn, J.P., Brown, J.E., Kovacs, K.M., Lydersen, C., 2006. The derivation of radionuclide transfer parameters for and dose-rates to an adult ringed seal (Phoca hispida) in an Arctic environment. J. Environ. Radioact. 90 (3), 197e209. Hamilton, T., Seagars, D., Jokela, T., Layton, D., 2008. 137Cs and 210Po in Pacific walrus and bearded seal from St. Lawrence Island, Alaska. Mar. Pollut. Bull. 56 (6), 1158e1167. International Commission on Radiological Protection (ICRP), 2013. Compendium of Dose Coefficients Based on ICRP Publication 60, vol. 119. ICRP Publication. Ann. ICRP 42(4). Macdonald, C.R., Ewing, L.L., Elkin, B.T., Wiewel, A.M., 1996. Regional variation in radionuclide concentrations and radiation dose in caribou (Rangifer tarandus) in the Canadian Arctic; 1992-94. Sci. Total Environ. 182 (1e3), 53e73. National Oceanic and Atmospheric Administration (NOAA), 2016. Bearded Seals. Available at: http://www.afsc.noaa.gov/nmml/education/pinnipeds/bearded. php. Nielsen, S.P., Joensen, H.P., 2009. Recent trends of environmental radioactivity in Greenland and the Faroe Islands. Radioprotection 44, 843e848. Pauly, D., Trites, A.W., Capuli, E., Christensen, V., 1998. Diet composition and trophic levels of marine mammals. ICES J. Mar. Sci. 55, 467e481. Solatie, D., Rissanen, K., Vesterbacka, P., 2005. 210Po and 210Pb in seals from the Baltic Sea and Lake Saimaa, Finland. In: Valentin, J., Cederlund, T., Drake, P., Finne, I.E., Glansholm, A., Jaworska, A., Paile, W., Rahola, W. (Eds.), Radiological Protection in Transition e Proceedings of the XIV Regular Meeting of the Nordic Society for Radiation Protection. Rattvik, Sweden, 27e31 August 2005. Statistics Canada, 2007. Inuit in Canada: Findings from the Aboriginal Peoples Survey e Survey of Living Conditions in the Arctic, Harvesting and Country Food: Fact Sheet 2001. Available at: http://www.statcan.gc.ca/pub/89-627-x/89627-x2007001-eng.pdf. Statistics Canada, 2010. Food Statistics 2009. Available at: http://www.statcan.gc.ca/ pub/21-020-x/21-020-x2009001-eng.htm?contentType¼application%2Fpdf. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), 2000. Exposures from Natural Radiation Sources. UNSCEAR 2000 Report, Annex B. United Nations, New York. United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), 2014. Levels and Effects of Radiation Exposure Due to the Nuclear Accident after the 2011 Great East-Japan Earthquake and Tsunami. UNSCEAR 2013 Report, Volume I. United Nations, New York. World Health Organization (WHO), 2013. Health Risk Assessment from the Nuclear Accident after the 2011 Great East Japan Earthquake and Tsunami. United Nations, Geneva. Young, B.G., Loseto, L.L., Ferguson, S.H., 2010. Diet differences among age classes of Arctic seals: evidence from stable isotope and mercury biomarkers. Polar Biol. 33 (2), 153e162. Young, B.G., Ferguson, S.H., Lunn, N.J., 2015. Variation in ringed seal density and

J. Chen et al. / Journal of Environmental Radioactivity 169-170 (2017) 48e55 abundance in western Hudson Bay estimated from aerial surveys, 1995 to 2013. Arctic 68 (3), 301e309. Yurkowski, D.J., Ferguson, S.H., Semeniuk, C.A.D., Brown, T.M., Muir, D.C.G., Fisk, A.T., 2015. Spatial and temporal variation of an ice-adapted predator's feeding

55

ecology in a changing Arctic marine ecosystem. Oecologia 180 (3), 631e644. Zhang, W., Keeshan, B., Mekarski, P., Yi, J., Ungar, K., 2013. Performance evaluation and optimization for a newly developed digital list-mode data acquisition Compton suppression spectrometer. Appl. Radiat. Isotopes 81, 96e102.