Journal of Environmental Radioactivity 102 (2011) 473e478 Contents lists available at ScienceDirect Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad Radionuclides in marine mammals off the Portuguese coast Margarida Malta, Fernando P. Carvalho* Instituto Tecnológico e Nuclear, Departamento de Protecção Radiológica e Segurança Nuclear, E.N. 10, 2686-953 Sacavém, Portugal a r t i c l e i n f o a b s t r a c t Article history: Received 18 June 2010 Received in revised form 21 February 2011 Accepted 7 March 2011 Available online 14 April 2011 Radionuclide analyses were performed in tissue samples including muscle, gonad, liver, mammary gland, and bone of marine mammals stranded on the Portuguese west coast during JanuaryeJuly 2006. Tissues were collected from seven dolphins (Delphinus delphis and Stenella coeruleoalba) and one pilot whale (Globicephala sp.). Samples were analyzed for 210Po and 210Pb by alpha spectrometry and for 137Cs and 40K by gamma spectrometry. Po-210 concentrations in common dolphin’s muscle (D. delphis) averaged 56  32 Bq kg 1 wet weight (w.w.), while 210Pb averaged 0.17  0.07 Bq kg 1 w.w., 137Cs averaged 0.29  0.28 Bq kg 1 w.w., and 40K 129  48 Bq kg 1 w.w. Absorbed radiation doses due to these radionuclides for the internal organs of common dolphins were computed and attained a 1.50 mGy h 1 on a whole body basis. 210Po was the main contributor to the weighted absorbed dose, accounting for 97% of the dose from internally accumulated radionuclides. These computed radiation doses in dolphins are compared to radiation doses from 210Po and other radionuclides reported for human tissues. Due to the high 210Po activity concentration in dolphins, the internal radiation dose in these marine mammals is about three orders of magnitude higher than in man. Ó 2011 Elsevier Ltd. All rights reserved. Keywords: Marine mammals Polonium-210 Lead-210 Potassium-40 Caesium-137 radiation dose 1. Introduction Previously, it was assumed that when human beings are protected against the harmful effects of ionizing radiation the remaining biological species would be protected as well (ICRP 1971, 1991). However, this line of thought has been questioned (Pentreath and Woodhead, 2001; Bréchignac, 2003). Recent developments in the field of radiation protection now regard the environment as a system that must be protected on its own merits (NEA/OECD, 2002; ICRP, 2008). This viewpoint requires the risk assessment to be performed for non-human biota when subject to ionizing radiation exposure. Several collaborative projects have been implemented with the objective of developing relevant methodologies, namely to set up criteria and methodologies for use in the assessment of biological and ecological effects following exposure of biota to ionizing radiation. Amongst these projects one may highlight, for example, the European Union FASSET project (Framework for Assessment of Environmental Impact) (Brown et al., 2003a). In general, marine mammals are at the top of marine food chains, and dolphins in particular are top predators consuming common coastal fish species (Culik, 2004). Contrasting to fish and other marine organisms, marine mammals do not absorb radionuclides directly from sea water and most of the internally accumulated radionuclides are ingested with the diet (Brown et al., 2005; Gwynn * Corresponding author. Tel.: þ351 21 9946332; fax: þ351 21 9941995. E-mail address: carvalho@itn.pt (F.P. Carvalho). 0265-931X/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jenvrad.2011.03.004 et al., 2006). Furthermore, radiosensitivity of marine mammals may be comparable to terrestrial mammals and, thus, the knowledge on radionuclide absorption into internal organs may be used as a proxy for radionuclide accumulation and effects in other mammals including man (Bréchignac, 2003). Notwithstanding, the database on radionuclide accumulation in marine mammals is scarcer than for other marine biota (Brown et al., 2004; Carvalho, 2010; Holm et al., 2005). Radionuclides currently present in the marine environment are both naturally-occurring and of anthropogenic origin. Previous research in assessing the accumulation of radionuclides in marine biota, concluded that amongst the natural radionuclides the alpha emitter polonium-210 (210Po; T1/2 ¼ 138.4 d), generally gives the largest contribution to the internal radiation dose received by those organisms (Carvalho, 1988; Carvalho and Oliveira, 2008; Cherry and Heyraud, 1982) and by consumers of sea food including humans (Aarkrog et al., 1997; Carvalho, 1995; Livingston and Povinec, 2000; Yamamoto et al., 2009). Lead-210 (210Pb; T1/2 ¼ 22.3 y), grand parent of 210Po, is a weak energy beta-gamma emitter but its distribution influences the biogeochemistry of 210Po in the oceans, and it is also largely accumulated by marine organisms and man (Carvalho, 1995; Cherry and Shannon, 1974; Parfenov, 1974; UNSCEAR, 1982). For these reasons, it is of great interest to investigate further those radionuclides and radiation dose distributions in internal organs and tissues in mammals, including marine species. Anthropogenic radionuclides, such as tritium, plutonium, americium, and caesium, are present in the world ocean and mainly 474 M. Malta, F.P. Carvalho / Journal of Environmental Radioactivity 102 (2011) 473e478 originated in fallout from nuclear weapons tests, waste discharges from spent nuclear fuel reprocessing activities, and nuclear accidents such as the Chernobyl accident. Amongst the radionuclides of anthropogenic origin, caesium-137 (137Cs; T1/2 ¼ 30.07 y) is the main contributor to the absorbed radiation dose both to marine organisms and to man, especially in the muscle tissue (Livingston and Povinec, 2000; Carvalho and Oliveira, 2008). Potassium-40 (40K; T1/2 ¼ 1.27  109 y), a long lived primordial radionuclide present in the sea water and in all marine organisms, is fairly abundant and accounts for about 18 Bq L 1 in sea water (Brown et al., 2004). However, in the internal tissues of living organisms the potassium element is maintained in constant concentration and, thus, the absorbed radiation dose from the 40K radioactive isotope is stable (UNSCEAR, 1982). Other radionuclides are not subjected to metabolic regulation and their activity concentrations in biota depend upon sea water concentrations and food chain transfer and, thus, their contributions to radiation doses may vary. Tissue samples from marine mammals stranded ashore at the Portuguese coast were analysed for determining radionuclide activity concentrations and for assessing radiation doses due to internally accumulated radionuclides. This paper gives an account on current radioactive concentrations in internal tissues of several marine mammal species and compares them with concentrations reported for marine mammals in other regions, and for man. 2. Materials and methods Marine mammal corpses found ashore are usually communicated to maritime authorities for recording the occurrence and removal of corpses from the beaches. Samples from marine mammals stranded on the west coast of Portugal during the first half of 2006 were obtained through collaboration with the Institute for Nature Conservation (ICN, Portugal) and Câmara Municipal de Alcobaça. As the knowledge of the time of death is important for radioactive decay correction of the activity determined, especially for 210Po, mammal corpses sampled were only those clearly fresh or with minimal tissue decomposition. This effect was minimized as much as possible through consulting with veterinary expertise assisting the project. In the assessment of radionuclide accumulation in marine mammals it is important to take also into consideration that radionuclide concentrations may vary with the age, sex, feeding location, and diet composition. However, the availability of samples of these protected marine mammals was limited to the stranded specimens and not all those factors could be addressed in this research. After species identification and biometric data recording, tissue samples were collected by a veterinarian into jars and transported on ice to the laboratory. Tissues samples of eight specimens of marine mammals, namely six common dolphins Delphinus delphis, one striped dolphin Stenella coeruleoalba, and one pilot whale Globicephala sp., were analyzed. Weighted amounts of tissues were frozen, lyophilized and homogenized. Aliquots of the homogenized powder were used for triple determination of 210Po and 210Pb following methods described earlier (Carvalho, 1995; Carvalho and Oliveira, 2007; Carvalho et al., 2011). In brief, to the weighted sample aliquot a known activity of 209Po (T1/2 ¼ 102 y) was added to be used as internal isotopic tracer, to allow for determining the radiochemical yield of the analytical procedure. The sample was than completely dissolved in mineral acids (HNO3 and HCl) and H2O2. Polonium was spontaneously deposited onto a silver disc from a 0.5 M HCl solution in the presence of 500 mg ascorbic acid. The alpha particle emission from the disc surface was measured with an alpha spectrometer OctectePlus (Ortec EG&G) equipped with 450 mm2 surface barrier silicon detectors. After this first polonium plating the sample solution was stored for about 6 months and then, after the addition of a new 209Po spike, evaporated to dryness and the residue dissolved in 0.5 M HCl solution. A second polonium deposition onto a new disc was made, allowing the determination of 210 Pb through the in growth of 210Po. The alpha particle emission was measured for the new disc. Radionuclide activities were computed and decay corrected using the Bateman equations and 210 Po and 210Pb activities referred to the day of the mammal stranding on the beach. Results for the triplicate aliquots were averaged. Aliquots of the homogenate powder tissue samples, of approximately 10 g dry weight each, were compacted in Millipore air tight Plexiglas Petri dishes and measured for gamma emitting radionuclides. Determinations of 137Cs and 40K were performed using the gamma peak energies of 661.66 keV and 1460.82 keV, respectively. Gamma spectrometry was performed in HpGe detectors for a period of 24 h. Gamma spectra were analyzed with Genie2000Ò software from Canberra and screened for the presence of other artificial gamma emitters. The Quality Assurance of analytical determinations was performed through using IAEA certified reference materials (e.g., IAEA134 cockle flesh) and participating in international intercomparison exercises, such as those with IAEA-414 (fish muscle) and (IAEA-384 marine sediment) with good results (Pham et al., 2006; Povinec et al., 2007). For gamma measurements the radionuclide activity concentrations reported are given with the 1 sigma (1s) confidence level propagated uncertainty. For 210Po and 210Pb determinations, the average activity concentrations determined are given with the one standard deviation of the mean. All reagents used were of analytical grade and analytical blanks were run with internal isotopic 209Po tracer, as for the samples. The radionuclide concentrations are expressed in Bq kg 1 wet weight. The dry:wet weight ratios (D:W) are shown in the tables to enable unit conversion. Table 1 Polonium (210Po) activity concentrations in tissues of marine mammals off the Portuguese coast (Bq kg D:W Common ratios dolphin #1 Sex Body length (cm) Dorsal muscle Mammary gland Liver Fat tissue Gonad Kidney Bone 1  1 SD, wet weight). Common dolphin #2 Common dolphin #3 Common dolphin #4 Common dolphin #6 Common dolphin #8 Striped dolphin #5 Pilot whale #7 Average for common dolphins Female 197 Male 168 Female 208 Male 180 Undetermined Undetermined Undetermined n.c. 170 n.c. 177  24 (n ¼ 5) e e Female 140 0.31 0.24 9.08  0.13 79.87  1.58 81.67  1.94 87.17  1.87 n.c. 29.48  0.88 n.c. n.c 42.49  1.51 n.c 34.24  0.79 8.19  0.21 42.01  0.78 n.c. 13.69  0.27 n.c. 56  32 (n ¼ 6) 19  15 (n ¼ 2) 0.25 0.64 0.22 0.22 0.47 n.c. n.c. n.c. n.c. n.c. 74.97  1.91 22.01  0.92 9.28  0.30 104.58  2.66 n.c n.c. n.c. n.c. n.c. n.c. n.c. n.c. n.c. n.c. n.c. n.c. 0.70  0.06 n.c. n.c. n.c. 123  42 (n ¼ 3) 11  11 (n ¼ 4) 11  2 (n ¼ 4) 110  49 (n ¼ 3) 4.63  0.12 (n ¼ 1) 143.03 19.17 12.01 161.40 4.63      3.03 0.46 0.17 2.23 0.12 n.c. 2.71  0.12 13.30  0.31 n.c. n.c. 151.33  2.98 1.41  0.11 8.92  0.24 63.02  1.32 n.c. D:W, dry:wet weight ratio; n.c., not collected. Common dolphin, Delphinus delphis. Striped dolphin, Stenella coeruleoalba. Pilot whale, Globicephala sp. M. Malta, F.P. Carvalho / Journal of Environmental Radioactivity 102 (2011) 473e478 6 A X fi Ei yi i Where: _ e Dose rate (Gy h 1); D DCF e Dose conversion factors (mGy h 1 per Bq kg 1). Low energy (<10 keV) beta doses are weighted by a radiation quality factor Qb ¼ 3; alpha doses are weighted by a radiation quality factor Qa ¼ 10. A e Radionuclide concentration (Bq kg 1, wet weight); Ei e Energy of “i” in gamma radiation; yi e Ei energy photons emission rate; 4i e Absorbed fraction for Ei energy. Units of computed absorbed radiation doses, weighed with radiation quality factors, are given below in mGy h 1, according to the criteria that the dose equivalent concept and conversion to mSv h 1 developed for humans may be not applicable to biota (Brown et al., 2003b). 3. Results and discussion Table 1 and Table 2 show respectively the 210Po and 210Pb activity concentrations determined in the tissues of six common dolphins (D. delphis), one striped dolphin (S. coeruleoalba) and one pilot whale (Globicephala sp.). Results for the six common dolphin specimens were averaged. In the dolphins, 210Po averaged activity concentrations were higher in the liver and kidneys, often above 100 Bq kg 1, and up to a maximum value of 161.4  2.2 Bq kg 1 in the kidney. These concentrations were followed by those in the dorsal muscle tissue, averaging 56  32 Bq kg 1 (n ¼ 6), and the lowest 210Po concentration being in the bone, 4.63  0.12 Bq kg 1 (n ¼ 1) (Table 1). In all tissues 210Pb activity concentrations were generally below 1 Bq kg 1, with the exception of the bone (Table 2). Amongst soft tissues slightly higher 210Pb activity concentrations were measured in the liver and kidneys, averaging respectively 0.47  0.12 Bq kg 1 (n ¼ 3) and 0.23  0.11 Bq kg 1 (n ¼ 3), and then in muscle averaging 0.17  0.07 Bq kg 1 (n ¼ 6). Pb-210 activity concentration was higher in the bone, 3.60  0.12 Bq kg 1 (n ¼ 1), owing to the preferential fixation of 210Pb in the calcified bone structure as documented in the literature (Cherry et al., 1994; UNSCEAR, 1982) (Table 2). Po-210 and 210 Pb activity concentrations in the mammary gland were in the range of concentrations measured in other internal tissues and nearly comparable to the gonad (Tables 1e3). In the tissues analyzed, the 210Po activity concentrations were systematically higher than those of 210Pb. High Po/Pb ratios are concentration (Bq kg-1 wet weight) _ ¼ DCF  A ¼ 5:04  10 D 120 210Po activity The absorbed radiation doses originated by the radioactive decay of 210Po, 210Pb, 40K and 137Cs, were computed, assuming that these radionuclides are uniformly distributed in the tissue and using radiation quality weighting factors (Golikov and Brown, 2003), through using the equation 100 #4 #3 80 #2 60 #5 40 #6 y = 1.0471x - 128.43 R² = 0.6596 20 #1 0 120 140 160 180 200 220 240 Body length (cm) Fig. 1. Correlation between 210Po activity concentration in muscle tissue and body length of dolphins. Sample numbers as in Table 1. a consequence of the preferential 210Po absorption through gut walls comparatively to 210Pb, followed by 210Po accumulation in the internal organs of marine organisms (Carvalho and Fowler, 1993, 1994) and in man (Hunt and Allington, 1993). Results for the pilot whale and striped dolphin were treated separately because of the different biology and ecology of these species. However, radionuclide concentrations were not very different and fell in the range of values for dolphins (Tables 1 and 2). Activity concentrations of 210Po in the muscle tissue were very similar in dolphins #2, 3 and 4 (Table 1). However, specimens #1, 5 and 6 displayed lower concentrations which could be a consequence of the more advanced decomposition of corpses of these two specimens. Post-mortem decomposition leads to tissue dehydration and destruction of amino acid chains in proteins, followed by cellular destruction. Due to the substitution of sulphur compound radicals (eSH) by 210Po in amino acids (Durand et al., 1999), decomposition may result in physical loss of 210Po atoms. This fact supports the idea that the state of the body conservation could be extremely important to the 210Po activity concentration determined in the organs. Nevertheless, the post-mortem elapsed time apparently didn’t affect the 210Pb concentration. Notwithstanding the activity differences in muscle tissue, 210Po concentrations were similar in the liver of all specimens. 210Po concentrations in the gonad were similar amongst specimens as well, although not all of them did belong to the same gender (Table 1). As amongst internal tissues the muscle contributes with the largest fraction (64%) to the whole dolphin body weight (Dubois et al., 1948), that tissue is also the main reservoir of 210Po radionuclide in dolphins, contributing to 41 Bq kg 1 on a whole body weight basis. A plot of 210Po concentration in muscle tissue against animal body length, demonstrated that there is a positive correlation (R2 ¼ 0.66) with a statistically significant association (ManneWhitney test, p < 0.05) between 210Po concentration and body length, and thus Table 2 Radioactive lead (210Pb) activity concentrations in tissues of marine mammals off the Portuguese coast (Bq kg Dorsal muscle Mammary gland Liver Fat tissue Gonad Kidney Bone 475 1  1 SD, wet weight). D:W Ratios Common dolphin #1 Common dolphin #2 Common dolphin #3 Common dolphin #4 Common dolphin #6 Common dolphin #8 Striped dolphin #5 Pilot whale #7 Average for common dolphins 0.31 0.24 0.25 0.64 0.22 0.22 0.47 0.12  0.01 n.c. n.c. n.c. n.c. n.c. n.c. 0.15 0.47 0.54 0.20 0.15 0.34 3.60 0.18  0.01 n.c. n.c. 0.26  0.02 0.34  0.02 n.c. n.c. 0.08 n.c 0.34 0.11 0.04 0.13 n.c. 0.30 n.c 0.54 0.28 0.11 0.21 n.c. 0.16  0.02 0.13  0.01 n.c. n.c. n.c. n.c. n.c. 0.16  0.01 n.c. n.c. n.c. n.c. n.c. n.c. 0.18  0.01 n.c. n.c. 0.17  0.02 n.c. n.c. n.c. 0.17 0.30 0.47 0.20 0.16 0.23 3.60  0.02  0.06  0.03  0.02  0.01  0.01  0.12  0.01     0.04 0.02 0.01 0.01  0.04     0.04 0.04 0.01 0.08 D:W, dry:wet weight ratio; n.c., not collected. Common dolphin, Delphinus delphis. Striped dolphin, Stenella coeruleoalba. Pilot whale, Globicephala sp.  0.07  0.24  0.12  0.07  0.13  0.11  0.12 (n (n (n (n (n (n (n ¼ ¼ ¼ ¼ ¼ ¼ ¼ 6) 2) 3) 4) 4) 3) 1) 476 M. Malta, F.P. Carvalho / Journal of Environmental Radioactivity 102 (2011) 473e478 Table 3 Polonium (210Po) activity concentrations (Bq kg Cherry et al. (1994) Folsom et al. (1974) Carvalho et al. (2007) Peniche Portuguese west coast Cape Town South Africa San Diego California, USA Azores Islands Portugal a Common dolphin Dorsal muscle Mammary gland Liver Fat tissue Gonad Kidney Bone 56  32 (9.08e87.2) 19  15 (8.19e29.5) 123  42 (75e151.3) 11  11 (1.4e22.0) 11  2 (8.92e13.3) 110  49 (105e161) 4.63  0.12 a c d e f e e e e e e  1 SD, wet weight) in tissues of marine mammals from several regions. This study Species b 1 Striped dolphin 42.01  0.78 e e e e e e b Pilot whale c 13.69  0.27 e e 0.7  0.06 e e e Dolphin d 83  2.4 e 124  4 e 4.7  0.3 136  4.6 26  0.5 #1 Dolphin d #2 Whale 80  1.8 e 124  2 7.23  0.7 3.9  .3 242  2.8 e e Dolphin 3.7  0.1 e 72  1 e 8.3  0.4 196  4 5.4  0.4 d 94.5 (78e111) e e e e e e Sperm whale f 5.0 e e e e e e Average and range of values shown in Table 1 (Delphinus delphis). Stenella coeruleoalba. Globicephala sp. Delphinus delphis. Hyperoodon planifrons. Physeter catodon. with age (Fig.1). Pb-210 concentration was higher in the dolphin bone and as the bone contributes to 3.61% of body weight, it is still the largest 210Pb reservoir in dolphins, even larger than the 210Pb muscle reservoir, and averaging 0.13 Bq kg 1 whole body weight basis. K-40 activity concentration in the muscle tissue of the six common dolphins ranged from 75 to 218 Bq kg 1, averaging 129  48 Bq kg 1 (Table 4). Cs-137 was detected in the muscle tissue of 5 out of 8 mammal specimens. In the 6 common dolphins 137 Cs was detected in 4 specimens, and concentrations ranged from <0.06 to 0.81 Bq kg 1 and averaged 0.29  0.28 Bq kg 1. Cs-137 and 40 K in the muscle tissue and in the liver of several marine mammals reported in the literature are compared with results for dolphins (D. delphis and S. coeruleoalba) and pilot whale (Globicephala sp) in Table 4. Concentrations of 40K were very similar in these marine mammals, but 137Cs seemed slightly higher in mammals from the coast of United Kingdom than in those off the Portuguese coast, which is a trend related probably to past coastal discharges of radioactive liquid wastes in UK and currently higher 137Cs levels in UK coastal seas than in other European seas (RIFE-14, 2009). Po-210 activity concentrations in mammals were of the same order of magnitude as those of 40K, but since 210Po is a pure alpha emitter it was expectedly more relevant to the absorbed radiation dose than 40K (beta-gamma emitter) due to the higher alpha radiation quality factor (Qa ¼ 10, Qb ¼ 3). Furthermore, 210Pb and 137 Cs contributions to the absorbed dose were much smaller than that of 40K because of lower concentrations of those radionuclides in comparison with 40K. Table 5 shows the radionuclide activity concentrations in tissues, the weighted absorbed dose computed for each radionuclide on a whole body basis, and the sum of their contributions to the whole body absorbed dose. Considering these internal radiation sources, computed whole body weighted Table 4 Average activity concentrations of 137 Cs and 40 K (Bq kg 1  1 SD, wet weight) and range of values in liver and muscle of marine mammals of the Northeast Atlantic. Species Tissue Local Delphinus delphis (This work) Stenella coeruleoalba (This work) Globicephala sp. (This work) Delphinus delphis (Yoshitome et al., 2003) Stenella longirostris (Yoshitome et al., 2003) Stenella attenuata (Yoshitome et al., 2003) Phocoena phocoena (Watson et al., 1999) Phocoena phocoena (Watson et al., 1999) Delphinus delphis (This work) Phocoena phocoena (Watson et al., 1999) Muscle Muscle Muscle Muscle Muscle Muscle Muscle Muscle Liver Liver Peniche, Portuguese Peniche, Portuguese Peniche, Portuguese Pacific Ocean Pacific Ocean Pacific Ocean UK coast Ireland coast Peniche, Portuguese UK coast n.d., not detected; n, number of specimens analyzed. absorbed dose rate in common dolphins is 1.50 mGy h 1. Po-210 is the main contributor to this dose rate, with an absorbed radiation dose of 1.46 mGy h 1, i.e., more than 97% for the total. In contrast to this, 137Cs in dolphin’s internal tissues gives a negligible contribution to the absorbed dose (Table 5). These radionuclides, namely the naturally-occurring 210Pb, 210Po, 40 K, are accumulated in the tissues of human body as well. In the adult man, the average activity concentrations of these radionuclides are about 0.2, 0.2 and 60 Bq kg 1, respectively (UNSCEAR, 1982). Cs-137 accumulation, although small, is more variable (average value 0.52 Bq kg 1, range 0.22e1.1 Bq kg 1). Based on these concentrations, the average absorbed radiation dose (not weighted with the radiation quality factor) in the human muscle from internally accumulated 210Pb was computed at 4.6  10 6 mGy h 1, from 210Po at 6.2  10 4 mGy h 1, from 40K at 1.9  10 2 mGy h 1, and from 137Cs at about 4.3  10 4 mGy h 1. Absorbed radiation doses from these radionuclides in human tissues, if computed using the same DCF as defined in the section Materials and methods above and such as used for dolphins, for 210Pb, 210Po, 40K, and 137Cs would be 5.2  10 5, 6.2  10 3, 2.1  10 2 and 2.1  10 4 mGy h 1 respectively. A comparison of the above radionuclide concentrations and absorbed radiation doses for the adult man with the adult marine mammals (dolphins; Table 5) highlights that 210Pb, 40K and 137Cs activity concentrations and doses may be similar, but the 210Po activity concentration and the absorbed radiation dose are three orders of magnitude higher in these marine mammals than in man. Taking into account the available knowledge on 210Po transfer in marine food chains it seems likely that the diet of marine mammals accounts for the observed 210Po activity concentrations and the relative enrichment of 210Po in comparison to 210Pb (Carvalho, 1995, 2010; Carvalho and Fowler, 1994; Hunt and Allington, 1993). coast coast coast coast Year n 137 40 2005e2006 2005e2006 2005e2006 1977e1983 1977e1983 1977e1983 1988e1995 1989e1993 2005e2006 1988e1995 6 1 1 8 7 37 30 25 3 30 0.29  0.28 (<0.06e0.81) <0.06 <0.06 0.39 0.44 0.52 6.9 (n.d.e66.6) 7.0 (<0.5e45.0) <0.06 2.7 (n.d.e30.5) 129  48 (75e218) 31.7  18.3 140  13 132 188 130 89 (69e116) 93 (54.0e125.9) 78  22 (61.4e103) 85 (41e116) Cs K M. Malta, F.P. Carvalho / Journal of Environmental Radioactivity 102 (2011) 473e478 Table 5 Activity concentrations of radionuclides and their contributions to the whole body weighted internal absorbed dose rate (mGy h 1) and total whole body weighted absorbed dose rate in dolphins off the Portuguese coast. Tissues Body weight Average activity concentrations (%) (arithmetic mean  1SD, n¼6) (Bq kg 1) 210 Muscle and remaining 74.0 tissues Liver 1.92 Fat tissue 17.4 Gonad 2.33 Kidney 0.70 Bone 3.61 Whole body 100 Internal absorbed radiation dose rate (mGy h 1) per nuclide Internal absorbed radiation dose rate (mGy h 1) - total Po 40 K 210 Pb 137 5632 12948 0.170.07 - 12342 1111 112 11049 4.630.12 47 1.46 7822 176 10253 8311 9266 106 0.036 0.470.12 0.200.07 0.160.13 0.230.11 3.600.12 0.31 8.110 5 Cs 0.29 910 5 1.50 Dolphins, which feed upon small pelagic fish show higher 210Po activity concentrations in muscle tissue than Sperm whales, which mainly feed upon cephalopods that have been shown to contain lower activity concentrations of 210Po (Carvalho, 2010). The whole body absorbed dose in dolphins estimated in this study at 1.50 mGy h 1, is far below the threshold dose level of 100 mGy h 1 above which significant biological effects of radiation have been observed in mammals (Real et al., 2004). However, important knowledge gaps do exist concerning the effects of alpha radiation in mammals and the radiosensitivity of different mammal species. 4. Conclusions Measurement of the more common artificial and natural radionuclides in the tissues of marine mammals confirmed that 210Po and 40 K are the radionuclides with higher activity concentrations. Concentrations of 210Po (pure alpha emitter) approached those of 40 K (beta and gamma emitter), and both were much higher than 210 Pb and 137Cs concentrations. In the dolphins, the contribution of 210 Po to the total weighted absorbed radiation dose in tissues from the internally deposited main radioactive elements exceeded 97%. The internal radiation dose received by marine mammals is much higher than the dose received by human tissues, and this is due to the higher 210Po activity accumulated in marine mammal tissues. The source of these high and unsupported 210Po activity concentrations in marine mammals is likely due to the ingestion of 210 Po with their food. Po-210 activity concentrations are higher in seafood in comparison with terrestrial foods (Carvalho, 1995), and, thus, expectedly much higher in marine mammals’ diet than in terrestrial mammals’ diet, including man. The differences noticed also in the 210Po activity concentrations between marine mammal species, such as the dolphin and the sperm whale, are most likely due to differences in their diet and food chain structure as well. Acknowledgements Thanks are due to Mrs S.Quaresma and Mrs. C.António, staff members of the Camara Municipal de Alcobaça, for their assistance with the sampling. 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