Comparison of trace element accumulation in Baikal seals (Pusa sibirica), Caspian seals (Pusa caspica) and northern fur seals (Callorhinus ursinus)

Environmental Pollution 127 (2004) 83–97 www.elsevier.com/locate/envpol

Comparison of trace element accumulation in Baikal seals (Pusa sibirica), Caspian seals (Pusa caspica) and northern fur seals (Callorhinus ursinus) Tokutaka Ikemotoa, Takashi Kunitoa,1, Izumi Watanabeb, Genta Yasunagaa,2, Norihisa Babac, Nobuyuki Miyazakid, Evgeny A. Petrove, Shinsuke Tanabea,* a Center for Marine Environmental Studies (CMES), Ehime University, Bunkyo-cho 2-5, Matsuyama 790-8577, Japan Department of Environmental Conservation, Tokyo University of Agriculture and Technology, Saiwai-cho 3-5-8, Fuchu, Tokyo 183-8509, Japan c National Research Institute of Fisheries Science, Fukuura 2-12-4, Kanazawa, Yokohama, Kanagawa 236-8648, Japan d Otsuchi Marine Research Center, Ocean Research Institute, The University of Tokyo, Akahama 2-106-1, Otsuchi, Iwate 028-1102, Japan e Limnological Institute of the Siberian Division of the Academy of Science of Russia, Ulan Batorskaya 3, Irkutsk 664033, Russia

b

Received 19 September 2002; accepted 20 June 2003

‘‘Capsule’’: Hair samples may be useful in monitoring trace elements in seals. Abstract Concentrations of 18 trace elements (V, Cr, Mn, Co, Cu, Zn, Se, Rb, Sr, Zr, Mo, Ag, Cd, Sb, Cs, Hg, Tl and Pb) were determined in liver, kidney, muscle and hair of Baikal seals, Caspian seals and northern fur seals. All the three species showed the highest concentrations of Hg, V, Mn, Se and Ag in liver, Cd, Co and Tl in kidney, and Cs in muscle among the soft tissues examined. The highest burdens of Zn, Rb and Cs were observed in muscle, Mo and Ag in liver, and Sb and Pb in hair in all the three species. Concentrations of non-essential elements, Rb, Cd, Cs and Hg, showed significant positive correlations among liver, kidney and muscle, whereas correlation coefficients for essential elements, Mn, Co, Cu, Zn and Se, between the three tissues were generally low for all the species, suggesting that homeostasis controls the concentrations of essential elements but not the non-essential elements in the tissues of these animals. Significant age-dependent increase was found in the concentrations of V, Se and Ag in liver and Hg in liver and kidney of all the three species. Hair concentrations showed significant positive correlations with Zn levels in liver and kidney and Hg in muscle for Caspian seals, Hg in liver and kidney for Baikal seals, and Pb in liver for northern fur seals. Furthermore, regression analysis using the data in the present study and in the literature showed significant positive correlations between Hg levels in hair, and liver, kidney and muscle for various species of pinnipeds. These results indicate the possibility of using hair samples for monitoring these trace elements in pinnipeds. # 2003 Elsevier Ltd. All rights reserved. Keywords: Pinnipeds; Trace elements; Hair; Seals; Heavy metals

1. Introduction Marine mammals have a potential for accumulating trace elements in their tissues because of their high position in the food chain and their long lifespan. In the past few decades, mass mortalities occurred in several

* Corresponding author. Tel./fax: +81-89-927-8171. E-mail address: [email protected] (S. Tanabe). 1 Present address: Department of Environmental Sciences, Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 3908621, Japan. 2 Present address: The Institute of Cetacean Research, 4-5 Toyomicho, Chuo-ku, Tokyo 104-0055, Japan. 0269-7491/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0269-7491(03)00251-3

marine mammal populations (Harvell et al., 1999) including Baikal and Caspian seals (Miyazaki, 2001) and toxic contaminants might be responsible for such events (Ross et al., 1996). Hence, there has been some concern regarding possible adverse effects of anthropogenically-derived trace elements on marine mammals (De Guise et al., 1996; Siebert et al., 1999; Bennett et al., 2001; Anan et al., 2002). Human and industrial activities have greatly increased the fluxes of various trace elements to the environment (Nriagu and Pacyna, 1988; Nriagu, 1989, 1996). Of these elements, accumulation of Hg, Cu, Zn and Cd has been extensively studied in marine mammals (see reviews of Wagemann and Muir, 1984; Thompson,

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1990; Law, 1996; O’Shea, 1999), but information on other trace elements is still limited. Investigation of a wider range of elements enables a better assessment of the significance of metal concentrations in marine mammal tissues (Law, 1996). Recently, some studies reported the concentrations of various trace elements in marine mammals (Zeisler et al., 1993; Mackey et al., 1995; Krone et al., 1999; Law et al., 2001; Parsons and Chan, 2001). However, because almost all the studies focused on the concentrations in liver tissue and the sample size was very small, there is very little information on the tissue distribution and effects of biological parameters (e.g., age and sex) on trace element accumulation. Also, comparative studies on trace element accumulation between species is needed to get an insight into species difference of their susceptibility to these contaminants in marine mammals. Non-destructive monitoring of residue levels of contaminants in marine mammals has received increased attention (Fossi and Marsili, 1997). In the non-destructive techniques, fur and skin biopsy are the most promising samples to evaluate the levels of trace elements in marine mammals (Fossi and Marsili, 1997; Monaci et al., 1998; Kunito et al., 2002; Yang et al, 2002a). However, in pinnipeds, there have been few efforts to investigate the relationship of trace element concentration in hair to those in internal tissues, and hence much information is necessary to find out the suitability of hair as an indicator of trace element levels in the internal tissues of pinnipeds. The aim of the present work was to delineate the pattern of trace element accumulation in the tissues of pinnipeds, which can provide information on the fate and potential effects of trace elements in pinnipeds. An additional objective was to investigate whether the hair would be a good non-destructive indicator of trace element contamination for evaluation of its ecotoxicological risk in pinnipeds. In the present study, accumulation of 18 trace elements in Baikal seals, Caspian seals and northern fur seals were characterized with respect to tissue distribution, influence of sex and age, and species difference, and also relationship of trace element concentrations in hair to those in internal tissues was investigated.

2. Materials and methods 2.1. Samples Liver, kidney, muscle and hair of Baikal seals (Pusa sibirica), Caspian seals (Pusa caspica) and northern fur seals (Callorhinus ursinus) were used in this study. Baikal seals (n=20) were collected from Lake Baikal, Russia in 1992, Caspian seals (n=20) from the Caspian Sea in 1998, and northern fur seals (n=24) from off Sanriku, Japan in

1997 and 1998. These samples were collected under appropriate permits. Age was determined by counting the growth layers in canine tooth as described by Kasuya (1976). Samples were stored in a deep-freezer at 20  C until analysis. 2.2. Trace element analysis Prior to analysis, hair was cleaned ultrasonically with 3% polyoxyethylene lauryl ether for 40 min, washed with acetone, and rinsed with distilled water to remove exogenous contaminants. Samples were dried for 12 h at 80  C. Trace element levels were analyzed using the procedure described previously by Yasunaga et al. (2000) and Anan et al. (2001). Briefly, 0.1 g of the sample was digested in 1.5 ml of concentrated HNO3 in a Teflon PTFE tube in a microwave oven. The elemental content (V, Cr, Mn, Co, Cu, Zn, Rb, Sr, Zr, Mo, Ag, Cd, Sb, Cs, Tl and Pb) was determined with an inductively coupled plasma–mass spectrometer (ICP-MS) (Hewlett-Packard, HP-4500). Indium was used as the internal standard. Concentrations of Se and Hg were determined with a hydride generation atomic absorption spectrometer (Shimadzu, HVG-1 hydride system) and a cold vapor atomic absorption spectrometer (Sanso, Model HG-3000), respectively. All data were expressed on a dry weight basis (mg g 1 dry weight). Moisture content averaged 67.6% in liver, 75.2% in kidney and 68.8% in muscle of Baikal seals, 68.8% in liver, 75.7% in kidney and 70.1% in muscle of Caspian seals, and 65.5% in liver, 75.6% in kidney and 70.0% in muscle of northern fur seals. To guarantee the accuracy and precision of the methods, standard reference materials DORM2 (National Research Council Canada), NIES No. 13 (National Institute for Environmental Studies, Japan) and SRM1577b (National Institute of Standards and Technology, USA) were used. Recoveries of the elements ranged from 88.8–104%. 2.3. Statistical analyses One-half value of the respective limit of detection was substituted for those values below the limit of detection and used in statistical analyses. Data were tested for goodness of fit to a normal distribution using the chi-square test. Because concentrations of some trace elements did not follow a normal distribution pattern, non-parametric tests were used to compare different groups in the present study. Mann–Whitney’s U-test was employed to detect species, gender and tissue differences of trace element concentrations. Spearman’s rank correlation coefficient was used to measure the strength of the association between age and trace element concentration in tissues and between trace element concentrations in hair and internal tissues. Liberal P

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values with the potential for Type I error were used due to the following reasons: risk of missing a potential relationship (i.e. Type II error) and small sample size but many variables. Relationship of trace element concentrations in hair to those in internal tissues was also examined using regression analysis. A P value of less than 0.05 was considered to indicate statistical significance. These analyses were executed by the program STATCEL (OMS Publishing Inc.).

3. Results and discussion 3.1. Species and regional differences in trace element accumulation Biometry of these animals is shown in Table 1. Among these specimens, hair sample was not obtained for 4 individuals of Caspian seals, and kidney, muscle and hair samples were not available for 4 individuals of northern fur seals. Concentrations of trace elements in liver, kidney, muscle and hair of Baikal seals, Caspian seals and northern fur seals are shown in Table 2. For most of the elements, concentrations in tissues of northern fur seals were higher than those of other two species. Northern fur seals exhibited the highest concentrations of Cr, Co, Cu, Ag, Cd, Sb, Cs, Pb and Hg in liver (Mann–Whitney’s U-test, P < 0.05), Cr, Zn, Se, Mo, Cd and Cs in kidney (P < 0.01), V, Cr, Mn, Co, Cu, Se, Zr, Mo, Cd, Cs, Tl and Pb in muscle (P < 0.05), and V, Zn, Se, Sr, Mo, Ag, Cd and Hg in hair (P < 0.01) among the three species examined. In contrast, concentrations of Rb in liver, kidney and muscle (P < 0.001), Zr in liver and kidney (P < 0.001), Ag, Tl and Hg in kidney (P < 0.05), and Sb in hair (P < 0.01) were

highest in Baikal seals and Sr in liver, kidney and muscle (P < 0.001), Mn in liver (P < 0.001), Pb in kidney (P < 0.01), Zn and Zr in muscle (P < 0.001), and Co and Zr in hair (P < 0.001) were highest in Caspian seals. Concentrations of Zn, Se and Mo in liver, Mn in kidney, and Hg in muscle were not significantly different between northern fur seals and Caspian seals (P > 0.05), and were lowest in Baikal seals (P < 0.05). Levels of V and Tl in liver, V, Co and Cu in kidney, and Pb in hair were comparable in Baikal seals and northern fur seals (P > 0.05) and were lowest in Caspian seals (P < 0.05). Baikal and Caspian seals showed higher concentrations of Mn in hair than that of northern fur seals (P < 0.001). Because Hg levels in biota depend on trophic levels (Cabana and Rasmussen, 1994; Atwell et al., 1998), top predators in a marine ecosystem with a long food chain usually show high Hg concentrations. Although the length of the food chain in the Caspian Sea is relatively short (Karpinsky, 1992; Dumont, 1998), Hg level in Caspian seals is relatively high (Table 2). Similar results were also reported by Watanabe et al. (2002) and Anan et al. (2002). Increasing metal pollution from local sources to the Caspian Sea (Karpinsky, 1992) may be the cause of elevated Hg concentrations. In contrast, the Hg level was extremely low in Baikal seals as shown in Table 2. This is likely due to a short food chain and low ambient level of Hg in Lake Baikal. A very low concentration of Hg in the water of Lake Baikal was reported by Falkner et al. (1997). Although there are some pollution sources around Lake Baikal, contamination of trace elements is not pronounced (Beim et al., 2000; Grosheva et al., 2000; Munawar et al., 2000). High accumulation of Rb in tissues of Baikal seals was remarkable (Table 2). The hepatic Rb concentration in

Table 1 Biometry of Baikal seals, Caspian seals and northern fur seals Species

Location

Sex

Baikal seal (Pusa sibirica)

Lake Baikal

Caspian seal (Pusa caspica)

Caspian Sea

Northern fur seal (Callorhinus ursinus)

Sanriku, Japan

Male n=7 Female n=13 Total n=20 Male n=4 Female n=16 Total n=20 Male n=3 Female n=20 Total n=24

Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range Mean Range

Age (years)

Body length (cm)

Body weight (kg)

7.55.4 0.5–16.5 9.16.6 0.3–23.5 8.56.1 0.3–23.5 7.03.7 2.5–11.5 25.711.8 0.5–43.5 21.813.1 0.5–43.5 8.75.8 2.0–22.0 2.00.0 2.0–2.0 10.15.5 2.0–22.0

132 20 100–156 125 18 94–147 128 18 94.2–156 105 19 78.0–120 104 14 65.6–117 104 14 65.6–120 121 12 89.0–137 105 6 98.0–109 124 11 89.0–137

48.315.1 25.1–67.7 48.419.4 22.1–90.0 48.417.6 22.1–90.0 33.013.5 16.5–49.5 38.414.5 12.0–66.0 37.314.1 12.0–66.0 34.49.1 13.0–47.0 22.23.6 18.0–24.6 36.38.2 13.0–47.0

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Baikal seals (21.5 mg g 1 dry weight) is much higher than those of ringed seals (7.9 mg g 1 dry weight) and belugas (5.1 mg g 1 dry weight) from Alaska (Zeisler et al., 1993) and harbor porpoises (5.3 mg g 1 dry weight) from the USA (Mackey et al., 1995). A relatively high accumulation of Rb was also observed in the benthic organisms of Lake Baikal (Grosheva et al., 2000). However, the concentration of Rb in water is considerably lower in Lake Baikal (607 ng/kg; Falkner et al., 1991) than in the oceanic water (120,000 ng/kg; Nozaki, 1997). Although trophic transfer rate of Rb was known to be much lower than those of Hg and Cd in sea turtles (Anan et al., 2001), an opposite tendency was seen in the aquatic organisms of Lake Baikal (Grosheva et al., 2000). Hence, a unique bioaccumulation process of Rb might exist in Lake Baikal ecosystem. Table 2 Trace element concentrations (mean S.D. and range on mg g V Liver Baikal seal

Caspian seal

Northern fur seal

Kidney Baikal seal

Cr 1.81.5 0.12–4.6 (20/20)a 0.410.38 0.017–1.2 (20/20) 1.91.2 0.38–5.0 (24/24)

0.36 0.07 0.26–0.56 (20/20) 0.26 0.27 <0.001–0.87 (16/20) 1.5 0.5 0.48–2.3 (24/24)

Mn 7.852.23 4.11–12.4 (20/20) 20.36.1 11.6–31.7 (20/20) 12.82.3 7.65–18.8 (24/24)

1

3.2. Tissue distribution of trace elements Among the three soft tissues, concentrations of V, Mn, Se, Rb, Zr, Mo, Ag, Sb, Pb and Hg were highest in liver (Mann–Whitney’s U-test, P < 0.05), Co, Cu, Sr, Cd and Tl in kidney (P < 0.001), and Cs in muscle (P < 0.001) in Baikal seals (Table 2). In Caspian seals, levels of V, Mn, Cu, Se, Mo, Ag and Hg were highest in liver (P < 0.01), Co, Cd and Tl in kidney (P < 0.05), and Cs in muscle (P< 0.01). In northern fur seals, concentrations of V, Mn, Co, Cu, Se, Mo, Ag, Sb, Pb and Hg were highest in liver (P < 0.05), Co, Cd and Tl in kidney (P < 0.01), and Rb, Zr and Cs in muscle (P < 0.05). It is well known that Hg accumulates in liver and Cd in kidney of marine mammals (Thompson, 1990; Law, 1996). The present study suggests that, in

dry wt.) in tissues of Baikal seals, Caspian seals and northern fur seals

Co

Cu

0.066 0.024 12.84.5 0.037–0.12 6.27–26.4 (20/20) (20/20) 0.028 0.020 42.930.3 <0.001–0.091 11.9–140 (19/20) (20/20) 0.100 0.024 66.120.2 0.052–0.17 35.6–109 (24/24) (24/24)

0.320.23 0.43 0.17 3.630.56 0.13 0.05 0.070–1.0 0.20–0.93 2.68–5.00 0.060–0.23 (20/20) (20/20) (20/20) (20/20) Caspian seal 0.110.07 0.32 0.39 5.030.96 0.092 0.039 <0.001–0.19 <0.001–1.3 3.11–6.67 0.038–0.19 (19/20) (16/20) (20/20) (20/20) Northern fur seal 0.250.07 1.8 0.2 4.840.98 0.12 0.02 0.11–0.39 1.5–2.3 3.32–7.58 0.096–0.15 (20/20) (20/20) (20/20) (20/20) Muscle Baikal seal 0.0170.023 0.37 0.09 0.3960.181 0.014 0.018 0.001–0.108 0.23–0.59 0.178–0.813 0.005–0.090 (20/20) (20/20) (20/20) (20/20) Caspian seal 0.0050.016 0.05 0.10 0.6710.316 0.001 0.001 <0.001–0.072 <0.001–0.36 0.311–1.67 <0.001–0.006 (2/20) (6/20) (20/20) (2/20) Northern fur seal 0.0700.024 1.8 0.3 0.9640.192 0.027 0.007 0.032–0.12 1.2–2.8 0.680–1.51 0.015–0.045 (20/20) (20/20) (20/20) (20/20) Hair Baikal seal 1.00.8 0.94 0.88 1.810.91 0.059 0.048 0.063–2.5 0.28–4.0 0.498–3.60 0.002–0.15 (20/20) (20/20) (20/20) (20/20) Caspian seal 0.710.39 1.2 1.4 1.751.55 0.18 0.14 0.026–1.8 0.44–6.3 0.398–6.65 0.024–0.66 (16/16) (16/16) (16/16) (16/16) Northern fur seal 3.11.0 0.74 0.25 0.3490.295 0.041 0.018 1.5–5.5 0.28–1.4 0.086–1.05 0.015–0.078 (20/20) (20/20) (20/20) (20/20)

Zn

Se

Rb

Sr

12934 87.1–229 (20/20) 22654.9 133–338 (20/20) 25454 135–349 (24/24)

8.45.3 2.4–18 (20/20) 6042 6.9–144 (20/20) 7645 21–170 (24/24)

21.5 4.9 12.9–35.3 (20/20) 6.48 3.51 3.20–16.9 (20/20) 5.95 1.28 2.88–7.97 (24/24)

0.1040.028 0.065–0.176 (20/20) 0.6800.356 0.136–1.56 (20/20) 0.3380.169 0.115–0.707 (24/24)

22.89.3 13.8–53.6 (20/20) 17.15.7 11.4–32.0 (20/20) 21.76.1 10.7–32.6 (20/20)

14056 75.5–263 (20/20) 19955 114–350 (20/20) 22842 136–310 (20/20)

7.51.2 5.3–10 (20/20) 15 5 9.1–31 (20/20) 3610 23–68 (20/20)

12.0 3.0 7.77–19.8 (20/20) 4.47 2.29 2.16–11.1 (20/20) 6.02 0.88 4.67–7.72 (20/20)

0.2430.093 0.139–0.534 (20/20) 2.120.72 1.01–3.40 (20/20) 0.7300.247 0.324–1.38 (20/20)

3.510.92 2.14–5.90 (20/20) 3.631.13 2.08–5.95 (20/20) 7.550.96 5.51–9.17 (20/20)

74.921.6 45.3–120 (20/20) 14138 77.6–227 (20/20) 82.120.8 55.7–133 (20/20)

1.00 0.2 0.75–1.46 (20/20) 2.20.6 1.3–3.8 (20/20) 15 6 8.7–33 (20/20)

16.5 3.9 10.7–29.0 (20/20) 5.87 3.02 3.13–15.7 (20/20) 6.90 0.86 5.72–9.01 (20/20)

<0.001 <0.001 (0/20) 3.255.98 0.145–28.0 (20/20) 0.7130.349 0.108–1.32 (20/20)

5.371.97 3.61–13.3 (20/20) 33.859.7 3.30–219 (16/16) 6.131.79 4.05–10.7 (20/20)

10513 81.4–127 (20/20) 98.126.4 58.7–169 (16/16) 18655 150–401 (20/20)

2.30.7 1.4–3.8 (20/20) 2.31.9 1.1–9.0 (16/16) 6.12.0 3.4–11 (20/20)

0.0270.019 0.002–0.070 (20/20) 0.1950.713 <0.001–2.87 (12/16) 0.0040.005 <0.001–0.041 (11/20)

3.731.95 0.593–7.01 (20/20) 7.6512.1 0.256–50.5 (16/16) 22.45.8 14.5–36.0 (20/20)

(continued on next page)

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T. Ikemoto et al. / Environmental Pollution 127 (2004) 83–97 Table 2 (continued) Zr Liver Baikal seal

Mo

0.0500.076 0.8890.241 0.010–0.362 0.526–1.48 (20/20) (20/20) Caspian seal <0.001 2.04 0.49 <0.001 1.12–2.88 (0/20) (20/20) Northern fur seal 0.0030.003 1.82 0.36 <0.001–0.016 1.17–2.98 (23/24) (24/24) Kidney Baikal seal 0.0120.005 0.4310.130 0.005–0.028 0.248–0.677 (20/20) (20/20) Caspian seal 0.0080.035 0.6570.155 <0.001–0.157 0.485–1.01 (1/20) (20/20) Northern fur seal 0.0010.002 0.7860.131 <0.001–0.008 0.598–1.04 (2/20) (20/20) Muscle Baikal seal 0.0100.003 0.0180.005 0.006–0.018 0.013–0.034 (20/20) (20/20) Caspian seal 0.0040.016 0.0080.010 <0.001–0.071 <0.001–0.036 (1/20) (16/20) Northern fur seal 0.0170.048 0.0400.009 <0.001–0.221 0.020–0.063 (19/20) (20/20) Hair Baikal seal 0.0590.031 0.1230.185 0.013–0.141 0.049–0.877 (20/20) (20/20) Caspian seal 0.7961.15 0.0960.094 0.119–4.26 0.037–0.415 (16/16) (16/16) Northern fur seal 0.0480.025 0.4870.194 0.018–0.112 0.114–0.985 (20/20) (20/20) a

Ag

Cd

Sb

Cs

Hg

0.0390.049 0.728 0.506 0.005–0.20 0.011–1.68 (20/20) (20/20) 0.130.12 2.37 1.94 <0.001–0.40 0.225–6.23 (17/20) (20/20) 0.690.30 47.5 29.5 0.23–1.4 11.1–136 (24/24) (24/24)

0.010.00 <0.01–0.02 (9/20) 0.010.00 <0.01–0.01 (1/20) 0.010.01 <0.01–0.02 (21/24)

0.0090.005 0.001–0.019 (20/20) <0.001 <0.001 (0/20) 0.0040.003 0.001–0.014 (20/20)

0.010.00 0.070.02 6.72.9 <0.01–0.01 0.03–0.11 2.7–14 (2/20) (20/20) (20/20) <0.01 0.020.02 8.115.4 <0.01 <0.01–0.05 1.5–73 (0/20) (19/20) (20/20) <0.01 0.1080.016 4.41.4 <0.01 0.080–0.140 2.1–7.6 (0/20) (20/20) (20/20)

7.83 5.73 0.086–17.4 (20/20) 51.4 44.3 2.57–158 (20/20) 209 88 86.0–497 (20/20)

Tl

Pb

0.050.01 8.810.1 0.0100.005 0.0660.050 0.02–0.08 0.98–34 0.001–0.020 <0.001–0.187 (20/20) (20/20) (20/20) (19/20) 0.010.01 8574 0.0020.003 0.0060.024 <0.01–0.02 2.4–259 <0.001–0.014 <0.001–0.108 (15/20) (20/20) (6/20) (1/20) 0.100.02 165132 0.0090.004 0.1490.124 0.06–0.12 23–478 0.002–0.020 0.062–0.667 (24/24) (24/24) (24/24) (24/24) 0.0310.009 0.020–0.048 (20/20) 0.0070.007 <0.001–0.021 (11/20) 0.0140.003 0.010–0.019 (20/20)

0.0380.048 <0.001–0.198 (19/20) 0.1160.311 <0.001–1.09 (5/20) 0.0720.054 0.030–0.225 (20/20)

<0.001 <0.001 (0/20) <0.001 <0.001 (0/20) <0.001 <0.001 (0/20)

<0.001 <0.001 (0/20) 0.054 0.116 <0.001–0.525 (13/20) 0.539 0.286 0.142–1.16 (20/20)

0.010.00 0.100.03 0.920.51 < 0.001 0.0190.029 <0.01–0.01 0.05–0.17 0.27–2.3 < 0.001 <0.001–0.128 (1/20) (20/20) (20/20) (0/20) (18/20) <0.01 0.040.02 1.50.8 < 0.001 0.0180.050 <0.01 0.01–0.09 0.38–3.6 < 0.001 <0.001–0.208 (0/20) (20/20) (20/20) (0/20) (4/20) <0.01 0.1620.022 1.70.5 0.0030.001 0.0880.086 <0.01 0.126–0.196 1.2–3.0 0.002–0.005 0.005–0.263 (0/20) (20/20) (20/20) (20/20) (20/20)

0.0020.005 <0.001–0.019 (6/20) 0.0200.015 <0.001–0.052 (15/16) 0.140.04 0.088–0.24 (20/20)

0.094 0.065 <0.001–0.230 (19/20) 0.394 0.352 0.038–1.44 (16/16) 0.635 0.245 0.373–1.368 (20/20)

0.1700.118 0.027–0.558 (20/20) 0.08 0.11 <0.01–0.49 (15/16) 0.0740.017 0.034–0.111 (20/20)

<0.01 <0.01 (0/20) 0.010.04 <0.01–0.15 (3/16) 0.0050.001 <0.01–0.008 (1/20)

3.61.7 0.69–7.6 (20/20) 1.60.9 0.56–3.5 (18/18) 4.91.1 2.9–7.6 (20/20)

<0.001 <0.001 (0/20) 0.0010.001 <0.001–0.003 (1/16) 0.0020.003 <0.001–0.012 (11/20)

13.415.3 2.57–58.0 (20/20) 3.532.14 0.047–6.72 (16/16) 7.685.60 2.38–26.1 (20/20)

Number of samples with detectable concentration.

general, V, Mn, Se and Ag are predominantly accumulated in liver, Co and Tl in kidney, and Cs in muscle in pinnipeds. Species difference in tissue distribution of trace elements was also observed. Level of Cu was highest in kidney of Baikal seals (P < 0.001), whereas liver showed the highest Cu concentration in Caspian seals and northern fur seals (P < 0.001). Concentrations of Rb (P < 0.001) and Zr (P < 0.001) were highest in liver of Baikal seals, whereas these levels were highest in muscle of northern fur seals (Rb, P < 0.05; Zr, P < 0.01). These results might be attributed to the differences in metabolism and accumulation patterns among the species. For most of the elements, the concentration in hair was relatively low; however, Cr, Sr, Sb and Pb in Baikal seals (P < 0.01), V, Cr, Co, Sr, Zr, Sb and Pb in Caspian

seals (P < 0.05), and V, Sr, Zr, Sb and Pb in northern fur seals (P < 0.01) were highest in hair (Table 2). Until now, almost all the studies on hair of pinnipeds are limited to some elements, particularly Hg. To our knowledge, this is the first report on the multielement determination in hair of pinnipeds. Percentage of trace element burdens in individual tissues were calculated and shown in Table 3. Tissue distribution was similar in all the three species for Zn, Rb, Mo, Ag, Sb, Cs and Pb. Zinc, Rb and Cs are mainly distributed in muscle, Mo and Ag in liver, and Sb and Pb in hair of these animals. Saeki et al. (2001) also reported the highest Ag burden in liver of northern fur seals. Largest distribution of Zn in muscle was also reported for Weddell seals (Yamamoto et al., 1987) and

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T. Ikemoto et al. / Environmental Pollution 127 (2004) 83–97

Table 3 Distribution of trace elements burdens (%) in the muscle, liver, kidney and hair of Baikal seals, Caspian seals and northern fur seals Species Baikal seal

Tissue

Liver Kidneys Muscle Hair Caspian seal Liver Kidneys Muscle Hair Northern fur seal Liver Kidneys Muscle Hair a

TW (%)a V

Cr

Mn

Co

Cu

Zn

Se

Rb

Sr

Zr

Mo

Ag

Cd

Sb

6.4 0.7 87.5 5.4 16.6 1.9 69.8 11.7 5.0 1.1 80.6 13.3

6.7 0.8 82.2 10.3 21.8 1.7 11.5 65.0 5.3 1.3 87.6 5.8

54.3 3.3 30.6 11.8 80.9 2.2 10.2 6.7 43.1 3.4 51.0 2.5

29.4 5.0 42.3 23.3 16.5 5.5 1.5 76.5 16.0 3.8 64.9 15.3

19.5 4.1 68.4 8.0 54.6 2.1 15.4 27.9 31.4 2.1 58.4 8.1

9.2 1.2 82.9 6.7 24.1 2.5 65.8 7.6 12.5 2.3 64.4 20.8

40.3 3.2 49.7 6.8 87.4 1.8 9.6 1.2 30.0 2.2 63.6 4.2

8.6 0.5 90.9 0.0 20.6 1.6 77.7 0.1 5.4 1.1 93.5 0.0

3.7 1.0 0.2 95.1 2.6 1.0 63.9 32.5 0.5 0.2 14.9 84.4

27.7 0.5 50.7 21.1 0.1 0.0 0.3 99.6 1.3 0.1 49.0 49.6

68.7 3.8 19.6 7.9 92.7 3.1 1.7 2.5 47.4 4.2 15.3 33.1

85.7 1.8 10.2 2.3 91.1 0.0 1.1 7.8 69.6 0.1 0.7 29.6

44.2 52.4 0.3 3.1 27.3 66.8 3.0 2.9 51.3 38.9 8.5 1.3

4.3 3.3 35.1 50.8 1.1 0.3 0.5 2.4 15.4 0.1 34.7 95.9 52.2 31.8 5.8 60.7 0.3 10.3 2.0 93.0 7.5 7.0 92.9 41.2 0.3 0.8 1.2 0.9 9.6 0.1 30.6 89.5 5.3 42.1 2.4 61.1 2.3 0.9 7.1 97.3 5.2 3.4 84.9 16.4 0.7 0.4 0.8 0.3 4.7 0.1 28.2 95.3 10.3 72.5 7.1 66.2 0.5 4.5 6.4 92.1

62.5 1.0 8.9 27.6 48.5 1.2 2.5 47.8 21.0 0.5 9.2 69.3

Cs

Hg

Tl

Pb

TW (%): Percentage of weight of liver, kidney, muscle and hair in the total weight of all the four tissues.

Baikal seals (Watanabe et al., 1996). To our knowledge, there are no data on the tissue distribution of Rb, Mo, Sb and Cs in marine mammals. In a hawksbill turtle, the majority of the body burden of Rb was in muscle, and Mo in the liver (Anan et al., 2001), which is consistent with the results on pinnipeds in the present study. In contrast, for other trace elements, tissue distribution was largely different among the three species of pinnipeds (Table 3). The largest percentage in hair was found for Sb and Pb in all the species, Sr in Baikal and northern fur seals, Zr in Caspian and northern fur seals, and V in northern fur seals (Table 3). These results indicate that molting plays an important role in excretion of these elements in the pinnipeds. Similarly, high accumulation of Pb has been reported in the feathers of birds (Honda et al., 1986; Kim et al., 1998). 3.3. Relationships of trace element levels among tissues Relationship of trace element concentrations among liver, kidney and muscle was remarkably different among the trace elements in the pinnipeds (Table 4). For essential elements, Mn, Co, Cu, Zn and Se, most of the intertissue relationships was not significant, whereas correlation coefficients for non-essential elements, Rb, Cd, Cs and Hg, tend to be high in these pinnipeds. This is mostly due to the homeostatic control of the concentrations of essential elements in tissues but not for non-essential elements. Among the elements with significant intertissue correlation, Cd and Hg are classified into soft acids or chalcophile elements (Haraguchi, 1999). Because elements belonging to this group have high affinity to SH group in cysteine, these elements show high accumulation in tissues (Haraguchi, 1999). In contrast, Rb and Cs are present as free ions in the body (Wang et al., 1998) and therefore these elements generally show very similar behavior in all the tissues (Ando et al., 1989).

Furthermore, relationship of trace element concentrations between liver, kidney and muscle was substantially different among the species of pinnipeds (Table 4). In Baikal seals, significant positive correlations of V were found between liver and kidney (Spearman’s rank correlation, P < 0.001), liver and muscle (P < 0.001), and kidney and muscle (P < 0.05), whereas this relationship was not apparent in the other two species [significant correlation was found only between liver and kidney (P < 0.05) in Caspian seals]. For Rb, significant positive correlations between liver, kidney and muscle were observed for Baikal seals (P < 0.05) and Caspian seals (P < 0.001), whereas this was not true in northern fur seals. In the case of Cs, significant positive correlations between the three tissues were observed for Baikal seals (P < 0.05) and Caspian seals (P < 0.001), whereas northern fur seals exhibited a significant correlation only between kidney and muscle (P < 0.01). It seems likely that these species differences are due to the metabolism of elements and exposure levels. In contrast, significant positive correlations were found between Cd levels in liver and kidney (P < 0.05), Cs levels in kidney and muscle (P < 0.01) and Hg levels in liver and kidney (P < 0.01) for all the species examined. 3.4. Effect of age on accumulation of trace elements In all the three species, hepatic V, Se, Ag and Hg and muscular Hg levels increased with age (Table 5). Cadmium and Hg have strong affinity to SH group in cysteine as described above. Vanadium is also known to bind covalently to amino acids such as cysteine and histidine (Rehder and Jantzen, 1998). Thus, their biological half-life is rather long in animals, leading to agedependent increase in concentration. There have been a number of studies showing positive correlation between Hg concentration in the liver of marine mammals and

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T. Ikemoto et al. / Environmental Pollution 127 (2004) 83–97

Table 4 Spearman’s rank correlation coefficients of trace elements between muscle, liver and kidney of Baikal seals, Caspian seals and northern fur sealsab V Liver–Kidney

Baikal seal Caspian seal Northern fur seal Liver–Muscle Baikal seal Caspian seal Northern fur seal Kidney–Muscle Baikal seal Caspian seal Northern fur seal

Cr 0.720 0.562 0.387 0.820 0.235 0.387 0.550 0.342 0.215

*** * ***

*

Zr Liver–Kidney

Baikal seal Caspian seal Northern fur seal Liver–Muscle Baikal seal Caspian seal Northern fur seal Kidney–Muscle Baikal seal Caspian seal Northern fur seal a b

Mn

0.247 0.116 0.056 0.184 0.031 0.414 0.215 0.014 0.074

0.187 0.277 0.059 0.423 0.365 0.024 0.146 0.576 ** 0.164

Mo

0.116 nd 0.185 0.359 nd 0.080 0.137 0.053 0.293

Co 0.353 0.639 ** 0.484 * 0.328 0.062 0.129 0.248 0.354 0.188

Ag

0.456 0.316 0.245 0.165 0.447 0.202 0.585 0.700 0.153

*

* ** **

Cu 0.574 ** 0.528 * 0.214 0.265 0.194 0.235 0.044 0.078 0.021

Cd

0.666 ** nd 0.543 * nd nd nd nd nd nd

Sb

0.717 0.796 0.513 nd 0.728 0.877 nd 0.865 0.241

*** *** *

0.180 nd nd 0.240 nd nd 0.076 nd nd

*** *** ***

Zn

Se

0.456 * 0.230 0.481 * 0.206 0.113 0.168 0.388 0.041 0.053 Cs 0.635 0.921 0.412 0.805 0.900 0.402 0.716 0.931 0.590

Rb

0.439 0.054 0.069 0.468 * 0.262 0.574 * 0.271 0.614 ** 0.054 Hg

** ***

0.608 0.806 0.611 0.651 0.531 0.278 0.355 0.590 0.361

*** *** *** *** **

0.535 0.863 0.338 0.447 0.755 0.359 0.532 0.761 0.155

Sr * *** * *** * ***

Tl ** *** ** ** *

**

0.468 * 0.538 * 0.289 nd 0.318 0.144 nd nd 0.227

0.559 * 0.570 ** 0.281 nd 0.212 0.045 nd 0.048 0.205 Pb 0.159 0.131 0.155 0.028 0.541 * 0.062 0.081 0.068 0.048

nd: not determined because concentration was below the limit of detection in many samples. *, **, and *** indicate significance at the 5, 1, and 0.1% level, respectively.

Table 5 Spearman’s rank correlation coefficient between age and trace element concentrations in the liver, kidney, muscle and hair of Baikal seals, Caspian seals and northern fur sealsab V Liver

Kidney

Muscle

Hair

Baikal seal Caspian seal Northern fur seal Baikal seal Caspian seal Northern fur seal Baikal seal Caspian seal Northern fur seal Baikal seal Caspian seal Northern fur seal

Cr 0.757 0.602 0.905 0.804 0.588 0.207 0.568 0.338 0.328 0.167 0.284 0.104

Zr Liver

Kidney

Muscle

Hair

a b

Baikal seal Caspian seal Northern fur seal Baikal seal Caspian seal Northern fur seal Baikal seal Caspian seal Northern fur seal Baikal seal Caspian seal Northern fur seal

0.342 nd 0.014 0.155 0.302 0.182 0.347 0.259 0.041 0.092 0.331 0.022

*** ** *** *** ** **

0.410 0.580 ** 0.446 * 0.109 0.081 0.374 0.385 0.030 0.138 0.120 0.334 0.490 * Mo 0.257 0.198 0.528 ** 0.410 0.264 0.148 0.397 0.156 0.272 0.150 0.009 0.003

Mn 0.415 0.088 0.018 0.177 0.077 0.359 0.630 0.313 0.538 0.235 0.652 0.520

Co

** * ** *

Ag 0.522 0.537 0.871 0.582 nd 0.555 nd nd nd 0.072 0.091 0.575

Cu

0.749 *** 0.409 0.540 ** 0.411 0.223 0.004 0.345 0.073 0.011 0.068 0.247 0.284 Cd

* * *** ** *

**

0.747 0.114 0.842 0.805 0.369 0.168 nd 0.403 0.839 0.480 0.125 0.698

0.214 0.209 0.057 0.053 0.029 0.653 ** 0.708 *** 0.311 0.132 0.032 0.089 0.225 Sb

*** *** ***

*** * **

0.396 0.345 0.370 0.335 nd nd 0.100 nd nd 0.247 0.109 0.537 *

nd: not determined because concentration was below the limit of detection in many samples. *, **, and *** indicate significance at the 5, 1, and 0.1% level, respectively.

Zn 0.049 0.195 0.566 ** 0.015 0.406 0.078 0.169 0.298 0.612 ** 0.230 0.254 0.647 ** Cs 0.088 0.462 * 0.160 0.045 0.572 * 0.039 0.048 0.429 0.439 nd 0.069 0.320

Se 0.705 0.800 0.934 0.301 0.062 0.214 0.570 0.103 0.595 0.026 0.256 0.596

Rb ** *** ***

** **

**

Hg 0.631 0.735 0.923 0.413 0.737 0.684 0.524 0.479 0.488 0.546 0.446 0.032

0.401 0.194 0.228 0.296 0.199 0.222 0.569 ** 0.183 0.213 0.102 0.273 0.250 Tl

** *** *** *** ** * * * *

0.451 * 0.203 0.846 *** 0.220 0.593 ** 0.318 nd nd 0.290 nd 0.248 0.075

Sr 0.098 0.227 0.269 0.481 0.028 0.374 nd 0.194 0.109 0.481 0.520 0.480

*

* * *

Pb 0.404 0.345 0.036 0.057 0.049 0.259 0.308 0.009 0.110 0.143 0.581 * 0.412

90

T. Ikemoto et al. / Environmental Pollution 127 (2004) 83–97

age (e.g., Honda et al., 1983; Wagemann et al., 1996). Age (or body length)-dependent accumulation of V was also observed in the livers of harbor seals and grey seals from Swedish waters (Frank et al., 1992), belugas and ringed seals from Alaska (Mackey et al., 1996) and northern fur seals, Steller sea lions, harbor seals and ribbon seals from the North Pacific (Saeki et al., 1999). Similarly, positive correlations of hepatic Ag concentration with age (or body length) were reported for belugas from Alaska and pilot whales from the North Atlantic (Becker et al., 1995) and northern fur seals and Steller sea lions from the North Pacific (Saeki et al., 2001). Hence, it seems likely that V and Ag as well as Hg tend to increase with age in the livers of marine mammals. The age-dependent increase in hepatic Se concentration was most likely due to the interactions of Hg and Se in the liver (Ping et al., 1986; Wagemann et al., 2000; Yang et al., 2002b). Age-dependent accumulation of Cd has been occasionally reported in the tissues of marine mammals (e.g., Honda et al., 1983; Honda et al., 1987; Wagemann, 1989; Noda et al., 1995). Similar results were obtained for liver and kidney of Baikal seals and liver and muscle of northern fur seals in the present study (Table 5). Interestingly, age-dependent accumulation of Cd was not found in Caspian seals (Table 5), in spite of the fact that their accumulation levels in the liver and kidney were 3.3 and 6.6 times higher than those of Baikal seals, respectively (Table 2). However, Watanabe et al. (2002) reported age-dependent increase in Cd level in kidney and muscle of Caspian seals. This inconsistency is probably due to the difference in age distribution of seals between the two studies. According to Watanabe et al. (2002), Cd concentration increased with age until about 15 years and thereafter decreased gradually in the tissues of Caspian seals. In the present study also, age showed a significant positive correlation with Cd levels in liver (Spearman’s rank correlation, r=0.850, n=8, P < 0.05) and kidney (r=0.826, n=8, P < 0.05) in Caspian seals of< 21 years of age. In northern fur seals, although Cd levels in liver and muscle showed significant positive correlations with age, this relationship was not observed for kidney which had the highest Cd concentration (Table 5). As shown in Fig. 1, the renal Cd concentration was relatively constant, which was independent of age in northern fur seals. These results led to the decrease in renal–hepatic ratio of Cd in older individuals. The renal–hepatic ratio in northern fur seals of > 10 years of age (mean, 3.3; range, 1.8–4.6; n=11) was significantly lower than that of seals of < 10 years of age (mean, 6.2; range, 3.0–10.0; n=8) (Mann–Whitney’s U-test, P < 0.01) and was also lower than those of striped dolphins (mean, 4.25; range, 1.20–6.82), Steller sea lions (mean, 8.14; range, 4.23– 16.59), belugas (range, 3–5) and bottlenose dolphins (range, 10–15) (Honda and Tatsukawa, 1983). This low

renal–hepatic ratio of Cd might indicate renal tubular damage attributable to Cd exposure (Larison et al., 2000; Yasunaga et al., 2000) in northern fur seals. According to the World Health Organization (1992), the threshold concentration for renal damage in the human population is 200 mg g 1 wet weight in renal cortex. The critical concentration should be 100 mg g 1 wet weight (corresponding to 400 mg g 1 dry weight when moisture content is assumed to be 75%) when the concentration is expressed on whole kidney basis (Beyer, 2000). Also in wildlife studies, it was found that renal Cd concentration greater than 100 mg g 1 wet weight (corresponding to 400 mg g 1 dry weight) caused renal tubular damage and skeletal thinning in whitetailed ptarmigan (Larison et al., 2000). However, renal effects may develop even at lower concentrations. Nicholson and Osborn (1983) and Nicholson et al. (1983) reported kidney lesions in seabirds, puffins, Manx shearwaters and fulmar petrels with mean renal Cd levels of 114, 94.5 and 228 mg g 1 dry weight, respectively. Recent studies also suggest that the lowest level of Cd at which renal effects can be detected in a small percentage of human population is around 50 mg g 1 wet weight in the renal cortex (see review of Ja¨rup et al., 1998). This value would be 25 mg g 1 wet weight (corresponding to 100 mg g 1 dry weight) when the concentration is expressed on the whole kidney basis. Furthermore, it is recently reported that Cd would act as an endocrine disrupter at extremely low concentration in human (Stoica et al., 2000) and rainbow trout (Le Gue´vel et al., 2000). In the present study, the highest renal Cd concentration was 497 mg g 1 dry weight (113 mg g 1 wet weight) in northern fur seals (Table 2), exceeding these critical concentrations. However, Dietz et al. (1998) could not find any histopathological lesions in the kidneys of ringed seals although their renal Cd levels were very high (high Cd group contains 259–581 mg g 1 wet weight of Cd in the kidney). Further studies should clarify the possible adverse effects or adaptation mechanisms to the stress of Cd in northern fur seals. Baikal seals showed positive correlations between age and Ag concentration in both liver (Spearman’s rank correlation, P < 0.05) and kidney (P< 0.01) (Table 5). In contrast, northern fur seals showed a negative correlation between age and renal Ag level (P< 0.01), whereas a positive correlation was found between age and the hepatic Ag level (P < 0.001) (Table 5). This difference may be attributed to considerably higher accumulation of Ag in liver than in kidney in northern fur seals. In Baikal seals, the hepatic Ag level was 4.3 times the renal level, whereas this value was 173 in northern fur seals (Table 2). Notably, there are large differences in the rate of increase in the concentration of trace elements in tissues with age between the species (Fig. 1). These results might reflect the differences in the level of trace elements

T. Ikemoto et al. / Environmental Pollution 127 (2004) 83–97

91

Fig. 1. Variations of V, Ag and Cd concentrations (mg/g dry wt.) in the liver and kidney with age in Baikal seals, Caspian seals and northern fur seals.

among the three ecosystems and their diet composition. The large regression slope on age for Ag in liver and Cd in liver and kidney of northern fur seals is probably due to the fact that squids occupy about 30% of their diet (Pauly et al., 1998). It is well known that squids contain Cd and Ag at high concentration (Bustamante et al., 1998; Ichihashi et al., 2001) and thus marine mammals feeding on squids retain high Cd concentration (e.g., Honda et al., 1983; Noda et al., 1995). In contrast, both Baikal and Caspian seals feed mostly on fish (Miyazaki, 2001). Remarkably, the regression slope on age for V in liver and kidney was great for Baikal seals (Fig. 1). According to Falkner et al. (1997), V level in water is influenced by anthropogenic activities in the Lake Baikal; however, the level is seven times lower than normal value of seawater. Currently, no information is available on V level in the diet of Baikal seals. Two possibilities, (i) elevated V levels in the diet and (ii) specific metabolism of V in Baikal seals, are worthy of further investigation. It has been generally accepted that there is no sex difference in accumulation of trace elements in marine mammals (O’Shea, 1999). Interestingly, Watanabe et al. (1998) observed an apparent male–female difference in age-dependent accumulation of Hg and Cd in tissues of Baikal seals: Hg and Cd concentrations in adult males decreased with age, while those in adult females did not exhibit a declining trend. In contrast, the sex difference was not obvious in the Baikal seals of the present study.

This may be due to the smaller number of adults in our Baikal seal specimens. According to Watanabe et al. (1998), the sex difference in the metal accumulation was apparent after ten years of age. However, the number of Baikal seal samples of > ten years of age was only one for males and eight for females in the present study. Significant positive correlations between age and concentration in hair were found for some trace elements in these seals (Table 5). These results might reflect the association between the concentration in hair and those in internal tissues as described below. 3.5. Relationship of trace element concentrations in hair to those in internal tissues Hair is the promising sample to evaluate the level of trace elements in pinnipeds (Fossi and Marsili, 1997). Hence, the concentrations of trace elements in hair was determined in the three species to assess the suitability of hair in monitoring trace elements in pinnipeds. While sufficient information is not available, the levels in hair of Baikal seals, Caspian seals and northern fur seals seem to be comparable to those of other seals, polar bears and human (Table 6). Zinc levels in liver and kidney and Hg in muscle of Caspian seals, Hg in liver and kidney of Baikal seals, and Pb in liver of northern fur seals showed significant positive correlations with those in hair (Fig. 2). Even when the highest value is excluded, the relationship is also significant for Hg in liver of

Species

1

Location

dry wt.) of trace elements in hair of mammals Year

V

Cr

Mn

Co

Cu

Zn

Se

Rb

Sr

Zr

Mo

Ag

Cd

Sb

Cs

Southern Australia

Hg

Tl

Pb

9.59

Lake Baikal, Russia Lake Baikal, Russia White Sea, Russia

1992 1.0 1992 1990–1993

0.94 1.81

0.059 5.37 105 2.3

0.027 3.73

0.059 0.123 0.002 0.094 0.17

Caspian Sea Eastern Canada

1998 1972

Northern Germany

1988

Eastern Canada Eastern Canada Pangnirtung, Canada

1971 1972 1998

Eastern Canada

1972

2.3

Eastern Canada

1971

5.06

Ionian Sea, Greece

1986–1991

Sanriku, Japan

1997

Northeastern Japan

1990–1991 1.1

5.77 146

0.71 1.2

1.75

0.18

33.8 98.1 2.3

0.67 0.29 0.073 0.057 3.69 124 1.9

1.30 0.195 7.65

0.005 0.452

0.796 0.096 0.02

3.1

0.74 0.349 0.041 6.13 186 6.1

0.004 22.4

0.394 0.080 0.01

1.6 6.0

0.120

33.5

0.044 0.047 0.398 0.03

12.6 129 0.048 0.487 0.14

<0.01 3.6 3.5 0.78

1.56 1.8 <0.01 4.24

0.203

22.4

0.635 0.074 0.005

4.9

Bacher (1985) <0.001 13.4 1.42 0.001

3.53

0.60

This study Watanabe et al. (1998) Medvedev et al. (1997) This study Freeman and Horne (1973) Wenzel et al. (1993)

Sergeant and Armstrong (1973) Freeman and Horne (1973) <0.001 0.478 Unpublished data Freeman and Horne (1973) Sergeant and Armstrong (1973) 0.785 Yediler et al. (1993) 0.002

7.68

0.048

1972

Reference

This study Saeki et al. (1999), Saeki et al. (2001) Kim et al. (1974)

4.64

White Sea, Russia

1990–1993

14.1 178

1.45

4.26

1.58

Medvedev et al. (1997)

Lake Ladoga, Russia

1990–1993

22.5 324

0.960

17.5

6.34

Medvedev et al. (1997)

0.620

12.1

5.52

Hyvarinen and Sipila (1984)

Lake Saimaa, Finland Mar del Plata, Argentina

0.92 1995

Antarctic

Eastern Greenland Northwestern Greenland Svalbard

0.713

4.38 99.2

0.53

1984–1989 1978–1989 1980

19.16

Fossi et al. (1997)

0.773

Yamamoto et al. (1987)

4.58 8.38 1.98

Born et al. (1991) Born et al. (1991) Born et al. (1991)

20.0 0.856 5.6 4.2 0.379

Barbosa et al. (2001) Saeki et al. (1996) Suzuki et al. (1993) Takeuchi et al. (1982) Hac et al. (2000) Nowak (1998)

Human Aamazon, Brazil 1998 Eastern Papua New Guinea 1994 Japan 1986–1987 Japan 0.04 0.82 1.08 Northern Poland 1997–1998 Poland 1990–1994 0.60 2.41

15 189 0.64 0.084 12.7 183 1.18 0.44

7.96 129

0.39

0.33 0.61

0.10

4.99

T. Ikemoto et al. / Environmental Pollution 127 (2004) 83–97

Seal Australian fur seal (Arctocephalus pusillus) Baikal seal (Pusa sibirica) Baikal seal (Pusa sibirica) Bearded seal (Erignathus barbatus) Caspian seal (Pusa caspica) Grey seal (Halichoerus grupus) Harbour seal (Pusa vitulina) Harbour seal (Pusa vitulina) Harbour seal (Pusa vitulina) Harp seal (Pusa groenlandica) Harp seal (Pusa groenlandica) Hood seal (Cystophora cristata) Mediterranean monk seal (Monachus monachus) Northern fur seal (Callorhinus ursinus) Northern fur seal (Callorhinus ursinus) Northern fur seal (Callorhinus ursinus) Ringed seal (Pusa hispida hispida) Ringed seal (Pusa hispida ladogensis) Saimaa ringed seal (Pusa hispida saimensis) Southern sea lion (Otaria flavescens) Weddell seal (Leptonychotes weddellii) Bear Polar bear (Ursus maritimus)

92

Table 6 Comparison of the mean concentrations (mg g

T. Ikemoto et al. / Environmental Pollution 127 (2004) 83–97

93

Fig. 2. Relationship between metal concentrations (mg/g dry wt.) in hair and internal tissues of Baikal seals, Caspian seals and northern fur seals.

Caspian seals and Hg in muscle of Caspian seals. These results suggest that hair is useful for assessing the levels of trace elements, especially for Hg, in internal tissues of these seals. Watanabe et al. (1996) also found significant positive correlations between Hg levels in hair, and muscle, liver and kidney of Baikal seals. Medvedev et al. (1997) reported significant positive correlations between Cd levels in hair and liver of Ladoga ringed seals and Cd levels in hair and kidney of ringed seals of the White Sea. Using the data of Sergeant and Armstrong (1973), significant positive correlation was observed between Hg levels in hair and liver of harbour seals from eastern Canada (Spearman’s rank correlation, r=0.762, n=8, P < 0.05). Bacher (1985) reported a positive correlation between Hg levels in hair and liver of Australian fur seals. Born et al. (1991) reported that Hg concentration in hair was correlated positively with Hg concentrations in liver and kidney of polar bears from Greenland. Mierle et al. (2000) found positive correlations of Hg between hair, and liver and brain of otters from Ontario, Canada. Regression analysis also showed significant positive correlations between Hg levels in hair, and liver [(Hg in hair)=0.118(Hg in liver)+2.40, (r=0.910, n=15, P < 0.0001)], kidney [(Hg in hair)=3.05(Hg in kidney)+0.099, (r=0.934, n=13, P < 0.0001)] and muscle [(Hg in hair)=6.31(Hg in muscle)+0.429, (r=0.962,

n=15, P < 0.0001)] in 15 populations of seals (Fig. 3). The relationships excluding the highest two mean values of southern sea lion [liver, 261.2 mg g 1 wet weight; kidney, 9.87 mg g 1 wet weight; muscle, 4.74 mg g 1 wet weight; hair, 33.30 mg g 1 dry weight; Fossi et al., 1997 (dry weight basis concentration was converted to wet weight basis concentration assuming that moisture content was 70%)] and ringed seal (liver, 35.40 mg g 1 wet weight; kidney, 6.15 mg g 1 wet weight; muscle, 3.22 mg g 1 wet weight; hair, 17.5 mg g 1 dry weight; Medvedev et al., 1997) were also significant between Hg levels in hair, and liver [(Hg in hair)=0.077(Hg in liver)+2.32, r=0.697, n=13, P < 0.01] and muscle [(Hg in hair)=3.81(Hg in muscle)+1.78, r=0.570, n=13, P < 0.05] but not significant between hair and kidney. These results suggest that hair samples may be used for monitoring Hg in seals at least at the population level. In general, trace elements in hair are derived both from deposition into growing hair from circulating elements in the blood and from external deposition onto the surfaces of hair in pinnipeds. Hence, the levels in hair may be related to the ambient levels (in water and soil) and/or exposure levels in the diet of pinnipeds. The strong positive correlation between Hg concentrations in hair and internal tissues (Figs. 2 and 3) suggests that the contribution of deposition from blood is larger than that of the external deposition on hair surfaces for Hg in

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Fig. 3. Relationship between Hg concentrations (mg/g wet wt.) in hair, and liver, kidney and muscle of various seal species; Baikal seal (this study and Watanabe et al., 1998), Caspian seal (this study), northern fur seal (this study), ringed seal (Lake Ladoga and White Sea) (Medvedev et al., 1997), harp seal (Freeman and Horne, 1973), grey seal (Freeman and Horne, 1973), Australian fur seal (Bacher, 1985), hood seal (Sergeant and Armstrong, 1973), Weddell seal (Yamamoto et al., 1987), and southern sea lion (Fossi et al., 1997). Dry weight basis concentration in southern sea lion (Fossi et al., 1997) was converted to wet weight basis assuming that moisture content was 70%.

the hair of pinnipeds. Since available information on the trace elements in hair of pinnipeds is extremely sparse, further work is needed to establish an unambiguous relationship between Hg concentrations in hair and internal tissues at the population level.

4. Conclusions The present study revealed the species difference in accumulation of trace elements in Baikal seals, Caspian seals and northern fur seals. For most of the elements, northern fur seals showed the highest concentrations in their tissues, whereas the high accumulation of Rb in Baikal seals and Sr in Caspian seals were remarkable. On the other hand, high accumulation of V, Mn, Se and Ag in liver, Co and Tl in kidney, and Cs in muscle was a characteristic common to all the three species. All the three species showed significant positive correlations between age, and concentrations of V, Se and Ag in liver and Hg in liver and muscle. These data may provide a basis for evaluation of species difference in the susceptibility to trace elements. Furthermore, this study determined the multielement concentrations in hair of pinnipeds for the first time. Concentrations in hair were positively correlated with Zn levels in liver and kidney and Hg in muscle of Caspian seals, Hg in liver and kidney of Baikal seals, and Pb in liver of northern fur seals. When the data in the present study and other studies were combined and used for regression analysis, significant positive correlations were found between Hg levels in hair, and liver, kidney and muscle from various species of pinnipeds. This indicates the potential utility of hair samples for monitoring of Hg in seals at the population level. However, this result is inconclusive

because of the insufficient data on pinniped hair, and warrants further investigation.

Acknowledgements We are grateful to Prof. An. Subramanian of Annamalai University, India for critical reading of the manuscript. This study was supported by Grants-in-Aid for Scientific Research (A) (No. 12308030) from Japan Society for the Promotion of Science, and for Scientific Research on Priority Areas (A) (No. 13027101) and ‘‘21st Century COE Program’’ from the Ministry of Education, Culture, Sports, Science and Technology, Japan.

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