Arch Environ Contam Toxicol DOI 10.1007/s00244-015-0191-2
Transplacental Transfer of Polychlorinated Biphenyls, Polybrominated Diphenylethers, and Organochlorine Pesticides in Ringed Seals (Pusa hispida) T. M. Brown1,2 • P. S. Ross3 • K. J. Reimer4
Received: 11 March 2015 / Accepted: 5 June 2015 Ó Springer Science+Business Media New York 2015
Abstract The transplacental transfer of persistent organic pollutants in marine mammals takes place at a formative developmental period, thereby exposing the fetus to endocrine-disrupting compounds. We evaluated the transplacental transfer of polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs), and organochlorine pesticides (OCPs) in five pregnant ringed seals in Northern Labrador, Canada. PCBs, PBDEs, and OCPs were transferred from the mother to the fetus with average concentrations in the fetuses ranging from 0.3 ng/g lipid weight (lw) of mirex to 94 ng/g lw of PCBs. The average percent transferred to the blubber in the fetus was very low with \0.02 % for each of the compounds studied. Based on relationships observed, transfer for full-term fetuses is estimated to range from 0.03 to 0.27 %. Log Kow explained the transfer of PCBs (r2 = 0.67, p \ 0.001) and OCPs (r2 = 0.62, p \ 0.001) with those PCB congeners and OCP compounds having a log Kow of \6.0 and 4.6, respectively, because they are preferentially transferred to the fetus. Adult females transferred a contaminant mixture to their fetuses, which correlated with estimated fetal age
& T. M. Brown [email protected] 1
Raincoast Conservation Foundation, P.O. Box 2429, Sidney, BC V8L 3Y3, Canada
2
Present Address: Memorial University of Newfoundland, St. John’s, NL A1B 3X9, Canada
3
Ocean Pollution Research Program, Vancouver Aquarium Marine Science Center, P.O. Box 3232, Vancouver, BC V6B 3X8, Canada
4
Environmental Sciences Group, Royal Military College of Canada, P.O. Box 17000, Stn Forces, Kingston, ON K7K 7B4, Canada
(p \ 0.001; r2 = 0.697), with younger fetuses showing a greater proportion of compounds with low Kow compared with later-term fetuses. The implications for the prenatal exposure to these developmental toxicants remains unknown because current toxicity thresholds in marine mammals have only been derived from juveniles or adults.
Persistent organic pollutants (POPs)—such as polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs), and organochlorine pesticides (OCPs)—are lipophilic compounds that can bioaccumulate to very high concentrations in many marine mammals (Muir et al. 2000). Ringed seals (Pusa hispida) are vulnerable to heightened exposure to these compounds as a result of their high trophic level, large lipid reserves, and long life span (Boon et al. 1992; Nyman et al. 2003). Exposure to these pollutants has been associated with endocrine disruption, reproduction impairment, and immunotoxicity in ringed seals and other marine mammal species (Helle et al. 1976a, b; Ross et al. 1996; Routti et al. 2010; Brown et al. 2014b). Ringed seals inhabiting the Labrador coast are exposed to elevated levels of PCBs due to a combination of longrange transport from distant sources as well as a significant local PCB source associated with a military radar station in Saglek Bay (Brown et al. 2014a). Consequently, ringed seals from this region have PCB levels that are higher than anywhere else in the Canadian Arctic, and are at heightened risk for toxic effects including alteration of vitamin A levels and its receptor, altered thyroid hormone physiology and receptor function, and impaired immune function (Brown et al. 2014a; Mos et al. 2007). Recently, changes in hepatic mRNA transcript levels for genes that play a critical role in endocrine and immune function in ringed seals
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from this area have been associated with PCBs (Brown et al. 2014b). Female pinnipeds are able to lower their POP burden by transferring a proportion of their contaminant load to offspring by way of placental and lactational transfer (Gaden et al. 2012). A number of studies have shown that lactation is the dominant route for this transfer due to the mobilization of lipids and associated contaminants to synthesize milk (Wolkers et al. 2004; Debier et al. 2003; Sormo et al. 2003; Wolkers et al. 2002; Addison and Brodie 1987; Pomeroy et al. 1996). However, fewer studies have described the transplacental transfer of these compounds in pinnipeds (Donkin et al. 1981; Wang et al. 2012; Greig et al. 2007) with no studies describing the transfer dynamics in ringed seals. Such data are important because prenatal exposure to these toxic compounds occurs during critical phases of fetal development. Further, prenatal exposure to POPs has been shown to impair mammalian fetal development (Jacobson and Jacobson 2002; Gauger et al. 2004) and has been associated with intrauterine fetal growth retardation in humans (Siddiqui et al. 2003). The present study examines the transplacental transfer dynamics for PCBs, PBDEs, and OCPs in free-ranging ringed seals. The objective of the study was to characterize the transplacental transfer of these POPs in five mother– fetus ringed seal pairs and to investigate changes in the transfer of these compounds at different stages of the gestation period.
Materials and Methods Sample Collection Blubber samples from adult female ringed seals (n = 5) were obtained from Inuit hunters along the Labrador coast in 2008 and 2009. Full-depth blubber samples over the sternum were taken from the mothers and their near-term fetuses. All samples were placed in aluminum foil and Whirl Pak bags and frozen at -20 °C until analyzed for OCPs within 1 year of sample collection. Length, mass, and blubber thickness were measured on each dead animal, and the maternal age was determined by Matson’s Laboratory, USA, by longitudinally thin-sectioning a lower canine tooth and counting the annual growth layers in the cementum using a compound microscope and transmitted light (Stewart et al. 1996). Fetus age (in days) was estimated from fetal weight using relationships described in Lyderson (1995). For all samples collected, appropriate permits and community approval were obtained from the Nunatsiavut Government, Nunatsiavut Health, and Environment Review Committee and Department of fisheries and oceans Canada.
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Chemical Analysis The following were measured in ringed-seal blubber samples by the Laboratory of Expertise in Aquatic Chemical Analysis (Fisheries and Oceans Canada): concentrations of 91 PCB congeners (underlined is the dominant congener for the coeluting PCBs), (4, 5/8, 6, 16/32, 18, 20, 22, 26, 28, 31, 33, 40, 42/68, 43/49, 44, 47/48/75, 52, 60, 63, 64/ 71, 66, 70/76, 74, 85, 86/97, 87, 90, 91, 92, 95, 99, 101, 105, 107/108, 110, 113, 114, 111/115, 118, 119, 123, 124, 126, 128, 129, 130, 132, 133, 135, 137, 138/163/164, 139, 141, 144, 146, 147, 149, 151, 153, 154, 156, 157, 158/160, 162, 167, 168, 170/190, 171, 172/192, 174, 175, 177, 178, 180, 183, 185, 187, 189, 191, 193, 194, 195, 196/203, 197, 198, 201, 202, 205, 206, 208, and 209); 15 organochlorine pesticides (dichlorodiphenyl dichloroethylene [p,p’-DDE], dichlorodiphenyl dichloroethane [p,p’-DDD], dichlorodiphenyl trichloroethane [p,p’-DDT], a-hexachlorocyclohexane [a-HCH], [b-HCH], trans- and cis-chlordane, trans- and cis-nonachlor, dieldrin, 1,2,4,5-tetrachlorobenzenes [1,2,4,5-TetraClBz], 1,2,3,4-TetraClBz, pentaClBz, hexaClBz, mirex); and 6 PBDE congeners (47, 100, penta8, 99, 154, 153) and percentage lipid. The extraction and clean-up procedures, instrumental analysis, and conditions, and quality-assurance/quality-control criteria used for contaminant analysis are described elsewhere (Ikonomou et al. 2001; Ross et al. 2000). All PCB, OCP, and PBDE data were blank-corrected. The sample batch for PCBs, OCPs, and PBDEs included a procedural blank, a replicate, and either a certified reference material (herring) or a standard reference material (ringed seal) sample (Ikonomou et al. 2001). Reference material data met established laboratory criteria of fewer than ±2 SDs before batch data were deemed acceptable. Total concentrations for PCBs, DDT, hexachlorocyclohexane, chlordanes, chlorobenzenes, and PBDEs were calculated as the sum of the concentrations of the peaks that were detectable in C70 % of the seal samples. Where congeners were undetectable, the detection limit was substituted with a random number between the detection limit and zero. Replacing an undetectable value with a random number influences the PCA algorithm less than an arbitrary substitution such as the detection limit or one half of the detection limit (Ross et al. 2004). Congeners that were detected in \70 % of the samples were not included in calculations. All results are expressed on a lipid-weight (lw) basis. P Hereinafter, PCBs refers to the sum of the 91 PCB P congeners; DDT refers to the sum of p,p’-DDE, p,p’P DDD and p,p’-DDT; HCH refers to the sum of the aP and b-hexachlorocyclohexane, chlordanes refers to the sum of trans- and cis-chlordane and trans- and cis-nonaP chlor, ClBz refers to the sum of 1,2,4,5-TetraClBz,
Arch Environ Contam Toxicol
1,2,3,4-TetraClBz, pentaClBz and hexaClBz and refers to the sum of the 6 PBDE congeners.
P
PBDEs
Data Analysis The relative percent blubber (to total body weight) was estimated using an equation described in Ryg et al. (1990): relative percent blubber ðB %Þ pffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ 4:44 þ 5693 length in m=body mass in kg blubber thickness in m The total contaminant blubber burden, expressed in micrograms, (Borrell and Anguilar 2005) was calculated using the following equation: POP burden ¼ body weight relative percent blubber lipid content POP concentration The contaminant transfer rate was defined as the ratio of fetal blubber burden to the combined fetal and maternal burden. The partition ratio was calculated as the ratio between fetal to maternal blubber PCB, PBDE, and OCP lw concentrations for all congeners and compounds. Principal components analysis (PCA) was used to elucidate differences in PCB patterns in mother and fetus ringed seals. Samples were standardized to the total concentration before PCA to remove artifacts related to concentration differences between samples. The centered log ratio transformation (division by the geometric mean of the concentration-normalized sample followed by log transformation) was then applied to these data sets to produce a data set that was unaffected by negative bias or closure (Ross et al. 2004). Data were autoscaled before PCA. Linear regression analysis was used to assess the relationships between PCA projections and log octanol–water partition coefficient (Kow) values (a proxy for particle affinity) and fetus weight. Log Kow values for the PCB and PBDE congeners and OCP compounds were taken from Hawker and Connell (1988); Braekevelt et al. (2003) and Mackay et al. (1992) respectively.
Results and Discussion Contaminant Concentrations in Mothers and Fetuses The transplacental transfer of POPs in ringed seals was investigated by analyzing the blubber of mother–fetus pairs at different times of the 241—active day gestation period (Lyderson 1995). The mean age of the adult females was 14 ± 4 years (Table 1). Fetuses ranged from 1.5 to 6 months old (Table 1). The lipid content in the five adult
females was similar and did not vary (p [ 0.05) with age. In contrast, lipid content increased (p = 0.07; r2 = 0.094) with the age of the fetuses (Table 1). This observation is consistent with previous findings for lipid content and fetal age in California sea lions (Zalophus californianus) (Greig et al. 2007). P Concentrations of OCPs and PBDEs (lw) measured in the present study did not differ (p [ 0.05) withP fetal or maternal age. The mean concentration of PCBs, P DDTs, and p,p’-DDE was threefold greater in the mothers than in their fetuses (Table 2). The mean concentration of p,p’-DDT was ninefold greater in the mothers than in their fetuses (Table 2). Mean concentrations of P PBDEs and other OCPs did not differ (p [ 0.05) between mother and fetus. The top five contaminants in the adult females were ranked as follows: P P P P PCBs [ DDTs [ chlordanes [ HCHs [ dieldrin. The top five contaminants in the fetuses were ranked P P P P as follows: PCBs [ DDTs [ HCHs [ chlorP danes [ dieldrin. HCHs ranked third in fetuses comP pared with chlordanes, which ranked third in mothers. P This observation is consistent with HCHs having a greater percentage of transfer (0.01) compared with the P percentage of transfer (0.004) calculated for chlordanes (Table 2). These results are also consistent with the transplacental transfer being greater for compounds of low molecular-weight and reduced chlorination or bromination (e.g., HCHs) than for those with high molecular weight (e.g., chlordanes) (Greig et al. 2007; Ando et al. 1985). For all compounds measured in the present study, the average percent transfer was greatest for 1,2,3,4-TetraClBz (0.02 %) and lowest for mirex (0.002 %) (Table 2). As expected, the blubber percent transfer in the ringed-seal fetuses in the present study increased with fetal age (p \ 0.05) and weight (proxy for age) (p \ 0.05) for all compounds. Using the slope calculated from the relationship between these two compounds and weight (Fig. 1), we estimate that the percent transferred to the blubber of a fullterm ringed-seal fetus (4.5 kg [Smith 1987; Hammill 1987]) to range from only 0.03 to 0.27 % of the maternal blubber burden. We consider this to be a conservative estimate based on a linear relationship extending through the active gestation period. The estimated transfer is consistent with a previous estimate for PCBs and DDT (\1 % of the maternal blubber burden) or a full-term grey seal fetus (Donkin et al. 1981). This very limited transfer to the fetal blubber likely reflects, in part, the limited subcutaneous fat in the pinniped fetus (Donkin et al. 1981). Although to our knowledge no studies have documented the lactational transfer of contaminants in ringed seals, the documented transfer of POPs in other phocids suggests that milk is responsible for the bulk of maternal transfer from mother to offspring (Addison and Brodie 1977; Debier
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Arch Environ Contam Toxicol Table 1 Length, weight, blubber thickness, estimated age, and percentage lipid (blubber) for five mother–fetus ringed-seal pairs collected from northern Labrador, Canada ID
Length (cm)
Mass (kg)
Blubber thickness (cm)
Estimated age of mother (year) and fetus (day)
Lipid (%)
M1
127
59
6.0
19
95
M2 M3
113 126
66 65
4.8 5.5
10 18
95 94
M4
135
82
6.0
13
96
M5
121
66
5.0
10
93
Mean ± SD
124 ± 8
68 ± 9
5.5 ± 0.6
14 ± 4
94 ± 1
F1
15.8
0.228
0.50
64
2.4
F2
20.1
0.363
0.70
92
2.3
F3
14.7
0.127
0.40
43
0.7
F4
26.2
0.775
0.32
170
5.7
F5
19.8
0.297
0.52
79
1.9
Mean ± SD
19.3 ± 5
0.358 ± 0.249
0.49 ± 0.14
90 ± 49
2.6 ± 1.9
Mother
Fetus
Table 2 Mean (±SE) PCB, PBDE, and OCP concentrations in blubber, estimated blubber burdens, and percentage of total transfer from mother to fetus in ringed seal mother–fetus pairs Mother concentration (ng/g lw)
Fetus concentration (ng/g lw)
Mother blubber burden (lg)
286 ± 50
94 ± 7.1a
8520 ± 1480
0.26 ± 0.11
0.004
5.4 ± 1.7
5.5 ± 1.9
154 ± 44
0.008 ± 0.002
0.006
115 ± 30
37 ± 6.5a
3390 ± 857
0.08 ± 0.03
0.004
p,p’-DDE
103 ± 27
35 ± 6.4
a
3050 ± 790
0.0006 ± 0.0001
0.004
p,p’-DDD
2.7 ± 0.7
1.0 ± 0.2
78 ± 20
0.003 ± 0.001
0.005
p,p’-DDT P HCH
9.1 ± 3.9
1.1 ± 0.3a
258 ± 102
0.003 ± 0.001
0.003
30 ± 5.2
27 ± 2.4
887 ± 157
0.07 ± 0.03
0.01
a-HCH
20 ± 3.3
19 ± 1.8
585 ± 102
0.05 ± 0.03
0.01
b-HCH P Chlordanes
10 ± 2.0 44 ± 16
7.9 ± 1.2 16 ± 5.0
302 ± 57 1240 ± 421
0.02 ± 0.01 0.03 ± 0.01
0.01 0.004
P PCBs P PBDEs P DDT
Fetus blubber burden (lg)
Transfer (% of total burden)
t-Chlordane
1.4 ± 0.5
0.4 ± 0.1
39 ± 14
0.0006 ± 0.0001
0.003
c-Chlordane
7.7 ± 2.6
2.2 ± 0.6
222 ± 68
0.005 ± 0.002
0.004
t-Nonachlor
30 ± 12
11 ± 4.2
861 ± 318
0.02 ± 0.01
0.004
c-Nonachlor
4.0 ± 1.0
1.7 ± 0.3
114 ± 26
0.004 ± 0.001
0.005
Dieldrin P ClBz
21 ± 2.5
15 ± 1.5
632 ± 87
0.03 ± 0.01
0.006
9.1 ± 1.2
10 ± 1.2
277 ± 51
0.03 ± 0.02
0.01
1,2,4,5-TetraClBz
1.8 ± 0.5
2.0 ± 0.5
54 ± 17
0.004 ± 0.002
0.01
1,2,3,4-TetraClBz
0.4 ± 0.1
0.7 ± 0.2
12 ± 3.5
0.001 ± 0.001
0.02
PentaClBz
2.0 ± 0.5
2.3 ± 0.5
61 ± 17
0.005 ± 0.002
0.01
HexaClBz
4.9 ± 0.7
5.2 ± 1.2
150 ± 29
0.02 ± 0.01
0.01
Mirex
2.4 ± 1.1
0.3 ± 0.1
68 ± 29
0.0007 ± 0.0002
0.002
a
Indicates significant difference between mother and fetus
et al. 2003; Wolkers et al. 2004). Results from the present study support the idea that milk represents the dominant route of transfer from a mother to her offspring.
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The percent transfer calculated for PCBs (0.004 %) and PBDEs (0.006 %) in the present study (Table 2) is 1833and 2750-fold lower than the average percent transfer
Arch Environ Contam Toxicol
Fig. 1 Percent transfer of 1,2,3,4-TetraClBz and mirex from mother to fetus in ringed seals correlated with fetal weight
reported for PCBs and PBDEs in beluga whale mother– fetus pairs (Desforges et al. 2012). This large difference in transfer between ringed seals and beluga whales is likely due to the younger age of the sampled ringed-seal fetuses (3 ± 1.5 months) and a lower blubber lipid content (2.6 ± 1.9 %). The arctic beluga whale fetuses were approximately 10 months old (Desforges et al. 2012) and had a mean percent lipid of 83 ± 4 % (J. P. Desforges, personal communication). Partition Ratios in Mother–Fetus Pairs We calculated the fetal-to-maternal blubber PCB, PBDE, and OCP concentration ratios for all congeners and compounds. The average trend for PCBs showed a lower proportion of the heavier congeners in fetuses compared with their mothers such that congeners with three or fewer chlorine atoms were being preferentially transferred to the fetus (Fig. 2). No trend was found among the PBDE congeners (data not shown). However, the average partition ratio was lowest for PBDEs 47 and 153 and greatest for PBDE 99. The average partition-trend for the OCPs showed a greater proportion of compounds that have a lower log Kow value (e.g., HCHs and ClBzs) appearing in the fetus than in the mothers (Fig. 2). To further explore the transfer dynamics between mother and fetus, partition ratios for the different contaminants were plotted against log Kow (Fig. 3). The results showed a negative relationship between log Kow and the partition ratios for PCB congeners (r2 = 0.67, p \ 0.001) and OCPs (r2 = 0.62, p \ 0.001). No relationship (p = 0.79) was found between log Kow and the partition ratios for PBDE congeners. Similar log Kow-based partitioning relationships have been observed in mother–fetus pairs for PCB congeners and for DDT isomers in other species (Greig et al. 2007; Desforges et al. 2012). However, our observation of no relationship between log Kow
and the partitioning ratio for PBDE congeners differed from findings in arctic beluga whale (Delphinapterus leucas) mother–fetus pairs. The low number of PBDE congeners (n = 6) detected in the present study may explain the lack of relationship. The log Kow values at which concentrations of PCB congeners and OCP compounds were in equilibrium in mothers and their fetuses (i.e., partition ratios were zero) were 6.0 and 4.6, respectively (Fig. 3). Partition values \0 represent contaminants that are being preferentially retained by the mother, whereas at greater than these values they would be readily transferred to the fetus. The intersectional log Kow value for PCBs (6.0) in the present study is similar to that reported for the transplacental transfer of PCBs (6.5) in arctic beluga whales (Desforges et al. 2012) as well as for lactational transfer of PCBs in harbour seals (Wolkers et al. 2004). Overall, these results support previous reports of more efficient transfer to the fetus for the lower-molecular weight chemicals compared with highermolecular weight compounds (Borrell and Anguilar 2005; Tanabe et al. 1982; Aguilar and Borrell 1994). This physicochemical variation in transfer efficiencies can be explained by differences in the blood transport mechanisms among the individual congeners and OCP compounds, whereby the high molecular-weight congeners or compounds have a lower affinity to polar lipids in the blood and placenta compared with the nonpolar lipids in the maternal blubber (Desforges et al. 2012; Tanabe et al. 1982; Addison and Brodie 1987). Transfer of Contaminants Varies with the Stage of Gestation To assess whether the transfer of PCBs, PBDEs, and OCPs changed over the course of the gestation period, we compared the contaminant patterns in the mothers and fetuses. The first PC (t1; p1: 44.6 %) clearly differentiates the
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Fig. 2 Mean ± SE of PCB congener and OCP compound partition ratios (lipid weight) between mother and fetus ringed seals. Partition ratios were calculated as the blubber concentration in the fetus divided by that in the mother and were logarithmically transformed
Fig. 3 Mean partition ratios plotted against logarithmic log Kow for PCB congeners and OCP compounds in ringed seal mother–fetus pairs. Partition ratios were calculated as the blubber concentration in
the fetus divided by that in the mother and were logarithmically transformed. The dashed line represents partition parity
mothers from the fetuses, as mothers are dominated by a greater proportion of the heavier (more chlorinated) congeners and the more lipophilic compounds (e.g., chlordanes) (Fig. 4; Table 1). The younger fetuses have a greater proportion of the less chlorinated and brominated congeners and the less lipid-soluble compounds, as illustrated by their association with these lighter contaminants in the PCA (Fig.4; Table 1). The distance on the t1 axis (the samples scores of the first PC) for mother–fetus pairs
correlated with fetal age (p \ 0.001; r2 = 0.697) and fetal weight (a proxy for age) (p \ 0.001; r2 = 0.736). This suggests that a later-term fetus has a profile that is more similar to that of its mother compared with a younger-term fetus. Furthermore, log Kow of the PCBs, PBDEs, and OCPs correlated with p1 (the variable loadings of the first PC; p \ 0.001; r2 = 0.47). This is consistent with previous observations whereby the transfer of POPs varied with gestational stage in California sea lions with younger
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life-history bioaccumulation models for ringed seals and P other pinniped species. Although the mean PCB TEQs P (2.2 ± 0.9 ng/kg lw) and PCB concentrations for the fetuses were below immunotoxicity and endocrine thresholds for marine mammals (Ross et al. 2000; Mos et al. 2010; Brown et al. 2014b), consequent risks to their development in utero are unclear because these thresholds were derived from concentrations of adults. Acknowledgments Funding and support were provided by the Northern Contaminants Program of Aboriginal Affairs and Northern Development Canada, the Director General Environment of the Department of National Defence, the Torngat Joint Fisheries Board, the ArcticNet Canadian Networks of Centres of Excellence: Project ArcticNet Nunatsiavut Nuluak, the Nunatsiavut Government, and Natural Sciences and Engineering Research Council of Canada (NSERC) awards to T. M. Brown. We thank Tamara Fraser and Cory Dubetz for laboratory and data analysis support. We are grateful for the support, expertise, and assistance of Joey Angnatok and the crew of the Motor Vessel Whats Happening, S. Sturman, B. Sjare, D. Angnatok, and K. J. Reimer.
References
Fig. 4 PCA of PCB, OCP, and PBDE patterns in ringed seal mother– fetus pairs show that younger fetuses (see Table 1 for estimated ages) to the left of the score plot (A) are dominated by lighter compounds, whereas the mothers and older fetuses (B) are dominated by heavier compounds. Numbers identify the degree of chlorination or bromination of each PCB or PBDE congener
fetuses showing lower partition ratios than later-term fetuses (Greig et al. 2007).
Conclusion Although the pattern of transplacental transfer of POPs has been reported for some pinniped species (Donkin et al. 1981; Wang et al. 2012), this is the first such study in ringed seals. Our results show that very small quantities of PCBs, PBDEs, and OCPs are transferred from the mother to the fetus in ringed seals representing \0.05 % of the maternal burden for all compounds studied. Ringed-seal mothers transferred a contaminant mixture to their fetuses that varied with fetal age and size with older-term fetuses showing an increase in the proportion of compounds with higher Kow as well as a pattern that increasingly aligned with that of their mothers. These results will help inform
Addison RF, Brodie PF (1977) Organochlorine residues in materinal blubber, milk, pup blubber from grey seals (Halichoerus grypus) from Sable Island, Nova Scotia. J Fish Res Board Can 34:937–941 Addison RF, Brodie PF (1987) Transfer of organochlorine residues from blubber through the circulatory system to milk in the lactating gray seal (Halichoerus grypus). Can J Fish Aquat Sci 44:782–786 Aguilar A, Borrell A (1994) Reproductive transfer and variation of body load of organochlorine pollutants with age in fin whales (Balaenoptera physalus). Arch Environ Contam Toxicol 27:546–554 Ando M, Saito H, Wakisaka I (1985) Transfer of polychlorinated biphenyls (PCBs) to newborn infants through the placenta and mother’s milk. Arch Environ Contam Toxicol 14:51–57 Boon JP, van Arnhem E, Jansen S, Kannan N, Petrick G, Schulz D et al (1992) The toxicokinetics of PCBs in marine mammals with species reference to possible interactions of individual congeners with the cytochorme P450-dependent monooxygenase system. In: Walker CH, Livingstone D (eds) An overview persistant pollutants in marine ecosystems. Elsevier, Oxford, pp 119–159 Borrell A, Anguilar A (2005) Mother-calf transfer of organochlorine compounds in the common dolphin (Delphinus delphis). Bull Environ Contam Toxicol 75:149–156 Braekevelt E, Tittlemier SA, Tomy GT (2003) Direct measurement of octanol–water partition coefficients of some environmentally relevant brominated diphenyl ether congeners. Chemosphere 51:563–567 Brown TM, Fisk AT, Helbing CC, Reimer KJ (2014a) PCB profiles in ringed seals (Pusa hispida) reveal historical contamination by a military radar station in Labrador, Canada. Environ Toxicol Chem 33:592–601 Brown TM, Ross PS, Reimer KJ et al (2014b) PCB related effects threholds as derived through gene transcript profiles in locally contaminated ringed seals (Pusa hispida). Environ Sci Toxicol 48:12952–12961 Debier C, Pomeroy PP, Dupont C et al (2003) Quantitative dynamics of PCB transfer from mother to pup during lactation in UK grey seals Halichoerus grypus. Mar Ecol Prog Ser 247:237–248
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Arch Environ Contam Toxicol Desforges JW, Ross PS, Loseto LL (2012) Transplacental transfer of polychlorinated biphenyls and polybrominated diphenyl ethers in Arctic Beluga whales (Delphinapterus leucas). Environ Toxicol Chem 31:296–300 Donkin P, Mann SV, Hamilton EI (1981) Polychlorinated biphenyl, DDT and dieldrin residues in grey seal (Halichoerus grypus) males, females and mother-feotus pairs sampled at the Farne Islands, England, during the breeding season. Sci Total Environ 19:121–142 Gaden A, Ferguson SH, Harwood L, Melling H, Alikamik J, Stern GA (2012) Western Canadian Arctic ringed seal organic contaminant trends in relation to sea ice break-up. Environ Sci Technol 46:4427–4433 Gauger KJ, Kato Y, Haraguchi K et al (2004) Polychlorinated biphenyls (PCBs) exert thyroid hormone-like effects in the fetal brain but do not bind to thyroid hormone receptors. Environ Health Perspect 112:516–523 Greig DJ, Ylitalo GM, Hall AJ, Fauquier DA, Gulland FMD (2007) Transplacental transfer of organochlorines in California sea lions (Zalophus californianus). Environ Toxicol Chem 26:37–44 Hammill MO (1987) Ecology of the ringed seal (Phoca hispida Schreber) in the fast-ice of Barrow Strait. Macdonald College of McGill University, Sainte-Anne-de-Bellevue Hawker DW, Connell DW (1988) Octanol–water partition coefficients of polychlorinated biphenyl congeners. Environ Sci Technol 22:382–387 Helle E, Olsson M, Jensen S (1976a) DDT and PCB levels and reproduction in ringed seals from the Bothnian Bay. Ambio 5:188–189 Helle E, Olsson M, Jensen S (1976b) High frequencies of pathological changes in seal uteri correlated with PCB levels. Ambio 5:261–263 Ikonomou MG, Fraser T, Crewe N, Fischer MB, Rogers IH, He T (2001) A comprehensive multiresidue ultra-trace analytical method, based on HRGC/HRMS, for the determination of PCDDs, PCDFs, PCBs, PBDEs, PCDEs, and organochlorine pesticides in six different environmental matrices. Can Tech Rep Fish Aquat Sci 2389:1–95 Jacobson JL, Jacobson SW (2002) Association of prenatal exposure to an environmental contaminant with intellectual function in childhood. J Toxicol Clin Toxicol 40:467–475 Lyderson C (1995) Energetics of pregnancy, lactation and neonatal development in ringed seals (Phoca hispida). In: Blix AS, Walløe L, Ulltang Ø (eds) Developments in marine biology 4: Whales, seals, fish and man. Elsevier, Amsterdam, pp 319–327 Mackay D, Shiu WY, Ma KC (1992) Illustrated handbook of physical–chemical properties and environmental fate for organic chemicals. Lewis, Boca Raton Mos L, Tabuchi M, Dangerfield N, Jeffries SJ, Koop BF, Ross PS (2007) Contaminant-associated disruption of vitamin A and its receptor (RARa) in free ranging harbour seals (Phoca vitulina). Aquat Toxicol 81:319–328 Mos L, Cameron M, Jeffries SJ, Koop BF, Ross PS (2010) Risk-based analysis of polychlorinated biphenyl toxicity in harbor seals. Integr Environ Assess Manag 6:631–640 Muir D, Riget F, Cleeman M et al (2000) Circumpolar trends of PCBs and organochlorine pesticides in the arctic marine environment
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inferred from levels in ringed seals. Environ Sci Technol 34(12):2431–2438 Nyman M, Bergknut M, Fant ML et al (2003) Contaminant exposure and effects in Baltic ringed and grey seals as assessed by biomarkers. Mar Environ Res 55:73–99 Pomeroy PP, Green N, Hall AJ, Walton M, Jones K, Harwood J (1996) Congener-specific exposure of grey seal (Halichoerus grypus) pups to chlorinated biphenyls during lactation. Can J Fish Aquat Sci 53:1526–1534 Ross PS, De Swart RL, Timmerman HH et al (1996) Contaminantrelated immunosuppression in harbor seals fed herring from the Baltic Sea. Fundam Appl Toxicol 30:136 Ross PS, Ellis GM, Ikonomou MG, Barrett-Lennard LG, Addison RF (2000) High PCB concentrations in free-ranging pacific killer whales, Orcinus orca: effects of age, sex and dietary preferences. Mar Pollut Bull 40:504–515 Ross PS, Jeffries SJ, Yunker MB, Addison RF, Ikonomou MG, Calambokidis JC (2004) Harbor seals (Phoca vitulina) in British Columbia, Canada, and Washington State, USA, reveal a combination of local and global polychlorinated biphenyl, dioxin, and furan signals. Environ Toxicol Chem 23(1):157–165 Routti H, Arukwe A, Jenssen BM et al (2010) Comparative endocrine disruptive effects of contaminants in ringed seals (Phoca hispida) from Svalbard and the Baltic Sea. Comp Biochem Physiol 152:306–312 Ryg M, Lydersen C, Markussen NH (1990) Estimating the blubber content of phocid seals. Can J Fish Aquat Sci 47:1223–1227 Siddiqui MK, Srivastava S, Srivastava SP, Mehrotra PK, Mathur N, Tandon I (2003) Persistent chlorinated pesticides and intrauterine fetal growth retardation: a possible association. Int Arch Occup Environ Health 76:75–80 Smith TG (1987) The ringed seal, Phoca hispida, of the Canadian Western Arctic. Can Bull Fish Aqu Sci 216:81 Sormo EG, Skaare JU, Lydersen C, Kovacs KM, Hammill MO, Jensen BM (2003) Partitioning of persistent organic pollutants in grey seal (Halichoerus grypus) mother-pup pairs. Sci Total Environ 302:145–155 Stewart REA, Stewart BE, Stirling I, Street E (1996) Counts of growth layer groups in cementum and dentine in ringed seals (Phoca hispida). Mar Mamm Sci 12:383–401 Tanabe S, Tatsukawa R, Maruyama K, Miyazaki N (1982) Transplacental transfer of PCBs and chlorinated pesticides from the pregnant striped dolphin (Stenella coeruleoalba) to her fetus. Agric Biol Chem 46:1249–1254 Wang D, Atkinson S, Hoover-Miller A, Shelver WL, Li QX (2012) Organic halogenated contaminants in mother–fetus pairs of harbor seals (Phoca vitulina richardii) from Alaska, 2000-2002. J Hazard Mater 223–224:72–78 Wolkers H, Burkow IC, Hammill MO, Lydersen C, Witkamp RF (2002) Transfer of polychlorinated biphenyls and chlorinated pesticides from mother to pup in relation to cytochrome P450 enzyme activities in harp seals (Phoca groenlandica) from the Gulf of St. Lawrence. Can Environ Toxicol Chem 21:94–101 Wolkers H, Lydersen C, Kovacs KM (2004) Accumulation and lacatational transfer of PCBs and pesticides in harbor seals (Phoca vitulina) from Svalbard, Norway. Sci Total Environ 319:137–146
Transplacental Transfer of Polychlorinated Biphenyls, Polybrominated Diphenylethers, and Organochlorine Pesticides in Ringed Seals (Pusa hispida) T. M. Brown1,2 • P. S. Ross3 • K. J. Reimer4
Received: 11 March 2015 / Accepted: 5 June 2015 Ó Springer Science+Business Media New York 2015
Abstract The transplacental transfer of persistent organic pollutants in marine mammals takes place at a formative developmental period, thereby exposing the fetus to endocrine-disrupting compounds. We evaluated the transplacental transfer of polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs), and organochlorine pesticides (OCPs) in five pregnant ringed seals in Northern Labrador, Canada. PCBs, PBDEs, and OCPs were transferred from the mother to the fetus with average concentrations in the fetuses ranging from 0.3 ng/g lipid weight (lw) of mirex to 94 ng/g lw of PCBs. The average percent transferred to the blubber in the fetus was very low with \0.02 % for each of the compounds studied. Based on relationships observed, transfer for full-term fetuses is estimated to range from 0.03 to 0.27 %. Log Kow explained the transfer of PCBs (r2 = 0.67, p \ 0.001) and OCPs (r2 = 0.62, p \ 0.001) with those PCB congeners and OCP compounds having a log Kow of \6.0 and 4.6, respectively, because they are preferentially transferred to the fetus. Adult females transferred a contaminant mixture to their fetuses, which correlated with estimated fetal age
& T. M. Brown [email protected] 1
Raincoast Conservation Foundation, P.O. Box 2429, Sidney, BC V8L 3Y3, Canada
2
Present Address: Memorial University of Newfoundland, St. John’s, NL A1B 3X9, Canada
3
Ocean Pollution Research Program, Vancouver Aquarium Marine Science Center, P.O. Box 3232, Vancouver, BC V6B 3X8, Canada
4
Environmental Sciences Group, Royal Military College of Canada, P.O. Box 17000, Stn Forces, Kingston, ON K7K 7B4, Canada
(p \ 0.001; r2 = 0.697), with younger fetuses showing a greater proportion of compounds with low Kow compared with later-term fetuses. The implications for the prenatal exposure to these developmental toxicants remains unknown because current toxicity thresholds in marine mammals have only been derived from juveniles or adults.
Persistent organic pollutants (POPs)—such as polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs), and organochlorine pesticides (OCPs)—are lipophilic compounds that can bioaccumulate to very high concentrations in many marine mammals (Muir et al. 2000). Ringed seals (Pusa hispida) are vulnerable to heightened exposure to these compounds as a result of their high trophic level, large lipid reserves, and long life span (Boon et al. 1992; Nyman et al. 2003). Exposure to these pollutants has been associated with endocrine disruption, reproduction impairment, and immunotoxicity in ringed seals and other marine mammal species (Helle et al. 1976a, b; Ross et al. 1996; Routti et al. 2010; Brown et al. 2014b). Ringed seals inhabiting the Labrador coast are exposed to elevated levels of PCBs due to a combination of longrange transport from distant sources as well as a significant local PCB source associated with a military radar station in Saglek Bay (Brown et al. 2014a). Consequently, ringed seals from this region have PCB levels that are higher than anywhere else in the Canadian Arctic, and are at heightened risk for toxic effects including alteration of vitamin A levels and its receptor, altered thyroid hormone physiology and receptor function, and impaired immune function (Brown et al. 2014a; Mos et al. 2007). Recently, changes in hepatic mRNA transcript levels for genes that play a critical role in endocrine and immune function in ringed seals
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from this area have been associated with PCBs (Brown et al. 2014b). Female pinnipeds are able to lower their POP burden by transferring a proportion of their contaminant load to offspring by way of placental and lactational transfer (Gaden et al. 2012). A number of studies have shown that lactation is the dominant route for this transfer due to the mobilization of lipids and associated contaminants to synthesize milk (Wolkers et al. 2004; Debier et al. 2003; Sormo et al. 2003; Wolkers et al. 2002; Addison and Brodie 1987; Pomeroy et al. 1996). However, fewer studies have described the transplacental transfer of these compounds in pinnipeds (Donkin et al. 1981; Wang et al. 2012; Greig et al. 2007) with no studies describing the transfer dynamics in ringed seals. Such data are important because prenatal exposure to these toxic compounds occurs during critical phases of fetal development. Further, prenatal exposure to POPs has been shown to impair mammalian fetal development (Jacobson and Jacobson 2002; Gauger et al. 2004) and has been associated with intrauterine fetal growth retardation in humans (Siddiqui et al. 2003). The present study examines the transplacental transfer dynamics for PCBs, PBDEs, and OCPs in free-ranging ringed seals. The objective of the study was to characterize the transplacental transfer of these POPs in five mother– fetus ringed seal pairs and to investigate changes in the transfer of these compounds at different stages of the gestation period.
Materials and Methods Sample Collection Blubber samples from adult female ringed seals (n = 5) were obtained from Inuit hunters along the Labrador coast in 2008 and 2009. Full-depth blubber samples over the sternum were taken from the mothers and their near-term fetuses. All samples were placed in aluminum foil and Whirl Pak bags and frozen at -20 °C until analyzed for OCPs within 1 year of sample collection. Length, mass, and blubber thickness were measured on each dead animal, and the maternal age was determined by Matson’s Laboratory, USA, by longitudinally thin-sectioning a lower canine tooth and counting the annual growth layers in the cementum using a compound microscope and transmitted light (Stewart et al. 1996). Fetus age (in days) was estimated from fetal weight using relationships described in Lyderson (1995). For all samples collected, appropriate permits and community approval were obtained from the Nunatsiavut Government, Nunatsiavut Health, and Environment Review Committee and Department of fisheries and oceans Canada.
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Chemical Analysis The following were measured in ringed-seal blubber samples by the Laboratory of Expertise in Aquatic Chemical Analysis (Fisheries and Oceans Canada): concentrations of 91 PCB congeners (underlined is the dominant congener for the coeluting PCBs), (4, 5/8, 6, 16/32, 18, 20, 22, 26, 28, 31, 33, 40, 42/68, 43/49, 44, 47/48/75, 52, 60, 63, 64/ 71, 66, 70/76, 74, 85, 86/97, 87, 90, 91, 92, 95, 99, 101, 105, 107/108, 110, 113, 114, 111/115, 118, 119, 123, 124, 126, 128, 129, 130, 132, 133, 135, 137, 138/163/164, 139, 141, 144, 146, 147, 149, 151, 153, 154, 156, 157, 158/160, 162, 167, 168, 170/190, 171, 172/192, 174, 175, 177, 178, 180, 183, 185, 187, 189, 191, 193, 194, 195, 196/203, 197, 198, 201, 202, 205, 206, 208, and 209); 15 organochlorine pesticides (dichlorodiphenyl dichloroethylene [p,p’-DDE], dichlorodiphenyl dichloroethane [p,p’-DDD], dichlorodiphenyl trichloroethane [p,p’-DDT], a-hexachlorocyclohexane [a-HCH], [b-HCH], trans- and cis-chlordane, trans- and cis-nonachlor, dieldrin, 1,2,4,5-tetrachlorobenzenes [1,2,4,5-TetraClBz], 1,2,3,4-TetraClBz, pentaClBz, hexaClBz, mirex); and 6 PBDE congeners (47, 100, penta8, 99, 154, 153) and percentage lipid. The extraction and clean-up procedures, instrumental analysis, and conditions, and quality-assurance/quality-control criteria used for contaminant analysis are described elsewhere (Ikonomou et al. 2001; Ross et al. 2000). All PCB, OCP, and PBDE data were blank-corrected. The sample batch for PCBs, OCPs, and PBDEs included a procedural blank, a replicate, and either a certified reference material (herring) or a standard reference material (ringed seal) sample (Ikonomou et al. 2001). Reference material data met established laboratory criteria of fewer than ±2 SDs before batch data were deemed acceptable. Total concentrations for PCBs, DDT, hexachlorocyclohexane, chlordanes, chlorobenzenes, and PBDEs were calculated as the sum of the concentrations of the peaks that were detectable in C70 % of the seal samples. Where congeners were undetectable, the detection limit was substituted with a random number between the detection limit and zero. Replacing an undetectable value with a random number influences the PCA algorithm less than an arbitrary substitution such as the detection limit or one half of the detection limit (Ross et al. 2004). Congeners that were detected in \70 % of the samples were not included in calculations. All results are expressed on a lipid-weight (lw) basis. P Hereinafter, PCBs refers to the sum of the 91 PCB P congeners; DDT refers to the sum of p,p’-DDE, p,p’P DDD and p,p’-DDT; HCH refers to the sum of the aP and b-hexachlorocyclohexane, chlordanes refers to the sum of trans- and cis-chlordane and trans- and cis-nonaP chlor, ClBz refers to the sum of 1,2,4,5-TetraClBz,
Arch Environ Contam Toxicol
1,2,3,4-TetraClBz, pentaClBz and hexaClBz and refers to the sum of the 6 PBDE congeners.
P
PBDEs
Data Analysis The relative percent blubber (to total body weight) was estimated using an equation described in Ryg et al. (1990): relative percent blubber ðB %Þ pffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ 4:44 þ 5693 length in m=body mass in kg blubber thickness in m The total contaminant blubber burden, expressed in micrograms, (Borrell and Anguilar 2005) was calculated using the following equation: POP burden ¼ body weight relative percent blubber lipid content POP concentration The contaminant transfer rate was defined as the ratio of fetal blubber burden to the combined fetal and maternal burden. The partition ratio was calculated as the ratio between fetal to maternal blubber PCB, PBDE, and OCP lw concentrations for all congeners and compounds. Principal components analysis (PCA) was used to elucidate differences in PCB patterns in mother and fetus ringed seals. Samples were standardized to the total concentration before PCA to remove artifacts related to concentration differences between samples. The centered log ratio transformation (division by the geometric mean of the concentration-normalized sample followed by log transformation) was then applied to these data sets to produce a data set that was unaffected by negative bias or closure (Ross et al. 2004). Data were autoscaled before PCA. Linear regression analysis was used to assess the relationships between PCA projections and log octanol–water partition coefficient (Kow) values (a proxy for particle affinity) and fetus weight. Log Kow values for the PCB and PBDE congeners and OCP compounds were taken from Hawker and Connell (1988); Braekevelt et al. (2003) and Mackay et al. (1992) respectively.
Results and Discussion Contaminant Concentrations in Mothers and Fetuses The transplacental transfer of POPs in ringed seals was investigated by analyzing the blubber of mother–fetus pairs at different times of the 241—active day gestation period (Lyderson 1995). The mean age of the adult females was 14 ± 4 years (Table 1). Fetuses ranged from 1.5 to 6 months old (Table 1). The lipid content in the five adult
females was similar and did not vary (p [ 0.05) with age. In contrast, lipid content increased (p = 0.07; r2 = 0.094) with the age of the fetuses (Table 1). This observation is consistent with previous findings for lipid content and fetal age in California sea lions (Zalophus californianus) (Greig et al. 2007). P Concentrations of OCPs and PBDEs (lw) measured in the present study did not differ (p [ 0.05) withP fetal or maternal age. The mean concentration of PCBs, P DDTs, and p,p’-DDE was threefold greater in the mothers than in their fetuses (Table 2). The mean concentration of p,p’-DDT was ninefold greater in the mothers than in their fetuses (Table 2). Mean concentrations of P PBDEs and other OCPs did not differ (p [ 0.05) between mother and fetus. The top five contaminants in the adult females were ranked as follows: P P P P PCBs [ DDTs [ chlordanes [ HCHs [ dieldrin. The top five contaminants in the fetuses were ranked P P P P as follows: PCBs [ DDTs [ HCHs [ chlorP danes [ dieldrin. HCHs ranked third in fetuses comP pared with chlordanes, which ranked third in mothers. P This observation is consistent with HCHs having a greater percentage of transfer (0.01) compared with the P percentage of transfer (0.004) calculated for chlordanes (Table 2). These results are also consistent with the transplacental transfer being greater for compounds of low molecular-weight and reduced chlorination or bromination (e.g., HCHs) than for those with high molecular weight (e.g., chlordanes) (Greig et al. 2007; Ando et al. 1985). For all compounds measured in the present study, the average percent transfer was greatest for 1,2,3,4-TetraClBz (0.02 %) and lowest for mirex (0.002 %) (Table 2). As expected, the blubber percent transfer in the ringed-seal fetuses in the present study increased with fetal age (p \ 0.05) and weight (proxy for age) (p \ 0.05) for all compounds. Using the slope calculated from the relationship between these two compounds and weight (Fig. 1), we estimate that the percent transferred to the blubber of a fullterm ringed-seal fetus (4.5 kg [Smith 1987; Hammill 1987]) to range from only 0.03 to 0.27 % of the maternal blubber burden. We consider this to be a conservative estimate based on a linear relationship extending through the active gestation period. The estimated transfer is consistent with a previous estimate for PCBs and DDT (\1 % of the maternal blubber burden) or a full-term grey seal fetus (Donkin et al. 1981). This very limited transfer to the fetal blubber likely reflects, in part, the limited subcutaneous fat in the pinniped fetus (Donkin et al. 1981). Although to our knowledge no studies have documented the lactational transfer of contaminants in ringed seals, the documented transfer of POPs in other phocids suggests that milk is responsible for the bulk of maternal transfer from mother to offspring (Addison and Brodie 1977; Debier
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Arch Environ Contam Toxicol Table 1 Length, weight, blubber thickness, estimated age, and percentage lipid (blubber) for five mother–fetus ringed-seal pairs collected from northern Labrador, Canada ID
Length (cm)
Mass (kg)
Blubber thickness (cm)
Estimated age of mother (year) and fetus (day)
Lipid (%)
M1
127
59
6.0
19
95
M2 M3
113 126
66 65
4.8 5.5
10 18
95 94
M4
135
82
6.0
13
96
M5
121
66
5.0
10
93
Mean ± SD
124 ± 8
68 ± 9
5.5 ± 0.6
14 ± 4
94 ± 1
F1
15.8
0.228
0.50
64
2.4
F2
20.1
0.363
0.70
92
2.3
F3
14.7
0.127
0.40
43
0.7
F4
26.2
0.775
0.32
170
5.7
F5
19.8
0.297
0.52
79
1.9
Mean ± SD
19.3 ± 5
0.358 ± 0.249
0.49 ± 0.14
90 ± 49
2.6 ± 1.9
Mother
Fetus
Table 2 Mean (±SE) PCB, PBDE, and OCP concentrations in blubber, estimated blubber burdens, and percentage of total transfer from mother to fetus in ringed seal mother–fetus pairs Mother concentration (ng/g lw)
Fetus concentration (ng/g lw)
Mother blubber burden (lg)
286 ± 50
94 ± 7.1a
8520 ± 1480
0.26 ± 0.11
0.004
5.4 ± 1.7
5.5 ± 1.9
154 ± 44
0.008 ± 0.002
0.006
115 ± 30
37 ± 6.5a
3390 ± 857
0.08 ± 0.03
0.004
p,p’-DDE
103 ± 27
35 ± 6.4
a
3050 ± 790
0.0006 ± 0.0001
0.004
p,p’-DDD
2.7 ± 0.7
1.0 ± 0.2
78 ± 20
0.003 ± 0.001
0.005
p,p’-DDT P HCH
9.1 ± 3.9
1.1 ± 0.3a
258 ± 102
0.003 ± 0.001
0.003
30 ± 5.2
27 ± 2.4
887 ± 157
0.07 ± 0.03
0.01
a-HCH
20 ± 3.3
19 ± 1.8
585 ± 102
0.05 ± 0.03
0.01
b-HCH P Chlordanes
10 ± 2.0 44 ± 16
7.9 ± 1.2 16 ± 5.0
302 ± 57 1240 ± 421
0.02 ± 0.01 0.03 ± 0.01
0.01 0.004
P PCBs P PBDEs P DDT
Fetus blubber burden (lg)
Transfer (% of total burden)
t-Chlordane
1.4 ± 0.5
0.4 ± 0.1
39 ± 14
0.0006 ± 0.0001
0.003
c-Chlordane
7.7 ± 2.6
2.2 ± 0.6
222 ± 68
0.005 ± 0.002
0.004
t-Nonachlor
30 ± 12
11 ± 4.2
861 ± 318
0.02 ± 0.01
0.004
c-Nonachlor
4.0 ± 1.0
1.7 ± 0.3
114 ± 26
0.004 ± 0.001
0.005
Dieldrin P ClBz
21 ± 2.5
15 ± 1.5
632 ± 87
0.03 ± 0.01
0.006
9.1 ± 1.2
10 ± 1.2
277 ± 51
0.03 ± 0.02
0.01
1,2,4,5-TetraClBz
1.8 ± 0.5
2.0 ± 0.5
54 ± 17
0.004 ± 0.002
0.01
1,2,3,4-TetraClBz
0.4 ± 0.1
0.7 ± 0.2
12 ± 3.5
0.001 ± 0.001
0.02
PentaClBz
2.0 ± 0.5
2.3 ± 0.5
61 ± 17
0.005 ± 0.002
0.01
HexaClBz
4.9 ± 0.7
5.2 ± 1.2
150 ± 29
0.02 ± 0.01
0.01
Mirex
2.4 ± 1.1
0.3 ± 0.1
68 ± 29
0.0007 ± 0.0002
0.002
a
Indicates significant difference between mother and fetus
et al. 2003; Wolkers et al. 2004). Results from the present study support the idea that milk represents the dominant route of transfer from a mother to her offspring.
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The percent transfer calculated for PCBs (0.004 %) and PBDEs (0.006 %) in the present study (Table 2) is 1833and 2750-fold lower than the average percent transfer
Arch Environ Contam Toxicol
Fig. 1 Percent transfer of 1,2,3,4-TetraClBz and mirex from mother to fetus in ringed seals correlated with fetal weight
reported for PCBs and PBDEs in beluga whale mother– fetus pairs (Desforges et al. 2012). This large difference in transfer between ringed seals and beluga whales is likely due to the younger age of the sampled ringed-seal fetuses (3 ± 1.5 months) and a lower blubber lipid content (2.6 ± 1.9 %). The arctic beluga whale fetuses were approximately 10 months old (Desforges et al. 2012) and had a mean percent lipid of 83 ± 4 % (J. P. Desforges, personal communication). Partition Ratios in Mother–Fetus Pairs We calculated the fetal-to-maternal blubber PCB, PBDE, and OCP concentration ratios for all congeners and compounds. The average trend for PCBs showed a lower proportion of the heavier congeners in fetuses compared with their mothers such that congeners with three or fewer chlorine atoms were being preferentially transferred to the fetus (Fig. 2). No trend was found among the PBDE congeners (data not shown). However, the average partition ratio was lowest for PBDEs 47 and 153 and greatest for PBDE 99. The average partition-trend for the OCPs showed a greater proportion of compounds that have a lower log Kow value (e.g., HCHs and ClBzs) appearing in the fetus than in the mothers (Fig. 2). To further explore the transfer dynamics between mother and fetus, partition ratios for the different contaminants were plotted against log Kow (Fig. 3). The results showed a negative relationship between log Kow and the partition ratios for PCB congeners (r2 = 0.67, p \ 0.001) and OCPs (r2 = 0.62, p \ 0.001). No relationship (p = 0.79) was found between log Kow and the partition ratios for PBDE congeners. Similar log Kow-based partitioning relationships have been observed in mother–fetus pairs for PCB congeners and for DDT isomers in other species (Greig et al. 2007; Desforges et al. 2012). However, our observation of no relationship between log Kow
and the partitioning ratio for PBDE congeners differed from findings in arctic beluga whale (Delphinapterus leucas) mother–fetus pairs. The low number of PBDE congeners (n = 6) detected in the present study may explain the lack of relationship. The log Kow values at which concentrations of PCB congeners and OCP compounds were in equilibrium in mothers and their fetuses (i.e., partition ratios were zero) were 6.0 and 4.6, respectively (Fig. 3). Partition values \0 represent contaminants that are being preferentially retained by the mother, whereas at greater than these values they would be readily transferred to the fetus. The intersectional log Kow value for PCBs (6.0) in the present study is similar to that reported for the transplacental transfer of PCBs (6.5) in arctic beluga whales (Desforges et al. 2012) as well as for lactational transfer of PCBs in harbour seals (Wolkers et al. 2004). Overall, these results support previous reports of more efficient transfer to the fetus for the lower-molecular weight chemicals compared with highermolecular weight compounds (Borrell and Anguilar 2005; Tanabe et al. 1982; Aguilar and Borrell 1994). This physicochemical variation in transfer efficiencies can be explained by differences in the blood transport mechanisms among the individual congeners and OCP compounds, whereby the high molecular-weight congeners or compounds have a lower affinity to polar lipids in the blood and placenta compared with the nonpolar lipids in the maternal blubber (Desforges et al. 2012; Tanabe et al. 1982; Addison and Brodie 1987). Transfer of Contaminants Varies with the Stage of Gestation To assess whether the transfer of PCBs, PBDEs, and OCPs changed over the course of the gestation period, we compared the contaminant patterns in the mothers and fetuses. The first PC (t1; p1: 44.6 %) clearly differentiates the
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Fig. 2 Mean ± SE of PCB congener and OCP compound partition ratios (lipid weight) between mother and fetus ringed seals. Partition ratios were calculated as the blubber concentration in the fetus divided by that in the mother and were logarithmically transformed
Fig. 3 Mean partition ratios plotted against logarithmic log Kow for PCB congeners and OCP compounds in ringed seal mother–fetus pairs. Partition ratios were calculated as the blubber concentration in
the fetus divided by that in the mother and were logarithmically transformed. The dashed line represents partition parity
mothers from the fetuses, as mothers are dominated by a greater proportion of the heavier (more chlorinated) congeners and the more lipophilic compounds (e.g., chlordanes) (Fig. 4; Table 1). The younger fetuses have a greater proportion of the less chlorinated and brominated congeners and the less lipid-soluble compounds, as illustrated by their association with these lighter contaminants in the PCA (Fig.4; Table 1). The distance on the t1 axis (the samples scores of the first PC) for mother–fetus pairs
correlated with fetal age (p \ 0.001; r2 = 0.697) and fetal weight (a proxy for age) (p \ 0.001; r2 = 0.736). This suggests that a later-term fetus has a profile that is more similar to that of its mother compared with a younger-term fetus. Furthermore, log Kow of the PCBs, PBDEs, and OCPs correlated with p1 (the variable loadings of the first PC; p \ 0.001; r2 = 0.47). This is consistent with previous observations whereby the transfer of POPs varied with gestational stage in California sea lions with younger
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life-history bioaccumulation models for ringed seals and P other pinniped species. Although the mean PCB TEQs P (2.2 ± 0.9 ng/kg lw) and PCB concentrations for the fetuses were below immunotoxicity and endocrine thresholds for marine mammals (Ross et al. 2000; Mos et al. 2010; Brown et al. 2014b), consequent risks to their development in utero are unclear because these thresholds were derived from concentrations of adults. Acknowledgments Funding and support were provided by the Northern Contaminants Program of Aboriginal Affairs and Northern Development Canada, the Director General Environment of the Department of National Defence, the Torngat Joint Fisheries Board, the ArcticNet Canadian Networks of Centres of Excellence: Project ArcticNet Nunatsiavut Nuluak, the Nunatsiavut Government, and Natural Sciences and Engineering Research Council of Canada (NSERC) awards to T. M. Brown. We thank Tamara Fraser and Cory Dubetz for laboratory and data analysis support. We are grateful for the support, expertise, and assistance of Joey Angnatok and the crew of the Motor Vessel Whats Happening, S. Sturman, B. Sjare, D. Angnatok, and K. J. Reimer.
References
Fig. 4 PCA of PCB, OCP, and PBDE patterns in ringed seal mother– fetus pairs show that younger fetuses (see Table 1 for estimated ages) to the left of the score plot (A) are dominated by lighter compounds, whereas the mothers and older fetuses (B) are dominated by heavier compounds. Numbers identify the degree of chlorination or bromination of each PCB or PBDE congener
fetuses showing lower partition ratios than later-term fetuses (Greig et al. 2007).
Conclusion Although the pattern of transplacental transfer of POPs has been reported for some pinniped species (Donkin et al. 1981; Wang et al. 2012), this is the first such study in ringed seals. Our results show that very small quantities of PCBs, PBDEs, and OCPs are transferred from the mother to the fetus in ringed seals representing \0.05 % of the maternal burden for all compounds studied. Ringed-seal mothers transferred a contaminant mixture to their fetuses that varied with fetal age and size with older-term fetuses showing an increase in the proportion of compounds with higher Kow as well as a pattern that increasingly aligned with that of their mothers. These results will help inform
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