Persistent organic pollutants are environmental contaminants that, because
of their lipophilic properties and long half-lives, bioaccumulate
within aquatic food webs and often reach high concentrations in marine
mammals, such as harbor seals (Phoca vitulina). Exposure to these contaminants has been associated with developmental
abnormalities, immunotoxicity, and reproductive impairment in marine
mammals and other high-trophic-level wildlife, mediated via a disruption
of endocrine processes. The highly conserved thyroid hormones (THs) represent
one vulnerable endocrine end point that is critical for metabolism, growth, and
development in vertebrates. We characterized the
relationship between contaminants and specific TH receptor (TR ) gene expression in skin/blubber biopsy samples, as well as serum THs, from
free-ranging harbor seal pups (n = 39) in British Columbia, Canada, and Washington State, USA. We
observed a contaminant-related increase in blubber TR-α gene expression [total polychlorinated biphenyls (∑PCBs); r = 0.679; p < 0.001] and a concomitant decrease in circulating total thyroxine
concentrations (∑PCBs; r = −0.711; p < 0.001). Consistent with results observed in carefully controlled
laboratory and captive feeding studies, our findings suggest that the
TH system in harbor seals is highly sensitive to disruption by environmental
contaminants. Such a disruption not only may lead to adverse effects
on growth and development but also could have important ramifications
for lipid metabolism and energetics in marine mammals.
We measured persistent organic pollutant (POP) concentrations in chinook salmon (Oncorhynchus tshawytscha) in order to characterize dietary exposure in the highly contaminated, salmon-eating northeastern Pacific resident killer whales. We estimate that 97 to 99% of polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), dichlorodiphenyltrichloroethane (DDT), and hexachlorocyclohexane (HCH) in returning adult chinook were acquired during their time at sea. Highest POP concentrations (including PCBs, PCDDs, PCDFs, and DDT) and lowest lipids were observed in the more southerly chinook sampled. While feeding by salmon as they enter some more POP-contaminated near-shore environments inevitably contribute to their contamination, relationships observed between POP patterns and both lipid content and delta13C also suggest a migration-related metabolism and loss of the less-chlorinated PCB congeners. This has implications for killer whales, with the more PCB-contaminated salmon stocks in the south partly explaining the 4.0 to 6.6 times higher estimated daily intake for sigmaPCBs in southern resident killer whales compared to northern residents. We hypothesize that the lower lipid content of southerly chinook stocks may cause southern resident killer whales to increase their salmon consumption by as much as 50%, which would further increase their exposure to POPs.
The Strait of Georgia (British Columbia, Canada) is a hydrologically complex inland sea with a rich abundance and diversity of species of aquatic life. Marine sediments, as both a sink for hydrophobic contaminants and a potential source for aquatic food webs, were collected from 41 sites throughout the 6,900-km(2) Strait of Georgia. The congener-specific concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), including BDE-209, were measured. Urban harbors represented hotspots for both PCBs and PBDEs, whereas PBDEs were also found at high concentrations near municipal outfalls. Patterns of PCB distribution were consistent with historical point source emissions in urban areas and environmental distillation toward lighter profiles in remote sites over time. The single congener BDE-209 dominated the PBDEs, accounting for 52% of the average total concentration. However, nonurban deep-water sediment PBDE profiles were both heavier and had higher concentration-weighted average log K(OW) (octanol-water partition coefficient) values compared to shallow samples (percent BDE-209 of total PBDE, 66 versus 32%; log K(OW) , 9.5 versus 8.2, respectively). Collectively, our results suggest that although source signals largely explain PCB and PBDE hotspots in the Strait of Georgia, the combination of physicochemical properties and environmental processes drive divergent compositional fates for the PCBs and the heavier PBDEs in the sediments of the Strait of Georgia.
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