Abstract

Dioxins are a group of chemically-related environmental persistent bioaccumulative toxins that include chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans. They are formed in small concentrations when organic materials are burned in the presence of chlorine. Major sources of environmental dioxins include coal-fired utilities, metal smelting, diesel vehicles, municipal incineration plants, and chlorine paper bleaching. Dioxin concentrations in the environment have been declining during the past decade as a result of regulations and public education. In vertebrates, dioxins cause reproductive and developmental toxicity, immuno-, cardio-, and neurotoxicity, and teratogenicity. They produce their effects by acting as ligands for the aryl hydrocarbon receptors (AHR). The AHR pathway, which has been studied in several vertebrates including mammals and fish, controls a variety of developmental and physiological events including cell growth and function, neurogenesis, circadian rhythms, hormone receptor function and the metabolism of toxins. The concentrations of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like PCBs in a number of marine mammal species from multiple locations have been reported in the scientific literature during the past two decades.^{1,3,4,6,7,8,9} Several studies reported impaired immunity in harbor seals (Phoca vitulina) exposed to bioaccumulative environmental contaminants, including dioxins.² The concentrations of toxins in harbor porpoises (Phocoena phocoena) stranded on the Dutch coast were found to partially be due to PCBs, with dioxins present in relatively lower concentrations.¹⁰ A number of studies have examined the concentrations of PCBs and dioxins in the North Pacific killer whales (Orcinus orca) with emphasis on the effects of age, sex, reproductive status and diet on these concentrations.⁵ In 2009, we conducted a pilot study to determine the concentrations of dioxins in blubber samples obtained opportunistically from marine mammals stranded in the central Puget Sound region from 1996–2011 (primarily 2008–2011). A 20–30g sample of frozen blubber from 31 animals (6 species) was shipped over dry ice to Pace Analytical Services (Minneapolis, MN). The samples were analyzed for polychlorodibenzo-p-dioxins and polychloro-dibenzofuranes using USEPA Method 1613B. Results are reported as the Total 2,3,7,8,-TCDD Equivalence in ng/kg sample weight and in ng/kg lipid weight (Table 1). The Total 2,3,7,8-TCDD equivalence was calculated using the 2005 WHO Factors. Dioxins were found in all the samples examined. The profiles of the native isomers (congeners) in each of the samples were different suggesting that the pollutants came from multiple sources and not a single source. Alternatively, the differences in the profiles reflect individual differences in the rates of biodegradation of the congeners. In general, dioxin concentrations were moderate except for the sample obtained from a California (Zalophus californianus) and Steller (Eumetopias jubatus)sea lion. Concentrations of dioxins were lowest in the gray whales (Eschrichtius robustus). The differences in the concentrations of dioxins reflect either differences in levels of contamination of the diet or differences in the rates of biodegradation in these species. The relatively high concentrations of dioxin in the California and Steller sea lion samples underscore the need for studying additional samples of tissues obtained from animals stranded in the Puget Sound ecosystem.

Table 1. Concentrations of dioxins in blubber samples obtained from marine mammals stranded in central Puget Sound (1996–2011)

Acknowledgments

The authors thank the volunteers and supporters of the Central Puget Sound Marine Mammal Stranding Network, and P. Gearin for samples from a harbor and Dall's porpoise. Funding for sample testing was provided by the John H. Prescott Marine Mammal Stranding Response Program.

* Presenting author

Literature Cited

1.  Addison RF, Ikonomou MG, Stobo WT. 1999. Polychlorinated dibenzo-p-dioxins and furans and non-ortho- and mono-ortho-chlorine substituted polychlorinated biphenyls in grey seals (Halichoerus grypus) from Sable Island, Nova Scotia, in 1995. Mar Environ Res 47(3):225–240.

2.  de Swart RL, Ross PS, Vos JG, Osterhaus ADME. 1996. Impaired immunity in harbor seals (Phoca vitulina) exposed to bioaccumulated environmental contaminants: review of a long-term feeding study. Environ Health Prospect 104(Suppl 4):823–828.

3.  Gaus C, Correll R, Mueller J, Holt E, Ellis D, Prange J, Shaw M, Bauer U, Symons R, Burniston D. 2005. Dioxins and dioxin-like PCBs in marine mammals from Australia. Organohalogen Compounds 67:1271–1275.

4.  Jimènez B, Gonzàlez MJ, Hernández LM, Eljarrat E, Rivera J, Fossi MC. 1999. 2,3,7,8-Substituted PCDDs and PCDFs in sea lion (Otaria flavescens) skin biopsies from two south-western Atlantic populations. Chemosphere 38(3):507–515.

5.  Kahn MM, Hanson MB, Schorr GS, Emmons CK, Burrows DG, Bolton JL, Baird RW, Ylitalo GM. 2009. Effects of age, sex and reproductive status on persistent organic pollutant concentrations in "Southern Resident" killer whales. Mar Pollut Bull 58(10):1522–1529.

6.  Moon H-B, Choi H-G, An Y-R, Park K-J, Choi S-G, Moon D-Y, Kannan K. 2010. Contamination status and accumulation features of PCDDs, PCDFs and dioxin-like PCBs in finless porpoises (Neophocaena phocaenoides) from Korean coastal waters. J Hazard Mater 183(1–3):799–805.

7.  Moon H-B, Kannan K, Choi H-G, An Y-R, Choi S-G, Park J-Y, Kim Z-G. 2010. Concentrations and accumulation features of PCDDs, PCDFs and dioxin-like PCBs in cetaceans from Korean coastal waters. Chemosphere 79(7):733–739.

8.  Norstrum RJ, Simon M, Muir DC. 1990. Polychlorinated dibenzo-p-dioxins and dibenzofurans in marine mammals in the Canadian North. Environ Pollut 66(1):1–19.

9.  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.

10. van Scheppingen WB, Verhoeven AJIM, Mulder P, Addink MJ, Smeenk C. 1996. Polychlorinated biphenyls, dibenzo-p-dioxins, and dibenzofurans in harbor porpoises (Phocoena phocoena) stranded on the Dutch coast between 1990 and 1993. Arch Environ Contam Toxicol 30(4):492–502.