Abstract

Heavy metal contamination of mercury (Hg) in cetaceans has been documented worldwide in tissues from dead and stranded animals, reflecting a growing environmental burden of this metal in marine ecosystems. However, the physiological effects of Hg contamination on free-ranging live cetaceans remain largely unexplored. The current study examined both blood and skin samples collected from two populations of free-ranging Atlantic bottlenose dolphins (Tursiops truncatus) to examine the correlation between increasing levels of mercury with measures of hepatic, thyroid, renal, and endocrine function.^3,4 A total of 121 dolphins examined between 2002 and 2005 were screened for trace metals as a part of the Bottlenose Dolphin Health and Environmental Risk Assessment study (HERA). Animals were sampled in the Indian River Lagoon, FL and the estuarine waters of Charleston, SC. We used multivariate linear regression to evaluate the effects skin and blood Hg on multiple endpoints while controlling for animal age and capture site. A positive association between blood Hg concentration and blood urea nitrogen (BUN) (p < 0.01) was observed. The increase in BUN suggests possible renal impairment but the lack of similar findings for other kidney function measures such as creatinine warrants further investigation. Total 3,3'-5 triiodothyronine (T3) and free thyroxine (T4) were negatively associated with skin Hg in the linear model. In addition, adrenocorticotrophin (ACTH) (p < 0.05) and estradiol (p < 0.01) were positively associated with skin Hg. Previous work in terrestrial mammals suggests selenium (Se) deficiency could play a role in decreased thyroid hormone production.^1,2 A negative association between both measures of Hg and Se was observed in this study. Free T4, testosterone, aldosterone, and progesterone were not associated with Hg concentration in any models. Results of the study indicate possible physiological impairments as a consequence of increasing burden of Hg. Negative associations between Hg and thyroid hormones have not been previously reported in marine mammals. This study describes the first attempt to link Hg exposure to physiological impairment in free-living dolphins in order to fully explore the detrimental role of Hg contamination on free-ranging marine mammal health.

Acknowledgments

This work was conducted under NMFS permit 998-1678 issued to Dr. Gregory Bossart as part of the Health and Risk Assessment of Bottlenose Dolphins Project (HERA) conducted in the Indian River Lagoon, FL and the Coastal waters of Charleston, SC. Special thanks toStephen D. McCulloch and the numerous collaborators and volunteers who participated in the HERA project.

References

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2.  Beckett G.J., F. Nicol, D. Proudfoot, K. Dyson, G. Loucaides, and J.R Arthur. 1990. The changes in hepatic enzyme expression caused by selenium deficiency and hypothyroidism in rats are produced by independent mechanisms. Biochem J 266: 743-747.

3.  Stavros H.C., G.D. Bossart, T.C. Hulsey, and P.A Fair. 2007. Trace element concentrations in skin of free-ranging bottlenose dolphins (Tursiops truncatus) from the southeast Atlantic coast. Sci Total Envir 388: 300-315.

4.  Stavros H.C., G.D. Bossart, T.C. Hulsey, and P.A. Fair. 2008. Trace element concentrations in blood of free-ranging bottlenose dolphins (Tursiops truncatus): Influence of age, sex and location. Mar Pollut Bull 56: 348-379.