Date of Award

8-2013

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (Medical Science)

Department

Biochemistry and Molecular Biology

Advisor

John Pierce Wise, Sr.

Second Committee Member

Douglas A. Currie

Third Committee Member

Stephen C. Pelsue

Abstract

Pollution of the ocean by persistent pollutants including metals and polybrominated diphenyl either (PBDE) flame retardants is a global concern due to their ability to be bioaccumulative and potentially toxic putting high trophic consumers at risk. The sperm whale (Physeter macrocephalus) is a sentinel of ocean health due to its wide distribution, longevity and high trophic level. The overarching aim of this study was to survey the concentrations of toxic metals, mercury (Hg), lead (Pb), silver (Ag) and arsenic (As), the essential element, selenium (Se), and twenty-five different PBDEs worldwide in the skin of free-ranging sperm whales considering region, gender and age. Over 900 samples were collected in 17 regions during the voyage of the research vessel, Odyssey, between 2000 and 2005.

Hg levels in the skin were detected in 340 of the 343 sperm whale sampled with a global mean of 2.5 ± 0.1 ug/g ww ranging from 0.1 to 16.0 ug/g ww. The Mediterranean Sea had the highest regional mean with 6.1 ug/g ww followed by Australia with 3.5 ug/g ww. Considering gender and age, neither caused a significant difference in Hg concentrations.

Pb concentrations were detectable in 315 of the 337 samples with a global mean of 1.6 ug/g ww ranging from 0.1 to 129.6 ug/g ww. Papua New Guinea, Bahamas and Australia had the highest means with 6.1, 3.4, and 3.1 ug/g ww, respectively. Global mean levels were not significantly different between males and females or adult and subadult males.

Ag levels were detectable in 178 of the 298 sperm whales sampled with a global mean of 16.9 ± 14.1 ug/g ww ranging from 0.1 to 4,179.0 ug/g ww. The highest mean regional level was found in Seychelles with 123.3 ug/g ww. When comparing gender and age, there were not significant differences between females and males or adult and subadult males.

Arsenic was detectable in 337 of the 342 samples with a mean of 1.9 ± 0.1 ug/g ww ranging from 0.1 to 15.6 ug/g ww. Female and male sperm whales were found to have significant differences in As levels when controlling for region. Adult and subadult males did not have statistically different As levels.

Selenium levels, an essential element known to interact and reduce the toxicity of some metals, were analyzed in sperm whale skin samples. The global mean Se concentration was 33.1 ± 1.1 ug/g ww. Levels were not significantly different when considering gender or age.

Selenium concentrations were compared in molar ratios to the metals previously analyzed. Selenium concentrations were found to be several fold higher than Hg concentrations with a Se:Hg molar ratio of 59:1. Research has shown that a 1:1 ratio reduces Hg-induced toxicity. The Bahamas and the Mediterranean and molar ratios closest to 1:1 with 13:1 and 14:1. Selenium concentrations were also much higher than Pb concentrations with Se:Pb molar ratios being 300:1. Selenium has been shown to have antagonistic effects against Pb toxicity; however, the optimal molar ratio to reduce toxicity is unknown. Se binds to Ag and has been shown to prevent Ag toxicity. The mean Se:Ag ratio was 165:1 varying widely in samples from 1229:1 to 1:207. Se also binds to As and reduces As toxicity. The mean Se:As molar ratio was 12:1 ranging from 200:1 to 1:1.1.

The total metal, Hg, Pb, As and Ag, compared to Se was then measured. The mean total metal concentration was 22.9 ± 14.5 ug/g ww. The samples with the highest metal levels were in Seychelles with 4191 ug/g ww. In samples where all four metals had been analyzed, a mean Se:metal molar ratio of 9:1 was found. Samples with a Se:metal molar ratio were found in Australia or Papua New Guinea.

The Hg and Se concentrations found in the skin biopsies were used to treat cultured sperm whale skin cells developed from the skin biopsies. MeHg induced cytotoxicity and an alteration in cell cycle distribution that was protected by cotreatment with Se. MeHg is known to induced aneuploidy, but we did not find a significant induction of aneuploidy in sperm whale skin cells after 72 h exposure with 2, 3 or 4 uM MeHg.

An organic chemical, PBDEs, were also analyzed in 100 sperm whale skin samples. Twenty-five different PBDE congeners and two methoxylated PBDEs, likely of natural origin, were analyzed. PBDEs were detected in 98% of the samples, and six of the congeners had detection frequencies >50%. BDE47 was the dominant congener being detectable in 92% of samples and had a geometric mean of 3.2 ng/g ww. BDE 47 was the dominant congener detected in most samples with the highest mean concentration found in the Mediterranean with 13.3 ng/g ww. The sum of the six congeners (ΣPBDE) had concentrations ranging from 0.9 to 44.9 ng/g ww. Lipid content was not positively correlated with ΣPBDE level. The two methoxylated PBDEs were folds higher than the anthropogenic PBDEs. The two methoxylated PBDEs (6-MeO PBDE 47 and 2-MeO PBDE 68) had the highest mean level in Papua New Guinea with 137.2 and 78.8 ng/g ww, respectively.

These data help to establish global baselines for metals, Hg, Pb, Ag and As, in sperm whale skin. The analysis takes into account the possible antagonistic effects Se may have on the toxicity of these metals. Also an organic, PBDEs, were analyzed that gave insight into their wide dispersal and their concentrations in a wide ranging toothed whale.

Download

Share