Sharks often bioaccumulate mercury (Hg) concentrations in their muscle to levels that threaten the health of human consumers. However, few published studies have examined if the high Hg levels seen in shark muscle also occur in the shark brain, or if Hg accumulation affects shark neurophysiology. Therefore, this study examined if shark brains accumulate significant levels of Hg, if Hg accumulation occurs in certain subcomponents of the brain, and if Hg accumulation is associated with oxidative stress effects on the shark central nervous system, with special focus on the Atlantic sharpnose shark (Rhizoprionodon terraenovae). Sharks were collected along the U.S. Southeastern coast throughout most of the sharkâs geographical range. Known biomarkers of Hg-induced neurological effects (markers of glial cell damage, S100b, and markers of oxidative stress) in the shark cerebrospinal fluid were examined. Brain Hg levels were correlated with muscle Hg levels, but were significantly lower and did not exceed most known thresholds for neurological effects, suggesting limited potential for such responses. Data on known biomarkers of Hg-induced neurological effects support this premise, because they were not correlated with brain Hg levels. Organic methylmercury did not compose of a high percentage of the total mercury in the brain, indicating demethylation of Hg is occurring in the brain. Higher Hg levels were measured in the forebrain of the shark in comparison with the midbrain and hindbrain, but levels in both were below threshold levels for effects. This study is the first to demonstrate the correlation and significant difference of Hg in the brain and muscle of sharks, and it identifies significantly higher Hg levels in the forebrain; making this study one of the most extensive analysis of Hg in a single shark species.
| Identifer | oai:union.ndltd.org:unf.edu/oai:digitalcommons.unf.edu:etd-1774 |
| Date | 01 January 2017 |
| Creators | Ehnert, Samantha L |
| Publisher | UNF Digital Commons |
| Source Sets | University of North Florida |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | UNF Theses and Dissertations |
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