Relationship of blood mercury levels to health parameters in the loggerhead sea turtle (Caretta caretta).
BACKGROUND
Mercury is a pervasive environmental pollutant whose toxic effects have not been studied in sea turtles in spite of their threatened status and evidence of immunosuppression in diseased populations.


OBJECTIVE
In the present study we investigate mercury toxicity in loggerhead sea turtles (Caretta caretta) by examining trends between blood mercury concentrations and various health parameters.


METHODS
Blood was collected from free-ranging turtles, and correlations between blood mercury concentrations and plasma chemistries, complete blood counts, lysozyme, and lymphocyte proliferation were examined. Lymphocytes were also harvested from free-ranging turtles and exposed in vitro to methylmercury to assess proliferative responses.


RESULTS
Blood mercury concentrations were positively correlated with hematocrit and creatine phosphokinase activity, and negatively correlated with lymphocyte cell counts and aspartate amino-transferase. Ex vivo negative correlations between blood mercury concentrations and B-cell proliferation were observed in 2001 and 2003 under optimal assay conditions. In vitro exposure of peripheral blood leukocytes to methylmercury resulted in suppression of proliferative responses for B cells (0.1 microg/g and 0.35 microg/g) and T cells (0.7 microg/g).


CONCLUSIONS
The positive correlation between blood mercury concentration and hematocrit reflects the higher affinity of mercury species for erythrocytes than plasma, and demonstrates the importance of measuring hematocrit when analyzing whole blood for mercury. In vitro immunosuppression occurred at methylmercury concentrations that correspond to approximately 5% of the individuals captured in the wild. This observation and the negative correlation found ex vivo between mercury and lymphocyte numbers and mercury and B-cell proliferative responses suggests that subtle negative impacts of mercury on sea turtle immune function are possible at concentrations observed in the wild.
Day
Rusty D
RD
National Institute of Standards and Technology, Hollings Marine Laboratory, Charleston, South Carolina 29412, USA. russell.day@nist.gov
Segars
Al L
AL
Arendt
Michael D
MD
Lee
A Michelle
AM
Peden-Adams
Margie M
MM
D000820:Animal Diseases / Q000139:chemically induced; D000818:Animals; D001219:Aspartate Aminotransferases / Q000097:blood / Q000187:drug effects; D001267:Atlantic Ocean; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D003402:Creatine Kinase / Q000097:blood / Q000187:drug effects; D004781:Environmental Exposure / Q000009:adverse effects* / Q000032:analysis; D004784:Environmental Monitoring; D006400:Hematocrit / Q000662:veterinary; D007107:Immune System / Q000187:drug effects; D018655:Lymphocyte Count; D008628:Mercury / Q000097:blood* / Q000633:toxicity; D008767:Methylmercury Compounds / Q000097:blood* / Q000633:toxicity; D015144:Southeastern United States; D014426:Turtles / Q000097:blood* / Q000502:physiology
D008767:Methylmercury Compounds; D001219:Aspartate Aminotransferases; D003402:Creatine Kinase; D008628:Mercury