Relationship of Blood Mercury Levels to Health Parameters in the Loggerhead Sea Turtle ( Caretta caretta )

Abstract

BackgroundMercury 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.ObjectivesIn the present study we investigate mercury toxicity in loggerhead sea turtles (Caretta caretta) by examining trends between blood mercury concentrations and various health parameters.MethodsBlood 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.ResultsBlood 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 μg/g and 0.35 μg/g) and T cells (0.7 μg/g).ConclusionsThe 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.

Understanding the vertebrate immune system: insights from the reptilian perspective

“…Lymphocyte proliferation in the loggerhead sea turtle was positively correlated with concentrations of polychlorinated biphenyls (PCBs) in the blood (Keller et al, 2006) whereas mercury levels were negatively correlated with lymphocyte proliferation (Day et al, 2007). Modulation of the immune system by environmental contaminants could put reptiles at a greater risk for disease, in part because they are common inhabitants of contaminated areas and also because many reptiles are long-lived, increasing the likelihood that they will accumulate contaminants (Guillette et al, 1994).…”

The current state and future directions of marine turtle toxicology research

“…The majority of these publications investigated health parameters in blood (n = 7, 47%). Of these, four publications drew correlations between blood parameters and metal concentrations (Day et al, 2007;Innis et al, 2008;Komoroske et al, 2011;Camacho et al, 2013b), while four Table 2 Number of toxicity studies organised by marine turtle species and sub-category of toxicological research. Some publications were counted more than once as they included more than one species or research sub-category.…”

Compromised immune competence in free-living tree swallows exposed to mercury

“…In vivo and in vitro, mercury is a potent immune suppressor and/or modulator across a range of vertebrate taxa (Zelikoff et al 1994;Day et al 2007). The effects of mercury on avian health have been particularly well studied in poultry (Kumar et al 1999) and a range of piscivorous, or fish-eating, bird species due to their susceptibility to bioaccumulation.…”

“…Therefore, studies of the health impacts of mercury toxicity are relevant and sorely needed in non-piscivorous taxa subject to high levels of mercury contamination. Furthermore, studies of mercury effects on health in free-living populations are critical (Day et al 2007) in order to understand the effects of mercury toxicity in an ecological context.…”