Cytotoxicity of environmentally relevant organic contaminants in fibroblast skin cells from the critically endangered hawksbill sea turtle (Eretmochelys imbricata)



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The hawksbill sea turtle (Eretmochelys imbricata) is listed as critically endangered in the IUCN red list. Past and present causes for this species decline include over-exploitation, habitat degradation, and pollution. Assessing pollution threat is critical for conservation and management, yet intrinsically challenging due to limitations associated with access to endangered animals and scope of allowed experimental research. Here we review the current state of knowledge in hawksbill sea turtle toxicology, identify trends and data gaps, and provide recommendations for future research. Significant data gaps were seen including geographical distribution, contaminant variation and age class. Providing current available data to IUCN could potentially assist in future hawksbill assessments and conservation efforts. A total of 33 peer reviewed papers spanning 1987 to 2021, were reviewed and included data on toxicant exposure, quantification, and potential effects. The data portion of this project examined the cytotoxicity of crude oil, Corexit™9500A, perfluorooctanoic acid (PFOA, 0.05-500 µM), polychlorinated biphenyl and benzo[a]pyrene (PCB77 & B[a]P, 0.01-10µM) via both MTT (methylthiazolyldiphenyl-tetrazolium bromide) at 24h and 96h and LDH (Lactate Dehydrogenase) assays at 24h. Corexit exposure led to higher toxicity than either oil or the oil and corexit mixture, resulting in only 1% cell viability after 96 hours. In the PFOA study and for both timepoints, significant toxicity compared to the control due to concentration and due to time were observed after exposure to the 5, 50, and 500µM concentrations, and at all concentrations, respectively. Exposure to the 500µM concentration for 24h resulted in only 57% cell viability. In the PCB77 study, significant toxicity compared to the control was observed after 96h exposure to 0.1, 1.0 and 10µM doses, resulting in as low as 69% cell viability. In the B[a]P study, significant toxicity compared to the control was observed after 96h exposure to 0.1µM,1.0µM and 10µM concentrations. Exposure to10µM B[a]P for 96h resulted in 87% cell viability. The MTT assay showed greater sensitivity in determining cell viability after contaminant exposure than the LDH assay. Median lethal concentrations were derived from MTT viability data for PCB77 and B[a]P, resulting in 20, and 36μM, respectively for 24hLC50 and 17 and 31 μM, respectively for 96hLC50. PFOA LC50 could only be derived with confidence from 24h MTT viability data, resulting in 577μM. Amongst all toxicants tested, Corexit was the most toxic to the cells at both timepoints with a maximal efficacy corresponding to 99% cell death. Toxicity measured by maximal efficacy was observed in decreasing order as follows: Corexit> PFOA> MAF> CEMAF> B[a]P > PCB77 at 24h and Corexit> PCB77> PFOA>B[a]P>MAF>CEMAF at 96h Among PFOA, PCB77 and B[a]P, PCB77 had the highest potency, as determined by the derived LC50s.



Hawksbill, Sea Turtle, Toxicology, Marine Contaminants