## 5 Conclusions  
This is the first study that was conducted on loggerhead sea turtles, where the response of erythrocytes to MeHg-induced oxidative stress is evaluated. Erythrocytes resulted in being an excellent, simple, and inexpensive model to perform bioassays for ecotoxicological evaluation with heavy metals and other environmental pollutant molecules, specifically for MeHg in this study. Being loggerhead turtles considered a threatened or endangered species, RBCs represent an excellent ethical experimental in vitro model, allowing ecotoxicological studies to be carried out without the need to sacrifice animals. In addition, SOD, GST, and MDA were sensitive biomarkers of environmental pollution and oxidative stress in loggerhead turtles. However, these biomarkers presented high standard deviations due to the low number of individuals (n = 5) used. Future studies are suggested for carrying out further evaluations with a larger sample to improve the statistical significance of these results and confirm the benefits of these biomarkers as indicators of pollution and oxidative stress. It was observed that exposure to methylmercury in low concentrations induce protective redox defenses in RBCs, as seen from the induction of anti-oxidant enzyme SOD and GST activity. However, when the methylmercury concentration increases, these defenses are overcome and lipid peroxidation injury increases. Erythrocytes of loggerhead turtles in this study survived when kept in plasma in vacutainer tubes with Na-heparin at 4 \({}^{\circ}\)C for about eight weeks. This important characteristic allows for the use of these cells in sequential experiments.  
Conceptualization, J.H.-F. and E.A.L.-B.; methodology, J.H.-F., P.R.-B. and E.A.L.-B.; software, [PERSON]-F. and P.R.-B; validation, [PERSON]-F., P.R.-B., L.M.-R., A.P.-V. and E.A.L.-B.; formal analysis, [PERSON]-F. and E.A.L.-B.; investigation, [PERSON]-F. and P.R.-B.; resources, [PERSON]-F., P.R.-B. and E.A.L.-B.; data curation, [PERSON]-F., P.R.-B., L.M.-R., A.P.-V. and E.A.L.-B.; writing--original draft preparation, J.H.-F. writing--review and editing, [PERSON]-F., P.-R.-B., L.M.-R., A.P.[PERSON] and [PERSON]; supervision, [PERSON], [PERSON] and [PERSON], project administration, [PERSON]; funding acquisition, [PERSON], [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the Office of Research, Creation and Innovation of the Universidad Jorge Tadeo Lozano (340-07-10). Additional funding came from the Intramural Research Program of the National Institutes of Health (NIH, USA), National Library of Medicine (USA), National Center for Biotechnology Information (NCBI) ZIA LM082713-06. There was no additional external funding received for this study.  
We are grateful to Rodadero Aquarium in Santa Marta for their collaboration in obtaining and providing samples of loggerhead for the development of this study. Samples were obtained under a research permit that was granted by the Ministry of Environment and Territorial Development (#24 of 22 June 2012) Contract for Access to Genetic Resources (#64 of 23 April 2013), and permit for the collection of samples of Colombian biodiversity, issued to the Jorge Tadeo Lozano University (Resolution 1271 of 23 October 2014, IDB040I File). The authors thank [PERSON] for critical review of the manuscript.  
The authors declare that they have no known competing financial interests or personal relationships that could have influenced the results reported in this paper.