## 4 Discussion
In the present study, the average total mercury (Hg-T in RBCs) concentration of 0.031 \(\pm\) 0.011 mg L\({}^{-1}\) was obtained prior to bioassay and, after 12 h of bioassay with erythrocytes at 1 mg L\({}^{-1}\) MeHg, the concentration of Hg-T increased approximately 10 times (0.309 \(\pm\) 0.10 mg L\({}^{-1}\)). At 5 mg L\({}^{-1}\) of MeHg, the Hg-T concentrations increased to 2.183 \(\pm\) 0.77 mg L\({}^{-1}\), being 70 times higher than controls and seven times higher than RBCs that were subjected to 1 mg L\({}^{-1}\) of MeHg. Various studies have shown that the different dissolved forms of mercury have a high affinity for the sulfhydryl groups present in the cells, and that in their methylated state it has an affinity of over 90% for human RBCs, where it adheres in less than an hour [22, 57, 58]. Studies of RBCs of mammalian species have also shown that MeHg is evenly distributed between intra and extracellular hemoglobin [59, 60]. In this study, these results demonstrate the high affinity of RBCs for Hg and their great capacity to retain it inside of the cell. Moreover, the MeHg median lethal concentration (LC\({}_{50}\)) of RBCs for loggerhead turtles exposed in vitro was determined in this study, eight MeHg doses ranging from 0.5-100 mg L\({}^{-1}\), in addition to seawater controls. At the two highest concentrations, there was 100% cell mortality (Figure 3). In the control group, mortality was 13% and it increased with the MeHg concentration. The LC\({}_{50}\) for loggerhead turtle RBCs was 8.32 mg L\({}^{-1}\) after 96 h of incubation. To date, there are no published studies  
Figure 7: Comparison between the percentages relative to white cells in the blood counts for the loggerhead turtles (_Caretta caretta_) (ours) and the minimum and maximum ranges published by [PERSON] et al. (2019). on LC\({}_{50}\) of MeHg on loggerhead sea turtle RBCs, so there are no literature values to compare these results with. Recently, the use of RBCs was reported in turtle studies of the red eared sliders species (_Trachemys callirostris_) to assess the genotoxic effect of environmental pollutants [61]. [PERSON] et al. [62] described the use of primary erythrocyte cell cultures as in vitro models for evaluating the effects of different endocrine disrupting chemicals. [PERSON] et al. [55] established primary cell cultures from the intestine, heart, liver, ovary, and skin of green sea turtles (_Chelonia mydas_), and skin for loggerhead turtles and determined the mean effective concentration (EC\({}_{50}\)) with an average for all cell types of 18,4 uM for Hg\({}^{+2}\), being skin tissue the most sensible. In this study, LC\({}_{50}\) was found to be almost double this value (33.05 uM). They found significant differences between the different cell types evaluated. In this study, other cell types, RBCs, were evaluated in loggerhead turtles, also showing great differences. The differences in response to Hg contamination between cells and between different species are appreciable [63; 64; 65]. Cytotoxicityicity is generally due to non-specific molecular and cellular effects [55]. Some pollutants, such as Hg, have higher accumulation values in loggerhead turtles [66; 67]. Loggerhead sea turtles' RBCs appear to have a higher sensitivity and affinity for Hg than skin cells and other tissues (as described above), which would produce the big difference between these two results. RBCs could represent a better in vitro model for toxicological studies than primary cell cultures according to this result, and due to the high sensitivity of the RBCs presented here. However, primary cell cultures can be used to specifically study the response of organs to environmental pollutants. Viability studies that were conducted in RBCs in marine fish species as _Sparus aurata_ and _Dicentrarchus labrax_ have reported LC\({}_{50}\) of 5.25 and 7.25 mg L\({}^{-1}\), respectively, in RBCs that were exposed to MeHg for 24 h [49].