## 3 Results
### Bioassay and Oxidative Stress  
The SOD activity presented variations in each of the different treatments. At 6 h, the SOD activity of RBCs exposed to 1 mg L\({}^{-1}\) of MeHg was slightly more than double that in controls (1.56 \(\pm\) 0.58 vs. 0.72 \(\pm\) 0.24 U/mL of RBCs), and slightly greater than at 5 mg L\({}^{-1}\) MeHg (1.20 \(\pm\) 0.52 U/mL), which, in turn, was higher than in the control, demonstrating that RBCs at 1 and 5 mg L\({}^{-1}\) of MeHg experienced oxidative stress (Figure 4A). After 12 h of exposure, SOD activity was higher in RBCs that were exposed to 5 mg L\({}^{-1}\) MeHg (1.39 \(\pm\) 0.45 U/mL) than in controls (0.82 \(\pm\) 0.24 U/mL) and those RBCs exposed to 1 mg L\({}^{-1}\) of MeHg (1.08 \(\pm\) 0.25 U/mL), again indicating oxidative stress. There were no statistically significant differences between RBCs' SOD activity for the two MeHg exposure concentrations (1 and 5 mg L\({}^{-1}\)) for either of the two exposure durations (6 and 12 h), no correlation between the SOD activity and MeHg concentration to which the RBCs were exposed after 6 h of exposure (in all cases \(p>0.05\)). The glutathione transferase activity of loggerhead turtle RBCs at 6 and 12 h of exposure showed variations in cells that were exposed to 1 and 5 mg L\({}^{-1}\) of MeHg with respect to the control. At 6 h, the GST activity was higher for the 1 and 5 mg L\({}^{-1}\) MeHg treatments as compared to the control (12.72 \(\pm\) 5.41 and 11.93 \(\pm\) 9.54 vs. 6.76 \(\pm\) 4.93 nmol/min/mL of RBCs, respectively, demonstrating high response to the concentration and exposure time to MeHg. However, after 12 h of MeHg exposure, the GST activity was lower in RBCs exposed to 5 mg L\({}^{-1}\) MeHg when compared to those exposed to 1 mg L\({}^{-1}\) MeHg and to the control (5.96 \(\pm\) 6.36 vs. 9.54 \(\pm\) 8.91 and 6.92 \(\pm\) 5.16 nmol/min/mL of RBCs), respectively. Nevertheless, the observed differences between MeHg treatments and the control were not statistically significant for any exposure concentrations or time point (in all cases \(p>0.05\)) (Figure 4B). Figure 3: Cell viability of erythrocytes of loggerhead sea turtle against different concentrations of methylmercury, used for calculating lethal concentration (LC\({}_{50}\)). Error bars indicate mean and standard deviation. Treatments with significant differences (ANOVA, \(p<0.05\)) indicated by asterisk (*). Treatments with non-significant differences indicated by same letter (a, b, c, d, e). The malondialdehydedehyde (MDA) levels increased with respect to the control with increasing MeHg concentration and exposure time. After 6 h, the MDA concentrations were 38.31 \(\pm\) 20.92 and 46.65 \(\pm\) 13.42 uM for 1 and 5 mg L\({}^{-1}\) MeHg, respectively, when compared to 27.58 \(\pm\) 0.42 uM in the controls. After 12 h, the MDA concentrations increased to 49.15 \(\pm\) 15.75 and 56.38 \(\pm\) 13.97 uM of MDA for 1 and 5 mgL\({}^{-1}\) MeHg, respectively, whereas MDA in controls remained virtually unchanged (28.91 \(\pm\) 9.35 uM, Figure 5). While the observed differences between treatments were not considered to be statistically significant (ANOVA, \(p>\) 0.05), a positive correlation was observed between the MDA concentrations and MeHg concentrations after 12 h of exposure time (r Spearman = 0.56, \(p<\) 0.05, Figure 6). This result is preliminary; therefore, it is necessary to carry out evaluations with a larger sample to improve the statistical significance of this analysis and verify this possible correlation. Figure 4: Activities of (A) Superoxide dismutase (SOD) and (B) glutathione S-transferase (GST) in erythrocytes of loggerhead turtles exposed to methylmercury (MeHg) at 0, 1 and 5 mg L\({}^{-1}\) for 6 and 12 h (mean \(\pm\) standard error of the mean, (n = 5). Differences between treatments were statistically non-significant in all cases (\(p>\) 0.05).