## 4 Discussion
One of the possibilities for the lower values of LC\({}_{50}\) computed with the data obtained from the MTT assay may be due to the mode of action of the surfactants, since membrane destabilization and hydrolysis of cell membrane proteins and enzymes might impair the conversion of MTT to formazan by cellular membrane enzymes. The work from [PERSON] al. [31] demonstrates that SLE\({}_{0}\)S promotes denaturation of lipase with the consequent loss of function, but the increase in the number of EO units of the polar head of SLE\({}_{2}\)S stabilizes the enzyme, maintaining its function. Surfactants that are prone to forming micelles, including SLE\({}_{0}\)S, tend to induce curvature stress, causing membrane disordering and culminating in cellular lysis [32]; but recent developments have demonstrated that this effect is diminished with the incorporation of EO, with SLE\({}_{1}\)S having a critical micelle concentration of 0.7 mM in comparison to SLE\({}_{0}\)S with 8.7 mM and a membrane stiffness that increases instead of decreasing, diminishing membrane disordering [33]. Despite the differential sensitivity between the MTT and resazurin assays, the micelles composed of each of the six variants of SLE\({}_{n}\)S and LAS were able to impair the viability of the A6 cells at low concentrations: for MTT the LC\({}_{50,48\text{h}}\) ranged from 0.398 to 0.554 mg/L and for resazurin from 0.557 to 0.969 mg/L. These values are within the range of toxicity reported by [PERSON] et al. [1] for the bacterium _V. fisherii_; as mentioned above, EC\({}_{50,15\text{min}}\), values were between 0.56 and 8.60 mg/L. Though, comparing the toxicity of SLE\({}_{0}\)S here reported with that of other studies, a higher toxicity was observed in the present work. [PERSON] et al. [34] tested SLE\({}_{0}\)S on the mouse fibroblast-like cells L-929 (ATCC, CCL-1) and reported an LC\({}_{50}\) of 173.6 mg/L in 72 h of exposure (converted from the original result of 602 uM reported in their article), which is considerably higher than the values estimated for the A6 cells in the present study. [PERSON] et al. [7] report LC\({}_{50}\) values ranging between 1 mg/L and 13.9 mg/L for aquatic organisms (invertebrates and fish) exposed for 96 h to sodium lauryl sulphate (SLE\({}_{0}\)S). Nevertheless, this toxicity was influenced, apart from the target species, by several environmental factors such as water temperature and hardness [10; 35]. [PERSON] et al. [36] showed that human keratinocytes and fibroblasts cell lines, when exposed to 1.65 mg/L of SLE\({}_{0}\)S (converted from the original result of 5% concentration reported in their article), have no active metabolism and, therefore, no viability after 24 h of exposure, with our work demonstrating far lower concentrations for LC\({}_{90}\), but this higher cytotoxicity may be due to the presence of LAS. Several studies focusing on the effect of SLE\({}_{n}\)S and LAS in keratinocytes and other cellular models demonstrate that the exerted cytotoxic effects are not exclusive to membrane damage but also involve the formation of reactive oxygen species (ROS) together with altered calcium metabolism [37; 38; 39]. [PERSON] et al. [37] using the same cellular model, A6 cell line, demonstrated that LAS was able to activate calcium channels in the apical membrane and destabilize ion homeostasis, contributing to a higher chloride secretion due to the activation of calcium-dependent chloride channels from the apical membrane [37]. Alterations to calcium metabolism induced by sodium lauryl sulphate (SLS) at concentrations higher than 7.21 mg/L (converted from the original result of 25 uM reported in the article) were also found in keratinocytes and in a reconstructed human epidermal skin model [38]. [PERSON] et al. [39] demonstrated that membrane damage due to SLE\({}_{0}\)S activates calcium channels, inducing an increase in intracellular calcium promoting the formation of ROS and the activation of IL-1, leading to skin roughness.