## 3 Results and Discussions
### Mass Balance
vulgaris_ in the presence of 0.8 mg MeP/L over 7 days, reinforcing the theory that parabens do not diffuse into the cells of this species [59]. Thus, biodegradation appeared as the main pathway for paraben degradation in _C. vulgaris_. BP exhibited a remarkable abiotic degradation pathway (Figure 5a,b). As previously explained, no significant differences were observed between the BP removal efficiency in the LO experiments (abiotic conditions) and the LOM experiments, regardless of the microalgae used, obtaining a \(p\)-value \(>\) 0.05 in both cases. In addition, BP showed low adsorption onto the cell wall, and this fraction was higher when using _C. vulgaris_ (Figure 5b) compared to _Scenedesmus_ sp. (Figure 5a). As can be observed in Figure 5a,b, the contribution of the bioaccumulation pathway was negligible for both microalgae species. In the case of _Scenedesmus_ sp., values ranging between 0.09 and 0.52% (concentrations between LQD and LOD) were obtained from day 1 to day 7 for bioaccumulation. A similar trend was observed for _C. vulgaris_, its bioaccumulation percentages of BP ranging between less than 0.12% (concentrations below the LOD) and 0.53% from day 1 to 7, respectively. Comparing the obtained results with previous studies on unsubstituted BP is challenging due to the scarcity of such studies. The most similar compounds found in the literature were BP-3 and BP-4. In this way, [PERSON] et al. (2020) achieved 97% biodegradation of 0.5 ppm of BP-3 within 10 days using _S. obliquus_, and approximately 3% attributed to abiotic removal [53]. Similarly, [PERSON] et al. (2018) found negligible BP-4 adsorption and absorption onto _C. vulgaris_ strains, with the concentration decreasing solely due to biodegradation, achieving 14% at 1 mgBP-4/L within 13 days [87]. The lower abiotic degradations observed in the literature compared to our research are attributed to differences in cultivation conditions. Specifically, other studies' cultures were maintained only with agitation, without aeration, leading to the absence of oxygen-derived ROS in the culture medium, which promoted BP removal. Figure 5: Contribution (%) of abiotic degradation (yellow), and biosorption (red) and biodegradation (green _Scenedesmus_ sp. And orange _C. vulgaris_) in BP removal by _Scenedesmus_ sp. (**a**) and _C. vulgaris_ (**b**). Error bars represent \(\pm\) standard error of the mean (\(n\) = 3). The contribution of bioaccumulation and biodegradation (for both _Scenedesmus_ sp. And _C. vulgaris_) are not plotted because they are negligible. The main removal pathway for BPA using _Scenedesmus_ sp. was biodegradation (Figure 6a). Adsorption accounted for less than 1% of the total removal during the two first days, decreasing to less than 0.06% in the following days. Additionally, BPA was not detected inside the cell, indicating that the bioaccumulated fraction was negligible, remaining below 0.06% (under the LOD). The contributions of biosorption and bioaccumulation to BPA removal using _C. vulgaris_ (Figure 6b) were higher. Both pathways were similar during the first three days, with bioaccumulation becoming predominant from day 4 onwards. These results agree with other authors, such as [PERSON] et al. (2018), who reported the abiotic removal of BPA by 19%, with the fractions removed by accumulation, adsorption, and biodegradation by 1.3%, 11.6%, and 40%, respectively, within 5 days using the alkaliophilic Chlorophyta _Picocystis_ with an initial concentration of 25 mg BPA/L [89]. Similarly, the abiotic removal values of BPA were 15.0% with a biodegradation pathway contribution of 25% using _C. mexicana_ and _C. vulgaris_, respectively, at the end of a 10-day experiment with initial concentrations of 1 mg BPA/L [55]. As can be observed in Figure 7a,b, abiotic degradation and biodegradation were the main pathways to remove E. Comparing _Scenedesmus_ sp. (Figure 7a) and _C. vulgaris_ (Figure 7b), it can be observed that E removal occurred at earlier stages in the former species than in the latter. In contrast, _C.