## 3 Results and Discussion
As shown in both figures, the OC concentration measurements obtained by electroanalytic and chromatographic methods are in close agreement, with no significant differences observed between the data sets. The results indicate that OC pollution in water is effectively reduced even at low current densities. However, the decay in OC concentration becomes more pronounced over time when a current density of 10 mA cm\({}^{-2}\) is applied. This behavior is consistent with previous studies [5; 8; 16], which suggest that the removal of OC is more efficient at higher current densities [40]. The results highlight that the extent of OC removal is dependent on the applied current density, with higher values leading to more efficient degradation. The mechanism behind OC removal from water matrices involves the reaction of OC with electrochemically generated hydroxyl radicals (\({}^{\bullet}\)OH) at the BDD electrode surface, and other oxidizing species produced by electrochemical processes, such as chloride-based mediators. This finding is supported by the existing literature [41; 42], which demonstrates that OC is efficiently degraded through these oxidative processes when higher current densities are applied during electrochemical treatment. Figure 5: Quantification of OC using HPLC (blue-green circles) and electroanalysis (blue-red circles) in various sunscreens (S1, S2, S3, S4, S5) and a known amount of OC in swimming pool water samples (S6). The bars represent the mean OC concentration obtained. As demonstrated in previous studies [43; 44], electrochemical measurements in the presence and absence of chloride in water reveal distinct behaviors. In particular, the potential for the oxygen evolution reaction (OER) shifts toward less positive values when NaCl is added to the solutions. This shift is related to the chloride concentration in the aqueous matrix, which increases the ionic strength and thus the conductivity of the solution. This leads to higher current densities, which benefits electrochemical oxidation (EO) by reducing energy requirements. Additionally, the observed shift in potential of the polarization curves suggests that active chlorine species [45] are produced simultaneously with hydroxyl radicals [46]. This occurs under oxygen evolution conditions [46; 47], as described in the following equations:  
\[2\mathrm{Cl}^{-}\ \rightarrow\ \mathrm{Cl}_{2}+2\mathrm{e}^{-} \tag{5}\]  
\[\mathrm{Cl}_{2}\ +\ 2\mathrm{H}_{2}\mathrm{O}\ \rightarrow\ \mathrm{H}\mathrm{O} \mathrm{Cl}+\mathrm{H}_{3}\mathrm{O}^{+}+\mathrm{Cl}^{-} \tag{6}\]  
\[\mathrm{H}\mathrm{O}\mathrm{Cl}+\mathrm{H}_{2}\mathrm{O}\ \rightarrow\ \mathrm{H}_{3}\mathrm{O}^{+}+\mathrm{ClO}^{-} \tag{7}\]  
\[\mathrm{Cl}^{-}+\mathrm{OH}\ \rightarrow\ \mathrm{ClO}^{-}\ +\ \mathrm{H}^{+}\ +\ \mathrm{e}^{-} \tag{8}\]  
\[\mathrm{ClO}^{-}+\mathrm{OH}\ \rightarrow\ \mathrm{ClO}_{2}^{-}\ +\ \mathrm{H}^{+}\ +\ \mathrm{e}^{-} \tag{9}\]  
\[\mathrm{ClO}_{2}^{-}+\mathrm{OH}\ \rightarrow\ \mathrm{ClO}_{3}^{-}\ +\ \mathrm{H}^{+}\ +\ \mathrm{e}^{-} \tag{10}\]  
\[\mathrm{ClO}_{3}^{-}+\mathrm{OH}\ \rightarrow\ \mathrm{ClO}_{4}^{-}\ +\ \mathrm{H}^{+}\ +\ \mathrm{e}^{-} \tag{11}\]  
\[\mathrm{BDD}+\mathrm{H}_{2}\mathrm{O}\ \rightarrow\ \mathrm{BDD}(\cdot\mathrm{OH})\ +\ \mathrm{H}^{+}\ +\ \mathrm{e}^{-} \tag{12}\]  
As illustrated in Figure 6, the degradation of OC was enhanced when a higher current density was applied due to the increased production of active chlorine species. The synergistic effect between hydroxyl radicals (\({}^{\bullet}\)OH) electrogenerated at the anode surface (Equation (12)) and the electrochemically/chemically formed oxidizing species in the bulk solution (Equations (5)-(11)) contributes to the greater degradation of OC.