Ecotoxicity Analysis of Bentazone Under the Albufera Lake Conditions Before and After Electrooxidation and Photoelectrooxidation Processes

This study first analyzes the ecotoxicity of bentazone (BTZ), an herbicide detected in the Albufera Natural Park. BTZ exhibits an EC₅₀ (5 days) towards Lactuca sativa of 900 mg L⁻¹, showing a hormetic effect. The toxic effects of a BTZ, $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$, and ${\mathrm{N}\mathrm{a}}_2\mathrm{S}{\mathrm{O}}_4$ mixture are generally lower than the individual toxic effects considered additively. However, possible synergy on ecotoxicity was observed at 600 mg L⁻¹ of BTZ in the presence of 2.8 g L⁻¹ of ${\mathrm{N}\mathrm{a}}_2\mathrm{S}{\mathrm{O}}_4$ and 0.8 g L⁻¹ of $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$. A statistical model was obtained to predict the ecotoxicity thresholds towards Lactuca sativa for combinations of the three compounds. In general, when the concentration of one compound increases, a lower concentration of the others is necessary for the mixture to be toxic. However, in the presence of $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$, below 382 mg L⁻¹ of BTZ, the concentrations of both compounds need to be increased. This is attributable to the hormetic behavior of BTZ. This BTZ concentration decreases as the ${\mathrm{N}\mathrm{a}}_2\mathrm{S}{\mathrm{O}}_4$ concentration increases. Secondly, the effectiveness of electrooxidation and photoelectrooxidation processes to eliminate BTZ was studied. A ceramic anode made of Sb-${\mathrm{S}\mathrm{n}\mathrm{O}}_2$ and coated with a ${\mathrm{B}\mathrm{i}}_2{\mathrm{W}\mathrm{O}}_6$ photocatalyst was used. The degradation and mineralization degrees achieved using a mixture of 0.46 g L⁻¹ of $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$ and 1.3 g L⁻¹ of ${\mathrm{N}\mathrm{a}}_2\mathrm{S}{\mathrm{O}}_4$ (like the Albufera lake conditions) show intermediate values between those achieved with pure electrolytes. Specifically, applying 0.6 A, they are very close to the maximum values achieved with pure $\mathrm{N}\mathrm{a}\mathrm{C}\mathrm{l}$. Moreover, the final effluent’s toxicity is significantly lower, especially when light is applied. Therefore, the photoelectrooxidation process applying 0.6 A with the mixed electrolyte is the most effective technique from the combined point of view of final degradation (90.9%), mineralization (62.4%), and toxicity.