Photocatalytic oxidation of pharmaceutical contaminants of emerging concern using sunlight and visible radiation: Mechanism and ecotoxicological evaluation

Pharmaceutical and personal care products are released in watercourses due to the inefficiency of conventional wastewater treatment and photocatalytic oxidation has been pointed out as an alternative. Thus, this study aimed at gaining an insight on the mechanism of reaction using different radiation sources (solar and visible) and catalysts (Ag-TiO2 and Pd-TiO2) for the abatement of a mixture of pharmaceutical contaminants of emerging concern (CEC) - Sulfamethoxazole (SMX), Carbamazepine (CBZ) and Lorazepam (LRZ). Moreover, aiming to evaluate the effectiveness of these treatments to improve their environmental friendliness, an ecotoxicological evaluation was carried out by assessing the responses of several indicator organisms (fish, cladocerans, plants, microalgae and bacteria). The hydroxyl radical had a major role on photocatalytic oxidation. 90% of CBZ degradation was achieved after 60 min using sunlight and Ag-TiO2 whereas this removal was reduced to 15% with hydroxyl radical scavengers. Concerning the ecotoxicological evaluation, the untreated mixture was mildly toxic to these organisms (approximately 30% depression in the assessed endpoints), except for microalgae, where a pronounced toxicity (85% of growth inhibition). Treated solutions achieving lower concentrations of the parent compounds, were generally found to be more toxic than the untreated mixture. For example, after solar photocatalytic oxidation using Ag-TiO2 the toxicity of the mixture to the microalgae and Daphnia magna increased or remained unaffected. This suggests the formation of toxic by-products during the treatments, highlighting that effective treatments do not always translate into improved environmental friendliness. These results raise concern on the environmental safety of the water treatment technologies.