The added value of a zebrafish embryo-larval model in the assessment of wastewater tertiary treatments

Conventional treatment technologies applied in wastewater treatment plants are not efficient to remove pharmaceuticals from effluents. Consequently, the ever-growing presence of these emerging contaminants in aquatic environments has been reported. There is great concern about their potential adverse effects on organisms, and increasing interest in technologies to minimize these effects. More efficient technologies are needed to solve these problems. The aim of this study was to evaluate the efficiency and safety of two wastewater tertiary treatments. A mixture of 9 pharmaceuticals (acetaminophen, norfloxacin, metoprolol, caffeine, antipyrine, sulfamethoxazole, ketorolac, hydroxybiphenyl and diclofenac at 10 mg L-1 each) was added to a wastewater sample to further be ozonated and subjected to photocatalytic oxidation (black-light radiation/TiO2/O-2) for different time regimes (30 and 120 min). Resultant effluents were assessed for chemical efficacy (total organic carbon and chemical oxygen demand) and toxicity (through a zebrafish embryo-larval bioassay including mortality and sublethal effects). Ozonation (120 min) and photocatalytic oxidation (30 min and 120 min) were effective processes to decrease both total organic carbon (TOC) and chemical oxygen demand (COD), with the latter under Directive 91/271/CEE recommended values. However, only the effluent subjected to 120 min photocatalytic oxidation was actually safe for the embryo-larval development and its functionality, with behavioral effects as the most sensitive endpoint. Thus, the toxic response of the zebrafish embryo-larval model proved to be more sensitive than the effluent physical-chemical monitoring itself, providing a tool to better characterize wastewater suitability.