Investigation of toxicity of antiviral drugs in the presence of microplastics and their removal through ozonation and LDH-based catalytic ozonation

Abstract

Following global outbreaks such as SARS-CoV-2 and influenza, the heightened use of pharmaceuticals to treat infected individuals has led to the presence of antiviral drugs and their metabolites in wastewater at significant levels. Since wastewater treatment plants (WWTPs) are not designed to remove antiviral drugs, these contaminants are discharged into receiving environments without treatment. If these substances are not adequately degraded during wastewater treatment, they could potentially harm human and ecosystem health when released into aquatic systems. To address this concern, tertiary treatment applications have to be employed. In this study, in order to assess the treatability of two commonly used antivirals, Oseltamivir (OSE) and Favipiravir (FAV), advanced oxidation processes, involving ozonation and catalytic ozonation were applied. Additionally, the potential ecotoxicological impacts of treated wastewater effluent were investigated on soil and aquatic environments. Moreover, the efficiency of the applied processes was also explored in the presence of microplastics (MPs). In this study, the concentrations of OSE and FAV were selected based on the occurrence of these antivirals in environment ranging from low (500 ng/L) to high (50 µg/L). A biologically treated synthetic wastewater sample, mirroring a typical domestic effluent, was exposed to ozonation with three different ozone dosages: 0.2, 0.6, and 1 mg O3/mg DOC (dissolved organic carbon) at pH values of pH: 7±0.1 and pH: 10±0.1. The degradation of these compounds was also assessed in the presence of catalyst 0.1 g/L of ZnFe LDH (layered double hydroxide), which is a nanocomposite catalyst. The widely found polyethylene (PE) microplastic (0.1 mg/L) was introduced into samples during the ozonation and catalytic ozonation applications. Antiviral compounds and their corresponding removal rates were assessed using liquid chromatography tandem mass spectroscopy (LC-MS/MS), employing the isotope dilution method. Solid phase extraction was employed to facilitate accurate quantification of antivirals in samples. Finally, to assess the potential reusability of treated wastewater, soil organisms Enchytraeus crypticus and acute organisms Vibrio fischeri were exposed to ozonated and catalytic ozonated samples according to OECD and ISO 11348-3 methods. According to the findings, by evaluating conventional parameters in ozonated and catalytic ozonated effluent samples, it was concluded that both ozonation and catalytic ozonation can effectively decrease the amount of organic matter in wastewater, while MPs had a negligible effect on the wastewater characterization. In this regard, the maximum removal rates in chemical oxygen demand (COD), dissolved organic carbon (DOC), and ultraviolet absorbance at 254 nm (UV254) parameters were achieved by catalytic ozonation at pH 10 with 1 mg O3/mg DOC, reaching approximately 27.2%, 17.7%, and 71%, respectively. Additionally, particle size distribution (PSD) analysis was conducted for non-ozonated and ozonated samples revealed an 11% decrease in the COD fraction within the particle size interval of <2nm, contributing to an overall removal efficiency of 21%. This finding underscores the significance of the soluble fraction (<2nm) in COD removal, constituting 54% of the total COD removed. In the case of antiviral removal, it was observed that in single ozonation and without the presence of MPs, both OSE and FAV showed a removal efficiency of 85% at high antiviral concentrations, regardless of the specific ozone dose. However, at low antiviral concentrations, while FAV was completely removed with 100% efficiency, OSE only exhibited a 26% removal under the same conditions. At high concentrations of antiviral compounds, catalytic ozonation did not perform as effectively as single ozonation. When considering the presence of MPs, it can be concluded that they negatively impact the removal efficiency of antiviral compounds. To assess the effectiveness of the treatment process and the potential reusability of ozonated and catalytic ozonated effluent samples, ecotoxicological analysis was conducted on Enchytraeus crypticus and Vibrio fischeri. The soil experiments carried out on high antiviral concentrations did not indicate any toxic effect on E. crypticus organisms; instead, the reproduction rate of organisms increased. Moreover, when these organisms were exposed to the samples containing MPs, their reproduction rate increased significantly. The toxicity evaluation using Vibrio fischeri bacteria indicated that biologically treated synthetic wastewater exhibited higher toxicity compared to ozonated wastewater. Furthermore, ozonated wastewater demonstrated slightly higher toxicity than catalytic ozonated wastewater. The leaset toxicity was observed in distilled water. The presence of individual antivirals in the wastewater resulted in lower toxicity compared to their combined presence, revealing the synergistic effect of FAV and OSE. Since antivirals were not completely removed during ozonation and catalytic ozonation at the high initial concentration (50 µg/L), they contributed considerably to the observed toxicity. The experimental results indicated that ozonation and catalytic ozonation could serve as favorable options to upgrade existing wastewater treatment plants. These processes not only contributed to the reduction in the release of antivirals from domestic effluents, but also significantly enhanced the suitability of treated wastewater for irrigation of agricultural areas.