Ecotoxicological assessment of photo-ozonation applied to emerging contaminants in single and mixed systems: evidence of increased toxicity after treatment

Emerging contaminants are chemically diverse compounds that persist and migrate across environmental compartments, including water, soil, sediments, and food. Their removal from wastewater is particularly challenging, especially when present as mixtures, due to their persistence, low biodegradability, and formation of toxic byproducts. This study aimed to investigate the efficiency of photo-ozonation for degrading the emerging pollutants octocrylene, methylparaben, and benzophenone, individually and in binary and ternary mixtures, using ecotoxicological bioassays, addressing a knowledge gap still little explored in the literature. Aqueous solutions containing 100 µg/L of each compound were prepared and subjected to photo-ozonation, generating treated samples. Raw and treated solutions were assessed using the bioindicators Allium cepa and Eisenia fetida. In the plant assay, benzophenone exhibited cytotoxicity prior to treatment, while benzophenone, octocrylene, and their mixture displayed mutagenic effects. After photo-ozonation, increased cytotoxic and mutagenic responses were observed, and additional mixtures became toxic, attributed to the formation of transformation products. In the avoidance test, only the ethylparaben-benzophenone mixture produced toxicity to earthworms, although higher avoidance rates were noted in benzophenone samples following treatment. Taken together, photo-ozonation showed limited effectiveness in reducing ecotoxicity. Data demonstrated that treatment strategies need to consider mixture interactions and byproduct formation, reinforcing the need for optimized and environmentally safe advanced oxidation processes.