The Complex Impact of Organic UV Filters in the Estuarian Environment: Environmental Flux, Photodegradation Process, and Combined Ecotoxic Effects with Microplastics

Abstract

There is strong evidence suggesting the co-existence of microplastics (MPs) and organic pollutants, including organic UV filter (OUVFs), in the coastal environment of the Great Bay Area. Microplastics can adsorb other micropollutants, potentially increasing their toxicity. A knowledge gap remains regarding the adsorption of OUVFs onto microplastic particles and their combined toxic effects on marine organisms. Therefore, the overall objectives of this PhD thesis are to evaluate the complex impact of OUVFs concerning their environmental loads, photodegradation, and combined ecotoxicity with microplastics in the estuarine environment.

First, ethylhexyl methoxycinnamate (EHMC) was identified as one of the primary OUVFs with the highest potential risk in the Pearl River Delta region through quantitative analysis of 11 common OUVFs. The mechanisms of photodegradation kinetics and the generation process of transformation products (TPs) of EHMC were investigated through quantitative analysis of EHMC and qualitative analysis of EHMC-TPs. EHMC self-sensitive photolysis was confirmed through the detection of singlet oxygen (¹O₂) in the EHMC photodegradation system combined with Density Functional Theory (DFT) calculations. In the subsequent research, the adsorption process of EHMC onto polyethylene (PE), polypropylene (PP) and polycarbonate (PC) MPs was shown to fit the Pseudo-first-order kinetics for adsorption and be linear for adsorption isotherms. The production and consumption of reactive radicals were associated with the rapid accumulation of EHMC around MPs in the water. Based on the obtained results, photodegradation pathways and reaction sites of EHMC were identified. The mixture of EHMC and PP MPs was exposed to fertilized marine medaka embryos, demonstrating that the EHMC solution interfered with embryo development and increased mortality during the embryonic stage. The complex EHMC/EHMC-TPs mixture caused significant malformation and differential expression genes (DEGs) at low concentrations under the interactive effect of MPs, warranting more attention in the future assessment of ecotoxicological risk of EHMC.

This study provides fundamental information on the hazard assessment of two important groups of contaminants, microplastics and OUVFs, and contributes to the marine pollution and conservation research in the coastal region of the Greater Bay Area.

Date of Award	20 Sept 2024
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Yuhe HE (Supervisor)