Preliminary insights into the release behavior of dissolved organic matter from aged microplastics in seawater: Effects of aging types.

Microplastics (MPs) entering the ocean experience multiple aging driven by photochemical and biological processes, resulting in substantial release of dissolved organic matter (DOM). However, limited attention has been paid to the differences and correlations in the influences of ultraviolet irradiation (UV), biofilm formation (Bio), and their coupled process (Bio-UV) on the release behavior of MP-DOM in complex marine environments. Herein, polyethylene terephthalate (PET)-MPs, as commonly encountered plastic particles in marine environments, were first subjected to UV-, Bio- and coupled Bio-UV aging, and then leached in artificial seawater for 10 days. The collected MP-DOM was analyzed in terms of the contents and optical characteristics. The results showed that three aging processes led to obviously different alterations in MPs surface properties, including morphological changes, decreased hydrophobicity, and accumulation of biomass. During seawater immersion, Bio-UV-MPs experienced much higher release of DOM than others, presenting the synergistic promoting effect of UV- and Bio-aging on the release of MP-DOM. According to spectroscopic analysis, the DOM from UV-MPs and Bio-MPs had their own specific humic-like components, which were derived from UV oxidation and biofilm formation respectively, and fluorescent component composition for Bio-UV-MPs resembled Bio-MPs. The results indicated that Bio-aging process may impair the potential contribution of prior UV-aging to the fluorescence components. This study elucidates the distinct effects of aging types on the release behavior of MP-DOM, thereby advancing our understanding of the environmental fate of MPs and their derivatives in complex marine environments.