Photochemical Aging Triggers Zn(II) Mobilization and Toxicity in Metallopolymer Microplastics to the Green Macroalga Ulva

High Resolution Image Download MS PowerPoint Slide UV-induced aging alters the chemical composition and leaching of metal-containing polymer microparticles, influencing the environmental fate of microplastics in marine systems. Two stimuli-responsive metallopolymers (based on histidine methacrylate, butyl methacrylate, zinc triflate) were artificially aged, and three sample types were tested on germinating gametes of the macroalga Ulva (Chlorophyta): (i) the untreated polymers, (ii) substances released during UV exposure (Leaching Extract1), and (iii) substances released after UV exposure (Leaching Extract2). Aged polymers and their leachates exhibited higher toxicity than virgin samples. UV irradiation enhanced the release of Zn-containing species; however, the LC 50 of Zn(II) alone (1.24 mg L –1 ) exceeded that of the variously treated polymer samples (0.05–0.99 mg L –1 ), indicating that Zn(II) alone cannot account for the toxicity and that additional leached substances contribute to the toxic response. In some cases, Leaching Extract2 exhibited higher toxicity than Leaching Extract1, suggesting that bioactive compounds continued to be released after aging. These findings demonstrate that UV-induced aging alters the chemical composition and release behavior of metallopolymers, thereby enhancing their toxicity to marine organisms and resulting in continuous zinc mobilization that can impair algal growth. This highlights the importance of considering aging-driven leaching when assessing the environmental risks of metal-containing microplastics.