TRACKING THE PHOTOOXIDATION PRODUCTS OF PRIMARY PLASTIC PELLETS (NURDLES) IN THE MARINE ENVIRONMENT

Marine plastic debris often undergoes photooxidation through sunlight exposure, potentially releasing substances that impact ecosystem health and carbon cycling. However, the photochemical modification of plastic polymers is still poorly understood. In this study, we investigated the photooxidation of two common plastic pellets (nurdles), polyethylene (PE) and polycarbonate (PC).  Nurdles were exposed to simulated sunlight for 8 weeks, equivalent to 1.5 years of natural sunlight along the Texas coast, and their leachates were analyzed. FTIR confirmed surface oxidation of nurdles, showing oxygen incorporation into polymer chains as carbonyl and carboxyl groups. This exposure also facilitated the leaching of dissolved organic carbon (DOC) to seawater, PE nurdles released 18 times more DOC than PC nurdles. No nano-sized particles were detected through ultrafiltration (3k Da cut-off) or microscopy scanning. High-resolution mass spectrometry revealed an increase in molecular formulas within plastic-derived DOC by sunlight exposure. Over time, the oxygen-to-carbon ratio in PE-derived DOC increased, while the hydrogen-to-carbon ratio in PC-derived DOC decreased, indicating an enrichment of oxygenated compounds, likely due to an increase in carboxyl groups on nurdle surface during later stages of photooxidation, consistent with the FTIR results. Overall, these results demonstrate that sunlight exposure drives the release of plastic leachates, which consist of small molecules rather than nano-sized particles, offering new insights into the environmental fate of primary plastics.

Presentation Preference: Oral

Primary Presenter: Xiangtao Jiang, University of Texas at Austin MSI (xtao.jiang@utexas.edu)

Authors:

Kaijun Lu, University of Texas at Austin  (kaijun.lu@utexas.edu)

Zhanfei Liu, University of Texas at Austin  (zhanfei.liu@austin.utexas.edu)