Plastic pollution has become a global environmental issue, yet little is known about how plastics degrade and interact with microbes under polar conditions, especially upon entering the marine environment. Here, we report the first in situ time-series experiment investigating early microbial colonization and surface oxidation of virgin plastics in Antarctic coastal waters. Virgin pellets of polystyrene (PS), low-density polyethylene (LDPE), and polyethylene terephthalate (PET) were deployed in Potter Cove (King George/25 de Mayo Island) for 31 days. Biofilm communities were characterized using 16S rRNA amplicon sequencing, while polymer surface chemistry was assessed by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR). Across all polymers, plastisphere assemblages were dominated by psychrophilic or psychrotolerant taxa. Plastic-associated communities showed consistent temporal changes over the 31-day exposure, with shifts in the relative abundance of taxa associated with different stages of biofilm development. Exposure time was a stronger determinant of community composition than polymer type. FTIR analyses revealed significant surface oxidation in PS and LDPE, particularly at days 21 and 31, with increases in hydroxyl, carbonyl, and carbon–oxygen indices. PET showed great variability and no consistent oxidative signals over the study period. The chemical shifts partially covaried with taxa associated with later sampling points, suggesting potential, but not yet conclusive, links between biofilm succession and polymer weathering. Our results provide some novel insights into the early dynamics of microbial colonization on plastic surfaces and polymer surface alteration in Antarctic waters, highlighting the importance of integrating microbial and chemical perspectives to understand plastic fate in polar ecosystems.

Microplastics (MPs) are pervasive contaminants in marine ecosystems, yet information on small particles (90% 97%), with few fibers. Polymer composition was dominated by polyamide under background conditions, while higher abundances showed increased polytetrafluoroethylene and acrylonitrile butadiene styrene contributions, indicating stronger anthropogenic influence. These results highlight the coupled role of continental sources and ocean circulation in transporting MPs from populated continental margins toward remote polar regions.