Nathalie Bernard

Microplastics (MPs) are widely recognized as pervasive contaminants in marine environments, yet their distribution throughout the water column remains poorly constrained, particularly for particles <300 µm, which are often under-sampled due to methodological limitations. Here, we present the first full-depth characterization of 20–300 µm MPs across five stations in the central Mediterranean Sea (n = 75). Using a state-of-the-art contamination-controlled closed-loop filtration system coupled with strict QA/QC procedures and automated laser direct infrared (LDIR) chemical imaging, MPs were detected in all samples, with a median abundance of 2.00 MP L⁻¹ (IQR = 1.33–2.92). MP abundance differed significantly among stations, while no common Depth Group effect was detected. A significant Station × Depth interaction showed that vertical abundance patterns differed among stations. Polymer composition also varied significantly among stations but showed no consistent depth-related pattern, whereas particle size distribution and morphology were broadly similar across stations and depths. These findings show that small MPs occur throughout the full water column and that their vertical distribution cannot be described by a single depth-related pattern across the sampled stations. The study further demonstrates the value of contamination-controlled full-depth sampling for characterizing small MPs in the ocean interior.

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.

Monitoring microplastics (MPs) has become a global priority requiring equitable analytical capacity, particularly in the Global South. Through the NUTEC Plastics initiative, the IAEA has addressed this need by developing a harmonized protocol and providing training and equipment to its Member States. The initial phase targeted large MPs (0.3–5 mm) in beach sand. To assess data comparability and analytical performance, a proficiency test was organized in which 49 laboratories from 41 countries analyzed a blind beach-sand sample spiked with a defined number and composition of MPs, reporting counts and polymer identity by size fraction. Recovery was strongly size-dependent. Performance was reliable for the large fraction (1–5 mm), where 22 laboratories (~45%) recovered the exact spiked count, in contrast to one laboratory (~2%) for the small fraction (0.3–1 mm). Of the 41 laboratories identifying polymers, 18 (~44%) failed to detect any transparent polystyrene particles. Generalized linear modelling identified the agitation method during density separation as the only significant predictor of polystyrene recovery, with mechanical shaking yielding ~1.77 fold higher recovery than magnetic stirring. Approximately one in four reported particles could not be attributed to spiked polymers.These findings identify targets and define priorities for the next capacity-building phase: improving recovery of small and transparent particles, and further standardizing agitation, contamination control, and data reporting. Altogether, this study provides a framework for method refinement and a step toward standardized global MP monitoring.

Microplastic contamination in coral reef environments is increasingly recognized as a global concern; however, the extent to which polymer composition can help distinguish contamination sources and transport-related processes remains poorly understood. In this study, we assessed the abundance, composition, and diversity of microplastics (20–300 µm) across multiple reef systems in the Cuban archipelago using high-resolution Laser Direct Infrared (LDIR) spectroscopic analysis. Microplastic abundance varied substantially among sites, with a median concentration of 66 particles L⁻¹ (IQR: 45–115 particles L⁻¹), ranging from 8 to 218 particles L⁻¹. A total of 11 polymer types were identified, with polyethylene (PE), polypropylene (PP), and polyamide (PA) dominating the assemblages and accounting for approximately 77% of detected particles. While these polymers were consistently observed across all sites, suggesting a pervasive regional background signal, highly impacted reefs exhibited more heterogeneous polymer profiles, including increased contributions of polyurethane (PU), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC), consistent with localized anthropogenic influence. Multivariate analysis revealed moderate compositional structuring among reef sites and suggested broad differences in polymer assemblages associated with contrasting contamination settings. Notably, some reefs exhibited elevated microplastic abundances while remaining dominated by common polymers, indicating a partial decoupling between contamination levels and polymer-specific signatures. This pattern is consistent with the influence of regional transport and mixing processes across the Caribbean basin, potentially including circulation associated with the Yucatán Channel, although hydrodynamic processes were not directly assessed in this study. Overall, the findings highlight the value of polymer-resolved analysis for improving interpretation of microplastic contamination patterns in coral reef environments. The integration of polymer composition with abundance and diversity metrics provides a useful framework for distinguishing between localized contamination signals and broader regional background influences. This study represents a regional baseline assessment of small microplastics in Caribbean coral reef systems using high-resolution spectroscopic characterization.

Microplastic contamination in coral reef environments is increasingly recognized as a global concern; however, the extent to which polymer composition can resolve contamination sources and transport processes remains poorly understood. In this study, we assessed the abundance, composition, and diversity of microplastics (< 300 µm) across multiple reef systems in the Cuban archipelago using high-resolution spectroscopic analysis. Microplastic abundance varied substantially among sites, with a median concentration of 66 particles L⁻¹ (IQR: 45–115 particles L⁻¹), ranging from 8 to 218 particles L⁻¹. A total of 11 polymer types were identified, with polyethylene (PE), polypropylene (PP), and polyamide (PA) dominating the assemblages and accounting for approximately 77% of detected particles. While these polymers were consistently observed across all sites, indicating a pervasive regional background signal, highly impacted reefs exhibited more complex polymer profiles, including the enrichment of polyurethane (PU), polytetrafluoroethylene (PTFE), and polyvinyl chloride (PVC), reflecting localized anthropogenic inputs. Multivariate analysis revealed distinct compositional groupings associated with different contamination regimes. Notably, some sites exhibited elevated microplastic abundances while remaining dominated by common polymers, indicating a decoupling between contamination levels and source-specific signatures. This pattern suggests that regional transport and mixing processes, including circulation through the Caribbean basin and the Yucatán Channel, play a major role in shaping microplastic distributions in reef environments. These findings demonstrate that polymer composition provides critical information beyond abundance alone, enabling the differentiation between source-driven contamination and transport-driven accumulation. The integration of polymer-specific analysis with abundance and diversity metrics offers a robust framework for improving source apportionment and informing monitoring and management strategies in coral reef systems.

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.