Investigating metal distribution patterns in pristine and ocean-weathered plastics using LA-ICP-TOFMS

Abstract

Plastic pollution in marine environments poses ecological risks, in part because plastic debris can release hazardous substances, such as metal-based additives. While microplastics have received considerable attention as vectors of contaminants, less is known about larger macroplastics and their role in the spatial and temporal redistribution of substances. In this study, pristine, store-bought plastic items and macroplastics recovered from the North Pacific Subtropical Gyre (NPSG) were analysed using Fourier-Transform Infrared Spectroscopy (FTIR) to identify polymer types, and bulk acid digestion followed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) for total metal quantification. These techniques were complemented by high resolution elemental mapping by Laser Ablation Inductively Coupled Plasma Time-of-Flight Mass Spectrometry (LA-ICP-TOFMS). Detailed elemental maps revealed native metal distribution in pristine plastics, and evidence of both sorption and intrinsic metal depletion in weathered plastics. In particular, weathered plastics showed surface depletion of intrinsic metals, and enrichment of seawater-derived elements (e.g., Na, Mg, I). Linear regressions were used to quantify spatial distribution trends across cross sections, providing statistical support for directional gradients. Since pristine and weathered plastics were opportunistically collected, variability in product type, polymer chemistry, and weathering time limited direct comparisons. Instead, this study demonstrates the utility of LA-ICP-TOFMS for mapping elemental distribution in plastics, offering a novel analytical approach for investigating spatial metal distribution in plastics and laying the groundwork for future studies on weathering processes in marine environments.