Investigating Plastic–Metal Interactions in Aquatic Environments Using Laser Ablation ICP–MS and Chemical Markers

Plastics in aquatic environments interact with metals, influencing their fate and transport. Biotic aging of plastics plays a pivotal role in this process, but the mechanisms are still unclear. Here, we employed laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) to track elemental cross-sectional distribution in biotically aged plastics and assess metal enrichment within the biofilm. Copper, sorbed from the water environment, was used as a marker of biofilm presence, while antimony and tin marked the plastic phase for polyethylene terephthalate (PET) and polylactic acid (PLA), respectively. Aged samples revealed distinct metal distribution patterns tracking copper enrichment on the surface, whereas physicochemical changes happened on the plastic surface after aging, highlighting the biofilm presence. Copper depletion in water during the aging experiment confirmed that aged plastics accumulate this metal, showing the key role of biofilms in governing this process. Conventional analysis based on acid digestion of plastic fragments only partially captured this enrichment, underscoring the added value of LA-ICP-MS to specifically track metals accumulated from the water in comparison to those present in the polymer matrix. These results highlight the need to account for biofilm-mediated processes in risk assessments and establish LA-ICP-MS as a powerful tool for investigating metal-plastic interactions.