Plastic additives and related contaminants of emerging concern are widely used as UV stabilizers, antioxidants, plasticizers, epoxy resin components, flame retardants, and processing-related chemicals, and may pose ecological risks in marine systems. Understanding their exchange between seawater and plastic debris is important for assessing whether floating plastics act primarily as passive reservoirs or secondary sources of chemical additives. This study investigates the occurrence and seasonal dynamics of 75 target contaminants of emerging concern across the North Sea during winter and summer 2023. Polyethylene and polypropylene debris were identified using near-infrared hyperspectral imaging and extracted by ultrasound-assisted extraction, while dissolved contaminants in seawater were isolated by solid-phase extraction. All extracts were analysed using a unified UHPLC-Orbitrap-HRMS method.

Preliminary seawater results quantified 18 target compounds and revealed clear spatial, seasonal, and depth-related patterns. Several PFAS, representing persistent surfactant- and processing-related chemicals, including NfBSA, PFHpA, PFOA, and PFOS, were widely detected, with highest concentrations towards the eastern North Sea, indicating a likely influence of Elbe-derived riverine inputs. Seasonal differences were also pronounced. Summer samples were characterized by widespread detection of the UV stabilizer Tinuvin P, with concentrations up to 260 ng L⁻¹, whereas winter samples showed higher contributions of the epoxy resin-related compound bisphenol A diglycidyl ether and the exclusive detection of the light stabilizer Tinuvin 770, particularly in western stations. Additional localized patterns were observed for the antioxidant diphenylamine, which was restricted mainly to central and eastern deep-water samples, while plasticizers were largely below detection.

These preliminary data demonstrate that the aqueous occurrence of plastic-associated contaminants in the North Sea is highly variable and shaped by seasonality, water-mass structure, and riverine inputs. Ongoing analysis of paired marine plastic debris will enable the estimation of apparent plastic–water distribution ratios and help determine whether pelagic plastics function predominantly as passive sinks or active secondary sources of additives in the marine environment.