Occurrence and fate of polyethylene pellets in the Galician coast (N.W. Spain) after the Toconao spillage: study of associated plastic additives and chemical weathering

This work addresses the occurrence and fate of the polyethylene (PE) pellet spillage from the Toconao vessel off the NW Portuguese coast in 2023. Samples from 42 Galician beaches (NW Spain) were collected and subsequently analysed in the laboratory by attenuated total reflectance infrared spectrometry (ATR), thermodesorption and pyrolysis gas chromatography with mass spectrometry detection (TD/Py-GC-MS) and inductively coupled plasma-mass spectrometry (ICP-MS). They ascertained the polymer type, additives and metals in the pellets, and demonstrated that the spillage affected 62% of the 42 studied beaches. The major additive of the product, Tinuvin 622, was key to fingerprint and track the spillage. Many pellets that confounded the naked eye were demonstrated to be PE (33%) and polypropylene (PP) (18%) from other sources. A six-month weathering study was performed using sunlight-simulating lamps and seawater, and it revealed chemical changes after the 13th week for submerged pellets. These yielded small micro- and nanoplastics that retained the UV-radiation stabilizer Tinuvin 622 in their composition while weathered. Despite this, the PE backbone changed, as evidenced by higher signals for alkadienes than for alkanes in the weathered pellets and powder, opposite to the original pellets. This variation in the characteristic triplets observed in Py-GC-MS had not been described before, and constitutes a major finding which allows us to propose it as a new marker for Py-GC-MS to identify weathered PE. Overall, the results suggest a wide distribution of the pellets along the Galician coastline and a tendency to fragment into secondary microplastics during weathering.