The first geochemical assessment of plastitar and clastic plastitar found on Brazilian coast: a new threat to marine life and coastal communities

Plastic and oil pollution in the oceans constitutes a threat to marine life and coastal communities. The combination of these two pollutants has also been recorded worldwide, termed plastitar and clastic plastitar. However, studies in the Southern Hemisphere remain scarce. In this context, this study aimed to report and geochemically investigate plastic-oil agglomerates on Brazilian beaches with high environmental and economic relevance, to confirm their petrogenic nature and assess their source and oil types. A total of 36 samples were collected between 2022 and 2024 in three Brazilian states: Pernambuco (PE, Fernando de Noronha Archipelago), Ceará (CE), and Rio de Janeiro (RJ). The plastic fraction was characterized by visual inspection and infrared spectroscopy, and the related whole oil was assessed by GC-FID. Then, 16 representative samples were further investigated with a forensic organic geochemistry approach using GC-MS to assess their sources and correlations with known oil spill events based on terpanes, steranes, tetracyclic polyprenoids (TTPs) ratios, and type of oil based on triaromatic steranes (TAS), phenanthrenes (P), anthracene (An), 2- methylanthracene (MAn), methylphenanthrenes (MP), and methydibenzothiophenes (MDBT). Among the 36 samples, one was classidied as plastitar, six as clastic plastitar, and 29 as plastic-oiled debris. The plastics diplayed a range of colors, shapes, and original uses, indicating multiple sources, and were composed of low-density polymers, such as polypropylene and polyethylene. Petrogenic signatures were identified in all oil samples, confirming the interaction of plastic debris with oil. GC-FID analysis revealed severely weathered oil profiles with high unresolved complex mixture, pristane and phytane enrichment, and the presence of C29 and C30 hopanes. In contrast, a distinct n-alkanes distribution from C31 to C40 was observed in three samples, which may be related to oil residues from illegal discharge or accidents involving ship activities. Similarity assessment using biomarker diagnostic ratios indicates multiple oil sources. Additionally, the PE samples are geochemically correlated with one another and the known to have affected Fernando de Noronha Archipelago in 2021. Two CE samples show geochemical similarities with the waxy tarballs that reached northeastern Brazil in late 2022, and one sample is geochemically related to the 2019 Brazilian Northeast oil spill. Aromatic fraction analysis revealed that only one sample, from CE, has heavy fuel oil features, with high abundance of An and MAn, the presence of naphtenoaromatic compounds at m/z 231, and a typical MDBT profile. This work shows for the first geochemical evidence linking low-density plastic debris from multiple sources with spilled oils, underscoring the chronic input of these two pollutants into the Atlantic Ocean. Therefore, more efforts are needed to monitor and improve regulatory measures to protect the Brazilian coast.