Geoquímica forense aplicada aos múltiplos derramamentos de óleo na costa do Ceará, Brasil, de 2019 a 2022

Abstract

In January 2019, Brazil was impacted by the largest oil spill ever recorded in tropical oceans, with over 5,000 tons of oil reaching the coasts of the Northeast and Southeast regions. In January 2022, a new incident involving more than 11 tons of spilled oil affected the coast of Ceará. In August 2022, tons of tarballs contaminated large portions of the northeastern coastline. In addition, during 2021 and 2022, oily residues continued to wash up along the Ceará coast. In this context, this study applied forensic geochemistry to investigate the characteristics, origins, and degree of weathering of 56 oil samples collected between 2019 and 2022. The first published article addressed 16 tarballs samples collected in August 2022, which showed mutual similarity based on biomarker-derived diagnostic ratios. When compared to oils from the 2019 and early 2022 events, these samples exhibited significant differences, indicating distinct sources and spill events. The tarballs displayed a bimodal profile, with n-alkanes ranging from nC13 to nC41, characterizing them as paraffinic crude oil(non-fuel), thermally mature, and of marine origin. Results obtained through ESI(-) FT-ICR MS indicated that the samples had undergone biodegradation and photooxidation, with a high abundance of fatty acids, consistent with waxy characteristics. The second article presents results from oil samples collected in Ceará during 2021 and 2022. Of the 32 samples analyzed, 26 showed a high abundance of long-chain n-alkanes (nC31 to nC41), typical of paraffinic oils. No low molecular weight n-alkanes (<nC31) or the isoprenoids pristane (Pr) and phytane (Ph) were detected. Biomarker analysis using diagnostic ratios indicated that 26 samples did not show mutual similarity, suggesting multiple sources. However, three samples from 2021 showed similarity to the 2019 event, and three samples from 2022 were linked to the early 2022 spill. Multivariate analysis supported the biomarker results, revealing that six samples clustered with the 2019 and early 2022 events, while the remaining samples showed significant dispersion and no similarity with each other or with past events. As for aromatic compounds, no polycyclic aromatic hydrocarbons (PAHs) were detected—only the presence of triaromatic steroids (TAS). The analysis of polar acidic compounds by ESI(-) FT-ICR MS revealed five distinct groups: the 2019 oil exhibited the classes N1, O2, NS, O1, and NO; the early 2022 oil showed the classes N1, O2, O3, O1, NO, and NO2; and the paraffinic tarballs were characterized by the classes N1, O2, O1, O4S, and NS. Sample P03#2021, which was similar to the 2019 oil, showed higher abundances of O2, O3, O3S, and O4 classes. The three 2022 samples associated with the early 2022 event presented the classes O2, O4S, O6, and O6S, indicating photooxidation. The DBE vs. carbon number distributions for the N1 and O2 classes showed higher abundances between C20 and C40, an uncommon pattern for crude oil, suggesting that these residues had undergone thermal processes. This study highlighted the vulnerability of the Ceará coastline to the continuous arrival of petroleum residues, which have been silently accumulating and impacting the environment.