Synergy of analytical approaches enables a robust assessment of the Brazil mystery oil spill

Abstract

From August 2019 to June 2021, viscous oil residues appeared along the Brazilian coast spanning 11 states and more than 3,000 km of tropical shoreline. Forensic results published to date indicate that the majority of oil samples collected share a common origin, yet the exact source of the mystery oil has yet to be conclusively determined. The proposed sources include illegal discharges from vessels traversing near, within, or downstream of Brazilian waters, leaking offshore platforms, natural seeps, and historic shipwrecks. To constrain the potential sources of oil and provide additional insights into the composition of the oil, we analyzed samples collected from the Cearástate coastal zone in 2019 with a broad suite of geochemical tools and approaches. These approaches included bulk elemental analyses and state-ofthe-art analytical platforms including comprehensive two-dimensional gas chromatography (GC × GC), gas chromatography with triple-quadrupole mass spectrometry, and Fourier transform ion cyclotron resonance mass spectrometry. Based on bulk and molecular features, field samples collected from northeast Brazil share the same source as other 2019 mystery oil samples collected over ∼2400 km to the south. A shared source across the Brazilian coast points to an input location east of Brazil within the southern branch of the South Equatorial Current, allowing transport both north and south of the bifurcation. The relative abundance and composition of diagnostic markers were consistent with the published analyses of Venezuelan petroleum. The composition of the field samples is consistent with the blending of, at least, two different petroleum products, a common practice to produce an “on spec” product such as a fuel oil used to power an underway vessel. The two components appear to be the residuum from atmospheric distillation and a thermally altered, aromatics-rich, nondistilled material. To the best of our knowledge, no samples from potential sources are available for a direct comparison to field samples. Hence, these results play a supporting role in determining the source, and benefit efforts to understand short- and long-term weathering and recovery