Chronic oil spills revealed by the most important set of samples from the incident in northeastern Brazil, 2019.

In 2019, an oil spill of unprecedented dimensions and unknown source reached the Brazilian coast. Such incident, which occurred somewhere in the ocean and was detected only when the first oil patches reached the beaches in the northeastern region, is recognized as one of the most serious oil spills in the country. From the chromatographic analysis of the oily residues using n-alkanes, polycyclic aromatic hydrocarbons (PAH), and oil biomarkers, it was possible to characterize their coverage. The results confirmed that an oil of the same specification reached a length of coastline higher than 3,000 kilometers. However, were also found oily residues that did not match with the product involved in that incident, evidencing the occurrence of different discharges. This study documents the extension of the affected coastline during the incident and assesses the possible origin of such different oils from their geochemical characteristics by selecting 21 samples from more than 300 samples previously collected and analyzed during the response actions. The unexpected occurrence of these residues suggest chronic events. The results highlighted that unrelated oily residues were found even in a region far from the coast, indicating that discharges of oil in the open sea occur more regularly than initially expected.