Assessment of the effect of short-term weathering on the molecular-level chemical composition of crude oils in contact with aquatic environments

Multiple studies have focused on the effect of long-term weathering processes on oils after spill events, without considering the chemical compositional changes occurring shortly after the release of oil into the environment. Therefore, the present study provides a broad chemical characterization for understanding of the changes occurring in the chemical compositions of intermediate (& DEG;API = 27.0) and heavy (& DEG;API = 20.9) oils from the Sergipe-Alagoas basin submitted to two simulated situations, one under marine conditions and the other in a riverine environment. Samples of the oils were collected during the first 72 h of contact with the simulated environments, followed by evaluation of their chemical compositions. SARA fractionation was used to isolate the resins, which were characterized at the molecular level by UHRMS. The evaporation process was highlighted, with the GC-FID chromatographic profiles showing the disappearance of compounds from n-C-10 until n-C-16, as well as changes in the weathering indexes and pristane + n-C-17/phytane + n-C-18 ratios for the crude oils submitted to the riverine conditions. Analysis of the resins fraction showed that basic polar compounds underwent little or no alterations during the early stages of weathering. The marine environment was shown to be much less oxidative than the riverine environment. For both environments, a feature highlighted was an increase of acidic oxygenated compounds with the increase of weathering, especially for the crude oil with & DEG;API = 27.0.

Automated summary

This study investigates the changes in the chemical compositions of oils after spill events, focusing on the early stages of weathering. It finds that the marine environment has less oxidative effects compared to the riverine environment on the chemical compositions of crude oils. The results also show the evaporation process during the first 72 hours after oil release, with the disappearance of certain compounds and changes in weathering indexes and organic compound ratios.