The effects of photo-oxidation of oil spills in tropical climate regions are evaluated using a laboratory-scale simulation
Name: SANNYA MARIA BRITTO CÔGO
Publication date: 21/07/2025
Examining board:
Name |
Role |
|---|---|
| ALVARO CUNHA NETO | Examinador Interno |
| CLEOCIR JOSE DALMASCHIO | Examinador Interno |
| EUSTAQUIO VINICIUS RIBEIRO DE CASTRO | Presidente |
| FABIANA DIAS COSTA GALLOTTA | Examinador Externo |
| LAERCIO LOPES MARTINS | Examinador Externo |
Summary: Oil spills at sea, such as those involving the Exxon Valdez (1989), the Gulf War (1991) and the Deepwater Horizon (2011), as well as the recent appearance of oil on beaches along the Brazilian coast (2019), have significant environmental and socio-economic impacts. Following a spill, the oil undergoes weathering processes involving physical, chemical, and biological transformations that alter its properties. Evaporation and photooxidation play a key role in modifying the oil's chemical composition, especially in tropical regions with high levels of solar radiation. Photo-oxidation is the result of the interaction between ultraviolet (UV) radiation and oxygen. This process promotes the formation of oxygenated compounds and polyaromatic hydrocarbons, which can increase environmental toxicity and complicate remediation processes. This study investigated the physicochemical and compositional changes in five samples of Brazilian offshore oil subjected to weathering by evaporation and photo-oxidation under simulated tropical conditions. Initially, the samples were distilled at over 250°C+ at the top of the column to simulate evaporation. The evaporated samples were then exposed to ultraviolet radiation in an acrylic box for 219 days, with samples collected on days 7, 58, 107, 164 and 219 to assess photochemical weathering progression over time. Physico-chemical analyses were carried out on the frescode and evaporated oil samples, including the following properties: API grade; density; kinematic and dynamic viscosities; pour point; total sulphur content; asphaltene content; total acid number (TAN); and salinity index. Spectroscopy in the mid-infrared region (FTIR) revealed a decrease in similarity and structural changes between the oils in the assemblies throughout the weathering process. The saturated and aromatic fractions were analysed using gas chromatography coupled to mass spectrometry (GC-MS) through saturated, aromatic, and polar (SAP) fractionation, which allowed individual compounds to be identified, and their changes assessed throughout the simulation. The results revealed significant losses of the most volatile compounds following evaporation, as well as changes in the physicochemical properties and resistance of saturated biomarkers, even after prolonged exposure to UV radiation. An increase in the baseline was observed in the aromatic fractions from day 7 onwards, which was associated with the formation of an unresolved complex mixture (UCM). Ratios of aromatic compounds such as 2-methylnaphthalene/phenanthrene and nalkylbenzenes proved sensitive to changes caused by sunlight exposure. ¹H nuclear magnetic resonance analyses corroborated the high-resolution mass spectrometry (ESI(+)-Orbitrap-MS) data, which indicated a progressive increase in oxygenated and nitrogenated compounds that were possibly formed by photochemical oxidation. This study highlights the importance of evaporation and photochemical oxidation processes in the chemical transformation of oil in tropical environments. It provides relevant information for improving environmental emergency response strategies and contingency plans in the event of oil spills at sea.
