Sunlight has been shown to be an important factor in the fate of pollutants present in environments that are subject to solar exposure.  Energy provided by absorption of solar photons can overcome activation barriers and initiate a wide range of reactions, including direct and indirect photolysis.  Oil spills represent a recurring opportunity for contamination of aquatic, terrestrial, and atmospheric environments with petroleum compounds, predominantly linear and branched alkanes, aromatics, and alkyl aromatics.  Once released into the environment, sunlight plays a major role in oxygenating these compounds, which results in dramatically different fate, transport, and toxicity behavior.  Polycyclic aromatic hydrocarbons present in the oil are strong chromophores in the UV and visible regions.  These compounds can undergo direct photolysis or can participate in the formation of reactive transients such as singlet oxygen and hydroxyl radical.  High resolution mass spectrometry measurements have demonstrated that oil oxygenation occurs across a wide range of carbon numbers, double bond equivalencies, and heteroatom content, indicating that photochemistry impacts most if not all of the compound classes present.  The oxygenated oil photoproducts partition between the oil, water, and gas phases as well as the interfacial regions.  Interfacially active photoproducts support emulsification of oil and water, resulting in mousse that is more difficult to remediate or degrade naturally.  Furthermore, the aqueous phase photoproducts are bioavailable and can either be metabolized or cause toxicity to microorganisms; hence, there is an important connection between photochemistry and biological utilization of spilled oil.  Studies on oil photoproducts have identified a range of oxygen containing functional groups, including aldehydes, ketones, carboxylic acids, and alcohols.  These photoproducts are observable on a short time scale (minutes), demonstrating that photochemistry is a more rapid process than microbial action.  While sunlight has long been recognized as a factor in the fate of oil spills, our studies over the last decade have provided greater detail into the controlling factors, intermediates, and time frames for these processes.

Impact of sunlight on the fate of oil spilled in aquatic environments

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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