Hot and Cold: Photochemical Weathering Mediates Oil Properties and Fate Differently Depending on Seawater Temperature

Abstract

Photochemical weathering transforms petroleum oil and changes its bulk physical properties, as well as its partitioning into seawater. This transformation process is likely to occur in a cold water marine oil spill, but little is known about the behavior of photochemically weathered oil in cold water. We quantified the effect of photochemical weathering on oil properties and partitioning across temperatures. Compared to weathering in the dark, photochemical weathering increases oil viscosity and watersoluble content, decreases oil−seawater interfacial tension, and slightly increases density. Many of these photochemical changes are much larger than changes caused by evaporative weathering. Further, the viscosity and water-soluble content of photochemically weathered oil are more temperature-sensitive compared to evaporatively weathered oil, which changes the importance of key fate processes in warm versus cold environments. Compared to at 30 °C, photochemically weathered oil at 5 °C would have a 16× higher viscosity and a 7× lower water-soluble content, resulting in lower entrainment and dissolution. Collectively, the physical properties and thus fate of photochemically weathered oil in a cold water spill may be substantially different from those in a warm water spill. These differences could affect the choice of oil spill response options in cold, high-light environments.

Photochemistry of oil in marine systems: developments since the Deepwater Horizon spill

“…51 Furthermore, temperature was reported as a highly influential parameter in determining the bioavailability of various oil fractions such as PAHs and alkanes. Freeman et al 70 recently reported on changes in temperature-dependent oil properties caused by photochemical weathering. Sunlight exposure resulted in increased oil viscosity and water-soluble content and decreased oil–seawater interfacial tension.…”

Completing the Picture of How Oil Weathers in Seawater

“…Temperature and sunlight both affect the bulk properties of crude oil, but until now the relative importance of each was unclear. Now Danielle Haas Freeman, Collin Ward, and their colleagues at the Woods Hole Oceanographic Institution (WHOI), Massachusetts, report results of experiments that address that problem [1]. Their findings suggest that sunlight-weathered oil behaves differently in cold Arctic waters than in tropical oceans.…”