Impact of Photooxidation and Biodegradation on the Fate of Oil Spilled During the Deepwater Horizon Incident: Advanced Stages of Weathering

Abstract

While the biogeochemical forces influencing the weathering of spilled oil have been investigated for decades, the environmental fate and effects of “oxyhydrocarbons” in sand patties deposited on beaches are not well-known. We collected sand patties deposited in the swash zone on Gulf of Mexico beaches following the Deepwater Horizon oil spill. When sand patties were exposed to simulated sunlight, a larger concentration of dissolved organic carbon was leached into seawater than the corresponding dark controls. This result was consistent with the general ease of movement of seawater through the sand patties as shown with a 35SO4 2– radiotracer. Ultrahigh-resolution mass spectrometry, as well as optical measurements revealed that the chemical composition of dissolved organic matter (DOM) leached from the sand patties under dark and irradiated conditions were substantially different, but neither had a significant inhibitory influence on the endogenous rate of aerobic or anaerobic microbial respiratory activity. Rather, the dissolved organic photooxidation products stimulated significantly more microbial O2 consumption (113 ± 4 μM) than either the dark (78 ± 2 μM) controls or the endogenous (38 μM ± 4) forms of DOM. The changes in the DOM quality and quantity were consistent with biodegradation as an explanation for the differences. These results confirm that sand patties undergo a gradual dissolution of DOM in both the dark and in the light, but photooxidation accelerates the production of water-soluble polar organic compounds that are relatively more amenable to aerobic biodegradation. As such, these processes represent previously unrecognized advanced weathering stages that are important in the ultimate transformation of spilled crude oil.

Progress in Operational Modeling in Support of Oil Spill Response

“…Modeling tarball formation combines models of oil breakup into smaller droplets, then coalescence models for oil and particulates, which may be heavier sediments or lighter organic material. The analysis of Harriman et al [231] of wave-zone tarballs and tar patties showed differences in biodegradation products when exposed to sunlight or kept dark. Sunlight-exposed tarballs showed an accelerated production of water-soluble polar organic compounds.…”

Molecular-Level Characterization of Oil-Soluble Ketone/Aldehyde Photo-Oxidation Products by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Reveals Similarity Between Microcosm and Field Samples

“…Therefore, a comprehensive characterization of the photo-oxidation products derived from petroleum spills, especially ketone/aldehyde-containing compounds, is of paramount importance for toxicological studies. However, molecular-level characterization of these products is difficult due to petroleum’s complexity in composition, thermal lability, polarizability, and boiling point. − …”

Examining the Extraction Efficiency of Petroleum‐Derived Dissolved Organic Matter in Contaminated Groundwater Plumes

“…Islam et al () analyzed polymeric Amberlite (XAD) resin extracted water samples from four Bemidji wells using Fourier transform ion cyclotron resolution mass spectrometry and reported compounds containing up to 10 oxygens (Islam et al ). Harriman et al () also reported high oxygen content using Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR MS) on solid phase extracted (SPE) DOM from biodegraded oil sand patties (Harriman et al ). Therefore, analytically, the existing LLE‐based methods are potentially missing most of the polar compounds hampering the effort to study the safety of MNA for petroleum‐contaminated groundwater.…”