Photochemical fate of solvent constituents of Corexit oil dispersants

Abstract

In 2010, an estimated 1.87 million gallons (7079 cubic meters) of chemical dispersants were applied to open ocean waters in the Gulf of Mexico as part of the response to the Deepwater Horizon blowout. This unprecedented volume of dispersant application highlighted the importance of dispersant chemical formulations, raising questions of dispersant fate and transport in the open ocean and spurring research into formulation improvements. The research presented here elucidates the contribution of photolytic processes to the degradation of two solvent constituents of these dispersant mixtures: propylene glycol (PG) and 2-butoxyethanol (2-BE). A series of photodegradation experiments were conducted to determine the contribution of direct photolysis and indirect photolysis via hydroxyl radical (HO) to compound degradation. Experiments were performed using both deep UV light sources (low pressure (LP) and medium pressure (MP) mercury vapor ultraviolet (UV) lamps) and a solar simulator. Sample matrices included ultrapure water, nitrate amended water, hydrogen peroxide (H2O2) spiked water, Gulf of Mexico seawater, and a surface water from Boulder, CO. Experiments included determination of the molar absorption coefficients (ε) and the HO reaction rate constants (kHO) of the individual compounds. Data illustrated that significant direct photolysis of either PG or 2-BE from sunlight is unlikely. The kHO for PG and 2-BE were determined to be 6.15 × 10(8) M(-1) s(-1) and 1.15 × 10(9) M(-1) s(-1), respectively. Solar simulation and UV experiments indicate that in natural systems, neither PG nor 2-BE is expected to undergo significant, rapid degradation due to direct or indirect photolysis. PG and 2-BE are effectively degraded through indirect photolysis in the presence of high HO concentrations, suggesting UV/H2O2 is a feasible possibility for the treatment of waters containing PG and 2-BE.

Comparative Proteomics of Marinobacter sp. TT1 Reveals Corexit Impacts on Hydrocarbon Metabolism, Chemotactic Motility, and Biofilm Formation

“…Thus, the surfactant alkyl and acyl side chains might have been degraded by the detected AlkB1 homologue, cytochrome P450 hydroxylase, or lipases, while the proteins related to sulfur metabolism detected in Corexit treatments might have been involved in DOSS metabolism. Moreover, the solvent fraction of Corexit reportedly contains propylene glycol and dipropylene glycol monobutyl ether [81], which could also have been degraded by strain TT1 as shown for other isolates [18]. In order to establish a better connection of these potential substrates to the observed proteomic response of strain TT1, further experimental studies using only specific surfactants or glycols as carbon substrates are required.…”

Oil Irradiation Experiments Document Changes in Oil Properties, Molecular Composition, and Dispersant Effectiveness Associated with Oil Photo-Oxidation

“…A second factor that might affect dispersant effectiveness is the solvent compatibility between the co-solvent system of the dispersant and the oil residues . We tested solvent compatibility of our oil residues with two types of co-solvent that are known to be present in Corexit 9500: two different hydrotreated light petroleum distillates and dipropylene glycol n -butyl ether (DPnB). − DPnB has been used as a marker compound for Corexit during the Deepwater Horizon oil spill. − We found that oil residues irradiated for 4–11 days had a reduced solubility in the petroleum distillates (average solubility: 68 ± 13%); in contrast, DPnB, as well as 1:1 mixtures of DPnB and petroleum distillates, was able to completely dissolve irradiated oil residues (Figure S10). To test whether the decreased solubility of irradiated oil residues in petroleum distillates could explain the measured reduction in dispersant effectiveness, we pre-mixed Corexit 9500A with the photo-oxidized residue L8 prior to the Baffled Flask Test.…”

Optical properties of chromophoric dissolved organic matter (CDOM) in surface and pore waters adjacent to an oil well in a southern California salt marsh

“…The degree to which oil products are significant sources of organic carbon is not clear and transformations of oil products in salt marshes are poorly characterized. While a number of literature studies aim to understand the photo and biodegradation of oil compounds in marine environments associated with oil spills (Bugden et al, 2008;Islam et al, 2013;King et al, 2014;Kover et al, 2014), little is known about oil seeps and oil transformations in salt marshes. Understanding the contribution of oil to the DOM pool in salt marshes is important in evaluating the short and long term influence of oil pollution on coastal ecosystems and intertidal water chemistry (McClenachan et al, 2013;Wang et al, 2013;Marton and Roberts, 2014).…”