| dcterms.abstract | Corexit® formulations consist of petroleum and ether based solvents, along with anionic surfactant DOSS and a mixture of nonionic surfactants (Tween 80, Tween 85 and SPAN 80). Incomplete information on Corexit chemical compositions has hindered the ability to understand dispersant fate or risks of future use. DOSS, a component of the Corexit formulation was found to be relatively stable in deep waters during and after the Deep-Water Horizon spill. Relatively high levels of DOSS found in some Gulf of Mexico (GOM) sediments point to the need for better understanding of sediment-particle interactions as sorption can affect water column processes and longer term exposure in sediment and bottom water ecosystems. A comprehensive high performance liquid chromatography-time-of-flight-mass spectrometry (HPLC-Tof-MS) method was developed for determining the complex mixture of over 500 surfactants found in Corexits. The composition of Tweens was found to be more complex than generally realized, and it was shown that SPAN 80 is not simply sorbitol mono-oleate but a mixture of sorbitol mono- through tetra-esters comprised of fatty acids varying in alkyl chain length and unsaturation. The method was used to track the fate of Corexit 9500 components during early life stage toxicity tests with the sheepshead minnows (Cyprinodon variegatus). DOSS and diproplyene glycol butyl ether were persistent. However, Tween and SPAN components were lost rapidly (24 hrs.); accumulation of ester hydrolysis products and kinetic evidence suggested that the loss resulted from microbial communities growing on labile surfactants. The sorption of DOSS to marine sediments were affected by properties of solution and sediments; the effect DOSS concentration (1- 17,000 µg/L) was also studied to improve predictive capabilities across a range of environmental conditions. At low surface coverage, isotherms were often nearly linear, and the total organic carbon content was the sediment property that best described the variability in sorption. Carbon normalized sorption coefficients were surprisingly consistent for 12 sediments (7200 ± 2500 L/Kg at 2 µg/g sorbed). These results suggest and even more important role of organic matter than determined for linear alkylbenzene sulfonates (LAS), potentially related to well document unique properties of DOSS at H2O/oil interfaces. In regards to effects of solution properties, the dependence on pH was much less than described in prior studies of anionic surfactant sorption under low ionic strength conditions, and the increased sorption with salinity could be described empirically by a linear combination of the independently determined effects of Ca2+, Mg2+, and Na+. While the importance of Ca2+ on sorption of organo-sulfonates is well recognized, the increasing importance of Na+ with salinity at low surfactant concentrations presents questions about the mechanism responsible. The very important effects of Mg2+ (neglected in prior sorption studies with organic compounds) was a novel result, with implications for marine and freshwater systems, where the Mg2+/Ca2+ is highly variable. | |
