Letter pubs.acs.org/journal/estlcu
Long-Term Persistence of Dispersants following the Deepwater Horizon Oil Spill Helen K. White,*,† Shelby L. Lyons,† Sarah J. Harrison,† David M. Findley,† Yina Liu,‡ and Elizabeth B. Kujawinski‡ †
Department of Chemistry, Haverford College, 370 Lancaster Avenue, Haverford, Pennsylvania 19041, United States Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, United States
‡
S Supporting Information *
ABSTRACT: During the 2010 Deepwater Horizon (DWH) oil spill, 1.84 M gallons of chemical dispersant was applied to oil released in the subsurface and to oil slicks at the surface. We used liquid chromatography with tandem mass spectrometry to quantify the anionic surfactant DOSS (dioctyl sodium sulfosuccinate) in samples collected from environments known to contain oil persisting from the DWH oil spill. DOSS was found to persist in variable quantities in deep-sea coral communities (6−9000 ng/g) 6 months after the spill and on Gulf of Mexico beaches (1−260 ng/g) 26−45 months after the spill. These results indicate that the applied dispersant, which was thought to undergo rapid degradation in the water column, remains associated with oil in the environment and can persist for ∼4 years.
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INTRODUCTION To mitigate the impact of the ∼5.0 M barrels (∼210 M gallons) of oil released as a result of the Deepwater Horizon (DWH) blowout,1 dispersants were applied to surface and subsurface waters of the Gulf of Mexico in unprecedented quantities (1.07 and 0.77 M gallons, respectively).2 The dispersants used (Corexit 9527 and Corexit 9500A, from Nalco Co.) contain the anionic surfactant dioctyl sodium sulfosuccinate (DOSS), which has amphiphilic properties that can lower the interfacial tension between oil and water and hamper the formation of large oil slicks on the surface of the ocean. Little is known about the persistence of DOSS in the marine environment, and studies to date have focused primarily on detection techniques in aqueous samples.3−6 Examination of Gulf of Mexico subsurface waters following the DWH oil spill indicated that DOSS acts conservatively in the water column and is not removed significantly by biodegradation or sedimentation.7 In contrast, laboratory incubation experiments have shown that the hydrocarbon components of Corexit are degraded8 and that DOSS is also rapidly degraded at 25 °C.9 In addition, DOSS has found to be susceptible to hydrolysis and photodegradation under laboratory-simulated solar conditions that occur in surface waters.10 The biodegradation of DOSS in the absence of sunlight10 and at temperatures representative of the subsurface (5 °C),9 however, has been found to be much slower, reinforcing the finding that DOSS persists in subsurface waters following the DWH spill.7 Here we examine the longterm persistence of DOSS in deep-sea and coastal sediment environments. © 2014 American Chemical Society
EXPERIMENTAL PROCEDURES Sampling Information. Samples from deep-sea coral communities were collected in December 2010 from lease blocks Mississippi Canyon (MC) 294 at 28.67°N, 88.48°W, 11 km to the southwest of the site of the Macondo well at 1370 m depth, and MC 388 at 28.38°N, 88.10°W, 22 km east southeast of the Macondo well at 1850 m depth. At the MC294 site, coral colonies showed visible signs of stress and were covered in a brown, flocculent material (floc), which contained weathered oil from a source consistent with the Macondo well.11 At MC388, corals exhibited no visible signs of stress and were not covered in floc. Coral floc was therefore collected from only the MC294 site, while sediment samples were collected from both MC294 and MC388 (collection details described in ref 11). Additional oiled samples were collected between June 2012 and January 2014 from Florida, Alabama, Mississippi, and Louisiana beaches (see Figure S1 of the Supporting Information). These samples were similar to others that have washed onto Gulf coast beaches since July 2010 and are termed oil-soaked sand patties, tar balls, or surface residual balls. The weathered oil present in these types of samples has been found to be consistent with an origin from the DWH spill.12−14 After homogenization, each sample was split for the quantification of DOSS (50% of the sample) and oil (50% of the sample). Received: Revised: Accepted: Published: 295
May 30, 2014 June 20, 2014 June 23, 2014 June 23, 2014 dx.doi.org/10.1021/ez500168r | Environ. Sci. Technol. Lett. 2014, 1, 295−299
Environmental Science & Technology Letters
Letter
Table 1. Dates Collected, and Water, Oil, and DOSS Contents of Coral Flocculent Material and Sediment Samples sample flocculent material from MC294 coral (F6) coral (B8) coral (E3) coral (A5) surface sediments from MC294 4660 core 1 0−1 cm 4660 core 1 1−2 cm 4660 core 2 0−1 cm 4660 core 2 1−2 cm 4661 core 1 0−1 cm 4661 core 1 1−2 cm 4661 core 2 0−1 cm 4661 core 2 1−2 cm 4662 core 8 0−1 cm 4662 core 8 1−2 cm 4662 core 11 0−1 cm 4662 core 11 1−2 cm 4664 core 5 0−2 cm 4664 core 6 0−2 cm subsurface sediment from MC294 4664 core 5 2−5 cm 4664 core 6 2−5 cm 4662 core 8 4−5 cm 4662 core 11 4−5 cm sediments from MC388 4663 core 5 0−1 cm 4663 core 5 1−2 cm
date collected
water (%)
oil content (μg/g)a
12/09/10 12/14/10 12/10/10 12/14/10
NMe NMe NMe NMe
9.2 460 73 81
12/08/10 12/08/10 12/08/10 12/08/10 12/09/10 12/09/10 12/09/10 12/09/10 12/10/10 12/10/10 12/10/10 12/10/10 12/14/10 12/14/10
71 83 83 80 74 71 81 74 84 93 81 85 65 86
12/14/10 12/14/10 12/10/10 12/10/10 12/11/10 12/11/10
DOSS content (ng/g)b
dispersant:oil ratio (%)c
16 11 8.3 6.1
0.81 0.011 0.054 0.036
380 170 300 160 120 600 98 610 1200 32 1400 60 9300 120
22 BDd BDd BDd 3700 BDd BDd BDd BDd BDd 2400 BDd 19 BDd
0.028 BDd BDd BDd 15 BDd BDd BDd BDd BDd 0.85 BDd 0.0010 BDd
69 69 91 95
370 31 450 460
BDd BDd BDd BDd
BDd BDd BDd BDd
94 93
150 12
9000 BDd
29 BDd
Oil content measured by gas chromatography coupled to flame ionization detection [GC−FID (see SM)] reported as micrograms per gram of dry sediment for sediment samples and micrograms per filter for flocculent material. bDOSS (dioctyl sodium sulfosuccinate) reported as the average of dual or triplicate injections in nanograms per gram of dry sediment for sediment samples and micrograms per filter for flocculent material. c Dispersant:oil ratio calculated from DOSS concentrations where DOSS comprises 21% of the dispersant (as described in ref 6). dBelow detection determined to be
