Temporal and Spatial Assessment of PAHs in Water, Sediment, and Oysters as a Result of the Deepwater Horizon Oil Spill

On April 20, 2010, BP\u27s Deepwater Horizon oil rig exploded leaking over 200 million gallons of crude oil into the Gulf of Mexico for 84 days. Exposure to oil-associated polycyclic aromatic hydrocarbons (PAHs) in the water and sediment could severely impact the aquatic organisms inhabiting the Gulf of Mexico (i.e. developmental defects, reproductive effects, death, etc.). Therefore, water, sediment and oyster, Crassostrea virginica, samples were collected approximately bimonthly between May 26 and November 30, 2010 from multiple sites along the Gulf Coast, namely, two sites in Mobile Bay (Denton and Sand Reefs at 1 or 0.1 m above the bay floor), one site near Orange Beach, AL (Perdido), and one near Pointe aux Pines, MS. Water, sediment, and oysters were extracted for quantitation of 24 PAHs by gas chromatography mass spectrometry (GC/MS). The concentration range for total PAHs (tPAH) in water was non-detectable to 1100 ng/L and non-detectable to 7450 ng/g for sediment. The highest water tPAH concentrations were observed on 6/28/10 for Sand (1 m), 7/21/10 for Denton (0.1 m), 9/9/10 for Perdido, and 9/22/10 for Pointe aux Pines. The highest sediment concentrations were observed on 9/20/10 for Denton Reef, 7/7/10 for Sand Reef, 7/28/10 for Perdido, and 9/22/10 for Pointe aux Pines. Twenty other sites along the northern Gulf coast collected less frequently also indicated relatively low (\u3c20 ng/L) tPAH water concentrations. Fundulus heteroclitus embryos were exposed to water collected from three of the sites from 4.5 hours post-fertilization (hpf) to 10 days post-fertilization (dpf). Embryos were assessed on 5 and 10 dpf for lethality and cardiac toxicities (including blood clot, edema and tube heart), and cytochrome P450 enzyme induction was measured by an in ovo ethoxyresorufin-O-deethylase assay. F. heteroclitus embryos were not significantly affected by the water collected from these sites. There was less than 4% and 2% incidence of edema and blood clot, respectively, and there were no significant differences in deformity index or lethality. None of the 73 sediment and 70 water samples collected between May 26, 2010 to February 9, 2011 was definitively impacted by the Deepwater Horizon Oil Spill at the times collected based on the tPAHs measured. However, samples with relatively higher percent compositions of naphthalenes and/or phenanthrene occurred in the Sand and Denton 6/28/10 water samples and in the 7/12/10 Gulf Island National Seashore sediment sample. Other sediment samples with tPAH concentrations greater than 1300 ng/g dry weight had diverse mixtures of the individual PAH compounds suggesting multiple potential sources of contamination. Also, none of the sediment samples at the times collected had tPAH concentrations which exceeded NOAA regulatory SQuiRT guidelines. Therefore, none of the PAH concentrations measured were expected to cause acute toxicity to aquatic life, a result supported by the F. heteroclitus bioassay