Petroleum hydrocarbons in semipermeable membrane devices deployed in the Northern Gulf of Mexico and Florida keys following the Deepwater Horizon incident.

The Deepwater Horizon (DWH) oil spill from April to July of 2010 contaminated Gulf of Mexico waters through release of an estimated 4.1 × 106 barrels of oil. Beginning in June of 2010, semipermeable membrane devices (SPMDs) were deployed near areas with sensitive marine habitats (Alabama Alps and Western Shelf) potentially exposed to that oil. Elevated TPAH50 concentrations, flux rates and similarity of histograms and diagnostic ratios for polycyclic aromatic hydrocarbons (PAH) from SPMDs to weathered floating oil collected during the DWH spill indicates the Alabama Alps habitats were affected. While not affected by oil from the DWH spill, the temporal pattern of PAH contamination of SPMDs deployed near the Western Shelf between July 2010 and March 2011 could indicate prevailing currents affected contaminant transport to the Western Shelf Area (East and West Flower Garden, Sonnier, and Stetson Banks) from non-DWH sources, including oil and gas exploration, shipping, and Mississippi River effluent.

Characterization and flux of marine oil snow settling toward the seafloor in the northern Gulf of Mexico during the Deepwater Horizon incident: Evidence for input from surface oil and impact on shallow shelf sediments.

Sediment trap samples from the shelf edge area (400-450m water depth), 58km northeast of the failed Macondo well, were collected before, during and after the Deepwater Horizon oil spill. Detailed chemical analyses of particulates revealed that fluxes of spill-derived TPH (2356µg/m2/day), total PAH (5.4µg/m2/day), and hopane (0.89µg/m2/day) settling to the seafloor directly beneath the surface-plume were 19- to 44-times higher during the active spill than pre- and post-spill background values. The oil was variably biodegraded, evaporated and photo-oxidized indicating that it derived from the sinking of surface oil. The hopane-based oil flux that we calculate (10bbl/km2) indicates that at least 76,000bbl of Macondo oil that reached the ocean surface subsequently sank over an area of approximately 7600km2. We explore how this flux of sunken surface oil contributed to the total volume of oil deposited on the seafloor following the Deepwater Horizon incident.

Footprint, weathering, and persistence of synthetic-base drilling mud olefins in deep-sea sediments following the Deepwater Horizon disaster.

Olefin-based synthetic-based drilling mud (SBM) was released into the Gulf of Mexico as a result of the Deepwater Horizon (DWH) disaster in 2010. We studied the composition of neat SBM and, using conventional GC-FID, the extent, concentration, and chemical character of SBM-derived olefins in >3600 seafloor sediments collected in 2010/2011 and 2014. SBM-derived (C14-C20) olefins occurred (up to 10cm deep) within a 6.5km2 "footprint" around the well. The olefin concentration in most sediments decreased an order of magnitude between 2010/2011 and 2014, at least in part due to biodegradation, evidenced by the preferential loss C16 and C18 linear (α- and internal) versus branched olefins. Based on their persistence for 4-years in sediments around the Macondo well, and 13-years near a former unrelated drill site (~62km away), weathered SBM-derived olefins released during the DWH disaster are anticipated to persist in deep-sea sediment for (at least) a comparable duration.

Assessing the footprint and volume of oil deposited in deep-sea sediments following the Deepwater Horizon oil spill.

The lateral and vertical extents of Macondo oil in deep-sea sediments resulting from the 2010 Deepwater Horizon oil spill were determined using chemical forensics and geostatistical kriging of data from 2397 sediment samples from 875 cores collected in 2010/2011 and 2014. The total mass of Macondo-derived hopane on the seafloor in 2010/2011 was conservatively estimated between 2.00 and 2.26metric tons, derived from 219,000 to 247,000barrels of oil; or 6.9 to 7.7% of the 3.19millionbarrels spilled. Macondo-derived hopane was deposited over 1030 to 1910km2 of the seafloor, mostly (>97%) in surface (0-1cm) and near-surface (1-3cm) sediments, which is consistent with short-term oil deposition. Although Macondo oil was still present in surface sediments in 2014, the total mass of Macondo-derived hopane was significantly lower (~80 to 90%) than in 2010/2011, affirming an acute impact from the spill and not long-term deposition from natural seeps.

Macondo oil in deep-sea sediments: Part 2 - Distribution and distinction from background and natural oil seeps.

Following the Deepwater Horizon oil spill, the spilled Macondo oil was severely weathered during its transport within the deep-sea plume as discrete particles, which were subsequently deposited on the seafloor. The Macondo oil deposited in deep-sea sediments was distinguished from ambient (background) hydrocarbons and naturally-seeped and genetically-similar oils in the Mississippi Canyon region using a forensic method based upon a systematic, multi-year study of 724 deep-sea sediment cores collected in late 2010 and 2011. The method relied upon: (1) chemical fingerprinting of the distinct features of the wax-rich, severely-weathered Macondo oil; (2) hydrocarbon concentrations, considering a core's proximity to the Macondo well or to known or apparent natural oil seeps, and also vertically within a core; and (3) results from proximal cores and flocculent material from core supernatants and slurp gun filters. The results presented herein establish the geographic extent of "fingerprintable" Macondo oil recognized on the seafloor in 2010/2011.

Macondo oil in deep-sea sediments: Part 1 - sub-sea weathering of oil deposited on the seafloor.

Chemical analysis of sediment cores collected up to 8km from the Macondo well in 2010/2011 demonstrates the extent of weathering of the Macondo oil deposited in deep-sea sediments following the Deepwater Horizon disaster. On average, dissolution and biodegradation of the oil on the seafloor increased with distance from the well indicating that weathering occurred rapidly and overwhelmingly during the oil's transport as dispersed oil droplets within the deep-sea plume. Beyond about 5km from the well, the oil deposited on the seafloor had lost most mass below C25, was relatively enriched in n-C25+ n-alkanes and C3- and C4-alkylated benz[a]anthracenes/chrysenes, the latter owing to 95% depletion of total PAHs. Biodegradation of C28 and C29 tricyclic terpanes, C34 and C35 17α(H),21ß(H)-homohopanes, C27 13ß(H),17α(H)-dia and C27 14ß(H),17ß(H)-steranes and dissolution of C26 to C28 triaromatic steroids occurred. The results provide a means to distinguish Macondo oil in deep-sea sediments from naturally-occurring seep oils and pervasive ambient background hydrocarbons.

Chemical composition of floating and sunken in-situ burn residues from the Deepwater Horizon oil spill.

In-situ burning during the Deepwater Horizon oil spill generated tens of thousands of barrels of in-situ burn (ISB) residues in the northern Gulf of Mexico (GoM), most or all of which eventually sank to the seafloor. Chemical analyses showed that floating and sunken (~1400m deep) ISB residues (1) exhibited distinct n-alkanes and UCM profiles inconsistent with vapor-pressure driven evaporation, (2) were relatively enriched in pyrogenic PAHs, particularly less stable (mostly) linear PAH isomers formed during burning, and (3) had lost petroleum biomarkers, relative to their volatility. PAH concentrations in ISB residues indicate that between 26,800 and 37,800kg of total PAHs (TPAH51) and 2880 and 4060kg of 16 Priority Pollutant PAHs were potentially deposited on the seafloor in discrete ISB residue particles. Despite this additional benthic impact, ISB reduced the total mass loadings of PAH from the burned oil to the GoM by 89% (ignoring any re-deposition from atmospheric emissions).

Weathering of field-collected floating and stranded Macondo oils during and shortly after the Deepwater Horizon oil spill.

Chemical analysis of large populations of floating (n=62) and stranded (n=1174) Macondo oils collected from the northern Gulf of Mexico sea surface and shorelines during or within seven weeks of the end of the Deepwater Horizon oil spill demonstrates the range, rates, and processes affecting surface oil weathering. Oil collected immediately upon reaching the sea surface had already lost most mass below n-C8 from dissolution of soluble aliphatics, monoaromatics, and naphthalenes during the oil's ascent with further reductions extending up to n-C13 due to the onset of evaporation. With additional time, weathering of the floating and stranded oils advanced with total PAH (TPAH50) depletions averaging 69±23% for floating oils and 94±3% for stranded oils caused by the combined effects of evaporation, dissolution, and photo-oxidation, the latter of which also reduced triaromatic steroid biomarkers. Biodegradation was not evident among the coalesced floating oils studied, but had commenced in some stranded oils.

Gas emissions, minerals, and tars associated with three coal fires, Powder River Basin, USA.

Ground-based surveys of three coal fires and airborne surveys of two of the fires were conducted near Sheridan, Wyoming. The fires occur in natural outcrops and in abandoned mines, all containing Paleocene-age subbituminous coals. Diffuse (carbon dioxide (CO(2)) only) and vent (CO(2), carbon monoxide (CO), methane, hydrogen sulfide (H(2)S), and elemental mercury) emission estimates were made for each of the fires. Additionally, gas samples were collected for volatile organic compound (VOC) analysis and showed a large range in variation between vents. The fires produce locally dangerous levels of CO, CO(2), H(2)S, and benzene, among other gases. At one fire in an abandoned coal mine, trends in gas and tar composition followed a change in topography. Total CO(2) fluxes for the fires from airborne, ground-based, and rate of fire advancement estimates ranged from 0.9 to 780mg/s/m(2) and are comparable to other coal fires worldwide. Samples of tar and coal-fire minerals collected from the mouth of vents provided insight into the behavior and formation of the coal fires.

Quantitative source apportionment of PAHs in sediments of Little Menomonee River, Wisconsin: weathered creosote versus urban background.

Polycyclic aromatic hydrocarbons (PAHs) in urban environments are often derived from point and nonpoint sources, the latter collectively considered as urban background. Quantifying the contributions of point sources and urban background is important for managing and remediating urban sediments. In this work, the sources of PAHs in 350 sediments from a 1.5-mile portion of the Little Menomonee River (Milwaukee, WI) were determined using principal component analysis (PCA), chemical fingerprinting, and positive matrix factorization (PMF), the combination of which mitigates weaknesses of any one method. At issue was quantifying the contributions of a creosote point-source formerly located 3.5 to 5.0 miles upstream versus urban background-derived PAHs in the sediments. In total, creosote and urban background contributed 27 and 73% (+/-14%) of eight carcinogenic PAHs (CPAHs), respectively, in this part of the River. The concentrations of CPAHs derived from urban background were highest in surface sediments (0-6 in.; 20 +/- 17 mg/kg), particularly near major roadway crossings, increased in the downstream direction, and (on average) exceeded the 15 mg/kg regulatory cleanup threshold. Weathered creosote-derived CPAHs were widespread at low concentrations (4.8 +/- 8.1 mg/kg) although some discrete sediments, mostly at depths below 6 in., contained elevated CPAHs derived from creosote. This work demonstrates the value of combining multiple techniques in source apportionment studies in urban sediments. It further demonstrates a means to determine the concentration of PAHs attributable to nonpoint sourced background in urban sediments without the need to identify, collect, and analyze (assumedly) "representative" background samples, which may not even exist in heterogeneous urban watersheds.

Use of chemical fingerprinting to establish the presence of spilled crude oil in a residential area following Hurricane Katrina, St. Bernard Parish, Louisiana.

Hurricane Katrina's storm surge displaced and damaged a 250,000 barrel storage tank causing a Nigerian crude oil blend (API 36.4 degrees) to be released and dispersed into the adjacent evacuated residential area by the retreating floodwaters. The subsequent environmental assessment involved sampling and chemical fingerprinting of nearly 15,000 wipe and soil samples collected both inside and outside of buildings to determine which properties were impacted by the spilled crude oil. Tier 1 qualitative analysis of gas chromatograms and Tier 2 quantitative (revised Nordtest-type) and qualitative (ASTM D5739-type) analysis of petroleum biomarkers revealed the extent of crude oil contamination-as well as the widespread occurrence of hydrocarbons derived from (i) lubricating, hydraulic, and transmission oils, most likely from vehicles in the flooded area, and (ii) allochthonous natural organic matter (NOM) from the surrounding bayous. Conventional oil spill fingerprinting protocols and two-component mixing models (crude oil/lube oil and crude oil/NOM) were used to confirm the presence of the spilled crude oil-even when mixed at low concentrations with other hydrocarbon sources-as a means to develop and govern a settlement and remedial program with the affected property owners.

Ecological risk assessment of polycyclic aromatic hydrocarbons in sediments: identifying sources and ecological hazard.

Polycyclic aromatic hyftovst ond (PAH) are nearly ubiqutous contaminants of freshwater and marine sediments. Sediment PAHs are derived from combustion of organic matter, fossil fuels, and biosynthesis by microbes. Pyrogenic PAHs, particularly those associated with combustion particles (soot), have a low accessibility and bioavailability in sediments. Polycyclic aromatic hydrocarbons associated with petroleum, creosote, or coal tar in sediments may have a moderate accessibility/bioavailability, particularly if the PAHs are part of a nonaqueous phase liquid (NAPL) phase that is in contact with sediment pore water. We present a method for estimating the hazard of complex PAH assemblage in sediments to benthic organisms. Concentrations of all PAHs in sediment pore water are estimated by an equilibrium partitioning model relative to concentrations in bulk sediment. Predicted log Koc values can be used for predicting sediment/water partitioning of petrogenic PAH, but empirically derived log Kd values are needed to predict partitioning of pyrogenic PAH. A hazard quotient (HQ) for each PAH is calculated as the ratio of the estimated concentration in pore water to the chronic toxicity of the PAH determined by a log Kow/toxicity model. Hazard quotients for all PAH in a sample are summed to produce a hazard index (HI), which is a measure of the worst-case estimated hazard of the sediment PAH to benthic organisms. The results of this study show that the integration of HI results with PAH source data provides insights into the causes of sediment toxicity that are useful in an ecological risk assessment.

Comparative evaluation of background anthropogenic hydrocarbons in surficial sediments from nine urban waterways.

Anthropogenic hydrocarbons in surficial urban sediments derived from nonpoint sources (e.g., stormwater runoff, surface runoff, direct atmospheric deposition, and small but persistent discharges) are the principal characteristics of "urban background". Establishing the character and concentration of urban background helps determine the incremental impacts from point sources and develop successful remedial strategies. In this study, we compared the nature and amount of total extractable hydrocarbons (THC) and polycyclic aromatic hydrocarbons (PAHs), including alkylated PAHs, within 280 surficial (mostly 0-10 cm) sediments from nine, well-studied urban waterways on the East and West U.S. Coasts. These 280 sediments were predominantly impacted by urban background. All the sediments were analyzed by consistent preparation and analytical methods and met consistent data quality objectives, thereby minimizing variations attributable to methodology. The data demonstrate that the anthropogenic hydrocarbons comprising urban background from all locations exhibit a generally consistent nature, dominated by (1) a variably shaped unresolved complex mixture (UCM) within the residual (C20+) range and (2) a variable distribution of resolved 4- to 6-ring nonalkylated (parent) PAHs, mostly dominated by fluoranthene and pyrene (and exhibiting a FL/PY ratio of 0.9 +/- 0.2). The variable nature of both the THC and PAH distributions testifies that, while there is a general consistency to urban background, there are definite differences between (and even within) different urban settings. This indicates thatthere is no single "representative" urban background THC or PAH signature. The greatest mass of THC is reasonably attributable to heavy petroleum(s) comprising the UCM, whereas the greatest mass of PAHs is reasonably attributable to combustion-derived particulate matter. The mean concentration of THC attributable to urban background was 415 mg/kg (dry wt). The concentration of EPA 16-Priority Pollutant PAHs was less than 20 000 microg/kg (dry wt) in 96% of the sediments studied. Thus, sediments containing significantly more than 20000 microg/kg of the EPA 16 Priority Pollutant PAHs (or more the 30000 microg/kg of 43 parent and alkylated PAHs) should be suspected to contain PAHs not entirely attributable to urban background, unless site- or regional-specific survey data supports a different urban background concentration profile.

Characterization and FATE of PAH-contaminated sediments at the Wyckoff/Eagle Harbor Superfund Site.

Eagle Harbor, a shallow marine embayment of Bainbridge Island, WA approximately 10 miles west of Seattle, WA), was formerly the site of the Wyckoff wood-treatment facility. The facility used large quantities of creosote in its wood-treating processes from the early 1900s to 1988. Historical creosote seepage into the harbor resulted in substantial accumulation of polycyclic aromatic hydrocarbon (PAH) contamination in the harbor sediments over time. This investigation focused on the distribution and fate of the PAH-contaminated harbor sediments. Analyses of 10 sediment cores using total petroleum hydrocarbon (TPH) fingerprinting, the distribution of 50 PAH analytes, and sediment age dating revealed the contributions of three distinct sources of PAHs to sediment contamination in the harbor during various periods over the past 100 years; namely, creosote, urban runoff, and natural background. Surface sediments (upper 20-30 cm) in the cores closestto the Wyckoff wood-treatment facility and southeast of an existing cap were dominated by urban runoff and weathered creosote; the deeper sediments (> 30 cm) were heavily contaminated with relatively unweathered creosote and some pure-phase creosote. Cores located the furthest from the area of contamination, in the center of the harbor, were dominated by urban runoff, showed no signs of creosote contamination, and had much lower PAH and TPH concentrations than those adjacent to the facility. In the four cores in the center of the Harbor, farthest from the former Wyckoff facility, PAH concentrations increased significantly (p < 0.01) with proximity to the northern shore of the harbor, which is more heavily developed than the southern shore and is where all automobile traffic enters and exits the island through the Bainbridge Island ferry terminal. Deeper portions of these cores were contaminated primarily with natural background PAHs, likely representing preurbanization sediments. Sedimentation rates ranged from 0.54 to 1.10 gm/ cm2 in the four cores located in the middle of the harbor, and for the single nearshore core that could be used to calculate sedimentation rates. Recognition that urban runoff has been a fairly consistent and ongoing source of PAHs to the harbor's sediments for the past 50-70 years may influence future sediment management decisions for this site with respect to long-term monitoring of surface sediments to assess cap performance. The results provided information on the ability of Eagle Harbor sediments to recover under natural conditions, identified the occurrence of creosote-derived PAH weathering in off-cap surface sediments, and distinguished between these distinct PAH sources in the harbor (creosote, urban runoff, and natural background).