Edward B. Overton

Oil Impacts on Coastal Wetlands: Implications for the Mississippi River Delta Ecosystem after the Deepwater Horizon Oil Spill

On 20 April 2010, the Deepwater Horizon explosion, which released a US government—estimated 4.9 million barrels of crude oil into the Gulf of Mexico, was responsible for the death of 11 oil workers and, possibly, for an environmental disaster unparalleled in US history. For 87 consecutive days, the Macondo well continuously released crude oil into the Gulf of Mexico. Many kilometers of shoreline in the northern Gulf of Mexico were affected, including the fragile and ecologically important wetlands of Louisianas Mississippi River Delta ecosystem. These wetlands are responsible for a third of the nations fish production and, ironically, help to protect an energy infrastructure that provides a third of the nations oil and gas supply. Here, we provide a basic overview of the chemistry and biology of oil spills in coastal wetlands and an assessment of the potential and realized effects on the ecological condition of the Mississippi River Delta and its associated flora and fauna.

Portable gas chromatograph

Gas chromatographs are disclosed that may be constructed to be portable, light, rugged, fast, sensitive, and to use only utilities (compressed gas and electricity) that are readily available in the field. The gas chromatographs can also perform novel extractions of analytes from gaseous, liquid, or solid samples. The chromatographs can be truly portable; they can operate with approximately 100 watts of power (at peak power consumption); and they are extremely fast. The chromatographs are not limited just to portable applications, but will also find many uses within laboratories, because they require minimal laboratory bench or other space, because they can operate at high speed, and because they can operate with minimal consumption of utilities (compressed gases, air conditioning, etc.).SummaryAn improved inexpensive portable gas chromatograph for the acetylene reduction assay of nitrogenase is described. The instrument is more convenient to use than a previously described model. Modifications permit the detection of hydrogen or methane.

Distribution and recovery trajectory of Macondo (Mississippi Canyon 252) oil in Louisiana coastal wetlands

We measured the concentration of petroleum hydrocarbons in 405 wetland sediment samples immediately before the April 2010 Deepwater Horizon disaster led to their broad-scale oiling, and on nine trips afterwards. The average concentrations of alkanes and PAHs were 604 and 186 times the pre-spill baseline values, respectively. Oil was distributed with some attenuation up to 100m inland from the shoreline for alkanes, but increased for aromatics, and was not well-circumscribed by the rapid shoreline assessments (a.k.a. SCAT) of relative oiling. The concentrations of target alkanes and PAHs in June 2013 were about 1% and 5%, respectively, of the February 2011 concentrations, but remained at 3.7 and 33 times higher, respectively, than in May 2010. A recovery to baseline conditions suggests that the concentration of alkanes may be near baseline values by the end of 2015, but that it may take decades for the PAH concentrations to be that low.

Changes in the concentration and relative abundance of alkanes and PAHs from the Deepwater Horizon oiling of coastal marshes.

We determined changes of 28 alkanes and 43 different PAHs in 418 wetland soil samples collected on ten sampling trips to three Louisiana estuaries before and after they were oiled from the 2010 Deepwater Horizon disaster. There was a significant decline in 22 of the 28 alkane analytes (0.42% day(-1)), no change in 6, over 2.5 years. The concentration of five aromatic petroleum hydrocarbons (PAHs) increased (range 0.25-0.70% day(-1)), whereas the total PAH pool did not change. Of these five, naphthalene and C-1-naphthalenes are suggested to be of higher toxicity than the other three because of their relatively higher volatility or solubility. The relative proportions of alkane analytes, but not PAHs, does not yet resemble that in the pre-oiled marshes after 3 years, The trajectories of nine indicators for degradation/weathering were either inconclusive or misleading (alkanes) or confirmed the relatively meager degradation of PAHs.

Fabrication and Preliminary Results for LiGA Fabricated Nickel Micro Gas Chromatograph Columns

High aspect ratio nickel microfluidic columns were fabricated using the LiGA technique. The 2-m-long 50-mum-wide high aspect ratio columns will be the separation component of a handheld gas chromatograph device for detecting semivolatile and volatile compounds. As a first step, 600-mum-deep electrodeposited nickel columns were fabricated. The serpentine columns were sealed and pressure-flow rate characteristics compared with the theoretical values. The response of the sealed columns was studied by running methane gas plugs through uncoated columns with a flame ionization detector at the exit. Negligible flow-induced dispersion was observed in the sealed metal columns. Unretained peak widths of ~15 ms were measured, and the experimental pressure and flow rate distributions matched those predicted by established analytical models within plusmn2.5%. Columns were coated with OV-1 stationary phase using static coating methods. A mixture of four hydrocarbons C6, C8, C10, and C12 was separated in a coated 50 mum by 600 mum by 0.5 m column in less than 2 s at 70 degC

Trends and advances in portable analytical instrumentation

The evolution of dedicated microcomputers and microcontrollers, in addition to silicon microfabrication and other micromachining technologies, and the integration of these technologies, is having a profound impact on both the functioning and the applications of analytical instrumentation. In essence, analytical instruments are moving from the domain of functioning as pure analyzers into the domain of functioning as problem solvers. This new functioning implies that the output from the new generation of instruments will not only be the analytical results but also the logical consequences that can be derived from the analytical data. The output from these devices will be decisions rather than analytical data. This has particularly important consequences for the vast expansion in applications for fieldable analytical chemistry.

Evaluation of Polycyclic Aromatic Hydrocarbons Using Analytical Methods, Toxicology, and Risk Assessment Research: Seafood Safety after a Petroleum Spill as an Example

Background: Polycyclic aromatic hydrocarbons (PAHs) are abundant and widespread environmental chemicals. They are produced naturally and through man-made processes, and they are common in organic media, including petroleum. Several PAHs are toxic, and a subset exhibit carcinogenic activity. PAHs represent a range of chemical structures based on two or more benzene rings and, depending on their source, can exhibit a variety of side modifications resulting from oxygenation, nitrogenation, and alkylation. Objectives: Here we discuss the increasing ability of contemporary analytical methods to distinguish not only different chemical structures among PAHs but also their concentrations in environmental media. Using seafood contamination following the Deepwater Horizon accident as an example, we identify issues that are emerging in the PAH risk assessment process because of increasing analytical sensitivity for individual PAHs, and we describe the paucity of toxicological literature for many of these compounds. Discussion: PAHs, including the large variety of chemically modified or substituted PAHs, are naturally occurring and may constitute health risks if human populations are exposed to hazardous levels. However, toxicity evaluations have not kept pace with modern analytic methods and their increased ability to detect substituted PAHs. Therefore, although it is possible to measure these compounds in seafood and other media, we do not have sufficient information on the potential toxicity of these compounds to incorporate them into human health risk assessments and characterizations. Conclusions: Future research efforts should strategically attempt to fill this toxicological knowledge gap so human health risk assessments of PAHs in environmental media or food can be better determined. This is especially important in the aftermath of petroleum spills. Citation: Wickliffe J, Overton E, Frickel S, Howard J, Wilson M, Simon B, Echsner S, Nguyen D, Gauthe D, Blake D, Miller C, Elferink C, Ansari S, Fernando H, Trapido E, Kane A. 2014. Evaluation of polycyclic aromatic hydrocarbons using analytical methods, toxicology, and risk assessment research: seafood safety after a petroleum spill as an example. Environ Health Perspect 122:6–9; http://dx.doi.org/10.1289/ehp.1306724

Polycyclic Aromatic Hydrocarbons in Louisiana Rivers and Coastal Environments: Source Fingerprinting and Forensic Analysis

Polycyclic aromatic hydrocarbons (PAHs), many of which are toxic and recalcitrant compounds, are ubiquitous in rivers and coastal environments. Anthropogenic introduction of these chemicals into the environment compromises the assessment of cleanup responsibility and environmental damage liability. Natural background and anthropogenic PAHs in Louisiana coast and major rivers were differentiated based on PAH profiles in samples selected from a pool of 3,540 samples collected over a 3-year period. Several groupings of 2- to 6-ring parent and their C1–C4 alkylated PAH homologs were quantified by gas chromatography/mass spectrometry. Sampling stations were delineated in terms of pyrogenic, petrogenic, and biogenic/diagenetic source PAHs. Fragmentograms indicated that petrogenic inputs generally dominated at more stations than pyrogenic and diagenetic inputs. Most of the results reflected multiple sources of contamination, as would be expected. Preexisting environmental forensic techniques were selected and applied to compare several different source differentiation and allocation methods to evaluate PAH sources in samples from a wide geographical coastal system influenced by myriad sources and complex mixing dynamics. This article covers diagnostic ratios and plots utilizing petroleum biomarker constituents, ratios within homologous PAH categories, pollution indices, and qualitative comparisons to reference profiles suspected as PAH sources.

Oil source-fingerprinting in support of polarimetric radar mapping of Macondo-252 oil in Gulf Coast marshes

Polarimetric synthetic aperture radar (PolSAR) data exhibited dramatic, spatially extensive changes from June 2009 to June 2010 in Barataria Bay, Louisiana. To determine whether these changes were associated with the Deepwater Horizon (DWH) oil spill, twenty-nine sediment samples were collected in 2011 from shoreline and nearshore-interior coastal marsh locations where oil was not observed visually or with optical sensors during the spill. Oil source-fingerprinting and polytopic vector analysis were used to link DWH oil to PolSAR changes. Our results prove that DWH oil extended beyond shorelines and confirm the association between presence of DWH oil and PolSAR change. These results show that the DWH oil spill probably affected much more of the southeastern Louisiana marshland than originally concluded from ground and aerial surveys and verify that PolSAR is a powerful tool for tracking oil intrusion into marshes with high probability even where contamination is not visible from above the canopy.

A Primer on in Situ Fluorometry to Monitor Dispersed Oil

ABSTRACT A flow-through fluorometry system is a valuable tool for measuring dispersed oil concentrations real-time in freshwater and marine environments. As part of the new Scientific Monitoring of...