Characterizing the efficiency of low-cost LED lights for conducting laboratory studies to investigate polycyclic aromatic hydrocarbon photodegradation processes.

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants ubiquitously present in various waste products such as biosolids (e.g. wastewater sludges), oil spill residues (e.g. tarballs), road asphalts, and combustion byproducts. In this study, the photodegradation of PAHs is investigated under natural sunlight (cloudy and sunny/clear weather conditions), and using two types of artificial LED light sources. This is the first study to investigate the relative efficiency of low-cost LED light sources for conducting laboratory-scale PAH photodegradation experiments and directly comparing the results against those obtained using natural sunlight. Two types of LED light sources are investigated in this study: a light source with a full-spectrum range (380 nm-780 nm) that can cover the broad wavelength range of solar light reaching the Earth's surface, and a light source with a UV-A range (365 nm) that covers the UV range of the solar spectrum reaching the Earth's surface. The results show that the degradation of high molecular weight (HMW) PAHs is primarily due to photodegradation, and other lighter PAHs are degraded by both photodegradation and evaporation processes. HMW PAH photodegradation reactions follow the first-order degradation kinetics. The degradation rate constants of different PAHs are used to compare the relative efficiency of the light sources. The data show that the full-spectrum LED induced PAH photodegradation rates are similar to the natural sunlight induced rates. Furthermore, when the values of the rate constants are normalized to respective irradiance levels, the normalized rates for HMW PAH photodegradation under both full-spectrum LED light and natural sunlight are almost identical. However, the normalized photodegradation rate constants of HMW PAHs under the UV-A LED light are about two to three orders of magnitude higher than the sunlight as well as the full-spectrum-LED values. Therefore, the UV-A LED light is the optimal low-cost light source for studying PAH photodegradation processes under laboratory conditions.

Understanding the relative performance of SCAN, SIM, PMRM and MRM methods for quantifying polycyclic aromatic hydrocarbons in crude oil samples.

RATIONALE: Polycyclic aromatic hydrocarbons (PAHs) present in oil spill samples are analyzed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/tandem mass spectrometry (GC/MS/MS) using four different methods: (1) full scan (SCAN), (2) selected ion monitoring (SIM), (3) multiple reaction monitoring (MRM), and (4) pseudo multiple reaction monitoring (PMRM). This study quantifies the relative performance of these methods. METHODS: Novel experiments were designed to measure the signal-to-noise (S/N) ratios of all four methods. This was accomplished by spiking the crude oil with five deuterated PAHs (dPAHs) in two distinct ways: (1) varying the background noise by changing crude oil concentrations before spiking the samples with 1 ng/mL of dPAHs, and (2) varying the signal by spiking dPAHs concentrations of 0.5 and 5 ng/mL into a crude oil sample. RESULTS: The MRM method is the most selective and sensitive of the four methods. It also provides the lowest limit of detection (LOD) and limit of quantitation (LOQ). MRM is the optimal approach for quantifying PAHs in complex petroleum samples containing high levels of background noise. Also, our data show that the PAHs in complex oil spill samples can be quantified by MRM without using any complicated sample preparation steps. CONCLUSIONS: Based on our experimental data, the relative performance of the four methods used for quantifying PAHs in crude oil samples can be ranked as MRM > PMRM > SIM > SCAN.

Authorship matrix: a rational approach to quantify individual contributions and responsibilities in multi-author scientific articles.

We propose a rational method for addressing an important question-who deserves to be an author of a scientific article? We review various contentious issues associated with this question and recommend that the scientific community should view authorship in terms of contributions and responsibilities, rather than credits. We propose a new paradigm that conceptually divides a scientific article into four basic elements: ideas, work, writing, and stewardship. We employ these four fundamental elements to modify the well-known International Committee of Medical Journal Editors (ICMJE) authorship guidelines. The modified ICMJE guidelines are then used as the basis to develop an approach to quantify individual contributions and responsibilities in multi-author articles. The outcome of the approach is an authorship matrix, which can be used to answer several nagging questions related to authorship.

Implications of the Mississippi v. Tennessee Supreme Court Decision for Interstate Groundwater Management.

Groundwater allocation is rapidly becoming a contentious water resource management problem around the world. It is anticipated that the effects of climate change would further aggravate this problem. Conflicts over the distribution of freshwater are expected to increase as stakeholders want to access more groundwater to meet their growing demands. In the United States, water conflicts are settled through a litigation process. Water litigations can be expensive, protracted, and fraught with complex legal and technical difficulties. A landmark groundwater case involving Tennessee (TN) and Mississippi (MS) was recently litigated in the Supreme Court of the United States (SCOTUS). In this case, MS sued TN for stealing their groundwater and SCOTUS unanimously ruled that the water contained in the aquifer that naturally crosses the border between TN and MS is subject to equitable apportionment. This decision has significant ramifications for groundwater management as it established a precedent for resolving future interstate groundwater litigations. Although the Court has previously applied the legal doctrine of equitable apportionment to settle disputes involving surface water use, this is the first instance in which the doctrine has been applied to resolve an interstate groundwater dispute. Therefore, currently, there are little or no guidelines available for equitably distributing groundwater resources between two states. The objective of this article is to examine this historic legal dispute to fully understand the scientific justification for the judicial stances taken by the plaintiff and defendants, and the legal reasoning for the final verdict. We also discuss the challenges this ruling presents for managing interstate groundwater resources.

Environmental fate of petroleum biomarkers in Deepwater Horizon oil spill residues over the past 10 years.

The long-term fate of three groups of petroleum biomarker compounds (terpanes, steranes, and triaromatic steranes) was investigated in the Deepwater Horizon (DWH) oil spill residues collected from Alabama (USA) beaches over the past 10 years. This is the first study to investigate the long-term fate of these three groups of petroleum biomarkers in DWH oil spill samples over 10 years. We employed the highly recalcitrant C30 αß-hopane as an internal biomarker to quantify the degradation levels of different biomarker compounds, and also to estimate the overall weathering levels of DWH oil spill residues. The data show that four lower molecular weight tricyclic terpanes (TR21, TR22, TR23, and TR24), three lower molecular weight steranes (S21, S22, and C27), and all triaromatic steranes degraded over the 10-year study period. All other terpanes (including hopanes) and steranes remained recalcitrant. There have been contradicting literature data on the degradation levels of homohopanes, and this field study demonstrates that all the homohopanes remained recalcitrant after 10 years of natural weathering. Our data also show that despite some degradation, the relative diagnostic ratios of the biomarkers remained stable for all three groups of biomarkers over the 10-year period.

Field and laboratory investigation of tarmat deposits found on Ras Rakan Island and northern beaches of Qatar.

Beaches of Ras Rakan Island, located off the northern tip of Qatar, are extensively contaminated by highly weathered tarmat deposits. The focus of this study is to determine the possible source of the contamination and complete a preliminary assessment of its potential environmental impacts. The field data collected at this site indicated that the tarmat residues contained highly weathered, black, asphalt-like material and the contamination problem was widespread. Based on these field observations, the following two hypotheses were formulated: (1) the tarmats must have formed from the residual oil deposited by a relatively large, regional-scale oil spill event, and (2) the oil spill must be relatively old. As part of this study, we collected tarmat residues from several beaches located along the northern region of Qatar Peninsula. We found the hopane fingerprints of these tarmat samples were identical to the fingerprints of the samples collected from Ras Rakan Island. These results together with our physical field observational data validated our hypothesis that the oil spill should have been a regional-scale event. Furthermore, we compared the measured hopane fingerprints of our field samples with fingerprints of reference crude oils from Qatar, Saudi Arabia, and Basrah (located close to Kuwait border), and with the literature-derived hopane fingerprints of Kuwaiti and Iranian crude oils. This analysis indicated that the hopane fingerprints of the tarmat samples closely matched the Kuwaiti and Basrah crude oil fingerprints. Since there were no known oil spills of Basrah crude in this region, the highly weathered, asphalt-looking tarmats should have most likely formed from the 1991 Gulf War oil spill, an old oil spill. The concentrations of parent and alkylated PAHs in the tarmat samples were also quantified to provide a preliminary assessment of potential environmental risks posed by these tarmats to Qatar's coastal ecosystem.

Understanding the thermal degradation patterns of hopane biomarker compounds present in crude oil.

In-situ burning (ISB) is a common oil spill response technique used for managing marine oil spills. The burnt residues generated from ISB can have several toxic compounds and therefore their impacts on aquatic ecosystem are of major environmental concern. When quantifying the fate of the toxic compounds in ISB residues, C30-αß hopane is routinely used as a conservative biomarker since it has shown to be resistant to most natural weathering processes. However, a recent laboratory study has shown that C30-αß and other hopane compounds have the potential to degrade when crude oil was physically burnt under controlled conditions. When crude oil is burnt, the temperature of the oil can raise up to 350-500 °C; however, so far, no one has studied the fate of hopanes when crude oil is simply heated to very high temperatures. In this study, we hypothesize that heating crude oil to very high temperatures would result in the degradation of hopane compounds. Results of our study show that C30-αß hopane in crude oil will start to degrade at around 160 °C and the degradation pattern follows first order kinetics. Other types of hopanes and their diagnostic ratios can also change when the oil is exposed to severe heating conditions. We conclude that removal of hopane biomarkers via thermal degradation is a possible depletion pathway during ISB. Therefore, caution should be exercised when using hopanes as conservative biomarker compounds for characterizing ISB residues.

Investigation of transient freshwater storage in island aquifers.

Fresh groundwater in an island aquifer is an extremely important resource that is highly vulnerable to variations in natural weather cycles and climate change effects. On small islands, precipitation creates subsurface freshwater lenses that float on top of coalesced saltwater that has intruded from the surrounding seawater. The volume and shape of these highly vulnerable freshwater lenses depend on the size and shape of the island, underlying geology, and the rate and duration of groundwater recharge. This study focuses on the transient changes in freshwater storage volume within these lenses. We completed a sand tank experiment to visualize an evolving freshwater lens that undergoes a dry- and -wet recharge cycle resulting in forming a shrinking and an expanding lens. The physical experiments provided a dataset to develop a robust numerical model that can rigorously simulate different types of evolving transient freshwater lenses. Our laboratory data along with past literature information have indicated that the shrinking of a freshwater lens occurred at a slower rate relative to an expanding freshwater lens. This aspect of a rather rapid freshwater volume recovery was investigated further using the numerical model by imposing cyclic recharge patterns to study the impacts of shortened recharge periods on freshwater storage in island aquifers. The results show that a sustainable dynamic equilibrium condition can be achieved within a few cycles of periodic recharge. Unsustainable conditions were only encountered at extremely short recharge periods. The model was then extended to simulate a freshwater lens in Dauphin Island, Alabama, to assess changes in freshwater storage under realistic wet and dry recharge cycles. The experimental data together with the modeling results presented in this study provide a better understanding of transient changes in freshwater storage patterns in small islands.

Development of a scalable model for predicting arsenic transport coupled with oxidation and adsorption reactions.

Understanding the fundamentals of arsenic adsorption and oxidation reactions is critical for predicting its transport dynamics in groundwater systems. We completed batch experiments to study the interactions of arsenic with a common MnO2(s) mineral, pyrolusite. The reaction kinetics and adsorption isotherm developed from the batch experiments were integrated into a scalable reactive transport model to facilitate column-scale transport predictions. We then completed a set of column experiments to test the predictive capability of the reactive transport model. Our batch results indicated that the commonly used pseudo-first order kinetics for As(III) oxidation reaction neglects the scaling effects with respect to the MnO2(s) concentration. A second order kinetic equation that explicitly includes MnO2(s) concentration dependence is a more appropriate kinetic model to describe arsenic oxidation by MnO2(s) minerals. The arsenic adsorption reaction follows the Langmuir isotherm with the adsorption capacity of 0.053micromol of As(V)/g of MnO2(s) at the tested conditions. The knowledge gained from the batch experiments was used to develop a conceptual model for describing arsenic reactive transport at a column scale. The proposed conceptual model was integrated within a reactive transport code that accurately predicted the breakthrough profiles observed in multiple column experiments. The kinetic and adsorption process details obtained from the batch experiments were valuable data for scaling to predict the column-scale reactive transport of arsenic in MnO2(s)-containing sand columns.

Development of a field testing protocol for identifying Deepwater Horizon oil spill residues trapped near Gulf of Mexico beaches.

The Deepwater Horizon (DWH) accident, one of the largest oil spills in U.S. history, contaminated several beaches located along the Gulf of Mexico (GOM) shoreline. The residues from the spill still continue to be deposited on some of these beaches. Methods to track and monitor the fate of these residues require approaches that can differentiate the DWH residues from other types of petroleum residues. This is because, historically, the crude oil released from sources such as natural seeps and anthropogenic discharges have also deposited other types of petroleum residues on GOM beaches. Therefore, identifying the origin of these residues is critical for developing effective management strategies for monitoring the long-term environmental impacts of the DWH oil spill. Advanced fingerprinting methods that are currently used for identifying the source of oil spill residues require detailed laboratory studies, which can be cost-prohibitive. Also, most agencies typically use untrained workers or volunteers to conduct shoreline monitoring surveys and these worker will not have access to advanced laboratory facilities. Furthermore, it is impractical to routinely fingerprint large volumes of samples that are collected after a major oil spill event, such as the DWH spill. In this study, we propose a simple field testing protocol that can identify DWH oil spill residues based on their unique physical characteristics. The robustness of the method is demonstrated by testing a variety of oil spill samples, and the results are verified by characterizing the samples using advanced chemical fingerprinting methods. The verification data show that the method yields results that are consistent with the results derived from advanced fingerprinting methods. The proposed protocol is a reliable, cost-effective, practical field approach for differentiating DWH residues from other types of petroleum residues.

Fate of hopane biomarkers during in-situ burning of crude oil - A laboratory-scale study.

In-situ burning (ISB) is a remediation strategy that is used for managing oil spills. ISB generates heavy residues that can submerge and negatively impact benthic environments. To track the fate of toxic contaminants in ISB residues, a conservative hopane biomarker, such as C30-αß hopane, is often used. Furthermore, diagnostic ratios of various hopanes are used for source oil identification. Use of these biomarkers assume that during ISB the quantity of C30-αß hopane will be conserved, and the diagnostic ratios of various hopanes will be stable. The objective of this study is to test the validity of these two assumptions. We conducted laboratory-scale ISB experiments using a model oil prepared from commercial C30-αß hopane standard, and a reference crude oil. Laboratory data collected under controlled burning conditions show that C30-αß hopane will not be conserved; however, the diagnostic ratios of hopanes will still remain fairly stable.

Effects of weathering on the dispersion of crude oil through oil-mineral aggregation.

Crude oil that is inadvertently spilled in the marine environment can interact with suspended sediment to form oil-mineral aggregates (OMA). Researchers have identified OMA formation as a natural method of oil dispersion, and have sought ways to enhance this process for oil spill remediation. Currently there is a lack of understanding of how the weathering of oil will affect the formation of OMA due to a lack of published data on this relationship. Based on literature, we identified two conflicting hypotheses: OMA formation 1) increases with weathering as a result of increased asphaltene and polar compound content; or 2) decreases with weathering as a result of increased viscosity. While it is indeed true that the viscosity and the relative amount of polar compounds will increase with weathering, their net effects on OMA formation is unclear. Controlled laboratory experiments were carried out to systematically test these two conflicting hypotheses. Experimental results using light, intermediate, and heavy crude oils, each at five weathering stages, show a decrease in OMA formation as oil weathers.

A three-dimensional analytical tool for modeling reactive transport.

In this note, we present a public domain analytical reactive transport modeling tool (ART3D, version 2.0). The tool is developed in FORTRAN and can be used for solving a system of a set of partial differential equations coupled with a first-order reaction network. ART3D uses a novel analytic solution technique proposed by Clement. The new software includes options for performing Monte Carlo simulations and automated parameter estimation.

Evaluating the neurotoxic effects of Deepwater Horizon oil spill residues trapped along Alabama's beaches.

AIMS: The Deepwater Horizon oil spill (also known as the BP spill) is one of the largest oil spills in the U.S. HISTORY: To manage the spill, BP used an oil spill dispersant (Corexit 9500A) to disperse the oil. However, a portion of undispersed oil eventually got emulsified and interacted with near shore sediments along the Alabama shoreline and sank to the bottom forming tarmats, also known as submerged residual oil mats (SRMs). Natural shoreline transport processes have often broken these tarmats to form smaller oil fragments, known as surface residual oil balls (SRBs) or tarballs. The long-term human and the ecological health impacts of various toxic chemicals trapped in tarmat deposits are currently unknown. The purpose of this study is to investigate the in vitro cytotoxic effects of the chemicals trapped in tarmat fragments using hippocampal (neuron), kidney (nephron) and epithelial cells. MAIN METHODS: Water accommodated fraction (WAF) of tarmat fragments was used in this study. Cytotoxicity was elucidated by the MTT assay and cellular morphology assessment. Markers of oxidative stress and apoptosis were assessed to study the toxicity effects. Statistical analysis was performed using Sigma-stat. KEY FINDINGS: Tarmat WAF induced dose-dependent cellular toxicity. Chemicals trapped in tarmat WAF inhibited cell viability in the hippocampal (H19), kidney (HEK-293) and epithelial (MCF-10A) cells. Tarmat WAF also generated reactive oxygen species and increased activity of superoxide dismutase in hippocampal cells. SIGNIFICANCE: The study has provided preliminary data to elucidate the toxic potential of BP oil spill residues trapped along the Alabama shoreline.

Weathering patterns of polycyclic aromatic hydrocarbons contained in submerged Deepwater Horizon oil spill residues when re-exposed to sunlight.

The Deepwater Horizon (DWH) oil spill event released a large amount of sweet crude oil into the Gulf of Mexico (GOM). An unknown portion of this oil that arrived along the Alabama shoreline interacted with nearshore sediments and sank forming submerged oil mats (SOMs). A considerable amount of hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), were trapped within these buried SOMs. Recent studies completed using the oil spill residues collected along the Alabama shoreline have shown that several PAHs, especially higher molecular weight PAHs (four or more aromatic rings), are slowly weathering compared to the weathering levels experienced by the oil when it was floating over the GOM. In this study we have hypothesized that the weathering rates of PAHs in SOMs have slowed down because the buried oil was isolated from direct exposure to sunlight, thus hindering the photodegradation pathway. We further hypothesized that re-exposing SOMs to sunlight can reactivate various weathering reactions. Also, SOMs contain 75-95% sand (by weight) and the entrapped sand could either block direct sunlight or form large oil agglomerates with very little exposed surface area; these processes could possibly interfere with weathering reactions. To test these hypotheses, we completed controlled experiments to study the weathering patterns of PAHs in a field recovered SOM sample after re-exposing it to sunlight. Our experimental results show that the weathering levels of several higher molecular weight PAHs have slowed down primarily due to the absence of sunlight-induced photodegradation reactions. The data also show that sand particles in SOM material could potentially interfere with photodegradation reactions.

Correction: a tale of two recent spills-comparison of 2014 Galveston Bay and 2010 Deepwater Horizon Oil Spill Residues.

[This corrects the article DOI: 10.1371/journal.pone.0118098.].

A tale of two recent spills--comparison of 2014 Galveston Bay and 2010 Deepwater Horizon oil spill residues.

Managing oil spill residues washing onto sandy beaches is a common worldwide environmental problem. In this study, we have analyzed the first-arrival oil spill residues collected from two Gulf of Mexico (GOM) beach systems following two recent oil spills: the 2014 Galveston Bay (GB) oil spill, and the 2010 Deepwater Horizon (DWH) oil spill. This is the first study to provide field observations and chemical characterization data for the 2014 GB oil spill. Here we compare the physical and chemical characteristics of GB oil spill samples with DWH oil spill samples and present their similarities and differences. Our field observations indicate that both oil spills had similar shoreline deposition patterns; however, their physical and chemical characteristics differed considerably. We highlight these differences, discuss their implications, and interpret GB data in light of lessons learned from previously published DWH oil spill studies. These analyses are further used to assess the long-term fate of GB oil spill residues and their potential environmental impacts.