Photolytic and photocatalytic degradation of surface oil from the Deepwater Horizon spill

Time dependence of aldehyde and ketone oxocarboxylic acid photoproduct generation from crude oil-seawater systems under solar irradiation

Aldehyde and ketone oxocarboxylic acid photoproducts were semi-quantitated in the aqueous phase after subjecting Macondo (MC252) crude oil-seawater systems to simulated solar irradiation. Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was applied after derivatizing the samples with 2,4-dinitrophenylhydrazine (DNPH). Oil-seawater was irradiated at 27.0 °C using a solar simulator for 1 to 18 h. Following irradiation, the aqueous phase was treated with DNPH to generate aldehyde-DNPH and ketone-DNPH derivatives. Solid-phase extraction enriched the samples before analyzing them using (-) ESI-MS/MS. Precursor and product ion spectra were used to select carboxylic acid-containing aldehydes and ketones and provide semi-quantitation using surrogate standards and an internal standard. Loss of m/z 44 (CO2) in the product ion spectra further confirmed the carboxylic acid character. Near-linear increases in photoproduct concentration in the aqueous phase were observed over the 18 h irradiation period. Among the aldehyde and ketone oxocarboxylic acid photoproducts studied, photoproduction rates ranged from 0.6 - 69 µmol/h·m2 of oil surface. Despite some fluctuations, a general trend of lower production rate with higher molecular weight was observed. These results demonstrate the near-linear dependence of photoproduction on irradiance and provide ranges of rates that can be applied to modeling aldehyde and ketone oxocarboxylic acid photoproduction in ocean spills. STATEMENT OF ENVIRONMENTAL IMPACT: Crude oil on seawater degrades when exposed to sunlight. Oxygenated molecules are produced, including carboxylic acid-containing aldehydes and ketones. The formation of these photoproducts from oil films behaves linearly with solar exposure time. These photoproducts are more soluble than the original oil molecules, allowing them to have increased bioavailability and potentially increased toxicity. The rate of formation of these species when oil is exposed to sunlight determines their environmental impact.

High temperature and solar radiation in the Red Sea enhance the dissolution of crude oil from surface films

The Red Sea is a hotspot of biodiversity susceptible to oil pollution. Besides, it is one of the warmest seas on the Earth with highly transparent waters. In this study, we estimated the oil dissolution rates under natural sunlight spectra and temperature conditions using coastal oil slicks collected after the 2019 Sabiti oil spill in the Red Sea. Optical analyses revealed the significant interactive effect of sunlight and temperature in enhancing the dissolution of oil into dissolved organic matter (DOM). The highest oil dissolution rate (38.68 g C m-3 d-1) was observed in full-spectrum sunlight. Oil dissolution significantly enhanced total organic carbon (TOC) and polycyclic aromatic hydrocarbons (PAHs) in seawater. High nucleic acid (HNA) bacteria, likely the oil degraders, proliferated from 30 to 70 - 90% after 4 days. The heavier stable carbon isotopic composition of methane (δ13C-CH4) and lighter stable carbon isotopic composition of carbon dioxide (δ13C-CO2) indicate the putative role of bacterial processes in the natural degradation of crude oil. The results indicated that the combined effect of temperature and solar radiation enhanced the biological and photochemical dissolution of oil on the Red Sea surface.

Dispersant-enhanced photodissolution of macondo crude oil: A molecular perspective

Previous laboratory studies developed a conceptual model based on elevated non-volatile dissolved organic carbon (NVDOC) concentrations after photodegradation and subsequent dissolution of Macondo oil following the Deepwater Horizon blowout. However, those experiments did not account for the effects of ∼1 million gallons of dispersant applied to the surface oil. Here, laboratory results show photodissolution in the presence of dispersant results in > 2x increase in NVDOC concentrations after extensive photoprocessing relative to oil without dispersant. This result corresponds with an apparent increase in the percentage of surface oil photodissolution from approximately 4% in the absence of dispersant to 7% in the presence of dispersant. The oil and dissolved products were analyzed by excitation-emission matrix spectroscopy and ultrahigh resolution mass spectrometry. The compounds that persisted in the oil phase are relatively aromatic without dispersant, while those in the presence of dispersant are highly aliphatic, paraffinic, wax-like compounds. The composition of the dissolved compounds produced from both treatment types are nearly identical after 240 h of exposure to simulated sunlight. The NVDOC and chemical composition information indicate that the photodissolution of MC252 oil in the presence of dispersant is enhanced and accelerated, suggesting that the effects of dispersants should be included in mass transfer calculations from the oil to the aqueous phase.

Photochemistry of oil in marine systems: developments since the Deepwater Horizon spill

Oil spills represent a major source of negative environmental impacts in marine systems. Despite many decades of research on oil spill behavior, photochemistry was neglected as a major factor in the fate of oil spilled in marine systems. Subsequent to the Deepwater Horizon oil spill, numerous studies using varied approaches have demonstrated the importance of photochemistry, including short-term impacts (hours to days) that were previously unrecognized. These studies have demonstrated the importance of photochemistry in the overall oil transformation after a spill and more specifically the impacts on emulsification, oxygenation, and microbial interactions. In addition to new perspectives, advances in analytical approaches have allowed an improved understanding of oil photochemistry after maritime spill. Although the literature on the Deepwater Horizon spill is extensive, this review focuses only on studies relevant to the advances in oil photochemistry understanding since the Deepwater Horizon spill.

Study on the hematological toxicity of Cyprinus carpio exposed to water-soluble fraction of crude oil and TiO2 nanoparticles in the dark and ultraviolet

This study is addressing the potential toxicity concerns of crude oil in common carp (Cyprinus carpio) with the novel use of TiO2-NP for enhancing photocatalytic degradation of WSF of crude oil prepared under UV light or darkness. Blood samples were taken, and the biochemical parameters were analyzed. The levels of ALT, AST and ALP were significantly higher in fish exposed to UV-treated WSF. However, they were significantly lower in the groups exposed to UV-treated TiO2-NPs and the combination of WSF and TiO2-NPs. The levels of total protein, triglycerides, albumin and cholesterol were significantly lower in treatments exposed to UV-treated and dark-conditioned WSF compared to the control group, but they were significantly higher in fish exposed to UV-treated TiO2-NPs and the combination of WSF and TiO2-NPs compared to fish exposed under dark conditions and were not significantly different from the control group. The toxicity of UV-treated WSF was significantly higher than that of dark-conditioned WSF. The toxicity of TiO2-NPs was lower in the presence of UV and was similar to the control treatment. The results of the study suggests that photocatalytic TiO2-NPs and UV radiation reduce toxicity of the water-soluble fraction of crude oil on common carp.

Marine oil spill photodegradation: Laboratory simulation, affecting factors analysis and kinetic model development

Photodegradation significantly influences marine oil spill behavior, yet its role remains underrepresented in current models, impairing predictive accuracy. Addressing this, our study rigorously examined oil properties and environmental determinants affecting marine oil spill photodegradation through laboratory simulations. We identified and quantified key factors and their interactions, noting particularly the positive influence of asphaltene and negative implications of oil density. We also discerned a negative correlation between n-alkane degradation and carbon numbers. Our findings underscored the pivotal roles of temperature and irradiance in photodegradation. All tested oils adhered to first-order kinetics, with rate constants ranging from 0.0348 to 0.0645 day-1. Finally, we introduced a novel model incorporating temperature, irradiance and their interactions, ensuring reasonable simulations for marine oil spill photodegradation, fortifying marine oil spill management strategies.

Visible-Light-Active BiOI/TiO2 Heterojunction Photocatalysts for Remediation of Crude Oil-Contaminated Water

In this study, BiOI-sensitized TiO2 (BiOI/TiO2) nanocomposites with different levels of BiOI deposited via sequential ionic layer adsorption and reaction (SILAR) have been explored for the degradation of methyl orange, 4-chlorophenol (4-CP), and crude oil in water under visible (>400 nm) irradiation with excellent degradation performance. The reaction progress for methyl orange and 4-chlorophenol was monitored by a UV-vis spectrophotometer, and the degradation of the crude oil hydrocarbons was determined by GC-MS. The BiOI/TiO2 heterojunction improves separation of photogenerated charges, which enhances the degradation efficiency. Evaluation of the visible-light photocatalytic performance of the synthesized catalysts against methyl orange degradation confirmed that four SILAR cycles are the optimal deposition condition for the best degradation efficiency. The efficiency was further confirmed by degrading 4-CP and crude oil, achieving 38.30 and 85.62% degradation, respectively, compared with 0.0% (4-CP) and 70.56% (crude oil) achieved by TiO2. The efficiency of TiO2 in degrading crude oil was mainly due to adsorption along with photolysis. This study provides a simple and cost-effective alternative to traditional remediation methods requiring high energy consumption for remediation of crude oil-polluted water and refinery wastewater using visible-light photocatalysis along with adsorption.

Photochemical mobilization of dissolved hydrocarbon oxidation products from petroleum contaminated soil into a shallow aquifer activate human nuclear receptors

Elevated non-volatile dissolved organic carbon (NVDOC) concentrations in groundwater (GW) monitoring wells under oil-contaminated hydrophobic soils originating from a pipeline rupture at the National Crude Oil Spill & Natural Attenuation Research Site near Bemidji, MN are documented. We hypothesized the elevated NVDOC is comprised of water-soluble photooxidation products transported from the surface to the aquifer. We use field and laboratory samples in combination with complementary analytical methods to test this hypothesis and determine the biological response to these products. Observations from optical spectroscopy and ultrahigh-resolution mass spectrometry reveal a significant correlation between the chemical composition of NVDOC leached from photochemically weathered soils and GW monitoring wells with high NVDOC concentrations measured in the aquifer beneath the contaminated soil. Conversely, the chemical composition from the uncontaminated soil photoleachate matches the NVDOC observed in the uncontaminated wells. Contaminated GW and photodissolution leachates from contaminated soil activated biological targets indicative of xenobiotic metabolism and exhibited potential for adverse effects. Newly formed hydrocarbon oxidation products (HOPs) from fresh oil could be distinguished from those downgradient. This study illustrates another pathway for dissolved HOPs to infiltrate GW and potentially affect human health and the environment.

Coral skeletons reveal the impacts of oil pollution on seawater chemistry in the northern South China Sea

Oil pollution can release trace metals (TMs) with cumulative toxicity into seawater, harming marine ecosystems in the long term. However, the lack of studies has inhibited our understanding of the effects and mechanisms of oil pollution on TMs in seawater. Hence, we investigated the 10-year monthly variation of TMs in Porites coral skeletons from the northern South China Sea (SCS), complemented by spatial distribution of TMs in seawater, sediments and characterization of TMs in fuel oil. The results of principal component-multivariate linear regression showed that the total contribution of oil pollution as a source to TMs in surface seawater was 77.2%, where the residence time of TMs (Ni, V, Cr, Co, Cu, Mn, Fe, and Mo) released from oil spills in surface seawater was approximately 1.4 months. Due to the geochemical nature of the metals, their seasonal variations are controlled by tropical cyclones (Ni, V, Cr, Co, Cu, Mn, Fe, and Mo), winter monsoons (Pb, Cd, Ba, and Zn) and sea surface temperature (Sr). This study shows that coral skeletons can be used as a new tool to study marine oil pollution. This provides valuable reference data for accurately identifying and quantifying the effects of oil pollution on TMs in seawater from a spatial and temporal perspective.

Emerging Chemical Methods for Petroleum and Petroleum-Derived Dissolved Organic Matter Following the Deepwater Horizon Oil Spill

Despite the fact that oil chemistry and oils spills have been studied for many years, there are still emerging techniques and unknown processes to be explored. The 2010 Deepwater Horizon oil spill in the Gulf of Mexico resulted in a revival of oil spill research across a wide range of fields. These studies provided many new insights, but unanswered questions remain. Over 1,000 journal articles related to the Deepwater Horizon spill are indexed by the Chemical Abstract Service. Numerous ecological, human health, and organismal studies were published. Analytical tools applied to the spill include mass spectrometry, chromatography, and optical spectroscopy. Owing to the large scale of studies, this review focuses on three emerging areas that have been explored but remain underutilized in oil spill characterization: excitation-emission matrix spectroscopy, black carbon analysis, and trace metal analysis using inductively coupled plasma mass spectrometry.

Recommendations for the advancement of oil-in-water media and source oil characterization in aquatic toxicity test studies

During toxicity testing, chemical analyses of oil and exposure media samples are needed to allow comparison of results between different tests as well as to assist with identification of the drivers and mechanisms for the toxic effects observed. However, to maximize the ability to compare results between different laboratories and biota, it has long been recognized that guidelines for standard protocols were needed. In 2005, the Chemical Response to Oil Spills: Ecological Effects Research Forum (CROSERF) protocol was developed with existing common analytical methods that described a standard method for reproducible preparation of exposure media as well as recommended specific analytical methods and analyte lists for comparative toxicity testing. At the time, the primary purpose for the data collected was to inform oil spill response and contingency planning. Since then, with improvements in both analytical equipment and methods, the use of toxicity data has expanded to include their integration into fate and effect models that aim to extend the applicability of lab-based study results to make predictions for field system-level impacts. This paper focuses on providing a summary of current chemical analyses for characterization of oil and exposure media used during aquatic toxicity testing and makes recommendations for the minimum analyses needed to allow for interpretation and modeling purposes.

Weathering impacts on petroleum biomarker, aromatic, and polar compounds in the spilled oil at the northeast coast of Brazil over time

After the wide oil spill reached the northeast of Brazil, the resurgence of oil was recorded and to evaluate this oil in detail, two samples collected in the state of Pernambuco in 2019 and 2021 were submitted to multiple analytical techniques. For both, we have found similar saturated biomarkers and triaromatic steroid ratios, implying that they are from the same spilled source. The n-alkanes, isoprenoids, and cycloalkanes were almost completely degraded due to evaporation, photooxidation, and/or biodegradation processes. The preferential loss of less alkylated PAHs than the more alkylated ones suggests that biodegradation was the most active process. This hypothesis is reinforced by the formation of mono and dicarboxylic acids assessed by GC × GC-TOFMS and ESI(-) FT-ICR MS high-resolution techniques. Furthermore, based on the ESI(-) FT-ICR MS results, three new ratios were proposed to evaluate the progress of the biodegradation process over time: O_x>2/O, SO_x/SO, and SO_x/N.

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.

Efficient photocatalytic degradation of petroleum oil spills in seawater using a metal-organic framework (MOF)

Photocatalysis is a green approach that has appeared to be a viable option for the degradation of a variety of organic contaminants. This work outlines the process of preparing the titanium-based metal-organic framework (MIL-125) photocatalysts using a simple solvothermal method. Structural, morphological, and optical analysis of samples (MT18 and MT48) was carried out by XRD, FT-IR, Raman, SEM, TGA, BET, and UV-Vis. Results indicated that the sample prepared at 150 °C and reaction time of 48 h (MT48) has a low crystal size of 7 nm with an optical band gap of 3.2 eV and a surface area of 301 m² g^-1. Under UV-visible light irradiation, the as-prepared MOFs proved to upgrade photocatalytic activity in degrading crude oil spills in saltwater. Effects of catalyst dosage and exposure time on the degradation of an oil spill in seawater were studied and analyzed using UV-Vis spectrophotometry and gas chromatography (GC-MS) which emphasized that the use of 250 ppm of MT48 photocatalyst under UV-Vis irradiation can degrade about 99% of oil spills in water after 2 h of exposure. The study's data revealed that MIL-125 could be used to photocatalyzed the cleanup of crude oil spills.

Temporal chemical composition changes in water below a crude oil slick irradiated with natural sunlight

Photooxidation can alter the environmental fate and effects of spilled oil. To better understand this process, oil slicks were generated on seawater mesocosms and exposed to sunlight for 8 days. The molecular composition of seawater under irradiated and non-irradiated oil slicks was characterized using ion mobility spectrometry-mass spectrometry and polyaromatic hydrocarbons analyses. Biomimetic extraction was performed to quantify neutral and ionized constituents. Results show that seawater underneath irradiated oil showed significantly higher amounts of hydrocarbons with oxygen- and sulfur-containing by-products peaking by day 4-6; however, concentrations of dissolved organic carbon were similar. Biomimetic extraction indicated toxic units in irradiated mesocosms increased, mainly due to ionized components, but remained <1, suggesting limited potential for ecotoxicity. Because the experimental design mimicked important aspects of natural conditions (freshly collected seawater, natural sunlight, and relevant oil thickness and concentrations), this study improves our understanding of the effects of photooxidation during a marine oil spill.

PAH depletion in weathered oil slicks estimated from modeled age-at-sea during the Deepwater Horizon oil spill

During time-periods oil slicks are in the marine environment (age-at-sea), weathering causes significant changes in composition and mass loss (depletion) of oil spill chemicals including the more toxic polycyclic aromatic hydrocarbons (PAHs). The goal of this study was to estimate the age-at-sea of weathered oil slicks using the oil spill module of the Connectivity Modeling System and to use this age to interpret PAH concentration measurements. Percent depletion (PD) for each measurement was computed as the percentage difference between the original and measured PAH concentration in the crude oil and weathered oil slicks, normalized upon the mass losses relative to hopane. Mean PD increased with estimated age-at-sea for all PAHs. Less PD was observed for alkylated than for parent PAHs, likely due to decreasing vapor pressure with increasing degree of alkylation. We conclude that estimated age-at-sea can be used to explain PAH depletion in weathered oil slicks. We propose PAH vapor pressure can be coupled with the model to expand capacity for predicting concentration distributions of individual parent and alkylated PAHs in weathered oil along the coastline. This new module will advance the science supporting oil spill response by providing more certain estimates of health risks from oil spills.

Complex Mixture Analysis of Emerging Contaminants Generated from Coal Tar- and Petroleum-Derived Pavement Sealants: Molecular Compositions and Correlations with Toxicity Revealed by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Pavement sealants are of environmental concern because of their complex petroleum-based chemistry and potential toxicity. Specifically, coal tar-derived sealants contain high concentrations of toxic/carcinogenic polycyclic aromatic hydrocarbons (PAHs) that, when weathered, can be transferred into the surrounding environment. Previous studies have demonstrated the effects of coal tar sealants on PAH concentration in nearby waterways and their harmful effects in aquatic ecosystems. Here, we investigate and compare the molecular composition of two different pavement sealants, petroleum asphalt- and coal tar-derived, and their photoproducts, by positive-ion (+) atmospheric pressure photoionization (APPI) and negative-ion (-) electrospray ionization (ESI) coupled with ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry to address species (high-boiling and/or high oxygen content) that lie outside the analytical window of other techniques due to ultra-high molecular complexity. In addition, we evaluate the toxicity of the water-soluble photoproducts by use of Microtox bioassay. The results demonstrate that the coal tar sealant contains higher amounts of PAHs and produces abundant water-soluble compounds, relative to unweathered materials, with a high abundance of PAH-like molecules of high toxicity. By comparison, the asphalt sealant produces fewer toxic water-soluble species, with molecular compositions that are consistent with natural dissolved organic matter. These results capture the mass, chemical diversity, toxicity, and source/photoproduct relationship of these compositionally complex emerging contaminants from the built environment.

Recent advances in chemical and biological degradation of spilled oil: A review of dispersants application in the marine environment

Growing concerns over the risk of accidental releases of oil into the marine environment have emphasized our need to improve both oil spill preparedness and response strategies. Among the available spill response options, dispersants offer the advantages of breaking oil slicks into small oil droplets and promoting their dilution, dissolution, and biodegradation within the water column. Thus dispersants can reduce the probability of oil slicks at sea from reaching coastal regions and reduce their direct impact on mammals, sea birds and shoreline ecosystems. To facilitate marine oil spill response operations, especially addressing spill incidents in remote/Arctic offshore regions, an in-depth understanding of the transportation, fate and effects of naturally/chemically dispersed oil is of great importance. This review provides a synthesis of recent research results studies related to the application of dispersants at the surface and in the deep sea, the fate and transportation of naturally and chemically dispersed oil, and dispersant application in the Arctic and ice-covered waters. Future perspectives have been provided to identify the research gaps and help industries and spill response organizations develop science-based guidelines and protocols for the application of dispersants application.

Effects of asphaltenes on the photolytic and toxic behavior of bitumen and conventional oil products on saltwater

The effects of asphaltenes on the photolytic and toxic behavior of petroleum oil on seawater was investigated by exposing five original oils and their maltenes to solar irradiation for seven days. Polycyclic aromatic hydrocarbons (PAHs) experienced the fastest photo-oxidation, but negligible photolytic loss was observed for most normal alkanes and all the petroleum biomarkers from tri-cyclic to pentyl-cyclic terpanes in the test total oil and maltenes. The removal of most PAHs from some maltenes was greater than the corresponding total oils. Deasphalting process did not affect the characteristics of naphthenic acid fraction components (NAFCs) in all control samples. In all test oils, solar irradiation formed abundant NAFCs, in particular those only containing oxygen as the heteroatoms (O_o species). The formed O_o species were abundant in congeners having highly saturated congeners, and shifted to a lighter carbon number after exposed. Deasphalting process significantly enhanced the formation of O_o species (o from 2 to 4) for all test oils, in particular for the Cold Lake Blend and Bunker C. The toxicity of exposed maltenes was generally higher than the exposed total oil for most oils, suggesting the aqueous toxicity level was positively related to the formed NAFC intermediates.

Oil Irradiation Experiments Document Changes in Oil Properties, Molecular Composition, and Dispersant Effectiveness Associated with Oil Photo-Oxidation

While chemical dispersants are a powerful tool for treating spilled oil, their effectiveness can be limited by oil weathering processes such as evaporation and emulsification. It has been suggested that oil photo-oxidation could exacerbate these challenges. To address the role of oil photo-oxidation in dispersant effectiveness, outdoor mesocosm experiments with crude oil on seawater were performed. Changes in bulk oil properties and molecular composition were quantified to characterize oil photo-oxidation over 11 days. To test relative dispersant effectiveness, oil residues were evaluated using the Baffled Flask Test. The results show that oil irradiation led to oxygen incorporation, formation of oxygenated hydrocarbons, and higher oil viscosities. Oil irradiation was associated with decreased dispersant efficacy, with effectiveness falling from 80 to <50% in the Baffled Flask Test after more than 3 days of irradiation. Increasing photo-oxidation-induced viscosity seems to drive the decreasing dispersant effectiveness. Comparing the Baffled Flask Test results with field data from the Deepwater Horizon oil spill showed that laboratory dispersant tests underestimate the dispersion of photo-oxidized oil in the field. Overall, the results suggest that prompt dispersant application (within 2-4 days), as recommended by current oil spill response guidelines, is necessary for effective dispersion of spilled oil.

Changes in Chemical Composition and Copepod Toxicity during Petroleum Photo-oxidation

Photoproducts can be formed rapidly in the initial phase of a marine oil spill. However, their toxicity is not well understood. In this study, oil was irradiated, chemically characterized, and tested for toxicity in three copepod species (Acartia tonsa, Temora longicornis, and Calanus finmarchicus). Irradiation led to a depletion of polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in oil residues, along with an enrichment in aromatic and aliphatic oil photoproducts. Target lipid model-based calculations of PAH toxicity units predicted that PAH toxicities were lower in water-accommodated fractions (WAFs) of irradiated oil residues ("irradiated WAFs") than in WAFs of dark-control samples ("dark WAFs"). In contrast, biomimetic extraction (BE) measurements showed increased bioaccumulation potential of dissolved constituents of irradiated WAFs compared to dark WAFs, mainly driven by photoproducts present in irradiated oil. In line with the BE results, copepod mortality increased in irradiated WAFs compared to dark WAFs. However, low copepod toxicities were observed for WAFs produced with photo-oxidized oil slicks collected during the Deepwater Horizon oil spill. The results of this study suggest that while oil photoproducts have the potential to be a significant source of copepod toxicity, dilution and dispersion of these higher solubility products appear to help mitigate their toxicity at sea.

Time-dependent molecular progression and acute toxicity of oil-soluble, interfacially-active, and water-soluble species reveals their rapid formation in the photodegradation of Macondo Well Oil

Photodegradation is a significant weathering process that transforms spilled oil, yet, the fate, degradation rate, and molecular transformations that occur through photoinduced pathways remain relatively unknown. The molecular complexity combined with the increased polarity of photoproducts challenges conventional analytical techniques. Here, we catalogue the molecular progression of photochemical transformation products of Macondo Well Oil by negative-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We track the molecular compositions of oil-soluble, interfacially-active, and water-soluble oil species formed at varying time intervals in photomicrocosm experiments. Short photoirradiation periods (<24 h), not previously reported, are included to reveal rapid photooxidation of native oil components. Surface oil films exposed to solar irradiation were shown to increasingly contribute to the dissolved organic carbon pool as a function of increased irradiation time. FT-ICR MS analysis of acidic species of each fraction identifies tens of thousands of oil-soluble, interfacially-active, and water-soluble phototransformation products, including O_x, NO_x, and SO_x species. Oil-soluble species incorporate oxygen as a function of irradiation periods. After 96 h of irradiation, ~14 wt% of the photooxidized oil film was interfacially active and contained phototransformed species with up to 12 oxygen atoms per molecule. Water-soluble species correspond to highly oxygenated compounds. Importantly, photochemical oxidation is shown to occur within the first hour. Beyond 24 h, photoproducts remain compositionally similar, highlighting the rapid effect of photodegradation to transform oil species into water-soluble compounds. Molecular fingerprints provided by FT-ICR MS highlight the oxygen dependence on oil/water solubility. Microtox® analysis indicates that the toxicity of water-soluble photoproducts rapidly increases at early irradiation time points (first 24 h) compared to the dark control and reaches a maximum at 6 h of irradiation. Results highlight the temporal, molecular progression of photoproducts as they partition from oil-soluble to oil-soluble interfacially-active, and finally to water-soluble species.

From Surface Water to the Deep Sea: A Review on Factors Affecting the Biodegradation of Spilled Oil in Marine Environment

Over the past century, the demand for petroleum products has increased rapidly, leading to higher oil extraction, processing and transportation, which result in numerous oil spills in coastal-marine environments. As the spilled oil can negatively affect the coastal-marine ecosystems, its transport and fates captured a significant interest of the scientific community and regulatory agencies. Typically, the environment has natural mechanisms (e.g., photooxidation, biodegradation, evaporation) to weather/degrade and remove the spilled oil from the environment. Among various oil weathering mechanisms, biodegradation by naturally occurring bacterial populations removes a majority of spilled oil, thus the focus on bioremediation has increased significantly. Helping in the marginal recognition of this promising technique for oil-spill degradation, this paper reviews recently published articles that will help broaden the understanding of the factors affecting biodegradation of spilled oil in coastal-marine environments. The goal of this review is to examine the effects of various environmental variables that contribute to oil degradation in the coastal-marine environments, as well as the factors that influence these processes. Physico-chemical parameters such as temperature, oxygen level, pressure, shoreline energy, salinity, and pH are taken into account. In general, increase in temperature, exposure to sunlight (photooxidation), dissolved oxygen (DO), nutrients (nitrogen, phosphorous and potassium), shoreline energy (physical advection—waves) and diverse hydrocarbon-degrading microorganisms consortium were found to increase spilled oil degradation in marine environments. In contrast, higher initial oil concentration and seawater pressure can lower oil degradation rates. There is limited information on the influences of seawater pH and salinity on oil degradation, thus warranting additional research. This comprehensive review can be used as a guide for bioremediation modeling and mitigating future oil spill pollution in the marine environment by utilizing the bacteria adapted to certain conditions.

Advances in Chemical Analysis of Oil Spills Since the Deepwater Horizon Disaster

Analytical techniques for chemical analysis of oil, oil photochemical and biological transformation products, and dispersants and their biodegradation products benefited significantly from research following the 2010 Deepwater Horizon (DWH) disaster. Crude oil and weathered-oil matrix reference materials were developed based on the Macondo well oil and characterized for polycyclic aromatic hydrocarbons, hopanes, and steranes for use to assure and improve the quality of analytical measurements in oil spill research. Advanced gas chromatography (GC) techniques such as comprehensive two-dimensional GC (GC × GC), pyrolysis GC with mass spectrometry (MS), and GC with tandem MS (GC-MS/MS) provide a greater understanding at the molecular level of composition and complexity of oil and weathering changes. The capabilities of high-resolution MS (HRMS) were utilized to extend the analytical characterization window beyond conventional GC-based methods to include polar and high molecular mass components (>400 Da) and to provide new opportunities for discovery, characterization, and investigation of photooxidation and biotransformation products. Novel separation approaches to reduce the complexity of the oil and weathered oil prior to high-resolution MS and advanced fluorescence spectrometry have increased the information available on spilled oil and transformation products. HRMS methods were developed to achieve the required precision and sensitivity for detection of dispersants and to provide molecular-level characterization of the complex surfactants. Overall, research funding following the DWH oil spill significantly advanced and expanded the use of analytical techniques for chemical analysis to support petroleum and dispersant characterization and investigations of fate and effects of not only the DWH oil spill but future spills.

Dissolved organic matter production from herder application and in-situ burning of crude oil at high latitudes: Bioavailable molecular composition patterns and microbial community diversity effects

Chemical herders and in-situ burning (ISB) are designed to mitigate the effects that oil spills may have on the high latitude marine environment. Little information exists on the water solubilization of petroleum residues stemming from chemically herded ISB and whether these bioavailable compounds have measurable impacts on marine biota. In this experiment, we investigated the effects of Siltech OP40 and crude oil ISB on a) petroleum-derived dissolved organic matter (DOM_HC) composition and b) seawater microbial community diversity over 28 days at 4 °C in aquarium-scale mesocosms. Ultra-high resolution mass spectrometry and fluorescence spectroscopy revealed increases in aromaticity over time, with ISB and ISB+OP40 samples having higher % aromatic classes in the initial incubation periods. ISB+OP40 contained a nearly 12-fold increase in the number of DOM_HC formulae relative to those before ISB. 16S rRNA gene sequencing identified differences in microbial alpha diversity between seawater, ISB, OP40, and ISB+OP40. Microbial betadiversity shifts were observed that correlated strongly with aromatic/condensed relative abundance and incubation time. Proteobacteria, specifically from the genera Marinomonas and Perlucidibaca experienced -22 and +24 log₂-fold changes in ISB+OP40 vs. seawater, respectively. These findings provide an important opportunity to advance our understanding of chemical herders and ISB in the high latitude marine environment.

Influences of petroleum hydrocarbon pyrene on the formation, stability and antibacterial activity of natural Au nanoparticles

The effect of pyrene on the formation of naturally Au nanoparticles (AuNPs) in the presence of humic acid (HA) under UV irradiation is described. TEM, EDS, FTIR and XPS were carried out to prove the formation of AuNPs and display their morphologies and formation mechanism. There are little differences between size, morphology and function groups of surface coated materials of AuNPs formed with and without pyrene. With the presence of HA, pyrene showed an inhibiting effect on the reduction of Au ion via competition for O₂^•-, thereby decreasing the production of AuNPs. However, AuNPs formed by HA-pyrene showed higher stability than AuNPs formed by HA with the sedimentation rates of 4.13% and 13.68% respectively after 30-d standing. As for the antibacterial activities against Staphylococcus aureus and Escherichia coli, AuNPs formed by HA-pyrene were more toxic than AuNPs formed by HA. Meanwhile, changes of environmental factors such as temperature, pH and ionic strength exhibited similar influence trend on the formation of AuNPs in the presence and absence of pyrene. The results suggest that the typical petroleum hydrocarbon pyrene contained in spilled oil could influence the formation, fate and ecotoxicity of AuNPs.

Bacterial responses to background organic pollutants in the northeast subarctic Pacific Ocean

Thousands of man-made synthetic chemicals are released to oceans and compose the anthropogenic dissolved organic carbon (ADOC). Little is known about the effects of this chronic pollution on marine microbiome activities. In this study, we measured the pollution level at three sites in the Northeast Subarctic Pacific Ocean (NESAP) and investigated how mixtures of three model families of ADOC at different environmentally relevant concentrations affected naturally occurring marine bacterioplankton communities' structure and metabolic functioning. The offshore northernmost site (North) had the lowest concentrations of hydrocarbons, as well as organophosphate ester plasticizers, contrasting with the two other continental shelf sites, the southern coastal site (South) being the most contaminated. At North, ADOC stimulated bacterial growth and promoted an increase in the contribution of some Gammaproteobacteria groups (e.g. Alteromonadales) to the 16 rRNA pool. These groups are described as fast responders after oil spills. In contrast, minor changes in South microbiome activities were observed. Gene expression profiles at Central showed the coexistence of ADOC degradation and stress-response strategies to cope with ADOC toxicities. These results show that marine microbial communities at three distinct domains in NESAP are influenced by background concentrations of ADOC, expanding previous assessments for polar and temperate waters.

Monitoring chemical compositional changes of simulated spilled Brazilian oils under tropical climate conditions by multiple analytical techniques

To comprehensively understand the chemical changes over time of spilled oils subject to tropical climate conditions and the active weathering processes, a spill simulation experiment was conducted along 210 days with two distinct Brazilian oils (19 and 24 API) under irradiation and non-irradiation of sunlight. Isoprenoids and n-alkanes showed a great loss after 40 days for both oils under the two conditions due to evaporation. Diagnostic ratios of saturated biomarkers showed no changes, whereas the polycyclic aromatic hydrocarbons had a decreasing concentration under both conditions mainly due to evaporation. Furthermore, oxygenated polar compounds produced by photooxidation were investigated by ESI(-) FT-ICR MS and showed changes only for the oils exposed to sunlight irradiation. Based on the observed polar compositional changes, new parameters are suggested using heteroatom classes to estimate oil spill time under tropical conditions: NO₃/NO₂; NO₃/(NO + NO₂); ∑NO_x/N₁; (O₄ + O₃)/(O₂ + O₁); O₄/(O₂ + O₁); and O₃/O₂.

Long-acting photocatalytic degradation of crude oil in seawater via combination of TiO2 and N-doped TiO2/reduced graphene oxide

N-doped TiO₂/ reduced graphene oxide (N/TiO₂/rGO) composite was prepared and used together with the commercial TiO₂ for comparative research on photocatalytic degradation of crude oil in seawater. Five test conditions were designed including a combined catalyst of TiO₂ and N/TiO₂/rGO (4:1) under UV-A light irradiation with a duration of 28 days. The changing trend of the water-soluble fraction (WSF) of crude oil in seawater was monitored by ultraviolet spectroscopy and fluorescence spectroscopy as well as dissolved organic carbon (DOC) measurement. The SARA fractions of oil residues were analysed by column chromatography, and the chemical composition changes of saturates and aromatics were investigated by gas chromatography-mass spectroscopy (GC-MS). The results reveal that although it had high efficiency in the degradation of aromatics, the nano-TiO₂ tended to self-agglomerate, which enhanced agglomeration of crude oil, causing its catalytic process actually terminating within seven days. By comparison, the N/TiO₂/rGO composite consistently dispersed crude oil in the whole experimental duration, subsequently, it presented a higher photocatalytic degradation rate than TiO₂. The combination of TiO₂ and N/TiO₂/rGO (4:1) shows concerted catalysis on photocatalytic degradation of crude oil, and the oil degradation rate reached to 54.80% while the aromatic degradation rate was 74.83%. The fluorescent components in WSFs were preferentially degraded, and the degradation products of aromatic fraction were CO₂ and H₂O as well as saturates, mainly C₂₀∼C₃₁ alkanes. Considering its long-acting photocatalysis, the N/TiO₂/rGO composite possesses practical utilization potentiality together with TiO₂ in spilled oil treatment in the marine environment.

Photocatalytic H2 Production from Naphthalene by Various TiO2 Photocatalysts: Impact of Pt Loading and Formation of Intermediates

This work presents a comparative study of the efficiency of two commercial TiO2 photocatalysts, Aeroxide P25 (ATiO2) and Sachtleben Hombikat UV100 (HTiO2), in H2 production from an aqueous solution of naphthalene. The TiO2 photocatalysts were platinized by the photodeposition method varying the platinum content of the suspension to 0.5, 1.0, and 5.0 wt%. A full physicochemical characterization for these materials was performed, showing no structural effects from the deposition method, and confirming a well dispersion of nanosized-Pt0 particles on the surface of both photocatalysts. Pristine ATiO2 shows around 14% higher photocatalytic fractional conversion of naphthalene than pristine HTiO2 after 240 min of irradiation, while both materials exhibit negligible activity for H2 formation. The 0.5 wt% Pt- HTiO2 increases the photocatalytic fractional conversion of naphthalene from 71% to 82% and produces 6 µmol of H2. However, using a higher Pt content than the optimal platinization ratio of 0.5 wt% dramatically inhibits both processes. On the other hand, regardless of the fractional ratio of Pt, the platinization of ATiO2 results in a decrease in the fractional conversion of naphthalene by 4% to 33% of the pristine value. Although the presence of Pt islands on the surface of the ATiO2 is essential for the H2 evolution, no dependency between the Pt ratio and the H2 formation rate was observed since all the platinized materials show a similar H2 formation of around 3 µmol. Based on the EPR results, the higher photocatalytic activity of the Pt-HTiO2 is attributed to the efficient charge carrier separation and its larger surface area. The recyclability test confirms that the inhibition of the photocatalytic process is related to the deactivation of the photocatalyst surface by the adsorption of the photoformed intermediates. A strong relationship between the photocatalytic activity and the kind of the aromatic compounds was observed. The H2 evolution and the photooxidation of the aromatic hydrocarbons exhibit higher photonic efficiencies than that of their corresponding hydroxylated compounds over the Pt-HTiO2.

Barium ion adduct mass spectrometry to identify carboxylic acid photoproducts from crude oil-water systems under solar irradiation

Petroleum derived dissolved organic matter (DOMHC) samples were successfully cationized with barium, revealing many [M-H + Ba]+ peaks in both dark and simulated sunlight treatments. The DOMHC samples generated after light exposure exhibited a greater number of [M-H + Ba]+ peaks compared to the dark control. Multiple [M-H + Ba]+ peaks were investigated in the irradiated DOMHC using low resolution MS/MS in order to confirm the presence of diagnostic fragment ions, m/z 139, 155 and 196 in each treatment. Due to the high complexity of the bariated DOMHC mixture, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS/MS) was employed to obtain molecular level information for both irradiated and dark treatments. The irradiated DOMHC treatments had more bariated oxygenated species over a wide range of H/C and O/C when compared to the dark controls. Doubly bariated species were also observed in DOMHC, which provides evidence that photochemistry transforms DOMHC to even more complex mixtures with multiple oxygenations per molecule. This study provides evidence that barium adduct mass spectrometry can be successfully applied to DOMHC screening for the presence of COOHs, both in dark samples and solar irradiated samples. Furthermore, direct evidence and molecular composition of aqueous phase crude oil photoproducts is provided by this technique.

Photocatalytic elimination of interfacial water pollutants by floatable photoreactive composite nanoparticles

Disastrous oil spills cause severe environmental issues. The shortcomings of current cleaning methods for remediating oil have prompted the latest research drive to create intelligent nanoparticles that absorb oil. We, therefore, synthesized 197 ± 50 nm floatable photoreactive hybrid nanoparticles with Ag-TiO₂ plasmonic photocatalyst (E_g = 3.08 eV) content to eliminate interfacial water pollutants, especially toluene-based artificial oil spill. We found that the composite particles have non-wetting properties in the aqueous media and float easily on the surface of the water due to the moderate hydrophobic nature (Θ = 113°) of the matrix of polystyrene, and these properties lead to elevated absorption of the interfacial organic pollutants (e.g., mineral oil). We showed that (28.5 mol%) divinylbenzene cross-linker content was required for adequate swelling capacity (2.15 g/g), whereas incorporated 15.8% Ag-TiO₂ content in the swollen particles was enough for efficient photodegradation of the artificial oil spill under 150 min LED light (λ_max = 405 nm) irradiation. The swollen polymer particles with embedded 32 ± 7 nm Ag-TiO₂ content increase the efficiency of photooxidation by increased the direct contact between both the photocatalysts and the artificial oil spill. Finally, it was also presented that the composite particles destroy themselves: after approximately one and a half months of continuous LED light irradiation, the organic polymer component of the composite was almost completely (88.5%) photodegraded by the incorporated inorganic photocatalyst particles.

Large Enrichment of Anthropogenic Organic Matter Degrading Bacteria in the Sea-Surface Microlayer at Coastal Livingston Island (Antarctica)

The composition of bacteria inhabiting the sea-surface microlayer (SML) is poorly characterized globally and yet undescribed for the Southern Ocean, despite their relevance for the biogeochemistry of the surface ocean. We report the abundances and diversity of bacteria inhabiting the SML and the subsurface waters (SSL) determined from a unique sample set from a polar coastal ecosystem (Livingston Island, Antarctica). From early to late austral summer (January–March 2018), we consistently found a higher abundance of bacteria in the SML than in the SSL. The SML was enriched in some Gammaproteobacteria genus such as Pseudoalteromonas, Pseudomonas, and Colwellia, known to degrade a wide range of semivolatile, hydrophobic, and surfactant-like organic pollutants. Hydrocarbons and other synthetic chemicals including surfactants, such as perfluoroalkyl substances (PFAS), reach remote marine environments by atmospheric transport and deposition and by oceanic currents, and are known to accumulate in the SML. Relative abundances of specific SML-enriched bacterial groups were significantly correlated to concentrations of PFASs, taken as a proxy of hydrophobic anthropogenic pollutants present in the SML and its stability. Our observations provide evidence for an important pollutant-bacteria interaction in the marine SML. Given that pollutant emissions have increased during the Anthropocene, our results point to the need to assess chemical pollution as a factor modulating marine microbiomes in the contemporaneous and future oceans.

Role of Molecular Structure in the Production of Water-Soluble Species by Photo-oxidation of Petroleum

Asphaltenes are high-boiling and recalcitrant compounds that are generally minor components of crude oil (∼0.1-15.0 wt %) but dominate the composition of heavily weathered spilled petroleum. These solid residues exhibit a high structural complexity, comprised of polycyclic aromatic hydrocarbons (PAHs) that are a mixture of single-core (island) and multicore (archipelago) structural motifs. The mass fraction of each motif is sample-dependent. Thus, knowledge of a potential structural dependence (single- versus multicore) on the production of water-soluble species from asphaltene samples is key to understanding the contribution of photochemically generated dissolved organic matter from oil spills. In this work, asphaltene samples with enriched mass fractions of either island (single-core) or archipelago (multicore) structural motifs are photo-oxidized on artificial seawater by the use of a solar simulator. Molecular characterization of oil- and water-soluble photoproducts, conducted by Fourier transform ion cyclotron resonance mass spectrometry, reveals that island motifs exhibit very limited production of water-soluble species, and their oil-soluble products reflect the molecular composition of the starting material. Conversely, archipelago motifs yield a water-soluble compositional continuum of O_x, S_xO_y, and N_xO_y containing hydrocarbons species that exhibit the typical molecular fingerprint of dissolved organic matter (DOM). The lower carbon number and aromaticity of the archipelago-derived asphaltene photoproducts suggest the occurrence of photofragmentation (or photolysis) reactions. To investigate the possibility of the opposite reaction (photopolymerization), the photo-oxidation of small PAHs isolated from a low-boiling petroleum distillation cut was also performed. It yielded water-soluble compounds with carbon number and aromaticity up to 2-fold higher than the starting material, strongly suggesting that polymerization (addition reactions) occurs. Collectively, the results indicate that the presence of archipelago motifs and the occurrence of cracking/polymerization reactions are central in the production of dissolved organic matter from fossil fuels.

Thermochemical study for remediation of highly concentrated acid spill: Computational modeling and experimental validation

The release of concentrated acid solutions by chemical accidents is disastrous to our environmental integrity. Alkaline agents applied to remedy the acid spill catastrophe may lead to secondary damages such as vaporization or spread out of the fumes unless substantial amount of neutralization heat is properly controlled. Using a rigorous thermodynamic formalism proposed by Pitzer to account short-range ion interactions and various subsidiary reactions, we develop a systematic computational model enabling quantitative prediction of reaction heat and the temperature change over neutralization of strongly concentrated acid solutions. We apply this model to four acid solutions (HCl, HNO₃, H₂SO₄, and HF) of each 3 M-equivalent concentration with two neutralizing agents of calcium hydroxide (Ca(OH)₂) and sodium bicarbonate (NaHCO₃). Predicted reaction heat and temperature are remarkably consistent with the outcomes measured by our own experiments, showing a linear correlation factor R² greater than 0.98. We apply the model to extremely concentrated acid solutions as high as 50 wt% where an experimental approach is practically restricted. In contrast to the extremely exothermic Ca(OH)₂ agent, NaHCO₃ even lowers solution temperatures after neutralization reactions. Our model enables us to identify a promising neutralizer NaHCO₃ for effectively controlling concentrated acid spills and may be useful for establishment of proper strategy for other chemical accidents.

Occurrence and weathering of petroleum hydrocarbons deposited on the shoreline of the North Saskatchewan River from the 2016 Husky oil spill

Following the 16TAN Husky oil spill along the North Saskatchewan River (NSR), the occurrence and natural attenuation of the petroleum hydrocarbons were assessed by analyzing the littoral zone sediments/oil debris collected from July 2016 to October 2017. Husky oil-free, mixed sediment-Husky oil, and Husky oil debris samples were identified for all the collected samples. Shoreline sediments were contaminated by mixed biogenic, pyrogenic and petrogenic inputs prior to the spill. Oil stranded on the shoreline of NSR was moved or buried due to the very dynamic conditions of the shoreline, or cleaned through a series of cleanup activities after the spill. Most normal alkanes were naturally weathered, whereas most of the branched alkanes and all of the saturated petroleum biomarkers remained. Some lighter molecular weight (e.g., 2 to 3-ring) polycyclic aromatic hydrocarbons (PAHs) were lost rapidly after the spill, whereas sulfur containing components, e.g., dibenzothiophenes and benzonaphthothiiophenes, and those having a heavier molecular weight did not change markedly even 15 months post-spill. Similarly, some light hydrocarbons (e.g., <C₁₀) were lost over the first kilometers from the point of entry (POE), while heavier hydrocarbons did not show any major differences away from the POE. Very large inter-site and inter-survey discrepancies were found for samples. Evaporation into the air and dissolution into water, combined with biodegradation, were together or independently the main contributors to the loss of the light molecular hydrocarbons.

BiOI-on-SiO2 microspheres: A floating photocatalyst for degradation of diesel oil and dye wastewater

The powder-based photocatalytic material is often difficult on wide application and then loaded on a matrix for separating conveniently from the liquid. Submerged photocatalysts may not take advantage of the light energy adequately. Thus, this boundedness may reduce their utilization and potentially cause the secondary pollution on the environment. In this paper, the micron-sized silica sphere is used as a floating substrate, and the visible-light-driven photocatalytic material iodine oxygen bismuth is prepared onto the hollow silica microspheres. The composite spheres as the visible-light-driven photocatalytic material have been characterized by XPS, XRD, SEM, EDX, PL, etc. It confirmed that BiOI combined on the SiO₂ microsphere (mSiO₂) by Bi-O-Si. The photogenerated electrons of the composite have a low probability of recombination and have a narrow band energy (1.82 eV). The composite was used to photodegrade diesel-containing wastewater and rhodamine B, and the superoxide group (·O₂^-) was found to be the main degradation active factor. And by GC-MS test, it is known that the superoxide group (·O₂^-) can degrade long-chain alkanes into short chains or form branches. Detailed studies on the acute exposure experiments of Vibrio qinghaiensis sp.-Q67 and zebrafish embryos showed that the composites can effectively reduce the toxicity of BiOI and mSiO₂.

Mesocosm experiments to better understand hydrocarbon half-lives for oil and oil dispersant mixtures

Concerns on the timing and processes associated with petroleum degradation were raised after the use of Corexit during the Deepwater Horizon oil spill. There is a lack of understanding of the removal of oil associated with flocculate materials to the sediment. Mesocosm studies employing coastal and open-ocean seawater from the Gulf of Mexico were undertaken to examine changes in oil concentration and composition with time. The water accommodated fractions (WAF) and chemically enhanced WAF (CEWAF) produced using Macondo surrogate oil and Corexit were followed over 3–4 days in controlled environmental conditions. Environmental half-lives of estimated oil equivalents (EOE), polycyclic aromatic hydrocarbons (PAH), n-alkanes (C10-C35), isoprenoids pristane and phytane, and total petroleum hydrocarbons (TPH) were determined. EOE and PAH concentrations decreased exponentially following first-order decay rate kinetics. WAF, CEWAF and DCEWAF (a 10X CEWAF dilution) treatments half-lives ranged from 0.9 to 3.2 days for EOE and 0.5 to 3.3 days for PAH, agreeing with estimates from previous mesocosm and field studies. The aliphatic half-lives for CEWAF and DECWAF treatments ranged from 0.8 to 2.0 days, but no half-life for WAF could be calculated as concentrations were below the detection limits. Biodegradation occurred in all treatments based on the temporal decrease of the nC₁₇/pristane and nC₁₈/phytane ratios. The heterogeneity observed in all treatments was likely due to the hydrophobicity of oil and weathering processes occurring at different rates and times. The presence of dispersant did not dramatically change the half-lives of oil. Comparing degradation of oil alone as well as with dispersant present is critical to determine the fate and transport of these materials in the ocean.

Environmental significance of lubricant oil: A systematic study of photooxidation and its consequences

Lubricant (lube) oil discharge from ships has been widely considered as normal "operational consumption", but is now deemed to be oil pollution. Despite the chronic contamination of the marine environment by lube oil, the number of studies related to its environmental impact, characteristics, and toxicity is limited. This study is the first attempt to investigate the environmental fate of lube oil subjected to photooxidation using in situ mesocosms. A tiered approach using thin-layer chromatography-flame ionization detection (TLC-FID), Fourier-transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS) demonstrated compositional changes in lube oil and the water-soluble fraction (WSF). Total polycyclic aromatic hydrocarbons (ΣPAHs) in lube oil after 96 h of photooxidation were measured at 79.8 and 41 μg/g in the control (Con) and exposure (Exp) groups, respectively. Meanwhile, the ΣPAHs concentration in WSF after 96 h was very low, at 0.25 and 0.45 μg/L in Con and Exp, respectively. FTIR and GC-MS helped identify bond changes and photoproducts in WSF. A wide range of photoproducts, including carboxylic acids, esters, anhydrides, aldehydes and ketones, were identified in WSF. Toxic effects of WSF in both the Con and Exp groups obtained after 96 h of photooxidation were evaluated on olive flounder (Paralichthys olivaceus) embryos. Morphological defects, especially tail fin fold defects, were found to be significantly elevated in both the Con and Exp groups, with marginally higher frequency in Exp. The results of this study demonstrate the need for further research on lube oil weathering, including monitoring over prolonged periods of time.

Molecular-Level Composition and Acute Toxicity of Photosolubilized Petrogenic Carbon

To examine the molecular-level composition and acute toxicity per unit carbon of the petroleum-derived dissolved organic matter (DOM_HC) produced via photo-oxidation, heavy and light oils were irradiated over seawater with simulated sunlight. Increases in dissolved organic carbon concentrations as a function of time were associated with changes in the DOM_HC composition and acute toxicity per unit carbon. Parallel factor analysis showed that the fluorescent dissolved organic matter (FDOM) composition produced from the heavy oil became more blue-shifted over time, while the light oil produced a mixture of blue- and red-shifted components similar to FDOM signatures. Ultrahigh-resolution mass spectrometry reveals that the composition of the DOM_HC produced from both heavy and light oils was initially relatively reduced, with low O/C. With time, the composition of the DOM_HC produced from the heavy oil shifted to unsaturated, high-oxygen compounds, while that produced from the light oil comprised a range of high O/C aliphatic, unsaturated, and aromatic compounds. Microtox assays suggest that the DOM_HC initially produced is the most toxic (62% inhibition); however, after 24 h, a rapid decrease in toxicity decreased linearly to 0% inhibition for the heavy DOM_HC and 12% inhibition for the light DOM_HC at extended exposure periods.

Decomposition of sediment-oil-agglomerates in a Gulf of Mexico sandy beach

Sediment-oil-agglomerates (SOA) are one of the most common forms of contamination impacting shores after a major oil spill; and following the Deepwater Horizon (DWH) accident, large numbers of SOAs were buried in the sandy beaches of the northeastern Gulf of Mexico. SOAs provide a source of toxic oil compounds, and although SOAs can persist for many years, their long-term fate was unknown. Here we report the results of a 3-year in-situ experiment that quantified the degradation of standardized SOAs buried in the upper 50 cm of a North Florida sandy beach. Time series of hydrocarbon mass, carbon content, n-alkanes, PAHs, and fluorescence indicate that the decomposition of golf-ball-size DWH-SOAs embedded in beach sand takes at least 32 years, while SOA degradation without sediment contact would require more than 100 years. SOA alkane and PAH decay rates within the sediment were similar to those at the beach surface. The porous structure of the SOAs kept their cores oxygen-replete. The results reveal that SOAs buried deep in beach sands can be decomposed through relatively rapid aerobic microbial oil degradation in the tidally ventilated permeable beach sand, emphasizing the role of the sandy beach as an aerobic biocatalytical reactor at the land-ocean interface.

Molecular-Level Characterization of Oil-Soluble Ketone/Aldehyde Photo-Oxidation Products by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Reveals Similarity Between Microcosm and Field Samples

We present a solid-phase extraction method followed by derivatization with a charged tag to characterize ketone/aldehyde-containing functionalities (proposed photo-oxidation transformation products) in weathered petroleum by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). A photo-oxidation-only microcosm mimics solar irradiation of crude oil in the environment after an oil spill. A biodegradation-only microcosm enables independent determination as to which of the two weathering processes contributes to the formation of oil-soluble ketone/aldehyde species. Results confirm that photo-oxidation produces ketones/aldehydes in crude oil when exposed to solar radiation in laboratory experiments, whereas biodegraded oil samples do not produce ketone/aldehyde compounds. Field samples collected after different time periods and locations after the Deepwater Horizon oil spill are also shown to contain ketones/aldehydes, and comparison of field and photo-oxidation-only microcosm transformation products reveal remarkable similarity. These results indicate that the photo-oxidation microcosm comprehensively represents ketone/aldehyde-formation products in the field, whereas the biodegradation microcosm does not. Solid-phase extraction coupled with derivatization leads to selective identification of ketone/aldehyde species by MS. Although improved dynamic range and slightly reduced mass spectral complexity is achieved by separation/derivatization, comprehensive molecular characterization still requires mass resolving power and mass accuracy provided by FT-ICR MS.

Changes in ecotoxicity of naphthalene and alkylated naphthalenes during photodegradation in water

Crude oil released into the environment contains many polycyclic aromatic hydrocarbons (PAHs). Alkylated PAHs are more abundant than unsubstituted PAHs and their toxicity is also of serious concern. Among the various physical, chemical, and biological weathering processes of crude oils, photodegradation is one of the most important for determining the environmental fate of oil residues. In this study, the photodegradation rate constants of naphthalene and alkylated naphthalenes were determined under simulated laboratory conditions at different temperature. Changes in the luminescence inhibition of Aliivibrio fischeri, as an indicator of the baseline toxicity, were observed in photodegradation mixtures. The major transformation products were also identified by gas chromatography-mass spectrometry. The photodegradation of naphthalene and the eight alkylated naphthalenes was described well by pseudo-first-order kinetics regardless of experimental temperature. The measured toxicity of the reaction mixtures obtained by photodegradative weathering slightly increased initially and then decreased with further weathering. In all cases, the observed toxicity was greater than accounted for by the parent compounds, indicating that the photodegradation products also contributed significantly to the overall toxicity of the mixtures. The identified photodegradation products were mostly oxygenated compounds such as alcohols, aldehydes, ketones, and quinones, which warrant further investigation.

Photochemical degradation of oil products in seawater monitored by 3D excitation emission matrix (EEM) fluorescence spectroscopy: implications for coloured dissolved organic matter (CDOM) studies

Fluorescence 3D excitation emission matrix (EEM) spectra of oil products in artificial seawater were monitored as a function of irradiation time in a solar simulator. EEMs were obtained for an excitation range of 240-400 nm and an emission range of 248-830 nm; this is the wavelength range typically used in chromophoric dissolved organic matter (CDOM) EEM studies in natural waters. This allows for comparison to prior work on CDOM in an oil-contaminated salt marsh that attributed a fluorescent component in the tryptophan/tyrosine protein-region to oil. For comparison, EEMs were also measured for a broader excitation range of 220-400 nm typically used in oil related studies to capture the primary oil peak at lower excitation wavelengths. Fluorescence intensities in both excitation wavelength ranges decayed exponentially with irradiation time consistent with first-order kinetics. There was little change in wavelength for primary oil peaks. However, in the CDOM, wavelength range peaks typically shifted to longer excitation and shorter emission wavelengths, moving into the protein peak region of the CDOM EEM spectrum. This is consistent with a decrease in the complexity of the structure of the organic material. Half-lives for photodegradation ranged from 0.36 to 7.2 days for the oil wavelength range and 0.14 to 28 days for the CDOM wavelength range. Higher density oils typically had higher degradation rate constants. Peak locations and peak behaviour are consistent with the primary fluorophore in the oil products being PAH-related.

Influence of variable ultraviolet radiation and oil exposure duration on survival of red drum (Sciaenops ocellatus) larvae

The toxicity of some polycyclic aromatic hydrocarbons (PAHs) increases with ultraviolet (UV) radiation. The intensity of UV radiation varies within aquatic ecosystems, potentially providing reprieves during which tissue repair may occur. Transient/short-term PAH exposure prior to UV exposure may initiate metabolism/clearance, potentially affecting outcomes. Larval Sciaenops ocellatus were exposed to oil and UV radiation, using either variable photoperiods or pre-UV oil exposure durations. Shorter PAH exposures exhibited greater toxicity, as did exposure to shorter photoperiods. Environ Toxicol Chem 2018;37:2372-2379. © 2018 SETAC.