Beyond TPH: health-based evaluation of petroleum hydrocarbon exposures

The formation, reactivity, and fate of oxygen-containing organic compounds in petroleum-contaminated groundwaters: A state of the science review and future research directions

Hydrocarbon (HC) contamination in groundwater (GW) is a widespread environmental issue. Dissolved hydrocarbons in water are commonly utilized as an energy source by natural microbial communities, which can produce water soluble intermediate metabolite compounds, herein referred to as oxygen containing organic compounds (OCOCs), before achieving complete mineralization. This review aims to provide a comprehensive assessment of the literature focused on the state of the science for OCOCs detected and measured in GW samples collected from petroleum contaminated aquifers. In this review, we discuss and evaluate two hypotheses investigating OCOC formation, which are major points of contention in the freshwater oil spill community that need to be addressed. We reviewed over 150 articles compiling studies investigating OCOC formation and persistence to uncover knowledge gaps in the literature and studies that recommend quantitative and qualitative measurements of OCOCs in petroleum-contaminated aquifers. This review is essential because no consensus exists regarding specific compounds and related concerns. We highlight the knowledge gaps to progressing the discussion of hydrocarbon conversion products.

Integrative description of changes occurring on zebrafish embryos exposed to water-soluble crude oil components and its mixture with a chemical surfactant

The effects of crude oil spills are an ongoing problem for wildlife and human health in both marine and freshwater aquatic environments. Bioassays of model organisms are a convenient way to assess the potential risks of the substances involved in oil spills. Zebrafish embryos (ZFE) are a useful to reach a fast and detailed description of the toxicity of the pollutants, including both the components of the crude oil itself and substances that are commonly used for crude oil spill mitigation (e.g. surfactants). Here, we evaluated the survival rate, as well as histological, morphological, and proteomic changes in ZFE exposed to Water Accumulated Fraction (WAF) of light crude oil and in mixture with dioctyl sulfosuccinate sodium (DOSS, e.g. CEWAF: Chemically Enhanced WAF), a surfactant that is frequently used in chemical dispersant formulations. Furthermore, we compared de hydrocarbon concentration of WAF and CEWAF of the sublethal dilution. In histological, morphological, and gene expression variables, the ZFE exposed to WAF showed less changes than those exposed to CEWAF. Proteomic changes were more dramatic in ZFE exposed to WAF, with important alterations in spliceosomal and ribosomal proteins, as well as proteins related to eye and retinal photoreceptor development and heart function. We also found that the concentration of high molecular weight hydrocarbons in water was slighly higher in presence of DOSS, but the low molecular weight hydrocarbons concentration was higher in WAF. These results provide an important starting point for identifying useful crude-oil exposure biomarkers in fish species.

Differential Gene Expression Induced by Acute Exposure to Water Accommodated Fraction (WAF) and Chemically Enhanced WAF (CEWAF) of Light Crude Oil and Nokomis 3-F4 in Limulus polyphemus Larvae

In 2018 we evaluated at 48 h and 96 h, the gene expression profile of larvae of Limulus polyphemus exposed to 10% and 100% of water-accommodated fraction (WAF) of light crude oil (API 35), and 10% and 100% of a chemically enhanced WAF (CEWAF) with the dispersant Nokomis 3-F4® in a static-acute (96 h) bioassay. Alkanes and PAHs concentrations were higher in CEWAF than in WAF stock solutions. Under the proved conditions, the expression profile of genes associated to detoxification processes (glutathione S-transferase and glutathione peroxidase), stress (heat shock protein), innate immunity (tumor necrosis factor receptor-associated factor 4 traf4), cell death (apoptosis inhibitor 5) and DNA repairing (E3 ubiquitin protein ligase), showed a deregulation at 48 h followed by an upregulation at 96 h, with exception of glutathione peroxidase, heat shock protein and innate immunity that remained low in CEWAF. In conclusion, by using genes that have been proposed as biomarkers to pollutants exposure, L. polyphemus larvae showed an early activation of genes related to the immune system, antioxidant, heat shock and NER.

Detailed chemical characterization of the composition and variability of soil gas at remediated residential heating oil discharges

Underground storage tanks containing petroleum or other hazardous substances are used widely for residential storage of home heating oil. Spills and leaks of fuel from these tanks are common, and resulting subsurface petroleum vapors may pose health risks. However, understanding of this risk is limited by a lack of observational data on the chemical composition of vapors from discharged fuel. We present here the composition of soil gas sampled at 66 remediated residential sites of underground heating oil discharges throughout Virginia using a newly developed data analysis technique that allows characterization of hydrocarbons by carbon number and degree of unsaturation. Measured concentrations of total petroleum hydrocarbons exceeded 100,000 μg/m³ at 12 sites, but its composition varied widely between sites. Concentrations of hydrocarbons from chemical classes differing by more than a few carbon numbers or degrees of unsaturation are found to be poorly correlated. Furthermore, differences in composition are poorly described by metrics expected to indicate subsurface weathering (e.g., discharge year, or ratio of n-heptadecane to pristane). These results suggest that the composition and magnitude of residual contamination at remediated subsurface discharges is driven by rarely documented spill characteristics (e.g., age and composition of source material, discharge rate, etc.).

Assessment of temporal and spatial water quality in international Gomishan Lagoon, Iran, using multivariate analysis

Coastal lagoon ecosystems are vulnerable to eutrophication, which leads to the accumulation of nutrients from the surrounding watershed over the long term. However, there is a lack of information about methods that could accurate quantify this problem in rapidly developed countries. Therefore, various statistical methods such as cluster analysis (CA), principal component analysis (PCA), partial least square (PLS), principal component regression (PCR), and ordinary least squares regression (OLS) were used in this study to estimate total organic matter content in sediments (TOM) using other parameters such as temperature, dissolved oxygen (DO), pH, electrical conductivity (EC), nitrite (NO₂), nitrate (NO₃), biological oxygen demand (BOD), phosphate (PO₄), total phosphorus (TP), salinity, and water depth along a 3-km transect in the Gomishan Lagoon (Iran). Results indicated that nutrient concentration and the dissolved oxygen gradient were the most significant parameters in the lagoon water quality heterogeneity. Additionally, anoxia at the bottom of the lagoon in sediments and re-suspension of the sediments were the main factors affecting internal nutrient loading. To validate the models, R², RMSECV, and RPDCV were used. The PLS model was stronger than the other models. Also, classification analysis of the Gomishan Lagoon identified two hydrological zones: (i) a North Zone characterized by higher water exchange, higher dissolved oxygen and lower salinity and nutrients, and (ii) a Central and South Zone with high residence time, higher nutrient concentrations, lower dissolved oxygen, and higher salinity. A recommendation for the management of coastal lagoons, specifically the Gomishan Lagoon, to decrease or eliminate nutrient loadings is discussed and should be transferred to policy makers, the scientific community, and local inhabitants.

Ecosystem effects and the management of petroleum-contaminated soils on subantarctic islands

Human activity in the Polar Regions has resulted in petroleum contamination of soils. In this context, subantarctic islands are a unique management challenge for climatic, biological and logistical reasons. In this review we identify the main abiotic factors affecting petroleum-contaminated soils in the subantarctic environment, the primary effects of such contamination on biota, and lessons learned with regards to remediation techniques in this region. The sensitivity of biota to contamination depends on organism life stage, on soil properties, and on the degree of contaminant weathering. Initial studies using species endemic to subantarctic islands suggest that for fresh diesel fuel, sensitivities may range between 103 and 20 000 mg total petroleum hydrocarbons (TPH) kg ^-1 soil. Diesel that has undergone a short period of weathering is generally more toxic, with sensitivities ranging between 52 and 13 000 mg TPH kg^-1 soil for an earthworm and a grass respectively (based on EC₂₀ and IC₅₀ values). A sufficient body of data from which to develop remediation targets for existing spills in the region does not yet exist for the region, but there has been a recent increase in research attention to address this data gap. A range of remediation methods have also now been trialled, and techniques such as in-ground aeration and nutrient addition have achieved some success. Passive management techniques such as permeable reactive barriers and phytoremediation are in preliminary stages of investigation for the region and show promise, not least because they cause less collateral disturbance than other methods.

Bioelectrochemical BTEX removal at different voltages: assessment of the degradation and characterization of the microbial communities

BTEX compounds (Benzene, Toluene, Ethylbenzene and Xylenes) are toxic hydrocarbons that can be found in groundwater due to accidental spills. Bioelectrochemical systems (BES) are an innovative technology to stimulate the anaerobic degradation of hydrocarbons. In this work, single chamber BESs were used to assess the degradation of a BTEX mixture at different applied voltages (0.8V, 1.0V, 1.2V) between the electrodes. Hydrocarbon degradation was linked to current production and to sulfate reduction, at all the tested potentials. The highest current densities (about 200mA/m² with a maximum peak at 480mA/m²) were observed when 0.8V were applied. The application of an external voltage increased the removal of toluene, m-xylene and p-xylene. The highest removal rate constants at 0.8V were: 0.4±0.1days^-1, 0.34±0.09days^-1 and 0.16±0.02days^-1, respectively. At the end of the experiment, the microbial communities were characterized by high throughput sequencing of the 16S rRNA gene. Microorganisms belonging to the families Desulfobulbaceae, Desulfuromonadaceae and Geobacteraceae were enriched on the anodes suggesting that both direct electron transfer and sulfur cycling occurred. The cathodic communities were dominated by the family Desulfomicrobiaceae that may be involved in hydrogen production.

The Interaction between Plants and Bacteria in the Remediation of Petroleum Hydrocarbons: An Environmental Perspective

Widespread pollution of terrestrial ecosystems with petroleum hydrocarbons (PHCs) has generated a need for remediation and, given that many PHCs are biodegradable, bio- and phyto-remediation are often viable approaches for active and passive remediation. This review focuses on phytoremediation with particular interest on the interactions between and use of plant-associated bacteria to restore PHC polluted sites. Plant-associated bacteria include endophytic, phyllospheric, and rhizospheric bacteria, and cooperation between these bacteria and their host plants allows for greater plant survivability and treatment outcomes in contaminated sites. Bacterially driven PHC bioremediation is attributed to the presence of diverse suites of metabolic genes for aliphatic and aromatic hydrocarbons, along with a broader suite of physiological properties including biosurfactant production, biofilm formation, chemotaxis to hydrocarbons, and flexibility in cell-surface hydrophobicity. In soils impacted by PHC contamination, microbial bioremediation generally relies on the addition of high-energy electron acceptors (e.g., oxygen) and fertilization to supply limiting nutrients (e.g., nitrogen, phosphorous, potassium) in the face of excess PHC carbon. As an alternative, the addition of plants can greatly improve bioremediation rates and outcomes as plants provide microbial habitats, improve soil porosity (thereby increasing mass transfer of substrates and electron acceptors), and exchange limiting nutrients with their microbial counterparts. In return, plant-associated microorganisms improve plant growth by reducing soil toxicity through contaminant removal, producing plant growth promoting metabolites, liberating sequestered plant nutrients from soil, fixing nitrogen, and more generally establishing the foundations of soil nutrient cycling. In a practical and applied sense, the collective action of plants and their associated microorganisms is advantageous for remediation of PHC contaminated soil in terms of overall cost and success rates for in situ implementation in a diversity of environments. Mechanistically, there remain biological unknowns that present challenges for applying bio- and phyto-remediation technologies without having a deep prior understanding of individual target sites. In this review, evidence from traditional and modern omics technologies is discussed to provide a framework for plant-microbe interactions during PHC remediation. The potential for integrating multiple molecular and computational techniques to evaluate linkages between microbial communities, plant communities and ecosystem processes is explored with an eye on improving phytoremediation of PHC contaminated sites.

Quantitative assessment of hydrocarbon contamination in soil using reflectance spectroscopy: a "multipath" approach

Petroleum hydrocarbons are contaminants of great significance. The commonly used analytic method for assessing total petroleum hydrocarbons (TPH) in soil samples is based on extraction with 1,1,2-Trichlorotrifluoroethane (Freon 113), a substance prohibited to use by the Environmental Protection Agency. During the past 20 years, a new quantitative methodology that uses the reflected radiation of solids has been widely adopted. By using this approach, the reflectance radiation across the visible, near infrared-shortwave infrared region (400-2500 nm) is modeled against constituents determined using traditional analytic chemistry methods and then used to predict unknown samples. This technology is environmentally friendly and permits rapid and cost-effective measurements of large numbers of samples. Thus, this method dramatically reduces chemical analytical costs and secondary pollution, enabling a new dimension of environmental monitoring. In this study we adapted this approach and developed effective steps in which hydrocarbon contamination in soils can be determined rapidly, accurately, and cost effectively solely from reflectance spectroscopy. Artificial contaminated samples were analyzed chemically and spectrally to form a database of five soils contaminated with three types of petroleum hydrocarbons (PHCs), creating 15 datasets of 48 samples each at contamination levels of 50-5000 wt% ppm (parts per million). A brute force preprocessing approach was used by combining eight different preprocessing techniques with all possible datasets, resulting in 120 different mutations for each dataset. The brute force was done based on an innovative computing system developed for this study. A new parameter for evaluating model performance scoring (MPS) is proposed based on a combination of several common statistical parameters. The effect of dividing the data into training validation and test sets on modeling accuracy is also discussed. The results of this study clearly show that predicting TPH levels at low concentrations in selected soils at high precision levels is viable. Dividing a dataset into training, validation, and test groups affects the modeling process, and different preprocessing methods, alone or in combination, need to be selected based on soil type and PHC type. MPS was found to be a better parameter for selecting the best performing model than ratio of prediction to deviation, yielding models with the same performance but less complicated and more stable. The use of the "all possibilities" system proved to be mandatory for efficient optimal modeling of reflectance spectroscopy data.

Kinetics study of the reaction of OH radicals with C5-C8 cycloalkanes at 240-340 K using the relative rate/discharge flow/mass spectrometry technique

Rate constants of reactions of hydroxyl radical with cyclopentane (k1), cyclohexane (k2), cycloheptane (k3), and cyclooctane (k4) have been acquired at 240-340 K and a total pressure of about 1 Torr using the technique of relative rate combined with discharge flow and mass spectrometry (RR/DF/MS). At 298 K, the rate constants are determined using two reference compounds, which are averaged to be k1 = (4.81 ± 0.88) × 10(-12), k2 = (6.41 ± 0.85) × 10(-12), k3 = (10.30 ± 1.44) × 10(-12), and k4 = (1.42 ± 0.27) × 10(-11) cm(3) molecule(-1) s(-1). The Arrhenius expressions at 240-340 K for these reactions are determined to be k1(T) = (2.43 ± 0.50) × 10(-11)exp[-(481 ± 58)/T], k2(T) = (3.96 ± 0.60) × 10(-11)exp[-554 ± 42)/T], k3(T) = (5.74 ± 0.66) × 10(-11)exp[-527 ± 33)/T], and k4(T) = (1.12 ± 0.21) × 10(-10)exp[-626 ± 53)/T]. Using the kcycloalkane+OH(277 K) values measured in the present work, the atmospheric lifetime for cyclopentane, cyclohexane, cycloheptane, and cyclooctane is estimated to be about 78, 64, 38, and 29 h, respectively.

The use of surface-enhanced Raman scattering (SERS) for detection of PAHs in the Gulf of Gdańsk (Baltic Sea)

A field operable surface enhanced Raman scattering (SERS) sensor system was applied for the first time under real conditions for the detection of polycyclic aromatic hydrocarbons (PAHs) as markers for petroleum hydrocarbons in the Gulf of Gdańsk (Baltic Sea). At six stations, seawater samples were taken, and the sensor system was applied in situ simultaneously. These measurements were compared to the results of conventional GC/MS laboratory analysis of the PAH concentrations in the seawater samples. For a PAH concentration above 150 ng(12PAH)l(-1), there was agreement between the SERS sensor and the GC/MS determinations. A standard addition experiment yielded a PAH concentration of 900 ng l(-1) at the Gdańsk Harbor, which was of the same order as the GC/MS determinations of 12PAHs (200 ng(12PAH)l(-1)). The high SERS detection limit for seawater samples is explained by the competition for PAHs between the sensor membrane and particulate matter surfaces. Thus, the SERS sensor can be applied, e.g., as a non-quantitative alarm sensor for relatively high PAH concentrations in heavily polluted waters. The spectral unmixing procedure applied for Gdańsk Harbor water confirmed the presence of phenanthrene at the highest concentration ([Phe]=140 ngl(-1)) and of Chr (2.7 ng l(-1)), but it did not detect the other PAHs present in the Gdańsk Harbor water, as determined by GC/MS. When compared to the past literature and databases, the SERS spectra indicated the presence of a mixture of molecules consisting of carotenoids, n-alkanes, amines or fatty acids, and benzimidazoles at the coastal station ZN2. The spectra in the offshore direction indicated carboxylic acids. Interpretation of the farthest offshore in situ SERS measurements is difficult, principally due to the limited availability of reference spectra. The detection of the lower PAH concentrations commonly found in Baltic coastal water needs further research and development to obtain better sensitivity of the SERS sensor. However, the high analytical specificity of the SERS sensor also allows the detection of other chemical species that require the development of a SERS/Raman library for specific in situ spectral interpretation.

Rapid identification of oil-contaminated soils using visible near-infrared diffuse reflectance spectroscopy

In the United States, petroleum extraction, refinement, and transportation present countless opportunities for spillage mishaps. A method for rapid field appraisal and mapping of petroleum hydrocarbon-contaminated soils for environmental cleanup purposes would be useful. Visible near-infrared (VisNIR, 350-2500 nm) diffuse reflectance spectroscopy (DRS) is a rapid, nondestructive, proximal-sensing technique that has proven adept at quantifying soil properties in situ. The objective of this study was to determine the prediction accuracy of VisNIR DRS in quantifying petroleum hydrocarbons in contaminated soils. Forty-six soil samples (including both contaminated and reference samples) were collected from six different parishes in Louisiana. Each soil sample was scanned using VisNIR DRS at three combinations of moisture content and pretreatment: (i) field-moist intact aggregates, (ii) air-dried intact aggregates, (iii) and air-dried ground soil (sieved through a 2-mm sieve). The VisNIR spectra of soil samples were used to predict total petroleum hydrocarbon (TPH) content in the soil using partial least squares (PLS) regression and boosted regression tree (BRT) models. Each model was validated with 30% of the samples that were randomly selected and not used in the calibration model. The field-moist intact scan proved best for predicting TPH content with a validation r2 of 0.64 and relative percent difference (RPD) of 1.70. Because VisNIR DRS was promising for rapidly predicting soil petroleum hydrocarbon content, future research is warranted to evaluate the methodology for identifying petroleum contaminated soils.

The potential and realistic hazards after a solar-driven chemical treatment of benzene using a health risk assessment at a gas station site in Korea

In order to evaluate the potential use for ex situ remediation, a solar-driven, photocatalyzed reactor system was constructed and applied for the treatment of groundwater contaminated with benzene using selected advanced oxidation processes (AOP) processes, such as H(2)O(2)/solar light, TiO(2) slurry/solar light and immobilized TiO(2)/solar light. However; to date, there have been few attempts to characterize the potential impact of residual levels of benzene on human health after treatment. Some papers have focused on the application of treatment methods of benzene, but most have not considered the effects of realistic hazards and human health. Therefore, potential and realistic hazards of benzene to human health were investigated at a gas station site using a risk-based assessment approach. Among the different remediation actions, the solar light/TiO(2) slurry/H(2)O(2) system (Action 5) showed higher removal efficiency than the solar light/TiO(2) slurry (Action 3) and the solar light/immobilized TiO(2) (Action 2) systems for the treatment of benzene. The Action 5 remediation method achieved 98% degradation, and lead to a substantial increase in the removal of benzene due to the synergetic effect of TiO(2) with the oxidant, H(2)O(2). Also, using the realistic and potential hazard assessment instead of the point estimation of concentration after benzene treatment, the total health risk exceeded the target risk value (1 x 10(-6)). However, the 95th percentile target cancer risk, found using a probabilistic analysis (Monte Carlo method), was around 1 x 10(-6), indicating a low potential carcinogenic risk. Therefore, it was concluded that no adverse health risk was unlikely to be posed if the Action 5 system, which included the addition of TiO(2) and H(2)O(2), or if an increased reaction time was applied. In addition, continuous efforts and proper actions must be taken on the "Soil and Groundwater Remediation Action" based on the risk assessment in Korea.

Relationship between hydrocarbon measurements and toxicity to a chironomid, fish larva and daphnid for oils and oil spill chemical treatments in laboratory freshwater marsh microcosms

This research investigated the extent to which various common hydrocarbon measures can be used to predict toxicity to freshwater aquatic organisms due to fouling by oil. Actual toxicity results, on laboratory freshwater marsh microcosms using two water-column species and a benthic species, were described earlier. The hydrocarbon measures used were TPH(g), TPH(FID), TPH(MS), TTAH (sum of 41 target aromatic hydrocarbons), principal components of 41 TAHs, and each individual TAH. In general, toxicity was more closely related to TPH(MS) levels than to TPH(FID) and (especially) TPH(g) levels. The strongest relationships were found for TTAH levels and for the principal components of the TAHs. Regressions of toxicity on many individual TAHs were also strong, with a single group of compounds explaining as much as 59% of the variation in survival. While the various regressions were highly significant statistically and at times able to accurately predict broad differences in toxicity, the high variation in survival at a specific hydrocarbon concentration indicates that these hydrocarbon measures can not substitute for actual toxicity determinations in accurately ranking the toxicity of samples from oiled freshwater marshes.

Calculation of human health risk-based screening levels (RBSLs) for petroleum

Hazardous waste site managers and regulators can decide easily whether site contamination requires remediation to protect human health, but defining the extent of cleanup is often an enormous challenge. When is the site clean enough for human access and use? Risk assessment tools can be used to help answer this question. One can calculate chemical-specific risk-based screening levels (RBSLs) in environmental media (e.g. soil, water, and food) that correspond to "acceptable" levels of risk. RBSLs can be calculated for individual chemicals and chemical mixtures, specific to various exposure pathways. In calculating RBSLs, one must account for the fact that people may be exposed to more than one chemical by more than one exposure pathway. Fate and transport models may be needed to predict how people might become exposed to site contamination in the future. Examples RBSLs for non-cancer effects are calculated to illustrate the utility and limitations of RBSLs for making risk-based decisions at petroleum release sites.