Total Petroleum Hydrocarbon Fractions Research Articles

Bioremediation study of a hydrocarbon-contaminated soil by profiling aromatic and aliphatic chains

Efficient decontamination of oil contaminated soils is not always easy, especially when the contamination is aged. In this work, we have opted for bioremediation techniques, with a low environmental impact, whose treatments were selected according to the area and soil to be treated. Thus, an industrial area, which had had fuel oil spills for decades, was our decontamination target, using bioremediation techniques that included bioaugmentation with bacteria (autochthonous bacterial consortium), phytoremediation with a plant (Medicago sativa L.) and bioaugmentation with a fungus (Pleurotus ostreatus). These treatments were tested alone and in combination to observe any possible synergies. The evaluation of these treatments for the degradation of the total aliphatic and aromatic fractions of total petroleum hydrocarbons (TPH), showed a higher efficiency (18–48 %) in the degradation of the aliphatic fractions for all the treatments compared with natural attenuation (11 %). By contrast, lower efficiencies were obtained for the aromatic fractions (0–35 %) compared with natural attenuation, which did not decrease. The removal of these fractions was only effective in the combined treatment using all three organisms: the plant, the bacteria, and the fungus, where the bioaugmentation enhanced the plant-microorganism interaction in the root system. The selection of the biological treatments to a specific contaminated site and the evaluation of decontamination by the aromatic and aliphatic chain profiles, leads to a better understanding of the degradation of the different fractions of fuel.

Enhanced bioremediation of oil-contaminated soil in a slurry bioreactor by H2O2-stimulation of oil-degrading/biosurfactant-generating bacteria: performance optimization and bacterial metagenomics.

Oil-contaminated soil is the main challenge for oil-rich countries, and this study aimed to investigate the performance of the H2O2-stimulated slurry bioreactor for the bioremediation of real oil-contaminated soil. The effect of biomass concentration, soil to water (S/W) ratio, slurry temperature, pH, and H2O2 concentration were optimized for the removal of total petroleum hydrocarbons (TPH) from oil-contaminated soil. TPH removal efficiency, biosurfactants production, and peroxidase and dehydrogenase activities were measured. The optimum conditions for the complete biodegradation of 32 [Formula: see text] in the slurry bioreactor during 6days were biomass of 2250mg/L, S/W ratio of 20%, the temperature of 30°C, pH of 7, and an H2O2 concentration of 120mg/L. The highest peroxidase, dehydrogenase, surfactin, and rhamnolipid formation were also obtained under optimum conditions. The results pointed out that complete biodegradation of 32g/kg of TPH in oil-contaminated soil at a short reaction time of 6days is achievable in the developed process operated under optimum conditions. The GC/FID analysis of solid and liquid phases showed that the bioprocess completely biodegraded the different TPH fractions. H2O2 efficiently stimulated the biosurfactant-generating bacteria to produce peroxidase and thereby accelerating the bioremediation rate. Accordingly, an H2O2-mediated slurry bioreactor inoculated with biosurfactant/peroxidase-generating bacteria is a promising technique for cleaning up oil-contaminated soils.

Bacterial community profile of the crude oil-contaminated saline soil in the Yellow River Delta Natural Reserve, China

Crude oil contamination greatly influence soil bacterial community. Proliferative microbes in the crude oil-contaminated soil are closely related to the living conditions. Oil wells in the Yellow River Delta Natural Reserve (YRDNR) region is an ideal site for investigating the bacterial community of crude oil-contaminated saline soil. In the present study, 18 soil samples were collected from the depths of 0–20 cm and 20–40 cm around the oil wells in the YRDNR. The bacterial community profile was analyzed through high-throughput sequencing to trace the oil-degrading aerobic and anaerobic bacteria. The results indicated that C15–C28 and C29–C38 were the main fractions of total petroleum hydrocarbon (TPH) in the sampled soil. These TPH fractions had a significant negative effect on bacterial biodiversity (Shannon, Simpson, and Chao1 indices), which led to the proliferation of hydrocarbon-degrading bacteria. A comprehensive analysis between the environmental factors and soil microbial community structure showed that Streptococcus, Bacillus, Sphingomonas, and Arthrobacter were the aerobic hydrocarbon-degrading bacteria; unidentified Rhodobacteraceae and Porticoccus were considered to be the possible facultative anaerobic bacteria with hydrocarbon biodegradation ability; Acidithiobacillus, SAR324 clade, and Nitrosarchaeum were predicted to be the anaerobic hydrocarbon-degrading bacteria in the sub-surface soil. Furthermore, large amount of carbon sources derived from TPH was found to cause depletion of bioavailable nitrogen in the soil. The bacteria associated with nitrogen transformation, such as Solirubrobacter, Candidatus Udaeobacter, Lysinibacillus, Bradyrhizobium, Sphingomonas, Mycobacterium, and Acidithiobacillus, were highly abundant; these bacteria may possess the ability to increase nitrogen availability in the crude oil-contaminated soil. The bacterial community functions were significantly different between the surface and the sub-surface soil, and the dissolved oxygen concentration in soil was considered to be potential influencing factor. Our results could provide useful information for the bioremediation of crude oil-contaminated saline soil.

Development of updated RfD and RfC values for medium carbon range aromatic and aliphatic total petroleum hydrocarbon fractions

ABSTRACT Using total petroleum hydrocarbon (TPH) measurements as a tool for assessing potential human health risks associated with exposures to petroleum products in the environment poses unique challenges, as TPH represents highly variable and complex mixtures containing hundreds of individual chemicals with wide-ranging chemical and physical properties. Current risk assessment practice generally involves analysis of environmental samples for various TPH fractions and summation of risk across those fractions. The United States Environmental Protection Agency (USEPA) derived provisional toxicity criteria for low, medium, and high carbon range aromatic and aliphatic hydrocarbon fractions over a decade ago. These criteria have been used, in whole or in part, to derive risk-based cleanup levels for TPH contamination in soil and groundwater. Herein, we evaluate and update oral and inhalation toxicity criteria for two of these fractions – medium carbon range aromatics and aliphatics – using, where applicable, newer data, updated modeling techniques, and new/alternative analyses of certain endpoints, human relevance, and uncertainty. The results of the analyses support an ~10-fold increase in the USEPA provisional reference concentration (p-RfC) values from 0.1 mg/m3 to 1 mg/m3 for both medium carbon range aromatics (different uncertainty factor) and aliphatics (new study and different judgment of toxicity data from existing study). Compared to the USEPA provisional oral reference dose (p-RfD) values for the medium carbon range aromatics and aliphatics of 0.03 mg/kg-day and 0.01 mg/kg-day, respectively, the present analyses suggest the RfD for medium carbon range aromatics could be increased >6.6-fold to 0.2 mg/kg-day (updated modeling and different uncertainty factors), and the RfD for medium carbon range aliphatics could be increased ~20-fold to 0.2 mg/kg-day (new study). These updated toxicity criteria could be used by regulatory agencies to reevaluate risk-based screening levels or by risk managers to support cleanup levels for medium carbon range aromatics and aliphatics, while still ensuring adequate health protection. Implications: Petroleum products represent complex mixtures of hydrocarbons broadly comprised of aliphatic compounds (straight-chain, branched-chain, and cyclic alkanes and alkenes) and aromatic compounds such as benzene, alkylbenzenes, and polycyclic aromatic hydrocarbons. The complex nature of petroleum products presents challenges for assessing potential health risks associated with exposure to petroleum hydrocarbon contamination in the environment. It has been over ten years since the U.S. Environmental Protection Agency derived provisional toxicity criteria for low, medium, and high carbon range aromatic and aliphatic hydrocarbon fractions. In that time, risk assessment guidance and tools have evolved, and new studies have been published. Our analyses indicate that current provisional toxicity criteria for medium carbon range aromatics and aliphatics fractions are overly conservative by approximately an order of magnitude.

Removal of Total Petroleum Hydrocarbons from Contaminated Soil through Microwave Irradiation.

In this study, we investigated the removal mechanism of total petroleum hydrocarbons (TPH) from soil by microwave heating. TPH contaminated soil was investigated to determine the desorption behavior of five carbon number-based fractions of TPH. The applied operating microwave power density influenced the final temperature that was reached during heating. For low operating power density applications, microwave effectiveness was limited due to the soil’s dielectric properties, which exhibited a direct relationship with temperature variation. Soil particle distribution could be attributed to permeability, which significantly influenced the evaporation of contaminated soil during the microwave treatment. The results indicate that the activation energy was correlated with the influence of particle size. The removal efficiency of the coarse soil reached 91.1% at 15 min, whereas that of fine soil was low. A total of 30 min had passed, and a removal efficiency of 71.2% was found for the fine soil. Residual TPH concentration was decreased when irradiation time was increased with a removal rate dependent on soil temperature variation. The surface functional groups of the contaminated soil were influenced by microwave irradiation, and changes in the hydrocarbon fraction affected contaminant removal.

Ultra-fast gas chromatographic with flame ionization detector (UFGC-FID) and sonication methods for determination of total petroleum hydrocarbons fractions and BTEX in soil

In the environmental monitoring at gas stations, total petroleum hydrocarbons (TPH) and aromatic hydrocarbons, such as benzene, toluene, ethylbenzene, and xylenes (BTEX), are determined to verify soil contamination. However, the determination by conventional GC requires a long time of analysis and expensive autosamplers for volatile compounds extraction. Therefore, the present work aimed at the development, validation, and application of ultra-fast chromatographic methods with flame ionization detector (UFGC-FID) capable of determining the TPH fractions (GRO, DRO, and ORO) and BTEX in a faster and less costly way than conventional methods. In addition, sonication extraction methods were developed and validated for two groups of compounds (volatile and semivolatile). The optimum conditions of the extraction methods were obtained through regression models generated from designs of experiment (DOE). The UFGC-FID methods provided determinations in 5 min and presented good linearity (R2 > 0.997), selectivity (Rs > 1.00), sensitivity (γ > 0.02 mg kg−1), precision (repeatability <7%), and accuracy (recoveries between 70% and 130%). Moreover, the BTEX solutions prepared in ethanol showed great intermediate precision (RSD < 1%) when stored at −19 °C over a period of 15 days. The optimized sonication method provided extractions in 13.5 min per sample and presented relative standard deviations (RSD) <7% and recoveries between 70% and 130%. Therefore, the environmental monitoring can be a faster, lower costly, and more environmentally friendly process through UFGC-FID associated with sonication extraction methods.

Assessment and comparison of PHCs removal from three types of soils (sand, silt loam and clay) using supercritical fluid extraction

ABSTRACTSupercritical fluid extraction (SFE) was applied to investigate the removal of petroleum hydrocarbons (PHCs) from contaminated soils. Per an initial set of tests for different extraction modes and time durations, the combination of 10 min static mode followed by 10 min dynamic mode, repeated for 3 cycles for a total time of 60 min resulted in the highest PHCs removal percentages. SFE experiments were performed at 33 MPa pressure and 75°C temperature to investigate the influence of soil texture and grain size. Three types of soils were formed and then were spiked with diesel fuel with a ratio of 5 wt%. Soil A, B and C had different particle sizes and were categorized as sand, silt loam and clay, respectively. Soil A (sand) which had the largest particle size resulted in the highest total petroleum hydrocarbon fractions (TPHF), sum of PHC F2, F3 and F4 fractions, removal percentage (90.4%) while soil C (clay) with the smallest particle size and the highest clay content led to the lowest TPHF removal percentage (47.4%). PHC F2 removal percentage for soil A (sand) was 27.3% greater than soil B (silt loam), and the removal efficiency for soil B was 20.4% higher than soil C (clay). While a similar trend was observed for the extraction of PHC F3, the extraction efficiency of PHC F4 for soil A, B and C were not statistically significant. Regarding soil A (sand), the extraction efficiency for PHC F2, PHC F3 and PHC F4 were 98.4%, 92.7%, and 50.2%, respectively. For soil C (clay), the removal efficiency of all PHC fractions were not statistically different.

Infrared spectroscopy and multivariate methods as a tool for identification and quantification of fuels and lubricant oils in soil.

Environmental contamination caused by leakage of fuels and lubricant oils at gas stations is of great concern due to the presence of carcinogenic compounds in the composition of gasoline, diesel, and mineral lubricant oils. Chromatographic methods or non-selective infrared methods are usually used to assess soil contamination, which makes environmental monitoring costly or not appropriate. In this perspective, the present work proposes a methodology to identify the type of contaminant (gasoline, diesel, or lubricant oil) and, subsequently, to quantify the contaminant concentration using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and multivariate methods. Firstly, gasoline, diesel, and lubricating oil samples were acquired from gas stations and analyzed by gas chromatography to determine the total petroleum hydrocarbon (TPH) fractions (gasoline range organics, diesel range organics, and oil range organics). Then, solutions of these contaminants in hexane were prepared in the concentration range of about 5-10,000mgkg-1. The infrared spectra of the solutions were obtained and used for the development of the pattern recognition model and the calibration models. The partial least square discriminant analysis (PLS-DA) model could correctly classify 100% of the samples of each type of contaminant and presented selectivity equal to 1.00, which provides a suitable method for the identification of the source of contamination. The PLS regression models were developed using multivariate filters, such as orthogonal signal correction (OSC) and general least square weighting (GLSW), and selection variable by genetic algorithm (GA). The validation of the models resulted in correlation coefficients above 0.96 and root-mean-square error of prediction values below the maximum permissible contamination limit (1000mgkg-1). The methodology was validated through the addition of fuels and lubricating oil in soil samples and quantification of the TPH fractions through the developed models after the extraction of the analytes by the EPA 3550 method adapted by the authors. The recovery percentage of the analytes was within the acceptance limits of ASTM D7678 (70-130%), except for one sample (69% of recovery). Therefore, the methodology proposed here provides faster and less costly analyses than the chromatographic methods and it is adequate for the environmental monitoring of soil contamination by gas stations.

Vertical screening distances for total petroleum hydrocarbon for vapour intrusion risk assessment at petroleum underground storage tank sites

The US Environmental Protection Agency Office of Underground Storage Tanks (US EPA OUST) and Interstate Technology and Regulatory Council (ITRC) have recently published guidance indicating that buildings separated from light non-aqueous phase liquid (LNAPL) sources by more than 15 ft (4.6 m) are not a concern for vapour intrusion at petroleum underground storage tank (UST) sites. At this distance, there is a greater than 95% probability that soil gas concentrations for all key constituents of potential concern are below risk-based screening levels (RBSLs) between the LNAPL source and building foundation. Vertical screening distances for bulk Total Petroleum Hydrocarbon (TPH), common TPH fractions (C 5 –C 8 aliphatics, C 9 –C 12 aliphatics, and C 9 –C 10 aromatics), and indicator compounds ( n -hexane and naphthalene) are less certain, however, because of a general lack of empirical data and highly variable soil-gas RBSLs. This study addresses these gaps through a statistical analysis of hundreds of soil-gas samples collected above LNAPL sources at more than 30 petroleum UST release sites. Resulting vertical screening distances for the various TPH fractions range between 0 and 7 ft (2.1 m) depending primarily on soil-gas RBSLs, which vary by over 5 orders of magnitude. Vertical screening distances for naphthalene are generally &lt;3 ft (0.91 m). Vertical screening distances for n -hexane range from 12 (3.7) to 16 ft (4.9 m) and vary geographically. Vertical screening distances for total (bulk) TPH generally exceed 15 ft (4.6 m). Petroleum vapour intrusion risk assessments involving total (bulk) TPH are not recommended, however, because of uncertainties in quantifying soil-gas and indoor-air concentrations and defining RBSLs for fuel mixtures with variable source composition, toxicity, and fate and transport properties. Overall, the findings of this study validate the 15-ft screening distance recommended by ITRC and US EPA for application at petroleum UST sites with LNAPL sources.

Comparative study techniques for TPH and PAH extraction from clayey and sandy soils for chromatography analyses

The objective of this study was to compare three extraction procedures: soxhlet (SOX), microwaves (MARS) and accelerate extraction with solvent (ASE) regarding the extraction efficiency of different fractions of total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAH) from sandy and clayey soil with aged contamination analyzed by gas chromatography. Besides the extraction efficiency, water, solvent and time consumption were considered. Regarding clayey soil, for the extraction of different fractions of total petroleum hydrocarbons (TPH), ASE resulted in better recovery of n-alkanes and hydrocarbons resolved fraction (HRF). SOX and MARS performed better for the heaviest fraction (non-resolved complex mixture-NRCM). Regarding sandy soil, ASE performed better during extraction of all TPH fractions. In the case of polycyclic aromatic hydrocarbons (PAH), extraction with ASE showed the best result in both clayey and sandy soils. When other variables were taken into account (water, solvent and time consumption), MARS is the most economical method, particularly when TPH is the group of interest and n-alkanes is relatively less important in the analysis. Therefore, in aged contaminations, soil texture and the petroleum fraction of interest in the first place and availability of resources such as water, solvent and time in the second place must be considered before deciding what is the most appropriate extraction method.

Effects of Soil Micro-particles and Micro-pores on Petroleum Hydrocarbons Released From Contaminated Soils During Solvent Extraction with Ultrasound

The effects of soil micro-particles and micro-pores on the release of total petroleum hydrocarbons (TPH) were investigated using long-term weathered, TPH-contaminated soil samples. The TPH concentrations were analyzed using various extraction schemes (i.e., total extraction, weak extraction, solvent extraction with or without ultrasound). The particle size distribution (<2 mm, 0.063–2 mm, <0.063 mm), micro-pore volume (<0.38 mm), and TPH fraction (C8–14, C16–28, C30–40) of selected samples were also determined to better understand the factors controlling TPH release from contaminated soils. TPH concentrations varied greatly among different fractions of each soil sample, but were highest in the micro-fraction (<0.063 mm) of each sample. In weathered soil samples, TPH was not only weakly or strongly adsorbed on soil particles, but also trapped in soil micro-pores. Moreover, heavier fractions of TPH were released slowly and lesser extent from contaminated soils. Results showed that the solvent extraction method with and without ultrasound could be used to assess relative binding strength of TPH to contaminated soils. These findings imply that to achieve a remediation goal, some contaminated soils require only relatively mild extraction with solvent, but soils with TPH trapped in micro-pores require physical destruction along with chemical extraction.

The Evaluation of Different Bioremediation Processes for Egyptian Oily Sludge Polluted Soil on a Microcosm Level

In this study, bioremediation of an Egyptian oily sludge polluted soil with total petroleum hydrocarbon content of 53,100 mg kg−1 was achieved on a microcosm level at 30°C over a 180-day period. The analysis of variance revealed that soil microcosms biostimulated with corn steep liquor and bioaugmented with Micrococcus lutes RM showed significant removal of total petroleum hydrocarbon relative to natural attenuation microcosms; recording total petroleum hydrocarbon removal of 44 and 54% with p = 0.004 and p = 7.69e-5, respectively. Kinetic study revealed that the degradation processes followed the first-order model. Bioaugmentation microcosms showed also the highest biodegradation efficiencies on different total petroleum hydrocarbon fractions: saturates, aromatics, resins, asphaltene, and the highest soil heterotrophic activity as measured by accumulative evaluation of CO2.

Prediction of landfarming period using degradation kinetics of petroleum hydrocarbons: test with artificially contaminated and field-aged soils and commercially available bacterial cultures

This study predicts the optimal landfarming period for the total petroleum hydrocarbons (TPHs)-contaminated field soils that are subject to the combined landfarming and Fenton oxidation treatment. The TPHs degradation in the artificially contaminated model soils and the field-aged contaminated soils were compared in a laboratory scale. The soils were bioaugmented with the 16 petroleum hydrocarbon-degrading microbial cultures that are commercially available in Korea. The TPHs degradation by bioaugmentation in the model soils was 81 ± 2% after 56 days, while it was only 27 ± 2% after 74 days in the field-aged soils. The lower degradation in the field-aged soils can be attributed to the removal of a large part of the biodegradable and volatile TPHs fractions during the weathering process. The two-compartment model that can depict a fast-degradation phase followed by a slow-degradation phase predicted that the remedial goal of 475 mg kg−1 of TPHs could be achieved in the model soils within the conventional landfarming period of 60–120 days in Korea; however, the predicted period for the field-aged soils (710–4,086 days) was not practical requiring a combined biological and chemical treatment approach. Based on the kinetics study, the optimal landfarming period for the field-aged soils was 3 weeks and pre-Fenton oxidation can be used to meet the remedial goal. The two-compartment model can be useful for predicting landfarming period for the combined landfarming and Fenton oxidation treatment of field-aged TPHs contaminated soils. The prediction of the optimal landfarming period could lead to the reduction in both the treatment cost and period.

An in silico approach for evaluating a fraction-based, risk assessment method for total petroleum hydrocarbon mixtures.

Both the Massachusetts Department of Environmental Protection (MADEP) and the Total Petroleum Hydrocarbon Criteria Working Group (TPHCWG) developed fraction-based approaches for assessing human health risks posed by total petroleum hydrocarbon (TPH) mixtures in the environment. Both organizations defined TPH fractions based on their expected environmental fate and by analytical chemical methods. They derived toxicity values for selected compounds within each fraction and used these as surrogates to assess hazard or risk of exposure to the whole fractions. Membership in a TPH fraction is generally defined by the number of carbon atoms in a compound and by a compound's equivalent carbon (EC) number index, which can predict its environmental fate. Here, we systematically and objectively re-evaluate the assignment of TPH to specific fractions using comparative molecular field analysis and hierarchical clustering. The approach is transparent and reproducible, reducing inherent reliance on judgment when toxicity information is limited. Our evaluation of membership in these fractions is highly consistent (˜80% on average across various fractions) with the empirical approach of MADEP and TPHCWG. Furthermore, the results support the general methodology of mixture risk assessment to assess both cancer and noncancer risk values after the application of fractionation.

Self-induced bio-potential and graphite electron accepting conditions enhances petroleum sludge degradation in bio-electrochemical system with simultaneous power generation

Bio-electrochemical treatment (BET) documented effective degradation of real field petroleum sludge over the conventional anaerobic treatment (AnT). BET (41.08%) operation showed enhanced total petroleum hydrocarbons (TPH) removal over AnT (20.72%). Aromatic fraction visualized higher removal (75.54%) compared to other TPH fractions viz., aliphatics, asphaltenes and NSO (nitrogen, sulfur and oxygen) during BET operation. Higher ring aromatics (5–6) documented easy degradation in BET, while AnT was limited to lower ring (2–3) compounds. Voltammetric analysis evidenced simultaneous redox behavior during BET operation due to presence of graphite electrode as electron acceptor, while AnT showed extended reduction behavior only. Self-induced primary and secondary oxidation reactions and capacitive-deionization might have enhanced the degradation capability of BET. BET documented higher charge/capacitance (2810mJ/1120mF) than AnT (450mJ/180mF). Power output corroborated well with observed results supporting BET performance as fuel cell. Electrodes offer a potential alternative electron acceptor for promoting the degradation of organic contaminants.

An experimental study on the bio-surfactant-assisted remediation of crude oil and salt contaminated soils

The effect of bio-surfactant (rhamnolipid) on the remediation of crude oil and salt contaminated soil was investigated in this study. The experimental results indicated that there was a distinct decline of total petroleum hydrocarbon (TPH) concentration within the soil when using rhamnolipid during a remediation period of 30 days, with maximum TPH reduction of 86.97%. The most effective remediation that was observed was with rhamnolipid at a concentration of 2 CMC in soil solution, and a first-order TPH degradation rate constant of 0.0866 d−1. The results also illustrated that salts in soil had a negative impact on TPH reduction, and the degradation rate was negatively correlated with NaCl concentration in soil solution. The analysis of soil TPH fractions indicated that there was a significant reduction of C13-C30 during the remediation process when using bio-surfactant.

Comparison of the effects of variable site temperatures and constant incubation temperatures on the biodegradation of petroleum hydrocarbons in pilot-scale experiments with field-aged contaminated soils from a cold regions site

Temporal atmospheric temperature changes during summers at sub-Arctic sites often cause periodic fluctuations in shallow landfarm and surface soil temperatures. However, little information is available on the effect of site-relevant variations on biodegradation performance in cold climates. This study compares the rate and extents of biodegradation of petroleum hydrocarbons at variable site temperatures (1–10 °C) representative of summers at a sub-Arctic site reported previously with those obtained under a constant average temperature of 6 °C. The biodegradation was evaluated in pilot-scale landfarming experiments with field-aged petroleum-contaminated soils shipped from Resolution Island (61°30′N, 65°00′W), Nunavut, Canada. Under the variable site temperature conditions biodegradation rate constants of semi- (F2) and non-volatile (F3) hydrocarbon fractions were enhanced by over a factor of two during the 60-d experiment, compared to the constant temperature mode. The decrease in total petroleum hydrocarbons (TPH) under the variable site temperature mode was 55% compared to only 19% under the constant average temperature mode. The enhanced biodegradation is attributable to the non-linear acceleration of microbial activity between 4.7 and 10 °C and faster growth of indigenous hydrocarbon-degrading microbial populations. The first-order biodegradation rate constants of 0.018, 0.024 and 0.016 d −1 for TPH, F2 and F3 fractions at the variable site temperature were in agreement with those determined by an on-site experiment at the same site.

Determination of a risk management primer at petroleum-contaminated sites: Developing new human health risk assessment strategy

Total petroleum hydrocarbon (TPH) is an important environmental contaminant that is toxic to human and environmental receptors. However, human health risk assessment for petroleum, oil, and lubricant (POL)-contaminated sites is especially challenging because TPH is not a single compound, but rather a mixture of numerous substances. To address this concern, this study recommends a new human health risk assessment strategy for POL-contaminated sites. The strategy is based on a newly modified TPH fractionation method and includes an improved analytical protocol. The proposed TPH fractionation method is composed of ten fractions (e.g., aliphatic and aromatic EC8–10, EC10–12, EC12–16, EC16–22 and EC22–40). Physicochemical properties and toxicity values of each fraction were newly defined in this study. The stepwise ultrasonication-based analytical process was established to measure TPH fractions. Analytical results were compared with those from the TPH Criteria Working Group (TPHCWG) Direct Method. Better analytical efficiencies in TPH, aliphatic, and aromatic fractions were achieved when contaminated soil samples were analyzed with the new analytical protocol. Finally, a human health risk assessment was performed based on the developed tiered risk assessment framework. Results showed that a detailed quantitative risk assessment should be conducted to determine scientifically and economically appropriate cleanup target levels, although the phase II process is useful for determining the potency of human health risks posed by POL-contamination.

Remediation of petroleum contaminated soils by joint action of Pharbitis nil L. and its microbial community

The plot-culture experiments were conducted for examining the feasibility of Pharbitis nil L. and its microbial community to remedy petroleum contaminated soils. The petroleum contaminated soil, containing 10% (w/w) of the total petroleum hydrocarbons (TPHs), was collected from the Shengli Oil Field, Dongying City, Shandong Province, China. The collected soil was applied and diluted to a series of petroleum contaminated soils (0.5%, 1.0%, 2.0% and 4.0%). Root length, microbial populations and numbers in the rhizosphere were also measured in this work. The results showed that there was significantly ( p < 0.05) greater degradation rate of TPHs in vegetated treatments, up to 27.63–67.42%, compared with the unvegetated controls (only 10.20–35.61%), after a 127-day incubation. Although various fractions of TPHs had an insignificant concentration difference due to the presence of the remediation plants, there was a much higher removal of saturated hydrocarbon compared with other components. The biomass of P. nil L. did not decrease significantly when the concentration of petroleum hydrocarbons in soil was ≤ 2.0%. The trends of microbial populations and numbers in the rhizosphere were similar to the biomass changes, with the exception that fungi at 0.5% petroleum contaminated soil had the largest microbial populations and numbers.

A novel total petroleum hydrocarbon fractionation strategy for human health risk assessment for petroleum hydrocarbon-contaminated site management

Human health risk assessments for petroleum, oil, and lubricant (POL)-contaminated sites are more complicated than for sites contaminated by single compounds due to the complex composition and various analytical methods associated with total petroleum hydrocarbons (TPH). Although several TPH fractionation methods are commonly used, including that of the TPH Criteria Working Group (TPHCWG), an efficient and economical human health risk assessment method is not yet available. To address this concern, a new modified fractionation strategy is recommended in this study, which resolves the problems of the current TPH fractionation methods while retaining reliability in the results. For the purpose of this study, the distribution characteristics of the 13 TPHCWG fractions were examined, and human health risk assessments for the POL-contaminated sites were performed. The results show that aliphatic EC8–16 and aromatic EC10–21 among the 13 TPH fractions are major contributors to human health risks along all exposure routes, making up approximately 96% of the hazard index (HI) of the TPH fractions, on average. Therefore, it is reasonable to concentrate on aliphatic EC8–16 and aromatic EC10–21 fractions, rather than to study all of the TPH fractions, in evaluating human health risk for TPH-contaminated sites.