Toxicity Of Petroleum Hydrocarbons Research Articles

Long-term effects of oil contamination on soil quality and metabolic function.

Widespread soil contamination with oil and the toxicity of petroleum hydrocarbons to soil biota make it extremely important to study microbial responses to oil stress. Soil metabolites reflect the main metabolic pathways in the soil microbial community. The examination of changes in the soil metabolic profile and metabolic function is essential for a better understanding of the nature of the pollution and restoration of the disturbed soils. The present study aimed to assess the long-term effect of oil on the ecological state of the soil, evaluate quantitative and qualitative differences in metabolite composition between soil contaminated with oil and non-contaminated soil, and reveal biologically active metabolites that are related to oil contamination and can be used for contamination assessment. A long-term field experiment was conducted to examine the effects of various oil concentrations on the biochemical properties and metabolic profile of the soil. Podzolic soil contaminated with oil demonstrated the long-term inhibition of soil biological activity and vegetation. Oil affected the metabolic activity of soil fungi increasing the production of toxic metabolites. A metabolomic approach was employed to determine soil metabolites. The metabolite profile was found to vary greatly between oil-contaminated and non-contaminated soils. Carbohydrates had the largest number of metabolites negatively affected by oil, while the content of organic acids, phenolic compounds, and terpenoids was mainly increased in oil-contaminated soil. The evaluation of the long-term impact of oil on microbial metabolism can make a valuable contribution to the assessment of soil quality and the activity of soil microorganisms being under stress from oil pollution. The results contribute to a further understanding of the role of microorganisms in the ecological functions of contaminated soil, which can be useful in the development of rehabilitation strategies for disturbed sites.

Bioremediation of polycyclic aromatic hydrocarbons contaminated soils: recent progress, perspectives and challenges.

The life of all creatures is supported directly or indirectly by soil, which is a significant environmental matrix. The soil has been polluted partly due to increased human activities and population growth, releasing several foreign substances and persistent contaminants. When toxic substances like polycyclic aromatic hydrocarbons (PAHs) are disposed of, the characteristics of the soil are changed, microbial biodiversity is impacted, and items are destroyed. Because of the mutagenicity, carcinogenicity, and toxicity of petroleum hydrocarbons, the restoration and cleanup of PAH-polluted areas represent a severe technological and environmental challenge for long-term growth and development. Although there are several ways to clean up PAH-contaminated soils, much attention is paid to intriguing bacteria, fungus, and their enzymes. Various factors influence PAH breakdown, including pH, temperature, airflow, moisture level, nutrient availability, and degrading microbial populations. This review discusses how PAHs affect soil characteristics and shows that secondary metabolite and carbon dioxide decomposition are produced due to microbial breakdown processes. Furthermore, the advantages of bioremediation strategies were assessed for correct evaluation and considered dependable on each legislative and scientific research level, as analyzed in this review.

Petroleum-contaminated soil: environmental occurrence and remediation strategies.

Soil is an environmental matrix that carries life for all living things. With the rise of human activities and the acceleration of population, the soil has been exposed in part to pollution by the discharge of various xenobiotics and persistent pollutants into it. The disposal of toxic substances such as polycyclic aromatic hydrocarbons (PAHs) alters soil properties, affects microbial biodiversity, and damages objects. Considering the mutagenicity, carcinogenicity, and toxicity of petroleum hydrocarbons, the restoration and clean-up of PAH-polluted sites represents an important technological and environmental challenge for sustainable growth and development. Though several treatment methods to remediate PAH-polluted soils exist, interesting bacteria, fungi, and their enzymes receive considerable attention. The aim of the present review is to discuss PAHs' impact on soil properties. Also, this review illustrates physicochemical and biological remediation strategies for treating PAH-contaminated soil. The degradation pathways and contributing factors of microbial PAH-degradation are elucidated. This review also assesses the use of conventional microbial remediation compared to the application of genetically engineered microorganisms (GEM) that can provide a cost-effective and eco-friendly PAH-bioremediation strategy.

Toxicity of petroleum hydrocarbons to Brachyuran crabs: a review of deleterious effects of oil-related xenobiotics on life stages

AbstractPetroleum hydrocarbons (PH) toxicity and bioaccumulation in aquatic organisms have been investigated for almost 50 years. Continuous oil spillages necessitate a further understanding of the toxicological effects of PH on brachyuran crabs. Crabs can be exposed to PH through various routes such as the water column, sediment and diet. Numerous investigations have been dedicated to evaluating PH toxicity on different life stages of crab species, but the majority of them have focused on the blue crab Callinectes sapidus as it represents an edible and favourable seafood commodity for human consumption. The objective of the review is to critically assess studies related to PH toxicity on different life stages of 41 crab species representing 13 families across the world. Several physiological, biochemical and genetic endpoints of marine crabs were evaluated in addition to the sublethal effects of PH on crab metabolism, behaviour, moulting, growth and survival. A concise summary of PH deleterious effects on different taxonomic species of marine crabs is discussed and provides evidence that crabs can be used as indicator organisms of biomarker significance for marine pollution. Overall, larval stages appeared to be the most sensitive to the deleterious effects of PH compared with juveniles and adults. However, adult stages have received more research attention than other life stages, followed by larval stages, and juvenile stages are the least investigated stages with respect to PH toxicity. Finally, hepatopancreas and gills were the organs where greatest accumulation of PH was recorded.

Whole-cell bioreporters for evaluating petroleum hydrocarbon contamination

Whole-cell bioreporter (WCB) is a category of biological analytical tools using living microorganisms to sense chemicals by producing quantifiable signals. Comparing to conventional chemical analysis, WCBs have the features of rapidness, cost-effectiveness and easy operation. This paper critically reviews the concept and recent progress in constructing and applying WCBs for sensing petroleum hydrocarbons, including n-alkanes and aromatic hydrocarbons. Additionally, some WCBs can evaluate the toxicity of petroleum hydrocarbons, linking their natural occurrence to ecological risks. Further discussions address the state-of-art design of WCBs for petroleum hydrocarbons, comprehensively assessing the key challenges in improving their sensitivity and limit of detection, including host strains, reporter genes and regulatory systems. Regarding the significant gaps between laboratory trials and real-world scenarios, we also discuss some restriction factors influencing bioreporter performance in sensing petroleum hydrocarbons in environmental samples, e.g., low solubility, and suggest some solutions as biosurfactant and chemotaxis. Further development of sensing devices and multisensing WCBs can provide more feasibilities overcoming the applicable barriers. This review comprehensively summarizes the current progress of WCBs for petroleum hydrocarbons, and raises new insights into their bright future in practices of environmental monitoring and risk assessment.

Environmental applications of microbial extremophiles in the degradation of petroleum hydrocarbons in extreme environments

The ubiquitous occurrence, recalcitrance, bioaccumulation potential and toxicity of petroleum hydrocarbons have gained significant environmental concern. The petroleum hydrocarbon contaminations are frequent in the extreme environments where the temperature, pH, salt concentrations, and/or pressure vary from normal conditions. Bioremediation using naturally occurring microorganisms is a promising tool for removal of hydrocarbons from contaminated environments, since it is effective, inexpensive and eco-friendly. Degradation of hydrocarbons depends on various factors including structure and other properties of the target hydrocarbon, environmental conditions and, quantity and type of the microbes present at contaminated sites. Hydrocarbon-degrading microorganisms are usually present in diverse environments and the ability of these microbes to adapt under extreme environments are often exploited for bioremediation. In this review, the processes of extremophiles to degrade different constituents of petroleum hydrocarbons including polyaromatic and aliphatic hydrocarbons, have been explained for soil and marine ecosystems, in extreme environments.

Combination of rhamnolipid and biochar in assisting phytoremediation of petroleum hydrocarbon contaminated soil using Spartina anglica

Biochar (BC) and rhamnolipid (RL) is used in bioremediation of petroleum hydrocarbons, however, the combined effect of BC and RL in phytoremediation has not been studied until now. In this paper, the phytoremediation of petroleum hydrocarbon-contaminated soil using novel plant Spartina anglica was enhanced by the combination of biochar (BC) and rhamnolipid (RL). Samples of petroleum-contaminated soil (10, 30 and 50 g/kg) were amended by BC, BC+ RL and rhamnolipid modified biochar (RMB), respectively. After 60 day's cultivation, the removal rate of total petroleum hydrocarbons (TPHs) for unplanted soil (UP), planted soil (P), planted soil with BC addition (P-BC), planted soil with BC and RL addition (P-BC + RL) and planted soil with addition of RMB (P-RMB) were 8.6%, 19.1%, 27.7%, 32.4% and 35.1% in soil with TPHs concentration of 30 g/kg, respectively. Compared with UP, the plantation of Spartina anglica significantly decreased the concentration of C8–14 and tricyclic PAHs. Furthermore, the application of BC and RMB alleviated the toxicity of petroleum hydrocarbons to Spartina anglica via improving plant growth with increasing plant height, root vitality and total chlorophyll content. High-throughput sequencing result indicated that rhizosphere microbial community of Spartina anglica was regulated by the application of BC and RMB, with increase of bacteria and plant mycorrhizal symbiotic fungus in biochar and RMB amended soil.

The synergistic effect of a consortium of protozoan isolates (Paramecium sp., Vorticella sp., Epistylis sp. and Opercularia sp.) on the biodegradation of petroleum hydrocarbons in wastewater

Many bioremediation studies have demonstrated that bacteria, fungi, algae and even protozoan counterparts possess catabolic abilities that may be applied for the remediation of soil and water contaminated with polycyclic aromatic hydrocarbons (PAHs). The aim of this study was to investigate the synergistic effect and toxicity tolerance of a consortium of protozoan species (Paramecium sp., Vorticella sp., Epistylis sp. and Opercularia sp.) during the biodegradation of petroleum hydrocarbons in wastewater. During this study, the synergistic indices were calculated and the toxicity of petroleum hydrocarbons and their degradation products present in wastewater were tested, in terms of LD50 at 24 h. The individual isolates were able to biodegrade approximately >65% with a consortium having biodegradation capabilities of <70%. Based on the synergistic effect of the isolates, most of these microbes were able to have a positive interaction during biodegradation from the 2nd to the 16th day with synergistic indices of>0.5. However, after the 16th day of the study period, either no interactions or negative and fewer activities were observed amongst the target microbes. Minimal or no toxicity (<10%) of the petroleum hydrocarbons to the individual isolates as well as the consortium of isolates was observed, especially during the first two days. However, as the study progressed, the toxicity gradually increased from <10% to <40% [calculated as percentage of inhibition (%E)] up to the 16th day of the study period.

Phototoxic effects of two common marine fuels on the settlement success of the coral Acropora tenuis

Coral reefs are at risk of exposure to petroleum hydrocarbons from shipping spills and uncontrolled discharges during extraction. The toxicity of petroleum hydrocarbons can substantially increase in the presence of ultraviolet radiation (UVR), therefore spills in shallow coral reef environments may be particularly hazardous to reef species. Here we investigated the sensitivity of coral larvae (Acropora tenuis) to dissolved hydrocarbons from heavy fuel oil (HFO) and diesel in the absence and presence of UVR. Larval settlement success decreased with increasing concentrations of dissolved HFO, and co-exposure to UVR doubled the toxicity: 50% effect concentrations (EC50) decreased from 96 (−UVR) to 51 (+UVR) total petroleum aromatic hydrocarbons (TPAH). Toxic thresholds for HFO were similar to concentrations reported during marine spills: EC10s of 24 (−UVR) and 15 (+UVR) µg l−1. While less toxic, diesel also reduced settlement and exhibited phototoxicity: EC10s of 122 (+UVR) and 302 (−UVR) µg l−1. This study demonstrates that the presence of UVR increases the hazard posed by oil pollution to tropical, shallow-water coral reefs. Further research on the effects of oils in the presence of UVR is needed to improve the environmental relevance of risk assessments and ensure appropriate protection for shallow reef environments against oil pollution.

A method linking the toxic effects at community-level with contaminant concentrations

In this study, we developed a method to quantify and link the toxic effects in community-level ecosystems with concentrations of petroleum hydrocarbons. The densities of Platymonas helgolandica var. tsingtaoensis, Isochrysis galbana, and Brachionus plicatilis in single-species tests and customized ecosystems were examined in response to a concentration gradient of petroleum hydrocarbons ranging from 0 to 8.0mgL−1. A three-population ecological model with interspecies competition-grazing relationships was used to characterize population sizes with concentrations of petroleum hydrocarbons. A threshold concentration of the simplified plankton ecosystem of 0.376mgL−1 for petroleum hydrocarbons was calculated from the proposed model, which was higher than the no-effect concentration of 0.056mgL−1 derived from the single-species toxicity tests and the predicted no-effect concentration of 0.076mgL−1 calculated from the species sensitivity distribution. This finding indicates that interspecies competition and grazing reduced the toxic effect of petroleum hydrocarbons at the community level. The sensitivity analysis for model parameters demonstrates that plankton population biomasses are highly sensitive to filtration rates. Antagonism between interspecies interactions and petroleum hydrocarbon toxicity was attributed to the reduced filtration rate and zooplankton grazing pressure. The proposed method is a simple means to address the concern regarding the impacts of ecological interactions on ecological risk assessments of pollutants.

A rapid bioassay to screen soils for toxicity of residual petroleum hydrocarbons

Ashworth, J. and Bullecer, I. 2012. A rapid bioassay to screen soils for toxicity of residual petroleum hydrocarbons. Can. J. Soil. Sci. 92: 901-904. The following 2-h procedure is proposed as a screen to indicate how soils contaminated with petroleum hydrocarbons (PHC) might perform in bioassays required for site remediation in Canada. Bio-available PHC in soil is extracted by aqueous cyclodextrin; a centrifuged extract portion is treated with amylase, then subjected to a standard Microtox® bioassay. Extract toxicity is correlated to available PHC content.

Validating potential toxicity assays to assess petroleum hydrocarbon toxicity in polar soil

Potential microbial activities are commonly used to assess soil toxicity of petroleum hydrocarbons (PHC) and are assumed to be a surrogate for microbial activity within the soil ecosystem. However, this assumption needs to be evaluated for frozen soil, in which microbial activity is limited by liquid water (θ(liquid)). Influence of θ(liquid) on in situ toxicity was evaluated and compared to the toxicity endpoints of potential microbial activities using soil from an aged diesel fuel spill at Casey Station, East Antarctica. To determine in situ toxicity, gross mineralization and nitrification rates were determined by the stable isotope dilution technique. Petroleum hydrocarbon-contaminated soil (0-8,000 mg kg(-1)), packed at bulk densities of 1.4, 1.7, and 2.0 g cm(-3) to manipulate liquid water content, was incubated at -5°C for one, two, and three months. Although θ(liquid) did not have a significant effect on gross mineralization or nitrification, gross nitrification was sensitive to PHC contamination, with toxicity decreasing over time. In contrast, gross mineralization was not sensitive to PHC contamination. Toxic response of gross nitrification was comparable to potential nitrification activity (PNA) with similar EC25 (effective concentration causing a 25% effect in the test population) values determined by both measurement endpoints (400 mg kg(-1) for gross nitrification compared to 200 mg kg(-1) for PNA), indicating that potential microbial activity assays are good surrogates for in situ toxicity of PHC contamination in polar regions.

Influence of liquid water and soil temperature on petroleum hydrocarbon toxicity in Antarctic soil

Fuel spills in Antarctica typically occur in rare ice-free oases along the coast, which are areas of extreme seasonal freezing. Spills often occur at subzero temperatures, but little is known of ecosystem sensitivity to pollutants, in particular the influence that soil liquid water and low temperature have on toxicity of petroleum hydrocarbons (PHC) in Antarctic soil. To evaluate PHC toxicity, 32 locations at an aged diesel spill site in Antarctica were sampled nine times to encompass frozen, thaw, and refreeze periods. Toxicity was assessed using potential activities of substrate-induced respiration, basal respiration, nitrification, denitrification, and metabolic quotient as well as microbial community composition and bacterial biomass. The most sensitive indicator was community composition with a PHC concentration effecting 25% of the population (EC25) of 800 mg/kg, followed by nitrification (2,000 mg/kg), microbial biomass (2,400 mg/kg), and soil respiration (3,500 mg/kg). Despite changes in potential microbial activities and composition over the frozen, thaw, and refreeze period, the sensitivity of these endpoints to PHC did not change with liquid water or temperature. However, the variability associated with ecotoxicity data increased at low liquid water contents. As a consequence of this variability, highly replicated (n = 50) experiments are needed to quantify a 25% ecological impairment by PHCs in Antarctic soils at a 95% level of significance. Increases in biomass and respiration associated with changes in community composition suggest that PHC contamination in Antarctic soils may have irrevocable effects on the ecosystem.

Soil biogeochemical toxicity end points for sub‐Antarctic islands contaminated with petroleum hydrocarbons

Sub-Antarctic islands have been subjected to petroleum hydrocarbon spills, yet no information is available regarding the toxicity of petroleum hydrocarbons to these subpolar soils. The purpose of the present study was to identify soil biogeochemical toxicity end points for petroleum hydrocarbon contamination in sub-Antarctic soil. Soil from Macquarie Island, a sub-Antarctic island south of Australia, was collected and exposed to 10 concentrations of Special Antarctic Blend (SAB) diesel fuel, ranging from 0 to 50,000 mg fuel/kg soil, for a 21-d period. The sensitivity of nitrification, denitrification, carbohydrate utilization, and total soil respiration to SAB fuel was assessed. Potential nitrification activity was the most sensitive indicator of SAB contamination assessed for nitrogen cycling, with an IC20 (concentration that results in a 20% change from the control response) of 190 mg fuel/ kg soil. Potential denitrification activity was not as sensitive to SAB contamination, with an IC20 of 950 mg fuel/kg soil for nitrous oxide production. Nitrous oxide consumption was unaffected by SAB contamination. Carbohydrate utilization (respiration caused by sucrose) was a more sensitive indicator (IC20, 16 mg fuel/kg soil) of SAB contamination than total respiration (IC20, 220 mg fuel/kg soil). However, total soil respiration was a more responsive measurement end point, increasing soil respiration over a 72-h period by 17 mg of CO2, compared to a change of only 2.1 mg of CO2 for carbohydrate utilization. Our results indicate that IC20s varied between 16 to 950 mg fuel/kg soil for Macquarie Island soil spiked with SAB diesel fuel. These results indicate that current cleanup levels derived from temperate zones may be too liberal for soil contamination in sub-Antarctic islands.

Hydrocarbon-induced changes to metabolic and detoxification enzymes of the Australian crimson-spotted rainbowfish (Melanotaenia fluviatilis).

The toxicity of petroleum hydrocarbons to marine aquatic organisms has been widely investigated; however, the effects on freshwater environments have largely been ignored. Selected biomarkers were measured in a freshwater species, the crimson-spotted rainbowfish (Melanotaenia fluviatilis). Fish were exposed to either a water-accommodated fraction (WAF) of crude oil or a dispersed crude oil water-accommodated fraction (DCWAF) for 3 days and were depurated for 14 days. Generally, biomarkers were altered following the short-term exposures but recovered after 14 days of depuration. Metabolic enzymes measured in gill tissue were citrate synthase and lactate dehydrogenase (LDH). As a result of WAF and DCWAF exposures, citrate synthase and LDH activities increased. Enzyme activities returned to control levels following depuration. Subsequent to the WAF exposure, hepatic ethoxyresorufin-O-deethylase (EROD) activity levels were higher than controls and they returned to control levels during depuration. For the DCWAF exposure, EROD was induced by a TPH (total petroleum hydrocarbons) concentration of 14.5 mg/L; however, after depuration the 14.5 mg/L TPH group had lower EROD activity than did controls. There were no changes in liver- to body-weight ratios or the histopathological organization of gill or liver tissues. As the majority of biomarkers returned to control levels after 14 days of depuration, rainbowfish were able to recover from short-term exposures to crude oil and dispersed crude oil.

Toxicity Testing of Crude Oil and Related Compounds Using Early Life Stages of the Crimson-Spotted Rainbowfish (Melanotaenia fluviatilis)

The toxicity of petroleum hydrocarbons to marine aquatic organisms has been widely investigated; however, the effects on freshwater environments have largely been ignored. In the Australian freshwater environment, the potential impacts of petroleum hydrocarbons are virtually unknown. The toxicity of crude oil and related compounds were measured in the sensitive early life stages of the crimson-spotted rainbowfish (Melanotaenia fluviatilis). Waterborne petroleum hydrocarbons crossed the chorion of embryonic rainbowfish, reducing survival and hatchability. Acute exposures resulted in developmental abnormalities at and above 0.5 mg/L total petroleum hydrocarbons (TPH). Deformities included pericardial edema, disturbed axis formation, and abnormal jaw development. When assessing the acute toxicities of the water-accommodated fraction (WAF) of crude oil, dispersants, dispersant–oil mixtures, and naphthalene to larval rainbowfish, the lowest to highest 96-h median lethal concentrations for day of hatch larvae were naphthalene (0.51 mg/L), dispersed crude oil WAF (DCWAF)-9527 (0.74 mg/L TPH), WAF (1.28 mg/L TPH), DCWAF-9500 (1.37 mg/L TPH), Corexit 9500 (14.5 mg/L TPH), and Corexit 9527 (20.1 mg/L). Using naphthalene as a reference toxicant, no differences were found between the sensitivities of larval rainbowfish collected from adults exposed to petroleum hydrocarbons during embryonic development and those collected from unexposed adults.

Endocrine, Physiological and Histopathological Responses of Fish and their Larvae to Stress with Emphasis on Exposure to Crude Oil and Various Petroleum Hydrocarbons

Various endocrine and physiological responses of fish exposed to forceful physical and chemical stimuli are reviewed with emphasis on the effects of crude oils and their hydrocarbon constituents. The chemistry and toxicity of petroleum hydrocarbons are examined and methods for experimental exposure of fish to crude oil and petroleum hydrocarbons are considered. A variety of blood-borne parameters recognized as reliable tools in determining the relative severity of stress in fish are reviewed. The effects of stress and petroleum hydrocarbons on endocrine responses including changes in plasma catecholamines, corticosteroids, and thyroid hormones are reviewed. The physiological responses: changes in plasma glucose, osmotic and ionic regulation, blood oxygen, hematocrit and hemoglobin concentration are explored, and histopathological effects of crude oil on fish are reviewed. Recent studies of the effects of petroleum hydrocarbons on fish larvae are considered and the increased sensitivity of the early life stages of fish are highlighted.

Effects of Dispersant Treatment on the Acute Aquatic Toxicity of Petroleum Hydrocarbons

The acute effects of both untreated and dispersant-treated Prudhoe Bay crude oil on the early life-stages of three marine species were investigated. Identification of which water-accommodated fraction (undispersed or chemically dispersed) was considered "more toxic" was dependent on species, time, and endpoint (and by inference, test protocol). Generally, the data showed that at roughly equivalent hydrocarbon concentrations untreated oil solutions resulted in higher initial effects (< 1 h) in mysid and topsmelt tests, whereas dispersed oil solutions elicited higher levels of larval abnormality in abalone tests and higher levels of mortality in mysid tests. While differences in test protocols existed among the species tested, topsmelt were the most sensitive species to untreated oil solutions, with mysids being most sensitive to dispersed oil solutions.

Comparative effects of the water accommodated fraction of three oils on mussels—3. Quantitative histochemistry of enzymes related to the detoxication metabolism

1. The reaction products derived from the histochemical demonstration of catalase and gamma-glutarnyl transpeptidase (GGT) activities have been quantified in digestive tissue cells of mussels treated for 21, 49 and 91 days with the water accommodated fraction (WAF) of two different crude oils and of one commercial lubricant oil. 2. Although not in a dose-dependent manner, the mean absorbance of the catalase reaction product is significantly increased (up to 40% increases over control values) in digestive tubule cells after exposure to the 3 types of WAF. 3. These results could support the hypothesis that petroleum hydrocarbon toxicity is mediated in part by an increased generation of oxygen free radicals. 4. The elevation of catalase activity in digestive tubule cells could then represent an adaptative response that exerts a protective role against petroleum hydrocarbon-induced free radical toxicity. 5. Mean absorbance values of GGT, enzyme involved in phase II metabolism of electrophilic xenobiotics that catalyzes the second step of the mercapturic acid pathway, is transiently decreased under certain hydrocarbon exposure-conditions in both digestive tubule cells and stomach cells. 6. This reduction in GGT activity is discussed in relation with the overall effects of organic xenobiotics on mussel biotransformation enzymes.

Determination of petroleum hydrocarbon toxicity with Microtox®

The goal of this toxicity investigation was to determine the toxicity of petroleum fuels and fuel components which are likely to contaminate the subsurface environment. Various fuels and individual components, water soluble fractions of fuels, and soil leachates were tested for toxicity using the Microtox{reg sign}. The fuels used included diesel, unleaded gas, and the aviation fuels JP4 and JP5. Individual components were chosen from the following chemical groups: alkanes, cycloalkanes, alkenes, alkylbenzenes, and polynuclear aromatic hydrocarbons.