Water-accommodated Fraction Of Crude Oil Research Articles

Water-accommodated fractions of crude oil and its mixture with chemical dispersant impairs oxidase stress and energy metabolism disorders in Oryzias melastigma embryos

In this study, marine medaka (Oryzias melastigma) embryos were exposed to different concentrations of water-accommodated fractions (WAFs) and chemically enhanced water-accommodated fractions (CEWAFs) of Oman crude oil for 14 d by semi-static exposure methods. The effects on growth and development and energy metabolism process were evaluated. Results showed that embryo survival and hatchability were decreased in a dose-dependent manner with an increase in the concentration of petroleum hydrocarbon compounds, whereas the malformation exhibited a dose-dependent increase. Compared to the control, the adenosine triphosphate (ATP) content and Na+-K+–ATPase (NKA) activities of embryos exposed to both WAFs and CEWAFs were reduced, while intracellular reactive oxygen species (ROS) levels and NADH oxidase (NOX) activities were increased. Our study demonstrated that exposure to crude oil dispersed by chemical dispersant affected the growth and development of marine medaka embryos, caused oxidative stress while produced a series of malformations in the body and dysregulation in energy metabolism. In comparison, the toxic effects of chemically dispersed crude oil might be more severe than the oil itself in the equivalent diluted concentration treatment solution. These would provide more valuable and reliable reference data for the use of chemical dispersants in oil spills.

Biomarker responses in mussels (Mytilus trossulus) from the Baltic Sea exposed to water-accommodated fraction of crude oil and a dispersant at different salinities

Oil spills pose significant environmental risks, particularly in cold seas. In the Baltic Sea, the low salinity (from 0 to 2 up to 18) affects the behaviour of the spilled oil as well as the efficiency and ecological impacts of oil spill response methods such as mechanical collection and the use of dispersants. In the present study, mussels (Mytilus trossulus) were exposed under winter conditions (5 °C) to the water-accommodated fraction (WAF) of Naphthenic North Atlantic crude oil prepared by mechanical dispersion or to the chemically enhanced fraction (CEWAF) obtained using the dispersant Finasol OSR 51 at salinities of 5.6 and 15.0. Especially at the lower salinity, high bioaccumulation of polycyclic aromatic hydrocarbons was recorded in mussels in the CEWAF treatments, accompanied by increased biomarker responses. In the WAF treatments these impacts were less evident. Thus, the use of dispersants in the Baltic Sea still needs to be carefully considered.

Cold sediment microbial community shifts in response to crude oil water-accommodated fraction with or without dispersant: a microcosm study.

In cold environments, the low temperature slows down microbial metabolisms, such as the biodegradation processes of hydrocarbons, which are often stimulated by the addition of dispersants in oil spill disasters. In this study, we investigated the effects of hydrocarbon water-accommodated fraction (WAF) prepared with and without dispersant on benthic microbial communities in a microcosm experiment in which hydrocarbon removal was observed. Both WAFs contained similar polycyclic aromatic hydrocarbon (PAH) content. The microcosm experiment, set up with either pristine or contaminated sediments, was conducted for 21days at 4°C under WAF and WAF + dispersant conditions. The behavior of bacterial communities in response to WAF and WAF + dispersant was examined at both DNA and RNA levels, revealing the effect of WAF and WAF + dispersant on the resident and active communities respectively. The contaminated sediment showed less taxa responsive to the addition of both WAF and WAF + dispersant than the pristine sediment, indicating the legacy effect by the presence hydrocarbon-degrading and dispersant-resistant taxa inhabiting the contaminated sediment.

Physical Evidence of Oil Uptake and Toxicity Assessment of Amphiphilic Grafted Nanoparticles Used as Oil Dispersants

Herein, we report the toxicity evaluation of a new prototype dispersant system, silicon dioxide nanoparticles (NPs) functionalized with (3-glycidoxypropyl)triethoxysilane (GPS) and grafted poly(ε-caprolactone)-block-poly[oligo(ethylene glycol)methyl methacrylate mono-methyl ether] (NP-PCL-POEGMA). This serves as a follow up of our previous study where grafted silicon dioxide NPs functionalized with GPS and grafted hyperbranched poly(glycidol) (NP-HPG) were evaluated for reducing the toxicity in embryo, juvenile, and adult fish populations. In this study, the NP-HPG sample is used as a baseline to compare against the new NP-PCL-POEGMA samples. The relative size was established for three NP-PCL-POEGMA samples via cryogenic transmission electron microscopy. A quantitative mortality study determined that these NPs are non-toxic to embryo populations. An ethoxyresorufin-O-deethylase assay was performed on these NP-PCL-POEGMA samples to test for reduced cytochrome P450 1A after the embryos were exposed to the water-accommodated fraction of crude oil. Overall, these NP-PCL-POEGMA NPs better protected the embryo populations than the previous NP-HPG sample (using a protein activity end point), showing a trend in the right direction for prototype dispersants to replace the commercially utilized Corexit.

Cellular accumulation of crude oil compounds reduces the competitive fitness of the coral symbiont Symbiodinium glynnii

Oil spill events in the marine environment can have a deleterious impact on the affected ecosystems, such as coral reefs, with direct consequences for their socioeconomic value. The mutualistic relationship between tropical corals and their dinoflagellate symbionts (Symbiodiniaceae) provide structural and nutritional basis for a high local biodiversity in oligotrophic waters. Here, we investigated effects of crude oil water-accommodated fraction on the competitive fitness of the model zooxanthellae species Symbiodinium glynnii. Results of laboratory essays demonstrate that crude oil carbon is incorporated into the cellular biomass with a concomitant change of δ13C isotopic value. Carcinogenic/mutagenic polycyclic aromatic hydrocarbons were identified in the culture media and were responsible for a linear reduction in population growth of S. glynnii, presumably related to energy relocation for DNA repair. Additionally, the experiments revealed that physiological effects induced by crude oil compounds are genetically inherited by the following generations under non-contaminated growth conditions, and induce a reduction in the competitive fitness to cope with other environmental parameters, such as low salinity. We suggest that the effects of crude oil contamination represent an imparing factor for S. glynnii coping with anthropogenic drivers (e.g. warming and acidification) and interfere with the delicate symbiont-host relationship of tropical corals. This is especially relevant in the coastal areas of northeastern Brazil where an oil spill event deposited crude oil on shallow water sediments with the potential to be resuspended to the water column by physical and/or biological activity, enhancing the risk of future coral bleaching events.

A Comparison of Short-Term and Continuous Exposures in Toxicity Tests of Produced Waters, Condensate, and Crude Oil to Marine Invertebrates and Fish.

Petroleum hydrocarbons can be discharged into the marine environment during offshore oil and gas production or as a result of oil spills, with potential impacts on marine organisms. Ecotoxicological assay durations (typically 24–96 h) used to characterize risks to exposed organisms may not always reflect realistic environmental exposure durations in a high‐energy offshore environment where hydrocarbons are mixed and diluted rapidly in the water column. To investigate this, we adapted 3 sensitive toxicity tests to incorporate a short‐term pulse exposure to 3 petroleum‐based products: a produced water, the water‐accommodated fraction (WAF) of a condensate, and a crude oil WAF. We measured 48‐h mobility of the copepod Acartia sinjiensis, 72‐h larval development of the sea urchin Heliocidaris tuberculata, and 48‐h embryo survival and deformities of yellowtail kingfish Seriola lalandi, after exposure to a dilution series of each of the 3 products for 2, 4 to 12, and 24 h and for the standard duration of each toxicity test (continuous exposure). Effects on copepod survival and sea urchin larval development were significantly reduced in short‐term exposures to produced water and WAFs compared to continuous exposures. Fish embryos, however, showed an increased frequency of deformities at elevated concentrations regardless of exposure duration, although there was a trend toward increased severity of deformities with continuous exposure. The results demonstrate how exposure duration alters toxic response and how incorporating relevant exposure duration to contaminants into toxicity testing may aid interpretation of more realistic effects (and hence an additional line of evidence in risk assessment) in the receiving environment. Environ Toxicol Chem 2021;40:2587–2600. © 2021 CSIRO. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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 48h and 96h, 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 (96h) 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 48h followed by an upregulation at 96h, 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.

Phenotypic and transcriptomic responses of the rotifer Brachionus koreanus by single and combined exposures to nano-sized microplastics and water-accommodated fractions of crude oil

Sorption of organic pollutants on microplastics can be an alternative uptake route for organic pollutants in aquatic organisms. To assess the combined effects of microplastics and organic pollutants, we employed phenotypic and transcriptomic analyses to the responses of the marine rotifer Brachionus koreanus to environmentally relevant concentrations of nano-sized microplastic (0.05 µm), water-accommodated fractions of crude oil, and binary mixtures thereof. Our multigenerational in vivo experiments revealed more than additive effects on population growth of B. koreanus in response to combined exposure, while a single exposure to nano-sized microplastic did not induce observable adverse effects. Synergistic transcriptome deregulation was consistently associated with dramatically higher numbers of differentially expressed genes, and increased gene expression was associated with combined exposure. The majority of synergistic transcriptional alteration was related to metabolism and transcription, with impaired reproduction resulting from energetic reallocation toward adaptation. As further supported by chemistry analysis for polycyclic aromatic hydrocarbons sorption on microplastic, our findings imply that nano-sized microplastics can synergistically mediate the effects of organic pollutants in aquatic organisms.

Antioxidant Response and Oxidative Stress in the Respiratory Tree of Sea Cucumber (Apostichopus japonicus) Following Exposure to Crude Oil and Chemical Dispersant

Sea cucumber (Apostichopus japonicus) is mainly cultured in the coastal zone, where it is easily threatened by accidental oil spills. Chemical dispersant is one of the efficient oil spill responses for mitigating the overall environmental damage of oil spills. However, the impact of crude oil and chemical dispersants on sea cucumber is less well known. Hence, the present study focused on exploring the antioxidant response and oxidative stress in the respiratory tree of sea cucumber following exposure to GM-2 chemical dispersant (DISP), water-accommodated fractions (WAF), and chemically enhanced WAF (CEWAF) of Oman crude oil for 24 h. Results manifested that WAF exposure caused a significant increase in the reactive oxygen species (ROS) level (5.29 ± 0.30 AU·mgprot−1), and the effect was much more obvious in CEWAF treatment (5.73 ± 0.16 AU·mgprot−1). Total antioxidant capacity (T-AOC), as an important biomarker of the antioxidant defense capacity, showed an increasing trend following WAF exposure (0.95 ± 0.12 U·mgprot−1) while a significant reduction in T-AOC was observed following CEWAF exposure (0.23 ± 0.13 U·mgprot−1). Moreover, we also evaluated the oxidative damage of the macromolecules (DNA, protein, and lipid), and our results revealed that the presence of chemical dispersant enhanced oxidative damage caused by crude oil to sea cucumber.

Differential detoxifying responses to crude oil water-accommodated fraction in Hyallela curvispina individuals from unpolluted and contaminated sites

Sublethal effects of water-accommodated fraction (WAF) from crude oil of Neuquén basin, Northern Patagonia-Argentina, were examined on both antioxidant and detoxification system of Hyalella curvispina adults collected in Los Barreales (LB) lake and in an oil-polluted stream (DS). The effects of WAF exposure during 6, 24 and 48 h were evaluated in the glutathione content (GSH) and glutathione S-transferase (GST), catalase (CAT) and cytochrome P450 (CYP450) activities. Populations from DS and LB showed not only different basal GSH content and enzyme activities but also different behavior to WAF exposure. LB population exposed to WAF showed a significant increase in GSH content, CAT and CYP450 activities, compared to control group. DS population presented high basal levels in CAT and CYP activity compared with LB population, but their response to WAF exposure was minor. Amphipods from DS, chronically exposed to hydrocarbons, were adapted to their environment.

Toxicity comparison of water-accommodated fraction and chemically enhanced fraction of bonny light crude oil and dispersit SPC 1000 to mudskipper (<i>Periophthalmus papilio</i>) fish

This study assessed the physicochemical characteristics and toxicity of water-accommodated fraction (WAF) and chemically enhanced WAF (CEWAF) of Bonny Light Crude oil and Dispersit SPC 1000 (dispersant) to Mudskipper fish (Periophthalmus Papilio). There were variations in the levels of the physicochemical parameters. The coefficient of variation (CV) indicated that the temperature show the least variation of 2.24% and salinity the highest 98.12%.Hypothesis test for significant differences at p < 0.05 significance level however, showed that there were no significant differences in the levels of the measured parameters over the 96 hours. All the mudskippers fish samples exposed to the water accumulated water fraction of 10% bonny oil survived beyond 96 hours. An increase in toxicity of the oil was observed after 72-96 hour exposures of the mudskipper to the oil and dispersant CEWAF. For dispersant concentrations of 540 ml/L and 630 ml/L the survival of mudskippers was 80%. These mortalities might be due to the toxic effect of the dispersant, Dispersit SPC 1000.The Total Petroleum Hydrocarbon (TPH) and the Polycyclic Aromatic Hydrocarbon (PAH) in the test media were respectively 7.66-63.18 ppm and 0.82-5.26 ppm.10% Bonny light crude oil WAF had no effects on mudskipper survival. Exposures to 540 ml/L and 630 ml/L Dispersit SPC 1000 dispersed oil WAF (CEWAF) resulted in 20 % mortality. The lethal dose concentration was 885.5 ml/L (88.55%). The lowest observed effect concentration (LOEC) was found to be 540 ml/L.Keywords: Water-accommodated fraction, chemically enhanced fraction, Dispersant, Mudskipper fish

Toxicity of Water-Accommodated Fractions (WAF), Chemically Enhanced WAF (CEWAF) of Oman Crude Oil and Dispersant to Early-Life Stages of Zebrafish (Danio rerio).

This study focused on comparing the lethal and sublethal toxicity of water-accommodated fractions (WAF) and chemically enhanced WAF (CEWAF) of crude oil to zebrafish (Danio rerio) on early life stages (ELS). Results showed that the addition of GM-2 dispersant caused an increase in the levels of total petroleum hydrocarbons (TPHs) and total priority polycyclic aromatic hydrocarbons (ΣPAHs). Based on ΣPAHs, the LC20 estimates for WAF and CEWAF were 4.88 µgL-1 and 1.19µgL-1, respectively, indicating that CEWAF was approximately four times more toxic. CEWAF exposure caused markedly lower hatching rates and higher malformation frequencies than WAF. Meanwhile, the general morphology score (GMS) values in CEWAF were about fourfold lower than that in WAF, indicating that CEWAF exposure induced more significant developmental delay. The results suggested that chemical dispersant enhanced the toxicity of crude oil to zebrafish on ELS and its application could increase the exposure of fishes to crude oil.

Feminizing effects of exposure to Corexit-enhanced water-accommodated fraction of crude oil in vitro on sex determination in Alligator mississippiensis

Deepwater Horizon spilled over 200 million gallons of oil into the waters of the Gulf of Mexico in 2010. In an effort to contain the spill, chemical dispersants were applied to minimize the amount of oil reaching coastal shorelines. However, the biological impacts of chemically-dispersed oil are not well characterized, and there is a particular lack of knowledge concerning sublethal long-term effects of exposure. This study examined potential estrogenic effects of CWAF, Corexit 9500-enhanced water-accommodated fraction of oil, by examining its effect on estrogen receptors and sex determination in the American alligator, Alligator mississippiensis. The alligator exhibits temperature-dependent sex determination which is modulated by estrogen signals, and exposure to 17β-estradiol (E2) and estrogenic compounds in ovo during the thermosensitive period of embryonic development can induce ovarian development at a male-producing temperature (MPT). CWAF induced transactivation up to 50% of the maximum induction by E2 via alligator estrogen receptors in vitro. To determine potential endocrine-disrupting effects of exposure directly on the gonad, gonad-adrenal-mesonephric (GAM) organ complexes were isolated from embryos one day prior to the thermosensitive period and exposed to E2, CWAF, or medium alone in vitro for 8–16 days at MPT. Both CWAF and E2 exposure induced a significant increase in female ratios. CWAF exposure suppressed GAM mRNA abundances of anti-Müllerian hormone (AMH), sex determining region Y-box 9, and aromatase, whereas E2 exposure suppressed AMH and increased Forkhead box protein L2 mRNA abundances in GAM. These results indicate that the observed endocrine-disrupting effects of CWAF are not solely estrogenically mediated, and further investigations are required.

Estrés oxidativo, metabolismo lipídico y neurotransmisión en el caracol dulceacuícola (Pomacea patula) expuesto a la fracción hidrosoluble de petróleo crudo

Background. Crude oil is a super mixture of chemical compounds and is commonly found in aquatic environments. The tegogolo ( Pomacea patula Baker, 1922) is a Mexican freshwater snail endemic to Lake Catemaco in Veracruz; currently, however, its distribution has expanded to many freshwater ecosystems that suffer the impact of crude oil spills and oil byproducts like fuels. Goals . To assess a series of biomarkers involved in oxidative stress, neurotransmission, and fatty acid metabolism in tegogolos exposed to the water-accommodated fraction (WAF) of Maya crude oil (MCO). Methods . Tegogolo specimens were exposed to WAF of MCO obtained from loads of 0.1, 1, 10 and 100 mg/L. We evaluated ROS ( O2 -* and H2O2), oxidative stress (TBARS and RC=O), enzymes involved in antioxidant defense (SOD, CAT, and GPx), some enzymes involved in neurotransmission (AChE, GDA, and CbE activities), and biomarkers of fatty acids metabolism (fatty acids levels and AOX activity). Results. Clear biomarkers responses were observed only in some tissues. ROS were clearly higher than controls in the foot, head, and kidney; however, others biomarkers of oxidative stress remain statistically unchanged. SOD response was irregular with respect to controls and treatments. In contrast, CAT (foot) and GPx (foot and intestine) were the more active enzymes and their activities were higher than in controls. The responses of some enzymes involved in neurotransmission suggest that compensation mechanisms exist between AChE and GDA in the foot and head. Fatty acids metabolism increased with exposure to WAF; however, these types of biomarkers seem unsuitable for monitoring the toxic effects produced by WAF at low environmental concentrations. Conclusions. We can conclude that under the exposure conditions discussed herein, the tegogolos showed acclimation to WAF of Maya crude oil by complex mechanisms.

Estrés oxidativo, metabolismo lipídico y neurotransmisión en el caracol dulceacuícola (Pomacea patula) expuesto a la fracción hidrosoluble de petróleo crudo

Estrés oxidativo, metabolismo lipídico y neurotransmisión en el caracol dulceacuícola (Pomacea patula) expuesto a la fracción hidrosoluble de petróleo crudo

Chemical Analysis of Water-accommodated Fractions of Crude Oil Spills Using TIMS-FT-ICR MS

Chemical Analysis of Water-accommodated Fractions of Crude Oil Spills Using TIMS-FT-ICR MS

Chemical Analysis of Water-accommodated Fractions of Crude Oil Spills Using TIMS-FT-ICR MS.

Multiple chemical processes control how crude oil is incorporated into seawater and also the chemical reactions that occur overtime. Studying this system requires the careful preparation of the sample in order to accurately replicate the natural formation of the water-accommodated fraction that occurs in nature. Low-energy water-accommodated fractions (LEWAF) are carefully prepared by mixing crude oil and water at a set ratio. Aspirator bottles are then irradiated, and at set time points, the water is sampled and extracted using standard techniques. A second challenge is the representative characterization of the sample, which must take into consideration the chemical changes that occur over time. A targeted analysis of the aromatic fraction of the LEWAF can be performed using an atmospheric-pressure laser ionization source coupled to a custom-built trapped ion mobility spectrometry-Fourier transform-ion cyclotron resonance mass spectrometer (TIMS-FT-ICR MS). The TIMS-FT-ICR MS analysis provides high-resolution ion mobility and ultrahigh-resolution MS analysis, which further allow the identification of isomeric components by their collision cross-sections (CCS) and chemical formula. Results show that as the oil-water mixture is exposed to light, there is significant photo-solubilization of the surface oil into the water. Over time, the chemical transformation of the solubilized molecules takes place, with a decrease in the number of identifications of nitrogen- and sulfur-bearing species in favor of those with a greater oxygen content than were typically observed in the base oil.

Thyroid Hormone Disruption by Water-Accommodated Fractions of Crude Oil and Sediments Affected by the Hebei Spirit Oil Spill in Zebrafish and GH3 Cells.

A crude oil and the coastal sediments that were affected by the Hebei Spirit Oil Spill (HSOS) of Taean, Korea were investigated for thyroid hormone disruption potentials. Water-accommodated fractions (WAFs) of Iranian Heavy crude oil, the major oil type of HSOS, and the porewater or leachate of sediment samples collected along the coast line of Taean were tested for thyroid disruption using developing zebrafish and/or rat pituitary GH3 cells. Major polycyclic aromatic hydrocarbons (PAHs) and their alkylated forms were also measured from the test samples. In zebrafish larvae, significant decreases in whole-body thyroxine (T4) and triiodothyronine (T3) levels, along with transcriptional changes of thyroid regulating genes, were observed following 5 day exposure to WAFs. In GH3 cells, transcriptions of thyroid regulating genes were influenced following the exposure to the sediment samples, but the pattern of the regulatory change was different from those observed from the WAFs. Composition of PAHs and their alkylated homologues in the WAFs could partly explain this difference. Our results clearly demonstrate that WAFs of crude oil can disrupt thyroid function of larval zebrafish. Sediment samples also showed thyroid disrupting potentials in the GH3 cell, even several years after the oil spill. Long-term ecosystem consequences of thyroid hormone disruption due to oil spill deserve further investigation.

Induction of reactive oxygen species in marine phytoplankton under crude oil exposure.

Exposure of phytoplankton to the water-accommodated fraction of crude oil can elicit a number of stress responses, but the mechanisms that drive these responses are unclear. South Louisiana crude oil was selected to investigate its effects on population growth, chlorophyll a (Chl a) content, antioxidative defense, and lipid peroxidation, for the marine diatom, Ditylum brightwellii, and the dinoflagellate, Heterocapsa triquetra, in laboratory-based microcosm experiments. The transcript levels of several possible stress-responsive genes in D. brightwellii were also measured. The microalgae were exposed to crude oil for up to 96 h, and Chl a content, superoxide dismutase (SOD), the glutathione pool (GSH and GSSG), and lipid peroxidation content were analyzed. The cell growth of both phytoplankton species was inhibited with increasing crude oil concentrations. Crude oil exposure did not affect Chl a content significantly in cells. SOD activities showed similar responses in both species, being enhanced at 4- and 8-mg/L crude oil exposure. Only H. triquetra demonstrated enhanced activity in GSSG pool and lipid peroxidation at 8-mg/L crude oil exposure, suggesting that phytoplankton species have distinct physiological responses and tolerance levels to crude oil exposure. This study indicated the activation of reactive oxygen species (ROS) in phytoplankton under crude oil exposure; however, the progressive damage in cells is still unknown. Thus, ROS-related damage in nucleic acid, lipids, proteins, and DNA, due to crude oil exposure could be a worthwhile subject of study to better understand crude oil toxicity at the base of the food web.

Identification of the Full 46 Cytochrome P450 (CYP) Complement and Modulation of CYP Expression in Response to Water-Accommodated Fractions of Crude Oil in the Cyclopoid Copepod Paracyclopina nana.

The 46 cytochrome P450 (CYP) gene superfamily was identified in the marine copepod Paracyclopina nana after searching an RNA-seq database and comparing it with other copepod CYP gene families. To annotate the 46 Pn-CYP genes, a phylogenetic analysis of CYP genes was performed using a Bayesian method. Pn-CYP genes were separated into five different clans: CYP2, CYP3, CYP20, CYP26, and mitochondrial. Among these, the principal Pn-CYP genes involved in detoxification were identified by comparing them with those of the copepod Tigriopus japonicus and were examined with respect to their responses to exposure to a water-accommodated fraction (WAF) of crude oil and to the alkylated forms of two polycyclic aromatic hydrocarbons (PAHs; phenanthrene and fluorene). The expression of two Pn-CYP3027 genes (CYP3027F1 and CYP3027F2) was increased in response to WAF exposure and also was upregulated in response to the two alkylated PAHs. In particular, Pn-CYP3027F2 showed the most notable increase in response to 80% WAF exposure. These two responsive CYP genes (Pn-CYP3027F1 and CYP3027F2) were also phylogenetically clustered into the same clade of the WAF- and alkylated PAH-specific CYP genes of the copepod T. japonicus, suggesting that these CYP genes would be those chiefly involved in detoxification in response to WAF exposure in copepods. In this paper, we provide information on the copepod P. nana CYP gene superfamily and also speculate on its potential role in the detoxification of PAHs in marine copepods. Despite the nonlethality of WAF, Pn-CYP3027F2 was rapidly and significantly upregulated in response to WAF that may serve as a useful biomarker of 40% or higher concentration of WAF exposure. This paper will be helpful to better understand the molecular mechanistic events underlying the metabolism of environmental toxicants in copepods.