Oil Fingerprinting Research Articles

Biological Marker Fingerprints of Crude Oils from Three Oilfields in the Central Niger Delta: Implication to Source Input, Conditions of Deposition, and Thermal Maturation

Crude oil samples recovered from three oilfields distributed within the central Niger Delta were used to investigate biological marker fingerprints, sources of organic matter, conditions of deposition, and thermal maturation. This was achieved by the application of gas chromatography-mass spectrometric (GC-MS) analyses on the saturated components of the crude oils. The biological marker ratios show low sterane/hopane (steranes/hopane ˂ 1) in the scope of 0.29 to 0.61 indicating that the crude oils initiated from rocks containing high terrigenous biota (mainly land plants). The n-alkanes distribution and the pristane/phytane ratios (0.63 to 2.08) suggested source deposition under oxic to suboxic environmental conditions. The percentage composition of C27, C28, and C29 steranes and oleanane index (18α (H)-oleanane/ C30 17α (H)-hopane) also indicated major contributions from terrigenous organic biota with minor marine source input. The studied crude oils have C32:22S/ (22S+22R) ratios in the scope of 0.55 to 0.64, and these values suggested high maturation level. This agrees with the oleanane index (0.64 to 0.95), CPI (0.92 to 1.06), C29: 20S/ (20S + 20R) sterane ratios (0.29 to 0. 61), Ts/(Ts+Tm) ratio (0.45 to 0.83) and moretane/C30 hopane proportion (0.16 to 0.24). Keywords: Biological marker; Depositional conditions; Niger Delta; Organic matter; Thermal maturation.

Analysis of sulfur compounds for crude oil fingerprinting using gas chromatography with sulfur chemiluminescence detector

Oil spills are a severe problem worldwide due to the resulting damage to marine and coastal ecosystems and to local economies. Identification of the source of spilled oils can be challenging, especially if the oils have undergone severe weathering. Due to their high durability, biomarker compounds (e.g. hopanes, steranes) are widely used for oil fingerprinting. Some sulfur-containing heterocyclic compounds e.g. alkylated dibenzothiophenes are also considered to be highly resistant. In this study, the use of Gas Chromatography with Sulfur Chemiluminescence Detection was investigated as a means of oil fingerprinting using the distribution the sulfur compounds in five different fresh and weathered crude oils. Chemometric analysis was also performed. The results indicate that the sulfur compounds distribution is unique for each crude oil. The distributions of the heavy sulfur compounds (i.e., C2DBTs and C3DBTs) are unchanged after weathering. Therefore, the GC-SCD technique can be considered to support the oil spill identification.

Tar ball pollution under the influence of ocean circulation in the Bohai Sea, China

The deposition of tar balls of unknown sources on the coast poses a great threat to the fishery, tourism and coastal biodiversity in the Bohai Sea. This work aimed to identify the sources of tar balls by using oil fingerprint technique. Tar ball samples were collected from the seashore of two islands of the western Bohai Sea and divided into two groups (Group I and Group II). Principal component analysis showed that although Caofeidian oilfield was one of the closest oilfields to the sampling area it was not a source. Fingerprints of characteristic hopanes and steranes showed that samples of Group I were similar to the crude oils from the nearby Jidong oilfield, and samples of Group II were similar to the Penglai-19-3 crude oils. Combined with cross-plots of the samples and the reference oils, it indicated that Group I may come from Jidong and Group II may come from Penglai-19-3. The weathering characteristics of alkanes and polycyclic aromatic hydrocarbons showed that the samples were affected by natural weathering processes (e.g., evaporation, photooxidation and biodegradation). It revealed that oil pollution from the nearby oilfields can also affect other areas under the influence of ocean circulation. It is the first study on source identification of tar balls from the Bohai Sea and the effects of ocean circulation on the tar ball transport. This study can considerably help to further understand the evolution of tar balls and consequently determine their sources.

Chemometric techniques in oil spill identification: A case study in Dalian 7.16 oil spill accident of China

Chemometric methods have unique advantages regarding comprehensive consideration of multiple parameters and the classification of samples or variables. Classification of oil spill sources was carried out by using chemometric techniques, such as Repeatability Limit, hierarchical cluster analysis (HCA), Student's t-test and Principal component analysis (PCA) Biplot. In addition, this paper takes the fingerprint identification of a Dalian “7.16″ oil spill accident as an example to illustrate the effectiveness of chemometric techniques in oil identification. PCA scores plot (explaining 82.77% of variance accounted for three PCs) showed that samples belong to four clusters and result of HCA method further confirmed that. The residual oil in Jinshatan Beach and Haibei Square may be caused by the explosion of Dalian “7–16” oil pipeline accident. The use of chemometric techniques is significant in providing independent validation for classifying the types of spilled oil in the investigation of oil spill pollution. The results will be of great significance to improve the accuracy and efficiency of oil spill identification based on oil fingerprint.

Chemical investigation and biological activities of Patchouli (Pogostemon cablin (Blanco) Benth) essential oil

Pogostemon cablin (Blanco) Benth. plant is known to synthesize the precious and most valuable essential oil available today on perfumers pellet. Because of its limited production in South East Asian countries like Indonesia, the high demand is always a challenge for the producing countries. In order to meet the market demand, CSIR-CIMAP has developed a high essential oil yielding patchouli var. CIM-Utkrisht for cultivation in India. Since the variety possessed a unique fingerprint of essential oil, furthermore, due to patchouli’s more acceptance as ingredients of many perfume preparations, the volatile oils are rarely investigated for biological action, anti-inflammatory, in particular. We investigated the essential oils obtained from dried aerial parts of the plant for their antimicrobial and anti-inflammatory potential. The anti-inflammatory activity (TNF-α) was significantly reduced (p < 0.05) in patchouli essential oil treated cells as compared to vehicle control. Essential oil exhibited In-vitro antimicrobial activity against five selected microorganisms’ viz., C. albicans , S. typhimurium , S. aureus , E. coli , and M. furfur . In particular, essential oil obtained from 14 days of drying showed the most potent action (zone inhibition, 16.0 ± 3.0) against M. furfur . The GC-FID, GC / -MS and NMR investigations revealed presence of an array of sesquiterpenoids such as curcumenes (γ-curcumene; 22.0–25.0% & ar -curcumene; 1.3–3.1%), 7- epi - cis -sesquisabinene hydrate (0.3–0.5%), and some guaiane-type sesquiterpenoids like guaia-1(5)-11-dien-3-ol (1.5–4.6%), guaia-11-en-5-ol (0.1–0.2%), guaia-4(5)-11-dien-6-ol (0.6–0.9%), guaia-1(10)-11-dien-9-one (0.4–1.2%) and guaia-1(10)-11-dien-9-one-8-ol (1.4–1.6%). The current work is the first report of bisabolane-type sesquiterpenoids from the genus Pogostemon with high γ-curcumene (22.0–25.0%). Being a highly esteemed basic ingredient of modern perfumery, the patchouli oil is frequently adulterated with non-volatiles compositions to comply with the market demands. We report herein simultaneous thermo-gravimetric analysis-based detection method for authentication of patchouli essential oils for the first time. • Pogostemon cablin essential oils in different drying stages were studied. • Guaia-1(10)-11-dien-9-one & Guaia-1(10)-11-dien-9-one-8-ol were identified. • Curcumenes (γ- & ar -) were the key markers of this oil. • A 14 days dried essential oil inhibits best growth of M. furfur (ZOI-16.0 ± 3.0). • TNF-α significantly reduced (p < 0.05) in essential oil.

Comparing Metabolomic and Essential Oil Fingerprints of Citrus australasica F. Muell (Finger Lime) Varieties and Their In Vitro Antioxidant Activity.

Comparative chemical analyses among peel and pulp essential oils (EOs) and methanolic extracts of four Citrus australasica varieties (Red, Collette, Pink Ice, and Yellow Sunshine), and the hybrid Faustrime, were performed using GC-MS and UHPLC-DAD-HR-Orbitrap/ESI-MS. Peel and pulp extracts were also analysed for their in vitro antioxidant activity on a Balb/3T3 clone A31 mouse embryo fibroblast cell line. The results of peel and pulp EOs were mainly characterised by monoterpenes and sesquiterpenes, respectively. All peels displayed a higher total phenol content (TPC) than pulps, and consequently a greater antioxidant activity. Collette peels and Pink Ice pulps showed the highest amount of identified flavonoids (e.g., luteolin, isosakuranetin, and poncirin derivatives). Collette and Red peels were rich in anthocyanins (delphinidin and petunidin glycosides), exhibiting the maximum protective activity against induced oxidative damage. In conclusion, finger lime fruits are good sources of health-promoting phytocomplexes, with the Red, Collette, and Pink Ice varieties being the most promising.

ICP-MS triple quadrupole as analytical technique to define trace and ultra-trace fingerprint of extra virgin olive oil

Extra virgin olive oil is a typical product of Mediterranean area, and its origin protection is continuously improved. 24 olive oil samples from different geographical origin were analyzed and 40 elements were evaluated with chemometric techniques. This study aims at elaborating a method to determine mineral composition of this matrix and at validating the method used to determine its reliability. The high-level laboratory facilities for trace element/isotopic analysis realized in ENEA Brasimone (Italy) is a useful tool to reduce the limit of detection of elements, cutting down pollutants. Both Clean Laboratory for sample pre-treatment and Clean Room Standard ISO 6 are constantly monitored to guarantee the control quality. The results obtained using ICP-MS Triple Quadrupoles show changes between the analysed samples. Finally, Principal Component Analysis was conducted to better characterize olive oil products from different geographical origin, providing a fingerprint of the element patterns in the samples.

Optimisation of the uncertainty of oil spill identification from replicate comparative analyses: Comparison of standardised and novel identification methods

Oil spill identifications involve the comparison of oil fingerprints between the oil spill and suspected oil sources, defined by ratios between the abundances of oil-discriminating compounds, Diagnostic Ratios (DR). The normalised Nordtest and EN 15522-2 methodologies use Student's t statistic (S-t) or a maximum relative difference (SC) to compare mean DR from replicate sample analysis. While the S-t method assumes the normality of DR distribution, the SC method is based on controlled DR dispersion. However, when false, the assumptions and approximations adopted can lead to low true identification rates. This work presents a novel computational tool for the statistically sound oil spill identification that allows following requirements defined by EN 15522–2, the comparison of replicate DR determinations, and the use of different DR sets and formats. The tool uses the Monte Carlo Method (MCM) to describe the probability distribution of the difference of mean DR, allowing estimating the probability of the true acceptance of fingerprints equivalence. The studied methods were applied to the comparison of signals from the same oil and to a real scenario reproduced in an International Round Robin Test. The methods were compared considering the probabilities of true acceptance of oil patterns equivalence based on a single, γ, or various, δ, DR. The MCM method performs identifications with γ equivalent to the defined confidence level for the comparison, P. Since the various DR studied are not perfectly correlated, the δ is below P. The number of replicate analyses performed and the DR considered in the comparison affect identification performance. The S-t produces comparison criteria with a γ lower than P. The SC criteria for duplicate analysis is associated with a δ lower than the obtained by the MCM. A user-friendly MS-Excel spreadsheet is available to perform oil pattern comparisons using various methods and conditions.

Trace and Rare Earth Element Partitioning in Organic Fractions of Mudstones during the Oil Formation

In order to investigate trace and rare earth element partitioning in organic fractions of mudstones, this study isolated organic fractions of mudstones, including insoluble organic fraction (kerogen), soluble organic fraction (extract), or expelled hydrocarbon (reservoir solid bitumen), and the isolated organic fractions and their corresponding whole rocks for trace and rare earth element compositions were measured. Analysis of trace and rare earth element compositions in organic fractions of lacustrine and marine mudstones revealed that mudstone kerogens were more enriched in rare earth elements (REE) and redox-sensitive trace elements (e.g., U, Mo, and Ni) relative to corresponding whole rocks. During the oil generation, middle rare earth elements (Sm-Ho), especially Eu, migrated from kerogen to extract more easily than the rest REE. The Eu was easily transferred to soluble hydrocarbon under the acidic and reducing environments formed by oil generation, resulting in the higher concentrations of Eu relative to its neighboring REE (Sm and Gd) and the pronounced positive Eu anomalies. Transition metal elements (e.g., Mo, V, Cr, Co, Ni, Cu, and Zn) also more easily released from kerogen than the rest elements, especially V and Ni. The enrichment and mobilization of trace elements in organic fractions of mudstones, such as Mo, U, V, Ni, and Ba, are closely related with their geochemical behaviors during the depositional and early digenetic processes, providing the potential information for predicting the distribution characteristics of trace elements in the expelled hydrocarbons of mudstones (e.g., crude oil and solid bitumen) and fingerprinting of oil to source.

Parallel quantitation of salt dioctyl sodium sulfosuccinate (DOSS) and fingerprinting analysis of dispersed oil in aqueous samples

In many jurisdictions, dispersants are included in contingency plans as a viable countermeasure that can help reduce the overall environmental impact of marine oil spills. When used, it is imperative to monitor the progression of dispersant and oil to assess their environmental fate and behaviour. Amphiphilic salt dioctyl sodium sulfosuccinate (DOSS) is the major effective component of the most commonly available dispersants, such as Corexit® EC9500A. Without proper sample preparation, dispersed oil in water samples could interfere with the accurate analysis of DOSS and easily contaminate the LC-MS system. In this work, solid phase extraction (SPE) weak anion exchange (WAX) cartridges were used to separate oil and DOSS in aqueous samples. DOSS was accurately determined by liquid chromatography coupled with a high resolution Orbitrap mass spectrometer (LC-HRMS). Oil fingerprinting analysis was conducted and total petroleum hydrocarbons (TPHs), polycyclic aromatic hydrocarbons (PAHs), and petroleum biomarkers were determined by gas chromatography-flame ionization detection (GC-FID) and mass spectrometry (GC-MS). This SPE-LC/GC-MS method was used for the analysis of oil-dispersant water samples containing a mixture of Corexit® EC9500A and a selection of crude oils and refined petroleum products. Nearly a 100% DOSS recovery was obtained for various oil-surfactant conditions. Parallel quantitation of oils with dispersants was achieved using this method. A portion of the TPH loss was possibly attributed to oil retained by the SPE column. Chemical fingerprints and diagnostic ratios of target compounds in recovered dispersed oil overall remain unchanged compared with those of all studied oils.

Applied aspects of geochemical parameters of oil

The given paper provides data on the fingerprints of Azerbaijani oils using biomarkers (GC/MS) and microelement composition (ICP/MS), as well as the main geochemical parameters of oil, such as CPI, Ki, QI, ITC, Ts/Tm, Pr/Ph, etc., and data on correlation dependencies of geochemical parameters on the horizon at particular oilfield. Characterization of oil accumulations belonging to the mid-Pliocene in the Caspian Sea in terms of hydrocarbons - biomarkers and geochemical parameters makes it possible to predict the composition and the predominant type of oil in the field with similar geological structure. Keywords: oil biomarkers; chromatographymass spectrometry; mass spectrometry with inductively coupled plasma; oil fingerprint.

Chemical Recycling of Plastic Marine Litter: First Analytical Characterization of The Pyrolysis Oil and of Its Fractions and Comparison with a Commercial Marine Gasoil

A detailed molecular fingerprint of raw pyrolysis oil from plastic wastes is a new research area. The present study focuses for the first time on the chemical recycling of plastic marine litter; we aim to chemically characterize the obtained raw pyrolysis oil and its distillates (virgin naphtha and marine gasoil) via GC-MS and FT-IR. For all samples, more than 30% of the detected compounds were identified. 2,4-dimethyl-1-heptene, a marker of PP pyrolysis, is the most represented peak in the chemical signature of all the marine litter pyrolysis samples, and it differentiates commercial and pyrolysis marine gasoil. The presence of naphthalenes is stronger in commercial gasoil, compared to its pyrolysis analog, while the opposite holds for olefins. The overlap between the two molecular fingerprints is impressive, even if saturated hydrocarbons are more common in commercial gasoil, and unsaturated compounds are more common in the gasoil derived from pyrolysis. A technical comparison between the commercial marine gasoil and the one obtained from the marine litter pyrolysis is also attempted. Gasoil derived from marine litter fully complies with the ISO8217 standards for distillate marine fuel. On the other hand, the virgin naphtha is particularly rich in BTX, ethylbenzene, styrene, and alpha olefins, which are all important recoverable platform chemicals for industrial upcycling.

Evaluation of Re-Os Geochronology and Os Isotope Fingerprinting of Late Cretaceous Terrestrial Oils in Taranaki Basin, New Zealand

Evaluation of Re-Os Geochronology and Os Isotope Fingerprinting of Late Cretaceous Terrestrial Oils in Taranaki Basin, New Zealand

Fingerprinting and biomarker analysis of oil from Akshabulak group for determining oil types

This article presents the results of fingerprinting of 128 oil samples derived from all production wells of three Akshabulak group fields to determine the types of oils. Based on the results of this analysis, four groups of oils were identified: The first group includes oils (red) of the lower hydrocarbon pay zones (III-IV-V) in Akshabulak Central, the upper zones of the I southern dome of Akshabulak Central and all pay zones of the northern dome at Akshabulak South. The second group of oils (green) was identified in the wells exploiting pay zone I in the northern dome of Akshabulak Central, while oils (blue) in the productive horizons of Akshabulak East and paleochannel sediments of Akshabulak Central form the third group. The fourth group includes one oil sample with different genesis from well № 37, which penetrates paleo-channel № 13 at South Akshabulak.&#x0D; Biomarker analysis was carried out for 39 oil samples, according to which the oils were formed in terrigenous (clayey) organic matter, deposited in lacustrine environment. In terms of thermal parameters, the oils of the Eastern Akshabulak are less mature than the oils of the Central Akshabulak and the South Akshabulak, despite their relative deeper depths. Based on the work performed, the conclusion presents the prospective hydrocarbon accumulation zones suitable for increasing hydrocarbon resources and reserves in the future. However it should be noted that the results of the studies performed provide valuable information only when integrated with the corresponding geological and seismic data.

Detection of Qinghai-Tibet Plateau flaxseed oil adulteration based on fatty acid profiles and chemometrics

Flaxseed oil is an important ingredient in functional foods, as it is rich in polyunsaturated fatty acids, phenolic compounds (lignans, ferulic and p -coumaric acid), and mucilage. Therefore, economically motivated flaxseed oil adulteration is a common occurrence. Developing effective approaches to detecting such adulteration is essential to preserve flaxseed oil quality and safety. Herein, similarity evaluation (SE), discriminant analysis (DA), principal component analysis (PCA), and heat map approaches were employed to differentiate between samples of flaxseed oil that had been adulterated with a range of concentrations of rapeseed, corn, peanut, safflower, soybean, or sesame oil (10–50%) based on their fatty acid composition. The standard fatty acid fingerprint of pure flaxseed oil was analyzed with 100% accuracy when the adulterant concentration was greater than 10%. DA approach was able to identify specific vegetable oil types in flaxseed oil samples that had been adulterated with less than 20% rapeseed, corn, peanut, sunflower, soybean, or sesame oil. Heat map indicated that linolenic acid was the reliable marker of flaxseed oil adulteration and PCA analyses was more effective in identifying adulteration concentration for all models other than rapeseed oil and corn oil. Overall, the stepwise hierarchical approach developed and outlined in the present study represents a valuable approach to asses flaxseed oil adulteration. • A stepwise approach was developed for the assessment of flaxseed oil adulteration. • Similarity evaluation differentiates between pure and adulterated flaxseed oils. • Discriminant analysis identify types of vegetable oil adulterated in flaxseed oil. • Principal component analysis accurately quantify the degree of adulteration.

Chemical Constituents, In Vitro Antioxidant Activity and In Silico Study on NADPH Oxidase of Allium sativum L. (Garlic) Essential Oil.

Allium sativum L., also known as garlic, is a perennial plant widely used as a spice and also considered a medicinal herb since antiquity. The aim of this study was to determine by gas chromatography–mass spectrometry (GC–MS) the chemical profile fingerprint of the essential oil (EO) of one accession of Peruvian A. sativum (garlic), to evaluate its antioxidant activity and an in- silico study on NADPH oxidase activity of the volatile phytoconstituents. The antioxidant activity was tested using DPPH and β-carotene assays. An in-silico study was carried out on NADPH oxidase (PDB ID: 2CDU), as was ADMET prediction. The results indicated that diallyl trisulfide (44.21%) is the major component of the EO, followed by diallyl disulfide (22.08%), allyl methyl trisulfide (9.72%), 2-vinyl-4H-1,3-dithiine (4.78%), and α-bisabolol (3.32%). Furthermore, the EO showed antioxidant activity against DPPH radical (IC50 = 124.60 ± 2.3 µg/mL) and β-carotene bleaching (IC50 = 328.51 ± 2.0). The best docking score on NADPH oxidase corresponds to α-bisabolol (ΔG = −10.62 kcal/mol), followed by 5-methyl-1,2,3,4-tetrathiane (ΔG = −9.33 kcal/mol). Additionally, the volatile components could be linked to the observed antioxidant activity, leading to potential inhibitors of NADPH oxidase.

Study on Gas Chromatographic Fingerprint of Essential Oil from Stellera chamaejasme Flowers and Its Repellent Activities against Three Stored Product Insects.

The objective of this study was to establish the chromatographic fingerprints of the essential oil (EO) from Stellera chamaejasme flowers collected from various natural sites by gas chromatography (GC) combined with chemometric methods. The EO was obtained by hydrodistillation, and its chemical composition was analyzed by gas chromatography−mass spectrometry (GC−MS). Most components were identified as ketones and the relatively high-content components were fitone (38.973%), n-hentriacontane (5.807%), myristic acid (4.944%) and phytol (3.988%). In addition, the repellent activities of the EO from S. chamaejasme flowers and its four main chemical compounds were evaluated against three stored product pests (Tribolium castaneum, Lasioderma serricorne, Liposcelis bostrychophila) for the first time. In this work, the EO and the four chemical compounds showed a repellent effect against three storage pests after 2 and 4 h exposure. The experimental method and repellent activity of S. chamaejasme flower EO could provide a basis for the development of botanical pesticide and the utilization of the rich plant resources of S. chamaejasme in the future.

Parent and alkylated PAHs profiles in 11 petroleum fuels and lubricants: Application for oil spill accidents in the environment

Eleven types of petroleum fuels and lubricants including regular gasoline, premium gasoline, jet fuel, kerosene, light oil, bunker A, bunker A–white, bunker A–low sulfur, bunker C, quench oil and lubricant samples were analyzed for parent and alkylated polycyclic aromatic hydrocarbons (PAHs). Naphthalene was the predominant compound in gasolines, jet fuel and kerosene, constituting > 95% of the parent PAHs, whereas dibenzothiophene and other high molecular weight PAHs were predominant in bunker A and bunker C. PAH compositions in petroleum fuels differ because of differences in their refining temperatures and the boiling points of individual PAHs. Principal component analysis classified into four groups of petroleum fuels. Further, oil samples were clearly separated into five groups based on their ratios of select alkyl homologs (C0/(C0+C1) and C4/(C2+C4) naphthalenes): ‘gasolines’ ‘light oil’ ‘bunker oils’ ‘kerosene’ and ‘quench oil’. A wide variety and detailed profiles of PAHs in petroleum fuels and lubricants in this study can be used for baseline data in oil fingerprinting analyses to identify the potential source of oil spill accidents in the environment.

Chemical Fingerprinting of the Geranium (Pelargonium graveolens) Essential Oil by Using FTIR, Raman and GC-MS Techniques

Geranium oil is known as a floral substitute of rose essential oil with its pungent rose-like odor and is one of the most valuable essential oils. Favorable quality properties make the geranium essential oil exigible for food industry applications. This study determined the chemical fingerprint of geranium essential oil using robust vibrational spectroscopy techniques (Fourier transform infrared spectroscopy and Raman spectroscopy). The mid-infrared characterization was accomplished on the basis of functional chemical groups of geranium essential oil. GC-MS (gas chromatography-mass spectroscopy) technique was used for the detection and quantification of the volatile constituents of geranium essential oil. 37 (thirty-seven) volatile compounds were determined by the GC-MS analysis. The most abundant compounds were determined as Citronellol (30.68 %), Geraniol (9.68%) and Citronelly formate (9.90%).

Evolution of the sources contribution of aliphatic hydrocarbons and their fate in Sepetiba Bay, Rio De Janeiro, Brazil

Sepetiba Bay basin hosts industrial and harbors since the 1950s. Despite this impact history, hydrocarbon levels and sources were evaluated only in the 2000s and 2010s. Therefore, this study aimed to assess the evolution of aliphatic hydrocarbon sources and their fate in Sepetiaba Bay sediments after a significant increase in population, industries, and cargo handling. Surface sediment was predominantly composed of sand and showed a significant difference between TOC (0.20–3.45%) and total n-alkanes concentrations (0.01–3.31 μg g−1) among internal and external sectors of the bay (Mann-Whitney's U test, p < 0.05; n = 26). The n-alkanes concentrations indicate unpolluted sediments and remain in the same order of magnitude of two decades ago. The diagnostic ratios based on major hydrocarbon, isoprenoids, odd/even n-alkanes, and unresolved complex mixture indicate a mixture of allochthonous and autochthonous sources at almost all stations. Even if an oil fingerprint between the internal sector and the harbor area were observed, further studies are required to be sure.