Characterisation of Polycyclic Aromatic Hydrocarbons in Mangrove Sediments of Ifiekporo Creek, Warri South Local Government Area, Delta State, Nigeria.

doi:10.21203/rs.3.rs-3462992/v1

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Characterisation of Polycyclic Aromatic Hydrocarbons in Mangrove Sediments of Ifiekporo Creek, Warri South Local Government Area, Delta State, Nigeria.

https://doi.org/10.21203/rs.3.rs-3462992/v1

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The occurrence and level of polycyclic aromatic hydrocarbons (PAHs) in the mangrove sediment of the Ifiekporo community in Warri South Local Government Area of Delta State were assessed in this study. A total of 10 sediment samples were collected from 10 sites along the Ifiekporo Creek. The extraction of PAHs from the sediment samples was achieved using the PAHs Analytical Test Method (USEPA 8270). This method measures individual concentrations of extractable PAHs in samples. The aliphatic and poly-aromatic hydrocarbons were quantified within C₁₁-C₂₂. The basic GC parameters for the analysis of polyaromatic hydrocarbons were analyzed using the Gas Chromatograph-Mass Selective Detector (GC-MSD). The individual PAH concentration in mangrove sediment samples varies from Not Detected (ND) to 3.47 µg/kg. The PAHs concentration of 3.47 µg/kg was highest in sampling point 5 across the sampling points. The PAH source apportionment employing isomeric ratios and multivariate statistics indicated both pyrogenic and petrogenic source inputs in sediment samples. The PAHs homologous distribution sequence for sediment is 3-ring > 2-ring > 1-ring > 6-ring. The sediment samples are mostly dominated by LMW PAHs. The result of the ecological risk assessment in the study area indicates that there is low ecological risk associated with PAH exposures in sediment. These results provide data on the concentrations and compositional patterns of PAHs, which is useful in understanding the effects, sources, fate, and transport of PAHs in sediment in the study area, as well as providing relevant information for environmental quality management and forensic studies.

Polycyclic Aromatic Hydrocarbons (PAHs)

Sediment

Ecological risk

Mangrove sediment

Distribution

The onset of industrial revolution in the mid-19th century brought about a major upset in the global biogeochemical cycle which significantly altered the sequences of ecosystems interactions in the biosphere (Raimi et al., 2021). As the world grew industrially, pollution of the atmosphere, surface water, soil and sediments progressively became a major global problem. These problems stems for the rise in anthropogenic activities characterized by increase in chemical use in agricultural practices, exploration and exploitation of fossil fuel, combustion of hydrocarbons and increase in waste generation occasioned by rise in human population (Kabir et al., 2023).

Polycyclic aromatic hydrocarbons (PAHs) are semi-volatile persistent organic compound that are ever-present in any ecological biota (Balmer et al., 2019). They are among the range of environmental pollutants that are resistant to degradation and can remain in the environment for a long period; they owe their persistency to their high degree of conjugation and aromaticity (Patel et al, 2020). PAHs are large groups of over 100 organic compounds that are made up of two or more fused benzene rings that consist of carbon and hydrogen atoms only in their molecules (Abdulazeez,& Fantke, 2017). These rings are arranged in linear, cluster or angular forms. PAHs are hydrophobic, with aqueous solubility decreasing almost linearly as molecular mass increases (Patel et al, 2020). PAHs are generally formed when incomplete combustion occurs with high temperature pyrolysis of combustible substances (Zhang et al., 2020). PAHs are ubiquitous environmental pollutants (Abdel-shafy & Manseur, 2016). Sometimes, PAHs exists as alkylated or substituted derivatives, and they can exist in many isomeric forms (Gurjar, et al., 2010). However, the most commonly occurring ones do not carry branching substituents on their rings (Wenzl, et al., 2006).

PAHs could originate or be derived from three main sources in the environment: fossil fuels (petrogenic PAH), burning of organic matter (pyrogenic PAH), and conversion of natural organic precursors in the environment by relatively rapid chemical/biological processes (biogenic PAH (Neff, et al., 2005). Petrogenic PAHs are introduced into the aquatic environment through accidental oil spills, discharge from routine tanker operations, municipal and urban runoff, etc (Baakhtiari, et al., (2005). Crude oil is a complex mixture of different organic compounds formed during different geological ages and under different geological conditions. The different depositional environments during oil formation are reflected in different PAH distributions (e.g., dibenzothiophenes: Dn) in crudes from different sources (Wang and Fingas, 2003). Pyrogenic PAHs are released in the form of by-product of combustion and solid residues, and are largely prevalent in aquatic environments (Zaakaria, et al., 2002; De Luca, et al., 2004).

In a number of areas, petrogenic PAHs appears to be much more than pyrogenic ones (Guo, et al., 2007). PAHs with High Molecular Weight which are mainly of pyrolytic origin reach aquatic biota through direct atmospheric deposition or via contaminated soil (Budzinski et al., 1997; Morillo et al., 2007).. Whereas Low Molecular Weight pyrogenic PAHs are mainly introduced to the environments by rain washout (Hussain et al., 2019). PAHs containing (2–4) planar rings are termed light or low-molecular-weight (LMW) PAHs while those containing more than four (4) planar rings are termed heavy or high molecular weight (HMW) PAHs (Hamidi et al., 2015). HMW (PAHs with 4 or more rings) have high resonance energies due to their dense clouds of π electrons surrounding the aromatic rings; making them persistent and recalcitrant to microbial degradation (Johnsen, et al., 2005). Low aqueous solubility and high soil sorption also contribute to their persistence and recalcitrance (Parrish, Banks, & Schwab, 2004). PAHs that are of heavy configuration are stable and exhibit more toxicity, whereas the light PAHs are more unstable, exhibit solubility and volatility that is high in aqueous medium and are less lipophilic (Hamidi, et al., 2015).

United States Environmental Protection Agency (US EPA) has only identified sixteen PAHs as 'priority pollutants' although there are hundreds of PAH compounds, which could be included for risk assessment (Barron & Holder, 2003, Hamidi, et al., 2015). These priority PAHs include; naphthalene (Nap), acenaphthylene (Acy), Acenaphthene (Ace), fluorine (Flu), phenanthrene (Phe), Pyrene (Pyr), anthracene (Ant), Fluoranthene (Flt), benzo(a)anthracene (BaA), Chrysene (Chy), benzo(b)fluoranthene, benzo(k)fluoranthene (BkF), benzo(a)pyrene (BaP), Indeno (1,2,3,-cd) perylene (IndP), dibenzo(a,h) anthracene (DahA) and benzo(g,h,i)perylene (BghiP) (Ossai et al. 2015). Of the 16 priority PAHs identified by USEPA, the International Agency for Research on Cancer (IARC) further classified benzo(a)pyrene as group 1A (carcinogenic to humans), dibenzo(a,h)anthracene (probably carcinogenic to humans) and benzo(a) anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene, chrysene and Indeno(1,2,3-cd) perylene as group 3B (possibly carcinogenic to humans) while other PAHs not listed are classified as not carcinogenic to humans (Ossai, et al., 2015).

According to the World Bank (1995), Nigeria's mangrove ecosystem is the third-largest in the world and covers roughly 975,000 km² of the low-lying area that borders the coastal wetlands of southern Nigeria, stretching from Bakassi in the east to Badagry in the west. The mangroves of the Niger Delta are a broad confluence of the wetlands with a web of creeks and rivers, which results in a significant inflow of nutrients and organic waste. This is where the ecosystem achieves its maximum extent. This abundant nutritional foundation is used by primary producers to boost biomass. Mangrove forests provide many ecosystem services, such as littoral protection, species habitat, and contaminant and sediment filtering (Lee et al., 2014). As a result of the high primary productivity, high levels of organic compounds, abundance of detritus, low energy and reduced current flow, and anoxic and sub-oxic conditions that characterize mangrove ecosystems, they are favorable environments for the preservation, accumulation, and significant uptake of PAHs (Oyo-Ita et al., 2013).

Fish, birds, reptiles, and mammals all use mangroves as breeding and growth grounds; they also serve as littoral protection, species habitat and contaminate, and sediment filtering (de Souza et al., 2008; Lee et al., 2014; Aghomi, 2019; Eriegha and Sam, 2020). According to Ke et al. (2005), there are "hot spots" of contamination even in relatively unpolluted swamps, indicating that the level of PAH contamination appears to vary greatly among mangrove sediments. It is against this backdrop that this study seeks to investigate the incidence and level Polycyclic Aromatic Hydrocarbons in Mangrove Sediments of Ifiekporo Community, Warri South Local Government Area, Delta State, Nigeria.

2.1 The Study Area

The study was carried out in Ifiekporo creek in Warri, Warri South Local Government Area of Delta State in Southern Nigeria. Ifiekporo community shares landmass with Ijala Community and its water bounders the Warri River to the South. It is often referred to as “that community behind Warri Refinery”. It plays host to the Warri Refining Petrochemical Company (WRPC) jetty and several Petroleum Tank Farms and Depots such as Matrix Energy Tank Farm, A& E Petroleum, AYM Shaffa Tank Farm, Taurus Oil and Gas Depot and Optima Energy Resources Depot. It is defined by latitudes 5°34'23.3"N and longitudes 5°41'14.5"E. (Fig. 1).

2.2 Materials/Reagents

PAHs Analytical Test Method: USEPA 8270 was used for the analysis of the samples. This method measures individual and total concentrations of extractable PAHs in samples. The aliphatic and poly-aromatic hydrocarbons are quantified within C₁₁-C₂₂. The basic GC parameters for the analysis of Polyaromatic hydrocarbons are as follows; Agilent 6890 5973N Gas Chromatograph-Mass Selective Detector (GC-MSD).

Agilent 6890 gas chromatography and Agilent 5973N Mass Selective Detector (GCMSD) manufactured by Agilent Technology, Palo, Alto CA, USA manufactured by Agilent Technology, Palo, Alto CA, USA, were used for this study. PAH reference mix standard (2000 ppm) containing 17 component PAHs obtained from Accu Standard Inc, New Haven, USA. Silica gel 60–120 mesh, Acetone obtained from BDH laboratories, and Dichloromethane, DCM (99% analytical grade) obtained from Fisher scientific (Loughborough, UK) used for this study.

Ten (10) sediment samples were collected using the grab method of sampling from ten designated sampling location inclusive of control point all within the study area in Delta State. Samples were kept in clean glass bottle prior to transfer to Jacio Environmental Limited laboratory located in Warri, Delta State.

2.2.1 Sample Collection

A total of 9 selected sampling points/sites sediments were identified along the Ifiekporo Creek in Warri South West Local Government Area of Delta State, Nigeria and one control sampling point/site for sediment were collected at the Okpe Local Government Area of Delta State, Nigeria axis of the Agbarho River, Delta State. Each sampling point/site produce surface water and sediments samples respectively. At every sampling location or point, sediment (depth of 0–15cm) samples were collected with the aid of soil sampler. The samples were collected in Ziploc plastic bags and then transported to Jacio Environmental Limited, Warri, Delta State, Nigeria for analysis.

2.2.2 Sample Preparation

Prior to extraction, glass fractionating column were packed with chromatograph glass wool 10, grams of silica gel was activated by oven-drying over-night at 105^oC. Dichloromethane (DCM) was added to the silica gel (1:1 v/v) and the mixture mixed to form slurry and the slurry was transferred to the column. 5 gram of anhydrous Sodium Sulphate (Na₂SO₄) was added to the fractionating glass column to absorb water and this was conditioned with 10ml of DCM prior to cleanup process.

2.2.3 Extraction and Clean-up of PAHs in Sediments

Water layer on sediment sample was decanted, while foreign objects such as sticks, leaves, and stones in the SED samples were discarded. The SEDs were mixed thoroughly for uniformity prior to extraction process. The extraction was carried out as recommended by USEPA 3550C method (USEPA, 2007).

The extracted samples were cleaned-up by passing them through individual silica gel column prepared by loading 20g of glass wool and 10g of activated silica gel onto a fractionating glass column (1cm internal diameter) to about 15cm. This was topped with 2cm of anhydrous Na₂SO₄. It was then conditioned with 10ml of dichloromethane. 2 ml of the concentrated extract was loaded and eluted with 10ml of dichloromethane. This method is able to remove the polar lipids and fats off the extract.

The eluate was collected in a solvent rinsed 100ml conical flask. The eluate was transferd to a round bottom flask and concentrated to 1ml final volume using a rotary evaporator. The concentrate was pipetted into a clean 2ml Teflon screw-cap vial and cap tightly, labelled and preserved to avoid oxidation prior to analysis with GC-MSD.

2.3 GC-MS Analysis

An Agilent 6890 gas chromatograph with auto sampler was utilized in conjunction with an Agilent 5973N mass selective detector. 1µl of sample solution was injected in the pulsed spiltless mode onto a 30m x 0.25mm META X5 coated fused capillary column with a film thickness of 0.25µm. The carrier gas used was Helium, while the column head pressure was retained at 13 psi to ensure constant flow of 1.0 ml/min. Other operating conditions were pre-set, purge time 2.00 mins, purge flow 20.0 ml/min, total flow of 23.7 ml/min, and injection temperatures 250^oC. The column temperature was initially held at 70^oC for 2mins, increased to a final temperature of 300^oC at a rate of 12^oC/min and held for 8 mins. The mass spectrometer (MS) condition was electron impact positive ion mode. The PAHs identification time was based on retention time since each of the PAHs has its separate retention time in the column. Those with lower retention times were identified first followed by those with longer retention time.

2.3.1 Preparation of PAH standard solutions

Five calibration standard solutions containing the 17 target compounds were prepared by diluting 0.5µl, 1.0 µl, 1.5µl, 2.0µl and 2.5µl of 2000ppm of standard PAH Mix with 1000µl of dichloromethane to give 1ppm, 2ppm, 3ppm, 4ppm and 5ppm respectively.

2.3.2 Quantification of Result

Agilent Technologies Inc MSD Chemstation G1701DA D.03.00.611 software was used in quantifying Aromatic component results in ppm (part per million), a suite of 17 priority polycyclic aromatic hydrocarbons recommended by EPA (Accu-standard, 17 PAHs) (Accu-standard); was used.

2.3.3 Quality Control/Assurance and Statistical Analysis

Quality control was assured by the use of spike recovery method. A known concentration of a standard PAH mixture was added to already analyzed samples and re-analyzed. Thereafter the percent recoveries were calculated. Also, all reagent that were used were analar grade reagents. Care was taken in handling of samples and containers to avoid cross contaminations.

2.4 Statistical analysis

Analysis of variance (ANOVA) was used to find out whether the PAHs concentrations varied significantly within and among sampling locations, with p-value less than 0.05 (p < 0.05) considered statistically significant. The statistical calculations were performed with SPSS version 19. Relationship between PAHs was established through the use of Principal component analysis and Pearson’s correlation coefficient was the tool used to measure the degree of correlation between the PAHs.

2.5 Source Identification

The PAHs isomeric ratios and its significance as compiled by Yunker, et al (2002) were adopted as a tool to identify the PAHs sources. The isomeric ratios used include; BaA/(BaA + Chry), IndP/(IndP + BghiP), Ant/(Ant + Phen), Flt/(Flt + Pyr), LMW/HMW, COMB PAHs/TPAHs, BaP/BghiP, PAH(4)/PAH(5 + 6) and Total Index.

3.1 Results

Table I shows the PAH concentrations found in sediment samples, whereas Table II shows the summary statistics of PAHs concentrations (ppm) in sediment. The sediment samples revealed a total of 10 PAH compounds, including naphthalene, acenaphthylene acenaphthene, fluorene, phenanthrene, anthracene, benzo(a)pyrene, pyrene, fluoranthene and chrysene. Over the sampling locations, the concentration of PAHs varied from 0.81 g/kg to 3.47 g/kg. When compared to other point sampled, sampling point 5 showed the highest concentration of PAHs (3.47 g/kg). The PAHs source apportionment employing isomeric ratios and multivariate statistics indicated both pyrogenic and petrogenic sources inputs (such as burning of biomass, wood, charcoal, liquid fossil fuel, and crude oil) in sediment samples (Table III). The PAHs homologous distribution sequence for sediment reveal 3-ring > 2-ring > 1-ring > 6-ring (Fig. 3). The sediment samples are mostly dominated by LMW PAHs. Table 3 shows the result of PCA in the sediments. The result of the ecological risk assessment from the study area indicates that there is low ecological risk associated with PAHs exposures in sediment.

3.2 Discussion

Anthropogenic activities like industrialization, urbanization, population explosion and modernization has in obvious and unobvious ways affected the environment especially land, water, sediment and air. PAHs are widespread pollutants in the environment and their major sources are human activities, generated from partial combustion of carbon-based materials like fossil fuels, wood, emissions from engines, smoke from cooking, industrial activities and natural occurrences such as when volcanoes erupts (Ossai, et al., 2015; Abdel-shafy et al., 2016),

Concentrations of PAHs in Sediment

A summary of the U.S EPA 16 PAHs concentrations in sediment indicated Not Detected (ND) in some locations, however the range of PAHs concentrations for locations with detectable values varies 0.81 µg/kg to 3.47 µg/kg. The highest PAHs concentration of 3.47 µg/kg record in s in all sampling point 5. The concentration of PAHs in the samples is P > 0.05 suggesting spatial significant difference (Table 2). CV% was less than 100% while the F-calculated is less than the F-critical.

The PAHs concentrations in some sampling points could be linked to illegal bunkering, illegal artisanal refinery and industrial activities like oil exploration and production of crude oil which make the environment prone to PAHs pollution (Abdel-shafy et al., 2015). Also, natural sources cannot be ruled out Abdel-shafy et al., 2015, Ossai et al., 2015). The behaviour of PAHs ecological matrices was documented in a study done by (Cornelissen et al., 2006). How toxic PAHs are detected and their prevalent and widespread dispersal has contributed to more interest of these compounds in most ecological biota (Aderemi, et al., 2003). Comparing with other reported studies, it is lower than the PAHs concentration in surface water of the Almendares River, Cuba ranged between 836 to 15811µg/L (Santana et al., 2015); 570.2 to 2318.6 µg/L surface water of Daliao River (Guo, et al., 2008); 99.60 to 3805.00 and 235.84 to 11812.2 µg/L in dry and wet season respectively for surface water in Songhua River Basin, Yangtze River Basin, Yellow River Basin, Pearl River Basin, Huai River Basin, Liao River Basin and Hai River Basin (Yu, et al., 2020). Also lower, in sediment samples obtained in Hoor Al-Azim wetland, Iran (15.78 to 410.2 µg/L (Fakhradini, Moore, Keshavarzi, & Lahijanzadeh, 2019). Results of sediment from River Niger, Ase and Forcados in the western Niger Delta areas which fall under same region of this study revealed that PAHs concentration range between 2400 to 19000 µg/kg, 2930 to 16100 µg/kg and 1620 to 19800 µg/kg for River Niger, Ase and Forcados respectively (Iwegbue et al., 2021).

Composition and Distribution Patterns of PAHs in Sediment

Figure 1 shows the compositional patterns of PAHs in this study. The sediment samples are mostly dominated by LMW PAHs. The HMW PAHs ranges between 4–6 rings and LMW is between 2–3 ring PAHs. HMW PAHs ones settled are not prone to surface exchange due to their low vapour pressure and HMW PAHs exhibit more resistance to degradation. In contrast LMW PAHs since they have vapour pressures are associated to gaseous phase. While LMW PAHs are susceptible to weathering through oxidation, photo-degradation and losses by leaching owing to high water solubility (Iwegbue et al., 2021; Najmeddin et al., 2019., Marynowski et al., 2018). The PAHs homologous distribution sequence for surface water is 4-ring > 3-ring > 5-ring > 1-ring, therefore confirming the prevalence of BaA, Chr, Flt, Pyr, Ace, Acy, Flu, Ant, and Phen as the major components, and 3-ring > 2-ring > 1-ring > 6-ring for sediment revealing Acp, Acy, Flu, Ant, Phen and Nap also as the dominant components. This study reveals that 6-ring PAHs; BghiP and IndP are the most recessive components because they were below detection limits of Not Detected as 5-ring PAHs were only detected in surface water samples. The presence of Flu and Phen in sampling point 1, 2, 4 and 8 are also indicative of combustion sources in those sampling points (Wang et al., 2015; Zhang, 2006).

Source Apportionment/Diagnostic Ratio

Isomeric ratios and multivariable statistical analysis were carried out to determine the sources of PAHs in sediments samples. This tool is used to design control strategies and evaluating both ecological and human risks associated within the study area. From previous studies, isomeric ratios like Ant/(Ant + Phen), Flt/(Flt + Pyr), BaA/(BaA + Chry), IndP/(IndP + BghiP) BaP/BghiP and others LMW/HMW, ƩCOMB/TPAHs, PAH(4)+(5)/TPAHs have been employed for PAHs analysis of input sources and transport properties (Iwegbue et al., 2021; Iwegbue et al., 2019; Effiong et al., 2016). Fossil fuel combustion and petroleum product leakage, are pyrolytic and petrogenic sources of PAH, and are the principal sources of anthropogenic PAH. To differentiate between petrogenic and pyrogenic sources of PAHs, ratios of Phe/Ant and Flu/Pyr have been commonly used. Phe/Ant values > 10 are typically associated with polycyclic aromatic hydrocarbons of petrogenic origin, whereas low Phe/Ant ratios 10 are frequently produced during combustion processes. Values > 1 have been utilized to denote pyrolytic origins, while values 1 are assigned to petrogenic sources for the Fl/Py ratio. (Chen & Liao, 2006, Magi et al., 2002).

Though PAHs compositional may be used in some instances in distinguishing sources, it’s not the only ultimate tool because of some other limitations. LMW/HMW can also be used to differentiate emissions from pyrogenic source and petrogenic sources (Effiong, et al., 2016; Soclo, Garrigues, & Ewald, 2000). LMW/HMW ratio from this study in Ifiekporo Creek ranged between 0.00 to 3.08 and this revealed that most of the samples (94.4%) had LMW/HMW values less than < 1 while only 5.6% LMW/HMW > 1. Similar to previous studies, it strongly suggests prevalence of pyrogenic source over petrogenic source inputs. Ant/ (Ant + Phen) ratio ranged from 0.00 to 1.00 thus suggesting prevalent inputs from combustion sources. The BaA/(BaA + Chry) values in sediment of Ifiekporo Creek ranges between 0.00 to 0.75. Only 16.6% were > 0.5, thus suggesting dominance input from biomass combustion sources. (Flt/ (Flt + Pyr) were between 0.00 and 0.51. Flt/Flt + Pyr < 0.4 is an indication of petroleum source, values between 0.4 and 0.5 depict petroleum combustion sources (especially carbon-based fuel, fumes from outboard engines and crude oil), while ratio value > 0.5 depicts contribution from biomass combustion, coal, and wood sources. Values of > 0.5 indicates dominant contribution from biomass combustion sources, < 0.2 indicates petroleum related sources, values between 0.20 and 0.30 suggest sources related to combustion of liquid fossil fuels, while values > 0.35 relates to coal/biomass combustion sources (Yunker, 2002). Both IndP/ (IndP + BghiP) and BaP/BghiP were absent in the samples collected from this creek. This suggests further studies should be carried out in the studied areas for confirmation or clarity. Although, IndP/(IndP + BghiP) ratio between 0.2 and 0.5 is an indication of the existence of biomass and liquid fossil fuel combustion as major source of PAHs contaminations, BaP/BghiP from other studies has utilized to distinguish between vehiculars traffic and non-vehicular traffic sources. COMBPAHs/TPAHs ratios are indicative of relationship between PAHs input sources and combustion of typical organics (Iwegbue, 2021; Dong, & Lee, 2009). The ƩCOMB-PAHs/Ʃ16 PAHs value of < 0.3 is an indication of petrogenic emission; the range of between 0.3 and 0.7 portray mixed sources of emission or deposition; while ratio values of > 0.7 is usually suggestive of input from a burning process of high magnitude (Iwegbue, et al., 2019; Ravindra, Wauters, & Van Grieken, 2008). In this research, 33.3% in sediment samples were between 0.3 and 0.7 which suggests dominance of mixed sources while the rest were below equipment detecting limits. Finally, PAH (4)/PAH (5 + 6) used to provide details on transport features of the PAHs from some related studies was not shown in this studies. For example, high PAH(4)/PAH(5 + 6), value is an indication that the contamination is related to PAHs transported from quite a distance, while low value suggests inputs from local or nearby emission sources. (Iwegbue, et al., 2021)

Principal Component Analysis (PCA)

Principal component analysis (PCA) is an important tool for identification of the source of PAHs (Tables 2 and 3) and it is resolved into different components/factors loading. For sediments PCA carried out revealed 28.855% having positive loadings for Flu, BaA and Chry for factor 1. BaA and Chry are makers for coal, wood, natural gas combustion, gasoline emissions (Lin, et al., 2011; Larsen, & Baker, 2003; Simcik, Eisenreich, & Lioy, 1999; Duval, & Friedlander, 1981).

While Flu is a 3-ring PAHs which is characterized with low temperature combustion process such as burning of wood, grass and other biomass (Dong & Lee, 2009). Factor or component 2 accounted for 56.398% with positive loadings comprising Nap, Acy, Phen and Carb. Nap is 2-ring while Acy and Phen are 3-ring PAHs. Nap is an index for incomplete combustion processes (Zhang, 2006). Although Carb is not among the major or priority US EPA 16 PAHs, it is semi-volatile and Factor or component 3 constituted for 70.997%, having Ant, Flt and Pyr as the main positive loadings. Flt and Pyr are tracers for combustion of coals (Liu et al., 2017). Flt and Ant are indicators of oil combustion (Soltani, et al., 2015; Harrison, Smith, & Luhana, 1996). Finally, factor 4 constituted for 84.860% with only Ace and Flt.

In the present study, sediment samples contained both low- and high-molecular-weight PAHs. Total PAH levels in the sediment samples were below safe levels, indicating that at the time of the investigation, there may not have been any significant threats to the environment, human health or the aquatic life around Ifiekporo Creek. Given the large ratio of LMW PAHs to HMW PAHs, it is possible that the PAH pollution in the area of Ifiekporo is of natural origin. Total PAH levels in sediment samples showed moderately high levels. With low molecular weight PAHs predominating, the results of the ecological health risk study in this area indicate that there is low ecological risk associated with PAH exposures in sediments from Ifiekporo Creek.

Conflict of interest

There is no potential conflict of interest.

Acknowledgements

The authors thank the Tertiary Education Trust fund (TETFUND) that provided funds for this research and Nigeria Maritime University, Okerenkoko for the enabling environment for the study.

Data Availability Statement

The authors declare that the data supporting the findings of this study are available within the paper. Should any raw data files be needed in another format they are available from the corresponding author upon reasonable request.

Informed Consent

Not applicable, as the research does not involve human subjects

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Table I

Concentrations of the 16 priority PAHs in the sediment samples from Ifiekporo Creek

	S1	S2	S3	S4	S5	S6	S7	S8	S9	S10
Nap	0.04	0.19	1.26	ND	1.46	0.16	ND	0.05	0.49	0.23
Acy	0.12	0.30	ND	0.73	ND	0.08	1.12	0.35	1.01	ND
Ace	0.17	0.16	ND	0.22	ND	0.57	ND	0.37	ND	ND
Flu	0.11	ND	ND	ND	ND	ND	ND	ND	ND	ND
Phen	0.19	0.08	ND	ND	2.01	ND	ND	0.12	ND	ND
Ant	0.11	0.12	ND	0.21	ND	ND	ND	0.11	ND	ND
Flt	0.09	0.53	ND	ND	ND	ND	ND	1.23	ND	ND
Pyr	0.11	0.51	ND	ND	ND	ND	ND	ND	ND	ND
BaA	0.03	ND	ND	ND	ND	ND	ND	ND	ND	ND
Chry	0.01	ND	ND	ND	ND	ND	ND	ND	ND	ND
BbF	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
BkF	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
BaP	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
DahA	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
IndP	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
BghiP	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
Total	0.98	1.89	1.26	1.16	3.47	0.81	1.12	2.23	1.50	0.23
2 Rings	0.04	0.19	1.26	ND	1.46	0.16	ND	0.05	0.49	0.23
3 Rings	0.70	0.66	ND	1.16	2.01	0.65	1.12	0.95	1.01	ND
4 Rings	0.24	1.04	ND	ND	ND	ND	ND	1.23	ND	ND
5 Rings	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
6 Rings	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
7C	0.04	ND	ND	ND	ND	ND	ND	ND	ND	ND

Table II

Summary statistics of PAHs concentrations (ppm) in sediments samples from Ifiekporo Creek

	MEAN	SD	MEDIAN	MIN	MAX	CV%
Nap	0.406	0.564	0.16	ND	1.46	139
Acy	0.412	0.435	0.3	ND	1.12	105
Ace	0.166	0.199	0.16	ND	0.57	120
Flu	0.012	0.037	0	ND	0.11	300
Phen	0.267	0.657	0	ND	2.01	247
Ant	0.061	0.078	0	ND	0.21	128
Flt	0.206	0.422	0	ND	1.23	205
Pyr	0.069	0.169	0	ND	0.51	246
BaA	0.003	0.010	0	ND	0.03	300
Chry	0.001	0.003	0	ND	0.01	300
BbF	0	0	0	ND	ND	ND
BkF	0	0	0	ND	ND	ND
BaP	0	0	0	ND	ND	ND
DahA	0	0	0	ND	ND	ND
IndP	0	0	0	ND	ND	ND
BghiP	0	0	0	ND	ND	ND
Total	1.602	0.832	1.260	0.810	3.470	52
2 Rings	0.406	0.564	0.160	ND	1.460	139
3 Rings	0.918	0.540	0.950	ND	2.010	59
4 Rings	0.279	0.494	0	ND	1.230	177
5 Rings	0	0	0	ND	ND	ND
6 Rings	0	0	0	ND	ND	ND
7C	0.004	0.013	0	ND	0.040	300

Table III

Diagnostic ratios of PAHs in sediments

Matrices	Samples	BaA/ (BaA + Chry)	Ant/ (Ant + Phen)	Flt/(Flt + Pyr)	LMW/HMW	COMB PAHs/T PAHs	Total Index
Sediment	S1	0.75	0.37	0.45	3.08	0.24	8.54
	S2	0.00	0.60	0.51	0.82	0.55	7.27
	S3	0.00	0.00	0.00	0.00	0.00	0.00
	S4	0.00	1.00	0.00	0.00	0.00	10.00
	S5	0.00	0.00	0.00	0.00	0.00	0.00
	S6	0.00	0.00	0.00	0.00	0.00	0.00
	S7	0.00	0.00	0.00	0.00	0.00	0.00
	S8	0.00	0.48	0.00	0.81	0.55	4.78
	S9	0.00	0.00	0.00	0.00	0.00	0.00
	S10	0.00	0.00	0.00	0.00	0.00	0.00

Table IV

ANOVA of PAHs concentrations in sediment samples

Source of Variation	SS	Df	MS	F	P-value	F crit.
Between Groups	0.449671	8	0.056209	0.656692	0.728745	2.003251
Within Groups	12.32553	144	0.085594
Total	12.7752	152

Table V

Principal components analysis (PCA) of PAHs in sediment samples

	Component
	1	2	3	4
Nap	− .185	.874	− .263	− .200
Acy	− .290	− .679	− .099	− .574
Ace	− .001	− .327	.015	.908
Flu	.994	− .048	.055	.007
Phen	− .006	.867	− .054	− .076
Ant	.204	− .305	.658	.152
Carb	− .091	.914	− .144	− .200
Flt	− .188	− .103	.579	.502
Pyr	.057	− .010	.851	− .096
BaA	.994	− .048	.055	.007
Chry	.994	− .048	.055	.007
Variance %	28.855	27.542	14.599	13.864
Cumm %	28.855	56.398	70.997	84.860

No competing interests reported.

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Characterisation of Polycyclic Aromatic Hydrocarbons in Mangrove Sediments of Ifiekporo Creek, Warri South Local Government Area, Delta State, Nigeria.

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1.0 INTRODUCTION

2.0 MATERIALS AND METHODS

2.1 The Study Area

2.2 Materials/Reagents

2.2.1 Sample Collection

2.2.2 Sample Preparation

2.2.3 Extraction and Clean-up of PAHs in Sediments

2.3 GC-MS Analysis

2.3.1 Preparation of PAH standard solutions

2.3.2 Quantification of Result

2.3.3 Quality Control/Assurance and Statistical Analysis

2.4 Statistical analysis

2.5 Source Identification

3.0 RESULTS AND DISCUSSIONS

3.1 Results

3.2 Discussion

4.0 CONCLUSION

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References

Tables

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