The distribution of polyaromatic hydrocarbons (PAHs) at different georeferenced sampling points: Nwata A, Nwata B, Nwata 3’, Ochani and Eyeyaro in one of the most contaminated mangrove swamp in Nigeria, Ejamah-Ebubu oil spill site was studied. The physico-chemical analysis of the sediment samples and trace metals were also conducted. PAHs were analyzed using gas-chroma-tography flame ionization detection while metals with atomic absorption spectrophotometry (AAS). The result showed that the total PAHs (summation of 16 US EPA priority PAHs) were present at all sampling points and the concentration ranged from 0.070 to 5.521 ppm with Nwatu A > Nwatu B > Ochani > Egeyaro > Nwatu 3’. The pH of the site is acidic. The concentration of trace metals for most sampling points is iron > chromium > lead > nickel > vanadium. Our result indicates that the concentration of PAHs is at level higher than the permitted level therefore; it is recommended that Ejamah-Ebubu oil spill site be remediated.
Polycyclic aromatic hydrocarbon (PAH) is a common term for high molecular aromatic hydrocarbons. PAHs constitute a class of hazardous organic chemicals consisting of two or more fused benzene rings in linear, angular, or cluster arrangements [
The carcinogenicity of PAHs has been known since the 1930s. But it was not until the 1970s that an understanding of the mechanisms of carcinogenesis by PAHs emerged [
PAHs behave alike in soil or water. They are not easily degraded by microorganisms. Polycyclic aromatic hydrocarbons provide more detailed compositional data that can be used to identify both the source and extent of degradation of released crude oil [
The objectives of our study were i) to estimate the level of PAHs in a historic contaminated site of more than 40 years; ii) to establish a georeferenced distribution of molecular pollutants in a typical Niger Delta wetland; iii) to determine physico-chemical parameters and trace metals present at the site.
Sediment sample was collected by stratified sampling method at depths 20 cm and 40 cm, from Egbara Stream (Ewenta Egbara) in Eleme, Rivers State, Nigeria. Egbara Stream is a swampy wetland and its choice was informed by the heavy crude oil it received from a damaged Trans Niger pipeline belonging to Shell Petroleum Development Company (SPDC) Limited more than 50 years ago. The location of sampling points was marked using global positioning system. (Model GPSMAP76, Am, serial no: 91090835). The GPS reading of the sampling points are: Egeyaro (A) (N04˚45'23.8''E 007˚09'47.0''), Ochani (B) (N04˚46'19.9''E 007˚09'33.5''), Nwatu A (C1) (N04˚46'22.4''E 007˚08'49.8'') Nwatu B (C2) (N04˚46'22.2''E 007˚08'51.6'') Nwatu 3’ (C3) (N04˚46' 23.9''E 007˚09'07.0''). Analyzed samples would indicate the distribution of molecules of potential concern (MOPC)-polyaromatichydracarbons-with time (
Nitrate was estimated using the Brucine method as described by Allen et al. [
Calculation
where C = mg
Phosphate was determined using the ascorbic acid method as determined in the standard methods for examina-
tion of water and waste water, APHA [
Calculation
where C = mg
The method used for the determination of sulphate was the turbidometric method adopted from APHA [
Calculation
where C = mg
Atomic absorption (using Buck Scientific Atomic Absorption Spectrometer 205A) has been found to be a satisfactory technique for the determination of metals in samples. About 2 g of the sample was digested with 2 ml conc. H2SO4 and diluted to 30 ml. The 248.3 nm wavelength was selected and air and gas flows were adjusted. A calibration curve was prepared from the standard range by setting the top standard to suitable scale deflection and 0 ppm standard. The calibration was used to obtain the ppm of the metal of choice in the sample solution.
Calculation
The pH of the sediment was measured using a pH meter (Jenway 015 model) while the conductivity was measured using the conductivity meter (SC-300).
Gas chromatographic analysis was done to determine the level of specific crude oil components in the samples before and after treatment. It was also to determine the extent of crude oil disappearance resulting from either biodegradation or other physical/chemical weathering processes. One way of distinguishing one from the other is by evaluating the ratios of target hydrocarbon concentration of the biomarkers pristine and phytane.
Gas chromatographic analysis was performed using Unican Pro GC. Crude oil was extracted from the sediment using dichloromethane as extracting solvent. The column length was 30 m with an ID of 0.25 mm. The initial and final column temperatures were 60˚C and 300˚C respectively with 20 minutes and 28 minutes as initial and upper times, respectively. Injector temperature was 300˚C and detector temperature was 350˚C with helium as carrier gas at 15 psi. Hydrogen was used as fuel at psi and compressed air as oxidant at 25 psi.
Analysis of Variance (ANOVA) was applied to test if there is significant difference between means of various tested parameters
The result of the analysis of physico-chemical properties and the metal content of the sediment sample are contained in
The Nitrate concentration of sampling points ranges from 4.2 - 8.9 (ppm). Nwata A has a higher nitrate concentration than Nwata B 4.2 ppm. Nwatu3’ have the highest value of 8.9 ppm The Phosphate level of the sampling point ranges from 38.63 - 53.80 (ppm). Nwata A recorded a higher phosphate concentration 41.6 ppm than Nwatu B while Nwatu3’ have the highest value 53.80 ppm.
The sulphate level of the sampling point ranges from 20 ppm - 75 ppm. Nwatu A recorded a higher sulphate level 32 ppm than Nwatu B 20 ppm. Ochani recorded the highest level.The Nitrate, phosphate and sulphate salts
Parameter | Nwata A | Nwata B | Nwata 3’ | Egeyaro | Ochani |
---|---|---|---|---|---|
pH | 4.54 ± 0.07 | 3.45 ± 0.08 | 5.34 ± 0.07 | 4.26 ± 0.14 | 3.46 ± 0.05 |
Cond (us/cm) | 12 ± 2 | 20 ± 2 | 250 ± 2 | 158 ± 2 | 150 ± 2 |
5.27 ± 0.1 | 4.20 ± 0.3 | 8.90 ± 0.2 | 4.97 ± 0.2 | 5.67 ± 0.2 | |
PO4 (ppm) | 41.60 ± 0.7 | 39.19 ± 0.4 | 53.80 ± 0.9 | 45.70 ± 0.9 | 38.63 ± 1.4 |
SO4 (ppm) | 32 ± 2 | 20 ± 2 | 38 ± 2 | 54 ± 2 | 75 ± 1 |
TPH (ppm) | 9892.2 ± 9.7 | 7578.46 ± 6.8 | 98.04 ± 0.4 | 312.17 ± 2.0 | 1165.3 ± 1.2 |
PAH (ppm) | 5.521 ± 0.01 | 4.155 ± 0.01 | 0.070 ± 0.002 | 0.131 ± 0.002 | 0.768 ± 0.003 |
are present at all sampling points. When a major oil spill occurs, the supply of carbon is dramatically increased and the availability of nitrogen and phosphorus generally becomes the limiting factor for oil degradation [
The phosphate concentration is moderate since 30 mg of phosphate is required to convert 1 g of hydrocarbon. Phosphate is limiting at Nwatu A and Nwatu B sampling points due to the high amount of TPH at these points, Nwatu A {9892.2 (ppm)} and Nwatu B {7578.46 (ppm)}. At Nwatu 3’, Egeyaro and Ochani sampling points phosphate is not limiting, as evidence in the result (
The presence of sulphate at the various sampling points (
The TPH concentration of the sampling point ranges from 98.04 ppm to 9,892.20 ppm with Nwata A recorded the highest value. The PAH concentration ranges from 0.070 ppm - 5.291 ppm with Nwatu A recorded the highest value. The concentration of polyaromatic hydrocarbons (PAHs) in the sediment from various sampling points of Ejamah Ebubu oil spill contaminated site at 0.05 (95%) level of confidence indicates significant difference between means of various sampling points Nwata A (N04˚46'22.4'' E 007˚08'49.8'') and Nwata B (N04˚46'22.2''E 007 08'51.6'') (
About 13 (81.25%) of the 16EPA PAHs were detected at all the sampling points (chromatogram not showed). Napthalene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, benzo (a)anthracene, chrysene, benzo (b)fluoranthene, benzo (a)pyrene, dibenz (a, h,) anthracene, indeno (1,2, 3-cd)pyrene and indeno (1, 2, 3)pyrene which is not a “16 EPA PAHs” showing that the environment is among the area labeled as contaminated sites. Benzo@anthracene, chrysene, benezo (b)fluoranthene, benezo (a)pyrene, Indeno (1, 2, 3) pyrene, dibenz (a, h) anthracene and indeno (1, 2, 3-cd) which are suspected as carcinogens and mutagens [
The fingerprints showed the level of high-molecular-weight (HMW) PAHs detected at various sampling points are higher than low-molecular-weight (LMW) PAHs (chromatogram not showed) indicating greater percentage of combustion-related PAHs (pyrogenic sources) than petroleum products [
The distribution of the n-alkane components of the analyzed sample presented in
The presence of n-C8?C40 and the isopreniods at the various sampling points after the spill of greater than forty years shows the state of the contamination; the isoprenoids which are used as biomarkers for evaluation of biodegradation [
The chromatograms indicate high concentrations of n-C10, n-C11, n-C14, n-C15, n-C16, n-C17, n-C17, n-C18, n-C19, n-C20, n-C21, n-C22, n-C25, n-C28, n-C29, and n-C30 for sampling point Nwata A. Nwata B had n-C10,, n-C14, n-C15, n-C16, n-C17, n-C17, n-C18, n-C19, n-C20, n-C21, and n-C27.
Iron concentration of the various sampling point is very high. Values range from 363.75 ppm to 2112.8 ppm with Nwata 3’ recorded the highest value. Nickel concentration of the sampling point is Ochani > Egegaro > Nwatu 3’ > Nwata A > Nwata B. Chromium concentration is Nwatu 3’ > Nwata B > Egegaro > Ochani > Nwata A.Vanadium concentration is Ochani > Egeyaro > Nwata 3’ > Nwata A > Nwata B. Lead concentration of the various sampling points range from 163 ppm-10.87 ppm. Nwatu A has a higher value than Nwata B. Egeyaro recorded the highest value of 10.87ppm. Trace metal such as iron, nickel, chromium, vanadium and lead are detected at all sampling points, the content of all trace metal increase down the stream. The iron content is very high. At the onset of anaerobic condition in most freshwater sediment, Fe (III) is the most abundant potential electron acceptor for organic matter oxidation [
The vanadium/nickel ratio at various sampling points (
One of the major prerequisites for the decontamination of crude oil contaminated sites is the knowledge of the
Sampling point | Concentration Fe | In ppm Cr | Pb | V | Ni | V/Ni |
---|---|---|---|---|---|---|
NwataA | 363.37 ± 4.7 | 2.18 ± 0.03 | 1.75 ± 0.04 | 0.08 ± 0.02 | 1.19 ± 0.02 | 0.07 |
NwataB | 857.2 ± 9.6 | 4.2 ± 0.03 | 1.68 ± 0.03 | 0.06 ± 0.01 | 1.1 ± 0.02 | 0.05 |
Nwata3’ | 2112.8 ± 6.4 | 8.74 ± 0.14 | 5.85 ± 0.08 | 0.13 ± 0.01 | 2.02 ± 0.01 | 0.06 |
Egeyaro | 948.27 ± 6.9 | 4.23 ± 0.08 | 10.87 ± 0.04 | 0.14 ± 0.01 | 2.08 ± 0.02 | 0.07 |
Ochani | 989.17 ± 9.6 | 3.73 ± 0.05 | 3.68 ± 0.03 | 0.16 ± 0.01 | 2.21 ± 0.02 | 0.04 |
true situation or fate of hydrocarbon at the sites. Ejamah-Ebubu spill site over 40 years showed an array of distributions of polyaromatic and n-alkane hydrocarbons. Generally, there was a predominance of four - six ring polyaromatic hydrocarbons (PAHs) over the two - three ring PAHs.
Pyrene, benezo (k) fluranthene, and benezo (g, h, i) perylene are not present. There is the presence of PAHs that are classified as probably/possibly carcinogenic. The concentration of PAHs decreases down the river as one approach the Bonny River.
The n-alkane hydrocarbons (TPH) are above the EGASPIN DPR limit. The isoprenoid ratio pristane/phytane is high, even after over 40 years of oil spillage.
Remediation by enhance natural attenuation (RENA) had been suggested to be applied on the site but deep into the soil, oxygen becomes limiting. Under such conditions, anoxic or anaerobic degradation mediated by denitrifying or sulphate-reducing bacteria can become a key pathway for the cleanup of contaminated sites. The understanding of anaerobic biodegradation of aromatic compounds has increased over the past decade. Isolation of denitrifying and sulphate-reducing organisms capable of degrading toluene has led to the elucidation of several biodegradation pathways and phylogenetic relationships among bacteria strains. The type and concentration of TEAs available in a contaminated environment will affect the outcome of natural attenuation or bioremediation. Common indigenous TEAs in Ejamah-Ebubu oil spill site include nitrate, sulphate and iron.
This work was supported by OWSDW grant 2010 fund reservation No. 324021348 and PTDF postgraduate local scholarship PTDF/TR/LS/PhD/AON/215/09.
The cooperation of Ejamah Ebubu community during field sampling is hereby greatly appreciated and acknowledged. GC-FID and AAS were obtained from ANAL Concept Ltd Port Harcourt.
Onyinyechi N. Akomah,Gideon O. Abu, (2015) Distribution of Polycyclic Aromatic Hydrocarbons (PAHs) and Trace Metals in Ejamah-Ebubu Oil Spill Site. Open Access Library Journal,02,1-8. doi: 10.4236/oalib.1101642