Assessment of Polycyclic Aromatic Hydrocarbons Contamination Level on Soil in Umuahia, Abia State, Nigeria

solution — with an electrical conductivity of 1.413dS/m at 25°C — to obtain the cell constant, which was prepared by dissolving 0.746g KCl AR (previously dried at 105°C for 2hours) and making volume to 1l with CO2 free deionised water. The cell was thoroughly rinsed, and then the electrical conductivity of the 0.01M KCl was measured at the same temperature as the soil suspension. Furthermore, the conductivity cell was rinsed with the soil suspension and refilled without disturbing the settled soil. The resistance value indicated on the conductivity meter was then recorded and the electrical conductivity at 25°C measured as follows: Electrical Conductivity, EC25 (dS/m) in soil = K ÷ (S × 0.708) 1 Where: K = Measured resistance of KCl solution S = Measured resistance of suspension Converting from dS/m to μS/cm, we have: EC25 (μS/cm) in soil = EC25 (dS/m), in soil × 1000 2 This procedure was carried out for all the samples respectively, with the cell rinsed with deionised water between samples to avoid cross contamination. 3.3.3. Determination of Soil Organic Carbon and Organic Matter Content The determination of soil organic carbon content was based on the Walkley-Black chromic acid wet oxidation method, in accordance with Chaturvedi and Sankar (2006). Oxidisable matter in the soil is oxidised by 1N K2Cr2O7 solution. The reaction is assisted by the heat generated when two volumes of H2SO4 are mixed with one volume of the dichromate. The remaining dichromate is titrated with ferrous sulphate. The titre is inversely related to the amount of carbon present in the soil sample. Procedure: 1. A representative sample was taken from the oven-dried sample and ground with mortar to pass through a 0.5-mm sieve. 2. Soil samples were weighed out in duplicate and transferred into a dry 250-ml Erlenmeyer flask. 3. 10ml of 1N potassium dichromate (K2Cr2O7) solution was accurately added into each flask and swirled gently to disperse the soil in the solution. 4. 20ml of concentrated sulphuric acid (H2SO4) was rapidly introduced into the conical flask using an automatic pipette, directing the stream into the suspension. The flask was immediately swirled gently until the soil and reagents were mixed, and then swirled more vigorously for one minute. 5. A 200°C thermometer was inserted into the flask and heated on a hot plate for about 30minutes while swirling the flask and the contents until the temperature reached 150oC using a hot plate, after which the flask was allowed to cool slowly standing on a sheet of asbestos in a fume cupboard for about 30minutes. 6. 100ml of distilled water was added into the flask and shook to ensure even mixing after standing for 30minutes. 7. 3 to 4 drops of 0.025M ferroin indicator was added and the solution was titrated with 0.5N ferrous sulphate solution. As the end point was approached, the solution took on a greenish cast and then changed to a dark green. At this point, the ferrous sulphate was added drop-by-drop until the colour changed sharply from bluish-green to reddish-grey (maroon colour) in reflected light against a white background, indicating the end point. 8. The blank titration was made in the same manner, but without steps 4 - 6, to standardize the dichromate. From the equation: 2Cr2O72- + 3C + 16H+ → 4Cr3+ + 8H2O + 3CO2↑ 3 1ml of 1N dichromate solution is equivalent to 3mg of carbon. Where the quality and normality of the acid/dichromate mixture used are as stated in the procedure, the percentage carbon is determined from the following (Bartlett et al., 1994): % Organic Carbon in soil = 0.003g ×N ×10ml×(1 - T/S) ×100 = 3(1 - T/S) ODW 4 Where: N = Normality of K2Cr2O7 solution T = Volume of FeSO4 used in sample titration (ml) S = Volume of FeSO4 used in blank titration (ml) ODW = Oven-dry sample weight (g) The organic matter content of the soil and sediment samples was then determined by converting the SOC% of the samples to SOM% using a conversion factor of 1.72 (Chaturvedi and Sankar, 2006) as follows: % Organic Matter in soil = % Organic Carbon, in soil × 1.72 5 This procedure was carried out for all the soil and sediment samples respectively. 3.3.4. Determination of Total Nitrogen in soil For the determination of the total nitrogen content in soil, different methods can be used but the regular macro-Kjeldahl method (Bremner, 1996) was used in this research, which is in accordance with ISO 11261: Soil Quality – Determination of total nitrogen – modified Kjeldahl method. This method permits the available nitrogen to be precisely determined in the soil, which involves the digestion of the soil sample with a catalyst in hot, concentrated sulphuric acid, converting the organic N to NH4+. The NH4+ is recovered by distillation and estimated by titration; the amount of acid used in the titration is proportional to the N-NH4 present in the sample. The method was found to be accurate, reproducible and efficient. Procedure: Digestion A quantity of the sample was air-dried and ground to pass through a 0.5-mm sieve. Afterwards, 10g of the ground sample was weighed into a dry 500-ml macro-Kjeldahi flask. 20ml of distilled water was added and the flask was swirled for few minutes then allowed to stand for 30 minutes. 1 tablet of mercury catalyst and 10g of potassium sulphate (K2SO4) was added, and then 30ml of concentrated sulphuric acid (H2SO4) was also added through an automatic pipette. The flask was heated cautiously at low heat on the digestion stand. When the water had been removed and frothing had ceased, the heat was increased until the digest became clear. The mixture was then boiled for 5 hours — the heating was regulated during this boiling so that the H2SO4 condenses about half way up the neck of the flask. After which the flask was allowed to cool and about 100ml of water slowly added to the flask. Titration The digest was carefully transferred into another clean macro-Kjedahl flask (750ml). All sand particles in the original digestion flask were retained because sand could cause severe bumping during Kjeldahl distillation. The sand residue was washed with 50ml of distilled water four times and the aliquot transferred into the same flask. 50ml boric acid (H3BO3) indicator solution was added into a 500-ml Erlenmeyer flask which was then placed under the condenser of the distillation apparatus. The end of the condenser was about 4cm above the surface of the H3BO3 solution. The 750-ml Kjeldahl flask was attached to the distillation apparatus. About 150ml of 10N sodium hydroxide was poured through the distillation flask opening the funnel stopcock and then the commencement of distillation. The condenser was kept cool, below 30°C, allowing sufficient cold water to flow through and the heat regulated to minimize frothing and prevent suck-back. 150-ml distillate was collected and then distillation was stopped. The NH4-N in the distillate was determined by titrating with 0.01N standard hydrochloric acid using a 25-ml burette graduated at 0.1ml intervals. The end point was then reached with a color change from green to pink. At least two blank determinations were carried out in each series and the average blank titre value was used for subsequent calculations. The %N content in the soil sample was then calculated as follows: % Nitrogen in soil = (T – B)×N ×1400 S 6 Where: T = Sample titration (ml) B = Blank titration (ml) N = Normality of H2SO4 S = Sample weight (g) This procedure was also carried out for all the respective samples accordingly. 3.3.5. Determination of Cation Exchange Capacity of soil Cation exchange capacity is a calculated value that is an estimate of the soil’s ability to attract, retain and exchange cation elements. It can therefore be determined by summing up the concentrations of exchangeable ions and an estimate of exchangeable acidity (Al + H), which are extracted from soils using an appropriate extraction method. The determination of exchangeable ions in soil requires that ions on soil exchange sites be forced into a solution in which they can be effectively measured. Generally, this involves flooding the exchange sites on clay and organic matter surfaces of a soil with ions from an extractant, usually a strong salt solution. The extractant, now containing exchangeable soil ions in addition to ions from the added salt, is separated from soil by filtering or centrifugation and is then analyzed for the ions of interest which include Ca2+, Mg2+, K+ and Na+. Furthermore, the exchangeable acidity in soil can be determined using the titrimetric method, according to the routine methodology adapted from McLean (1965). Primarily, the exchangeable acidity (Al3+ + H+tit) is determined by titrating 25ml of potassium chloride extract with sodium hydroxide, using phenolphthalein as an indicator, until a pink colour is observed, indicating the endpoint (titration from colourless to pink). The CEC is thus effectively determined by summing up all the exchangeable base cations and the exchange acidity in the soil, as carried out in this thesis. Procedure: Determining the exchangeable base cations A test portion of the air-dried soil sample was ground to less than 2mm, after which 25g of soil was weighed and put into a 500-ml Erlenmeyer flask. 125ml of 1M NH4OH (concentrated ammonium hydroxide, 58%, Sp.gr. 0.90) was added to the soil and the flask was shook thoroughly on a mechanical shaker and allowed to stand for 16hours (or overnight). For each sample, a 7-cm Buchner funnel was prepared by fitting it with a 7-cm Whatman No. 42 retentive filter paper. The filter paper was moistened with a minimum amount of 1M ammonium acetate (NH4OAc) solution and the funnel was inserted into 250- ml suction flask. The vacuum pump was turned on to seat the moistened filter, and then the soil-NH4OAc mixture was stirred with a stirring rod and transferred into the filter fitted in the Buchner funnel. The soil was gently washed (leached) four to five times with 25ml additions of the NH4OAc, allowing each addition to filter through but not allowing the soil to crack or dry — the soil was covered with a 7-cm Whatman No. 1 filter paper to keep the soil moist between leachings. The leachate was transferred to a 250-ml volumetric flask, after which it was diluted and brought to volume with NH4OAc. Then the exchangeable bases Ca, Mg, K and Na were determined using an atomic absorption spectrophotometer and flame photometer. Determining the exchangeable acidity Extraction with 1N KCl Furthermore, 5g of the representative sample was weighed into a 50-ml centrifuge tube and 30ml of 1N potassium chloride was added to the sample in the tube. The tube was tightly covered with a rubber stopper and shook for an hour on a reciprocal shaker, after which the clear supernatant was decanted into a 100ml volumetric flask. Another 30ml of KCl was added to the same soil sample, shook for 30minutes and the clear supernatant transferred into the same volumetric flask. 30ml of KCl was added for the third time and again the clear supernatant was combined into the same volumetric flask. Then the volume was made up to mark with the KCl. Titration for H and Al 25ml of the KCl extract was put into a 250-ml Erlenmeyer flask using an automatic pipette and approximately 100ml of distilled water added to the flask. 5 drops of phenolphthalein indicator was added and the solution was titrated with 0.05N sodium hydroxide to a permanent pink end point; as such, the amount of base used is equivalent to the total amount of acidity (H + Al) in the aliquot taken. The CEC was then calculated as an estimate of the sum of exchangeable bases (Ca, Mg, K, and Na) and exchangeable acidity (Al + H) expressed in cmol/kg as follows: CEC (cmol/kg) in soil = exch Ca2+ + exch Mg2+ + exch K+ + exch Na+ + exch acidity 7 Where: exch Ca2+, etc. = concentrations of individual ions expressed as cmol/kg dry soil This procedure was therefore carried out for all the soil and sediment samples respectively. 3.3.6. Determination of Soil Moisture Content The soil moisture content, also known as water content is the ratio, expressed as a percentage, of the weight of pore or free water to the weight of the dry soil grains in a given mass of soil. In this experiment, testing conforms to ASTM D2216-10: Standard Test Method for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass. The standard operating procedure of determining the moisture content is by oven – drying, hence a gravimetric method is used in which the soil sample is dried at 110±5°C to a constant weight (EPA, 2009). Procedure: An airtight moisture can made of non-corrodible material was cleaned, dried, properly labeled, weighed and recorded as M1. A required quantity of the wet (“undried”) composite sample was put into the moisture can, and the mass (mass of can with content) was determined and recorded as M2. The can was then placed in a thermostatically controlled oven, maintained at a temperature of 110±5°C till its mass became constant (normally for 12- 24hours, as the case may be); after which it was removed from the oven using tongs and allowed to cool using a desiccator. The mass of the can with dry soil sample was determined and recorded as M3. The moisture content (Mc) of the soil sample was therefore calculated as follows: % Moisture content in soil = Mass of water loss × 100 = M2 – M3 × 100 Mass of dry soil M3 – M1 8 Where: M1 = Mass of empty moisture can (g) M2 = Mass of can with wet soil (g) M3 = Mass of can with dry soil (g) 3.3.7. Determination of soil Bulk Density This is an in-situ experiment whereby the bulk density of soil samples are determined from core samples which are taken by driving metal core cutters into the soil at a desired depth and horizon (USDA, 2013), which gives soil samples of known total volume from which bulk density can be determined. Procedure: At the sampling site, an undisturbed flat horizontal surface of the soil was prepared with a spade and a cylindrical metal ring (which was initially cleaned, weighed and recorded as M1) was driven into the soil to a desired depth with the use of a mallet — a block of wood was used to protect the ring when driving it into the ground. The ring was then carefully removed (brought out of the soil) with the soil intact by excavating its surrounding without disturbing or loosening the soil it contains. Excess soil was then removed from outside the ring and plant roots cut off at the soil surface with scissors, after which the mass of the ring containing the soil was determined and recorded as M2. The volume of the soil was then determined using the volume of the ring which is cylindrical in shape (i.e. soil volume = ring volume), whereby the height and diameter of the ring was determined with the use of a ruler and the value for diameter halved to get the radius. The volume of the ring which equals that of the soil was therefore determined as follows: Volume of soil (cm3) = Volume of ring = Volume of a cylinder = π × r2 ×h 9 Where: π = pi, which has a constant value of 3.14 r = radius of cylindrical ring (cm) h = height of cylindrical ring (cm) Hence the bulk density of the soil was determined as follows: Bulk density of soil (g/cm3) = Mass of soil = M2 – M1 Volume of soil Vol. of soil 10 Where: M1 = Mass of ring (g) M2 = Mass of ring with soil (g) This procedure was thus repeated for all the soil and sediment samples respectively. 3.4. Poly Aromatic Hydrocarbon Analysis The PAH analysis of the soil samples was carried out in accordance with ASTM D7363- 07: Standard Test Method for Determination of Parent and Alkyl Polycyclic Aromatics in soil Pore Water Using Solid-Phase Microextraction and Gas Chromatography/Mass Spectrometry in Selected Ion Monitoring Mode, which describes the procedure for analysis of extractable poly aromatic hydrocarbon in surface and ground water. In this study, poly aromatic hydrocarbons were detected in the soil samples by Gas Chromatography-Flame Ionization Detection (GC-FID). Analytical procedures: The analytical procedures involved extraction, clean-up and analysis of the composite samples in the laboratory. Extraction A test portion of the screened homogenized sample was crushed in a mortar, after which 2g of the ground sample was weighed into a clean 100-ml conical flask. 10ml of hexane was then added to the sample and the mixture was stirred with a stirring rod, after which the flask was placed in a mechanical shaker, shook for 10minutes and allowed to stand for 30minutes. The mixture was then carefully decanted into a clean 50-ml beaker to produce a clear extract by removing the liquid layer from the settled solid layer. 5ml of hexane was added to what was left in the conical flask, shook and allowed to stand for 20minutes and also decanted into the same beaker. 5ml of hexane was added again and the clear extract was combined into the same beaker, making a total of about 15-20ml of the extract. Clean-up A separating column was cleaned, dried and clamped in a retort stand, and then conditioned by inserting approximately 1cm of activated glass wool at the base of the column with the aid of a glass rod and putting 4g of activated silica gel (gently and well packed to avoid airspaces in-between and underneath the column), after which 0.5g of sodium sulphate (to dry up any water that must have interfered during the extraction process) was put on top of the silica gel. 10ml of dichloromethane was then introduced into the column using a 25-ml measuring cylinder and allowed to elute into a 50-ml beaker, and just before it completely flowed out of the column (a little above the sulphate layer), 10ml of hexane was also introduced into the column and allowed to flow through the column into the same beaker, after which the stop cork of the column was locked and the eluate discarded. The 15-20ml sample extract was then introduced immediately into the column and after 3-5minutes, the stop cork was opened to flow at a rate of one drop per 5seconds and elute into a fresh beaker; then 5ml of hexane was used to flush the last of the sample out into the same beaker, which was transferred into a labeled 10-ml standard solution storage bottle for total petroleum hydrocarbon analysis and kept aside since the TPH analysis is not needed in this study. Afterwards, a mixture of DCM and hexane in the ratio of 3:1 (i.e. 7.5ml of DCM and 2.5ml of hexane) was introduced into the column. Note that as a result of the introduced hexane, the PAH is absorbed by the silica gel and not coming out of the column with the TPH; so when the 10ml of DCM and hexane mixture is introduced, the stop cork is locked again for about 5minutes to allow the absorbed PAH to be released, and then opened and allowed to elute into a fresh beaker. The cleaned-up extract for the PAH analysis was then concentrated (to be able to get a better concentration of the components during the analysis) using a fume cupboard — as soon as the volume of the extract got to 1.5ml, it was transferred into a well- labeled 2-ml sample vial (with Teflon rubber crimp cap) and the sample was ready for PAH analysis in the Gas Chromatograph Flame Ionization Detector (GC-FID). The extraction and clean-up processes were carried out on the respective samples and the PAH analysis of all the samples carried out in a batch. GC-FID analysis The determination and measurement of the 16 EPA priority PAHs concentrations in the purified soil sample extracts was carried out using Agilent 7890B Gas Chromatographic System, equipped with a single detector (Flame Ionization Detector), a capillary column inlet and liquid auto-sampler/injector; with hydrogen, air and helium as carrier gases — the flame comes from the burning of the air and hydrogen gas which ignites the sample extract while it elutes from the column at the FID and the response detected by the detector. The instrument was calibrated and the operating set-up done according to the instrument’s method development as specified in the operating instruction manual, then the sample vials were arranged manually in the sample gear of the instrument. Before the analysis began, a blank was run on the column to clear off any form of contamination and be sure that nothing would prevent the determination of any analyte during the process. In this case where the samples were analysed in a batch, the micro-syringe of the chromatograph was first rinsed with dichloromethane and further rinsed with the sample prior to each sample analysis. After the blanking, 1μl of concentrated extract was then injected into the chromatographic column (30m long, 1μm thick and internal diameter of 0.25mm) by the auto-sampler, with helium used as carrier gas at a constant flow rate of 1ml/min which was maintained during the entire separation. Separation of sample into constituent compounds was achieved by the injection of sample into the column, which occurs at the vapour constituent partition between the gas and liquid phases. The compounds after separation passed through the FID and were automatically detected by the detector whose response is dependent upon the composition of the vapour. Identification and quantification of the individual PAHs was based on internal calibration standard containing known concentrations of the 16 EPA target PAHs. The specificity of the 16 PAHs sought for in the samples was confirmed by the presence of transition ions (quantifier and qualifier) as shown by their retention times which corresponded to those of their respective standards. The measured peak area ratios of precursor to quantifier ion were in close agreement with those of the standards and the number of PAHs was resolved at a particular chromatogram. This process continued for the other samples in the batch until they were all analysed and results obtained were presented as mg/kg concentration per analyte. 3.5. Statistical Analysis The data obtained were subjected to one-way analysis of variance and the significant means were separated using Turkey method of significant differences at 5% probability level. Variation plots were used to represent the concentrations of PAHs and physicochemical parameters across the sampling locations. Pearson’s correlation was used to compare relationships between the soil chemical and soil PAH concentration. 4.0. Results Presentation 4.1.1 Poly Aromatic Hydrocarbon Concentration in the study area. The concentrations of poly aromatic hydrocarbons obtained in the soil samples from the study area is presented in Table 1, which revealed that acenaphthylene, phenanthrene, fluoranthene, chrysene, benzo{b}fluoranthene, benzo{k}fluoranthene and benzo{a}pyrene amongst the 16 EPA priority PAHs were not detected in any of the five samples analysed. It also revealed that PAH values ranged from 0.0±0.0mg/kg to 5.0±1.2mg/kg in the soil. Naphthalene, acenaphthene, fluorene, pyrene, 1,2-benzoanthracene, dibenz{ah}anthracene, benzo{ghi}perylene, and indeno{1,2,3-cd}pyrene showed significant differences amongst the sampling locations at 5% probability level. Naphthalene was only detected at location A and fluorine was detected across the five locations except in site A with highest concentration found in site C. the highest PAH occurrence was found in site C and was in pyrene. The benzo{ghi}perylene concentration ranged from below detection limit to 2.1± 0.2 mg/kg Table 1: The PAH Concentration in the study area Location ANA FL Pyrene ANTH mg/kg B{a}ANTH D{ah}AN B{ghi}PERY I{1,2,3- cd}PY Site A 0.21±0.01a 0.00±0.0d 0.00±0.0c 0.31±0.01a 4.2±0.1a 3.41±2.1a 2.00±1.2a 0.233±0.01a Site B 0.00±0.0b 3.21±0.2a 2.01±0.1b 0.00±0.0c 2.1± 0.1b 0.00±0.0c 1.22±0.2b 0.2±0.01a Site C 0.00±0.0b 4.20±0.4a 5.0±1.2a 2.0±0.1b 1.2±0.01c 0.00±0.0c 0.00±0.0c 0.00±0.0b Site D 0.00±0.0b 1.23±0.2c 0.00±0.0c 4.00±1.2a 1.8±0.2c 2.00±0.1b 0.00±0.0c 0.01±0.01b Site E 0.00±0.0b 2.0±0.4b 2.0±1.2b 1.20±0.2b 0.86±0.02d 2.31±0.01b 2.1± 0.2a 0.0±0.0b ANA = acenaphthene, FL = fluorene, ANTH = Anthracene, B{a}ANT = 1,2- benzoanthracene, D{ah}AN = dibenz{ah}anthracene, B{ghi}PERY = benzo{ghi}perylene, I{1,2,3-cd}PY = indeno{1,2,3-cd}pyrene: (Source: Authors’ Computation, 2011). 4.1.2 The Physicochemical Characteristics of the study area The concentrations of physicochemical parameters measured in the soil samples of the study area are presented in Table 2.The parameters significantly affected all the locations except Bulk density and pH. pH concentrations ranged from 4.5± 1.0-5.2±2.1.Electrical conductivity (EC) ranged from 116±2.3-235±4.2 μS/cm with the highest value in site B and lowest value in site E. cation exchange capacity ranged from 12.2±2.1- 17.2±3.5(cmol/kg). Table 4.2 also revealed that pH, EC, organic carbon, organic matter, nitrogen (N), CEC, moisture content and bulk density, differed significantly amongst the sampling locations (P<0.05). The result revealed that, the highest mean pH and EC values of 5.2 and 235±4.2 μS/cm respectively were recorded in siteE, and Site B. The organic carbon ranged from 0.16±0.02% to 1.61±0.2% and this value significantly differed from the result obtained from site A and site B. The organic matter values ranged from 1.2 ±0.02% to 3.2±0.2%. The highest value occurred in site D and the lowest in site A. Total N values ranged from 0.12±0.01% to 0.41±0.2%, and the values did not differ across the locations. Soil bulk density also did not differ across the locations. The bulk density values ranged from 1.2±0.2 to 1.9±0.02(g/cm3). The highest values occurred in site C and the lowest values in site A. Table 2: The Physicochemical parameters of the study area. Location pH EC(μS/cm) Org. C (%) Org. matter (%) Total N(%) CEC(cmol/kg), Bulk density (g/cm3) Site A 4.5±1.0a 200±3.5b 0.16±0.02b 1.2±0.02b 0.12±0.01a 12.2±2.1b 1.2±.02a Site B 5.0±1.2a 235±4.2a 0.72±0.02b 2.6±0.01a 0.21±0.01a 15.2±2.2a 1.4±.01a Site C 4.8±1.0a 205±2.4b 0.4±0.01b 2.1±0.02b 0.41±.02a 16.4±4.5a 1.9±.02a Site D 4.6±1.1a 214±4.3b 1.21±0.23a 3.2±0.2a 0.26±.03a 17.2±3.5a 1.6±.01a Site E 5.2±2.1a 116±2.3c 1.61±0.2a 2.1±0.02b 0.32±.01a 12.2±2.5b 1.3±.02a (Source: Authors’ Computation, 2011). 4.1.3 Relationship between Poly Aromatic Hydrocarbons and Physicochemical Parameters measured in soil and Sediment samples Karl Pearson’s correlation (r) was used to evaluate the possible relationships between the chemical parameters and individual PAHs analyzed in the study area. The correlation results are presented in Table 3. The result showed that at P ≤ 0.012, acenaphthene showed a positive correlation with org. Carbon, with correlation coefficient of 0.642 and 1,2-benzoanthracene also had positive correlation with org. carbon with coefficient of 0.712 but negatively correlated with indeno{1,2,3-cd} pyrene with coefficient of -0.672. Pyrene also showed a positive correlation with bulk density at P ≤ 0.002 with correlation coefficient 0.923. Naphthalene did not show significant correlation with any of the chemical parameters. Similarly, Anthracene had significant positive correlation with Total Nitrogen with correlation coefficients of 0.829 with p<0.001. Generally, the result showed weak and moderate negative and positive correlations between the PAH components and the chemical properties of the soil samples. Only the few significant and moderate correlations were described Table 3: Correlation between the PAHs Concentration in the soil and the Soil Physicochemical parameters Parameters PAH components NA ANA Pyrene ANTH B{a}ANTH D{ah}AN B{ghi}PERY I{1,2,3- cd}PY pH 0.706 0.061 0.302 0.183 0.570 0.212 0.385 0.125 0.012 0.946 0.152 0.221 -0.658 0.044* 0.211 0.477 EC OC 0.242 0.196 0.129 0.508 0.165 0.553 0.642 0.012* -0.372 0.578 -0.580 0.112 0.481 0.211 0.386 0.366 -0.016 0.903 0.712 0.030 -0.211 0.417 0.548 0.127 0.125 0.758 0.198 0.337 -0.205 0.325 -0.672 0.025* OM 0.470 0.227 0.321 0.557 -0.472 0.224 0.112 0.651 -0.023 0.954 0.353 0.123 -0.128 0.210 -0.462 0.348 N 0.713 0.060 0.431 0.284 -0.541 0.135 0.829 0.001*** 0.129 0.750 -0.021 0.957 -0.446 0.109 -0.275 0.252 CEC 0.242 0.373 0.504 0.327 0.340 0.634 0.140 0.599 0.410 0.218 0.324 0.121 0.327 0.254 0.322 0.225 BD - 0.324 0.573 -0.462 0.215 0.923 0.002*** -0.129 0.930 -0.294 0.627 -0.239 0.621 0.378 0.163 0.759 0.043* (Source: Authors’ Computation, 2011). 5.0. Discussion Amongst the sixteen USEPA priority PAHs investigated in the study area, eight of them were detected. The highest total concentration for individual PAHs recorded for fluorene in the study area is at 4.2 mg/kg. The decreasing order for individual PAHs concentration in the study area is fluorene> benzo(a)anthracene> pyrene> dibenzo(a,h)anthracene> anthracene> benzo{ghi}perylene> indeno{1,2,3-cd} pyrene> acenaphthene. The least individual PAH was 0.21mg/kg and occurred in site A. However, Site E recorded the highest concentration levels of PAHs in the study area and it encompasses the location carrying out abattoir and automobile activities which is about 50 m away from the bank of the stream of Umuobia. This closely followed by site A which is the high urban activity area. This indicates that PAH contamination in the study area may have greatly risen from these activities. These PAHs contamination in the study area can be attributed to the high level combustion of woods, tyres and organic materials (such as cattle horns and bones) and spent/waste oil spills during repairs of vehicles and other heavy automobiles. This may lead to PAH pollution in the Umuahia area. This may lead to the contamination of the nearby streamin the area. This may occur as a result of atmospheric deposition and runoff of PAH compounds into the water body. Site C was an old auto mechanic area and in the downstream of location E, average PAH was also high. The fluorene contamination in the locations suggested atmospheric deposition of the compound in the soil during the combustion of tyres and other activities. This explains the ubiquitous nature of these compounds. Polycyclic Aromatic Hydrocarbon physical and chemical characteristics vary with their molecular structure (number of rings) and molecular weight. The majority of the PAHs detected in the study area are the high molecular weight types. They are usually classified as Low Molecular Weight and High Molecular Weight PAHs. PAHs with low molecular weight are those with two or three fused benzene rings while high molecular weight PAHs are those with four or more fused benzene rings (Wick, 2011). Harvey (1997) stated that PAHs with LMW easily degrade and volatilize faster than the HMW PAHs. The higher the molecular weight of PAHs, the higher its hydrophobicity (that is, they cannot absorb water), toxicity, lipophilic property, the lower its solubility in water, vapour pressure, and degradability (Wick, 2011). The ability of HMW PAHs to persist in the environment is due to their low volatility, resistance to leaching, and difficulty in undergoing degradation easily (Jones et al., 1996; Wild and Jones, 1995). In this study, LMW PAHs with 3-rings and HMW PAHs with 4-rings were detected; but the HMW (4-ringed) PAHs dominated the study area. The major sources of PAHs amongst others are classified as petrogenic (petroleum sources) and pyrogenic (combustion sources). Munyengabe (2016) stated in his work that petrogenic sources give off organic particulates which are characterized by a high mole fraction of LMW PAHs. According to Harvey (1997), LMW PAHs usually originate from petrogenic sources and Benner et al. (1990) suggested HMW PAHs to originate from pyrogenic sources. LMW PAHs dominate petrogenic sources while pyrogenic sources are dominated by HMW PAHs (Kumar, 2014). It is detriment to identify PAH sources for effective pollution control, environment risk management and health risk assessment. PAH sources can be predicted using PAH molecular weights and diagnostic ratios. The ratios of LMW PAHs to HMW PAHs in the environment can be used as tool to identify the sources of PAHs. Pyrolytic (pyrogenic) sources (combustion of coal, biomass or petroleum) usually indicate the ratio of < 1 while the petrogenic sources (petroleum spills) usually indicate the ratio of >1 (Mastral& Callen, 2000; Wilcke, 2000). Diagnostic ratios have been used also in several studies viz. Brack&Olajire, (2005), Bobak (2010), Bayowa (2014), Munyengabe (2016). These ratios may include; Anth/Phen, Anth/Anth+Phen, Fluo/Fluo+Pyr, BaA/BaA+Chry, Ind/Ind+BghiP, Fluo/Pyr (Neff, 1979). 6.0. Conclusion The results from this study revealed that the soils from the study area are contaminated with Poly Aromatic Hydrocarbons at varying concentrations at different sampling locations. Amongst the 16 EPA priority PAHs investigated in the soil samples, only eight were detected in the order of fluorene>benzo(a)anthracene>pyrene>dibenzo(a,h)anthracene>anthracene>benzo{ghi}peryle ne>indeno{1,2,3-cd}pyrene>acenaphthenewith total concentrations of 10.64mg/kg, 10.16mg/kg, 2.784mg/kg, 9.37mg/kg, 9.01mg/kg, 7.51mg/kg, 5.32mg/kg and 0.443mg/kg , 0.21mg/kg respectively. PAHs distribution and mobility in the study area was influenced by the number of their rings and molecular weight which affected their water solubility. In this study, high molecular weight PAHs with four or more rings predominated in the soil samples, which indicates that the PAHs are of pyrolytic origin. 7.0. Recommendations This study assessed the concentration of PAH in soils within Umuahia municipality. Consequent upon the findings from this study, it is recommended as follows: i. that the government should provide a more appropriate place that will serve as automobile village where auto repairs are to be carried out in steady of the random siting of auto-mechanics within the city centre ii. Education and legislation on management of wastes in the municipality should be intensified to forestall the effects of waste oil related problems on the environment, particularly on groundwater. iii. Also, modern waste disposal facilities should be acquired by relevant authorities and appropriate waste disposal sites be chosen to avoid the injurious effects of indiscriminate disposal of wastes — used oils/lubricants. In addition, continuous monitoring and further studies on the level of these pollutants should be carried out in the near future to ascertain long-term effects of anthropogenic impact. References Abenchi, E. S., Okunola, O. J., Zubairu, S. M. J., Usman, A. A., &Apene, E. (2010). 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