3.1 Distribution of PAHs in Air and Water in the Wet and Dry Seasons
Result for PAH component concentrations in water and in suspended particulate matter of air in both the wet and dry seasons are presented in Table 1. In the wet season, the concentration of PAH in suspended particulate matter of air ranged between 7.659E-06 ppm and 2.01E-03 ppm while the concentration of PAHs in water ranged between 3.558E-07 mg/l and 4.43E-03 mg/l.
In the dry season, the concentration of PAH in suspended particulate matter of air ranged between 2.24E-05 ppm and 1.00E-03 ppm with the first five LMW-PAHs and two HMW-PAHs ( BaP and BghiP) not detected (ND) while the concentration of PAHs in water ranged between 2.15E-06 mg/l and 3.58E-03 mg/l with seven LMW-PAHs and two HMW-PAHs (BaP and BghiP) not detected (ND). The total PAHs concentration in the air is 4.603E-03 ppm and in water 7.782E-03 mg/l in the wet season while the total PAHs concentration in the air is 3.636E-03 ppm and in water 5.172E-03 mg/l in the dry season. Both the individual and total PAHs concentration in water are less than the available limit set by department of petroleum resources (DPR). The water environment is safe as its total PAHs concentration is lower than DPR permissible limit (7.782/5.172E-03 mg/l < 1mg/l).
3.2 Trend and Patterns of the Distribution of PAHs in Air and Water
The patterns of the distribution of PAHs in water followed the same patterns in the air as shown in Fig. 2. Though, the concentrations of PAHs in water were relatively higher than concentrations in air but their trend are identical.
3.3 Distribution of PAHs, LMW-PAHs and HMW-PAHs in Air and Water in the Wet and Dry Seasons
The distribution of each of the 17 PAHs in air (above) and swimming pool water (below it) in the wet and dry seasons is as shown in Figure 3. In the wet season, the concentrations of PAHs are in the order Chr > IcdP >BghiP > Acy > BaA > BbF > DahA> ….>Ant in the air and IcdP > BghiP > Flu > Acy > 2mNap> …. >Nap in the water. In the dry season, the order are: DahA > BbF > BkF > IcdP > Chr >…>Ant in the air and DahA > BbF > BaA > IcdP > Pyr >…Ant in the water.
In all of these high moleular weight PAHs (HMW-PAHs) concentration are considerably higher than low moleular weight PAHs (LMW-PAHs). This as shown in the Figures 3 and 4 where the total concentrations of HMW-PAHs 5.56 and 7.381 times higher than the concentrations of LMW-PAHs in the air and water respectively in the wet season. Though the LMW-PAHs and HMW-PAHs concentrations are relatively lower in the dry season than the values in the wet season but the total concentrations of HMW-PAHs 30.88 and 2400 times higher than the concentrations of LMW-PAHs in the air and water respectively in the dry season.
3.4 Ratios of PAHs between Air and Water Media in Wet and Dry Seasons
Table 2 presented the ratio of individual PAH in the air in dry season to the PAH in air in the wet season and also the ratio of individual PAH concentration in the water in dry season to the PAH in water in the wet season. The ratios of PAHs in the air in wet season to the PAHs in air in the dry season ranged between 0.0324 (DahA) and 9.45E (Chr) while the ratios of PAHs in the water in wet season to the PAHs in water in the dry season ranged between 0.012 (DahA) and 16.5 (IcdP)
3.5 Mutagenic Equivalent (MEQ) and Mutagenic Potential (MP) of PAHs
Result for mutagenic equivalent (MEQ) and mutagenic potential (MP) of PAH component of water and air in both the wet and dry seasons are presented in Table 3.
In the wet season, the MEQ concentration of the mutagenic PAH in suspended particulate matter of air ranged between 3.55E-06 ppm and 2.67E-04 ppm with total of 5.01E-04 ppm while the MEQ concentration of mutagenic PAHs in water ranged between 2.45E-06 mg/l and 1.37E-03 mg/l with total of 1.82E-03 mg/l.
In the dry season, the MEQ concentration of mutagenic PAH in air ranged between 3.61E-06 ppm and 2.90E-04 ppm with total of 6.90E-04 ppm and while the MEQ of mutagenic PAHs in water ranged between 2.55E-06 mg/l and 1.04E-03 mg/l with total MEQ of 1.29E-03 mg/l. In both the air and water, two PAHs ie BaP and BghiP were not detected (ND).
The total concentration of dry season air BaP-MEQ)∑8PAH is higher than wet season air (BaP-MEQ)∑8PAH (6.90E-04 > 5.01E-04 ppm) by 1.38 times. Conversely, The total concentration of dry season water BaP-MEQ)∑8PAH is lower than wet season water (BaP-MEQ)∑8PAH (1.29E-03 > 1.82E-03 mg/l) by 0.71 times.
3.6 Mutagenic Potential (MP)
In the wet season, the mutagenic potential (MP) of BaP-MEQ)∑8PAH are in the order IcdP 53.3 % > BghP 28% with the least recorded for BkF 0.7% in the air and IcdP 75.3% > BghP 18.8% with the least recorded for Chr 0.1% in the water. Average MP of 64.3% calculated for IcdP followed by BghP with 23.4% and BkF with the least MP of 0.7% in the season.
In the dry season, the order of the highest percentages are: DahA 42% > BbF 31.5% > BkF 12.5% > IcdP 11.2 % in the air and DahA 80.7% > BbF 9.3% > IcdP 6.4% in the water. Average MP of 61.3% for DahA followed by BbF with 20.4% and IcdP 8.8% and the least of 6.9% for BkF in the season.
3.7 Carcinogenic Equivalent (TEQ) and Carcinogenic Potential (CP) of PAHs
Result for carcinogenic equivalent (TEQ) and carcinogenic potential (CP) of PAH component of water and air in both the wet and dry seasons are presented in Table 4.
TEQ
In the wet season, the TEQ concentration of the carcinogenic PAH in suspended particulate matter of air ranged between 9.51E-09 ppm and 8.61E-05 ppm with total of 1.88E-04 ppm while the TEQ concentration of carcinogenic PAHs in water ranged between 3.56E-10 mg/l and 4.43E-04 mg/l with total of 5.90E-04 mg/l.
In the dry season, the TEQ concentration of carcinogenic PAH in air ranged between 2.24E-08 ppm and 1.00E-03 ppm with total of 1.21E-03 ppm and while the TEQ of carcinogenic PAHs in water ranged between 2.15E-08 mg/l and 3.58E-03 mg/l with total TEQ of 3.71E-03 mg/l. In both the air and water, LMW-PAHs and two HMW-PAHs ie BaP and BghiP were not detected (ND).
Different media across season/ Different media in the same season
The carcinogenic equivalent variation showed that the concentration for wet season water BaP-TEQ)∑17PAH is higher than wet season air (BaP-TEQ)∑17PAH (1.82E-03 > 5.01E-04) by 3.6 times. In the dry season, the concentration of Dry Season Water (BaP-TEQ)∑17PAH is higher than Dry Season Air (BaP-TEQ)∑17PAH (1.29E-03 > 6.90E-04) by 1.9 times.
Same medium within season/ Same medium in different seasons
The total concentration of dry season air BaP-TEQ)∑17PAH is higher than wet season air (BaP-TEQ)∑17PAH (1.21E-03 > 1.88E-04 ppm) by 6.44 times. The total concentration of dry season water BaP-TEQ)∑17PAH is higher than wet season water (BaP-TEQ)∑17PAH (3.71E-03 > 5.90E-04 mg/l) by 6.29 times.
3.8 Carcinogenic Potential (CP)
In the wet season, the carcinogenic potential CP of BaP-TEQ)∑17PAH are in the order: IcdP 45.9% % > DahA 17.3%% > BaP 11.6%> Chr 10.7% with the least recorded for Ace 0% in the air and the order: IcdP 74.9% > BaP 9.1% > DahA 7.3% with the least recorded for NaP 0% in the water. Average CP of 60.4% for IcdP followed by DahA with 12.3% and BaP 10.4% with the least CP of 0% for Ace in the season. In the dry season, the order are: DahA 82.55% > BbF 7.2% > BkF 6.5% with the least recorded for Flr 0% /ND in the air and DahA 96.6% > BbF 1.3% with the least recorded for Ant 0%/ND in the water. Average CP of 89.6% for DahA followed by BbF with 4.2% and BkF 3.4 with the least record of 0 % for Ant in the season.
Mutagenic Equivalent (MEQ) and Mutagenic Potential (MP)
The concentrations of eight PAHs and 17 PAHs in air and water as well as the mutagenic equivalent (BaP-MEQ)∑8PAH) of the former and carcinogenic PAHs (TEQ)∑17PAH) of the later respectively were compared using Mann-Whitney U and Wilcoxon Signed Ranks non-parametric tests and the results presented in Table 5.
These two tests were performed to compare air and water concentrations MEQ∑8PAH and TEQ∑17PAH in wet and dry seasons and were also performed to compare air and water concentrations (BaP-MEQ)∑8PAH wet and dry seasons.
PAH Diagnostic Ratios for Source Identification
The laboratory results of the concentrations of PAHs were used in calculating the diagnostic ratios presented in Table 1 below. 17 diagnostic ratios including isomeric and non-isomeric ratios were computed.
The first seven diagnostic ratios classify PAHs into petrogenic or pyrogenic sources while the 8th ratio ia a measure of combustion. The ratio of combustion PAHs to the total PAHs (∑COMB/∑PAHs ~1) approximately 1 indicates combustion source while close to zero indicates non-combustion origin. All the four profiles in this study showed combustion source. The last nine diagnostic ratios further differentiate petrogenic sources of PAHs into petroleum or diesel emission. And the pyrogenic sources were further classified into various types of combustions like petroleum, kerosene, vehicular or biomass.