Environmental Engineering Reference
In-Depth Information
Table 5
Results of PAH analysis compared with standard pollution criteria of PAH components for sediment matrix
Concentration (lg/kg) (Xu et al.
2007
)
This study concentration (lg/kg)
ERL
ERM
Odo Iya alaro
Shasha
Ibeshe
Lagos lagoon
Naphthalene
160
2,100
446.26
164.45
143.86
138.56
Acenaphthene
16
500
105.09
29.99
45.65
14.76
Fluorene
19
540
41.68
46.47
50.96
36.03
Phenanthrene
240
1,500
138.91
99.53
129.95
148.50
Anthracene
853
1,100
99.51
71.44
170.21
57.98
Fluoranthene
600
5,100
268.60
229.67
164.28
295.16
Pyrene
665
2,600
198.13
153.21
136.72
241.94
Benzo(a)Anthracene
261
1,600
124.62
86.84
137.02
84.39
Chrysene
384
2,800
101.76
61.95
84.17
41.95
Benzo(b)Fluoranthene
NA
NA
176.87
88.42
94.65
70.36
Benzo(k)Fluoranthene
NA
NA
75.90
72.63
59.21
60.37
Benzo(a)Pyrene
430
1,600
73.14
54.61
88.43
44.93
Dibenzo(a,h)Anthracene
NA
NA
43.56
36.45
35.33
29.84
Benzo(g,h,i)Perylene
63.4
260
106.85
77.72
80.93
49.53
Indeno(1,2,3-c,d)Pyrene
NA
NA
100.10
66.42
84.06
61.49
P
PAH
4,000
44,792
2,334.16
1,213.31
1,449.82
880.43
Source identification of PAHs
4
Sediment samples collected near sewage outlets, cities
and the harbour appeared to have extremely high concen-
trations of total PAHs. These suggest that PAHs accumu-
lated in the sediments of the Lagos lagoon and the adjoining
creeks came from different sources such as sewage dis-
charge from nearby human activities, untreated industrial
effluents and fuel combustion emissions.
The measured concentrations of PAHs were compared
with the effects range low (ERL) and the effects range
median (ERM) values which are used for assessment of
aquatic sediment using biological thresholds with a ranking
of low-to-high impact values (Long et al.
1995
). Table
4
lists the thresholds for sediments from the Lagos lagoon and
the adjoining creeks. In the sediments of the Odo Iya alaro,
the results showed that the average total PAH concentra-
tions at all sites were below the ERL and ERM (Table
5
).
It is well established that PAH congener distribution
generally varies with the production source as well as the
composition and combustion temperature of the organic
matter. Molecular indices based on ratios of selected PAH
concentrations may be used to differentiate PAHs from
pyrogenic and petrogenic origins. Four specific PAH ratios
were calculated for the studied samples: phenanthrene/
anthracene, fluoranthene/pyrene, benzo (a) anthracene/
chrysene, and indeno (1,2,3c,d) pyrene/(Indeno (1,2,3c,d)
pyrene + benzo (g,h,i) perylene).
3.62
Mean PAHs
Mean OCs
3.5
3
2.5
2
1.5
1
0.32
0.5
0.16
0.04
0
Dec., 2006 (n=11)
May 2007 (n=7)
Fig. 6
Mean concentrations of PBTs (ng/mL) in December 2006 and
May 2007 (PCB levels in Lagos Lagoon water during this study were
below detection limit)
Results from the analysis of sediments of the Odo Iya
alaro creek showed that Phe/Anth ratio ranged from 0.47 to
4.26. The ratios were mostly \1 except for a few sites. Flu/
Pyr ratio ranged from 0.17 to 2.74. Most of the sampling
sites had values less than 1, indicating pyrolytic origin or
coal combustion. The BaA/Chr ratios were greater than 1 in
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