Environmental Engineering Reference
In-Depth Information
Fig. 7
Mean concentrations of
PBTs in sediments from February
2004 to May 2007
800
Mean PAHs
Mean PCBs
Mean OCs
665.44
700
600
500
400
323.45
286.98
265.08
300
200
109.18
24.04
31.08
100
12.7
13.4
5.32
9.15
8.65
0
FEB 2004 (n=11)
Jun 2004 (n=10)
DEC 2006 (n=12)
May 2007 (n=12)
-100
YEARS
most of the samples and could also be indicative of pyro-
genic input of the PAHs. The pyrolytic PAH inputs at the
Odo Iya alaro creek are also further confirmed by the IP/
BgP + IP ratio. The values for this ratio ranged from 0.32
to 0.8 which is typical of fossil fuel combustion, coal, grass
and wood combustion, all of which are pyrolytic sources.
The results indicated that PAHs in the Odo Iya alaro had
presumably undergone similar environmental processes
independent of the sampling sites. A similar trend was
observed in other sediments of the remaining sampling
sites.
observed in several samples. CPI index ranged from 0.65 to
2.97 which indicated that the presence of n-alkanes in the
Lagos lagoon sediments and the adjoining creeks was from
both anthropogenic to pyrogenic sources. The sediment
samples that had CPI values close to 1 were taken from
areas associated with high anthropogenic impact
and port
activities such as Tin Can Island and Marina.
The temporal distribution of PBTs in the Lagos Lagoon
is shown in Figs.
6
and
7
.
Pattern of PBT Signatures Across Different
Media in Lagos Lagoon, Nigeria
N-Alkane Distribution in Sediment Samples
from Lagos Lagoon
Our studies on the PBT signatures of the Lagos Lagoon
System (Alani et al.
2012b
) showed highest mean PAHs of
0.080 ng/ml in the lagoon water at the mouth of the Ogun
River, a fluvial source, reflecting the effect of runoffs on the
PAH load in the lagoon. In coastal areas, direct deposition
of atmospheric PAHs may be relatively minor compared
with fluvial inputs, but in open ocean areas it can dominate
(Kowalewska and Konat
1997
). The levels of PAHs in the
lagoon water were also determined by Anyakora et al.
(
2004
). The highest mean OCs of 0.069 ng/ml was obtained
at Okobaba, a slum residence by the shore of the lagoon,
where the use of pesticides for the control of insect vectors
is relatively high. PCBs were not detected in water from the
lagoon. In the sediment, highest mean PAHs of 68.251 ng/g
d. w. was obtained at Okababa, highest mean OCs of
11.859 ng/g d. w. was obtained at Aja, while highest mean
PCBs of 1.331 ng/g d. w. was obtained at the mouth of the
Ogun River, confirming the effect of runoff load through
fluvial sources. In the invertebrates, the highest mean PAHs
of 18.659 ng/g d. w. was found in crayfish; the highest
mean PCBs of 17.070 ng/g d. w. was found in crayfish; and
The concentrations of total aliphatic hydrocarbons (C
9
-C
38
)
in sediment samples from the Lagos Lagoon have been
found to range from 14.89 to 148.29 lg/g dry weight, and
their distribution showed large spatial variations at various
sampling points. The distribution of both n-alkanes and
PAHs shows great spatial variations in the sediments, which
could be attributed to temporal and localized inputs of
contamination sources. By examining the distribution
indexes, it has been confirmed that the aliphatic hydrocar-
bons were mainly from anthropogenic to biogenic sources,
while the distribution of PAHs came from both pyrolytic
and petrogenic sources. The highest hydrocarbon concen-
trations in sediments were, in general, found in the areas
associated
with
high
anthropogenic
impact
and
port
activities.
The major hydrocarbon index in most samples was at
C
29
,C
31
and C
27
, indicating that vascular plant sources
played a very important role (Wang et al.
2006
). A lower
molecular
weight
Cmax
around C
21
and C
23
was
also
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