Environmental Engineering Reference
In-Depth Information
Table 4
Ratios indicating predominant sources of POPs in Lagos lagoon
Water (ng/mL)
Sediment
(ng/g)
Crayfish
ng/g)
Shrimp
(ng/g)
Blue crab
(ng/g)
Tilapia
ng/g)
Megalops
(ng/g)
P
PAHs
0.13
346.94
74.2
99.06
264.61
80.64
88.11
P
Lower PAHs
0.13
210.95
74.2
99.06
264.61
80.64
88.11
P
Higher PAHs
0
136
0
0
0
0
0
P
Low chlorinated PCBs
0
11.78
0.94
0.97
2.23
14.02
16.09
P
High chlorinated PCBs
0
3.25
0.33
0.78
44.15
17.32
29.85
P
PCBs
0
15.04
1.27
1.75
46.38
31.34
45.93
P
Ocs
0.02
2.79
21.03
8.41
69.4
39.94
32.09
PCBs/p,p'DDE
0
8.14
0.65
2.09
1.95
3.96
P
PAHs/
P
PCBs
23.07
58.44
56.61
5.71
2.57
1.92
observed to be associated with the acid exchangeable
fraction, while chromium and copper were observed to be
associated with the reducible and oxidizable fractions, and
lead with the reducible and residual fractions. Sediments
with higher pseudototal metals contents often contained
higher proportions of metals in more labile forms (released
earlier in the BCR procedure). This is of environmental
concern because it means that, where overall PTM con-
centrations are highest, the potential for remobilisation and
uptake into the food chain is also greatest.
60
50
40
30
20
10
0
Invert.
Fish
Biota
HCB
b-HCH
g-HCH
d-HCH
trans-chlordane
cis-chlordane
trans-nonachlor
p,p'DDE
p,p'-DDD
p,p'-DDT
Ecotoxicological Risk Assessment of Sediments
Fig. 4
Mean % OCs in fish and invertebrates
In another study by Oyeyiola and Alo et al., the risk asso-
ciated with the Lagos Lagoon system sediments was
assessed using the risk assessment code (RAC). This was
based on the percentage of acid exchangeable fraction of
metals (i.e. the most mobile) determined with a sequential
extraction procedure as per procedures developed by Dav-
utluoglu et al. (
2011
), Jain et al. (
2007
), Perin et al. (
1985
).
Based on these values, Cd was found in the Odo-Iyaalaro to
be mostly associated with the very high-risk group. The
other metals studied varied from no risk to medium risk,
while zinc varied from high risk to very high risk in most of
the sites in all the waterbodies.
The Hankanson potential ecological risk index was also
used in the assessment (Cai et al.
2011
; Hankanson
1980
).
In the absence of background values of metals in sediment
in Nigeria, the background value of metals in sediment
presented by the US National Oceanic and Atmospheric
Administration (NOAA) (SQuiRTs
2008
) was used, and the
toxic-response factor presented by Cai et al. (
2011
) was also
used. Cadmium was placed in the very high-risk category,
thus posing the highest ecological risk in the Odo-Iyaalaro
River (Table
3
). The highest RI value was also observed
during the dry season (March). Based on the ecological risk
assessment, the researchers observed a need for strength-
ening environmental pollution
control in other to prevent
ecological risks from metals .
Persistent Organic Pollutants Sources
and their Impacts on Lagos Lagoon, Nigeria
Studies in our laboratories have shown that industrial and
other anthropogenic sources predominated over agricultural
sources of Persistent Organic Pollutants (POPs) in the La-
gos Lagoon (Alani et al. 2011). Also pyrolytic sources of
PAHs were found to dominate natural or petrogenic sources
in the Lagoon. This result agreed with Pazdro (
2002
), who
reported that the occurrence of PAHs in the environment is
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