Environmental Engineering Reference
In-Depth Information
Fig. 5
Percentage distribution
of grouped PAHs in all the
sampling points
60
50
40
30
20
10
0
% 2-3 rings
% 4 rings
% 5 rings
% 6 rings
Odo Iya Alaro
Shasha
Ibeshe
Lagos lagoon
mainly due to combustion and pyrolysis of fossil fuels and
to release into the environment of petroleum products.
Environmentally, socially and economically, POPs have
impacted the Lagos lagoon negatively. Exposure to POPs in
the Lagos lagoon has negatively impacted human health by
increasing the risks of most modern diseases among the
inhabitants of Lagos (Table
4
).
PAH Distribution in Sediments of the Lagos
Lagoon System
Three trans-urban waterbodies of the Lagos lagoon system;
Odo Iya alaro, Ibeshe and Shasha creeks that receive
domestic, municipal and industrial effluents, and eventually
empty into the Lagos Lagoon, were studied (Alani et al.
2012a
). Sediment samples were collected bimonthly from 21
sampling points for a period of one year, covering both rainy
and dry seasons of the year. The distribution of the PAHs in
the sediment samples showed large variations in the sites
investigated. The concentration of total PAHs (
P
PAHs)
ranged from 9.76 to 6,448.66 lg/kg and showed a strong
influence from anthropogenic inputs. In general, naphtha-
lene, fluorene, phenanthrene, fluoranthene, pyrene, benzo (a)
anthracene, chrysene, benzo (b) fluoranthene, and benzo (a)
pyrene were the dominant PAHs found in the sediments.
The total PAH concentration for the Odo Iya alaro ran-
ged from 268 to 6,449 lg/kg, Shasha creek ranged from 127
to 3,509 lg/kg, Ibeshe creek ranged from 56 to 2,996 lg/
kg, while the Lagos lagoon ranged from 10 to 1,044 lg/kg.
The percentage distribution of PAHs was predominantly
2-3 ringed PAHs ranging from 42.35 to 100 %. Samples
obtained during the dry seasons of the year were also found
to contain higher levels of total PAHs. Significantly higher
total PAH concentrations were found at sampling points
close to the main metropolis of Lagos compared with points
in the lagoon which are far from the city, supporting the
conclusion that urbanized and industrialized areas are major
sources of PAH contamination in sediments.
The percentage distribution of grouped PAHs shown in
Fig.
5
indicated a similar trend in all the sampling points. 2-
and 3-ringed PAHs had the highest percentage distribution
while the 6-ringed PAHs had the least. This indicated that
the sediment samples in the Lagos Lagoon and the adjoin-
ing creeks had similar anthropogenic input of PAHs.
Bioaccumulation of Organochlorine Pesticide
Residues in Fish and Invertebrates of Lagos
Lagoon, Nigeria
Our studies have provided baseline information on the level
of OCs in the Lagos Lagoon System including their bio-
accumulation and the risk they pose to humans that depend
on fish and invertebrates from the Lagos lagoon for food.
The most bioaccumulated OCs in fish were beta-HCH
(22.72-0.90 ng/g d. w.) and p,p'DDE (16.04-0.44 ng/g d.
w.). The most bioaccumulative OCs in the invertebrates
were still beta-HCH (24.50-16.10 ng/g d. w.) and p,p'DDE
(22.20-1.85 ng/g d. w.). This agreed with the report that
p,p'DDE was found to be more stable and persistent
(refractory) than either p,p'DDT or p,p'DDD and under-
went strong biomagnification with transfer along food chain
(Walker
2009
). The sum OCs of 55.22 ng/g d. w. in crab
eggs, 63.90 ng/g d. w. in agaza (Caranx hippos) and
69.40 ng/g d. w. in young blue crabs (Callinectus amnicola)
revealed these biota as the most contaminated. Beta-HCH
and p,p'DDE were identified as the dominant OC in the
Lagos lagoon. Consumption of crab eggs, mature crabs,
young blue crabs (Callinectus amnicola) and Agaza (Car-
anx hippos), and some other seafoods from the Lagos
lagoon could pose a high risk of OC health effects on
humans as these biota bioaccumulated the contaminants
above allowable limits (Fig.
4
).
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