| dc.description.abstract | The occurrence of heavy metal contaminants in excess of natural loads
is a problem of increasing concern in aquatic ecosystems. This has been
caused by anthropogenic, industrial and urban wastes as well as natural
geochemical activities. Winam Gulf of Lake Victoria is no exception to
these contamination processes even though it is an important resource
for food, drinking water and communication to the local community and
an important habitat for fish and other aquatic organisms of great
biodiversity. This therefore, necessitated the study of the physical and
chemical properties which influence water quality and ecosystem
balance, the speciation and distribution of trace metals of environmental
concern, which include Cd, Cu, Zn and Pb in addition to Fe, which is
widely used in the construction industry. The study had a randomized
complete block design and the sampling sites were located upstreams
and river mouths of rivers Sio, Nyamasaria, Nyando and Sondu-Miriu,
and in Port Victoria, Kisumu Car Wash, Dunga and Hippo Point beaches
along the lake, as w.ell as Nyamasaria, Migosi and Nyawita Estates in
Kisumu City. The samples were taken during the wet months of May and
October, 2006 and the dry months of January and February, 2007. The
samples were extracted in quadruplets for total and bioavailable metal
concentration for solid samples and total metal concentration for water
samples. The samples were then analysed using atomic absorption
spectrophotometer, AAS (Shimadzu Corporation AA-6300 model) and
the results confirmed by inductively coupled plasma mass
spectrophotometer, X series 2 ICP-MS model.
Physicochemical properties of water were determined. The pH ranged
from 7.2-7.8 for estate waters and 6.5-8.8 for lake and upstream
waters. Total Alkalinity, Conductivity, Dissolved oxygen, Turbidity,
Acidity and Temperature for estate water samples averaged 47.0 mg/L,
333 IJS/cm, 5.4 mg/L, 1.0 NTU, NO and 26.3°C respectivel w . e)those
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of lake and upstream water samples averaged 47.1 rnq/L, 140.5 ~S/cm,
4.9 mg/L, 270.4 NTU, NO and 27.5°C respectively. The Cd, Pb, Cu, Zn
and Fe metal concentrations in ~g/L in estate water samples averaged
ND, 9.1, 44.6, 232.7 and 242.4 while those of lake and upstream river
water samples averaged NO, 12.7, 53.0, 232.3 and 2,588, respectively.
All the water samples analysed conformed to the set international
standards for drinking water for the metals investigated except lead and
iron in lake water samples. The amount of Fe in lake water samples was
beyond the maximum allowable limits in fisheries and aquatic life
internationally. The concentrations of the metals increased downstream
for both water and sediment signifying that these rivers are among the
major sources of the heavy metal load in Winam Gulf. The average total
heavy metal concentrations in ~g/g for Cd, Pb, Cu, Zn and Fe in
sediments on dry weight basis were 1.2, 32.5, 36.7, 163.3 and 45,990
respectively. The % average bioavailable Cd, Pb, Cu, Zn and Fe metal
concentrations in the sediments on dry weight basis were 55.8, 66.9,
57.1, 73.3 and 65.6 .respectively. Statistical analysis showed significant
variation (p < 0.05) between the sample sites, seasons and their
interactions. These significant variations were attributed to the wide
range of activities taking place in the vicinity of each sampling site in
addition to the effects of each season especially on the rivers feeding the
lake.
Total heavy metal concentrations were also determined in the three
most abundant fish species in the Winam Gulf (Lates niloticus,
Oreochromis niloticus and Rastrineobola argentea). The fish samples
were obtained from Ounga, Port Victoria, Sio Port and Hippo Point
beaches. The average total metal concentrations determined on dry
weight basis were 0.21 ~g/g Cd, 0.87 ~g/g Pb, 3.4 ~g/g Cu, 36.4 ~g/g
Zn and 45. 7 ~g/g Fe for Lates niloticus, 0.21 ~g/g Cd, 0.61 ~g/g Pb, 2.7
I-Ig/g Cu, 35.9 I-Ig/g Zn and 48.0 I-Ig/g Fe for Oreochromis niloticus and
0.26 I-Ig/g Cd, 1.2 I-Ig/g Pb, 6.5 I-Ig/g Cu, 250.1 I-Ig/g Zn and 139.1 I-Ig/g
Fe for Rastrineobola argentea. The % average bioavailable Cd, Pb, Cu,
Zn and Fe metal concentrations in the three species were 67.1, 27.5,
46.3, 79.4 and 29.8 respectively for Lates niloticus, 66.7, 40.9, 41.7,
71.0 and 37.3 respectively for Oreochromis niloticus and 59.1, 47.4,
65.7, 76.2 and 44.5 respectively for Rastrineobola argentea. Statistical
analysis showed significant variation (p < 0.05) between the fish
species, sample sites, seasons and their interactions. This situation was
attributed to the complex mobility trends of fish. The abundance trend of
the metals in Lates niloticus and Oreochromis niloticus was Fe > Zn >
Cu > Pb > Cd while that of Rastrineobola argentea species was Zn > Fe
> Cu > Pb > Cd. The difference in the trends was attributed to the fact
that Rastrineobola argentea was analysed whole while only muscle of
Lates niloticus was determined after removing the internal organs.
These parts were selected for analysis because they represent edible
parts of the fish species by man. The fish samples of the three species
conformed to the- limits set out by the international standards
organisations, however, the concentration of Zn on wet weight basis for
Rastrineobola argentea species went beyond the set out tnternational
upper limits during the wet season and this was attributed to it being
"
consumed with its internal organs in place.
The wet season generally registered higher metal concentrations in all
types of samples analysed in this study.
Sediments accumulated metals many more times compared to fish and
water. The order of accumulation was found to be Sediment> Fish>
Water. Metals in sediments are more bioavailable compared to the
metals in fish and therefore could be desorped into the water much
more readily than from fish. | en_US |
