dc.description.abstract | his
study assessed the quality of water in a tributary of the Nairobi River. The
study covered six
sampling points
stretching from Lenana dam to Chiromo Kirichwa Kubwa. Sampling was done
twice during the dry and the wet season
between July and December 2
013.
Physicochemical
characteristics were analyzed using standard procedures, concentrations of some heavy metals
using AAS and speciation analysis using the Joint Expert Speciation System (JESS).The range
observed for pH, temperature, DO, COD, BOD, TSS, e
lectrical conductivity, TDS, phosphate,
sulphate, chloride, fluoride and nitrite was 6.89
-
7.77, 18.3
-
25.0
o
C, 8.10
-
24.29 mg/L,
40
-
730
mg/L,10.93
-
25.26 mg/L, 131
-
414 mg/L, 348
-
881μS/cm 176
-
438 mg/L,0.03
-
5.96 mg/L, 0
-
68
mg/L, 0.0142
-
0.886 mg/L, 0.39
-
2.87
mg/L and 0.002
-
0.585 mg/L respectively. The range
observed for heavy metals was 0.0974
-
3.
1438 mg/L, 0.0092
-
3.6843 mg/L, <
0.01
-
0.
1799 mg/L,
<0.005
-
0.0197 mg/L, <
0.05
-
0.4415 mg/L and <
0.02
-
0.0846 mg/L for Fe, Mn, Cu, Zn, Pb and Cr
respectively. Speciation an
alysis indicated that 69.8% of total iron was in oxidation state III, and
the dominant species were free Fe
2+
ions, sulphates, hydroxides, fluorides, and hydroxide
-
sulphate complexes. Manganese was
observed to be
in oxidation state II, and its major chemica
l
forms were Mn
2+
ions, fluoride
and sulphate complexes. Copper was found mostly (>98%) in
oxidation state II, and Cu
2+
ions, sulphate
and hydroxide complexes were the major species. Zinc
and l
ead were divalent, and sulphates
were their major species. Chrom
ium was trivalent with
hydroxide
-
sulphate and hydroxide complexes being the predominant
chemical
forms. The results
show
th
at the concentrations of Zn, Cu,
SO
4
2
-
, Cl
-
, NO
2
-
and TDS
w
ere below the KEBS limits
.
However,
COD
, EC, TSS,
PO
4
3
-
, F
-
Pb
, Cr, Fe and
Mn were
above
the
KEBS limits
for natural
water
in some sampling points
. Cu, Fe and Mn were found to pose health risk since traces of
their free ions were obtained in some sampling points. It was generally found that speciation
varied with the total conce
ntration of the species and the pH of the system | en_US |