Jun. 2010, Volume 4, No.6 (Serial No.31)
Journal of Environmental Science and Engineering, ISSN 1934-8932, USA
Organochlorine Pesticide Residues and Metabolites in
Fish from Lake Naivasha, Kenya
Njogu, Paul1, Kitetu, Jackson1 and Keriko Joseph2
1. Institute for Energy and Environmental Technology, Jomo Kenyatta University of Agriculture and Technology, P.O. Box,
62000-00200, Nairobi, Kenya
2. Nairobi Campus, Jomo Kenyatta University of Agriculture and Technology, P.O. Box, 62000-00200, Nairobi, Kenya.
Received: March 15, 2010 / Accepted: May 20, 2010 / Published: June 20, 2010.
Abstract: This paper reports on the levels of 8 organochlorine pesticide residues and metabolites in three fish species; Tilapia
(Oreochromis leucostictus), Common carp (Cyprinus carpio) and Mirror carp (Cuprinus spectacularlus) from Lake Naivasha, Kenya.
p,p’-DDT, p,p’-DDE, p,p’-DDD, heptachlor, heptachlor epoxide, aldrin, dieldrin and methoxychlor were analyzed in fish specimens
collected from Lake Naivasha during the months of November - December 2008. The pesticide concentrations (in µg / Kg wet weight)
ranged within 0.42 – 4.185 µg / Kg, for Heptachlor, BDL – 0.291 Heptachlor epoxide, 0.433 - 4.733 Aldrin, BDL – 0.341 Dieldrin, p,p’
DDT, BDL – 6.691 p,p’ DDE, BDL – 27.153 p,p’ DDD, and BDL – 28.867 methoxychlor. The pesticide residue levels varied widely
between and within species. C. spectacularlus showed high pesticide levels followed by C. carpio and O. leucostictus respectively; this
was attributed to the trophic position and age / size of fish. The occurrences of the pesticides indicate recent use in the catchment. The
mean values and ranges of residues found in fish ware below the FAO / WHO maximum acceptable limits in fish and sea food [15]
however increased monitoring is recommended to detect any changes.
Key words: Pesticides, organochlorine, pollution, methoxychlor, ddt, heptachlor.
1. Introduction
Lake Naivasha is the second largest freshwater lake
in Kenya with an approximate surface area of 140
km2[1]. The lake is surrounded by Naivasha
municipality, which is approximately 941 km2, and is
one of the Kenya’s fastest growing municipalities with
a population of about 250,000 people [1]. Lake
Naivasha is characterized as a shallow basin that has an
underground outlet. Lake Naivasha has a total
catchment area of approximately 3,000 km2 [2]. The
surrounding soils are mainly sediments of the former
larger lake and are influenced by the volcanic origins of
the basin rocks and soils [2].
Despite the socio-economic and geographical
significance of Lake Naivasha, its ecosystem is
currently under serious threat due to intensive
Corresponding author addresss; njogupl@yahoo.com
irrigation farming, land subdivision and increased use
of agrochemicals. The growth of the township has also
led to increased runoff and siltation and nutrients being
discharged into the lake through inflowing rivers and
drainage channels. The southern part of the lake has
intensive agricultural practices which are concentrated
on the riparian land of the lake ranging from large
horticultural, floricultural and vegetable farms drawing
enormous quantities of water from the lake for
irrigation [1].
Organochlorine pesticides have been extensively
used for agriculture and vector control purposes in
Kenya [1, 3, 4]. Pesticides are transported to aquatic
bodies by rain runoff, rivers and streams and associate
with biotic and abiotic macro-particles [5, 6, 7]. They are
removed from the surface to the benthic layers by
settling of the particles into the water column [8]. The
lipophilic nature, hydrophobicity, low chemical and
2
Organochlorine Pesticide Residues and Metabolites in Fish from Lake Naivasha, Kenya
biological degradation rates of Organochlorine
pesticides have led to their accumulation in biological
tissues and subsequent magnification of concentrations
in organisms progressing up the food chain [1, 5, 4, 10].
Consumption of fish from contaminated water
bodies is considered to be an important route of
exposure to persistent Organochlorine compounds [9,
11]
. Detectable levels of pesticide residues have been
reported in inland waters in Kenya [1, 4, 5, 7]. The
objectives of this study is to determine the
concentration and distribution of Organochlorine
pesticide residues in fish from Lake Naivasha.
2. Experimental
2.1 Sampling locations
Fish samples were bought from fishermen while still
alive and identification done by officials from the
Kenya Marine and Fisheries Research Institute
(KEMFRI); these included C. spectacularlus, C.
carpio, and O. leucostictus. The samples were labeled
and stored in a Coleman box under ice and transported
to a Laboratory in Nairobi for extraction and analysis.
2.2 Extraction
Twenty grams samples were taken in triplicates and
mixed with 20 g analytical grade anhydrous sodium
sulfate in a mortar and crushed to give a homogeneous
dry mixture. The mixtures were transferred into flasks
and shaken for about 15 minutes with HPLC grade
dichloromethane. The extracts were filtered through a
glass wool plug into an evaporating flask and
extraction repeated three times, with 50 cm3 of
dichloromethane. The extracts were pooled and
evaporated completely at 30 ºC with a rotor vapor
leaving only the lipid portion.
The pesticides were salted out by through
partitioning by dissolving in HPLC grade petroleum
ether and 650 ml distilled water, 20 ml phosphate
buffer pH 6.0, and shaken with hexane. 500 ml distilled
water and 50 ml saturated sodium sulfate was then
added and shaken vigorously. The aqueous layer was
discarded and the hexane layers combined. The hexane
extract was concentrated in rotary vapour.
2.3 Clean up
The extracts were cleaned by passing through a
column packed with analytical grade florisil from
Florisin Company packed with a one inch layer of
anhydrous sodium sulfate both at the top and below the
florisil.
2.4 Analysis
Sample analysis was done using Varian CP 3800
Gas Chromatograph equipped with Electron Capture
Detector. Separation was done using BPX 5 capillary
column of dimensions 30 m x 0.25 mm x 0.25 µm film
thickness. Confirmatory analysis was done using
BPX35 capillary column of dimensions 50 m x 0.25
mm x 0.25 µm film thickness.
A temperature program was used starting from 90 0C
(with hold time of 3 minutes), increased to 215 0C at 8
0C / min (with hold time of 25 min), then increased to
270 0C at 5 0C / min (with hold time of 5.37 min), and
finally ramped to 275 0C at 5 0C / min (with hold time
of 18.63 min). The carrier gas was high purity helium
(99.9995%) with white spot nitrogen as the makeup
gas. Quantification followed external calibration
method using high purity pesticide reference standards
mixture obtained from Ultra Scientific USA.
2.5 Quality Control and Quality Assurance
All sampling, extraction and analysis were done in
triplicate to allow verification detected pesticide
residues. The samples were spiked with PCB 155
during extraction and PCB 198 during analysis to
minimize errors due to detector fluctuations. Recovery
tests were also carried out using the reference pesticide
standards to determine performance of the
methodology. Quantification of pesticide residues was
carried out using high purity pesticide reference
standards
3. Results and Discussion
Organochlorine Pesticide Residues and Metabolites in Fish from Lake Naivasha, Kenya
The precision was measured using relative standard
deviation an was found to be < 12%, accuracy was
>90%. The percentage recoveries were all above 75%
and no corrections were made, results are presented in
Table 1 below.
3.1 Levels of Heptachlor
Table 2 report concentrations of heptachlor in fish,
the highest concentration was found in C. carpio and
the lowest in O. leucostictus. This shows that
heptachlor has a high potential for bioaccumulation.
Compared to its main metabolite heptachlor epoxide,
heptachlor concentrations were 10 to 50 times higher
for most specimens. The highest level of heptachlor
epoxide is found in C. spectacurlus. (0.219 ± 0.12 µg /
Kg) which is 28 times lower than the highest recorded
in the same species (1.575 ± 0.23 µg / Kg).
The fact that heptachlor was detected in fish samples
indicate recent use of the pesticide in the catchment.
The national pesticide records indicate that the
agricultural use of heptachlor was banned in 1986 [13].
The only possible source of these compounds therefore
could be through unscrupulous business activities or
undeclared pesticide formulations.
3.2 Levels of DDTs
The DDTs analyzed in this study included
p,p’-DDT, p,p’-DDE and p,p’-DDD residues and
results presented in Table 2. The highest concentrations
of DDT were detected C. carpio. (7.261 ± 0.43 µg / Kg)
and the lowest in O. leucostictus. The concentration of
p,p’-DDD were highest in most of the cases, followed
by p,p’-DDT. The levels of p, p’ DDE range within
BDL – 6.691 µg / Kg, the highest was found in mirror
carp (6.691 ± 1.23 µg / Kg) and the lowest
concentrations in O. leucostictus (BDL). The high
levels of p,p’-DDD compared to p,p’-DDT implied
degradation of DDT to the DDD metabolite.
Nationally, the agricultural use of DDT was banned in
1986 [13] and this could partly explain the high ratio of
DDE to DDT. Currently, the use of alternatives such as
3
pyrethroids are strongly encouraged in the country,
while DDT use is restricted to emergency control of
mosquitoes under incidences of malaria epidemics
only.
3.3 Levels of Methoxychlor
Methoxychlor (C16H15Cl3O2) is an organochlorine
insecticide used for the control of livestock parasites
and a variety of pests on ornamentals, fruits and
vegetables. Due to persistence in environment, the use
of methoxychlor in Kenya was banned in 1984 [13]. The
levels of methoxychlor were significantly high in O.
leucostictus (28.867 ± 3.22 µg / Kg), followed by C.
carpio. (10.07 ± 1.12 µg / Kg), the low levels in C.
spectacurlus are unusually low compared to other
pesticides indicating potential of degradation of
methoxychlor in C. spectacurlus as indicated in Table
2. The presence of methoxychlor in fish also indicates
recent use of the pesticides in the catchment.
3.4 Levels of Aldrin and Diedrin
Aldrin and dieldrin detected in almost all samples
analyzed, the data is presented in Table 2. Aldrin
residues ranged from 0.169 – 4.733 µg / Kg, whereas
dieldrin was between BDL - 0.131 µg / Kg. The highest
concentrations of aldrin were detected in C.
spectacurlus due to its position in the food chain;
dieldrin was lower than aldrin in all samples analyzed.
The presence of higher levels of aldrin in most of the
sites compared to dieldrin would imply contamination
due to recent use of aldrin. In the soil, aldrin is
converted by epoxidation to dieldrin. Dieldrin is more
stable and highly persistent in the environment. Both
aldrin and dieldrin are known to strongly adsorb to soil
with high organic matter. The presence of these chemiTable 1 Percentage recoveries for pesticide residues in fish.
Pesticides
p,p’ DDE
p,p’ DDT
Methoxyxhlor
Aldrin
Heptachlor
Average % recovery
86.02 ± 2.33
79.56 ± 2.89
75 .52± 2.13
80.23 ± 2.12
76.12 ± 1.56
4
Organochlorine Pesticide Residues and Metabolites in Fish from Lake Naivasha, Kenya
Table 2 Organochlorine pesticide residue concentrations (µg / Kg wet weight), lipid content (% wt / wt) length (cm), moisture
content (%), and weight (g), of fish from Lake Naivasha.
O. leucostictus
Fat content
1.87 ± 0.97
0.78 ± 0.01
0.92 ± 0.19
81.89 ± 3.07
79.22 ± 3.81
79.78 ± 1.25
Weight
202.69 ± 3.05
829.96 ± 196.67
765.13 ± 29.75
Length
22.57 ± 1.02
41.1 ± 3.94
41.66 ± 0.76
ά - HCH
0.567 – 0.717
0.602 – 0.734
0.602 – 1.485
δ - HCH
0.543 – 0.699
0.678 – 0.834
0.565 – 2.286
p,p’ DDE
0.205 – 0.466
0.135 – 0.514
0.206 – 6.691
p,p’ DDT
BDL – 1.908
BDL – 7.261
BDL – O.716
p,p’ DDD
BDL – 21.127
BDL – 27.153
0.228 – 4.331
Methoxyxhlor
BDL - 28.867
0.169 – 10.07
BDL – 2.432
Heptachlor
0.410 – 1.007
0.421 – 4.185
0.809 – 1.575
Heptachlor epoxide
BDL – 0.032
BDL – 0.142
0.139 - 0.219
Aldrin
0.433 – 1.631
0.169 – 2.888
1.347 – 4.733
Dieldrin
BDL-0.131
BDL – 0.341
BDL – 0.131
Fat content
1.87 ± 0.97
0.78 ± 0.01
0.92 ± 0.19
4. Conclusion
The mean values and ranges of residues found in fish
were significantly below the FAO / WHO maximum
acceptable limits in fish and sea food [15] however
increased monitoring is recommended.
Acknowledgement
The authors wish to acknowledge Jomo Kenyatta
University of Agriculture and Technology. The authors
wish also to acknowledge the Lappeenranta University
of Technology, CIMMO- N-S-S project for providing
scholarship for the completion of the study.
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