Journal of Environmental Protection, 2011, 2, 761-768
doi:10.4236/jep.2011.26088 Published Online August 2011 (http://www.SciRP.org/journal/jep)
761
Levels of Agricultural Pesticides in Sediments and
Irrigation Water from Tono and Vea in the Upper
East of Ghana
Kenneth B. Pelig-Ba
Faculty of Applied Sciences, University for Development Studies, Navrongo, Ghana.
Received April 7th, 2011; revised May 15th, 2011; accepted June 19th, 2011.
ABSTRACT
Water and sediment samples were taken from selected irrigation dams located at Tono and Vea in the Upper East Re-
gion of Gha na and ana lyzed for o rganic pesticides using ga s chroma tography. Sixteen organ ic residues were id entified
of which thirteen had at least some trace concentrations ranging from 0.001 to 25.4 µg/L. It was found in the labora-
tory that the concentration s of DDT, BHC and heptachlor were above the upper limited recommended by WHO and the
concentrations of DDT in both reservoirs were higher than 20 times the recommended limits. High concentrations of
DDT were found in the water samples while the other two residues were identified in the sediments. The high DDT
concentratio n in wa ter was due to 1) th e initial amount o f DDT applied and the period in th e reservoirs , 2) a half-life of
350 days suggested that much of the DDT originally used was not destroyed if applied less than this period, 3) its low
solubility in water did not allow for dissolution and subsequent dispersal in water; 4) the indiscriminate uses of DDT
for fishing as confirmed by the local people The high DDT level suggested that the water is not safe for many aquatic
organisms and even humans. Generally the levels of these organic residues suggested that the dams have been polluted
due to human activities such as farming and the unorthodox method of fishing. Therefore, steps should be taken to re-
duce the levels of DDT concentrations to preserve the aquatic life in the dams.
Keywords: Pesticides, Sediments, Irrig atio n Da ms , Tono, Vea
1. Introduction
Various attempts to increase yield in agriculture, horti-
culture or forestry have been a preoccupation of mankind
to reduce poverty and eliminate hunger in the world at
large and developing countries in particular. This has
resulted in the effort to protect especially food crops
from being destroyed by insects and pests. Consequently,
it has led to the adoption of various crop protection
measures particularly the use of synthetic chemicals such
as pesticides. As a result of the ease in which these
chemicals eliminate their prey, most crop scientists have
adopted it as the saviour or the best way to reduce their
burden on the search for more appropriate, reliable, fast
and safer method of protection. Uses of these pesticides
have not only been extensive but also indiscriminate thus
creating problems in soil and water pollution. Since the
mode of application is sometimes not done according to
right prescriptions, pesticides can either miss their target
points or get drifted to other areas where they are not
required. Furthermore, the methods of applying these
chemicals also affect the target organisms. Frequent and
indiscriminate use of these chemicals have resulted in the
development of pesticide resistant insects, destruction of
beneficial organisms, rapid resurgence of target pest
population following treatment, uncontrolled outbreak of
secondary pest, undesirable environmental effects caus-
ing socio-economic problems and high mortality rate to
non-target organisms, including man [1]. Since the in-
troduction of these pesticides, farmers in Ghana and for
that matter, the Upper East Region in one way or the
other have participated in some of the indiscriminate uses
of these hazardous chemicals in the environment either
for the control of pests or in an attempt to improve the
fertility of soils. Another reason for indiscriminate ap-
plication is an attempt to provide needed protein sources
such as fish resulting in the use of these chemicals in
some water bodies. However, if these chemicals were
efficiently used, there would be minimal effect on the

Levels of Agricultural Pesticides in Sediments and Irrigation Water from Tono and Vea in the Upper East of Ghana 762
environment, but due to the ignorance and lack of educa-
tion on the right uses of these pesticides in many cases,
this has not been the case. It was in this light that this
study was undertaken to assess the level of organic-de-
rived pollutants in water and sediments in two selected
irrigation dams in the Upper East Region of Ghana and
the possible health impact on the local people who con-
tinue to consume fish and crop products from these
dams.
2. Location
The study was limited to water and sediments from Tono
and Vea irrigation dams in the Kassena-Nankana and
Bolgatanga Districts respectively, of the Upper East Re-
gion of Ghana. Tono is located on latitude 10˚60′N and
longitude 1˚07′W while Vea is on latitude 10˚45′N and
longitude 1˚W (Figure 1). The vegetation in the study
area is dry guinea savannah characterized by short
grasses and fire-resistant trees. The climate is sub-Sahe-
lian, with mean minimum and maximum temperatures of
14 and 40˚C, respectively.
The mean annual rainfall ranges from 850 to 1000 mm
which occurs in the months of May-October, followed by
a prolonged dry season. The first part of the dry season
from November to mid February is characteristically cold
and dry with dusty harmattan winds. The rest of the dry
season is usually characterized by a wide temperature
range from 14˚C at night and to over 35˚C during the day.
Humidity is also very low making the daytime tempera-
ture high and less comfortable [2]. The water reservoirs
of both dams are man-made. The Vea project serves
eight villages with a total farmer population of 6000
whiles the Tono project serves three villages. The maxi-
mum surface area of Vea reservoir is 405 ha with a
maximum storage of 1.7 × 107 m3 serving 21 km of main
canals. The Tono reservoir has a size of 16 ha and a
maximum storage of about 5.0 × 105 m
3. The irrigation
projects were constructed to provide water for livestock
and to facilitate dry season farming. Farmers at these
sites combine rudimentary tools with modern equipment
and fertilizers to increase yield. The main types of farm-
ing adopted in these irrigation sites are mono and mixed
cropping which are all at subsistence level. Fishing in
these dams is officially allowed under controlled and
limited scale.
3. Literature Review
Pollution has been defined as ‘introduction by man into
the environment of substances or energy liable to cause
hazards to human health, harm to living resources and
ecological systems, damage to structures or amenity, or
interference with legitimate uses of the environment [3].
The media that could be polluted are air, land and water.
Any substance that disallows the normal use of water or
air is regarded as a pollutant. Pollutants can either be
inorganic or organic. Inorganic pollutants are derived
from compounds of inorganic substances while those
from organic are from hydrocarbons and their derivatives.
Organic pollution was first manifested following the
increase in the use of pesticides in the years immediately
Figure 1. Location of Tono and Vea dams in the upper east region of Ghana.

Levels of Agricultural Pesticides in Sediments and Irrigation Water from Tono and Vea in the Upper East of Ghana763
after the Second World War. The first organochlorine
pesticides to be produced were DDT, Lindane and Diel-
drin. Over the period 1950-1970 the number of individ-
ual pesticides increased from about 20 to 140 types while
the number of insecticides rose from 40 to 170 types [4].
Pesticides are used on and around plants either to fight
off plant diseases or rid off bugs that feed on or kill them.
If the soil pH is very acidic, the applied pesticides will not
be absorbed by the plant but held on to the soil matrix and
washed away by water which subsequently run into
streams, rivers, lakes, or groundwater where they become
pollutants [12]. Application of fertilizers containing am-
monium or urea speeds up the rate at which acidity de-
velops. The decomposition of organic matter also adds to
soil acidity [13]. Soils contain carbon (C) in both organic
and inorganic forms. In most soils, more C is held as soil
organic carbon (SOC). Soil organic matter (SOM) is used
to describe the organic constituents in the soil such as
tissues from dead plant and animal products obtained
decomposing into the soil. Soil organic carbon is impor-
tant for the functioning of ecosystems and agro-ecosys-
tems, influences the physical structure of the soil, the
water holding capacity, its ability to form complexes with
metal ions and supply of nutrients. Loss of SOC can
therefore, lead to a reduction in soil fertility, land degra-
dation and even desertification [14]. For this study the
parameters to be analyzed are pH, electrical conductivity,
organic carbon and pesticides of both water and sediments
from the two irrigation dams in the study area. Various
pesticides have different half-lives which are dependent
on the medium in which the chemical is applied. It has
been reported for example that the half-life for DDT in the
water environment is 56 days in lake water and about 28
days in river water.
Chemical organic pollutants are toxic substances that
are synthesized, or are by-products of combustion or in-
dustrial processes. These organic pollutants are charac-
terized by their chemical properties such as toxicity and
persistence. As a result of their persistence, they remain
in the environment for a long time before degrading and
are normally termed Persistence Organic Pollutants
(POPs). This property makes them to be transported to
long distances by wind or water before being deposited.
The effects on human health due to exposure to these
pollutants vary according to the type, level and length of
the exposure. Well known POPs include dioxin, poly-
chlorinated biphenyls (PCBs), and dichlorodiphenyltri-
chloroethane (DDT). Many developed nations have
banned the use of many of these pollutants as their per-
sistence in the environment has been known for many
years and many alternatives are now available. The
health of fish and other organisms in an aquatic envi-
ronment is influenced by the complex interplay of phys-
icochemical factors. Some of these factors are tempera-
ture, pH, electrical conductivity and total dissolved solids
(TDS). It was observed that the optimum surface tem-
perature in the tropics favourable for fish growth oc-
curred in the range from 23˚C to 28˚C [5]. This work was
supported by others and they [6] also suggested that the
optimum temperature range favourable for the growth of
fish is between 20˚C and 30˚C. Other studies revealed
that, the desirable pH range for fish production is 6.5 -
9.0 [7,8]. It further suggested that, the optimum water pH
for culturing is from neutral to slightly alkaline 7.0 - 8.0
[5]. It was however, stated by [9] that, excessively low or
high pH is detrimental to fish production in the tropics.
Slow growth results from pH level below the range of 6.0 -
6.5. Acid death point is reported to be below pH 4.0 whilst
the alkaline death point pH is above 11.0.
Rainfall which is the main source of water into surface
water is considered acidic if the pH falls below 5.6, the
normal equilibration value of carbon dioxide and water at
25˚C [10]. Airborne material probably contributes to the
increase in the pH of subsequent rainfall [11]. The im-
pact of acidity due to decrease in pH of rainfall is re-
duced to a certain degree by the buffering capacity of the
area soils. Soil pH is an important factor for farmers and
gardeners for several reasons in that many plants and
some microorganisms prefer varied media for their sur-
vival. Some diseases tend to thrive well either in alkaline
or acidic soils. Also pH can affect the availability of nu-
trients in the soil.
4. Methodology
4.1. Selection of Farmer and Individuals
The study began with the selection and interview of
groups of farmers and individuals living around the vi-
cinity of the two dams on the type of chemicals used and
other relevant base information required. This work was
carried out in November, 2007 to May 2008. Farmers
who were known to be fisher men were targeted while
individuals from the communities were selected ran-
domly.
4.2. Collection of Water and Sediment Samples
Soil and water samples were collected from the two dams
at Tono and Vea irrigation sites. A PVC pipe of 101.6
mm (4 inches) diameter and 508 mm (20 inches) length
was sunk into the soil. The pipe was then removed with
the soil material captured and sealed in a polyethylene
bag to minimize adsorption and volatilization of analytes
during the transit period to the laboratory. Both water
and sediment samples were labelled as T and V for Tono
and Vea respectively. Water samples were collected from
a depth of 0.2 m into a well-cleaned glass of 1.5 litre

Levels of Agricultural Pesticides in Sediments and Irrigation Water from Tono and Vea in the Upper East of Ghana 764
capacity and sealed with double cap device. These sam-
ples were filled to the top without leaving any space in
order to prevent any release of dissolved gases during the
transit period. This was done monthly from January 2008
to May 2008. The pH, conductivity and temperature of
the water samples were determined at the sites.
In the laboratory, soil samples were carefully removed
from the PVC pipe and its total length recorded. Later, it
was sectioned into the various layers and left to dry un-
der laboratory temperature for about 7 days. The air-
dried samples were then disaggregated, after which 25 g
of each was ground with a porcelain mortar and pestle
and sieved through a 2 mm nylon sieve. The sediments
were then labelled accordingly and stored in enclosed
containers in a cupboard for analyses.
4.3. Sample Analyses
The soil pH was determined by shaking a sample in a
ratio of 1 part soil to 2 parts distilled water. SOC was
determined based on the Walkley-Black chromic acid
wet oxidation method. About 1.0 g of fine sediment
sample was weighed into a 250 mL conical flask, fol-
lowed by 10 mL of 1 M K2Cr2O7 solution, and swirling
gently to disperse the particles. Then 20 mL of concen-
trated H2SO4 was added, and further a 100 mL distilled
water added and allowed to stand for 30 minutes. About
3-4 drops of starch indicator was added and titrated
against 0.5 M FeSO4, and repeated two times.
Pesticide residues were estimated using international
standard methods [15]. One litre of water was put into a
separatory funnel and 75 mL of dichloromethane (DCM)
added and shaken for sometime to thoroughly mix the
solute and solvents and later allowed to stand to separate
out. The lower layer extract (DCM) was then released
into an evaporating tube and the upper layer (water) dis-
carded. A drop of iso-octane was added to the extract and
the volume reduced to 0.5 mL and later transferred into
another test tube. The extract was conditioned with 4 mL
(3 + 1 mL) cyclohexane (CH): dichloromethane (DCM)
mixture followed by 3 mL CH. With the SPE connected
to a test tube, the extract was dropped onto the SPE and
eluted with 4 mL CH. Elution was continued with 4 (3 +
1) mL CH:DCM mixture and the volume finally reduced
to 0.5 mL and transferred into a 2 mL sample vial for a
gas chromatography run. For sediments, about 10 g was
weighed into a centrifuge glass tube and 50 mL DCM
added. It was shaken vigorously and put in an ultrasonic
bath for 15 minutes, then on to a shaker for 60 minutes. It
was then centrifuged and the supernatant collected into
an evaporating tube and a drop of iso-octane added. The
volume was finally reduced to 0.5 mL. This was then
transferred into a test tube, rinsed and added to extract
and reduced to 0.5 mL. The concentration of the pesti-
cide reported in this study, was based upon the lowest
concentration that could consistently be reliably recov-
ered (>70%) in the laboratory from fortified samples [16].
If this percent recovery could not be achieved, the most
consistent pesticide recovery was used to establish the
quantification limit (QL). The QL for all pesticides de-
tected in both water and sediment samples in this study
was 0.001 µg/L and 0.001 mg/kg dry weight respec-
tively.
5. Results
5.1. Basic Information
The interviews conducted with the farmers and staff of
the irrigation companies, revealed that pesticides used by
farmers at the irrigation sites include roundup, atrazine,
selective endosulfan, kuzitrine and DDT. It was also ob-
served that some natives and fishermen use artificial
chemicals such as DDT for fishing. Some of the chemi-
cals are usually applied at night so that by daybreak the
fishes would have died and floated for collection. Some
of the chemicals were also sprayed on the cultivated
crops on farms.
5.2. Physicochemical Properties of Water and
Sediment Samples
The water temperatures varied monthly from 25.1˚C to
34.2˚C for Tono and 24.7˚C to 29.4˚C for Vea from
January 2008 to May 2008. The pH values of water ob-
tained during this period varied from 6.6 to 7.2 for Tono
and 6.8 to 6.9 for Vea. This is not different for normal
surface water. The electrical conductivity of the reser-
voirs was generally low, less than 30 µS/cm and did not
have any overall effect on the quality of the water from
both reservoirs. This therefore suggested, that the water
in the reservoirs was not mineralized, since it contained
low dissolved solids. Water from Vea recorded a TDS
value of 106 mg/L, while that of Tono recorded 57.1
mg/L. These values are low compared to what is nor-
mally observed in many surface water systems. Soil pH
values obtained for Tono and Vea ranged from 6.02 to
6.49 and 6.05 to 6.61 respectively for the three layers. In
Tono the highest pH was obtained in the third layer (C)
(Table 1) while the second layer in Vea recorded the
highest. No marked trend was observed probably because
either the sample size was low or that the factors affecting
the pH were not the same in the two reservoirs. However,
the soil pH was generally lower than that of the water in
both places.
Soil organic carbon values for the various layers are
also indicated in Table 1. The highest SOC was obtained
in Vea (2.89%) with the site giving relatively higher val-
ues than Tono. There was a decrease of SOC from top to

Levels of Agricultural Pesticides in Sediments and Irrigation Water from Tono and Vea in the Upper East of Ghana 765
bottom of the soil profile suggesting that decayed vegeta-
tive parts on top are responsible for the high values on
the top horizon. Also the higher value of SOC in Vea
could be attributed to the higher acidity of the top soil
relative to Tono since the destruction of organic matter is
facilitated by the acidity of the medium.
5.3. Levels of Pesticides in Water and Sediments
A total of 16 pesticides were analyzed of which thirteen
were detected in both water and soil sediments. Concen-
tration levels of some of the pesticide residues were be-
low the quantification limit (QL) of 0.001 µg/L in the
water and 1.0 µg/L in the sediments. Most of the residue
concentrations fell below the WHO (1993) guidelines.
However, a few pesticides such as p, p-DDT, were ob-
tained in water at levels of 22.4 µg/L at Tono and 25.4
µg/L at Vea, while for β-BHC it was 3 µg/L for Tono
and 5 µg/L for Vea in sediments, Heptachlor epoxide
level was 1.0 µg/L for sediments in the two places. These
were the only pesticides that were higher than the guide-
line limits. The guideline limit of p, p-DDT values is
1.00 µg/L while the value for β-BHC in the sediments is
2 µg/L (Table 2) and that for the heptachlor epoxide is
0.1 µg/L. The high value of DDT in the two dams sug-
gested that there is either an increase in use of these
chemicals in the two dams or a high drift from surround-
ing areas.
Although these dams are used for irrigation and wa-
tering of animals, fishing goes on and sometimes takes
place at odd hours of the day. The possible use of DDT
for fishing, as was revealed through the interviews, could
explain the high concentration in the dams. It is worth
noting that DDT is among the banned chemicals in
Ghana.
Furthermore, β-BHC is also used to dress seeds and
any run-off water can wash it into the dam while those
Table 1. Organic carbon and pH of soil sediment layers at various depths.
TONO TONO TONO VEA VEA VEA
DEPTH (cm) S.O.C. (%) SOIL pH DEPTH (cm)S.O.C. (%) SOIL pH
LAYER A 7.00 2.31 6.32 13.72 2.89 6.05
LAYER B 16.13 0.75 6.02 25.65 1.12 6.61
34.16 0.37 6.79 46.86 0.51 6.40
Table 2. Pesticide levels (µg/L) in water and sediment samples.
SAMPLES
TONO VEA PARAMETER
Water Sediment Water Sediment
WHO (1993)
Alpha BHC 0.007 <1 0.063 <1 2.00
Gamma BHC 0.006 <1 0.035 <1 2.00
Beta BHC 0.050 3 0.004 5 2.00
Delta BHC 0.004 1 0.004 1 2.00
Heptachlor <0.001 <1 0.009 <1 0.10
Aldrin 0.002 <1 <0.001 <1 0.03
Heptachlor Epoxide <0.001 1 <0.001 1 0.10
p, p’-DDE 0.002 <1 0.004 <1 1.00
Dieldrin 0.001 <1 0.007 <1 0.03
Beta Endosulfan 0.007 <1 <0.001 <1 0.03
p,p’-DDD <0.001 <1 0.099 <1 1.00
Endosulfan Sulphate <0.001 <1 0.007 <1 0.03
p,p-DDT 22.4 <1 25.4 <1 1.00

Levels of Agricultural Pesticides in Sediments and Irrigation Water from Tono and Vea in the Upper East of Ghana 766
that are applied to protect the vegetative cover against
flying insects and pests can also be blown by wind into
the dam water. Comparatively high β-BHC was obtained
in the soils than the water. The levels of δ-BHC and hep-
tachlor epoxide were similar in the two dam sites. This
may be because adsorption on sediments causes the bio-
degradation of the pesticides easily since biodegradation
of organic residues can be enhanced by both temperature
and microorganisms in the soil. This may not be possible
with water where the pesticides are not soluble and can
be maintained for a long period.
5.4. Comparison of Pesticide Levels in Vea and
Tono Dams
Among the 16 pesticides detected in the water samples
from the two dams, 9 were found in Vea and 8 in Tono.
These are all represented in Figure 2 except DDT. High
DDT was found in both places but, Vea recorded a
higher value of 25.4 µg/L than Tono, which had a value
of 22.4 µg/L. These values were far higher than the other
residues and could not therefore be represented in the
figure. From Figure 2, it is observed that heptachlor ep-
oxide and p,p-DDD were not detected in the water sam-
ples from Tono but were significant in the Vea dam sam-
ples. Similarly, Aldrin was detected in the Tono but
could not be seen in the Vea samples. In fact, p,p-DDD
recorded the highest level among the pesticides presented
and was found in Vea. β-BHC was highest in the Tono
dam but very low in the Vea dam. The α-BHC and
γ-BHC were higher in Vea as compared to that in Tono
dam. Figure 2 shows that pesticide residues generally
were higher in the water samples in Vea than Tono.
6. Discussion of results
6.1. Physicochemical Characteristics
Physicochemical parameters analyzed for the water
showed generally good conditions for the growth, devel-
opment and survival of aquatic life especially fish in the
reservoirs. The temperature values were within that sug-
gested by [6] and [5] indicating that fish production
could be favoured in these reservoirs. This is confirmed
by the regular fishing in the dams. The people do not use
prescribed methods for fishing but resort to the use of
chemicals such as pesticides without recourse to the
damage to the environment or their health. Water pH
values were within that obtained by [7] as well as [5] and
[9] for fish production. The pH obtained was not above
the optimum pH conditions for fish production but fa-
vours spawning.
6.2. Pesticides
The half-lives of DDT, β-BHC and heptachlor epoxide to
be respectively were estimated by [17] to be 8, 1 and 3
years in soil. Also [18] found the half-life of DDT to be
15 years in soil, 350 days in surface waters and 31 years
in groundwater. The detection of high levels of p, p-DDT
in the water samples from both reservoirs suggested that
DDT might have been used within a certain short period
of time. But in the soils, the level was lower even though
the half life is longer than in water suggesting a preferen-
tial use of the chemical in each of the environmental sys-
tems. Hence high DDT in both reservoirs can be attrib-
uted to 1) the initial amount of DDT applied and the pe-
riod within which it entered into the reservoirs; 2) a half-
life of 350 days suggested that much of the DDT origi-
nally used was not destroyed, if applied less than this
period, 3) its low solubility in water may not allow for
dissolution and subsequent dispersal in water; 4) the in-
discriminate uses of DDT for fishing as confirmed from
the local people could account for high level of DDT.
Since DDT is officially banned, it is less likely that ap-
plication would have been deliberate.
The half-life of BHC and heptachlor epoxide suggests
that they were also applied within a short period before
the study or that they have been accumulating in the en-
vironment. BHC is normally used for spraying crops and
dressing seeds against insect attack. Its high level in
sediments was due to the application on either water
bodies which settle onto the sediment or transported from
sprayed crops during the farming period. Due to the
acidic nature of the soils, pesticides are loosely adsorbed
to soil particles and surface runoff washes away most of
the applied pesticides to any nearby water body. Consid-
erable levels of other pesticides were observed in espe-
cially the water bodies suggesting that these might have
been applied in not a very distant time considering the
fact that the half-life in water is usually less than in soil.
6.3. Health Implications of Pesticides
Most pesticides have overall polarity and tend not to be
washed away by rain. Some are fat soluble and are parti-
tioned between fatty tissues and blood when food con-
taining them is eaten. The pesticides p,p-DDT BHC and
heptachlor epoxide have negative health implications that
has led to the ban on their use. Generally DDT is not
very toxic to humans but its LD50 in rats is 110mg/kg
[19]. It has been shown that a human test population
group ingested 35 mg daily for an extended period with-
out any ill effects but its fatal dose is estimated to be 500
mg/kg for humans [19]. Frequent use of DDT and other
pesticides can lead to resistance of some organisms in
water bodies where it is applied and therefore render it
useless when required for the purpose of eradication of
insects. It is possible that some fish will take and bio-
magnify it. It has been shown that some fish such as the

Levels of Agricultural Pesticides in Sediments and Irrigation Water from Tono and Vea in the Upper East of Ghana767
Figure 2. Plot of pesticide levels at Tono and Vea dams. (HE-Heptachlor epoxide, ES-Endosulphan).
rainbow trout has an LD50 for 96 hours is 7 µg/L and it is
also extremely toxic for cold blooded creatures. DDT
affects the reproduction of higher animals. Because of
the lipophilic properties of DDT and its breakdown
products, it tends to be accumulated in food chains and in
the environment. It has therefore been replaced by
non-persistent insecticides. It is moderately toxic to birds,
fish and aquatic life. It is resistant to degradation, has
widespread persistence in the environment, and high po-
tential for bioaccumulation; this work concludes that
DDT and its metabolites should be regarded as a major
hazard to the environment. In rats, following oral ad-
ministration, DDT is metabolized to DDE, DDD and
DDA among others. It accumulates in fatty tissues of

Levels of Agricultural Pesticides in Sediments and Irrigation Water from Tono and Vea in the Upper East of Ghana 768
mammals and is excreted in milk. DT50 in tropical re-
gions is about 3 months; in temperate regions, DT50 is 4 -
30 years. People depending on these reservoir waters are
at risk of nerve poisoning and reproduction disorders. It
is accumulated in food chains within the environment,
fatty tissues of mammals and milk. However, dieldrin is
more toxic to fish than aldrin. For example, the LD50 for
striped mullet for aldrin is about 100 µg/L while that for
dieldrin is 23 µg/L [19].
7. Conclusions
Of the 16 pesticides tested, only 3 were at higher levels
than recommended guideline values. These were DDT,
BHC and heptachlor epoxide. This was attributed to the
frequent uses of these particular chemicals for activities
such as fishing. DDT concentration was found to be
highest and this was explained by 1) the initial high
amount of DDT applied and the short period of stay in
the reservoirs; 2) a short half-life of 350 days suggested
that much of the DDT originally used was not destroyed
if applied less than a year before the study and 3) its low
solubility in water may not allow for dissolution and
subsequent dispersal in water; 4) the indiscriminate use
of DDT for fishing as confirmed from the interviews of
the local people.
8. Acknowledgements
This work could not have been possible without the ef-
forts of Mr. Alex Siaw who did the sampling and analy-
sis.
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