African Journal of Aquatic Science 2007, 32(2): 153–157
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AFRICAN JOURNAL OF
Lead levels in rivers, sediments and fish ponds in the Ibadan metropolitan
area, south-west Nigeria
Olanike K Adeyemo
Department of Veterinary Public Health and Preventive Medicine, University of Ibadan, Ibadan, Nigeria
Received 5 May 2006, accepted 15 November 2006
Lead levels in rivers, their surface sediments, and in fish ponds in Ibadan, Nigeria, were assessed in the 2003–2004 dry and wet
seasons. It was planned to reduce lead levels in petrol, regarded as the major source of lead in the Nigerian environment, to 0.15g
by the end of 2002 and to zero by 2004, while 2005 was to be the phase-out year for lead additives in petrol throughout the sub-
Saharan region. The WHO-recommended limit for lead levels in surface water is 0.01mg l
. Despite the now-reduced lead content
in petrol, lead levels in surface waters ranged between 0.5–2.35mg l
(mean 0.76mg l
) and 1.15–2.20mg l
(mean 1.34mg l
during the dry and rainy seasons, respectively. Lead levels in river sediments ranged between 0.9–4mg kg
(mean 1.86mg kg
and 1.15–2.2mg kg
(mean 1.49mg kg
) during the dry and rainy seasons, respectively. Lead levels in fish ponds were even
higher, at 1.09–2.9mg l
(mean 1.88mg l
). The present situation therefore indicates severe lead contamination of aquatic systems
in Ibadan City, which portends a serious public health risk to humans. A detailed assessment of other sources of lead pollution in
the Nigerian environment — besides vehicle emissions — is required if lead pollution is to be reduced effectively.
During the 20th century, emissions of lead into the environ-
ment have dominated biogeochemical cycles on a global
scale (Dunlap et al. 2000). Lead occurs naturally in uncont-
aminated aquatic and terrestrial ecosystems at relatively
low levels. Most of the lead in the environment is from
anthropogenic sources, far exceeding that from natural
sources (Maduka 2001, Abulude et al. 2006). Toxic organic
forms of lead are also present in the environment from
direct inputs, including the manufacture, transport, storage
and combustion of leaded petrol and the possible chemi-
cal/biological methylation of inorganic lead in anaerobic
sediments (Odiete 1999, Eja et al. 2003).
Due to increasing evidence of the harmful effects of lead
on human health, most Western industrialised nations started
to reduce lead additives in petrol in the 1980s, and since the
1990s only unleaded petrol has been marketed (Sridhar et al.
2000). In Nigeria, however, due to very low levels of environ-
mental awareness, these lead-generating processes and
products continue to be used and patronised. The lead limit
in petrol sold in Nigeria is 0.7g Pb l
. However, the lead level
in the Nigerian-produced petrol averages about 0.25g Pb l
However, the lead level in the Nigerian-produced petrol aver-
ages about 0.25g Pb l
; with a national consumption of 25
million litres per day and a 75% emission rate of lead as
particulate lead (Maduka 2001).
The main sources of lead pollution in Nigeria, besides
petrol, include lead mining and smelting, paints, piping,
fixtures and solder, and lead-based batteries. Although the
amount of lead pollution from leaded petrol in Nigeria
has been quantified with some level of accuracy, the contri
butions from other sources are still the subject of specula-
tion. Lead has no known nutritional, biochemical or physio-
logical function (Abulude et al. 2006). Lead is also toxic to
all aquatic biota and there is some evidence of the bioavail-
ability of sediment-bound lead to deposit-feeding species
(Bryan and Langston 1992, Davies et al. 2006). In compari-
son to water testing, sediment testing reflects the long-term
quality situation independent of current inputs (Hodson 1986,
Biney et al. 1994). Sediment tests are a better basis for
fundamental comparisons with other flowing waters. In addi-
tion, lead can be accumulated directly from sea and fresh
waters, especially in organisms that utilise gill tissue as their
major route of nutrition (Eja et al. 2003, Abulude et al. 2006).
This study assessed the lead levels in rivers and their
sediments and also in randomly-selected aquaculture
ponds in Ibadan City. Rivers serve as sinks for urban
drainage and agro-industrial effluents and are also impor-
tant in fisheries production, as a large number of settle-
ments and fish farms situated along rivers depend on them
for their water supply. The results of this study will therefore
help to assess the health risk implications to inhabitants of
water usage and fish consumption from these sources.
Materials and methods
Ibadan (3°5NE, 7°20NN), in Oyo state, Nigeria, is the
largest city in West Africa and the second largest in Africa,
Keywords: fish pond, lead, Nigeria, pollution sources, river, sediment
covering an area of 240km
. It is situated at an average
height of 200m above sea level and is drained by three
major river basins, the Ogunpa, Ona and Ogbere. Figure 1
illustrates the sampling points in the study area that
encompasses 11 local government areas. A GPS
) was used to determine the co-ordinates
of each sample site.
Water and sediment sampling
Two replicates — each of upstream and downstream
water samples — were collected from the rivers between
October 2003 and March 2004 during the dry season, and
repeated between August and September 2004 during the
rainy season. Two replicates of midstream water samples
were collected at each sample point, using clean polyeth-
ylene containers pre-washed in nitric acid and thoroughly
rinsed with deionised water. Sediment samples were
collected concurrently (using plastic spatulas) and stored
in polyethylene containers. Water samples were also
collected from three aquaculture ponds in each of 10
randomly-selected fish farms. Samples were stored on ice
in a dark cooler box, transported to the laboratory, stored
at 4°C and analysed within six hours of collection.
The lead content of the samples was determined by standard
spectrometric methods after UV irradiation of unfiltered water
samples and acid digestion of solid samples with analytical
(DWAF 1992). Digested samples were filtered
into a 20ml standard flask, made up to the mark with distilled-
deionised water and stored in a refrigerator prior to chemical
analysis. The water extracts were analysed for lead by an
atomic absorption spectrometer. Each sample was analysed
in duplicate and the average of the results was calculated.
General laboratory quality assurance measures were always
observed to prevent sample contamination and instrumental
errors. Spectrometer wavelengths were set daily by standard
instrumental procedures. No certified reference materials
were used to check analytical effciency.
Lead levels in surface water ranged between 0.5–2.35mg l
(mean 0.76) and 1.15–2.20mg l
(mean 1.34) during the dry
and rainy seasons, respectively (Figure 2). Sediments had
lead levels of 0.9–4mg kg
(mean 1.86) and 1.15–2.2mg
(mean 1.49) during the dry and rainy seasons, respec-
tively (Figure 3). At 1.09–2.9mg l
(mean 1.88) (Figure 4),
the lead content of fish pond water was even higher than that
of the river surface water. All data are presented as mean ±
standard error of mean (SEM).
The existence of heavy metals in aquatic environments has
led to much concern over their influence on plant and animal
life in these environments, and indeed on man’s need for
uncontaminated water and food (Obodo 2003, Chindah et al.
2004, Davies et al. 2006). The accumulation of these
elements has direct consequences for flora and fauna in
aquatic ecosystems, and also for man.
In this study, lead levels were found to be notably high.
The higher mean lead levels observed in the sediments
during dry and rainy seasons, respectively, confirmed that
pollutants accumulate and remain in sediments over long
periods of time, according to their chemical persistence and
the physicochemical and biochemical characteristics of the
substrata (Barbour et al. 1999, Eja et al. 2003). Sediment is
also the major depository of metals in some cases, holding
more than 99% of the total amount of a given metal present
in the aquatic system (Odiete 1999). The inverse proportion
of mean lead levels in rivers (0.76 and 1.34mg kg
sediments (1.86 and 1.49mg kg
) during the dry season,
relative to the rainy season, is in agreement with the findings
of Barbour et al. (1999) that, after sedimentation, portions of
fixed contaminants can be remobilised to re-enter the water
cycle as a result of desorption, whirling up, weathering and
the physical and physiological activity of benthic organisms.
The lead levels found in water, sediments and fish pond
water sampled in this study, during both seasons, are higher
than the recommended standards for drinking water set by
the WHO (1985) and for pollution control set by the Federal
Environmental Projection Agency of Nigeria (FEPA 2003),
and therefore the water should be considered unsafe for
drinking or aquaculture purposes. Toxicological studies have
shown that lead is especially toxic to fish. Sub-lethal effects
in fish include changes in morphology, metabolism and
enzymatic activity, increased mucous formation, delayed
embryonic development, suppressed reproduction, inhibition
of growth, and fin erosion (Rashed 2001). Avoidance behav-
Figure 1: Map of Ibadan city, indicating the sampling points
Gulf of Guinea
iour has also been observed in adult fish exposed to lead
levels ranging from 10–100mg l
(WHO 1989). Other effects
include altered gonadosomatic indices and oocyte growth
(Ruby et al. 2000) and significant haematological and
biochemical abnormalities (Ramalingam et al. 2000).
Most fish farms in Ibadan City received their water supply
from local rivers and streams. It was therefore not surprising
to observe that the mean lead level in fish pond water in
African Journal of Aquatic Science 2007, 32(2): 153–157
LEAD LEVEL (mg l
lead in rivers (dry season)
lead in rivers (rainy season)
LOCAL GOVERNMENT AREAS
Ibadan Iddo Ibadan
Ibadan Ona Ara Egbeda Lagelu Ibadan
North South West North West South East
Figure 2: Lead levels (mg l
) in rivers in Ibadan City during dry seasons (open columns) and rainy seasons (solid columns). Means, with
standard error of mean (SEM) bars
Figure 3: Lead levels (mg kg
) in river sediments in Ibadan city during dry seasons (open columns) and rainy seasons (solid columns).
Means with standard error of mean (SEM) bars
LOCAL GOVERNMENT AREAS
Lead in sediments (dry season)
Lead in sediments (rainy season)
Ibadan Iddo Ibadan
Ibadan Ona Ara Egbeda Lagelu Ibadan
North South-west North-west South-east
LEAD LEVEL IN SEDIMENTS (mg kg
Ibadan was as high as 1.88mg l
. This may be attributed to
the fact that most fish ponds are largely unmanaged, with
little or no water exchange over the culture period. This,
however, portends a serious health risk to the general
public, whose fresh fish consumption derives mainly from
this source (Obodo 2003, Abulude et al. 2006). This is
because the aquatic microflora and microfauna that consti-
tute fish food are capable of incorporating and accumulating
lead into their living cells from the environment.
Consequently, small fish become enriched with the accumu-
lated heavy metals. Predatory fish generally display higher
levels of heavy metals than do their prey and, eventually, on
consuming the predatory fish, man suffers from the results
of an enrichment having taken place at each trophic level
(Chindah et al. 2004, Abulude et al. 2006).
Blood lead levels as low as <10–100µg dl
and 10–100µg dl
in adults have been associated with a
wide range of adverse effects, including nervous system
disorders, anaemia and decreased haemoglobin synthesis,
cardiovascular disease and disorders in bone metabolism,
renal function and reproduction (Bernard et al. 1995,
ATSDR 1997, Pirkle et al. 1998).
Despite the plans by the Nigerian National Petroleum
Corporation (NNPC) to reduce the lead level in petrol to
by the end of 2002 and to zero by 2004 (Jalal
2001), it can be concluded from the results of this study that
the lead levels in the river systems of Ibadan are currently
unsafe for both human consumption and use (WHO 1985,
FEPA 2003). In Nigeria, the increasing consumption of fish
by the population, as well as its importance in animal feed,
underscores the importance of the potential risks of lead
and other heavy metals in fish.
It is therefore important to monitor lead pollution levels in
Nigerian aquatic systems carefully, so that approximate
measures of the potential hazard can be attained. These
measures should give an estimation of the type of effects
that could be expected in aquatic flora and fauna and also
in man, after exposure to lead. A detailed assessment of
other sources of lead entering Nigerian aquatic systems
and further research into the distribution of lead in different
biotia (e.g. aquatic plants, invertebrates and fish) in relation
to the environment are recommended.
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LEAD LEVEL IN POND WATER (mg l
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