ABSTRACT
The distribution and occurrence of heavy metals in water
column of the Anambra River were investigated in the dry season adopting
standard chemical methods. Following the establishment of the presence and
appreciable concentration of heavy metals in various stations (P<0 .05="" against="" and="" bioassays="" biological="" column="" copper="" effects="" fish="" heavy="" i="" in="" investigated="" laboratory="" metals="" of="" prevalent="" river="" species="" the="" two="" water="" were="" zinc="">Oreochromis
niloticus and Clarias gariepinus) based
on the toxicity scale of 96hLC50 to evaluate possible
risk effect of the metals on the aquatic species and human population depending
on the river. Toxicity ranking for zinc and copper in the water revealed copper
to be consistently more toxic to the test species with Oreochromis niloticus
being more sensitive. The binary mixtures in predetermined ratios
(1:1 and 1:2) of zinc and copper acting against the test animals showed
significant departures when compared to levels of toxicity attained by the
individual constituent metals when acting alone against the same species. In a
majority of cases, the resultant interactions (Zn-Cu against fish species) were
in conformity to the model of synergism while fewer instances portrayed
antagonism and additive action. There is high risk of heavy metal poisoning
among the human population depending on the river and heavy metal related
public health effects observed in a survey are circumstantial evidence. The
work recommends setting more realistic and effective safe limits and standards
to minimize and properly manage heavy metal polluted water bodies.CHAPTER ONE
INTRODUCTION
1.1 Background of
the Study
Amongst the several heavy metals that pose some risk to our
environment, thirty- five of them have been listed or known to have significant
occupational problems in man.
Interestingly, small amounts of these elements are common in
our environment and diet. Moreover these elements are actually necessary for
good health but large amounts of any of them may cause acute or chronic
toxicity (Glanze, 1996).
Heavy metal toxicity can result in damaged or reduced mental
and nervous functions, ATP depletion and damage to blood composition, lungs,
kidneys, liver and other vital organs (Wright, Welbourn and Martin, 1991). Long
term exposure may result in slowly progressing physical, muscular, and
neurological degenerative processes that mimic Alzheimer’s disease, Parkinson’s
disease, muscular dystrophy and multiple sclerosis (Wright et al., 1991).
Repeated long term contact with some metals or their compounds may even cause
cancer (International Occupational Safety and Health Information Centre, 1999).
For some heavy metals, toxic levels can be just above the
background concentrations naturally found in nature (Dupler, 2001). Therefore,
it is important for us to inform ourselves about these metals and to take
protective measures against excessive exposure. Based on the above background,
most widely used/encountered heavy metals are the focus of this work and these
are mercury, arsenic, cadmium, iron, manganese, chromium, zinc, copper, lead,
sodium and potassium. In most parts of the world, heavy metal toxicity is an
uncommon medical condition (International Safety and
Health Information Centre, 1999). When these metals are found in our immediate
environmental media unrecognized or inappropriately treated, toxicity can
result in significant illness and reduced quality of life (Ferner, 2001).
Industrial activities worldwide are characterized by the
production of a wide variety of end products that are useful to mankind;
however all production pathways are accompanied by emission of waste products
that enter the environment (Adetoro, 2004). Industrial wastes have been shown
to be a complex admixture of several classes of pollutants such as synthetic
chemicals of various types, hydrocarbons and heavy metals (Oyewo, 1998;
Otitoloju, 2003). Among the pollutants which find their way into the Anambra River,
heavy metals are important (Igwilo, Afonne, Maduabuchi, and Orisakwe, 2006).
Also important to mention is that they are non-biodegradable and remain in the
environment long after the elimination of source (Otitoloju, 2002). Although
most of these metal pollutions are anthropogenic, there are a few examples of
localized ones resulting from natural weathering of ore bodies (Hager and
Abrahamsen, 1990) mining and smelting (Walker, Hopkin, Sibly and Peakau, 2001).
They are considered priority pollutants because they easily bioaccumulate in
the food chain (Chukwu, 1991). Heavy metals, although usually considered
pollutants, are natural substances with the exceptions of radioisotopes
produced in man-made nuclear reactions (Walker et al., 2001). Heavy metal contents
of Anambra River have been earlier reported by Igwilo et al. (2006) and Obodo
(2004) attributing the loading to various anthropogenic activities in and
around the river.
Metals and other pollutants such as sewage, sawdust,
hydrocarbons and organic wastes, when introduced into water bodies, can bring
about alteration of physicochemical characteristics of such a water body and hence would affect species diversity
(Akpata, 1987, Oyewo 1998, Saliu and Ekpo 2006).
In many instances, heavy metals occur in natural bodies of
water at levels below their toxic thresholds. However due to their
non-degradable nature, such sublethal concentrations may still pose risk of
damage via uptake and subsequent bioaccumulation by organisms which cannot effectively
metabolise and excrete the absorbed metals.
The main route by which heavy metals enter the aquatic
environment is through the discharge of metal-laden municipal and industrial
effluents, directly into the water bodies or indirectly via drainages and
canals (Angino, Magnuson, Wangh, Galke, and Bredfeldt, 1970; Oyewo, 1998). The
discharge of these metals into the environment also occurs during industrial
processes and incineration of waste products containing metallic compounds.
Environmental research in any country conventionally should
concentrate among other things on the pollutants that are considered as
priority in terms of frequency and intensity of occurrence. Typically, the
Anambra River acts as a sink or reservoir that receives waste water effluent
from different parts of the locality and hinterland (Igwilo et al., 2006).
In response to this, there have been a few investigations on
the occurrence and distribution of heavy metals in the Anambra River. Such
authors have found measurable quantities of heavy metals although they failed
to relate such levels of occurrence to biological action such as acute toxicity
and sub lethal chronic action. Anambra River is the natural habitat of several
fish species such as Clarias and Tilapia species. These fish species
particularly the pelagic species are useful in assessing water quality in the
field and laboratory because they are ubiquitous, sedentary in nature and have
long life cycles; hence they act as continuous monitors of the water bodies they inhabit.
Earlier works (Okonkwo and Obiakor, 2008; 2009; Odo, Didigwu, and Eyo, 2009)
have provided information on the biology and ecology of these species. What was
lacking in their report is detailed empirical data on the interaction of these
locally important species with this important pollutant heavy metal detected in
the water column of Anambra River.
1.2 Statement of
the Problem
Surface water use has been of tremendous application across
the globe for various purposes: domestic, industrial, agricultural etc. But
studies by different people in both developing and developed countries of the
world show that pollutants from various sources get to the surface water and
pollute it. (Obodo 2004, Igwilo et al. 2006, Clark 1992, Matti 2001, Oyewo 1998
and Don-Pedro 1996). Otitoloju (2002) explained that industrial effluents
released into the environment get to the surface water and pollute it with
priority heavy metals; hence the author recommended the toxicity testing of the
most sensitive species in the field to assess possible ecological damage that
could result from these toxicants. Consequently, Igwilo et al. (2006) supported
the above fact and advocated for a means to avert possible imbalance in the
fish population structure and the residents around the river feeding on toxic
metals.
In Nigeria, and indeed many other developing countries, there
are host of unplanned and unorganized uses of river for various purposes,
including solid waste dumping, effluents disposal, siting of wide scale toilet
facilities, disposal of chemical wastes and wrong and frequent application of
artificial fertilizers. These are done without putting the water quality of the
river into consideration.
A casual inspection of Anambra River shows that there are unhealthy,
unplanned and unorganized uses of the river for various purposes like solid waste dumping,
effluents disposal, siting of wide scale toilet facilities, disposal of
chemical wastes, use of poisonous chemicals in fishing, and indiscriminate
application of fertilizers for farming activities around the banks of the river
at various locations. These activities have negatively affected the quality and
activities of the river in a number of ways.
Firstly, the aesthetic value of the river has long
disappeared. In addition, the river is heavily silted, especially at the lower
course. Consequently, the depth and width of the river have greatly reduced.
Moreover, some activities which greatly depend on the quality of the river like
swimming have been greatly affected. Furthermore, fishing in the river which
used to be one of the means of sustaining livelihood for the inhabitants of the
area has drastically reduced.
A preliminary survey
conducted prior to the main eco-survey showed that various wastes are
discharged into the river. Sewage dislodgers and various industries were seen
discharging their wastewater/ effluents into the river.
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