THE OCCURENCE OF HEAVY METALS
IN GILLS,MUSCLES, AND LIVER OF CHRYSICHTHYS NIGRODIGITATUS
The occurrence of heavy metals in gills, muscle, and liver of
Chrysichthys nigrodigitatus from Obufa Esuk Beech , Great Kwa River.
Department
of Zoology and Environmental Biology
CHAPTER ONE
1.1 Introduction
Heavy metals are those metallic elements
with high atomic or specific gravity that is at least five times greater than
that of water. Several elements have been listed in this group. The presence of
heavy metals in the aquatic environment in trace concentrations is important
for normal development of the organism (Kori-Siakpere and Ubogu, 2008).
They could be detected in the aqueous medium and in the bottom;
some however, are completely deleterious and need to be monitored continuously
in the bodies of organisms as they are capable of bioaccumulation, resulting to
morbidity and often mortality of organisms
(Ayotunde et. al, 2011, 2012., and Ada, et. al., 2012). Heavy metal
human health concern has stimulated a lot of research in this area, some of
which include the works of Muchuweti
et. al., (2006), Satarug et. al. (2000) and Adefemi et. al.
(2012).
When metals enter
aquatic environment, a great portion settles and is absorbed by the bottom mud
(Ayotunde, 2012). They could be recycled by chemical, physical and biological
processes such that some quantity remains dissolved in the water column and
some part is being absorbed by the inhabitants (Rayms- Keller et. al., 1998 and
Kori- Siakpere and Ubogu, 2008). Fishes are at the apex of the food chain and
can bio accumulate some of these substances into their tissues (Olaifa et. al.,
2004).
Kori- Siakpere and
Ubogu, (2008) observed decreased haematological parameter values and
heamodilution in fish exposed to sublethal concentrations of zinc for 15 days.
They explained that zinc accumulates in gills of fish and it is an indication
of depressive effect on respiration in tissues. It may lead to death due to
hypoxia, reduced hatchability of eggs, changes in ventilator heart physiology
and general change in fish behaviours such as lack of balance, agitated
swimming, air gulping, and death.
Some heavy metals
are not biodegradable and can continue to be accumulated in the tissue of
organisms until they reach intolerable levels resulting in morbidity or
mortality (Offem and Ayotunde, 2008). Man being higher in the food chain stands
the risk of higher bioaccumulation. The dangers of heavy metals have been long
noted, but the symptoms are poorly diagnosed and patients could be treated for
some other illness thereby aggravating heavy metal pollution problems of man
(Kaye et. al., 2002 and Nolan, 2003).
There is an
increasing concern regarding the roles and fates of trace metals in Nigerian
environment. Much of this concern arises from the low level of available
information on the concentrations of these metals within the environment. The
contamination of sea foods by trace metals is a potential problem to man.
Aquatic organisms accumulate metals to concentrations many times higher than
present in water.
The potentially
toxic are lead, zinc, nickel, chromium, arsenic, selenium, vanadium, beryllium
and barium. Natural and anthropogenic activities result in gaseous emissions
and waste water discharge into air, water and land. When substances in the emissions and effluent
discharges in the environment are in very minute amounts or in low concentrations, are not toxic to plants and
animals and have short residence time in the environment, they are described as
contaminants’ (Odiete, 1999).
Bioconcentration is
the net accumulation of a substance from water into an aquatic organism
resulting from the simultaneous uptake and elimination of the substance. Fish
and bivalve molluscs are used in bioaccumulation tests because they are higher
tropic level organisms and are usually eaten by man. Tissues such as liver,
kidney, muscle, viscera and whole organisms are analyzed to determine the
concentration of the metals (Dublin-Green, 1994).
Heavy metals are
commonly found in natural waters and some are essential to living organisms,
yet they may become highly toxic when present in high concentrations. These
metals also gain access into ecosystem through anthropogenic sources and yet
distributed in water body, suspended solids and sediments during the course of
their mobility. The rate of bioaccumulation of heavy metals in aquatic
organisms depends on the ability of the organisms to digest the metals and the
concentration of such metal in the river. (Kukusetging, Ochiai and Cornel
2006). Aquatic organisms (including fish) bioaccumulate trace metals in
considerable amounts and stay over a long period. Fishes have been recognized
as a good accumulator of organic and inorganic pollutions. Age of fish, liquid
content in the tissue and mode of feeding are significant factors that affect
the accumulation of heavy metals in fishes. They are finally transferred to
other animals including humans through the food chain. Odoemelam et al., 1989,
revealed high concentrations of heavy metals such as Cd, Pb, Cu, Ni, Zn, Mn,
Mg, and Co in some rivers within proximity of some industrial cities in
Nigeria. The discharge of industrial wastes containing toxic heavy metals into
water bodies may have significant effects on fish and other aquatic organisms,
which may endager public health through consumption of contaminated sea food
and irrigated food crops, Nwaedozie 2000 reported that zinc contamination
affects the hepatic distribution of other trace metals in fish.
Environmental
pollution is a worldwide problem, heavy metals belonging to the most important
group of pollutants. The growth of
industries has led to increased emission of pollution into the ecosystem.
Southern Caspian sea coast is one of the most important aqua system and the
Eastern south of Caspian, which receive effluent discharge from heavily
industrialized and highly populated settlement. Heavy metal can also occur
naturally in the ecosystem with large variation in concentration (Phipps,
1991).
In modern time,
anthropogenic sources of heavy metals, “that is” pollution, have been
introduced to the ecosystem. Waste derived fuel are especially prone to contain
heavy metals, so heavy metals are concern in consideration of water as fuel
(Cheng, 2003). Heavy metal pollution can arise from many sources but the most
common arises from the purification of metals, e.g melting of copper and
preparation of nuclear fuels. Electroplating is the primary source of Chromium
through precipitation of their compound or by ion exchange into soil and mud;
heavy metals pollutants can localize and lay dormant. Unlike organic
pollutants, heavy metals do not decay and thus pose a different kind of
challenge for remediation (Dufuss, 2002).
1.1
Aim and objectives
The purpose
of this research project is to:
1. Find out if fish in this river contain
concentrations of heavy metals in their tissues that could render them
dangerous for human consumption.
2. To analyze the level of heavy metals contamination in gills,
muscle and liver of Chrysichthys nigrodigitatus.