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IMPACTS OF HEAVY METALS ON THE BIODIVERSITY OF MACROBENTHOS
A MANUSCRIPT WRITTEN BY
ONYEKACHI STEPHEN ANTHONY
188787
DEPARTMENT: ZOOLOGY (ECOLOGY AND ENVIRONMENTAL BIOLOGY)
COURSE: ZOO 752 (RESEARCH TECHNIQUES)
DATE: 21ST JULY, 2105
LECTURER: DR. ADEKUNLE A. BAKARE
Impacts of Heavy Metals on the Biodiversity of Macrobenthos
Stephen A. Onyekachi
Environmental Biology Unit, Department of Zoology, Ekiti State University,
Ado Ekiti, Nigeria
ABSRTACT
This paper presents the effects of heavy metals on the abundance of macrobenthos in a dumpsite,
(Ilokun In-Used dumpsite) in Ado Ekiti, southwestern Nigeria using leachate samples at
collected at varying distances labeled A, B, C and D from the dumpsite. These samples were
analysed and compared with a control point E, a stream 70m away from the dumpsite.
Physicochemical characteristics and abundance of macrobenthos species were examined.
The colour of leachates varied from dark brown to colouless from the base of the dumpsite to the
control site. Turbidity is high at A and reduces gradually to point E. The concentration of
cadmium, iron and copper was huge at A and diminishes to point E.
Macrobenthos species found on the dumpsite varied abundantly on the sampling points A, B, C,
D and E. tolerant specis such as Coleoptera, Diptera, and blood worms live successfully in
polluted water and feed well on organic matter.
INTRODUCTION
There are 35 metals that concern us because of occupational or residential exposure; 23 of these
are heavy metals : antimony, arsenic, bismuth, cadmium, cobalt, copper, gallium, gold, iron,
lead, manganese, mercury, nickel, platinum, silver, tellurium, tin, uranium, vanadium and zinc
(Amusan, 2009).
Interestingly, small amounts of these elements are common in our environment and diet,
necessary for good health but large amount of them may cause acute or chronic toxicity or
poisoning.
Heavy metals toxicity can result in damaged or reduced mental and central nervous function,
lower energy levels, and damage to blood compositions, lungs, kidney, and other vital organs
(Amusan, 2009).
For some heavy metals, toxic levels can be just above the background concentration naturally
found in nature (Oviasagie et al, 2009). Therefore, it is important for us to inform ourselves
about heavy metals and to take protective measures against excessive exposure. In most part of
the United States, heavy metals toxicity is an uncommon medical condition. When it does occur,
unrecognized or inappropriately treated, toxicity can result to significant illness and reduced
quality of life (FEPA, 1994).
Bioaccumulation and Bioconcentration
A number of descriptions are found suitable for describing these biological terms. However, a
review of definitions by different researchers is detailed in this work.
Bioaccumulation is the biological sequential of a substance at a higher concentration than that at
which it occurs in the surrounding environment or medium (U.S. Geological Survey, 2007).
It is the uptake of organic compounds by biota from either food or water. (FEPA, 1998).
United States Environmental Protection Agency (2001) described bioaccumulation as a process
by which chemicals are taken by an organism directly from exposure to a contaminated medium
or by consumption of food containing the chemical.
Bioconcentration is a biological process that occurs when toxic chemicals are taken up directly
from the air, water or soil by an organism and stored in various tissues and organs in the body.
Biomagnification is the accumulation of a substance up the food chain by transfer of residues of
the substance and smaller organisms that are food for larger organisms in the food chain (FEPA,
2003).
Heavy Metals, Effect and Emission
Heavy metals are chemical elements with specific gravity that is at least five times the specific
gravity of water. The specific gravity of water is 1 at 4°C (39°F). Simply stated, specific gravity
is a measure of density of a given amount of solid substance when it compared to an equal
amount of water (US Environmental Protection Agency, 2001).
Some well-known toxic metals with specific gravity that is five or more times of water are
arsenic 5.7, cadmium 8.65, iron 7.9, lead 11.34 and mercury 13.546 (FEPA, 2003).
In small quantities, certain heavy metals are nutritionally essential for a healthy life. Some of
these are referred to as trace elements for example, iron, copper, manganese and zinc. These
elements or some form of them exist naturally in foodstuffs, fruits, vegetables and in
commercially available multivitamin products. These elements are called beneficial heavy metals
(International Occupational Safety and Health Information Centre, 1999).
Heavy metals become toxic when they are not metabolized by the body and accumulated in the
soft tissues. Heavy metals may enter human body through food, water, air or absorption through
the skin when they come in contact with human in agricultural, manufacturing, pharmaceutical,
industrial or residential settings (USEPA, 2001).
MATERIALS AND METHODS
Sampling Site
The study was carried out in Ado-Ekiti Local Government Area where Ilokun landfill is located.
The landfill is a government regulated dumpsite purposed to receive solid waste from industries
in Ado-Ekiti. Due to increased human population in the town, the site receives waste from both
domestic and industrial sources.
Not far from this site (about 110 metres away) is a small Igbira settlement. Located 180 metres
from this site is a radio station. The people of this settlement are predominantly farmers planting
different crops around this landfill. Very close to this landfill is stream which used by these
people for domestic and farming purposes.
This stream receives particles and run-off directly from the site especially when rain falls. The
liquid coming out the decaying waste is called “leachate”.
Sampling Points
Four points were chosen for sample collection and they were designated A, B, C, D and E.
Point A is highly polluted
Point B is highly polluted
Point C is polluted but not as A and B
Point D is least polluted
Point E is unpolluted
Water Sampling
Water samples were collected monthly between the hours of 0800 hours and 1100hours on every
sampling day as recommended by Adebisi (1981). The samples were collected from the surface
water flowing slowly near the waste with clean clear plastic cup into the sampling bottles with
gloves on the hands. Winkler A and B are carefully added to the sampling bottles to preserve
Dissolved Oxygen and Biochemical Oxygen Demand. Samples were then taken to laboratory for
physiochemical parameters and macrobenthos assessment.
Materials
1 litre plastic keg, gloves, Winkler A and B, mercury in glass thermometer, Seechi disc,
electrical pH meter, buffer solution, conductivity meter, crucible dish, oven, pipette, indicator
and hydrochloric acid, burrette and starch solution.
RESULTS
The statistics below show the results of the physicochemical parameters examined in all the
sampling points against the control point E.
Table 1: Calculated F-value and the corresponding P-values of the Analysis of Variance
(ANOVA) for the physicochemical parameters of the leachate from the sampling points A, B, C,
C and E.
Parameters Calculated F-value Calculated P-value
Temperature 1.586 0.229
pH 1.336 0.302
Dissolved Oxygen 6.797 0.002
Biochemical Oxygen Demand 4.221 0.017*
Total suspended solids 8.881 0.001**
Turbidity 11.500 <0.0001***
Alkalinity 1.765 0.188
Hardness 8.340 0.001**
Sulphate 0.967 0.454
Cadmium 23.041 <0.0001***
Iron 9.458 0.001**
Copper 7.969 0.001**
*Level of significance
Significant (0.01<p<0.05)
Very Significant (0.001<p<0.01)
Highly Significant (p<0.001)
Identification of macrobenthos
Macrobenthos communities are composed of species with relatively long lifespan that can with
time integrate with a wide set of fluctuating environmental conditions. Hence, those invertebrates
may be regarded as potentially better pollution indicators than instantaneous water quality
measurements (Lopez et al, 1990). Macrobenthos are important functional components of
landfill sites. These organisms alter the physical and chemical conditions of the sediments-water
interface, promote the decomposition of organic matter, recycle nutrients for photosynthesis and
transfer energy to other food web components (Gaston et al 1998).
Occurrence and distribution of macrobenthic communities.
A total of 9 macrobenthos species were examined at the points of sampling for the four replicates
and analysed. These comprises of 3 species of beetles, 5 species of dipteras and bloodworms.
The results show various degree of abundance of these organisms. Musca dosmestica (housefly)
has the highest number of occurrence it is cosmopolitan. Sand flies are also abundant but not as
housefly while the elst occurrence on the site is Glossina spp. Chironomus and Glossina are
blood suckers because they feed mostly on human blood and at times on decayed organic
materials which brings about their lesser occurrence on the site.
Midges were absent at points A, B, C, D and E of the first sampling. Melolontha species
appeared in all the sampling points except at point D and E (control).
Scarabeaus species is absent in point D and E of the first and third sampling. Elaterida species is
present in all except at point E.
Mosquito larvae appeared in all sampling points except at points C and D of the second sampling
results. Sand flies are present in all except on the control point E of the first and second
sampling. Also, blood worms are present in the entire sampling site except on the control point E
of the first and second sampling.
Table 2: Showing the Margalef Index for the abundance of macrobenthos.
MACROBENTHOS SAMPLING POINTS
A B C D E
Number of species 7 7 5 5 2
Margalef Index (D) 2.59 2.59 1.85 1.85 0.74
DICUSSION AND CONCLUSION
The study area has shown that leachate samples from Ilokun dumpsite have little dissolved
oxygen concentration because leachate is associated with little or no oxygen. The risk posed to
ground water source by waste disposal landfills or dumps can be considered in terms of three
controls – waste composition and loading, leachate production and migration, attention and
dilation (Dojligo et al, 1993).
Smith et al, 1996, discovered that continuous disposal of municipal waste in soil will increase
heavy metal concentration heavy metals detected in the leachate samples at Ilokun dumpsite
have harmful effect on soil, crops and human health. The impacts of these heavy metals may be
acute or chronic depending on their level of bioaccumulation in the body.
However, there is no strong relationship between the concentration of heavy metals in the soil
and plants because it depends on many factors such as sediment, bioavailability of plant growth
and metal distribution to plant parts (Vousta et al, 1996).
In the ideal circumstance, it would be of advantage to undertake biological monitoring for all the
metals in all situations.
In conclusion, as it is popularly said, “one man’s food is another’s poison”, these heavy metals
pose serious health risk to human health. Landfills must be constructed to environmental
specifications far away from settlements.
REFERENCES
Adebisi A.A., (1981): Standard methods for experimentation of water and waste water:
American Public Health Association and America Water Environment Federation, 20th
Edition. Pp. 575-580.
Amusan A.A., Ige D.V., Olawale R. (2005): Characteristics of soils and crop uptake of metals in
municipal waste dumpsites in Nigeria. Journal of Human Ecology. 17(3):167-171.
Dojligo J.R., Best G.A. (1993): Chemistry of Water and Water Pollution. Bush Harwood Ltd,
Crest Britain.
Federal Environmental Protection Agency (FEPA), (1994): Bioaccumulation of Heavy Metals in
Animals. Pp. 40-49.
Federal Environmental Protection Agency (FEPA), (1998): Present water quality status in
Nigeria. Pp. 35-41.
Federal Environmental Protection Agency (FEPA), (2003): Regulations on the effects of
dumpsites on human population. Pp. 256-258.
International Occupational Safety and Health Information Centre (1999): Human health and
heavy metals in the United States. Pp. 565-570.
Lopez Gappa, Gaston (1990): Identification of Macrobenthos. Invertebrate Zoology. Pg. 258-
267.
Oviasagie P.Q., Omoniyi E., Okoro D., Ndokuere C.L. (2009): Evaluation of physicochemical
properties and distribution of Pb, Cd, Cr, and Ni in soils and growing plants around
refuse dump sites in Akure, Nigeria. African Journal of Biotechnology. 8(12): 2757-
2762. http://www.academiajournals.org/ApB
Smith C.J., (1996): Accumulation of Cr, Pb, Cu, Ni, Zn, and Cd in soil following irrigation with
untreated effluents in Australia environment pollution. 94: 317-323.
United States Environmental Protection Agency (2001): Municipal solid waste in the United
States. 200 Facts and Figures. EPA-530-RO-2001. http://www.epa.gov/epaosuer/non-
hw/municipal/report-00/report00.bdf
United States Geological Survey (2007): Ground levels of heavy metals and impact on water
quality. Pp. 171-175.
Vousta P.B., Elmander V.E., (1996): Examination of the bioavailability of plants to heavy metal
concentration within the soil. Soil Ecology. 41(5): 101-107.
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