This work investigates the extent of Arsenic
pollution of borehole waters in Onitsha and environs. Fifteen samples of
drinking water sourced from boreholes were randomly collected and analyzed
using Atomic Absorption Spectrometry (AAS) and the technique employed is wet
oxidation method. The results of Arsenic concentration obtained from the
boreholes ranged from 0.00 mg/L (53.33% of boreholes) to 1.099mg/L (46.67% of
boreholes). Seven out of the fifteen samples were observed to be concentrated
with Arsenic ranging from 0.16mg/L to 1.099mg/L with majority of the
concentrations occurring at areas adjacent to River
Niger and Nwangene Lake. The results were
found to be above the Maximum
Contamination Level (MCL) of 0.01mg/L set
by the World Health Organization (W.H.O, 2011) therefore, the sources were
found to be contaminated with abnormal concentration of arsenic and the
inhabitants who consume this water without proper treatment are vulnerable to
severe health hazards. The high Arsenic concentrations in the study area could
be attributed to both natural and anthropogenic processes such as improper
discharge of untreated industrial effluents and sewage, urban storm runoff
dissolving and leaching organic and inorganic matter into the subsurface
ground, undersurface weathering, agro products, automobile workshops and
emissions. The discharge of these effluents into water bodies leads to the
bioaccumulation of heavy metals in fishes consequently, when humans feed on
these aquatic organisms it results to serious health issues therefore, there is
need for effluents to be treated before being discharged into the environment.
TABLE OF CONTENTS
AND OBJECTIVES OF STUDY
1.6.1 LOCATION AND ACCESSIBILITY
1.6.2 TOPOGRAPHY, DRAINAGE AND HYDROGEOLOGY
1.6.3 CLIMATE, VEGETATION AND OCCUPATION
3.3.1 DETERMINATION OF pH (ASTM D 1293B)
OF CONDUCTIVITY (ASTM D 1125)
3.3.3 ANALYSIS OF HEAVY METALS IN WATER
RESULTS, DISCUSSION AND INTERPRETATION
4.2.3 ELECTRICAL CONDUCTIVITY (EC)
SUMMARY, CONCLUSION AND
70% of the
Earth’s surface is covered with water and 97% of the water is saline the
quantity and the quality of water is equally important. Subsurface
(groundwater) makes about 30.1% of the Earths freshwater as compared to 0.3%
surface water and 68.7% Ice caps and Glaciers. Water is referred to as a universal
solvent because it can dissolve many types of substances, but human and animal
require water that contains fewer impurities. Drinking water comes from ground
(subsurface) sources such as ground water and aquifers. It can also be obtained
from surface water bodies such as rivers, streams and glacier other sources
including rain, hail, snow and sea through desalination, surface water picks up
different minerals resulting from the presence of animal or human activities.
While for the subsurface water, the contaminants come from leachate, landfills,
septic systems and the ambient rocks. Similarly, indiscriminate disposal from
agricultural chemicals (Pesticides, Herbicides, Insecticides and Fertilizers)
and household cleaning products. The contaminants in ground water take more
time to be cleaned because it moves slowly and isn’t exposed to the natural
cleansing benefits of air, sunlight and micro-organism.
the quality of drinking water is determined based on the appearance, taste,
colour and odour of the water but all these do not really tell if the water
should be free from hazardous compounds as the Geology of an area, its rock
types, their weathered products, precipitation from rainfall, urban storm-water
runoff and human activities in an environment contributes immensely to the
chemistry of subsurface and surface water. Also, the quality of water is a
measure of the suitability of the water for a designated use such as; drinking,
agriculture, recreation, laundry and industrial usage based on selected
physical, chemical and biological characteristics. The N.I.S (Nigerian
Industrial standard), S.O.N (StandardOrganization of Nigeria) and W.H.O (World
Health Organization) set a maximum contaminant level in drinking water supplied
to municipal or population. When a standard or guideline is exceeded in the
municipal or community water system, the state is required to take proper
action to improve water quality level including treating the water through
filtration or aeration blending water from several sources to reduce
contaminants including inorganic chemicals such as salts, metals and mineral.
These substances occur naturally in geological structures or sometimes caused
by mining, industrial and agricultural activities. These chemical can badly affect
human health when they are consumed in large amount.
There are two main sources of water supply
that are available to man, surface water that includes: rivers, lakes, stream,
drainage areas which funnels water toward the holding reservoirs and subsurface
or ground water which includes wells, springs and horizontal galleries. The
water resources are stressed by a number of factors, including cattle grazing,
pollution and rapidly-growing urban areas. Over a billion people lack access to
safe portable water supply globally and out of this number, more than 300
million people living in rural areas of SubSaharan Africa are being affected
Arsenic is an element that exists in
oxidation states of 5, 4, 3, 2, 1, 0, -1, -2, and -3, that is found naturally
in air, water, soil, rocks and minerals, food, and even living organisms in low
concentrations. In water, it is most likely to be present as arsenate, with an
oxidation state of 5, if the water is oxygenated. However, under reducing
conditions (<200 mV), it is more likely to be present as Arsenite, with an
oxidation state of 3.
Dimethylarsenic acid (DMA)
Monomethylarsonic acid (MMA)
Table 1.21 Occurrence of Arsenic (Source:
Adapted from W.H.O., 2011).
Arsenicals are used commercially and
industrially as alloying agents in the manufacture of transistors, lasers and
semiconductors, as well as in the processing of glass, pigments, textiles,
paper, metal adhesives, wood preservatives, paints, dyes and ammunition. They
are also used in the hide tanning process and, as well as pesticides,
herbicides, feed additives and pharmaceuticals.
Environmental Levels (Water, Soil and Food):
The level of Arsenic in natural waters,
including open ocean seawater, generally ranges between 1 and 2 µg/l.
Concentrations may be elevated, however, in areas with volcanic rock and
sulfide mineral deposits; in areas containing natural sources, where levels as
high as 12 mg/l have been reported; near anthropogenic sources, such as mining
and agrochemical manufacture; and in geothermal waters (mean 500 µg/l, maximum
25 mg/l). Mean Arsenic concentrations in sediment range from 5 to 3000 mg/kg;
the higher levels occur in areas of contamination but are generally unrelated
to Arsenic concentrations in water. The total estimated daily dietary intake of
Arsenic may vary widely, mainly because of wide variations in the consumption
of fish and shellfish. Most data reported are for total arsenic intake and do
not reflect the possible variation in intake of the more toxic inorganic
arsenic species. Limited data indicate that approximately 25% of the Arsenic
present in food is inorganic, but this is highly dependent upon the type of
food. Fish and meat are the main sources of dietary intake of Arsenic levels
ranging from 0.4 to 118 mg/kg have been reported in marine fish sold for human
consumption, and concentrations in meat and poultry can be as high as 0.44
Effects of Arsenic:
Many scientific studies conclude that long
term exposure to inorganic Arsenic through drinking water is associated with
relatively high risks of cancer of the lungs and bladder and, to a lesser
extent, with an increased risk of cancer of the skin, liver, and kidneys.
Recent studies have also associated chronic Arsenic exposure through drinking
water with a number of other serious health effects, including developmental defects,
stillbirth, and spontaneous abortion as well as heart attacks, strokes,
diabetes mellitus, and high blood pressure. Arsenic can also cause liver
damage, nerve damage, and skin abnormalities (for example; discoloration and
unusual growths, which may eventually turn cancerous). Some of these effects
may take years to develop. Arsine is considered to be the most toxic form,
followed by the Arsenites (Arsenic (III)), the arsenates (Arsenic (V)) and
organic arsenic compounds.
Early clinical symptoms of acute
intoxication include abdominal pain, vomiting, diarrhoea, muscular pain and
weakness, with flushing of the skin. These symptoms are often followed by
numbness and tingling of the extremities, muscular cramping and the appearance
of a papular erythematous rash. Within a month, symptoms may include burning
paraesthesias of the extremities, palmoplantar hyperkeratosis,
Mee’s lines on fingernails and progressive
deterioration in motor and sensory responses.
Signs of chronic Arsenicism, including
dermal lesions such as hyperpigmentation and Hypopigmentation, peripheral
neuropathy, skin cancer, bladder and lung cancers and peripheral vascular
disease, have been observed in populations ingesting Arsenic contaminated
drinking-water. Dermal lesions were the most commonly observed symptom,
occurring after minimum exposure periods of approximately 5 years. Effects on
the cardiovascular system were observed in children consuming Arsenic
contaminated water (mean concentration 0.6 mg/l) for an average of 7 years.
There have been numerous epidemiological
studies that have examined the risk of various cancers associated with arsenic
ingestion through drinking-water. Many of these studies are ecological-type
studies, and many suffer from methodological flaws, particularly in the
measurement of exposure. However, there is overwhelming evidence that
consumption of elevated levels of arsenic through drinking water is causally
related to the development of cancer at several sites, particularly skin,
bladder and lung. In several parts of the world, arsenic-induced disease,
including cancer, is a significant public health problem. Because trivalent
inorganic Arsenic has greater reactivity and toxicity than pentavalent
inorganic arsenic, it is generally believed that the trivalent form is the
carcinogen. However, there remain considerable uncertainty and controversy over
both the mechanism of carcinogenicity and the shape of the dose–response curve
at low intakes. Recently, the trivalent methylated metabolites, MMA (III) and DMA
(III), have been found to be more genotoxic than inorganic arsenic.
Targeted organs by Arsenic (Source: Adapted from W.H.O., 2011).
1.3 AIM AND OBJECTIVES OF STUDY
The objective of the study can be subdivided into the
To create both individual and public awareness
of Arsenic pollution in the study area.
To have knowledge regarding the diseases caused
by Arsenic poisoning and mitigating measures available to prevent
To identify Arsenic risk region, level of education,
gender and age as important determinants of Arsenic knowledge.
To know the extent of Arsenic pollution of the
subsurface water in the study area.
prepare a study report that integrates observations made in the field.
interpret through observations made in the field and laboratory results the
history and processes that lead to the sourcesof Arsenic pollution in this
1.4 SIGNIFICANCE OF STUDY
The findings of this study will aid in
making existing education programs more effective and in reducing the risk of
developing Arsenic-related illnesses. Also, it will assist policy makers in
considering the effectiveness of current education efforts and in crafting
future public awareness campaigns of Arsenic risks.
of Onitsha map was made from the Google Earth (map). The map covers Onitsha
North and South Local Government Area, Okpoko in Ogbaru Local Government Area
and part of Obosi and Nkpor, both in Idemili North Local Government Area. Some
of the boreholes from which water samples were collected are located in
residential buildings, markets, churches and boreholes close to dump sites.
study method employed was the direct observation, sampling and carrying out
in-situ test right there in the field.
1.6 STUDY AREA
Fig. 1.6 Map of the study area (Source: Adapted from Google
Onitsha is a
commercial, industrial, educational and ecclesiastical city on the East bank of
the River Niger in Anambra State, Southeastern Nigeria with a high population
density of over 1million. It lies between latitude 06002I56II
and 06038I34IINorth of the Equator and
longitude 06037I30II and 06059I30II
East of the Greenwich meridian and occupies an area of about 49,000km2.
It is bounded by Anambra West and East local government area and Oyi in the
North, Idemili North and South in the East, Ogbaru local government area in the
South and inthe West by the River Niger.
Onitsha and environs is accessible by
major roads such as the Onitsha-Asaba express way through the Niger Bridge
linking the Eastern states to the Western part of the country, Onitsha-Enugu
express way to the North and Onitsha-Owerri express way to the South and East.
There are many minor and street roads that interconnect the towns within and
outside the city.
1.6.2 TOPOGRAPHY, DRAINAGE AND HYDROGEOLOGY
The relief features of the study area are
unique. The elevation ranges from 33m to 450m above sea level with average
elevation of 250m. Onitsha falls into two main landform regions: a highland
region of moderate elevation that covers most of the North central-Northeast,
East-Southeast and a low plain to the Northwest-WestSouthwest of the highland.
The highland region is a low asymmetrical ridge or cuesta in the Northern portion
of the Awka-Orlu uplands, which trend roughly Southeast to Northwest, it is
highest in the Southeast about 450m above sea level and gradually decreases in
height to only 33m in the Northwest on the banks of the Anambra River and the
shows that the basin is having low relief of the terrain and is oval tending
towards elongated shape and the network of the drainage is the dendritic
pattern which indicates homogeneity in texture and lack of structural control. Dumping
of refuse along culverts and channels has eventually blocked the channel of
flow into the River Niger. The Niger River flows in the North-South direction.
The flow direction of the ground water
direction of the ground water is multidirectional which was influenced by the piezo
metric heights, there is also a depression (sinkhole) at the middle aquifer;
this is as result of the population density with several functional boreholes
taping its water from the middle aquifer on an hourly basis.
VEGETATION AND OCCUPATION
Onitsha climate is classified as tropical.
When compared with winter, the summers have much more rainfall. The average
temperature in Onitsha is 27.00C while the average rainfall is
1828mm. Rainfall (precipitation) is lowest in December, with an average of
12mm. In September precipitation reaches its peak, with an average of 316mm. At
an average temperature of 28.90C March is the hottest month of the
year while at 25.40C on average, July is the coldest month of the
year. Between the driest and wettest months, the difference in precipitation is
304mm and the variation in annual temperature is around 3.50C.
Relative humidity is generally high throughout the year, between 70% and 180%.
The highest figures are experienced during the wet season and the lowest during
the dry season.
The vegetation of this region is light
forest interspersed with tall grasses. The trees are not too tall and include
both hardwood and softwood varieties; domesticated trees such as the mango,
palm tree, guava, orange and almond are found. Much of the natural vegetation
has been felled and the land utilized for development.
The occupation in Onitsha and its environs
is mainly trading, services (tourism, hospitality, and civil service),and
manufacturing, industrial and religious activities. The Onitsha Main market is
reputed as the largest market in Africa which attracts people from different
parts of the continent while, the city is also reputed as the number one (1)
transit city in the country because most of the road transport services have
their headquarters at Onitsha and it hosts the largest River port in the
country which is on the River Niger.
1.7 LITERATURE REVIEW
An assessment of
heavy metal pollution of effluents from three food industries within Onitsha in
Anambra state, Nigeria (Nwosu et al, 2014) showed that the mean levels of all
the heavy metals were above the limit allowed by the Nigeria
Federal Ministry of Environment (FMENV,
1991) and the World Health
Organization (W.H.O, 2011) in industrial
effluent. It also revealed that apart from Arsenic, the concentrations of
Mercury, Iron, Lead, Chromium, and Cadmium were not significant when the
effluents were compared to each other. Arsenic concentration ranges from
0.205mg/L to 1.387mg/L.
Arsenic pollution of surface and
subsurface water in Onitsha, Nigeria (Ezeabasili et al, 2014) revealed the
pollution status of Onitsha metropolis water which indicates that the
concentration of both surface and subsurface water is above the World Health
Organization (W.H.O, 2011) standard. Surface concentration ranges from
0.2001mg/L (River Niger upstream) to 1.5883mg/L (River Niger central drainage
surface) while Groundwater concentration ranges from 0.00mg/L to 1.2507mg/L.
This also shows that the pollution of surface water is greater than that of the
Furthermore, Histopathological alterations
in the liver and kidney of the fish Chrysichthys nigrodigitatus due to heavy
metals in Niger River (Nsofor et al, 2014) revealed the harmful effects of
chemical pollutants like heavy metals in the fish Chrysichthys nigrodigitatus
of Niger River Onitsha as well as pathological alterations in liver and kidney
tissues of the fish. Also, Arsenic in water column is significantly lower than
those in the fish.
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