Abstract
Water samples from ground water and some rivers from Owerri Local
Government Area of Imo state Nigeria, were investigated for contaminants and
heavy metals. The results obtained showed that in the month of April 2009, the
ground water had mean maximum concentration 1.303 mg/dm3
of Pb,
1.048mgldm3
of Pb,1.488mgldm3
of Pb,for Otamiri and Oramiriukwa rivers
respectively.For the month of May 2009, the ground water results showed
maximum mean concentration 1.016mg/dm3
of Pb,1.069mg/dm3
of Pb,
1.7mg/dm3
of Pb and 1.488mg/dm3 of Pb,for Otamiri and Oramiriukwa rivers
respectively.The underground waters had mean concentration of 3.636mg/dm3
Cu,which exceeded WHO standard of 3.0mg/dm3
for drinking water.In the
month of may Oramiriukwa river had Mn with a maximum mean concentration
of 3.334mg/dm3 which exceeded the WHO standard of 2.0mg/dm3
. The results
showed lead of values 2.852mg/dm3
for the ground waters, 0.255mg/dm3
of
lead , 1.045mg/dm3
of Lead and 0.855mg/dm3
of
1.0 INTRODUCTION
Water is an essential raw material for human life and a vital factor to
the establishment of industries. Without water no life [1].
Water in its natural environment is characterized by impurities. Being a
universal solvent, water contains dissolved solids, gases and hosts a number
of microorganisms.
Hence the quality of water is defined by the level of its physical, chemical and
biological impurities. [2]
Different sources of water include stream, lakes, ponds, rain, springs
and wells. Sources of water in Old Owerri LGA of Imo State include rivers like
Otamiri, Nworie and Oramiriukwa; and the underground waters (Boreholes).
These rivers and underground waters (boreholes) supply water for the daily
activities of the people living along the banks, tributaries and environs. Well
asFor example Nworie River discharges intoOtamiri river as a tributary while
Oramiriukwa River has a number of streams discharging into it as crossed
many communities on its course.
Pure, safe and clean water can only exist briefly in nature but is polluted
immediately by human activities and environmental factors. Industrial
effluents, fertilizers from farm lands, diesel from pleasure boats, are possible
pollutants of rivers and thier environ.[3]
The use of surface water by man is as old as the existence of human beings.
Water is a natural resource, and indispensable to life. Water supplies for
human consumption should be adequate and free from bacteria harmful to
humans. The quality of river water depends on the quality of the feeding
sources which include surface run off water, glaciers, swamp, rain and
underground water.
Underground water, like springs, boreholes are better quality water
2
than surface water, such as lakes, rivers, streams, due to the purification of
the former prior to distribution. The underground water is rarely polluted by
both man and animals [4,5,6].
Industrial effluents like toxic chemicals and heavy metals pollute
several surface waters. Mercury is one of the heavy metals, in a group that
includes lead, cadmium, plutonium and others. A feature the heavy metals
have in common is that they tend to accumulate in the bodies of organisms
that ingest them, their concentrations increase up the food chain. Some
marine algae may contain heavy metals of concentrations of up to one
hundred times that of the water in which they are living, small fish eating the
algae develop higher concentrations of heavy metals in their flesh, larger
fishes who eat the smaller fishes concentrate the metal still further, and so on
up to fish eating birds or animals [7]
Some non-metallic elements commonly used in industries are also
potentially toxic to aquatic lives and to some extent to human beings.
Chloride is widely used to kill bacteria in municipal water, sewage treatment
plants and to destroy various microorganisms are found in plumbing lines in
water works stations. Chlorine can also kill algae and harm fish
populations.[8]
Acids from industrial operations and acid mine drainages especially in
coal and sulphide areas remain serious source of surface and ground water
pollutions [9,10]
The run-off water from fertilized fields carries some of the fertilizers to
rivers. In rivers and lakes the fertilizer provides nutrients that increase the
growth of algae. The algae use up the oxygen dissolved in the water, and the
lack of oxygen causes the death of fish and other aquatic lives. Phosphates in
laundry detergents have the same effect. Hence the use of fertilizers as well
3
as detergents result in entrophication of water. Pesticides used on crops get
into rivers in this way too [10,11] destroying aquatic lives.
Urbanization and industrialization develop countries economically but
lead to environmental pollution. The main effect of urbanization is increased
run-off, which causes increased erosion thereby making the water muddy
which is a type of pollution. In addition many new and sometimes toxic
chemicals are added to the environment, industrial activities unbalance the
natural cycles with harmful substances such as heavy metals [10,12].
Many organic compounds occurring naturally and the synthetic ones
are widely used as herbicides and pesticides, as well as in a variety of
industrial processes. The negative effects in organisms vary with the
particular type of compound, some are carcinogenic, toxic directly to humans
or other organisms, and make water unpalatable, and some accumulate in
organisms as heavy metals. Oil spills are a kind of organic compounds
pollution of surface water. Vinyl chloride vapor used in the production of
plastics is carcinogenic and it is not known how harmful traces of vinyl
chloride in water may be. Laboratory tests conducted on animals revealed
that polychlorinated biphenyl’s (PCBs) cause impaired reproduction, stomach
and lower alimentary disorders and other problems [10,13].
Polluted water may contain pathogens and disease-producing
organisms such as fungi, bacteria, viruses, protozoa, parasites and worms
which are vectors that carry and spread disease like skin infections,
dysentery, diarrhea, typhoid fever, malaria and other related diseases [14,
15].
Most industrial effluents contain non-biodegradable, toxic and
hazardous wastes which bioaccumulate in living organism when consumed.
These wastes pose high health risks as well as threatening coastal and
estuarine fishes on which most rural populace especially in the riverine areas
4
depend on for their livelihood. [16,17].
The principal causes and sources of pollution in groundwater have
been grouped into four categories, namely municipal, industrial, agricultural
and miscellaneous [17].
Municipal sources – These include sewage leakages, liquid wastes and
soil wastes. Industrial sources-include liquid wastes and leakages from tanks
and pipelines as well as mining activities and oil field brines. Agriculture
produces pollution as a consequence of irrigation return flows, animal wastes,
pesticides etc. Under miscellaneous are listed spills and surface discharges,
septic tanks and cesspools, roadway deicing, interchange through wells, etc
[18].
Nitrates are important pollutants of groundwater and indeed of the
environment in general. All over the world an increasing input of fertilizers
aimed at increasing agricultural output is occurring and concomitantly there is
a general deterioration in the quality of both surface water and ground water.
Today, in most rivers there is an abnormal increase in nitrogen and
phosphorus concentrations. There is evidence of a link between gastric
cancer and high nitrate concentration in ingested water [11,19]
Such addition of nutritive elements induces entrophication with
problems concerning the use of water by human populations. The leaching of
nitrate from agricultural land is a great concern to the soil chemist. [5,19].
Mining operations produce many ground water pollution problems. The
nature of the pollutant depends on the material actually being mined and also
on the mining processes. Very important contributors are the coal,
phosphate, uranium mines and bodies producing iron, copper, zinc and lead,
etc. Since surface and subterranean mines usually extend below the water
tables, expansion of mining activities necessitates de-watering. The water so
removed is highly mineralized and referred to as acid mine drainage. Acid
5
mine drainage is characterized by low pH, high iron, aluminum and sulphate
contents. Coal accumulations are usually associated with pyrite, which is
stable for sub-water table conditions, but oxidizes if the water table is lowered.
Oxidation succeeded by contact with water produces iron [III]sulphate and
tetraoxosulphate (VI) acid in solution, and of course, if they reach ground
water its pH will be reduced and its iron and sulphate contents will increase
[2,5].
Drainage from waste heaps produced by mining and run-offs contain
agricultural and industrial wastes, water flowing through municipal and
industrial wastes leaches soluble materials and these become contaminated.
Leachate contains poisonous substances and if disposal sites are not
carefully managed in other to collect and treat leachate effectively, it can enter
the ground water system [19].
Other sources of ground water contamination include widely used
substances such as highway salt, fertilizers that are spread across the land
surface and pesticides. In addition, array of chemicals and industrial
materials leak from pipelines, storage tanks, and holding ponds. Among
these pollutants are classified as hazardous meaning they are either
inflammable, corrosive, explosive or toxic. As rain water percolates through
the soil, it carries pollutants to the water table. Here they mix with the ground
water and contaminate the supply. Because groundwater movements are
usually slow, polluted water may go undetected for a long time [20].
Another common source of groundwater pollution is sewage, which
emanates from an ever-increasing number of septic tanks. Others are
inadequate or broken sewer systems and farm wastes [21,22]
Sewage water, which is contaminated with bacteria, enters the
groundwater system and gets it polluted. Sewage and manure contain both
ammonia and acid, organic forms of nitrogen. Organic nitrogen may be
6
converted into ammonia in the soil. Nitrate is a problem as a contaminant in
drinking water due to its harmful biological effects. High concentration of
nitrates causes methamoglobinemia which causes gastric and intestinal
cancer [19,23]. Several human activities have indirect or devastating effects
on water quality and aquatic environment. Such activities include accidental or
unauthorized release of chemical substances, discharge of untreated water or
leaching of noxious liquids from solid waste disposal [24-26].
A recent work by Yahaya in 2006[27] revealed that the cat fish has
been isolated as net accumulators or bio accumulators of pollutants such as
zinc, Mn, Cr, Co, Ni, Rb, C, Cd etc. Zinc, an indispensable trace element, is
essential for human and fish existence, and is as well regarded as a pollutant
in several areas. Compared to the other bio-available metals, it was the
second most abundant in the Shell fish . Industries producing pesticides,
plastics, chlorine, caustic soda, pulp and paper introduce into the environment
(soil, water) heavy metals such as mercury [28,29]. Acid rain breaks rocks,
releasing heavy metals into streams, lakes and ground water, by this aquatic
environments are heavily contaminated by these heavy metals. Heavy
metals can not be degraded bio-chemically in nature. The stability of these
metals therefore allows them to be transported to considerable distances by
water. As a result of this process, the level of heavy metals in the upper
member of the food chain can reach values significantly high to cause health
hazards, when such organisms are used as food by man [26]. Some of these
heavy metals are clearly in organic form at the time of discharge and do
undergo further bio-transformation inside the fish, which render them
extremely dangerous. For example mercury exists in zero, [O], plus one,[+],
and plus two,[+2], oxidation states.Methyl mercury CH3Hg+
is an important
feature of this cycle, particularly with regard to its uptake by fish and humans.
Methyl mercury CH3Hg+
is the major mercury species found in fish and about
7
95% of the mono methyl mercury CH3Hg + eaten is absorbed by human
[30,31].
Many cities in the developing countries have been developed without
adequate and proper planning thus leading to indiscriminate actions including
dumping of wastes in and around water, washing and taking baths in rivers
etc. The use of rivers varies from one locality to another and so are the
involvements, demand for its use accordingly, from fish farming to
transportation, laundry and convenient points of waste discharge from both
home and industries, to recreation and do serve the domestic needs of the
people for water [32].
Analysis on the use of whole organisms to evaluate the concentration
of heavy metals in lower animals such as fish and crabs gave startling results
[27,33].
Mining activities have been identified with the exposure of heavy metals that
were once buried deep in the heart of the Earth to the surface from where
they are easily leached to the nearby soil, rivers, streams and lakes. The
toxic metals of lead have been known to bind with the active sites of enzymes,
thus preventing the enzyme from carrying out its normal functions. Heavy
metals, particularly mercury [Hg], lead (Pb), cadmium (Cd) ,are sulphur
seeking and easily bind to S-CH3 and S–H (sulphydryl group) in enzymes,
protein, thus immobilize the enzyme[34].Enzyme
S-H
S-H
Hg +
Enzyme
S
S
Immobilized Enzyme
Active Enzyme
Hg
8
The immobilized enzyme cannot function and as a consequence the
host suffers. Heavy metals are natural components of the environment but
are of concern because they are being added to soil, water and atmosphere in
increasing amounts, leading to different types of pollution and unfavorable
alteration of the environment. The heavy metals have the tendency of being
non-biodegradable and to accumulate in living organisms [7].
1.1 HEAVY METALS
The term heavy metal refers to metallic chemical elements that have
relatively high density, toxic or poisonous at low concentration values. They
are natural components of the Earth’s crust that can not be degraded or
destroyed, which would mainly include the transition metals, some metaloids,
lanthanides and actinides. Examples include copper, zinc, selenium, iron,
lead, mercury, cadmium and silver etc [35]. Heavy metals are also classified
based on density, atomic weight, chemical toxicity in relation to living
organisms. An alternative term to heavy metals is ‘toxic metals’ of which no
consensus of exact definition exists [36]. Some of these metals such as
cobalt, chromium, copper, manganese, molybdenum and zinc are not left out
of the list of heavy metals [37]. Heavy metals may also be classified as “trace
elements” because they occur in concentrations of less than 1% (frequently
below 0.01% or 100mg/1kg) in rocks of the earth’s crust [38]. The trace
elements or heavy metals often called micronutrients such as zinc, copper
and manganese are useful to crops, while cobalt, manganese, copper and
zinc are to live stock [39].. These metals that can not be bio-degraded
chemically in nature include cobalt, zinc, manganese, magnesium, copper,
lead, nickel, cadmium and mercury [7], [40], [41],[42]. These toxic metals get
9
incorporated into the plant eduring the growth of the parent plant and remain
undegraded. Some heavy metals when present at high concentrations lead to
poisoning and these include lead, zinc, cadmium, mercury, nickel, copper etc.
The requirement, doses and tolerance levels of essential or trace elements
are decided on the basis of effects on growth, health, fertility and other
relevant criteria [13], [43].
In medicine and chemistry, heavy metals are defined and include all toxic
metals, irrespective of their atomic weights, members of the group VI, VII, VIII,
IX and X elements of the transition series of the periodic group [44] inclusive.
1.2 BENEFICIAL HEAVY METALS
Zinc [Zn] in the form of organo-zinc compounds is used in the
preparation of the organo metallic compounds, alkyl Zinc halides, RZnX; Zinc
alkyls, ZnR2.;[37].
Zinc is an essential component of about a hundred enzymes in total. This
number is smaller in vertebrates. In plants, zinc concentration levels are about
25-150mg/kg. At concentrations in excess of 400mg/kg it is toxic.
Zinc deficiency in man leads to dwarfism, reduced rates of blood clotting
and wound healing, skin abnormalities and other problems [13].
Lead [Pb] .The two major uses of lead are lead-acid storage batteries,
particularly for motor vehicles and as lead alkyl components added to petrol
such as tetramethyl lead used as anti-knock. From the ancient civilizations up
to the 1950’s, lead pipes were used for distribution of water in pipes in the
United Kingdom and other countries.
10
Mercury [Hg] is the only metal that is liquid at atmospheric . It is used
extensively in the manufacture of sodium hydroxide, chlorine, barometers and
thermometers. Dimethyl mercury is used in the dental industry.
1.3 HARMFUL HEAVY METAL
The Environmental Protection Agency (EPA) defined heavy metals as
harzadous substances, which on slight exposure can endanger human health.
Examples include mercury, cadmium, chromium, zinc, lead, nickel, copper,
iron, arsenic and selenium. Some of these metals exhibit extreme toxicity
even at low levels under certain conditions [45].
The presence of calcium and magnesium ions in water cause hardness.
This hardness provides protection possibly by preventing dissolution of lead
and calcium from water pipes as both metals can produce high blood
pressure, one of the precursors to heart attacks.
Lead binds strongly to a large number of molecules such as amino acids,
haemoglobin, many enzymes, ribonucleic acid, [RNA] and deoxyribonucleic
acid, [DNA]. It thus disrupts many metabolic path-ways. The effect of lead
toxicity is very wide and includes impaired blood synthesis, hypertension,
hyperactivity and brain damage [13].
The exhaust fumes from motor vehicles increase atmospheric lead levels
by factors of 20 (much more in urban areas). Further, the subsequent
contamination of soil and crop increases the amount of lead in food. The
average rate of absorption of dietary lead is about 5%, but about 40% of the
fine particulate lead retained in the lungs is absorbed, two thirds of the
11
absorption from the diet while one third comes from atmosphere. Again in
addition, lead intake is increased by about 5% for every 20 cigarettes smoked
per day. The absorbed lead enters the blood stream where over 95% is bound
to the red blood cells with a mean residence time of 1 month, [31.44]
Vanadium levels in the environment are rising as a consequence of the
burning of vanadium-containing fossil fuels and its mining and processing in
order to meet the growing needs for the metal in industry. Both acute and
chronic effects of occupational exposure to vanadium compounds are
manifested in the respiratory tract by irritation, including bronchitis and
pneumonia. Beryllium is a powerful phosphate inhibitor and strontium is a
competitor for calcium in the bone [31].
The toxic effects of cadmium received wide spread attention when some
Japanese developed Itai-Itai (“ouch ouch” disease. The main target organ for
cadmium are the kidney and liver, with critical effects occurring when a
concentration of 200. ?g /dm3 Cd(net weight) is reached in the kidney cortex.
The closeness between actual intake and suggested maximum is one of the
reasons for the concern over cadmium levels in soil, water and food. Smokers
are especially at risk because of the cadmium content of tobacco. Smoking 20
cigarettes per day corresponds to an oral intake of 40µgCd from food [44].
The target organ of organic mercury (methyl mercury [HgCH3), in
humans is the brain, where it disrupts the blood balance, upsetting the
metabolism of the nervous system. The main toxic effects of inorganic
mercury are that it tends to disrupt the functions of the kidney and liver.
Compared with the inorganic mercury, methyl mercury can much more easily
cross the placenta and affect the foetus. [34]
12
Since the industrial revolution, industrial and mining operations have
been accompanied by problems like industrial waste which may be toxic,
ignitable, corrosive or reactive. These wastes if not properly managed pose
dangerous health and environmental consequences. The introduction of
computers, drugs, textiles, paints and dyes, plastics-also brought hazardous
wastes which include toxic chemicals into the environment.[46,47]
Before substantial state and federal regulations began in 1970s, most
industrial wastes were disposed off in landfills, stored in surface
impoundments such as lagoons or pits, discharged into surface waters with
little or no treatment. Improper management of industrial as well as hazardous
waste has resulted in polluted groundwater, streams, lakes and rivers as well
as damage to wildlife and vegetation. Meanwhile, high levels of toxic
contaminations have been found in animals and human, particularly those like
firm workers, oil and gas workers, who are continually exposed to such waste
streams. [47]
Any waste that exhibits one or more of the following characteristics on
subjection to certain tests like ignitability, corrodibility, reactivity, toxicity is
hazardous.
1.4 HAZARDOUS WASTE
The Environmental Protection Agency (EPA) states that a solid waste is
hazardous if it is generated from specific industries such as refining, wood
preserving and secondary lead smelting, as well as sludges and production
processes.
The waste is classified hazardous if it is generated from common
manufacturing and industrial processes, including spent solvents, degreasing
13
operations, leachate from landfills and ink formulation wastes. Chemical
products such as pesticides and other commercial chemicals enter the
environment terminating in the water bodies (surface or underground). [47]
Hazardous wastes may result from manufacturing or other industrial
processes such as cleaning fluid, aerosols, paints or pesticides discarded by
commercial establishments or individuals.
The hazardous wastes which can get to the water bodies include
chemicals such as acids, bases, reactive waste, wastewater containing
organic solvents, heavy metal solutions, and solvents, ink sludges containing
benzene and other hydrocarbons, sludges from refining process from the
petroleum refining industries and heavy metals from paper industry and
leather products manufacturing.
The water bodies are seriously contaminated on taking their natural
course through the urban cities where metal manufacturing industries produce
heavy metals, cyanide and paints waste are in operation. These industries
discharge their effluents on the environment subsequently leading to
underground water contamination. [48][49]
1.5 NON- HAZARDOUS INDUSTRIAL WASTES
Some wastes are classified by the Environmental Protection Agency as
non- hazardous. These contain specific toxic chemical constituents which
exceed the regulated concentration levels, but not enough to be considered
hazardous. These are liquids which are ignitable at temperatures above
65.56
o
c.
Some solids which combine with water and exhibit corrosive properties
might be hazardous and some empty containers which held hazardous
14
substances are toxic unless the residue has been completely removed
through certain processes.[46]
These heavy chemicals and metals produced by manufacturing
industries have been the main cause of the alterations of the quality of the
surface and underground water bodies. In places where these heavy
chemicals and metals are produced, the concentrations of these contaminants
have been found to be very high on the soil, surface and underground water
bodies. The inhabitants of these environments consequently became the
endangered species. Cases of kidney failures, liver problems, blood
infections, heart failures, and extinction of aquatic organisms are common
hazards.[46,47]
The World Health Organization (WHO) stipulated respective minimum
standard concentrations for these elements as numbers that will be present in
the water bodies before they can be considered safe for use.
1.6 JUSTIFICATION FOR THE STUDY
It is on record that a lot of work have been done on many African rivers
by World known scientists. Obodo analysed the River Niger in 2001 and in
2002 Obodo again worked on some rivers in Imo State which included five
major rivers (Imo, Otamiri, Nworie, Aba and Mba). Egereonu in 1999 carried
out analysis on the nitrate level in the River Niger. Emezie and Durugbo in
1980 also took their toil in carrying out analysis on Rivers in Imo State and
Nigeria.
In 2004, Egeronu determined the nitrate levels of rivers Nworie and
Otamiri and the laboratory studies of groundwater in Owerri and environs for
corrosion and environmental studies. In 1986, an unpublished B.Sc thesis by
15
Uwume studied the pollution levels of some selected natural rivers in Imo
State like Imo, Urashi and Mbaa.
K,With these reports it is clear that an aggregate has not been arrived at
that took a wholesome analyses of the water bodies/resources in Owerri Local
Government as assembled in this project hence the need to carry out this
work.
1.7 AIM OF THE STUDY
i. A pollution watch of the underground and surface water
contaminants in old Owerri Local Government Area of Imo State.
This entails sampling and analyzing ground water for quality
investigation of water which might be contributing to pollution.
ii. To establish, where possible, a relationship between the pollution
indices of the water bodies and the pollutants in the area of study.
iii. Utilization of the information realized in controlling future
contaminations of the environment by the pollutants.
iv. To design a possible scientific and effective control measure to
remove contaminations in these areas. [17]
1.8 SCOPE OF THE STUDY
The analysis was carried out on five underground and three surface
water bodies. The samples were collected from the water bodies weekly
within the months of April through May to June 2009. The surface water
bodies visited were Otamiri River at the banks of Emmanuel College Bridge
head, Umumbazor Nekede Bridge head, FUTO Ihiagwa Bridge head. Nworie
River at the banks of Akanchawa Bridge head, at the Amakohia New road
Bridge Head and Ware house Bridge head. Oramiriukwa River at the
Nkwoemeke, Ogbeke-Amaeze Obibi and Okolochi river banks. The
16
underground water (bore holes) were taken from the catchment areas of the
surface water at Amakohia, Akwakuma, Emekuku, Ihiagwa, Amaeze and
Okolochi.
1.9 STATISTICAL INSTRUMENT OF ANALYSIS
(i) Histogram: This is the chat of a frequency distribution represented in
diagrams, graphs; values of variables are scaled along the x-axis[abscissa]
and the frequency along the y-axis[ordinate] [50].
(ii) Spearman’s correlation co-efficient equation
For R, we define
R = 1-6?d2
/n (n2
-1) [51]
Where, d = difference in each pair of ranks
n = Number of objects being ranked
R = Defined in such a way that when
The ranks are in perfect agreement
R equals +1 and when in perfect
Disagreement R equals -1
(iii) Pollution Index
The overall pollution index of a water body as developed by Horton
can be evaluated by using the multiple items of water qualities and
the permissible level of the respective item for use.
Horton pollution index equation
Pij = (maxCi/Lij)2
+ (mean C1/Lij)2
2
If Pij is the pollution index then
Pij = F {Ci/Lij, C2/L2j, C3/L3j ………. Ci/Lij}
The following contaminant items were recommended for the index
discussion and computation. For example, temperature, PH
, total dissolved
17
solids, total suspended solids, hardness, alkalinity, nitrate, chloride, sulphate
ions, acidity and heavy metals etc [52].
1.10 ATOMIC ABSORPTION SPECTROPHOTOMETRY
1.10.1 Principles of Atomic Absorption Spectrophotometer
In practice a solution of the element is sprayed into a relatively cool
flame in which the atom tends to remain in the ground state. Radiation of a
characteristic wavelength from a hallow cathode discharge lamp is passed
through the flame and the decrease in intensity is measured using a
monochromator and detector systems. The decrease is related to the
concentration of the element in solution.
Instrumentation: The Atomic Absorption Spectrophotometer (AAS)
instruments are basically instruments with a burner compartment instead of a
cell (for the sample). They consist of a source of radiation burners plus
sample compartment, monochromator and a detector and recorder.
Radiation source is a hollow cathode lamp. This contains substantial
proportions of the element to be analyzed. The radiation produced correspond
to the emission spectrum of that element and so the required line may be
readily isolated by the monochromator.
Individual hollow cathode lamps are available for large number of elements.
Techniques: Hollow cathode lamps must be run at their specified currents.
Too low a current may give insufficient sensitivity, but too high a current will
shorten the life of the lamp. The position of the lamp in relation to the flame is
critical and should be checked periodically.
In general, the design and the condition for using Nebulizer burner and
detection system are very similar to that discussed under flame emission.
18
After the elimination of flame and nebulizer interferences the most important
causes of error in AAS are:
1) Nebulizer blockage
2) Changes in air and flow rate
3) Very low acetylene cylinder pressure.
4) Hollow cathode lamp drift. The input of the hollow cathode lamp tends
to drift producing a gradual shift of the zero standard range. Note:
frequent checking and control is necessary.
5) Changes in burner heights are difficult to monitor accurately [53-55].
Sample
Atomizer
Final
Supply
Pressure
regulator
Optical
system
Detector Recorder
Fig 1: Block diagram of Atomic Absorption Spectrophotometer
19
Fig 2: Atomic Absorption Spectrophotometer