ABSTRACT
Effects of heavy metals on the Air Pollution Tolerance Indices (APTI) of five
medicinal plants growing within quarry site in Ishi-Agu, Ebonyi State, Nigeria
were studied. Following laboratory analysis of the leaves of the plants for metal
load and four biochemical parameters of APTI computation. The metal load was
determined by the Atomic Absorption spectrophotometric method, while the
ascorbic acid was determined by the titremetric method, leaf extract pH by the
electro-chemical techniques, relative water content by plant turgidity mass and
the total chlorophyll, by spectrophotometric method. Foliar photomicrography
of the leaf was also studied. Results of Plants from experimental site showed
changes in physical and internal structures of the leaves that lead to closure of
some stomata pores in test plants and damage of some epicelluler cells.
Quantification of phytochemical contents of the test plants showed higher
values than that of control which may be due to the multiplication of some
organic substances caused by oxidative stress, presence of inorganic subtances
like heavy metals and lime stone dust.The result of elemental analysis of both
experimental and control plants gave the range of concentration of the metals
in parts per million (ppm) as follows: – lead ( 2.75 – 14.13 ± 0.02); Nickle
(0.27 – 0.54 ± 0.01) ; Cadmium ( 2.25 – 24.30 ± 0.03); Zinc (0.11- 0.03 ±
0.02); and Arsenic (0.10 – 0.70 ± 0.04). Control –Lead ( 0.00 – 5.52 ± 0.01);
Nickle (0.13 – 0.23 ± 0.01); Cadmium (0.00 – 12.00 ± 0.03); Zinc ( 0.06 – 0.10
± 0.03); and Arsenic (0.02 – 0.20 ± 0.02). There was slight increase of
v
Cadmium above maximum daily permissible intake in C. ferruginea, A,
djalonensis, and R. communis, also there is high content of Arsenic in
R.communis which is the cause of oxidative strees in test plants that result in
the elicitation of antioxidants from plants and multiplication of ascorbic acid
content. The values for the percentage computation of APTI in test plants are
V.doniana (11.03), C.ferruginea (7.62), A.djalonesis (9.94), R. communis (11.5)
and M. esculenta (8.60). Control pants gave V.doniana (11.86), C.ferruginea
(8.21), A.djalonesis (11.86), R. communis (14.39), and M. esculenta (10.21)
that result in reduction of Relative water content, Ph value, Total chlorophyll
content and Ascorbic acid content.There is relative high content of heavy
metals, physiological and visible changes in some sensitive test plants. Owing
to information gotten from the result of this research it is not recommended that
plants from the quarry sites be used in herbal formulation because of possible
metal intoxication and attenuation of their phythopotency.
TABLE OF CONTENTS
Title page: i
Certification: ii
Dedication: iii
Acknowledgements: iv
Abstract: v
Table of contents: vii
List of Tables: x
List of Figures: xi
CHAPTER ONE: 1
1.1 Introduction 1
1.2 Quarry 2
1.2.1 Effect of quarry on environments 3
1.2.2 Quarry waste 4
1.2.3 Land pollution 5
1.2.4 Noise pollution 5
1.2.5 Damage to biodiversity 6
1.3 Pollution 7
1.3.1 Pollution and vegetation 7
1.3.2 Effect of pollution on leaf anatomy 9
1.4 Air Pollution 11
1.4.1 Air pollution and medicinal plants 13
1.4.2 Types of air pollution, and their sources 14
1.4.3 The threshold which air pollution affects medicinal plants 16
1.4.4 Effect of air pollution on leaf morphology 17
1.4.5 Effect of air pollution on plant sugar content 18
1.4.6 Effects of air pollution on leaf proline 19
1.4.7 General effects of air pollution on medicinal plants 20
1.4.8 Ways of controlling air pollution 23
vii
1.5 Heavy Metals 26
1.5.1 Effect of heavy metals on medicinal plants 27
CHAPTER TWO 29
2.1 Medicinal plants 29
2.2 Pharmacognostic profile of selected medicinal plants 30
2.2.1 Pharmacognostic profile of Cnestis ferruginea 30
2.2.2 Pharmacognostic profile of Ricinus communis 34
2.2.3 Pharmacognostic profile of Vitex doniana 38
2.2.4 Pharmacognostic profile of Anthocliestia djalonensis 41
2.2.5 Pharmacognostic profile of Manihot esculenta 45
2.3 Previous pharmacological invetigation of plants studied 48
2.4 Aim and objective 55
2.5 Significance of study 55
2.6 Definition of terms 56
CHAPTER THREE: MATERIALS AND METHODS 66
3.1 Collection and preparation of plants materials 66
3.2 Chemicals, reagents and equipments 67
3.3 Morphological and microscopic analysis 68
3.4 Qualitative Phytochemical analysis 69
3.5 Quantitative Phytochemical analysis 74
3.6 Determination of Analytical standard 76
3.7 Elemental analysis 80
3.8 Air pollution Tolerance index analysis 84
3.9 Statistical Analysis 86
CHAPTER FOUR: RESULT 87
4.1 Macroscopic /Morphological examination of the
leaves of test and control samples 87
4.2 Microscopical examination of the leaves of
test and control samples 90
viii
4.3 Summary of the morphological features and microscopic results
of leaf from experimental and control sites respectively. 95
4.4 Phytochemical analysis of the leaves of test and control
samples 96
4.5 Analytical standard of the plants leaves of the test and
control samples 98
4.6 Elemental analysis of the leaves of test and
control samples 99
4.7 Relative water contents of the leaves of the
leaves of test and control samples 101
4.8 Chlorophyll contents of the leaves of the leaves of
test and control samples 102
4.8 pH of the leaf extract of leaves of test and control
samples 102
4.9 Ascorbic acid contents of the leaves
of test and control samples 103
4.10 Air pollution tolerance indices (APTI) of the leaves
of test and control samples 103
CHAPTER FIVE: DISCUSSION AND CONCLUSION 104
5.1 Discussion 104
5.2 Conclusion 116
Recommendation 117
Reference 118
Appendix 127
ix
CHAPTER ONE
1.1 INTRODUCTION
Plants occupy vital position in the ecosystem because of their role as
primary producers.They are also the major recipients of environmental pollution
owing to their static disposition. While men and other animals move away from
the immediate vicinity of compromised environmental status, plants remain
relatively immobile receiving environmental pollutants within the ecosystem.
The effect of particulate air pollutants on vegetation have been studied always
before now (Manning,1971). Air Pollution Tolerance Indices (APTI) of plants
is an important measure to check the effect of air pollution on medicinal plants
and other plants generally. Nigerian as with orther developing country suffers
pollution burden associated with the ever increasing human population,
vehicular traffic, infrastractures and industries, with negative implications for
the sustainability of humans, animals and plants communities (Choudhury and
Banerjee, 2009). Since plants major systems and organs are exposed to the
atmosphere, any air pollution around the environments reflects on the plant
health making some plant show sensitivity, some show minimal or no effect
while some are tolerant. The plants response to air pollutant varies from species
to species, type of pollutant, its reacting mechanism, and duration of exposure.
World Health Organization (WHO, 1989) recommends that medicinal
plants which form the raw materials for the finished products may be checked
for the presence of heavy metals. This is because after collection and
transformation into final dosage form, the heavy metals resident in these plants
may find its way into human body and may inhibit or impair the normal
functions of central nervous system the liver, lungs, heart, kidney and brain,
leading to hypertension, abdominal pain, skin eruptions, intestinal cramp and
different types of cancers(Shad et al., 2008).
This work is to investigate on the effects of lime Stones dust from quarry site in
Obegu Amaeze village at Ishiagu, Ebonyi state, Nigeria, on some medicinal
plants (Vitex doniana, Anthocliestia djalonensis, Ricinus communis, Cnestis
Ferruginea and Manihot esculenta ). For the fact that single parameter cannot
provide clear picture of the pollution induced changes, different measures like
APTI, Phytochemical analysis, plant leaf macroscopy and microscopy, and
Elemental analysis were used to authenticate, compare and relate the result.
1.2 Quarry
Quarry is the process of obtaining quarrying resources, usually rocks, found on
or below the land surface. The difference between mining and quarrying is that
quarrying extracts non metallic rocks and aggregates while mining executes the
site for mineral deposits. Some of the stones extracted was sandstone, lime
stones, perlite, marble, ironstone, slate, granite, rock salt and phosphate. They
are cheap and always ready for conveyance to a large market and its inclination
and depth are below the surface. The two principal branches of the industry are
the so called dimension-stone and crushed-stone quarrying. In the former,
blocks of stone, such as marble, are extracted in different shapes and sizes for
different purposes. In the crushed-stone industry, granite, limestone, sandstone,
or basaltic rock is crushed for use principally as concrete aggregate or road
stone (James, 2012).
1.2.1 EFFECT OF QUARRY ON ENVIRONMENT
Quarrying carries the potential of destroying habitats and species they support.
Even if the habitats are not directly removed by excavation they can be
indirectly affected and damaged by environmental impacts such as changes in
ground water or surface water that cause some habitats to dry out or others to
become flooded. Even noise pollution can have a significant impact on some
species and affect their successful production . Quarries can also provide a good
opportunity to create new habitats or to restore existing ones. Both positive and
adverse societal impacts of modern manufacturing technologies have great
consequences on economic, health, safety and environment in general.
Limestone quarrying can have many effects on environment, like dirtying of the
environment and roads that lead to quarry. Also there are more serious
consequences that quarrying portrays, quarrying releases toxic mercury into the
air and surrounding soil and water. Even when mercury is not present in
significant quantities, the air and water can be polluted by the dust generated by
quarry activities (Vincent et al, 2012). Quarry has the ability of destroying
habitants and the species they depend on both directly or indirectly. Quarry
causes damage to the living species by causing some unfavorable changes to the
ground water, noises that prevent them from having sucessesfull reproduction.
Moreover, there is still potential for damage to the environment particularly
with water contamination. For example, suspended particles though
chemically inert, may imbalance freshwater ecosystem. (Omosanya and
Ajibade 2011). The green plants (machine) mostly with explosives in order to
extract material for processing gives rise to noise pollution, air pollution,
damage to biodiversity and habitat destruction.
1.2.2 QUARRY WASTE
Quarrying involves the production of significant amounts of waste. Some
types of quarries do not produce large amounts of permanent waste, such as
sand and gravel quarries, whereas others will produce significant amounts of
waste material such as clay and silt. The good news is that they are generally
inert and non-hazardous, unlike the waste from many other processes. However,
there is still potential for damage to the environment particularly with water
contamination. Plants are major components of the ecosystem, a complex
interaction between the biotic and abiotic entities of the environment. The
industry, unfortunately discharge dust that settles not only on land, plants and
trees but also on surface waters used for drinking and other domestic chores by
the community. All quarry activities produce enough waste on the process of
production, though some quarry do not produce large amount of waste like sand
and gravel while some produce permanent waste material like silt and clay
crushed for use principally as concrete aggregate or road stone ( Fisher, 1944).
Again, like many other man made activities, quarrying involves the production
of significant amounts of waste. For instance, lead content in water will prevent
plants from getting their nutrients from the soil. Also suspended particles may
imbalance fresh water ecosystem. Large amount of solid can lead to flooding if
it is dumped on flood plains. This waste has to be monitored and kept where it
will not affect the environment in a harsh way (Lameed, 2010).
1.2.3 LAND POLLUTION
Land pollution, is pollution of earth natural land surface by
industrialization, commercial, domestic and land agricultural activities. Some of
the factors that contribute to land pollution are; chemical and nuclear plants,
mining littering, deforestations, construction etc. (James, 2012).
1.2.4 NOISE POLLUTION
Unfortunately, quarrying involves several activities that generate significant
amounts of noise. It starts with the preparatory activities, such as establishing
road or rail access, compound and even mineral processing facilities.
The excavation of the mineral itself involves considerable noise, particularly if
blasting methods are used. Following this, the use of powered machinery to
transport the materials as well as possibly processing plants to crush and grade
the minerals, all contribute even more noise to the environment (Lameed, 2010).
Such extraction of raw materials from their natural habitats by mining, drilling,
harvesting and those that relate to large scale water resources development
projects, construction, agriculture, energy, industry and development projects,
considerably affect the natural environment.
The process of exposing the mineral to be extracted is usually done by
removing the top soil and other soft layers using a scraper or hydraulic
excavators and dump trucks. The excavations of the minerals itself will involve
considerable noise, particularly when blasting methods are used.
1.2.5 DAMAGE TO BIODIVERSITY
One of the biggest negative impacts of quarrying on the environment is the
damage to biodiversity. Biodiversity essentially refers to the range of living
species, including fish, insects, invertebrates, reptiles, birds, mammals, plants,
fungi and even micro-organisms. Biodiversity conservation is important as all
species are interlinked, even if this is not immediately visible or even known,
and our survival depends on this fine balance that exists within nature.
Nevertheless, with careful planning and management, it is possible to minimize
the effect on biodiversity. This is one of the disadvantages of quarry on the
environment, its negative effect on living organisms like fish, insects,
invertebrates, reptiles, birds, mammal, plants, fungi, and micro-organisms. and
1.3 POLLUTION
Pollution is the introduction of a contaminant into the environment. It is
created mostly by human actions, but can also be as a result of natural disasters.
Pollution has a detrimental effect on any living organism in an environment,
making it virtually impossible to sustain life. It is the human introduction into
the atmosphere of chemicals, particulate matter, biological materials that cause
harm to human or other living organism, or damage the environment
(Anonymous, 2008). The atmosphere is a complex dynamic natural gaseous
system that is esential to all living things. There are some substances in the
atmosphere which may impair the health of plants and animals. Pollutants could
be classified as either secondary or primary. Pollutants that are formed in the
atmosphere and directly pollute the air are called primary Pollutants, while
those that are formed in the air when primary pollutant react or interact are
known as secondary pollutants(Vincent, et al., 2012)
1.3.1 POLLUTION AND VEGETATION
Industrialization areas suffer pollution because of the chemical emission
and others like oil spillage, Noise etc. These also affect the weather of that
zone which leads to increase in temperature that might result to climate
change. Climate change has become increasingly recognized as one of the
greatest challenges to human and other living things on earth. Worldwide
changes in seasonal patterns, weather events, temperature ranges and other
related phenomena have all been reported and attributed to global climate
change. Numerous experts in a wide range of scientific disciplines have
warned that negative impacts of climate change will become much more
intense and frequent in the future particularly if environmentally destructive
human activities continue unabated. Like all living members of the biosphere,
medicinal and aromatic plants (MAPs) are not immune to the effects of climate
change. Climate change is causing noticeable effects on the life cycle and
distributions of the world’s vegetation including wild MAPs. Some MAPs are
endemic to geographic regions or ecosystems particularly vulnerable to climate
change, which could put them at risk. The possible effects on MAPS may be
particularly significant due to their value within traditional systems of
medicine and as economically useful plants. The changing temperature and
wind patterns associated with climate change are causing precipitation factors
and giving some trees and shrubs the ability to grow taller in more open areas.
Some production of plants secondary metabolites are influenced by multiple
factors including disease, competition between plants, animals grazing, light
exposure, soil moisture and those other factors that may mitigate the effects of
climate change on plants secondary metabolites (Herbal , 2009).
1.3.2 EFFECT OF POLLUTION ON LEAF ANATOMY
Developments of stomata are often considered as one of the most important
developments in plants evolution. By being environmentally controlled
gateways into the plants controlling Co2 uptake and transpiration they are
central determinants of photosynthesis, cooling and nutrient uptakes (Arvel,
2009). To be able to balance Co2 uptake and water transpiration through
stomatal movements is an important response to changes in the environmental
conditions. Low transpiration due to stomatal closure means less cooling of the
leaves and less uptake and transportation of nutrients. Stomatal closure occurs
when the guard cells surrounding the stomatal opening lose turgor pressure and
close the opening (Arvel, 2009). There are many signals that induce stomatal
closure, eg Absciscic Acid (ABA), Secondary messengers like Ca2+ and H2O2.
When there is an air pollution or oxidative stress in an environment, there are
pathwaysb that leads to stomatal closure. Hydro passive stomatal closure
occurs when water evaporation from the guard cells is too low to be balanced
by water movements into these cells. The water is reduced to the extent that
osmotic pressure is reduced and cell loses tugor pressure and shrink (Lucan,
2002).When this happens the guard cells are unable to maintain the shapes and
stomatal pores is covered. Active stomatal closures occur when there is
increase in ABA Co2 level. This activates signaling pathways leading to
stomatal closure. ABA is produced in the roots and leaves during water stress
and is transported to the guard cell by ATP binding cassette (ABC) transporters
that are located in the plasma membrane, but when the transporters are
knocked out during oxidative or water stress, the ABA uptake is low. The size
of the stomatal opening is regulated by the tugor pressure cell volume of the
guard cells. Regulation of stomatal opening is linked to transport of ions and
water through channel proteins across the plasma and vacuole membrane.
ABA induces the production of reactive oxygen species eg. H2O2 which in turn
acts as a trigger for low production, inhibition of membrane proton pumps and
Ca2+ across both the plasma and vacuole membranes. H+ AT-pase that are
hyperpolarizing the plasma membranes must be inhibited to induce ABA
mediated stomatal closure (Merlot et al., 2007).The increased ca2+ level
activate slow and rapid type of anion channels, generating an anions efflux
from the cells. The anion efflux depolarizes the membrane, which in turn
causes k+ channel across both the vacuole and the plasma membrane.
Simultaneously Ca2+ also inhibits k+ in channel. Malate is also converted to
starch reducing the osmotic potential and turgor pressure further (Kim and
Van, 2011).The plasma membrane is thus depolarized, the turgor pressure and
cell volume reduced, then the stomata closed.
Stomata must open to admit Co2 into the leaf for photosynthesis, but
when they open, they allow water vapour to diffuse out of the leaf .Thus,
stomata opens enough to support photosynthesis, but they must at the same
time prevent excessive water loss. This is called constrained optimization
problem (Michael, et al., 1997).
Plants grown under high relative air humidity caused by pollutants leads to the
malfunctioning stomata. This stomata are unable to close in response to the
darkness, that result in high stomatal conductance and frequent leaf drying in
other research done in different humidity it has also been found that the
number of stomata per leaf increased with development in higher soil
humidity. The stomatal index, the number of stomata relative to the number of
epidermal cells was also found to increase with soil moisture. The stomata
density has been found to increase in plant with decreased ABA
concentrations, which have increased transpiration (Atssman, et al., 2002).
1.4 AIR POLLUTION
Air pollution is one of the severe problems the world is facing today. It
deteriorates ecological conditions and can be defined as the fluctuation in any
atmospheric constituent from the value that would have existed without human
activity (Tripathi and Gautam, 2007). In recent past, air pollution is responsible
for vegetation injuring and crop yield losses. The increasing number of
industries and automobile vehicles are continuously adding toxic gases and
other substances to the environment (Jahan and Igbal, 1992). All combustion
releases gases and particles into the air. These can include sulphur and nitrogen
oxides, carbon monoxide and soot particles as well as smaller quantities or
toxic metals, organic molecules and radioactive isotope (Agbaire and
Esiefarienche, 2009). Over the years, there has been a continuous increase in
human population, road transportation, vehicle traffic and industries which has
resulted in further increase in concentration of gaseous and particulate
pollutants (Joshi, et al ., 2009).
Adverse effects of air pollution on biota and ecosystems have been
demonstrated worldwide. Environmental stress, such as air pollution is among
the factors that limits plants productivity and survivorship (Woo, et al., 2007)
Dust from quarry sites is a major source of air pollution, though the
severity will depend on factors like the local microclimate conditions, the
concentration of dust particles in the ambient air, the size of the dust particles
and their chemistry. For example, lime stone quarries produce highly alkaline
and reactive dusts, whereas coal mines produce acidic dust. The air pollution is
a nuisance in terms of deposition on surfaces and its possible effects on health,
especially for those with respiratory problems. It produces dust that can also
have physical effects on the surrounding plants, such as blocking their
photosynthetic activities that occupy an important position in the existence of
life because of their ability to maintain a balance in the volume of oxygen and
carbon dioxide which leads to the purification of the environment.
1.4.1 AIR POLLUTION AND MEDICINAL PLANTS
Higher temperature causes heat stress in plants. This means they grow
less and produce fewer crops. In some cases, the plants do not reproduce at all
since excessive heat causes sterility of the pollen grains. A temperature increase
may be beneficial in areas which are very cold at present. Changes to our
climate are happening more quickly now than they have ever done before in the
world due to different industries and developments. Though as natures may
have it some plants due adapt to the conditions often. Some studies have
demonstrated that temperature stress can affect the secondary metabolites and
other compounds that plants produce. Water availability directly affects the
growth of plants and how much crop they produce. In most part of Africa there
is not enough water even in normal conditions for high crop yields for instance,
in contrast in Nigeria most plant are grown with enough water and difference in
crop growth between the continents can be clearly seen. So changes in
temperature and precipitation patterns as a result of climate change are likely to
be bad for large areas of the world but may increase crop production in other
regions. However, one of the likely outcomes of climate change is also an
increase in severity of rain storms and drought. These are likely to have large
devastating effects on agriculture and medicinal plant plantation.
The increase in atmospheric carbon dioxide (C02) levels resulting from
Fossil fuel combustion has fertilizing effect on most plants since C02 is needed
for photosynthesis. Conversion of carbon dioxide and water into the simple
sugar (glucose) emits oxygen making it possible for animals to lives on Earth.
Sunlight is the energy that powers this reaction. Scientific experiment has
shown that increasing atmospheric CO2 levels leads to an increase in plant
growth (shad, et al., 2008).
1.4.2 TYPE OF AIR POLLUTANT AND THEIR SOURCES
There are many atmospheric pollutants that have been in existence but few
of them are to be discussed here. The sources of air pollutants include human
activities, domestic sectors, industry, agriculture, transport and nature as well.
Here, the pollutants, their sources and toxic effects to the environment are
being discussed.
1. Solid particles; These are mostly produced by combustion, plants
industrial processes like mineral extraction, cement work, steel works,
foundries, glass works, gypsum quarries and fine chemistry. They have
carcinogenic and mutanogenic effect.
2. Sulphur dioxide (So2):This is released by coal mining, lignites,
petroleum coke, and heavy fuel oil, domestic heating oil, diesel oil,
production of paper pulp, oil refining, nature and fire wood.
3. Nitrogen oxide (No2): This is produced by combustion of fossil fuel and
from new industrial processes like fertilizer production, surface
treatment and phytochemical oxidants. In the presence of oxygen, it is
converted to No2 in the furnace. The reaction continues slowly in the
atmosphere and gives a brownish color of the layer of polluted air 100
meters above town and causes green house effect.
4. Carbon monoxide: It is gotten from incomplete combustion,
agglomeration of mineral steel work, incineration of waste and car
exhaust fumes.
5. Volatile organic compounds: These are released from methane, solvents,
paint application, printing glues and adhesives, rubbers, biomass,
perfumes, cosmetic, News papers and tobacco.
6. Heavy metals: There are various sources of heavy metals which
contaminate the atmosphere. Examples of some of them are:
(a). Arsenic (As) comes either from trace of this metal in solid mineral fuels
and in heavy fuel oil , or else from certain raw materials used in
processes such as glass making, non-ferrous and ferrous metals working.
(b) Cadmium (Cd) is formed mainly through the manufacture of zinc and
the incineration of waste .Burning solid mineral fuel, heavy fuel oil and
biomass account for a significant proportion of emission.
(c) Chromium (Cr) comes essentially from the production of glasses,
cement, ferrous metallurgy and foundries.
(e) Copper (Cu) comes from the erosion of over headed cables by railway
traffic. In addition, as for the other heavy metals, ferrous and non-ferrous
metals from metal production processes, the treatment of waste, and
combustion are all, to varying degree major sources of copper emission.
(f) Mercury (Hg) is emitted in small but still excessive quantities by the
combustion of coal and oil, the production of chlorine, and also by the
incineration of household, hospital and industrial waste. Preventive
action has considerably reduced mercury emission in recent years. Other
type of pollutants are Nickel, Lead, Selenium, Zinc, carbon dioxide,
methane, Nitrous oxide, Chlorofluorocarbon, Hydroflurocarbons,
Perflurocarbons, Sulphur hexafluroxide , Hydrofluoric acid , Ozone, and
Hydrogen sulphide (Citepa, 2012).
1.4.3 THE THRESHOLD AT WHICH AIR POLLUTANT EFFECT
MEDICINAL PLANTS AND THEIR SYMPTOMS.
This is injury or symptoms shown by impact of metallic object on some
plant by pollutants. These symptoms are always triggered at some threshold
extent. The presence of pollutants like, Sulphur dioxide causes intervenial
necrotic blotches, red brown die back or banding in pines, in plants. Nitrogen
dioxide causes interveinial necrotic blotches similar to those symptoms
produced by Sulphurdioxide. Fluoride produces red brown distal necrosis in
pines. Ammonia leads to tip margin necrosis at the threshold dose of 55pm
(38×10μg/m3) for 1 hour. Chlorine causes interveinial necrotic blotches
similar to So2 at the threshold of 0.5-1.5ppm (1400-4530μg/m3) for 0.5-3hr.
Ethylene leads to chlorosis, necrosis, abscission, dwarfin, premature
defoliation of medicinal plants but the threshold variably undetermined. Ozone
causes upper surface broncing chlorosis and early senescence at the threshold
of (157μg/m-3) for 12-13 hrs. Acidic rain shows necrotic sports, distal necrosis
pines on medicinal plants at the pH < 3.0 (Citepa, 2012).
1.4.4 EFFECT OF AIR POLLUTION ON LEAF MORPHOLOGY
Pollutants can cause leaf injury, stomata damage, premature senescence,
decrease photosynthetic activity, disturb membrane permeability and reduce
growth and yield in sensitive plant species (Tiwari, et al., 2006). Reductions in
leaf number may be due to decreased leaf production rate and enhanced
senescence. The reduced leaf area result in the reduced absorbed radiations and
subsequently in reduced photosynthetic rate.
Air pollution stress leads to stomatal closure, which reduces co2
availability in leaves and inhibits carbon fixation. Plants that are constantly
exposed to environmental distress absorb, accumulate and integrate these
pollutants into their systems. Reports have shown that depending on their
sensitivity level, plants shows visible changes which would include alteration in
the biochemical processes or accumulation of certain metabolites (Agbarie and
Esiefarienrhe, 2009).
Sulphur dioxide, nitrogen oxides, acid co2 as well as suspended
particulate matter, when absorbed by the leaves may cause a reduction in the
Concentration of photosynthesis pigment like chlorophyll and carotenoids
which directly affected metabolites. One of the major impacts of air pollution is
the gradual disappearance of chlorophyll that leads to yellowing of leaves,
which may be caused by decrease in the capacity for photosynthesis.
Chlorophyll is the most photoreceptor in photosynthesis, the light driven
process in which carbon dioxide is fixed to yield carbohydrates and oxygen.
When plants are exposed to environmental pollution above the normal
physiological acceptable range, photosynthesis gets inactivated. What happen to
leaf morphology, pigment content also affects the efficacy of the crude extracts
(Joshi and Swami, 2007).
1.4.5 EFFECT OF AIR POLLUTION ON PLANT SUGAR CONTENTS
Mainly soluble sugar from plants and vegetation are source of energy for
living organisms. Studies have revealed that there is always loss of soluble
sugar in all tested species at all polluted sites. Loss of soluble sugar content in
polluted area can be related to increased respiration and decreased CO2 fixation
because of chlorophyll deterioration (Tripathi and Guatam, 2007). Reseachers
have found out that pollutants like SO2, NO2, and H2S under hardening
condition can lead to loss of soluble sugar in the leaves of plant grown in
polluted Area. They have also shown that even in sensitive trees loss of sugar
has occurred and is probably due to photosynthetic inhibition or stimulation of
respiration rate.
Increase in amount of soluble sugar is a protecting mechanism of leaves.
Soluble sugar in pine needle decreased on ozone exposure and the more a plant
is resistant to air pollution the more the increase in soluble sugar level eg
Dodonea viscoss and prosopis juliflora (Abedi, et al., 2009).
1.4.6 EFFECT OF AIR POLLUTION ON PLANT PROLINE
Proline is an osmotic accumulation in response to several stresses that
may have a role in defending plants life, pigment destruction, depletion of
cellular lipids and peroxidization of polyunsaturated fatty acid.
Many researchers have shown that environmental stress, causes increase
in tree proline Contents. Environmental stresses like high temperature, low
temperature, drought, air pollution and soil pollution can lead to reaction of
oxygen species in plant cells which is always cytotoxic to all organisms when a
plant is exposed to high environmental stress, this forces the chloroplast into an
excessive excitation energy level which in turn causes increase in generation of
reactive oxygen species and lead to oxidative stress. The proline is known as
free radical scavenger to protect plants. Some other amino acids such as
tryptophan, tyrosine etc, do the same but proline is counted more important
because of its high Concentration on a plant during environmental stress
(Tiwari, et al., 2006).
1.4.7 GENERAL EFFECT OF AIR POLLUTION ON MEDICINAL
PLANTS
Much experimental work has been conducted on the analysis of air
pollutant effects on crops and vegetations as various levels ranging from
biochemical to ecosystem levels. Environmental stress, such as air pollution is
among the factor that limits plants productivity and survivorship (Woo, et al.,
2007). When exposed to air bone pollutants, most plants experienced
physiological changes before exhibiting visible damage to leaves (Liu and
Ding, 2008). The atmospheric S02 adversely affects various morphological and
physiological characters of plants. High soil moisture and high relative
humidity aggregate S02 injury in plants.
Industrialization and the automobile are responsible for maximum amount
of air pollutants and the crop plants are very sensitive to gaseous and
particulate pollutions (Joshi, et al., 2009). Vegetation is an effective indicator
of the overall impact of air pollution and the effect observed is a time averaged
result that is more reliable than the one obtained from direct determination of
the pollution in air over short period. Although, a large number of trees and
shrubs have been indentified and used as dust filters to check the rising urban
dust pollution level (Rao, 1979).
Plants provide an enormous leaf tree impingement, absorption and
accumulation of air pollutants to reduce the pollutant level in the environment
with a various extents for different species. The use of plants as monitors
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