DEVELOPMENT OF THE HEART

DEVELOPMENT OF THE HEART

The first sign of heart development is the formation of cardiogenic cords.  These are canalized to form two endocardial tubes that fuse to make one heart tube.  Before we look at the development of the heart in detail, we will look at the development of the pericardial cavity.

Pericardial Cavity: 

Coelomic sacs in the adult are closed, independent, mesothelial-lined sacs of the trunk, and under normal (non-pathological) circumstances, they are empty except for a very small amount of lubricating fluid that allows the surfaces to move against one another without friction.  This is important because dissection of those organs that develop adjacent to coelomic sacs (lungs, heart, abdominal viscera) might give you the illusion that these organs develop within the sacs.  The organs are actually pushed into the lining of the related sac in a way that can be remembered by the image of pushing a fist into an inflated balloon.   The fist represents the organ and the balloon represents the coelomic sac.  Notice that the coelomic sac (balloon) is empty.

All coelomic sacs can be described as a cavity lined by a mesothelial membrane called a serosa.  It is the internal serosal surface that produces a serous fluid and enables opposing serous membranes to slide across one another.  The coelomic sac that surrounds the heart during its development is known as the pericardial sac.

A mesentery consists of two intact, opposed serous membranes that support a thoracic or abdominal organ.  Mesenteries are usually named for the organ that they suspend.  The mesentery relevant to heart development is the dorsal mesocardium (meso = mesentery, cardium = heart).  The heart pushes into the dorsal wall of the pericardial sac during development.  As the heart pushes into this empty sac, it becomes surrounded to such a degree that two layers of the dorsal tissue become opposed and are given the name, the dorsal mesocardium.  The dorsal mesocardium suspends the heart for a time but soon breaks down leaving the heart suspended at its cranial and caudal surfaces but not at the back.  The gap which persists where the dorsal mesocardium once was is called the transverse sinus.  You will explore this space in gross dissection laboratory.  The heart tissue is still encased by the visceral layer of pericardium and the parietal layer surrounds it.  All that has disintegrated is the dorsal mesocardium.  More will be said about the details of the anatomy of the adult pericardial sac in the lecture on the heart.

Early Development of the Heart:

Endocardial tubes (Day 19):  These thin-walled,

endothelial tubes develop from condensations of splanchnopleuric mesoderm in the cardiogenic region of the trilaminar germ disc.  The cardiogenic region is cranial to the neural plate. 

 Embryonic folding (begins Day 20):  Lateral and cephalic folding of the trilaminar germ disc over the course of several days brings the endocardial tubes together and tucks them ventrally in the thoracic region at the base of the yolk sac.  This process also brings the septum transversum into its adult position inferior to the heart.

Primary heart tube (Day 21):  The endocardial

tubes fuse together into a primary heart tube through which blood eventually flows in a cranial direction.  The mesenchyme surrounding the tube condenses to form the myoepicardial mantle (the future myocardium).  Gelatinous connective tissue called cardiac jelly separates this mantle from the endothelial heart tube (the

future endocardium).  In addition, a series of constrictions (sulci) divide the heart tube into sections: sinus venosus, into which the common cardinal veins, the umbilical veins and the vitelline veins drain; the primitive common atrium; the primitive ventricle; and the bulbus cordis, through which blood flows to the paired dorsal aortae.  The heart is beating at Day 22.  Contractions are of myocardic origin and are likened to peristalsis.  Several processes that are not restricted to the heart proper continue to occur during this time that have a great impact on heart development: embryonic head folding, embryonic lateral folding, and elongation of the heart tube in an increasingly restricted space.

Looping of heart tube

(Days 23-28):  The primitive atrium loops up behind and above the primitive ventricle and behind and to the left of the bulbus cordis.  Blood begins to circulate through the embryo by Day 24.  The looping process brings the primitive areas of the heart into the proper spatial relationship for development of the adult heart.

Circulation at 22 Days:

Three paired veins drain into the heart of the embryo during the fourth week:

Vitelline veins drain blood from the yolk sac; their formation has associations with formation of the liver and the portal system.

Umbilical veins bring oxygenated blood from the chorion (early placenta).  There are two at the start.  The right umbilical vein degenerates and disappears.  The left umbilical vein persists, carrying all blood from the placenta to the fetus.  The umbilical vein degenerates after it is cut at birth and is viewed in the adult cadaver as ligamentum teres.

Common cardinal veins return blood to the heart from the body of the embryo.  The derivation of the adult structures from the cardinal veins are complex but produce:  the left brachiocephalic v., the azygous v., the common iliac v., the left renal v., the suprarenal v., the hemiazygous v. and the IVC.

Three sets of paired arteries are evident in the embryo.  The first two carry blood to portions of the developing organism while the third carries blood away from the organism to the placenta.

The intersegmental arteries form 30-35 branches off the dorsal aortae.  Many of these are transient structures, but some persist to form the vertebral a., the intercostal a., and the common iliac a.  See Larsen (pp. 193-204) for a good discussion of arterial development.

The vitelline arteries pass to the yolk sac and later to the primitive gut which forms from the yolk sac.  Three of the vitelline arteries remain that provide blood to the gut in the adult.  These include: the celiac artery, the superior mesenteric artery and the inferior mesenteric artery.  The vitelline system becomes the portal system of the adult.  You will become intimately acquainted with this system during your dissection of the gut.

The umbilical arteries carry oxygen-depleted blood to the placenta.  The proximal parts of these arteries become the internal iliac arteries and the superior vesical arteries but the distal parts break down after birth and become the medial umbilical ligaments.

Formation of Heart Chambers:

Right atrium:  As the heart continues to grow, the right side of the sinus venosus is incorporated into the right side of the primitive atrium.  The primitive atrial wall is pushed ventrally, eventually becoming the right auricle.  In the adult heart, the right auricle contains pectinate muscle derived from the primitive atrium, whereas the sinus venarum is derived from the sinus venosus and therefore smooth-walled.

            Left atrium:  The left side of the primitive atrium sprouts a pulmonary vein which branches and sends two veins toward each of the developing lungs.  The trunk of this pulmonary vein is incorporated into the left side of the primitive atrium, forming the smooth wall of the adult left atrium.  The left side of the primitive atrium is pushed forward and eventually becomes the trabeculated left auricle.

            Interatrial septum:  The interatrial septum in the adult heart is formed by the combination of two embryonic septa:  the septum primum and the septum secundum.  The septum primum grows along the midsagittal plane like a waxing moon toward the atrioventricular canal.  This septum separates the two atria, except for a temporary space at the posteroinferior edge of the septum primum called the foramen primum which permits the right-to-left shunt of fetal blood.  At the superior edge of the septum primum clefts begin to form that provide a second opening, the foramen secundum.  The foramen secundum provides an alternate right-to-left shunt, and the foramen primum closes.  During this process a second, partial septa, the septum secundum, also begins to grow down from the roof of the right atrium, just lateral to the septum primum.  The septum secundum is thicker and more muscular than the membranous septum primum and permits the right-to-left shunt of blood through a space called the foramen ovale.  The septum secundum eventually fuses inferiorly, but foramen ovale remains patent enabling the shunting of blood from the right to  left side of  the heart.  Fetal blood is shunted from the right atrium to the left atrium through two staggered openings: the foramen ovale and the foramen secundum.  After birth, when pulmonary circulation increases blood pressure in the left atrium, the membranous septum primum is pressed against the septum secundum.  They eventually fuse and block the right-to-left shunt of blood. 

            Interventricular septum:  The left ventricle is formed primarily from the primitive ventricle.  The right ventricle is formed primarily from the bulbus cordis.  The superior portion of the bulbus cordis becomes the conus arteriosus and the truncus arteriosus.  A muscular interventricular septum begins to grow superiorly from the ventricular floor between the presumptive right and left ventricles. This septum stops short of the atrioventricular canal, leaving a space called the interventricular foramen which permits blood from both ventricles to exit via the conus arteriosus.  Within the conus arteriosus, spiral aorticopulmonary septae form, dividing the conus in half and extending inferiorly to fuse with and complete the interventricular septum.  These septae continue superiorly into the truncus arteriosus, creating outflow tracks from the right and left ventricles that are the vestigial pulmonary trunk and aorta.

neurotoxicity

What is Neurotoxicity?

The term neurotoxicity refers to damage to the brain or peripheral nervous system caused by exposure to natural or man-made toxic substances.

These toxins can alter the activity of the nervous system in ways that can disrupt or kill nerves. Nerves are essential for transmitting and processing information in the brain, as well as other areas of the nervous system.

Due to their high metabolic rate, neurons are at the greatest risk of damage caused by neurotoxins. This is followed, in order of risk, by oligodendrocytes, astroocytes, microglia and capillary endothelium cells.

Depending on a neurotoxin’s chemical profile, it will cause damage to certain parts or particular cellular elements of the nervous system. Non-polar substances are more soluble in lipids and can therefore access the nervous tissue more easily than polar compounds, which are less soluble in lipids. The body’s response to neurotoxins is influenced by factors such as the neurotransmitter affected, cellular membrane integrity and the presence of detoxifying mechanisms.

Some examples of substances that can be neurotoxic to humans include:

•Chemotherapy drugs that are used to kill fast growing cells

•Radiation

•Drug therapies or drugs of abuse

•Heavy metals such as mercury and lead

•Certain foods and food additives

•Insecticides/pesticides

•Cosmetics

•Industrial and cleaning solvents

Some examples of neurotoxic substances our environment has become polluted with and that it is difficult for people to avoid exposure to include:

•Mercury

•Cadmium

•Lead

•Insecticides

•Solvents

•Car exhaust

•Chlorine

•Formaldehyde

•Phenol

Effects of neurotoxicity

Some of the effects of neurotoxicity may appear immediately, while others can take months or years to manifest.

The effects of neurotoxicity depends on various different factors such as the characteristics of the neurotoxin, the dose a person has been exposed to, ability to metabolise and excrete the toxin, the ability of affected mechanism and structures to recover and how vulnerable a cellular target is.

Some of the symptoms of neurotoxicity include:

•Paralysis or weakness in the limbs

•Altered sensation, tingling and numbness in the limbs

•Headache

•Vision loss

•Loss of memory and cognitive function

•Uncontrollable obsessive and/or compulsive behavior

•Behavioral problems

•Sexual dysfunction

•Depression

•Loss of circulation

•Imbalance

•Flu-like symptoms

Other conditions that may develop as a result of neurotoxicity include chronic fatigue syndrome, attention deficit hyperactivity disorder, chronic sinusitis and asthma that does not respond to therapies. Symptoms may also resemble those seen in some autoimmune conditions such as irritable bowel syndrome or rheumatoid arthritis.

Some examples of toxins that occur naturally in the brain and can lead to neurotoxicity include oxygen radicals, beta amyloid and glutamate. Aside from causing movement disorders, cognitive deterioration and dysfunction of the autonomic nervous system, neurotoxicity has also been shown to be a major contributor to progressive neurological disorders such as Alzheimer’s disease.

Diagnosis

The best test to show whether the peripheral nervous system has been affected is the nerve conduction test. Tests used to detect damage to the brain include pupillography, computerized balance heart rate variability, brain imaging with the triple-camera SPECT system and psychiatric testing .

Treatment

The treatment approach to neurotoxicity is elimination or reduction of the toxic substance and therapy to relieve symptoms or provide support. Treatment may also involve avoiding air, food and water pollutants. Some examples of therapies used in the treatment of neurotoxicity include massage, exercise and immune modulaiton.

Prognosis

The outcome of neurotoxicity depends on the duration and extent of exposure to the toxic substance, as well as the degree of neural damage. Exposure to neurotoxins can be fatal in some cases, while in others, patients survive but may not completely recover. In other cases, patient do completely recover after receiving treatment.

Current research

Scientist are looking at whether occupational and environmental toxins may play a role in neurodegenerative diseases such as Alzheimer’s, Parkinson’s disease and multiple sclerosis. Another popular research topic in this area is the mechanisms behind neuroimmune responses that occur in the nervous system. Whether or not the interaction between environmental factors and genes contributes to brain disorders in children is another research question that is currently being investigated.

POLLUTION AND AWERNESS

POLLUTION AND AWERNESS

Introduction:

Pollution is the production of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e., physical systems or living organisms. Human activities directly or indirectly affect the environment adversely. A stone crush eradds a lot of suspended particulate matter and noise into the atmosphere. Automobiles emit from their tail pipes oxides of nitrogen, sulphur dioxide, carbon dioxide, carbon monoxide and a complex mixture of un-burnt hydrocarbons and black soot which pollute the atmosphere. Domestic sewage and run off from agricultural fields, laden with pesticides and fertilizers, pollute water bodies. Effluents from tanneries contain many harmful chemicals and emit foul smell. These are only a few examples which show how human activities pollute the environment. Pollution may be defined as addition of undesirable material into the environment as a result of human activities. The agents which cause environmental pollution are called pollutants. A pollutants may be defined as a physical, chemical or biological substance unintentionally released into the environment which is directly or indirectly harmful to humans and other living organisms. They can be can be foreign substances or energies or naturally occurring. In such case they are also known as contaminants. Pollution can take the form of chemical substances or energy, such as noise, heat or light.

TYPES OF POLLUTION

Pollution may be of the following types:

·         Air pollution

·         Noise pollution

·         Water pollution

·         Soil pollution

·         Thermal pollution

·         Radiation pollution

AIR POLLUTION

Air pollution is a result of industrial and certain domestic activity. An ever increasing use of fossil fuels in power plants, industries, transportation, mining, construction of buildings, stone quarries had led to air pollution. Air pollution may be defined as the presence of any solid, liquid or gaseous substance including noise and radioactive radiation in the atmosphere in such concentration that may be directly and indirectly injurious to humans or other living organisms, plants, property or interferes with the normal environmental processes. Air pollutants are of two types (1) suspended particulate matter, and (2) gaseous pollutants like carbon dioxide (CO2), NOx etc. Some of the major air pollutants, their sources and effects are given in table 1.

Table 1: Particulate air pollutants, their sources and effects

Pollutant	Sources	Effects
Suspended particulate matter/dust	Smoke from domestic, industrial and vehicular soot,	Depends on specific composition Reduces sunlight and visibility increases corrosion, Pneumoconiosis, asthma, cancer, and other lung diseases.
Fly ash	Part of smoke released from chimneys of factories and power plants	Settles down on vegetation, houses. Adds to the suspended participate matter (SPM) in the air. Leachates contain harmful material

10.3.1 Particulate pollutants

Particulate matter suspended in air are dust and soot released from the industrial chimneys. Their size ranges from 0.001 to 500 μm in diameter. Particles less than 10μm float and move freely with the air current. Particles which are more than 10μm in diameter settle down. Particles less than 0.02 μm form persisent aerosols. Major source of SPM (suspended particulate matter) are vehicles, power plants, construction activities, oil refinery, railway yard, market place, industries, etc.

·         Fly ash

Fly ash is ejected mostly by thermal power plants as by products of coal burning operations. Fly ash pollutes air and water and may cause heavy metal pollution in water bodies. Fly ash affects vegetation as a result of its direct deposition on leaf surfaces or indirectly through its deposition on soil. Fly ash is now being used for making bricks and as a land fill material.

·         Lead and other metals particles

Tetraethyl lead (TEL) is used as an anti-knock agent in petrol for smooth and easy running of vehicles. The lead particles coming out from the exhaust pipes of vehicles is mixed with air. If inhaled it produces injurious effects on kidney and liver and interferes with development of red blood cells. Lead mixed with water and food can create cumulative poisoning. It has long term effects on children as it lowers intelligence. Oxides of iron, aluminum, manganese, magnesium, zinc and other metals have adverse effect due to deposition of dust on plants during mining operations and metallurgical processes. They create physiological, biochemical and developmental disorders in plantsa nd also contribute towards reproductive failure in plants.

Table 2: Annual average concentration of pollutants in ambient air in

residential and industrial areas (year 2000) mg/m3 in 24 hours

SPM permissible- residential 140 – 200 mg/m3, industrial 360 – 500 mg/m3

City	Residential area	Industrial area
Agra Bhopal Delhi Kanpur Kolkata Nagpur	349 185 368 348 218 140	388 160 372 444 405 157

10.3.2 Gaseous pollutants

Power plants, industries, different types of vehicles – both private and commercial use petrol, diesel as fuel and release gaseous pollutants such as carbon dioxide, oxides of nitrogen and sulphur dioxide along with particulate matter in the form of smoke. All of these have harmful effects on plants and humans. Table 10.3 lists some of these pollutants, their sources and harmful effects.

• Carbon dioxide (CO₂) - This is by far the most emitted form of human caused air pollution. Although CO₂ is currently only about 405 parts per million in earth's atmosphere, billions of metric tons of CO₂ are emitted annually by burning of fossil fuels. CO₂ increase in earth's atmosphere has been accelerating.
• Sulfur oxides (SO_x) - particularly sulfur dioxide, a chemical compound with the formula SO₂. SO₂ is produced by volcanoes and in various industrial processes. Coal and petroleum often contain sulfur compounds, and their combustion generates sulfur dioxide. Further oxidation of SO₂, usually in the presence of a catalyst such as NO₂, forms H₂SO₄, and thus acid rain.[2] This is one of the causes for concern over the environmental impact of the use of these fuels as power sources.
• Nitrogen oxides (NO_x) - Nitrogen oxides, particularly nitrogen dioxide, are expelled from high temperature combustion, and are also produced during thunderstorms by electric discharge. They can be seen as a brown haze dome above or a plume downwind of cities. Nitrogen dioxide is a chemical compound with the formula NO₂. It is one of several nitrogen oxides. One of the most prominent air pollutants, this reddish-brown toxic gas has a characteristic sharp, biting odor.
• Carbon monoxide (CO) - CO is a colorless, odorless, toxic yet non-irritating gas. It is a product of incomplete combustion of fuel such as natural gas, coal or wood. Vehicular exhaust is a major source of carbon monoxide.
• Volatile organic compounds (VOC) - VOCs are a well-known outdoor air pollutant. They are categorized as either methane (CH₄) or non-methane (NMVOCs). Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. Other hydrocarbon VOCs are also significant greenhouse gases because of their role in creating ozone and prolonging the life of methane in the atmosphere. This effect varies depending on local air quality. The aromatic NMVOCs benzene, toluene and xylene are suspected carcinogens and may lead to leukemia with prolonged exposure. 1,3-butadiene is another dangerous compound often associated with industrial use.
• Particulates, alternatively referred to as particulate matter (PM), atmospheric particulate matter, or fine particles, are tiny particles of solid or liquid suspended in a gas. In contrast, aerosol refers to combined particles and gas. Some particulates occur naturally, originating from volcanoes, dust storms, forest and grassland fires, living vegetation, and sea spray. Human activities, such as the burning of fossil fuels in vehicles, power plants and various industrial processes also generate significant amounts of aerosols. Averaged worldwide, anthropogenic aerosols—those made by human activities—currently account for approximately 10 percent of our atmosphere. Increased levels of fine particles in the air are linked to health hazards such as heart disease,^[7][8] altered lung function and lung cancer.

Table 3: Gaseous air pollutants: their sources and effects

Pollutant	Source	Harmful effect
Carbon compound (CO and CO2) Sulphur compounds (SO2 and H2S) Nitrogen Compound (NO and NO2) Hydrocarbons ( benzene and ethylene) SPM(Suspended Particulate matter) (any solid and liquid matter) suspended in the air, (flush, dust, lead) Fibres( Cotton, wool)	Automobile exhaust burning wool and coal Power plants and refineries volcanic eruptions Motor vehicle exhaust atmospheric reaction Automobiles and petroleum industries Thermal power plants, construction activities metallurgical processes and automobiles Textiles and carpet weaving industries	Respiratory problems Green house effect Respiratory problems in humans Loss of chlorophyll in plants (chlorosis) Acid rain Irritation in eyes and lungs Low productivity in plants Acid rain damages material (metals and stone) Respiratory problem Cancer causing properties Poor visibility, breathing problems Lead interferes with the development of red blood diseases and cancer. Smog (smoke & fog) formation leads to poor visibility and aggravates asthma in patients. Lung disorders

10.3.3 Prevention and control of air pollution

(i) Indoor air pollution

·         Poor ventilation due to faulty design of buildings leads to pollution of the confined space.

·         Paints, carpets, furniture, etc. in rooms may give out volatile organic compounds (VOCs).

·         Use of disinfectants, fumigants, etc. may release hazardous gases. In hospitals, pathogens present in waste remain in the air in the form of spores. This can result in hospital acquired infections and is an occupational health hazard.

·         In congested areas, slums and rural areas burning of firewood and biomass results in lot of smoke. Children and ladies exposed to smoke may suffer from acute respiratory problems which include running nose, cough, sore throat, lung infection, asthma, difficulty in breathing, noisy respiration and wheezing.

(ii) Prevention and control of indoor air pollution

Use of wood and dung cakes should be replaced by cleaner fuels such as biogas, kerosene or electricity. But supply of electricity is limited. Similarly kerosene is also limited. Improved stoves for looking like smokeless chullahs have high thermal efficiency and reduced emission of pollutants including smoke. The house designs should incorporate a well ventilated

kitchen. Use of biogas and CNG (Compressed Natural Gas) need to be encouraged.

Those species of trees such as baval (Acacia nilotica) which are least smoky should be planted and used. Charcoal is a comparatively cleaner fuel. Indoor pollution due to decay of exposed kitchen waste can be reduced by covering the waste properly. Segregation of waste, pretreatment at source, sterilization of rooms will help in checking indoor air pollution.

(iii) Prevention and control of industrial pollution

Industrial pollution can be greatly reduced by:

(a)  use of cleaner fuels such as liquefied natural gas (LNG) in power plants, fertilizer plants etc. which is cheaper in addition to being environmentally friendly.

(b)  employing environment friendly industrial processes so that emission of pollutants and hazardous waste is minimized.

(c)  installing devices which reduce release of pollutants. Devices like filters, electrostatic precipitators, inertial collectors, scrubbers, gravel bed filters or dry scrubbers are described below:

(i)           Filters – Filters remove particulate matter from the gas stream. The medium of a filter may be made of fibrous materials like cloth, granular material like sand, a rigid material like screen, or any mat like felt pad. Baghouse filtration system is the most common one and is made of cotton or synthetic fibres ( for low temperatures) or glass cloth fabrics (for higher temperature up to 290oC).

(ii)          Electrostatic precipitators (ESP)- The emanating dust is charged with ions and the ionized particulate matter is collected on an oppositely charged surface. The particles are removed from the collection surface by occasional shaking or by rapping the surface. ESPs are used in boilers, furnaces, and many other units of thermal power plants, cement factories, steel plants, etc.

(iii)        Inertial collectors – It works on the principle that inertia of SPM in a gas is higher than its solvent and as inertia is a function of the mass of the particulate matter this device collects heavier particles more efficiently. ‘Cyclone’ is a common inertial collector used in gas cleaning plants.

(iv)         Scrubbers – Scrubbers are wet collectors. They remove aerosols from a stream of gas either by collecting wet particles on a surface followed by their removal, or else the particles are wetted by a scrubbing liquid. The particles get trapped as they travel from supporting gaseous medium across the interface to the liquid scrubbing medium.

Gaseous pollutants can be removed by absorption in a liquid using a wet scrubber and depends on the type of the gas to be removed e.g. for removal of sulphur dioxide alkaline solution is needed as it dissolves sulphur dioxide. Gaseous pollutants may be absorbed on an activated solid surface like silica gel, alumina, carbon, etc. Silica gel can remove water vapour. Condensation allows the recovery of many by products in coal and petroleum processing industries from their liquid effluents.

Apart from the use of above mentioned devices, other control measures are-

•      increasing the height of chimneys.

•      closing industries which pollute the environment.

•      shifting of polluting industries away from cities and heavily populated areas.

•      development and maintenance of green belt of adequate width.

(iv) Control of vehicular pollution

•      The emission standards for automobiles have been set which if followed will reduce the pollution. Standards have been set for the durability of catalytic converters which reduce vehicular emission.

•      In cities like Delhi, motor vehicles need to obtain Pollution Under Control (PUC) certificate at regular intervals. This ensures that levels of pollutants emitted from vehicle exhaust are not beyond the prescribed legal limits.

•      The price of diesel is much cheaper than petrol which promotes use of diesel. To reduce emission of sulphur-dioxide, sulphur content in diesel has been reduced to 0.05%.

•      Earlier lead in the form of tetraethyl lead was added in the petrol to raise octane level for smooth running of engines. Addition of lead in petrol has been banned to prevent emission of lead particles with the vehicular emission.

•      Alternate fuels like CNG is being encouraged for use in public transport vehicles.

10.4 OZONE HOLE-CAUSES AND HARM DUE TO OZONE

DEPLETION

The stratosphere has an ozone layer which protects the earth’s surface from excessive ultraviolet (UV) radiation from the Sun. Chlorine from chemicals such as

chlorofluorocarbons (CFCs) used for refrigeration, air conditioning, fire extinguishers, cleaning solvents, aerosols (spray cans of perfumes, medicine, insecticide) cause damage to ozone layer chlorine contained in the CFCs on reaching the ozone (O3) layer split the ozone molecules to form oxygen (O2). Amount of ozone, thus gets reduced and cannot prevent the entry of UV radiation. There has been a reduction of ozone umbrella or shield over the Arctic and Antarctic regions. This is known as ozone hole. This permits passage of UV radiation on earth’s atmosphere which causes sunburn, cataract in eyes leading to

blindness, skin cancer, reduced productivity of forests, etc. Under the “Montreal Protocol” amended in 1990 it was decided to completely phase out CFCs to prevent damage of ozone layer.

10.5 GLOBAL WARMING AND GREENHOUSE EFFECT

Atmospheric gases like carbondioxide, methane, nitrous oxide, water vapour, and

chlorofluorocarbons are capable of trapping the out-going infrared radiation from the earth. Infra-red radiations trapped by the earth’s surface cannot pass through these gases and to increase thermal energy or heat in the atmosphere. Thus, the temperature of the global atmosphere is increased. As this phenomenon of increase in temperature is observed in green houses, in the botanical gardens these gases are known as green house gases and the heating effect is known as green house effect. If greenhouse gases are not checked, by the turn of the century the temperature may rise by 50C. This will melt the polar ice caps and increase the sea level leading to coastal flooding, loss of coastal areas and ecosystems like swamps and marshes, etc.

10.6 NOISE POLLUTION

Noise is one of the most pervasive pollutant. A musical clock may be nice to listen during the day, but may be an irritant during sleep at night. Noise by definition is “sound without value” or “any noise that is unwanted by the recipient”. Noise in industries such as stone cutting and crushing, steel forgings , loudspeakers, shouting by hawkers selling their wares, movement of heavy transport vehicles, railways and airports leads to irritation and an increased blood pressure, loss of temper, decrease in work efficiency, loss of hearing which may be first temporary but can become permanent in the noise stress continues. It is therefore of utmost importance that excessive noise is controlled. Noise level is measured in terms of decibels (dB). W.H.O. (World Health Organization) has prescribed optimum noise level as 45 dB by day and 35 dB by night. Anything above 80 dB is hazardous. The

table10.4 gives the noise intensity in some of the common activities.

Table 10.4: Sources of some noises and their intensity

Source	Intensity	Source	Intensity
Quiet Conversation Loud Conversation Lawn Mower Aircraft Noise Beat Music Motor Cycle	20-30dB 60 dB 60-80 Db 90-120 dB 120 dB 105 dB	Radio Music Traffic Noise Heavy Truck Space Vehicle Launch Jet Engine	50-60 dB 60-90 dB 90-100 dB 140-179 dB 140 dB

10.6.1 Sources of noise pollution

Noise pollution is a growing problem. All human activities contribute to noise pollution to varying extent. Sources of noise pollution are many and may be located indoors or  outdoors.

Indoor sources include noise produced by radio, television, generators, electric fans, air coolers, air conditioners, different home appliances, and family conflict. Noise pollution is more in cities due to a higher concentration of population and industries and activities such as transportation. Noise like other pollutants is a by product of industrialization, urbanization and modern civilization.

Outdoor sources of noise pollution include indiscriminate use of loudspeakers, industrial activities, automobiles, rail traffic, aeroplanes and activities such as those at market place, religious, social, and cultural functions, sports and political rallies. In rural areas farm machines, pump sets are main sources of noise pollution. During festivals, marriage and many other occasions, use of fire crackers contribute to noise pollution.

10.6.2 Effects of noise pollution

Noise pollution is highly annoying and irritating. Noise disturbs sleep, causes hypertension (high blood pressure), emotional problems such as aggression, mental depression and annoyance. Noise pollution adversely affects efficiency and performance of individuals.

10.6.3 Prevention and control of noise pollution

Following steps can be taken to control or minimize noise pollution-

•              Road traffic noise can be reduced by better designing and proper maintenance of vehicles.

•              Noise abatement measures include creating noise mounds, noise attenuation walls and well maintained roads and smooth surfacing of roads.

•              Retrofitting of locomotives, continuously welded rail track, use of electric locomotives or deployment of quieter rolling stock will reduce noises emanating from trains.

• Air traffic noise can be reduced by appropriate insulation and introduction of noise

regulations for takeoff and landing of aircrafts at the airport.

• Industrial noises can be reduced by sound proofing equipment like generators and

areas producing lot of noise.

• Power tools, very loud music and land movers, public functions using loudspeakers,

etc should not be permitted at night. Use of horns, alarms, refrigeration units, etc. is to

be restricted. Use of fire crackers which are noisy and cause air pollution should be

restricted.

• A green belt of trees is an efficient noise absorber.

10.7 WATER POLLUTION Addition or presence of undesirable substances in water is called water pollution.

Water pollution is one of the most serious environmental problems. Water pollution is caused by a variety of human activities such as industrial, agricultural and domestic. Agricultural run off laden with excess fertilizers and pesticides, industrial effluents with toxic substances and sewage water with human and animal wastes pollute our water thoroughly. Natural sources of pollution of water are soil erosion, leaching of minerals from rocks and decaying of organic matter. Rivers, lakes, seas, oceans, estuaries and ground water sources may be polluted by point or non-point sources. When pollutants are discharged from a specific location such as a drain pipe carrying industrial effluents discharged directly into a water body it represents point source pollution. In contrast non-point sources include discharge of pollutants from diffused sources or from a larger area such as runoff from agricultural fields, grazing lands, construction sites, abandoned mines and pits, roads and streets.

10.7.1 Sources of water pollution

Water pollution is the major source of water born diseases and other health problems. Sediments brought by runoff water from agricultural fields and discharge of untreated or partially treated sewage and industrial effluents, disposal of fly ash or solid waste into or close to a water body cause severe problems of water pollution. Increased turbidity of water because of sediments reduces penetration of light in water that reduces photosynthesis by aquatic plants.

(i) Pollution due to pesticides and inorganic chemicals

• Pesticides like DDT and others used in agriculture may contaminate water bodies.

Aquatic organisms take up pesticides from water get into the food chain (aquatic in

this case) and move up the food chain. At higher trophic level they get concentrated and may reach the upper end of the food chain.

• Metals like lead, zinc, arsenic, copper, mercury and cadmium in industrial waste waters adversely affect humans and other animals. Arsenic pollution of ground water has seen reported from West Bengal, Orissa, Bihar, Western U.P. Consumption of such arsenic polluted water leads to accumulation of arsenic in the body parts like blood, nails and hairs causing skin lesions, rough skin, dry and thickening of skin and ultimately

skin cancer.

• Pollution of water bodies by mercury causes Minamata disease in humans and

dropsy in fishes. Lead causes displexia, cadmium poisoning causes Itai – Itai disease

etc.

• Oil pollution of sea occurs from leakage from ships, oil tankers, rigs and pipelines. Accidents of oil tankers spill large quantity of oil in seas which kills marine birds and adversely affects other marine life and beaches.

(ii) Thermal pollution

Power plants- thermal and nuclear, chemical and other industries use lot of water (about 30 % of all abstracted water) for cooling purposes and the used hot water is discharged into rivers, streams or oceans. The waste heat from the boilers and heating processes increases the temperature of the cooling water. Discharge of hot water may increase the temperature of the receiving water by 10 to 15 °C above the ambient water temperature. This is thermal pollution. Increase in water temperature decreases dissolved oxygen in water which adversely affects aquatic life. Unlike terrestrial ecosystems, the temperature of water bodies remain steady and does not change very much. Accordingly, aquatic organisms are adopted to a uniform steady temperature of environment and any fluctuation in water temperature severely affects aquatic plants and animals. Hence discharge of hot water from power plants adversely affects aquatic organisms. Aquatic plants and animals in the warm tropical water live dangerously close to their upper limit of temperature, particularly during the warm summer months. It requires only a slight deviation from this limit to cause a thermal stress to these organisms.

Discharge of hot water in water body affects feeding in fishes, increases their metabolism and affects their growth. Their swimming efficiency declines. Running away from predators or chasing prey becomes difficult. Their resistance to diseases and parasites decreases. Due to thermal pollution biological diversity is reduced. One of the best methods of reducing thermal pollution is to store the hot water in cooling ponds, allow the water to cool before releasing into any receiving water body

10.7.2 Ground water pollution

Lot of people around the world depend on ground water for drinking, domestic, industrial and agricultural uses. Generally groundwater is a clean source of water. However, human activities such as improper sewage disposal, dumping of farm yard manures and agricultural chemicals, industrial effluents are causing pollution of ground water.

10.7.3 Eutrophication

• ‘Eu’ maens well or healthy and ‘trophy’ means nutrition. The enrichment of water bodies with nutrients causes entrophication of the water body. Discharge of domestic waste, agricultural surface runoff, land drainage and industrial effluents

in a water body leads to rapid nutrients enrichment in a water body. The excessive nutrient enrichment in a water body encourages the growth of algae duckweed, water hyacinth, phytoplankton and other aquatic plants.The biological demand for oxygen (BOD) increases with the increase in aquatic organisms. As more plants grow and die, the dead and decaying plants and organic matter acted upon by heterotrophic prtozoans and bacteria, deplete the water of dissolved oxygen (DO). Decrease in DO result in sudden death of large population of fish and other aquatic organisms including plants, releasing offensive smell and makes the water unfit for human use. The sudden and explosive growth of phytoplankton and algae impart green colour to the water is known as water bloom, or “algal blooms”. These phytoplankton release toxic substances in water that causes sudden death of large population of fishes. This phenomenon of nutrient enrichment of a water body is called eutrophication. Human activities are mainly responsible for the eutrophication of a growing number of lakes and water bodies in the country

10.7.4 Methods for control of water pollution and water recycling

Control water pollution

Waste water from domestic or industrial sources or from garbage dumps is generally known as sewage. It may also contain rain water and surface runoff. The sewage water can be treated to make it safe for disposal into water bodies like rivers, lakes etc. The treatment involves three stages: primary, secondary and tertiary. This includes 1. sedimentation, 2. coagulation/flocculation, 3.filtration, 4.disinfection, 5.softening and 6.aeration. The first four steps are of primary treatment. The first three steps are involved in primary treatment remove suspended particulate matter. Secondary treatment removes organic solids, left out after primary treatment, through their microbial decomposition. Effluents after secondary treatment may be clean but contain large amounts of nitrogen, in form of ammonia, nitrates and phosphorous which can cause problem of eutrophication

upon their discharge into a receiving water body such as river, lake or pond. The tertiary treatment is meant to remove nutrients, disinfect for removing pathogenic bacteria, and aeration removes hydrogen sulphide and reduce the amount of carbon dioxide and make water healthy and fit for aquatic organisms. This treatment of waste water or sewage is carried out in effluent treatment plants especially built for this purpose. The residue obtained from primary treatment one known as sludge.

10.7.5 Water recycling

With increasing population the requirement for water is increasing rapidly. However, the availability of water is limited but an ever increasing water withdrawal from different sources such as rivers, lakes and ground water is depleting these sources and deteriorating their water quality. Therefore, it is essential to utilize the available water with maximum economy. This involves recycling of waste water for certain uses with or without treatment. Recycling refers to the use of waste-water by the original user prior to the discharge either to a treatment system or to a receiving water body. Thus the waste water is recovered and repetitively recycled with or without treatment by the same user.

10.7.6. Control of water pollution

The following measures can be adopted to control water pollution:

(a) The water requirement should be minimized by altering the techniques involved.

(b) Water should be reused with or without treatment.

(c) Recycling of water after treatment should be practiced to the maximum extent possible.

(d) The quantity of waste water discharge should be minimized.

10.8 SOIL POLLUTION

Addition of substances which adversely affect the quality of soil or its fertility is known as soil pollution. Generally polluted water also pollute soil. Solid waste is a mixture of plastics, cloth, glass, metal and organic matter, sewage, sewage sludge, building debris, generated from households, commercial and industries establishments add to soil pollution. Fly ash, iron and steel slag, medical and industrial wastes disposed on land are important sources of soil pollution. In addition, fertilizers and pesticides from agricultural use which reach soil as run-off and land filling by municipal waste are growing cause of soil pollution. Acid rain and dry deposition of pollutants on land surface also contribute to soil pollution.

10.8.1 Sources of soil pollution

Plastic bags – Plastic bags made from low density polyethylene (LDPE), is virtually indestructible, create colossal environmental hazard. The discarded bags block drains and sewage systems. Leftover food, vegetable waste etc. on which cows and dogs feed may die due to the choking by plastic bags. Plastic is non biodegradable and burning of plastic in garbage dumps release highly toxic and poisonous gases like carbon monoxide, carbon dioxide, phosgene, dioxine and other poisonous chlorinated compounds.

Industrial sources – It includes fly ash, chemical residues, metallic and nuclear wastes. Large number of industrial chemicals, dyes, acids, etc. find their way into the soil and are known to create many health hazards including cancer.

Agricultural sources – Agricultural chemicals especially fertilizers and pesticides pollute the soil. Fertilizers in the runoff water from these fields can cause eutrophication in water bodies. Pesticides are highly toxic chemicals which affect humans and other animals adversely causing respiratory problems, cancer and death.

10.8.2 Control of soil pollution

Indiscriminate disposal of solid waste should be avoided. To control soil pollution, it is essential to stop the use of plastic bags and instead use bags

of degradable materials like paper and cloth. Sewage should be treated properly before using as fertilizer and as landfills. The organic matter from domestic, agricultural and other waste should be segregated and subjected to vermicomposting which generates useful manure as a by product. The industrial wastes prior to disposal should be properly treated for removing hazardous materials. Biomedical waste should be separately collected and incinerated in proper incinerators.

10.9 RADIATION POLLUTION: SOURCES AND HAZARDS

Radiation pollution is the increase in over the natural background radiation. There are many sources of radiation pollution such as nuclear wastes from nuclear power plants, mining and processing of nuclear material etc. The worse case of nuclear pollution was the cherndoyl disaster in Russia occured in 1986 but the effects still longer today.

10.9.1 Radiation

Radiation is a form of energy travelling through space. The radiation emanating from the decay of radioactive nuclides are a major sources of radiation pollution. Radiations can be categorized into two groups namely the non-ionizing radiations and the ionizing radiations.

Non-ionizing radiations are constituted by the electromagnetic waves at the longer wavelength of the spectrum ranging from near infra-red rays to radio waves. These waves have energies enough to excite the atoms and molecules of the medium through which they pass, causing them to vibrate faster but not strong enough to ionize them. In a microwave oven the radiation causes water molecules in the cooking medium to vibrate faster and thus raising its temperature.

Ionizing radiations cause ionization of atoms and molecules of the medium through which they pass. Electromagnetic radiations such as short wavelength ultra violet radiations (UV), X-rays and gamma rays and energetic particles produced in nuclear processes, electrically charged particles like alpha and beta particles produced in radioactive decay and neutrons produced in nuclear fission, are highly damaging to living organisms. Electrically charged

particles produced in the nuclear processes can have sufficient energy to knock electrons out of the atoms or molecules of the medium, thereby producing ions. The ions produced in water molecules, for example, can induce reactions that can break bonds in proteins and other important molecules. An example of this would be when a gamma ray passes through a cell, the water molecules near the DNA might be ionized and the ions might react with the DNA causing it to break. They can also cause chemical changes by breaking the chemical bonds, which can damage living tissues. The ionizing radiations cause damage to biological systems and are, therefore, pollutants.

10.9.2 Radiation damage

The biological damage resulting from ionizing radiations is generally termed as radiation damage. Large amounts of radiation can kill cells that can dramatically affect the exposed organism as well as possibly its offspring. Affected cells can mutate and result in cancer. A large enough dose of radiation can kill the organism. Radiation damage can be divided into two types: (a) somatic damage (also called radiation sickness) and (b) genetic damage. Somatic damage refers to damage to cells that are not associated with reproduction. Effects of somatic radiation damage include reddening of the skin, loss of hair, ulceration, fibrosis of the lungs, the formation of holes in tissue, a reduction of white blood cells, and the induction of cataract in the eyes. This damage can also result in cancer and death. Genetic damage refers to damage to cells associated with reproduction. This damage can subsequently cause genetic damage from gene mutation resulting in abnormalities. Genetic damages are passed on to next generation.

10.9.3 Radiation dose

The biological damage caused by the radiation is determined by the intensity of radiation and duration of the exposure. It depends on the amount of energy deposited by the radiation in the biological system. In studying the effects of radiation exposure in humans, it is important to realize that the biological damage caused by a particle depends not only on the total energy deposited but also on the rate of energy loss per unit distance traversed by the particle (or “linear energy transfer”). For example, alpha particles do much more damage per unit energy deposited than do electrons.

Radiation effects and radiation doses

A traditional unit of human-equivalent dose is the rem, which stands for radiation equivalent in man. At low doses, such as what we receive every day from background radiation (< 1 m rem), the cells repair the damage rapidly. At higher doses (up to 100 rem), the cells might not be able to repair the damage, and the cells may either be changed permanently or die. Cells changed permanently may go on to produce abnormal cells when they divide and may become cancerous.

At even higher doses, the cells cannot be replaced fast enough and tissues fail to function. An example of this would be “radiation sickness.” This is a condition that results after high doses is given to the whole body (>100 rem). Nuclear explosions and accidents in nuclear reactors are a serious source of radiation hazard. The effects of atomic explosions in Nagasaki and Hiroshima are still not forgotten. The nuclear reactor accident at Chernobyl in 1986 led to deaths of many reactor personnel and a very large release of radionuclide to the environment causing a long term radiation damage to the people living in the neighboring regions.

Accidents at nuclear power plants

Nuclear fission in the reactor core produces lot of heat which if not controlled can

lead to a meltdown of fuel rods in the reactor core. If a meltdown happens by accident, it will release large quantities of highly dangerous radioactive materials in the environment with disastrous consequences to the humans, animals and plants. To prevent this type of accidents and reactor blow up, the reactors are designed to have a number of safety features. Inspite of these safety measures two disasters in the nuclear power plants are noteworthy- namely at ‘Three Mile Island’ in Middletown (U.S.A.) in 1979, at Chernobyl (U.S.S.R.) in 1986. In both these cases a series of mishaps and errors resulted in over heating of the reactor core and lot of radiation was released into the environment. The leakage from Three Mile Island reactor was apparently low and no one was injured immediately. However, in case of Chernobyl the leakage was very heavy causing death of some workers and radiation spread over large areas scattered all over Europe. People of the city had to be evacuated to safer places and the plant had to be closed down. These two disasters are a reminder that nuclear power reactors require a constant up gradation of safety measures. Accidents with nuclear submarines also points to the same.