UNIT III

Environmental Chemistry

and

Pollution Control

Bharati Vidyapeeth’s College of Engineering, New Delhi

2019 Notes compiled by the Teachers

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ENVIRONMENTAL POLLUTION DEFINITION -Pollution is the effect of undesirable changes in our surroundings that have harmful effects on plants, animals and human beings.

Causes, effects and control measures of

1. Air Pollution

2. Water Pollution

3. Soil Pollution

4. Marine Pollution

5. Noise Pollution

6. Thermal Pollution

7. Nuclear pollution

1. AIR POLLUTION

The origin of air pollution on the earth can be traced from the times when man started using firewood as a means of cooking and heating. Hippocrates has mentioned air pollution in 400 BC. With the discovery and increasing use of coal, air pollution became more pronounced especially in urban areas. It was recognized as a problem 700 years ago in London in the form of smoke pollution, which prompted King Edward I to make the first antipollution law to restrict people from using coal for domestic heating in the year 1273

Structure of the atmosphere:

The atmosphere is normally composed of 79 percent nitrogen, 20 percent oxygen and one percent as a mixture of carbon dioxide, water vapour and trace amounts of several other gases such as neon, helium, methane, krypton, hydrogen and xenon. The general structure of the atmosphere has several important features that have relevance to environmental problems. The atmosphere is divided into several layers.

The innermost layer the troposphere extends 17 kilometers above sea level at the equator and about 8 kilometers over the poles. It contains about 75 percent of the mass of the earth’s air.

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Types and sources of Air Pollutants

The air pollutants are classified into: According to origin: a) Primary pollutants: The pollutants that are emitted directly from identifiable sources produced by natural events ( eg: dust storms and volcanic eruptions) and human activities (eg: emissions from vehicles, industries etc.) are called primary pollutants. Eg: smoke, dust, oxides of sulphur & nitrogen, hydrocarbons and particulate matter etc. b) Secondary pollutants:

The pollutants that are formed in the atmosphere by chemical interactions between primary pollutants and atmospheric constituents are known as secondary pollutants. Eg. Sulphur trioxide, ozone, ketones, sulphuric acid, nitric acid, carbonic acid etc.

According to state of matter:

The pollutants are classified into:-

a) Gaseous air pollutants:

These pollutants exist in a gaseous state at normal temperature and pressure. They are carbon dioxide, nitrogen dioxide, sulphur oxides etc.

b) Particulate air pollutants

These are not gaseous substances. They are suspended droplets, solid particles or mixtures of the two.

According to sources: Pollutants originate from a) Natural sources: These include volcanic eruptions, deflation of sand and dust, forest or wild fires of natural vegetation, sulphur springs, natural geysers, organic and inorganic decays, vegetative decays, marsh gases, cosmic dust, pollen grains of flowers, photochemical reactions, soil debris etc. b) Man-made sources:

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These include human activities such as industries, factories, urban centres, aircraft, nuclear experiments, automobiles, agriculture, domestic burning of wood and burning of fossil fuels, deforestation, mining, waste treatment plants and power plants.

Sources of Outdoor Air Pollution

Effects of Air Pollution

1. Photochemical Smog

Photochemical smog is a type of air pollution due to the reaction of solar radiation with airborne pollutant mixtures of nitrogen oxides (NOx) and volatile organic compounds (hydrocarbons). Smog is a byproduct of modern industrialization. Due to industry and the number of motor vehicles, this is more of a problem in large cities that have a warm, sunny and dry climate.

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Formation (Mechanism) of Photochemical Smog

Step 1: People begin driving in the morning, nitrogen is burned or oxidized

N2 + O2 → 2NO

• Oxidation number of N2 is 0. The nitrogen in NO has acquired an oxidation number of +2.

Step 2: After a few hours, NO combines with O2, in another oxidation reaction

2NO + O2 → 2NO2

• The nitrogen in NO has an oxidation number of +2. The nitrogen in NO2 has an oxidation number of +4.

Step 3: Nitrogen dioxide absorbs light energy, resulting in a reduction reaction

NO2 → NO + O

• The nitrogen in NO2 has an oxidation number of +4 and the nitrogen in NO is +2.

Step 4: In sunlight, atomic oxygen combines with oxygen gas to form ozone

O + O2 → O3

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Step 5: Reaction is temperature and sunlight dependent

O3 + NO ⇌⇌⇌⇌ NO2 + O2

NO and NO2 can also react with the hydrocarbons instead of ozone to form other volatile compounds known as PAN (peroxyacetyl nitrate). The accumulation of ozone and volatile organic compounds along with the energy from the sun forms the brown, photochemical smog seen on hot, sunny days.

2. Global warming

Atmospheric changes induced by pollution contribute to global warming, a phenomenon which is caused due to the increase in concentration of certain gases like carbon dioxide, nitrogen oxides, methane and CFCs. Observations of the earth have shown beyond doubt that atmospheric constituents such as water vapors, carbon dioxide, methane, nitrogen oxides and Chloro Fluro Carbons trap heat in the form of infra-red radiation near the earth’s surface. This is known as the ‘Greenhouse Effect’.

There could be several adverse effects of global warming.

• With a warmer earth the polar ice caps will melt causing a rise in ocean levels and flooding of coastal areas.

• In countries like Bangladesh or the Maldives this would be catastrophic. If the sea level rises by 3m., Maldives will disappear completely beneath the waves.

• The rise in temperature will bring about a fall in agricultural produce.

3. Acid Rain: Sulfur dioxide and nitrogen dioxide emissions react with water vapor in the atmosphere and form acids that return to the surface as either dry or wet deposition .

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Reactions involved:

• CO2 + H2O → H2CO3 (Carbonic acid) • SO2 + O2 → 2 SO3

SO3 + H2O → H2SO4 (Sulphuric acid)

• NO + O3 → NO2 + O2

NO2 + O3 → NO3 + O2

NO2 + NO3 → N2O5

N2O5 + H2O → 2HNO3 (Nitric acid)

Effects of Air pollution:

1. Sulfur Dioxide and Particulate material- Irritate respiratory tract and impair ability of lungs to exchange gases

2. Nitrogen Dioxides- Causes airway restriction

3. Carbon monoxide-Binds with iron in blood hemoglobin, Causes headache, fatigue, drowsiness, death

4. Ozone -Causes burning eyes, coughing, and chest discomfort

Controlling Air Pollution techniques

Air quality monitoring India does not presently have a well established system of monitoring air pollution. When air quality monitoring began in India in the late 1960s planners focused only on a few pollutants namely sulphur dioxide, nitrogen oxides and suspended particulate matter. Other pollutants such as carbon monoxide and lead were monitored only on a limited scale. Some of the Air pollution control technics (devices) are given below.

1. Electrostatic precipitator - Electrostatic precipitator, also called electrostatic air cleaner, a device that uses an electric charge to remove certain impurities—either solid particles or liquid droplets—from air or other gases in smokestacks and other flues. The precipitator functions by applying energy only to the particulate matter being collected, without significantly impeding the flow of gases. Originally designed for recovery of valuable industrial-process materials, electrostatic precipitators are used for air pollution control, particularly for removing particles from waste gases at industrial facilities and power-generating stations.

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2. Scrubber- Scrubbers are effective air pollution control devices for removing particles and/or gases from industrial exhaust streams. A Wet Scrubber operates by introducing the dirty gas stream with a scrubbing liquid – typically water. Particulate or gases are collected in the scrubbing liquid. Wet Scrubbers are generally the most appropriate air pollution control device for collecting both particulate and gas in a single system.

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3. Gravity Settling Chambers o Settling chambers use the force of gravity to remove solid particles.

The gas stream enters a chamber where the velocity of the gas is reduced. Large particles drop out of the gas and are recollected in hoppers. Because settling chambers are effective in removing only larger particles, they are used in conjunction with a more efficient control device.

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4. Cyclone collectors o The general principle of inertia separation is that the particulate-laden gas is forced to

change direction. As gas changes direction, the inertia of the particles causes them to continue in the original direction and be separated from the gas stream.

o The walls of the cyclone narrow toward the bottom of the unit, allowing the particles to be collected in a hopper.

o The cleaner air leaves the cyclone through the top of the chamber, flowing upward in a spiral vortex, formed within a downward moving spiral.

o Cyclones are efficient in removing large particles but are not as efficient with smaller particles. For this reason, they are used with other particulate control devices.

Other Ways to Improve Air Quality

o Reduce sulfur content in gasoline from its current average of 330 ppm to 30 ppm Sulfur clogs catalytic converters

o Require federal emission standards for all passenger vehicles Including SUVs, trucks and minivans

o Require emission testing for all vehicles including diesel.

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2. WATER POLLUTION

71% of the earth’s surface is covered by water only a tiny fraction of this water is available to us as fresh water. About 97% of the total water available on earth is found in oceans and is too salty for drinking or irrigation. The remaining 3% is fresh water. Of this 2.997% is locked in ice caps or glaciers. Thus only 0.003% of the earth’ total volume of water is easily available to us as soil moisture, groundwater, water vapour and water in lakes, streams, rivers and wetlands.

When the quality or composition of water changes directly or indirectly as a result of man’s activities such that it becomes unfit for any purpose it is said to be polluted.

Causes of water pollution

Point sources of pollution: When a source of pollution can be readily identified because it has a definite source and place where it enters the water it is said to come from a point source. Eg. Municipal and Industrial Discharge Pipes.

When a source of pollution cannot be readily identified, such as agricultural runoff, acid rain, etc, they are said to be non-point sources of pollution.

disease-causing agents, oxygen depleting wastes, inorganic plant nutrient, water soluble inorganic chemicals, organic chemicals, Sediment of suspended matter, Oil, Water soluble radioactive isotopes, Hot water let out by power plants,

Groundwater pollution- Urban run-off of untreated or poorly treated waste water and garbage

• Industrial waste storage located above or near aquifers

• Agricultural practices such as the application of large amounts of fertilizers and pesticides, animal feeding operations, etc. in the rural sector.

Leakage from underground storage tanks containing gasoline and other hazardous substances

• Leachate from landfills

• Poorly designed and inadequately maintained septic tanks

• Mining wastes

Control measures for preventing water pollution-While the foremost necessity is prevention, setting up effluent treatment plants and treating waste through these can reduce the pollution load in the recipient water. The treated effluent can be reused for either gardening or cooling purposes wherever possible.

Control measures for preventing water pollution

While the foremost necessity is prevention, setting up effluent treatment plants and treating waste through these can reduce the pollution load in the recipient water. The treated effluent can be reused for either gardening or cooling purposes wherever possible. A few years ago a new technology called the Root Zone Process has been developed by Thermax. This system involves

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running contaminated water through the root zones of specially designed reed beds. The reeds, which are essentially wetland plants have the capacity to absorb oxygen from the surrounding air through their stomatal openings. The oxygen is pushed through the porous stem of the reeds into the hollow roots where it enters the root zone and creates conditions suitable for the growth of numerous bacteria and fungi. These micro-organisms oxidize impurities in the wastewaters, so that the water which finally comes out is clean.

Biochemical Oxygen Demand (BOD) and Chemical oxygen demand (COD)-

As BOD is only a measurement of consumed oxygen by aquatic microorganisms to decompose or oxidize organic matter and COD refers the requirement of dissolved oxygen for both the oxidation of organic and inorganic constituents by strong oxidizing reagents. COD levels in waste streams are always higher than BOD.

General Methods of water treatment

Physical Process: Filtration, Sedimentation (Primary treatment)

Biological Processes: (Secondary treatment)- Examples

1. Activated Sludge process - The activated sludge process is a type of wastewater treatment process for treating sewage or industrial wastewaters using aeration and a biological floc composed of bacteria and protozoa.

2. Trickling filters - A trickling filter is a type of wastewater treatment system. It consists of a fixed bed of rocks, coke, gravel, slag, polyurethane foam, sphagnum peat moss, ceramic, or plastic media over which sewage or other wastewater flows downward and causes a layer of microbial slime to grow, covering the bed of media.

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Chemical Processes: Flocculation, Chlorination (Tertiary treatment) Radiation: Ultraviolet Light (disinfection process)

3. SOIL POLLUTION:

The introduction of substances, biological organisms, or energy into the soil, resulting in a change of the soil quality, which is likely to affect the normal use of the soil or endangering public health and the living environment.

• Soil contaminants are spilled onto the surface through many different activities.

• Most of these are the result of accidents involving the vehicles that are transporting waste material from site of origin to a disposal site.

• Others Involve accident

• Involving vehicles (automobiles, trucks and airplanes) not transporting wastes, but carrying materials, including fuel, that when spilled contaminate the soil.

• Illegal dumping is the disposal of waste in unauthorized areas.

• It is also known as “open dumping”, “fly dumping”, and “mid-night dumping”.

• Illegal dumps occur most often along isolated roadsides in remote areas of the country.

• Agricultural practices, including the use of agricultural chemicals, are another primary source of pollution on or near the ground surface

Sustainable agriculture advocates the use of methods to produce adequate safe food in an economically viable manner while maintaining the state of the ecosystem. Organic agriculture advocates avoiding the use of chemical fertilizers and pesticides. A wide variety of techniques can be used to reduce this negative impact of agriculture. Leaving crop residue on the soil and

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incorporating it into the soil reduces erosion and increase soil organic matter. Introduction of organic matter into the soil also makes compaction less likely. Crop rotation is an effective way to enhance soil fertility, reduce erosion and control pests. There have been arguments both for and against organic farming. Critics argue that organic farming cannot produce the amount of food required for today’s population and it is economically viable only in certain conditions. However supporters for organic farming feel that of the hidden costs of soil erosion and pollution are taken into account it is a viable approach. Besides organic farmers do not have to spend on fertilizers and pesticides and also get a premium price for their products thus making it financially viable for them.

4. MARINE POLLUTION

Marine pollution can be defined as the introduction of substances to the marine environment directly or indirectly by man resulting in adverse effects such as hazards to human health, obstruction of marine activities and lowering the quality of sea water.

Some very specific causes that pollute marine waters are:

• The most obvious inputs of waste is through pipes directly discharging wastes into the sea. Very often municipal waste and sewage from residences and hotels in coastal towns are directly discharged into the sea.

• Pesticides and fertilizers from agriculture which are washed off the land by rain, enter water courses and eventually reach the sea.

• Petroleum and oils washed off from the roads normally enter the sewage system but stormwater overflows carry these materials into rivers and eventually into the seas.

Effects of marine pollution

Apart from causing eutrophication a large amount of organic wastes can also result in the development of red tides. These are phytoplankton blooms of such intensity that the area is discolored. Many important commercially important marine species are also killed due to clogging of gills or other structures.

Control measures

One way of reducing the pollution load on marine waters is through the introduction of sewage treatment plants. This will reduce the biological oxygen demand (BOD) of the final product before it is discharged to the receiving waters. Various stages of treatment such as primary, secondary or advanced can be used depending on the quality of the effluent that is required to be treated.

5. NOISE POLLUTION

Noise may not seem as harmful as the contamination of air or water but it is a pollution problem that affects human health and can contribute to a general deterioration of environmental quality.

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Noise is undesirable and unwanted sound. Not all sound is noise. What may be considered as music to one person may be noise to another. It is not a substance that can accumulate in the environment like most other pollutants. Sound is measured in a unit called the ‘Decibel’.

Decibel levels of common sounds

dB Environmental Condition

0 Threshold of hearing

10 Rustle of leaves

20 Broadcasting studio

30 Bedroom at night

40 Library

50 Quiet office

60 Conversational speech (at 1m)

70 Average radio

74 Light traffic noise

90 Subway train

100 Symphony orchestra

110 Rock band 120 Aircraft takeoff

146 Threshold of pain

Effects of noise pollution on:

a) Physical health

The most direct harmful effect of excessive noise is physical damage to the ear and the temporary or permanent hearing loss often called a temporary threshold shift (TTS). People suffering from this condition are unable to detect weak sounds. However hearing ability is usually recovered within a month of exposure. Permanent loss, usually called noise induced permanent threshold shift (NIPTS) represents a loss of hearing ability from which there is no recovery.

b) Mental health

Noise can also cause emotional or psychological effects such as irritability, anxiety and stress. Lack of concentration and mental fatigue are significant health effects of noise. It has been observed that the performance of school children is poor in comprehension tasks when schools are situated in busy areas of a city and suffer from noise pollution.

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Noise Control techniques

There are four fundamental ways in which noise can be controlled: Reduce noise at the source, block the path of noise, increase the path length and protect the recipient. In general, the best control method is to reduce noise levels at the source.

6. THERMAL POLLUTION

Sources: The discharge of warm water into a river is usually called a thermal pollution. It occurs when an industry removes water from a source, uses the water for cooling purposes and then returns the heated water to its source. Power plants heat water to convert it into steam, to drive the turbines that generate electricity. For efficient functioning of the steam turbines, the steam is condensed into water after it leaves the turbines. This condensation is done by taking water from a water body to absorb the heat. This heated water, which is at least 15oC higher than the normal is discharged back into the water body.

Effects: The warmer temperature decreases the solubility of oxygen and increases the metabolism of fish. This changes the ecological balance of the river. Within certain limits thermal additions can promote the growth of certain fish and the fish catch may be high in the vicinity of a power plant. However sudden changes in temperature caused by periodic plant shutdowns both planned and unintentional can change result in death of these fish that are acclimatized to living in warmer waters.

Control measures: Thermal pollution can be controlled by passing the heated water through a cooling pond or a cooling tower after it leaves the condenser. The heat is dissipated into the air and the water can then be discharged into the river or pumped back to the plant for reuse as cooling water. There are several ways in which thermal pollution can be reduced. One method is to construct a large shallow pond. Hot water is pumped into one end of the pond and cooler water is removed from the other end. The heat gets dissipated from the pond into the atmosphere. A second method is to use a cooling tower. These structures take up less land area than the ponds.

7. Nuclear Hazards

Nuclear energy can be both beneficial and harmful depending on the way in which it is used. We routinely use X-rays to examine bones for fractures, treat cancer with radiation and diagnose diseases with the help of radioactive isotopes topes. Approximately 17 % of the electrical energy generated in the world comes from nuclear power plants. However on the other hand it is impossible to forget the destruction that nuclear bombs caused the cities of Hiroshima and Nagasaki. The radioactive wastes from nuclear energy have caused serious environmental damage.

Sources - In order to appreciate the consequences of using nuclear fuels to generate energy it is important to understand how the fuel is processed. Low-grade uranium ore, which contains 0.2 percent uranium by weight, is obtained by surface or underground mining. After it is mined the ore goes through a milling process where it is crushed and treated with a solvent to concentrate

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the uranium and produces yellow cake a material containing 70 to 90 percent uranium oxide. Naturally occurring uranium contains only 0.7 percent of fissionable U-235, which is not high enough for most types of reactors. Hence it is necessary to increase the amount of U-235 by enrichment though it is a difficult and expensive process. The enrichment process increases the U-235 content from 0.7 to 3 percent. Fuel fabrication then converts the enriched material into a powder, which is then compacted into pellets. These pellets are sealed in metal fuel rods about 4 meters in length which is then loaded into the reactor. As fission occurs the concentration of U-235 atoms decreases. After about three years, a fuel rod does not have enough radioactive material to sustain a chain reaction and hence the spent fuel rods must be replaced by new ones. The spent rods are however still very radioactive containing about one percent U-235 and one percent plutonium. These rods are a major source of radioactive waste material produced by a nuclear reactor.

The degree and the kind of damage from nuclear accidents vary with the kind of radiation, the amount of radiation, the duration of exposure and the types of cells irradiated. Radiation can also cause mutations which are changes in the genetic makeup of the cells. Mutations can occur in the ovaries or the testes leading to the formation of mutated eggs or sperms which in turn can lead to abnormal offspring. Mutations can also occur in the tissues of the body ad may manifest themselves as abnormal tissue growths known as cancer. Two common cancers that are linked to increased radiation exposure are leukemia and breast cancer.

SOLID WASTE MANAGEEMNT: CAUSES, EFFECTS AND CONTROL MEASURES OF URBAN AND INDUSTRIAL WASTE

Major types of SW

Municipal Waste- Municipal solid waste contains a wide variety of materials. It can contain food waste such as vegetable and meat material, left over food, egg shells, etc which is classified as wet garbage as well as paper, plastic, tetra packs, plastic cans, newspaper, glass bottles, cardboard boxes, aluminum foil, metal items, wood pieces, etc. which is classified as dry garbage.

Hazardous Waste- which is any solid or liquid waste that is considered toxic, chemically reactive, flammable or corrosive. In terms of hazardous waste, something is considered toxic if it is harmful to human health when a person is exposed to the substance through inhalation, ingestion or touch. e.g nuclear power plant, chemical industries, oil and gas refineries.

Biomedical Waste - Biomedical waste is any kind of waste containing infectious (or potentially infectious) materials. ...Biomedical waste is generated from biological and medical sources and activities, such as the diagnosis, prevention, or treatment of diseases.

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Electronic Waste- Electronic waste or e-waste describes discarded electrical or electronic devices. Used electronics which are destined for reuse, resale, salvage, recycling, or disposal are also considered e-waste.

Control measures of urban and industrial wastes:

An integrated waste management strategy includes three main components:

1. Source reduction -is one of the fundamental ways to reduce waste. This can be done by using less material when making a product, reuse of products on site, designing products or packaging to reduce their quantity.

2. Recycling - is reusing some components of the waste that may have some economic value. Recycling has readily visible benefits such as conservation of resources reduction in energy used during manufacture and reducing pollution levels.

3. Disposal - is the process of burning municipal solid waste in a properly designed furnace under suitable temperature and operating conditions. A modern sanitary landfill is a depression in an impermeable soil layer that is lined with an impermeable membrane. The three key characteristics of a municipal sanitary landfill that distinguish it from an open dump are:

• Solid waste is placed in a suitably selected and prepared landfill site in a carefully prescribed manner.

• The waste material is spread out and compacted with appropriate heavy machinery.

• The waste is covered each day with a layer of compacted soil.

4. Incineration - is the process of burning municipal solid waste in a properly designed furnace under suitable temperature and operating conditions. Incineration is a chemical process in which the combustible portion of the waste is combined with oxygen forming carbon dioxide and water, which are released into the atmosphere.

5. Vermi – Composting

Nature has perfect solutions for managing the waste it creates, if left undisturbed. The biogeochemical cycles are designed to clear the waste material produced by animals and plants. We can mimic the same methods that are present in nature. All dead and dry leaves and twigs decompose and are broken down by organisms such as worms and insects, and is finally broken down by bacteria and fungi, to form a dark rich soil-like material called compost.

ROLE OF AN INDIVIDUAL IN PREVENTION OF POLLUTION

Develop respect or reverence for all forms of life.

• Each individual must try to answer four basic questions: Where do the things that I consume come from? What do I know about the place where I live? How am I connected to the earth and other living things? What is my purpose and responsibility as a human being?

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Try to plant trees wherever you can and more importantly take care of them. They reduce air pollution.

• Reduce the use of wood and paper products wherever possible. Manufacturing paper leads to pollution and loss of forests which releases oxygen and takes up carbon dioxide. Try to recycle paper products and use recycled paper wherever possible.

• From the mail you receive reuse as many envelopes that you can.

• Do not buy furniture, doors, window frames made from tropical hardwoods such as teak and mahogany. These are forest based.

• Help in restoring a degraded area near your home or join in an afforestation program.

• Use pesticides in your home only when necessary and use them in as small amounts as necessary. Some insect species help to keep a check on the populations of pest species.

• Advocate organic farming by asking your grocery store to stock vegetables and fruits grown by an organic method. This will automatically help to reduce the use of pesticides.

• Reduce the use of fossil fuels by either walking up a short distance using a car pool, sharing a bike or using public transport. This reduces air pollution.

• Shut off the lights and fans when not needed.

• Don’t use aerosol spray products and commercial room air fresheners. They damage the ozone layer.

POLLUTION CASE STUDIES (Self learning by students)

A case study of pesticide pollution in India

A case study of river pollution in India.

[R5] A. Kaushik and C.P. Kaushik, Perspectives in Environment Studies, 4th Edition, New Age International Publishers,2013

[R6] Environmental Engineering by Gerard Kiely, Tata McGraw-Hill Publishing Company Ltd., New Delhi, 2010.

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CHEMISTRY OF ENVIRONMENT

Green chemistry can be defined as the practice of chemical science and manufacturing in a manner that is sustainable, safe, and non-polluting and that consumes minimum amounts of materials and energy while producing little or no waste material.

GREEN CHEMISTRY

• Prevents pollution at the molecular level • Is a philosophy that applies to all areas of chemistry, not a single discipline of chemistry • Applies innovative scientific solutions to real-world environmental problems • Results in source reduction because it prevents the generation of pollution • Reduces the negative impacts of chemical products and processes on human health and

the environment • Lessens and sometimes eliminates hazard from existing products and processes • Designs chemical products and processes to reduce their intrinsic hazards

Twelve principles of Green Chemistry

These principles demonstrate the breadth of the concept of green chemistry: 1. Prevent waste: Design chemical syntheses to prevent waste. Leave no waste to treat or clean up. 2. Maximize atom economy: Design syntheses so that the final product contains the maximum proportion of the starting materials. Waste few or no atoms. 3. Design less hazardous chemical syntheses: Design syntheses to use and generate substances with little or no toxicity to either humans or the environment. 4. Design safer chemicals and products: Design chemical products that are fully effective yet have little or no toxicity. 5. Use safer solvents and reaction conditions: Avoid using solvents, separation agents, or other auxiliary chemicals. If you must use these chemicals, use safer ones. 6. Increase energy efficiency: Run chemical reactions at room temperature and pressure whenever possible. 7. Use renewable feedstocks: Use starting materials (also known as feedstocks) that are renewable rather than depletable. The source of renewable feedstocks is often agricultural products or the wastes of other processes; the source of depletable feedstocks is often fossil fuels (petroleum, natural gas, or coal) or mining operations. 8. Avoid chemical derivatives: Avoid using blocking or protecting groups or any temporary modifications if possible. Derivatives use additional reagents and generate waste. 9. Use catalysts, not stoichiometric reagents: Minimize waste by using catalytic reactions. Catalysts are effective in small amounts and can carry out a single reaction many times. They are preferable to stoichiometric reagents, which are used in excess and carry out a reaction only once. 10. Design chemicals and products to degrade after use: Design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment.

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11. Analyze in real time to prevent pollution: Include in-process, real-time monitoring and control during syntheses to minimize or eliminate the formation of byproducts. 12. Minimize the potential for accidents: Design chemicals and their physical forms (solid, liquid, or gas) to minimize the potential for chemical accidents including explosions, fires, and releases to the environment.

GREEN METHODOLOGIES

the contribution of innovation technology is a key issue, and it involves the development of adequate tools and methodology for the implementation of useful and environment-friendly technologies in compliance with the decrease of pollution and the sustainable exploitation of natural resources. The identified key tools can be grouped in four main categories:

1. Tools for a sustainable governance,

2. Tools and methods for the environmental, economic and social assessment,

3. Tools for the environmental management and certifications,

4. Tools for the sustainable design. Some examples are given below.

• IoT Integrated Automated Building Systems. ...

• Synthetic Roof Underlayment. ... • Green Roofs. ...

• Grid Hybrid System. ...

• Passive Solar. ...

• Greywater Plumbing Systems. ...

• Electrochromic Glass. ...

• Solar Thermal Cladding.

ATOM ECONOMY

Traditionally, synthetic chemists have used yield, defined as a percentage of the degree to which a chemical reaction or synthesis goes to completion to measure the success of a chemical synthesis. For example, if a chemical reaction shows that 100 grams of product should be produced, but only 85 grams is produced, the yield is 85%. A synthesis with a high yield may still generate significant quantities of useless byproducts if the reaction does so as part of the synthesis process. Instead of yield, green chemistry emphasizes atom economy, the fraction of reactant material that actually ends up in final product. With 100 percent atom economy, all of the material that goes into the synthesis process is incorporated into the product. For efficient utilization of raw materials, a 100% atom economy process is most desirable. Figure 1.4 illustrates the concepts of yield and atom economy.

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A reaction can have a high percentage yield but also make a lot of waste product. This kind of reaction has a low atom economy. Both the yield and the atom economy have to be taken into account when designing a green chemical process.

Look again at the reaction you considered in

CaCO3 → CaO + CO2

100 56 44

If we split up the formulae, we can look at what happens to each atom in the reaction. The atoms shown below in bold end up in the product we want, the rest do not: Ca C O O O → Ca O + C O O

From the original atoms, one C atom and two O atoms are wasted – they are not in the final, useful product.

Green chemists define atom economy as:

% Atom economy = Mass of wanted product(s) x 100

Total mass of products

So for this example, % Atom economy = 56 x100/100 = 56%

ZERO WASTE TECHNOLOGY

Zero Waste is a philosophy that encourages the redesign of resource life cycles so that all products are reused. The goal is for no trash to be sent to landfills, incinerators, or the ocean. Only 9% of plastic is actually recycled. The process recommended is one similar to the way that resources are reused in nature.

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Generally, “Zero Waste” is a philosophy of eliminating the generation of materials that have no viable or economic option for end-of-use management. In reality, there are varying interpretations for when (and if) it is achieved. Does zero waste really mean zero waste? Does it consider the waste that’s produced in the production of materials upstream? Is a small amount of waste acceptable at the end of a material’s end of life? What about Waste-to-Energy? The definition of zero waste varies widely, with various organizations defining zero waste differently, each with their own interpretation as to what it takes to get to “zero.” The generation of waste can be lowered through a variety of options, including reducing, reusing, recycling, or taking appropriate action to prevent waste through design and engineering solutions. Many individuals, companies and municipalities continue to strive to achieve zero waste goals.

CLEAN DEVELOPMENT MECHANISM

Clean Development Mechanism(CDM) is a unique instrument based on understanding and cooperation among the nations for adopting a new outlook for economic activities aiming at protecting the world eco-system.

Green House Gases

Accumulation of Carbon Di Oxide (CO2), Chloro Floro Carbons (CFC), Methane (CH4) & Nitrous Oxide (NOx) in the atmosphere cover the Green House Gases (GHG)

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GHGs are accumulated in the atmosphere due to combustion of fossil fuels like coal, oil and natural gases etc.

Kyoto Protocol

Industrialization since 18th century, generation of Green House Gases has resulted in progressive global warming.

Kyoto Protocol drafted at Kyoto, in 1992 to combat global climate change .

Joint implementation (Developed Countries)

Clean Development Mechanism (Developing Countries)

International Emission Trading (Emission Credit through special market)

Sustainable Development

This calls for balanced outlook between the pace of economic development & environmental conservation & discourages activities that could hurt the Environment.

Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

The primary objective of sustainable development is to reduce the absolute poverty of the world’s poor through providing lasting & secure livelihoods that minimise resources depletion, environmental degradation, natural disruption & social instability.

CDM Objectives

• To assist developing countries in achieving sustainable development & in contributing to ultimate objectives of United Nations Framework Convention on Climate Change (UNFCCC )

To assist developing countries in achieving compliance with their qualified emission limit & reduction commitments.

Eligibility Criterion

Social well being

Economic well being

Environmental well being

Technological well being

Indian Scenario

Formation of an Advisory Group on Climate Change under Ministry of Environment and Forest (MoEF) which is the nodal agency on climate change issue in India.

Energy Sector is main CO2 emitter accounting for 87% of CO2 emissions.

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Biomass burning and agriculture sector main source of NOx emission.

GHG emission in India is 3% of the world.

Because of high potential of GHG reduction, India can avail new opportunity through CDM projects.

India can capture 10% of Global CDM mark.

Annual revenue estimated range from US$ 10 million to 330 million

CDM Options

Projects prioritised for CDM

Coal power plant using IGCC (Integrated Gasification Combined Cycle)

Coal Power Plant using PFBC (Pressurised Fluidised Bed Combustion)

Renovation and Modernization of Power Plants

Wind based power generation

Solar Thermal Energy for Power generation

Underground Coal gasification technology projects

Wind Pumps for agriculture

Direct reduction process in the iron & steel industry

Continuous pulp digesters in the pulp & paper industry

Demand side management by efficient motors

Barriers

Clear methodologies yet to be defined.

Procedures and process still to be finalised.

Others barriers perceived by many countries are Lack of awareness

Financial barriers due to present low and uncertain returns Technology barriers Institutional barriers Infrastructure limitations High transaction cost

CONCEPT OF ENVIRONMENTAL IMPACT ASSESSMENT

The Rio treaties broadened the concept of common concern and global responsibility for protection of environment .Economic growth and environmental degradation can be de-linked by promoting more eco-efficient growth patterns. Despite the rapid economic growth the concern of

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environmental sustainability is the challenge of every country. The signs of unsustainable growth include high future infrastructure costs, an increasing tendency to produce waste and continuing declines in natural capital of country .Environment and its protection needs a wide approach irrespective of boundaries .An economic and social justification characterize all environmental protection measures aiming to protect human health and safety. Through effective legislation on environment issue and with national instrument of environmental impact assessment (EIA) the path of sustainable development can be easily achieved. The right to decent, healthy or viable environment is not only the right of present generation but is the right of human race on earth. This right becomes the root word for sustainable development .Effective implementation of Law and people participation is required to ensure environmental governance in India.

PRINCIPLE 17 of the Rio Declaration calls for all proposed activities that are likely to have a significant adverse effect and impact on environment and provide three fold limitations on its scope as

1) It does not apply on minor or transitory impacts.

2) Plans, policies or anything else not covered by the term ‘activity’ are excluded from assessment (in some cases projects also)

3) It sets a threshold forcibility which must be met before the obligation to do an EIA arises.

ENVIRONMENTAL QUALITY AND SUSTAINABLE DEVELOPMENT

Stockholm declaration (1972) recognizes the concept of viable environment, as a decent, healthy one and advocated the promotion of environment quality by active control on wrong practices in every member state.

1992 Rio declaration support the concept of collective , solidarity rights and proclaims that ,’all persons have the right to a secure ,healthy ,and ecologically sound environment , adequate to meet equitably the needs of present generations, so as not to impair the rights of future generations and their needs’’. This is right of sustainable development .It includes;

I. Freedom from pollution, environmental degradation and activities that adversely affect the environment or threaten life, health, livelihood, well being or sustainable development.

II. Protection and preservation of air, soil, water, sea, ice, flora, and fauna and all processes necessary to maintain biological diversity in ecosystem.

III. The highest attainable standard of health IV. Adequate housing, good living conditions in healthy ecologically sound environment.

Ecologically sound access to nature, conservation, sustainable use of natural resources.

V. Safe and healthy food, water, and working environment. VI. Enjoyment of traditional life and subsistence for indigenous people.

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ENVIRONMENTAL FRIENDLY POLYMER The environmental friendly polymers contain the polymers or their composites which are either biodegradable or biobased (from renewable resources). Their carbon-neutral lifecycle may reduce the emission of carbon dioxide and the dependence on petroleum-based materials, and then reduce the human footprint on the environment. Due to the concerns with the current increasing environmental issues and depletion of petroleum oil, it is definitely necessary for both academic and industry to attach the great importance to the development of the environmental friendly polymers materials or “green materials.” In fact, the significant achievements in this field have been obtained by chemists, physicists, and engineers who recognized the importance of developing environmentally responsible materials.

Degradable Polymers

• Bio-polymers- produced by biological systems (i.e. micro-organisms, plants and animals) (e.g. wood and paper, protein, )

• Bio-plastic- chemically synthesized from biological starting materials (e.g. sugars, starch, grass, natural fats or oils, etc.) are biodegradable.Micro-organisms in water and in the soil use them as food.

• Synthetic polymers (e.g. plastics) are non-biodegradable-can remain in the environment for a very long time.

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MANUFACTURING OF ECO-FRIENDLY POLYMER -

Bioplastics produced from classical chemical synthesis from biobased monomers(Fermentation)- Polylactic Acid (PLA) plastics, Polyhydroxybutyrate (PHB)

Bioplastics produced directly by natural or genetically modified organisms(Growing plastic in plants)-Polyamides ,Polycaprolactones

Production of PLA by Fermentation method

Polylactic acid or polylactide (PLA) is a thermoplastic aliphatic polyester derived from renewable resources, such as corn starch, tapioca products (roots, chips or starch) or sugarcane.

• It can biodegrade under certain conditions, such as the presence of oxygen, and is difficult to recycle. Highly crystalline, high melting point, low solubility.Bacterial fermentation is used to produce lactic acid from corn starch or cane sugar.

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APPLICATIONS

PLA is used in the preparation of sutures or orthopedic devices, packaging and drug delivery system.

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POLYCAPROLACTONE

• Polycaprolactone (PCL) is biodegradable polyester.

• It has a low melting point of around 60 C.

• It has a glass transition temperature of about −60 C.

• Slower degradation rate than PLA.

• It remains active as long as a year for drug delivery.

Applications:

Drug delivery applications of PCL include:

- Cyclosporin in the form of nanoparticles

- Ciprofloxacin in the form of dental implants

BIODEGRADABILITY OF ECOFRIENDLY POLYMERS

Mechanism of Degradation of polymers

• Two types of Degradation

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• Chain end degradation-

M-M-M-M-M M-M-M-M + M

• Random degradation-

M-M-M-M-M M-M-M+ M-M

Factors responsible for degradation

• Physical factors- heat, light

• Chemical factors- oxygen, ozone, acid or alkali

Types of degradability

I. Bio degradation II. Hydro biodegradation III. Photodegradation IV. Hydro-degradation

Biodegradation

• Made by incorporating starch or cellulose into the polymers during production, micro-organisms consume starch or cellulose, the plastics are broken down into small pieces.

Hydro Biodegradation

• Water penetration

• Preferential attack on the chemical bonds in the amorphous phase

• Conversion of the long polymer chains into shorter water-soluble fragments

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• Reduction in physical properties

Photodegradation

• Photodegradable plastics have light-sensitive functional groups (e.g. carbonyl groups and Metal Complexes ) incorporated into their polymer chains

• These groups will absorb sunlightuse the energy to break the chemical bonds in the polymer to form small fragments.

Why should we use Bioplastics?

Pros • Reduces or eliminates GHG in production • Requires less or no petrochemicals • Plants decreases CO2 in the atmosphere • Biodegradable - byproducts water, CO2, and organic materials

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• Can be utilized as fuel • Slow Release of CO2 allows for plants to absorb CO2 than release it in the atmosphere

Potential Cons

• Uses Genetically Modified processes • Cost up to three times more than regular Plastic • Use of fertilizers and pesticides for crops

BIOREMEDIATION

Bioremediation is a branch of biotechnology which deals with the use of living organisms such as microbes and bacteria to remove contaminants, pollutants and toxins from soil and water. It can be used to clean up environmental problems like an oil spill or contaminated groundwater.

Bioremediation Strategies

� In situ bioremediation

◦ Bioventing- a process of stimulating the natural in situ biodegradation of contaminants in soil by providing air or oxygen to existing soil microorganisms.

◦ Biosparging- In biosparging, air (or oxygen) and nutrients (if needed) are injected into the saturated zone to increase the biological activity of the indigenous microorganisms.

◦ Bioaugmentation- Bioaugmentation is the practice of adding cultured microorganisms into the subsurface for the purpose of biodegrading specific soil and groundwater contaminants

� Ex situ bioremediation

◦ Land farming - Land Farming is a bioremediation technology. Contaminated soils are mixed with soil amendments such as soil bulking agents and nutrients, and then they are tilled into the earth.

◦ Composting- In this process, various microorganisms, including bacteria and fungi, break down organic matter into simpler substances.

◦ Biopiles - Biopiles are aerated with the use of perforated pipes and blowers in order to control the progression of biodegradation more efficiently by controlling the supply of oxygen.

◦ Bioreactors- Engineered device or system that supports a biologically active environment.

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34

CHEMICAL TOXICOLOGY

INTRODUCTION

The name toxicology is derived from the Greek word “TOXIKON”, which means an

arrow. The traditional definition of toxicology is "the science of poisons." Toxicology is the

“study of harmful effects of chemical or physical agents on living organisms". Harmful effects

may occur in many forms, ranging from immediate death to subtle changes not realized until

months or years later.

Historical perspective

The ancient-Greek physician Hippocrates in his treatise Air, Water and Places (400 BC) said

“ the appearance of disease in human populations is influenced by the quality of air, water, and

food; the topography of the land; and general living habits”.

The historical development of toxicology began with early cave dwellers who recognized

poisonous plants and animals and used their extracts for hunting or in warfare. Written

recordings indicates that hemlock, opium, arrow poisons, and certain metals were used to poison

enemies or for state executions. Notable poisoning victims include Socrates, Cleopatra, and

Claudius. Certain concepts fundamental to toxicology began to take shape with the studies done

by Paracelsus (~1500AD) and Orfila (~1800 AD). Paracelsus is known as the “father of modern

toxicology”. Orfila (1815) established toxicology as a distinct scientific discipline

The Dose Makes the Poison

According to Paracelsus, “All substances are poisons; there is none which is not a

poison. The right dose differentiates a poison and a remedy” or the dose makes the poison.

FUNDAMENTAL TERMS RELATED TO TOXICOLOGY/TOXICOLOGY

TERMINOLOGY

TOXIC - This term relates to poisonous or deadly effects on the body by inhalation

(breathing), ingestion (eating), or absorption, or by direct contact with a chemical.

35

TOXICANT - any agent whether physical, chemical or biological, capable of producing

a deleterious response in a biological system. Example – Radiation (physical), Arsenic

(chemical) and snake venom (biological).

TOXIN - The term “toxin” usually is used when talking about toxic substances produced

naturally. A toxin is any poisonous substance of microbial (bacteria or other tiny plants or

animals), vegetable, or synthetic chemical origin that reacts with specific cellular

components to kill cells, alter growth or development, or kill the organism.

TOXICITY - The word “toxicity” describes the degree to which a substance is

poisonous or can cause injury. The toxicity depends on a variety of factors: dose, duration

and route of exposure. It is measured in terms of the amount of the particular material

that is required to kill half the organisms in the test, known as lethal dose 50% (LD50).

TYPES OF TOXICITY

a) Acute toxicity – refers to the immediate harmful effects generated by sufficiently

large doses.

b) Chronic toxicity – refers to the harmful effects of long-term exposure to relatively

low doses of toxicant. Chronic health effects are often irreversible. e.g.- Traces of

pesticides in food, air pollution, lead or mercury poisoning.

• A single toxicant may cause both acute and chronic toxicity depending on the

dose and duration of exposure.

TOXIC EFFECTS – refers to the health effects that occur due to exposure to a toxic substance.

It can be of two types:

LETHAL – effect which results to death.

SUBLETHAL – effects which do not directly result in death.

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Types of toxic effects

a) Acute effect – sudden and severe exposure and rapid absorption of the substance. Health

effects are often reversible.

b) Chronic effect – prolonged exposures of a long duration (weeks, months or years).

Symptoms may not be immediately apparent.

c) Local effect – adverse health effect that occurs at a point or area of contact. E.g. acid,

alkalis.

d) Systemic effect – adverse health effect that occurs at a location distant from the body’s

initial point of contact. e.g.- arsenic affects blood, liver, kidneys, skin.

e) Synergistic effect – when more than two toxic materials are present, the resulting effect

can be greater than the additive effect of the individual substances, e.g. alcohol and

chlorinated solvent.

f) Cumulative poisons – materials that tend to build up in the body due to numerous

chronic exposures. e.g. heavy metals.

DOSE - It is the actual amount of a chemical that enters the body. The amount of exposure and

the type of toxin will determine the toxic effect. This is usually given as mg of chemical/kg of

body weight = mg/kg. The dose is dependent upon:

• The environmental concentration

• The properties of the toxicant

• The frequency of exposure

• The length of exposure

• The exposure pathway

RESPONSE - Any biological effect caused by the exposure is called response.

TARGET ORGAN – organ damaged by the toxic substances.

XENOBIOTIC – (a foreign substance) a chemical which is found in an organism but not

normally produced or expected to be present in it. They may be beneficial or toxic.

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SELECTIVE TOXICITY – it is the differences in toxicity between two species when exposed

simultaneously. e.g.- antibiotics-selectively toxic to micro-organisms and non-toxic to humans.

SENSITIVITY - People varies widely in their sensitivity to the effects of a chemical. Many

factors determine how an individual react to a chemical (age, sex, diet, state of health, use of

medication, drugs, alcohol). Depending upon these characteristics, some people will experience

toxic effects of a chemical at a lower/higher dose than others.

DOSE-RESPONSE RELATIONSHIPS

According to Paracelsus, “All substances are poisons; there is none which is not a poison. The

right dose differentiates a poison and a remedy” or the dose makes the poison.

The dose-response relationship is a fundamental concept in toxicology and the basis for

measurement of the relative harmfulness of a chemical. A dose-response relationship is defined

as a consistent mathematical and biologically plausible correlation between the number of

individuals responding and a given dose over an exposure period. Dose is a very crucial factor in

toxicology. Naturally occurring chemicals in food may also be toxic if consumed in excess. e.g.-

Vitamin D- highly toxic, can lead to high blood pressure, kidney stones, deafness if taken too

much.

DOSE-RESPONSE CURVES

A dose-response relationship is represented by a dose-response curve. The curve is generated by

plotting the dose of the chemical versus the response in the test population. There are a number

of ways to present this data. One of the more common methods for presenting the dose-response

curve is shown in Graph 1. In this example, the dose is expressed in "mg/kg" and depicted on

the "x" axis. The response is expressed as a "cumulative percentage" of animals in the test

population that exhibits the specific health effect under study. Values for "cumulative

percentage" are indicated on the "y" axis of the graph. As the dose increases, the percentage of

the affected population increases. Dose-response curves provide valuable information regarding

the potency of the compound.

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Given the idea of a dose-response, there should be a dose or exposure level below which the

harmful or adverse effects of a substance are not seen in a population. That dose is referred to as

the ‘threshold dose’. Humans have a natural defense mechanism against many toxicants- cells in

human body (liver and kidney) break down chemical to non-toxic substances that can be

39

eliminated from the body in urine and faeces. Therefore, a human body can take some toxicants

at a dose less than threshold and still remain healthy.

TOXIC POTENCY – It is defined by the dose of the chemical that will produce a specific

response in specific organisms.

DOSE-RESPONSE TERMS - The National Institute for Occupational Safety and Health

(NIOSH) defines a number of general dose-response terms in the "Registry of Toxic Substances"

(1983, p.xxxii). A summary of these terms is as follows:

1. Lethal dose low (LDLO): The lowest dose, other than LD50 of a substance introduced by

any route, other than inhalation, which has been reported to have caused death in humans

or animals.

2. Lethal dose fifty (LD50): A calculated dose of a substance which is expected to cause

the death of 50 percent of an entire defined experimental animal population. It is

determined from the exposure to the substance by any route other than inhalation.

Likewise, LD0, LD10, LD90 are there.

3. Lethal concentration low (LCLO): The lowest concentration of a substance in air, other

than LC50, which has been reported to cause death in humans or animals.

4. Lethal concentration fifty (LC 50): A calculated concentration of a substance in air,

exposure to which for a specified length of time is expected to cause the death of 50 percent of

an entire defined experimental animal population. Likewise, LC0, LC10, LC90 are there.

5. Toxic dose low (TDLO): The lowest dose of a substance introduced by any route, other

than inhalation, over any given period of time, and reported to produce any toxic effect in

humans or to produce tumorigenic or reproductive effects in animals. Likewise, TD0, TD10,

TD50, TD90 are there.

6. Effective dose (EDLO): the lowest dose of a substance which indicates the effectiveness

of a substance. This term usually used for drugs.

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NOAEL and LOAEL

• NOAEL: No observed adverse effect level

• LOAEL: Lowest observed adverse effect level

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Examples:

Compound Non-toxic dose Toxic dose Lethal dose

Aspirin 0.65g or 2 tablets 9.75g or 30

tablets

34g or 105

tablets

Alcohol 0.05% 0.1% 0.5%

Significance of NOAEL

Results obtained from animal experiments must be corrected in order to be able to use them for

humans.

ROUTES OF ENTRY OF TOXICANTS IN THE BODY

There are four routes by which a substance can enter the body: inhalation, skin (or eye)

absorption, ingestion, and injection.

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• Inhalation : For most chemicals in the form of vapors, gases, mists, or particulates, inhalation is

the major route of entry. Once inhaled, chemicals are either exhaled or deposited in the

respiratory tract. If deposited, damage can occur through direct contact with tissue or the

chemical may diffuse into the blood through the lung-blood interface. Upon contact with tissue

in the upper respiratory tract or lungs, chemicals may cause health effects ranging from simple

irritation to severe tissue destruction. Substances absorbed into the blood are circulated and

distributed to organs that have an affinity for that particular chemical. Health effects can then

occur in the organs, which are sensitive to the toxicant.

• Dermal (or eye) absorption: Skin contact can cause effects that are relatively innocuous such

as redness or mild dermatitis; more severe effects include destruction of skin tissue or other

debilitating conditions. Many chemicals can also cross the skin barrier and be absorbed into the

blood system. Once absorbed, they may produce systemic damage to internal organs. The eyes

are particularly sensitive to chemicals. Even a short exposure can cause severe effects to the eyes

or the substance can be absorbed through the eyes and be transported to other parts of the body

causing harmful effects.

• Ingestion: Chemicals that inadvertently get into the mouth and are swallowed do not generally

harm the gastrointestinal tract itself unless they are irritating or corrosive. Chemicals that are

insoluble in the fluids of the gastrointestinal tract (stomach, small, and large intestines) are

generally excreted. Others that are soluble are absorbed through the lining of the gastrointestinal

tract. They are then transported by the blood to internal organs where they can cause damage.

• Injection : Substances may enter the body if the skin is penetrated or punctured by

contaminated objects. Effects can then occur as the substance is circulated in the blood and

deposited in the target organs.

Once the chemical is absorbed into the body, three other processes are possible: metabolism,

storage, and excretion. Many chemicals are metabolized or transformed via chemical reactions in

the body. In some cases, chemicals are distributed and stored in specific organs. Storage may

reduce metabolism and therefore, increase the persistence of the chemicals in the body. The

various excretory mechanisms (exhaled breath, perspiration, urine, feces, or detoxification) rid

the body, over a period of time, of the chemical. For some chemicals elimination may be a matter

43

of days or months; for others, the elimination rate is so low that they may persist in the body for

a lifetime and cause deleterious effects.

CHEMICAL INTERACTIONS

The effect of one chemical on the toxic effect of another chemical is called chemical interaction.

Human beings are normally exposed to several chemicals at one time i.e., multiple exposure. For

example – Drinking water may contain pesticides, heavy metals, organic chemicals; Air contains

automobile exhaust, cigarette smoke etc.

In many cases, the presence of one chemical drastically affects the response of another chemical.

The toxicity of a combination of chemicals may be less or more.

Types of Interaction

a) Additivity - when combination of two or more chemicals is the sum of the expected

individual responses. e.g.- two central nervous system depressants- tranquilizer along

with alcohol cause depression.

b) Antagonism – when exposure to one chemical leads to reduction in the effect of the

other chemical. e.g.- swallowed poison adsorbed by charcoal in the stomach.

c) Potentiation – when exposure to one chemical leads to other chemical producing greater

effect. e.g.- toxicity of carbon tetrachloride is enhanced by presence of iso-propanol (non-

toxic).

d) Synergism – when exposure to one chemical leads to a dramatic increase in the effect of

another chemical. e.g.- exposure to cigarette smoke and radon results in a enhanced risk

of lung cancer than the sum of the risk of each.

DAMAGES CAUSED BY THE TOXIC MATERIALS

Xenobiotics cause many types of toxicity by a variety of mechanisms. Toxicity can result

from adverse cellular, biochemical or macromolecular changes such as cell replacement,

damage to an enzyme system, distruption of protein synthesis, damage to DNA,

production of reactive chemicals in cells. There are four basic types of damage caused by

toxic materials –

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a) Physiological damage – reversible or irreversible damage to the health of the

organism.

b) Carcinogenesis – induction of cancer

c) Mutagenesis – induction of genetic mutation

d) Teratogenesis – induction of birth defects

TOXIC CHEMICALS IN THE ENVIRONMENT

A toxicant may affect the human health by different mechanisms. They may be systemic

or organ toxicant.

a) Systemic toxicant – it is the one that affects the entire body or many organs than a

specific site. e.g. – potassium cyanide.

b) Organ toxicant – it is the one that affects only specific tissues or organs while not

producing damage to the body as a whole. These specific sites are called target organs or

target tissues. e.g.- benzene attacks blood forming tissues, lead attacks kidneys, central

nervous system.

DIFFERENT TYPES OF TOXICANTS IN THE ENVIRONMENT

1. Outdoor air pollutants – like CO, SOx, NOx, O3 and particulates. They all are produced

in large amounts and produce toxic effects.

2. Heavy metals – Heavy metals are present everywhere in nature. Plants can absorb and

accumulate metals which may be toxic. Industrial development has also lead to increase in

heavy metal toxicity in various arenas of environment. e.g. As, Cd, Pb, Hg, Cr, Tl, Al, Fe, Pu

etc.

3. Radioactive materials – Radiation is the release and propagation of energy in space or

through a material medium in the form of waves, the transfer of heat or light by waves of

energy, or the stream of particles from a nuclear reactor. Radiation can be ionizing and non-

ionizing.

Ionizing radiation – affects bone marrow, reddening of the skin, cataract, birth defects, and

respiratory illness.

Non-ionizing radiation – includes mutagenic and carcinogenic effects mainly by ultraviolet

radiation.

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4. Pesticides – Several classes of pesticides cause adverse human health effects like

bactericides, fungicides, herbicides, insecticides, nematicides, rodenticides, virucides. They all

are mainly organochlorides, organophosphates and the carbamates.

5. Polychlorinated biphenyls (PCBs) – they are used in plasticizers and adhesives. They

accumulate in fat tissue and milk.

BIOCHEMICAL EFFECTS OF HEAVY METALS

Heavy metals are naturally occurring elements that have a high atomic weight and a density at

least 5 times greater than that of water. Their multiple industrial, domestic, agricultural,

medical and technological applications have led to their wide distribution in the environment;

raising concerns over their potential effects on human health and the environment. Their

toxicity depends on several factors including the dose, route of exposure, and chemical species,

as well as the age, gender, genetics, and nutritional status of exposed individuals. Because of

their high degree of toxicity, arsenic, cadmium, chromium, lead, and mercury rank among the

priority metals that are of public health significance. These metallic elements are considered

systemic toxicants that are known to induce multiple organ damage, even at lower levels of

exposure. They are also classified as human carcinogens (known or probable) according to the

U.S. Environmental Protection Agency, and the International Agency for Research on Cancer.

1. ARSENIC (As)

Arsenic is a ubiquitous element that is detected at low concentrations in virtually all

environmental matrices. It is an essential trace element for some animals and humans, but

the necessary intake may be as low as 0.01 mg/day. The major inorganic forms of arsenic

include the trivalent arsenite and the pentavalent arsenate. The organic forms are the

methylated metabolites – monomethylarsonic acid (MMA), dimethylarsinic acid (DMA)

and trimethylarsine oxide. Several studies have indicated that the toxicity of arsenic

depends on the exposure dose, frequency and duration, the biological species, age, and

gender, as well as on individual susceptibilities, genetic and nutritional factors. Most cases

of human toxicity from arsenic have been associated with exposure to inorganic arsenic.

Inorganic trivalent arsenite (AsIII ) is 2–10 times more toxic than pentavalent arsenate (AsV).

46

Sources:

• Environmental pollution by arsenic occurs as a result of natural phenomena such as

volcanic eruptions and soil erosion, and anthropogenic activities.

• Several arsenic-containing compounds are produced industrially, and have been

used to manufacture products with agricultural applications such as insecticides,

herbicides, fungicides, wood preservatives, and dye-stuffs.

• They have also been used in veterinary medicine for the eradication of tapeworms

in sheep and cattle.

• Arsenic compounds have also been used in the medical field for at least a century in

the treatment of syphilis, yaws, amoebic dysentery, and trypanosomaiasis. Arsenic-

based drugs are still used in treating certain tropical diseases such as African

sleeping sickness and amoebic dysentery, and in veterinary medicine to treat

parasitic diseases, including filariasis in dogs and black head in turkeys and

chickens.

• Several compounds of arsenic like Arsine gas (AsH3) is used in microelectronics;

Gallium arsenide is used in microdevices, lasers, LEDs, semiconductor devices.

• Recently, arsenic trioxide has been approved by the Food and Drug Administration

as an anticancer agent in the treatment of acute promeylocytic leukemia. Its

therapeutic action has been attributed to the induction of programmed cell death

(apoptosis) in leukemia cells.

Exposure pathways:

It is estimated that several million people are exposed to arsenic chronically throughout the

world, especially in countries like Bangladesh, India, Chile, Uruguay, Mexico, Taiwan,

where the ground water is contaminated with high concentrations of arsenic. Exposure to

arsenic occurs via the oral route (ingestion), inhalation and dermal contact.

Diet, for most individuals, is the largest source of exposure, with an average intake of about

50 µg per day. Intake from air, water and soil are usually much smaller, but exposure from

these media may become significant in areas of arsenic contamination. Workers who

produce or use arsenic compounds in such occupations as vineyards, ceramics, glass-

making, smelting, refining of metallic ores, pesticide manufacturing and application, wood

47

preservation, semiconductor manufacturing can be exposed to substantially higher levels of

arsenic.

Health effects:

Contamination with high levels of arsenic is of concern because arsenic can cause a number

of human health effects. Several epidemiological studies have reported a strong association

between arsenic exposure and increased risks of both carcinogenic and systemic health

effects. Arsenic exposure affects virtually all organ systems including the cardiovascular,

dermatologic, nervous, hepatobilliary, renal, gastro-intestinal, and respiratory systems

Acute exposure leads to death, fever, anorexia and liver enlargement.

a) Neurological effects – chronic exposure results in damage to nervous system and liver. It

also leads to peripheral vascular disease that causes Gangrene of lower limbs, also

known as BLACK FOOT disease, occurs due to narrowed blood vessels to reduce blood

flow to limbs. This occurred in Taiwan from arsenic contamination of drinking water.

b) Carcinogenic effects –chronic exposure leads to leukemia, skin, lung, kidney and

bladder cancers.

c) Renal effects – may cause acute renal failure or chronic renal insufficiency.

d) Cardiovascular effects – acute arsenic poisoning may cause both diffuse capillary leak

(leakage of fluid and protein out of blood vessels) and cardiomyopathy (shortness of

breath), leading to death.

e) Respiratory effects – Inhalation of arsenic compounds leads to irritation of the

respiratory mucosa.

f) Reproductive effects – High exposures to inorganic arsenic cause infertility and

miscarriages.

g) Gastrointestinal effects – leads to irritation of the stomach and intestines.

h) Also cause dermatitis, hyper pigmentation, keratosis (rough and scaly patch on skin)

BIOCHEMICAL EFFECTS OF ARSENIC

One of the mechanisms by which arsenic exerts its toxic effect is through impairment of cellular

respiration by the inhibition of various mitochondrial enzymes, and the uncoupling of oxidative

phosphorylation. Most toxicity of arsenic results from its ability to interact with sulfhydryl

48

groups of proteins and enzymes, and to substitute phosphorous in a variety of biochemical

reaction.

a) Complexation with coenzyme/enzyme:

Arsenic in vitro reacts with protein sulfhydryl groups to inactivate enzymes, such as

dihydrolipoyl dehydrogenase and thiolase, thereby producing inhibited oxidation of

pyruvate and betaoxidation of fatty acids. Thus, cell respiration is affected as ATP

formation is inhibited.

Enzyme

SH

SH

As

O

O

O

As (III)

Enzyme

S

S

As O 2OH

b) Uncoupling of phosphorylation

As (+5) substitute the phosphorus in many biochemical reactions as it is chemically

similar to phosphorus. Replacing the stable phosphorus anion with less stable As (+5)

leads to rapid hydrolysis of high energy bonds in compounds like ATP and effectively

uncouples oxidative phosphorylation.

CH2

CH

O

HC

O

OH

P

O

O

O

Phosphate

Glyceraldehyde-3-phosphate

CH2

CH

OPO32-

C

O

OH

OPO32-

1,3-diphospho glycerate

CH2

CH

OPO32-

C

O

OH

O

3-phospho-glycerate

ATP

ARSENOLYSIS

49

CH2

CH

O

HC

O

OH

P

O

O

O

Glyceraldehyde-3-phosphate

CH2

CH

OPO32-

C

O

OH

OAsO32-

CH2

CH

OPO32-

C

O

OH

O

3-phospho-glycerate

AsO3-

Arsenite

1-arseno-3-phospho glycerate

Non-enzymatic hydrolysis

Arsenate

c) Coagulation of proteins

Arsenic (III) compounds coagulate proteins by attacking sulfur bonds responsible for

primary and secondary structure of proteins.\

2. MERCURY (Hg)

It is the third most toxic substance in the environment. It occurs naturally in the

environment as – metallic mercury, inorganic mercury (HgS, HgCl2), and organic mercury

(CH3Hg).

Sources:

• Electronics and electrical industry –used in vapour lamps, fluorescent tubes,

thermometers and electrical products.

• Medicine – in dental amalgams for filling teeth, antiseptics etc.

• Chemical industry- Determining nitrogen by Kjeldahl’s method, manufacture of

vinyl chloride, millon’s reagent, cathode in electrolysis.

• Skin-lightening creams contain inorganic salts of Hg like ammoniated mercuric

chloride and mercuric iodide.

• Burning of coal, oil or wood

• Incineration of mercury containing waste

• Bioaccumlation/Biomagnification of methyl mercury (CH3Hg) in water bodies.

Exposure pathways:

50

Mercury in any form is toxic. It can enter the human body through the following routes:

Inhalation, Ingestion, Injection and dermal contact

Health effects:

• Organic mercury is the most toxic form and it primarily affects the brain. Its

accumulation in central nervous system result in neurotoxicity in adults, also lead to

toxicity in fetuses of mothers.

• Metallic mercury is slowly absorbed by the gastro-intestinal system. It is not as

toxic as methyl mercury.

• Inorganic mercury affects kidneys, leads to bloody diarrhoea and abdominal

cramps.

Biochemical effects of mercury

Biochemical effect of mercury depends on the chemical form and route of entry in the body.

Mercury has a strong affinity for sulfur, so it tends to bind with any molecule that has sulfur

(S) or thiol (SH) group. This process of complex formation in which the metallic ion is

sequestered and firmly bound is Chelation. Mercury interferes in the enzyme function and

protein synthesis by binding to thiol groups. Amino acids like cystine (-S-S-) and cysteine (-

SH), methionine, contain sulfur, so mercury binds to them via sulfur, that reduces the

molecule’s availability for normal metabolic functions.

a) Elemental/Metallic mercury

• Exists as liquid and vaporizes at room temperature.

• Well absorbed by inhalation, from lungs it dissolves in blood plasma; therefore it can

diffuse into any cell in the body. Once inside a cell, mercury vapor which is unreactive

is oxidized to +2 state which is highly toxic. The oxidation process is mediated by

enzyme catalase.

• Some mercury reaches the brain also and oxidized to divalent mercury which causes

Erethism/Mad hatter’s disease- state of abnormal mental excitement or irritation.

• Also leads to Gingivitis- redness or swelling of gums.

• Metallic mercury is not well absorbed by gastrointestinal tract and therefore when

ingested, is only mildly toxic.

b) Inorganic mercury

51

• Present in salt form and is highly toxic

• It enters orally or dermally and accumulates mostly in kidney, causing renal damage

• Leads to neurological toxicity

• Causes precipitation of proteins

• Breaks down barriers in capillaries –Capillary leak syndrome

c) Organic mercury

• Highly lipophilic i.e.; high affinity for fat tissues.

• It is absorbed in the body via gastrointestinal tract.

• Alkyl organic mercury distributes uniformly throughout the body accumulating in

brain liver, kidney, hair and skin.

• Organic mercurials cross the blood barrier and placenta and penetrate erthyrocytes

attributing to neurological symptoms, teratogenic effect and high blood plasma ratio

respectively.

• Methyl mercury directly react with important receptors in the brain/nervous

system which cause irritability, excitability, parasthesia (tingling or prickling sensation),

tremors, violent muscle spasms and even death.

3. CADMIUM (Cd)

Cd has no essential biological function and is extremely toxic to humans. It occurs

naturally as complex oxides, sulfides, carbonates in Pb, Zn and Cu ores. It also occurs as

byproduct of smelting of lead and zinc ores.

Sources:

• Weathering of rocks into river water and oceans

• Burning of fossil fuels (coal)

• Burning of household waste

• From fertilizers

• Tobacco (1 cigarette contains 1-2 μg of Cd)

• Present in alloys, pigments, batteries, metal coatings.

Exposure pathways:

Ingestion and Inhalation

52

Health effects:

• More efficiently absorbed in the lungs than GI tract.

• Organs affected are kidneys and lungs

• Also causes lung and prostate cancer as its carcinogenic

• Prolonged exposure to Cd results in disorders of calcium metabolism causing

Osteomalacia (softening of bones). It causes painful fractures so in Japan the

disease is named as Itai-Itai/Ouch-Ouch disease.

Biochemical effects of Cadmium

• The toxic effects of cadmium are due to inhibition of various enzyme systems,

containing thiol groups.

• It also produces uncoupling of oxidative phosphorylation.

• After absorption, Cd is transported in the blood bound albumin. Being similar to

zinc, its is taken up by liver, causes the liver to synthesize protein metallothionin to

which it binds and prevent it to reach target molecules.

• Long term exposure causes renal dysfunction.

• Cadmium induced proteinuria-excretion of low molecular weight proteins.

4. LEAD (Pb)

Lead is one of the most widespread toxic metals on earth. It is a bluish grey metal with a

low melting point. It is rarely found in free state, usually found in combined state.

Sources:

• Found in the earth’s crust and thus enters food and the water supply.

• From industries, mining and smelting processes

• From Petrol in the form of tetraethyl lead (TEL), an additive to petrol

• Used as a pigment, drying agent in primers, enamels, paints, inks etc.

• Used in the manufacture of batteries, plastics, ceramic glass

• Enters the drinking water as a result of corrosion of materials containing lead.

• From canned food that are sealed with lead-solder alloy

53

Routes of exposure:

Ingestion and Inhalation

Eating lead-based paint flakes, breathing contaminated dust, drinking contaminated water.

Total intake is 225μg/day, out of which 200μg/day is excreted and rest is stored in bones.

Health effects:

• Lead poisoning in children causes headaches, irritability, abdominal pain, anemia,

weight loss, slowed speech, development, hyperactivity, learning difficulty

• Leads to lowered IQ, neurological deficits, rental retardation, kidney and heart

disease, stroke and death.

• In adults, symptoms of lead poisoning pain, numbness or tingling, muscular

weakness, headache, memory loss, pale skin, weight loss, vomiting, anemia,

irritability, abdominal pain

• Lead at high concentration (80 μg/L or above) cause convulsions, coma and death

• Children are more vulnerable to lead exposure than adults as lead is easily absorbed

into growing bodies.

Biochemical effects of lead

Lead poisoning results from the interaction of lead with electron donor groups like –SH,

which interferes with enzymatic processes. It also interacts with cations like Ca2+, Fe2+,

Zn2+, and interferes with Na-K pump. It also alters cellular and mitochondrial membranes.

Lead also interferes with many enzyme systems of body, thereby affecting the function of

every organ.

Major health effects of lead occur in three organs system.

a) Haematological system

It affects the heme synthesis. Lead affects multiple enzyme system by combining with

thiol groups. Lead is absorbed into blood plasma, where it equilibrates rapidly with

extracellular fluid, crosses membranes like blood-brain barrier and placenta, and

accumulates in soft and hard tissues. 95-98% of lead is sequestered in RBCs where it

is bound to hemoglobin (Hb).

Lead poisoning leads to anemia due to impairment of the synthesis of haem and

increased rate of destruction of red blood cells

b) Neurological effects

54

It affects the central nervous system by multiple mechanisms. In the brain, lead alters

the function of cellular calcium and inactivate blood brain barrier which causes the

leakage of protein fluid which affects all parts of CNS.

c) Renal effects

It leads to functional impairment of the tubular region and is characterized by mild

amino acid, glucosuria and hyperphosphaturia. Lon term heavy exposure causes

irreversible neuropathy.

d) It has negative effects on reproductive system as it impairs the release of human

growth hormone and insulin growth factor.\

5. CHROMIUM (Cr)

Several form of chromium are present in the environment – Cr(0), Cr(III), Cr(VI)

Cr(III) - is an essential nutrient required by human body to promote the action of insulin in

body tissues so that sugar, protein and fat can be used by the body.

Cr(VI) is very toxic in nature.

Sources:

• Found in rocks, animals, plants, soil, volcanic eruptions.

• Cr(0) – used for making steel and other alloys.

• Cr(III)-from chromite, and used as brick-lining for high temperature furnaces for

making metals and alloys.

• Waste stream from electroplating discharge releases Cr(VI)

• Used in rust and corrosion inhibitors, textile industry

• Coal ash from electrical utilities.

Routes of exposure:

Inhalation, ingestion and dermal contact are the exposure pathways.

It is present in air we breathe, the water we drink.

Cr(III) occurs naturally in many fruits and vegetables, meat, yeast and grain.

Health effects:

An intake of 50-200 μg of Cr(III) per day is recommended for adults. Without Cr(III) in

the diet, the body loses its ability to use sugars, fat and protein properly which may result

in weight loss, decreased growth, improper function of nervous system, diabetes-like

condition. High dose of Cr(III) causes skin irritation.

55

Health hazards of chromium are dependent on its oxidation state.

Inhaling high levels of Cr(VI) cause irritation to the nose, sneezing, itching, nose bleeds,

ulcers etc. Cr(VI) effects kidneys and liver, it is a likely carcinogen, particularly of lungs.

Biochemical effects of chromium

Cr(VI) is absorbed in the body more easily than Cr(III), but once inside the body, Cr(VI)

changes to Cr(III) and distributes to various tissues of the body mainly in kidney, liver

and muscle.

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56

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