•	colour
•	texture
•	structure
•	mineral composition
•	permeability/drainage

climate is probably the most important factor (soils produced from the same parent material under different climate contrast). Climate governs the rate and type of soil formation and is also the main determinant of vegetation distribution. Soil climate has two major components; moisture (precipitation) and temperature, influencing evaporation. When precipitation exceeds evaporation, leaching of the soil will occur. Temperature determines the rate of reactions; chemical and biological decay and so has an influence on weathering and humification . Soils develop very slowly. In Britain it takes about 400 years for 10mm of soil to develop. Young soils retain many of the characteristics of the parent material. Over time they acquire other features resulting from the addition of organic matter and the activity of organisms. The soils of Britain are relatively young because they are largely post-glacial. An important feature of soils is that they pass through a number of stages as they develop, resulting in a deep profile with many well differentiated horizons. Weathering refers to the breakdown and decomposition of rocks and minerals by factors including air, water, sun and frost. Weathering Physical weathering involves continual breakdown or rocks into smaller and smaller particles. Chemical weathering involves alteration of the chemical composition of rock minerals.

Soil pollution is defined as the build-up in soils of persistent toxic compounds, chemicals, salts, radioactive materials, or disease causing agents, which have adverse effects on plant growth and animal health.

There are many different ways that soil can become polluted, such as:

•	Seepage from a landfill
•	Discharge of industrial waste into the soil
•	Percolation of contaminated water into the soil
•	Rupture of underground storage tanks
•	Excess application of pesticides, herbicides or fertilizer
•	Solid waste seepage

The most common chemicals involved in causing soil pollution are:

Soil pollution is caused by the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage links, application of pesticides, percolation of contaminated surface water to subsurface strata, oil and fuel dumping, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. This occurrence of this phenomenon is correlated with the degree of industrialization and intensities of chemical usage.

A soil pollutant is any factor which deteriorates the quality, texture and mineral content of the soil or which disturbs the biological balance of the organisms in the soil. Pollution in soil has adverse effect on plant growth.

Pollution in soil is associated with

Control of soil pollution

The following steps have been suggested to control soil pollution. To help prevent soil erosion, we can limit construction in sensitive area. In general we would need less fertilizer and fewer pesticides if we could all adopt the three R's: Reduce, Reuse, and Recycle. This would give us less solid waste.

Reducing chemical fertilizer and pesticide use
Applying bio-fertilizers and manures can reduce chemical fertilizer and pesticide use. Biological methods of pest control can also reduce the use of pesticides and thereby minimize soil pollution.

Reusing of materials
Materials such as glass containers, plastic bags, paper, cloth etc. can be reused at domestic levels rather than being disposed, reducing solid waste pollution.

Reforesting
Control of land loss and soil erosion can be attempted through restoring forest and grass cover to check wastelands, soil erosion and floods. Crop rotation or mixed cropping can improve the fertility of the land.

Air
Atmosphere is the gaseous cover over the earth surface. Usually air is the name given to this cover and three important gases (namely nitrogen (79 %) oxygen (20%) and carbon dioxide (0.03%)) are supposed to constitute the air. but the atmosphere contain many more things example water vapour, some inert gases (helium, argon, neon) and several gases arising out of the organic matter decomposition, various odours, various gaseous emission from the industries example sulphur dioxide. It may also contain ozone, formaldehyde, chlorofluorocarbons etc thus the composition of the air is varied.

Air which is in its initial condition or in general condition, whose constituents are such they do not harm man or other living beings can be called a clean air. If by different natural and anthropogenic sources the constituents of the air are imbalanced and this imbalancing causes harm to human, animal or plant lives then it is not a clean air. It is polluted or unclean. Clean air is in such a form that all living beings grow and develop in this environment. Thus it is clear that an air which is free from anthropogenic and natural pollutants and which is not harmful to living beings is clean air. However, there is little hope for such a clean air. Several foreign materials from industrial smokes, from burning of fossil fuels and moving automobile enter clean air and cause harm to plant and human life. Thus the clean air becomes polluted and we have a case of air pollution. Air pollution may be defined as a condition which is likely to cause adverse effect on man or his belonging. But there is no distinct boundary line between clean and polluted air. Environmental problems play a special role in our modern society. Such problems are not limited to a particular country but are on global scale and for this, chemical industry and chemistry are to be blamed.

Air pollution can affect our health in many ways. Numerous scientific studies have linked air pollution to a variety of health problems including: (1) aggravation of respiratory and cardiovascular disease; (2) decreased lung function; (3) increased frequency and severity of respiratory symptoms such as difficulty breathing and coughing; (4) increased susceptibility to respiratory infections; (5) effects on the nervous system, including the brain, such as IQ loss and impacts on learning, memory, and behavior; (6) cancer; and (7) premature death. Some sensitive individuals appear to be at greater risk for air pollution-related health effects, for example, those with pre-existing heart and lung diseases (e.g., heart failure/ischemic heart disease, asthma, emphysema, and chronic bronchitis), diabetics, older adults, and children. Although some types of air pollution are recent creations, others, such as London's infamous smoke creations, others, such as London's infamous smoke pollution, have been around for centuries. One of the pollution, have been around for centuries. One of the most tragic air pollution episodes ever occurred in most tragic air pollution episodes ever occurred in London in December 1952 when more than four thousand people died. Air pollutants are airborne particles and gasses that are airborne particles and gasses that occur in concentrations that endanger the heath and well being of organisms or disrupt the orderly functioning of the environment.

Pollutants can be grouped into two categories:

(1) Primary pollutants which are emitted directly from identifiable sources, and

(2) Secondary pollutants which are produced in the atmosphere when certain chemical reactions take place among primary pollutants.

Sulfur dioxide (SO2) is a gas formed when sulfur is exposed to oxygen at high temperatures during fossil fuel combustion, oil refining, or metal smelting. SO2 is toxic at high concentrations, but its principal air pollution effects are associated with the formation of acid rain and aerosols. SO2 dissolves in cloud droplets and oxidizes to form sulfuric acid (H2SO4), which can fall to Earth as acid rain or snow or form sulfate aerosol particles in the atmosphere. Nitrogen oxides are highly reactive gases formed when oxygen and nitrogen react at high temperatures during combustion or lightning strikes. Nitrogen present in fuel can also be emitted as NOx during combustion. Emissions are dominated by fossil fuel combustion at northern mid-latitudes and by biomass burning in the tropics. In the atmosphere NOx reacts with volatile organic compounds (VOCs) and carbon monoxide to produce ground-level ozone through a complicated chain reaction mechanism. It is eventually oxidized to nitric acid (HNO3). Like sulfuric acid, nitric acid contributes to acid deposition and to aerosol formation. Carbon monoxide (CO) is an odorless, colorless gas formed by incomplete combustion of carbon in fuel. The main source is motor vehicle exhaust, along with industrial processes and biomass burning. Carbon monoxide binds to hemoglobin in red blood cells, reducing their ability to transport and release oxygen throughout the body. Low exposures can aggravate cardiac ailments, while high exposures cause central nervous system impairment or death. Volatile organic compounds (VOCs), including hydrocarbons but also other organic chemicals are emitted from a very wide range of sources, including fossil fuel combustion, industrial activities, and natural emissions from vegetation and fires. Some anthropogenic VOCs such as benzene are known carcinogens. The importance of VOCs as precursors depends on their chemical structure and atmospheric lifetime, which can vary considerably from compound to compound. Large VOCs oxidize in the atmosphere to produce nonvolatile chemicals that condense to form aerosols. Short-lived VOCs interact with NOx to produce high ground-level ozone in polluted environments. Methane (CH4), the simplest and most long-lived VOC, is of importance both as a greenhouse gas and as a source of background tropospheric ozone. Major anthropogenic sources of methane include natural gas production and use, coal mining, livestock, and rice paddies.

Secondary air pollutants
Secondary air pollutants are produced in the air by the interaction of two or more primary pollutants or by reaction with normal atmospheric constituents, with or without photoactivation. Examples of secondary air pollutants are Ozone, Formaldehyde, PAN (peroxy acetyl nitrate), Smog) photochemical or smoke induced), Acid mist. Atmospheric sulfuric acid is one example of secondary pollutant. Air pollution in urban and industrial areas is often called smog. Photochemical smog, a noxious mixture of gases and particles, is produced when strong sunlight triggers photochemical reactions in the atmosphere .The major component of photochemical smog is ozone. Although considerable progress has been made in controlling air pollution, the quality of the air we breathe remains a serious public health problem.

The best way to protect air quality is to reduce the emission of pollutants by changing to cleaner fuels and processes. Pollutants not eliminated in this way must be collected or trapped by appropriate air-cleaning devices as they are generated and before they can escape into the atmosphere. These devices are described below. The emphasis of this article is air pollution control technology as it is designed to remove particulate and gaseous pollutants from the emissions of stationary sources, including power plants and industrial facilities. (The control of air pollution from mobile sources is described in emission-control system.)

Control devices
Mechanical collectors (dust cyclones, multicyclones) Electrostatic precipitators an electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient filtration devices that minimally impede the flow of gases through the device, and can easily remove fine particulates such as dust and smoke from the air stream.

Baghouses Designed to handle heavy dust loads, a dust collector consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system (distinguished from air cleaners which utilize disposable filters to remove the dust).

Particulate scrubbers Wet scrubber is a form of pollution control technology. The term describes a variety of devices that use pollutants from a furnace flue gas or from other gas streams. In a wet scrubber, the polluted gas stream is brought into contact with the scrubbing liquid, by spraying it with the liquid, by forcing it through a pool of liquid, or by some other contact method, so as to remove the pollutants.

Water
Water is an odourless, tasteless, transparent liquid that is colourless in small amounts but when present in large quantity exhibits a bluish tinge. About three fourth of the earth surface is covered with hydrosphere, the main component of which is water. Water is one of the most unusual natural compounds found on earth, and it is also one of the most important. The water remains in solid, liquid, and gaseous forms. Life on earth began in the seas, and water in some forms or the other is absolutely essential medium for several different ecosystems. It permeates the atmosphere and outer layers, of lithosphere and has uneven distribution on earth, so that, some of the great ocean depths are approximately six or seven miles. Further water in its two forms, salt water and fresh water, forms two chief environments namely marine environment and fresh water environment of earth.

The occurrence of water as liquid on the surface of the earth, under normal conditions, makes it invaluable for transport, for recreations and as habitat for myriad of animals and plants. Again, its anomalous properties like, having lower density in the solid form, as compared to its liquid forms, are great boon to aquatic life. Otherwise, its survival would have been repeatedly threatened during freezing winters. In short, water is essential to all living organisms, as a large proportion of their tissues consist of water. The quality of water is characterized by its physical, chemical and biological parameters a physical characteristic refer to turbidity, taste and colour. Chemical characteristics refer to dissolved gases and substance, salinity and electrolytic properties. Biological characteristics refer to the properties of water that affect health and wellbeing and are determined by the presence of undesirable organisms like algae, bacteria, coliform and pathogens.

Water is a unique substance, because it can naturally renew and cleanse itself, by allowing pollutants to settle out (through the process of sedimentation) or break down, or by diluting the pollutants to a point where they are not in harmful concentrations. However, this natural process takes time, and is difficult when excessive quantities of harmful contaminants are added to the water. And humans are using more and more materials that are polluting the water sources that we drink from.

There are two main sources of water pollution; point sources and non-point sources. Point sources include factories, wastewater treatment facilities, septic systems, and other sources that are clearly discharging pollutants into water sources. Non-point sources are more difficult to identify, because they cannot be traced back to a particular location. Non-point sources include runoff including sediment, fertilizer, chemicals and animal wastes from farms, fields, construction sites and mines. Landfills can also be a non-point source of pollution, if substances leach from the landfill into water supplies and in waste water treatment different treatments technologies are used.

Physico-chemical treatments
Physical processes are some of the earliest methods to remove solids from wastewater, by means of screening to remove debris and bigger solids and by settling of heavier solids by gravity. These physical processes are inexpensive, easy to use and are used as pre-treatment in wastewater treatment plants. Chemicals are added to aid the physical separation of undesirable substances from water in process such as coagulation- flocculation. Such treatments are generally used to eliminate organic substances. The chemicals normally used have no effect on the elimination of soluble dyestuffs. Simple chemicals such as alum, lime or iron salts can be added to wastewater to cause certain pollutants, such as phosphorus, to flocculate together into large, heavier masses which can be removed faster through physical processes. Over the past 30 years, the chemical industry has developed synthetic inert chemicals know as polymers to further improve the physical separation step in wastewater treatment. Polymers are often used at the later stages of treatment to improve the settling of excess microbiological growth or bio solids.1 The method of electrochemical coagulation is also attempted in which dye house wastewater is circulated in an electrolytic cell containing iron electrodes. Even though the advantage of these processes seems to be its capacity of adaptation to different volumes and pollution loads, its main disadvantage is that it generates huge volume of hazardous sludge and poses a problem of sludge disposal or further treatment.

Biological treatments
Biological treatments mimic the ability of microorganisms in nature to consume and convert waste to other less harmful substances or to produce by-products such as carbon dioxide and water. Any excess microbiological growth could be removed from the wastewater by physical processes. Techniques like activated sludge process has proved to be efficient in some cases.

Adsorption process
The adsorption process is used to removes colour and other soluble organic pollutants from effluent. The process also removes toxic chemicals such as pesticides, phenols, cyanides and organic dyes that cannot be treated by conventional treatment methods. Dissolved organics are adsorbed on surface as waste water containing these is made to pass through adsorbent. Most commonly used adsorbent for treatment is activated carbon.

Ion exchange process
Ion exchange process is normally used for the removal of inorganic salts and some specific organic anionic components such as phenol. All salts are composed of a positive ion of a base and a negative ion of an acid. Ion exchange materials are capable of exchanging soluble ions and cations with electrolyte solutions. Ion exchange resins are available in several types starting from natural zeolite to synthetics which may be phenolic, sulphonic styrenes and other complex compounds. The divalent ions such as calcium and magnesium in general have high affinity for the ion exchange resins and as such can be removed with high efficiencies. In the ion exchange process the impurities from the effluent streams is transformed into another one of relatively more concentrated with increased quantity of impurities because of the addition of regeneration chemicals. The process cannot be used for removal of non-ionic compounds.

Advanced oxidation process
Advanced oxidation processes (AOPs) is a common name refers to a number of chemical treatment procedures designed for the removal of organic pollutants from aqueous medium using highly reactive hydroxyl radical in-situ, second most powerful oxidizing agent reported. AOPs are more environmentally accepted techniques because in many case it leads to complete mineralization of the organic pollutants.

Due to the presence of organic pollutants in aquatic environment (many of them are reported to be stable in aqueous medium) and due to their environmental impacts, the removal of these compounds is very important for drinking and other water use or reuse applications. Conventional water purification techniques such as membrane filtration, adsorption on activated charcoal and reverse osmosis are not effective for the complete removal of these compounds and many of them are very expensive. The efficiency of advanced oxidation processes (AOPs) against many organic pollutants is reported in literature but the mechanism of oxidative transformation leading to the degradation of these compounds is still under investigation. The adverse effects of these compounds and their degradation products in aquatic and non-aquatic organisms are being extensively studied and still a long way to go for completely understanding their impact.

The various ways for the generation of these species include UV/H2O2 photolysis, ozonolysis, fenton, photofenton, photocataysis and sonolyisis.

Membrane Technologies
A membrane is defined as a phase that acts as a barrier to prevent mass movement but allows restricted and/or regulated passage of one or more species through it.14 Membrane filtration can be broadly defined as a separation process that uses semipermeable membrane to retain certain solutes. More specifically, membrane filtration can be further classified in terms of the size range of permeating species, the mechanisms of rejection, the driving forces employed, the chemical structure and composition of membranes, and the geometry of construction. The major membrane separation processes are pressure driven filtration processes including microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO).

Control of Water Pollution Domestic sewage In urban areas, domestic sewage is typically treated by centralized plants. Municipal treatment plants are designed to control BOD and suspended solids. Well-designed and operated systems (i.e., secondary treatment or better) can remove 90 percent or more of these pollutants. Some plants have additional sub-systems to treat nutrients and pathogens. Most municipal plants are not designed to treat toxic pollutants found in industrial waste water. Cities with sanitary sewer overflows or combined sewer overflows employ one or more approaches to reduce discharges of untreated sewage, including:

A household or business not served by a municipal treatment plant may have an individual, which treats the waste water on site and discharges into the soil. Alternatively, domestic waste water may be sent to a nearby privately-owned treatment system (e.g. in a rural community).

Industrial waste water
Some industrial facilities generate ordinary domestic sewage that can be treated by municipal facilities. Industries that generate waste water with high concentrations of conventional pollutants (e.g. oil and grease), toxic pollutants (e.g. heavy metals, volatile organic compounds) or other non conventional pollutants such as ammonia, need specialized treatment systems. Some of these facilities can install a pre-treatment system to remove the toxic components, and then send the partially-treated waste water to the municipal system. Industries generating large volumes of waste water typically operate their own complete on-site treatment systems.

Agricultural waste water
Non-point source controls washed off fields is the largest source of agricultural pollution. Farmers may utilize to reduce runoff flows and retain soil on their fields. Common techniques include contour plowing, crop mulching, crop rotation, planting perennial crops and installing riparian buffers. Nutrients nitrogen and phosphorus are typically applied to farmland as commercial fertilizer; animal manure; or spraying of municipal or industrial waste water (effluent) or sludge. Nutrients may also enter runoff from crop residues, irrigation water, wildlife, and atmospheric deposition. Farmers can develop and implement nutrient management plans to reduce excess application of nutrients. To minimize pesticide impacts, farmers may use Integrated Pest Management] (IPM) techniques to maintain control over pests, reduce reliance on chemical pesticides, and protect water quality. Point source wastewater treatment-Farms with large livestock and poultry operations, such as factory farms, are called concentrated animal feeding operations or confined animal feeding operations. Animal slurries are usually treated by containment in lagoons before disposal by spray or trickle application to grassland. Constructed wetlands are sometimes used to facilitate treatment of animal wastes, as are anaerobic lagoons. Some animal slurry are treated by mixing with straw and composted at high temperature to produce bacteriologically sterile and friable manure for soil improvement. Construction site Storm water.

Discharge of toxic chemicals such as motor fuels and concrete washout is prevented by use of:

Urban runoff (storm water)
Effective control of urban runoff involves reducing the velocity and flow of storm water, as well as reducing pollutant discharges. Local governments use a variety of storm water management techniques to reduce the effects of urban runoff. Pollution prevention practices include low impact development techniques, installation of green roofs and improved chemical handling (e.g. management of motor fuels & oil, fertilizers and pesticides). Runoff mitigation systems include basin infiltration basins, bio retention systems, constructed wetlands, retention basins and similar devices. Thermal pollution from runoff can be controlled by storm water management facilities that absorb the runoff or direct it into groundwater, such as bio retention systems and infiltration basins. Retention basins tend to be less effective at reducing temperature, as the water may be heated by the sun before being discharged to a receiving stream.