Chapter 3: Chemistry of the Environment PDF

**C H A P T E R 3** **THE CHEMISTRY OF THE ENVIRONMENT** ***3.1 Introduction*** Our environment is a hugely complex system that includes the air we breathe, the land we live on, the water we drink an­­d the climate around us. It is important that we work to ensure that our developments in some ar...

**C H A P T E R 3** **THE CHEMISTRY OF THE ENVIRONMENT** ***3.1 Introduction*** Our environment is a hugely complex system that includes the air we breathe, the land we live on, the water we drink an­­d the climate around us. It is important that we work to ensure that our developments in some areas do not adversely affect our environment whilst also ensuring that we mitigate any damage that has occurred. Chemistry can help us to understand, monitor, protect and improve the environment around us. Chemists are developing tools and techniques to make sure that we can see and measure air and water pollution. They have helped to build the evidence that shows how our climate has changed over time. ***3.2 Chemistry of the Atmosphere*** THE FORMATION OF THE ATMOSPHERE A. [The Primitive Atmosphere] Four and a half billion years ago, the Earth was formed as a hot molten rock, and with it the first atmosphere or *primitive atmosphere*. This atmosphere was primarily comprised of hydrogen and helium, and some simple compounds like ammonia (NH~3~) and methane (CH~4~), like that of Jupiter and Saturn have today. Since the young planet Earth did not yet have a magnetic field, strong solar winds from the Sun blew this early atmosphere away. B. [The Secondary Atmosphere] As the Earth cooled, a solid crust was formed, along with several active volcanoes. Strong volcanic activity helped release the gases contained from the hot interior of our planet. These gases, mainly water vapor, carbon dioxide, and ammonia, formed the *secondary* or *reducing atmosphere* of the Earth, similar to the atmospheres that Mars and Venus have today. As the atmosphere cooled down gradually, most of the water vapor condensed and formed clouds. Precipitation from these clouds created oceans, with these oceans simultaneously absorbing atmospheric carbon dioxide. On the other hand, inert nitrogen was formed by the breakdown of ammonia molecules through sunlight. Other gases present were hydrogen, methane, and carbon monoxide in trace amounts, with hydrogen sulfide (H~2~S), sulfur dioxide (SO~2~), and chlorine. C. [The Oxidizing Atmosphere] Through the photochemical dissociation of water vapor by strong ultraviolet radiation, oxygen was formed in the atmosphere. However, the amount produced from this process is negligible. Photochemical dissociation of water vapor Most of the first produced oxygen were released as a by-product by organisms known as *cyanobacteria* which were to the first to undergo photosynthesis. Chemical equation for photosynthesis  The oxygen released during photosynthesis was then used in oxidation of metals like iron. As the surface rocks were completely oxidized, oxygen levels in the atmosphere began to rise. In the atmosphere, O~2~ molecules were absorbing UV radiations and were converted to ozone (O~3~). The formation of the ozone layer made sustainability of life on Earth possible. As higher life forms emerged on the planet, plants helped the production of atmospheric O~2~ while animals consumed it, until the O~2~ levels stabilized to what we know today. ATMOSPHERIC CHEMISTRY A. [ History] The atmosphere is defined as the thick mixture of gases surrounding our planet. It serves as a shield used to protect life on Earth, making our planet unique among other planets in the solar system. The thick mixture of gases that comprise the atmosphere is collectively called as air. This mixture of gases is forced to remain near the Earth's surface due to gravity. A decrease in atmospheric material is observed with increase in altitude, until it gradually reaches outer space. Karman Line **--** an imaginary line which identifies the boundary between the atmosphere and outer space. -------------------------- ------------------ ------------------------------- Year of Discovery Element/Compound Discovered by 1750s Carbon dioxide Joseph Black 1766 Hydrogen Henry Cavendish 1772 Nitrogen Daniel Rutherford 1774 Oxygen Joseph Priestly and 1772 (published in 1777) Carl Wilhem Scheele 1840 Ozone Christian Friedrich Schonbein 1894 Argon Lord Rayleigh and William Ramsay -------------------------- ------------------ ------------------------------- Table 3.2.1. Important Discoveries of Atmospheric Elements ------ ---------------------- --------------------------------------------------------- Year Scientist Discovery 1924 Gordon Dobson Developed a spectrophotometer and started measurements of total-column ozone 1930 Sydney Chapman Described the theory that explains the existence of the ozone layer 1960 Arie Jan Haagen-Smit Described the emergence of the photochemical smog 1973 James Lovelock First detected chlorofluorocarbons (CFCs) in the Atmosphere 1995 Paul Crutzen, Mario Awarded jointly the Nobel Prize in Chemistry for their Molina and Frank work in atmospheric chemistry, particularly concerning Sherwood Rowland the formation and decomposition of ozone ------ ---------------------- --------------------------------------------------------- Table 3.2.2. Important Milestones of Atmospheric Chemistry B. [Atmospheric Composition] Atmospheric gases are generally classified by their amount and residence time. *Residence Time* refers to the average amount of time that a gas spends in the atmosphere. Residence time can be defined as the amount of the compound in the atmosphere divided by the rate at which this compound is removed from the atmosphere. Based on amount, atmospheric gases can be classified into *major components* and *tracegases*, while based on residence time, they can be classified into *constant gases, variable gases,* and *highly variable gases.* ----------------------- ---------------------------- ------------------------------- Amount Main components Trace gases Residence Time Constant Gases Nitrogen, oxygen and argon Other noble gases (neon, helium, krypton, xenon) Variable Gases Carbon dioxide Other long-lived trace gases (methane, hydrogen, nitrous oxide) Highly Variable Gases Water vapor Other short-lived trace gases (carbon monoxide, ozone, nitrogen dioxide, ammonia, sulfur dioxide, hydrogen sulfide) ----------------------- ---------------------------- ------------------------------- Table 3.2.3. Classification of Atmospheric Gases ---------------- -------- Nitrogen 78.08% Oxygen 20.95% Argon 0.934% Carbon Dioxide 0.035% Trace Gases 0.001% ---------------- -------- Table 3.2.4. Composition of the Atmosphere as Percent by Volume of Gases C. [Importance of Atmospheric Gases ] [Nitrogen] Nitrogen is an inert gas that is fundamental to all living systems. Nitrogen is removed the atmosphere through the nitrogen cycle and becomes part of living organisms. The cycle undergoes a process called nitrogen fixation wherein atmospheric N~2~ is reduced to formammonia. Nitrogen can be "fixed" by soil bacteria or by lightning during precipitation. Nitrogen can be returned to the atmosphere by *biomass combustion* and *denitrification.* [Oxygen] Oxygen also plays a fundamental role to living systems. Oxygen exchange between the atmosphere and biosphere is realized by photosynthesis and respiration. [Argon] Argon is the third most abundant gas in the atmosphere. Most of atmospheric argon is radiogenic ^40^Ar isotope derived from decay in ^40^K (potassium) in the Earth's crust. [Water Vapor] Water vapor is also a significant component of the atmosphere. Water vapor is mostly concentrated on the lower atmosphere with about 90% of total atmospheric water vapor found in the lower 5 km atmospheric layer, and 99% of it found in the troposphere. The capacity of air to hold water vapor (called saturation level) is a function solely of air temperature. The higher the temperature, the greater amount of water vapor that can be held without condensation. Water vapor plays important roles in radiation and energy budgets of the atmosphere, and in the formation of clouds and precipitation. Water vapor absorbs about 70% of the incoming shortwave solar radiation, and about 60% of outgoing long-wave radiations, making it the most significant greenhouse gas. [Carbon Dioxide] Carbon dioxide is an important greenhouse gas since it has a strong absorption capacity of infrared and near-infrared radiation. Just like oxygen, it is continually exchanged between the atmosphere and biosphere through photosynthesis and respiration. Some of atmospheric CO~2~ are dissolved by the seas and oceans. An increase in CO~2~ levels has been observed due to growing industries and human activities, like burning of fossil fuels, deforestation, and other forms of land-use change. Man-made activities like these contributed to global warming with the increase of the greenhouse effect. ***3.3 Chemistry of Water*** Water is a chemical compound of hydrogen and oxygen. It contains strong covalent bonds that hold two hydrogen atoms and one oxygen atom together. The three atoms are bonded as H-O-H with a bond angle of 105° between the two hydrogen atoms in liquid water and a large angle of 109° 6' for ice. In the gaseous state, it has the molecular formula H~2~O. The same formula is used to represent the liquid and solid phases of water. Three isotopes of hydrogen and three of oxygen exist in nature, therefore 18 varieties of water molecules are possible. The bonds between oxygen and each hydrogen atom are polar bonds with a 40% partial ionic character. This means that the electrons are unequally shared between the oxygen and hydrogen atoms, with more electrons attracted to the oxygen atom than each hydrogen atom. As a result, the hydrogen atoms are slightly positive in charge while the oxygen atom is slightly negative in charge, therefore forming *hydrogen bonds.* Hydrogen Bond **--** a weak bond between polar compounds where hydrogen atom of one molecule is attracted to an electronegative atom of another molecule. Water can form up to 4 hydrogen bonds. Water is expected to be gaseous at room temperature yet due to the many hydrogen bonds it contains, it is liquid. Since liquid water has a small bond angle, the molecules can be packed together more tightly, therefore having a higher coordination number. Ice has a smaller coordination number, making it less dense than liquid water. As a result, ice floats. Coordination Number **--** the average number of nearest neighbor atoms with respect to a central atom. The specific heat and latent heats for water are fairly high compared with most substances. Water has a specific heat 1 cal/g/°C. This means that it takes 100 calories to raise the temperature of 1 g of water from 0 to 100 °C. Water has two latent heats: latent heat of fusion and latent of vaporization. Latent Heat of Fusion **--** the energy required to convert 1 gram of ice to water at 0 °C and is 80 calories. Latent Heat of Vaporization **--** the energy required to convert 1 gram of liquid water into vapor at 100 °C and is 540 calories. When water is heated in a closed system, vapor molecules are formed and exert pressure of the liquid. This pressure is known as *vapor pressure*. When the vapor pressure is high, evaporation of the liquid is rapid, and a high number of vapor molecules exist. As a result, the boiling point is low. Conversely, a low vapor pressure results to a slow evaporation of the liquid and a fewer number of vapor molecules, resulting to a higher boiling point. Some of the factors that affect vapor pressure are temperature and impurities. An increase intemperature results to an increase in vapor pressure. At higher temperatures, the molecules have moreenergy, therefore, making it easier for molecules to vaporize from their liquid state, increasing the molecules in the vapor state. On the other hand, addition of solutes, like salts and sugars, decrease the vapor pressure. PROPERTIES OF WATER - [Excellent Solvent] -- this property is important for many biological processes use water as adispersing medium for the delivery of nutrients and waste products. It can be accounted from water's high dielectric strength. - [Cohesion] -- this property can be attributed to hydrogen bonds holding together water molecules for liquids. It plays an important role for water transport in plants and accounts for the high surface tension of water.  Figure 3.3.2 Insects "walking" on water due to high surface tension of water - [High Specific Heat Capacity] -- this property is of important consideration when water is usedas a medium of heat transfer. A considerable amount of energy is needed to raise the temperature of water, therefore making it an effective cooling agent. - [Expansion] --water is one of the only compounds that expands when it freezes. If it contractedas other compounds, it would sink (as ice) and destroy life. - [Osmosis and Capillary Action] - these properties enable water to climb tree tops. Osmosis allows plants to feed and for marine creatures to absorb fresh water in increasing salt-water environments. WATER AND THE ENVIRONMENT SOURCES OF WATER Seventy-five percent (75%) of our planet's surface is covered with water. However, about 97% of that water is present in the seas and oceans, making it unusable for drinking, agriculture, and industrial purposes. The remaining 3% is fresh water, with 75% of it found in the polar ice caps, glaciers, and in underground water. The usable fresh water comes down from two sources: surface water & ground water. a\. [Surface Water] Precipitation is a good natural resource of fresh water. About 1/3 of the total precipitation that falls on the earth is absorbed by plants, another 1/3 seeps down into the soil, and the remaining 1/3 flows on the planet's surface, forming streams and rivers. The part of precipitation, which "runs off" to form streams and rivers, is called *surface water.* The hydrological (or water) cycle continuously replenishes a small fraction of the usable surface water. The water cycle involves the evaporation of water from different sources, the condensation of water vapor to form clouds, and the return of water to the earth through precipitation. Evaporation begins again, and the cycle continues. Certain organisms are contained in surface water which break down pollutants into harmless substances. These organisms provide the natural tendency of surface water to clean itself. b. [Ground Water] Ground water is the part of precipitation that seeps into the ground due to gravity, filling pores between soil particles and rocks. Layers of soil and rocks that hold or bear water are called *aquifers.* Ground water can be accessed in the form of wells and springs. WATER POLLUTON A. [Parameters of Water Pollution] 1. 2. 3. B. [Sources of Water Pollution] Substances which can induce physical, chemical, or biological changes to a body of water are referred to as *water pollutants.* Most of the time, these substances cause an undesirable effect on living organisms. There are two types of fresh water pollution: surface water pollution and ground water pollution. [Surface Water Pollution] Sources of surface water pollution can be categorized as: - Point and Non-point Sources - Natural and Anthropogenic Sources [Point and Non-Point Sources] Sources that emit pollutants which directly influences different bodies of water are called *point sources.* Common examples would be domestic and industrial wastes for these wastes are directly dumped into bodies of water. On the other hand, sources of water pollution that indirectly affect bodies of water through environmental changes are called *non-point sources.* The common example would be contaminated water that runs off from farms, mines, and construction sites, affecting bodies of water. Non-point sources are more difficult to deal with than point sources. [Natural and Anthropogenic Sources] Pollution can also be termed as an increase in the concentration of naturally occurring substances. The sources of these substances are called *natural sources*. One common natural source is siltation. Siltation occurs when continuous deforestation makes soil loose and run-off water during precipitation bring silt and dirt from mountain into bodies of water. On the other hand, pollution due to human activities can be accounted to anthropogenic or man-made sources of water pollution. Domestic wastes, such as sewage and waste water, industrial wastes, and agricultural wastes are common examples of anthropogenic wastes. Figure 3.3.3. Natural and Anthropogenic Sources [Ground Water Pollution] As polluted water seeps into the ground and enters an aquifer, it results into ground water pollution. For many towns and cities, ground water is the only source of drinking water. Raw sewage dumped on soil, seepage pits, and septic tanks cause pollution of groundwater. Solid particles of sewage are held back by porous layers of soils, but the contaminated liquid part can pass through. This liquid part dissolves with the groundwater and cause contamination. Same as sewage, nitrogenous fertilizers and toxic wastes contribute to ground water pollution. This problem is more serious in areas with a higher water table (where water is available near the surface of the earth). Ground water can move over large distances due to the large space available below the earth's surface. What happens is that impurities which infiltrate the ground at one point may be found at a different point far away from the point of source. As a result, it is difficult to trace the source of the pollution. Another problem is that ground water does not have access to air, rendering the oxidation of pollutants into harmless products impossible. -------- -- -- -- -- **1.** **2.** **3.** **4.** **5.** **6.** -------- -- -- -- -- Table 3.3.1 Types of Water Pollutants FACTORS THAT AFFECT WATER QUALITY [Temperature] The physical condition of a body of water significantly affects the chemical and biological processes that occur in water. Distinct layers within non-flowing bodies of water (such as lakes) form due to temperature difference between the layers. During warm seasons, the surface layer (or *epilimnion*) of a body of water is constantly exposed to solar radiation. Its higher temperature results to a lower density, making it float over the bottom layer (or *hypolimnion*). This phenomenon is called *thermal stratification.* Thermal Stratification **--** a phenomenon wherein a significant temperature difference exists between two layers of a body of water, in which they do not mix, but they behave independently and have different chemical and biological properties.  Figure 3.3.4 Thermal Stratification A layer between the epilimnion and hypolimnion exist and is called the *thermocline.* Heavy growth of algae is observed in the epilimnion as it is exposed in the atmosphere and sunlight. Hence, this layer contains higher levels of dissolved oxygen. On the other hand, oxygen is consumed by biodegradable organic material in the hypolimnion, causing the water to be anaerobic. As a result, chemical species tend to predominate this layer. Temperature is an important factor for most physical, chemical, and biological properties of a body of water is directly affected by it. Properties of Water that are affected by temperature: 1. 2. 3. An increase in water temperature results to an increase of metabolic rates of aquatic organisms. This can cause an organism, e.g. fish, to use more energy just to survive, preventing fish from performing some of its activities necessary to survive, like finding food and escaping natural predators. Water temperature is affected by air temperature and thermal pollution. Thermal pollution occurs when water in an entering stream is warmer than the water already present in a body of water. Sources of thermal pollution would be industries like nuclear power plants, which discharge cooling water. [Dissolved Oxygen] Dissolved oxygen (DO) is a fundamental factor for underwater life. Aquatic organisms need dissolved oxygen to respire. It is necessary for the survival of fish, invertebrates, bacteria, and underwater plants. Most fish kills result from low levels of dissolved oxygen in bodies of water. Dissolved oxygen is also needed for the decomposition of organic matter. [Alkalinity] Another important characteristic for bodies of water is alkalinity. The alkalinity of water is a measure of its capacity to neutralize acids. Naturally, the alkalinity of waters can be attributed to the salts of weak acids, though weak or strong bases can contribute. *Bicarbonates* contribute the most to the alkalinity of water. Salts of weak acids and strong bases act as buffers to resist a drop in pH resulting from acid addition. Alkalinity, therefore, is a measure of buffer capacity which is greatly used in waste water treatment. [Acidity] The common source of acidity of water is carbon dioxide dissolved in bodies of water. The acidity due to dissolved CO~2~ is called *CO~2~ acidity*. Wastes dumped from industries, particularly metallurgical industries and those involved in the production of synthetic organic materials, contribute to increasing acidity of bodies of water Contaminated water from mines will contain significant amounts of sulfuric acid and salts of sulfuric acid also contribute to water acidity. Acidic waters are of major concern because of their corrosive characteristics. The pH level of bodies of water are usually maintained between 6 and 9.5. [Hardness] Divalent metallic cations cause the hardness of water. The principal hardness causing cations are calcium, magnesium, strontium, ferrous and manganous ions. Most hard waters originate in areas where the top soil is thick and limestone formations are present. Soft waters, on the other hand, originate in areas where the top soil is thin and limestone formations are sparse and absent. Hard water is as useful for human consumption as soft water. The only disadvantage of hard water is that it doesn't dissolve with soap. ***3.4 Soil Chemistry*** Soils are heterogeneous mixtures of air, water, inorganic and organic solids, and microorganisms (both plant and animal). The branch of science that deals with the chemical composition, properties and reactions of soils is called *soil chemistry*. Soil chemistry initially focused on the chemical reactions in soils that affect plant growth and nutrition. However, beginning in the 1970s and surely in the 1990s, concerns arose about the impact of inorganic and organic contaminants in water and soil to plant, animal and human health, leading to the birth of environmental soil chemistry. *Environmental soil chemistry* is the study of chemical reactions between soils and environmentally important plant nutrients, radionuclides, metals, metalloids, and organic chemicals. COMPOSITION OF SOIL A. [Inorganic Components of Soil] Inorganic sand, silt, clay and organic compose the solid portion of soil. These components interact to produce large soil features such as peds, profiles, pedons, and landscapes. *Peds* are formed by the aggregation of sand, silt, and clay particles to form larger soilstructure that result from the action of soil forming factors. *Profiles* develop in the loose material on the earth's surface and are composed of layers of varying texture, structure, color, bulk density and other properties. These layers are also of varying thickness. A *pedon* is the smallest unit that can be considered "soil" and consists of all horizons extending from the soil surface to the underlying geologic strata. An area consisting of similar pedons is called a *polypedon.* The elements found in soils with the highest quantities are the following: O, Si, Al, Fe, C, Ca, K, Na, and Mg. Oxygen is the most prevalent element in the Earth's crust and in soils. It comprises about 47% of the Earth's crust by weight and 90% by volume. The inorganic components of soils represent more than 90% of the solid components. These include both primary and secondary minerals. A *mineral* can be defined as a natural inorganic compound with definite physical, chemical and crystalline properties. A *primary mineral* is a mineral that has not been chemically altered since its deposition and deposition from molten lava. Common examples include quartz and feldspar. Other examples in smaller quantities include pyroxenes, micas, amphiboles and olivines. They primarily occur on sand and silt fractions of soils but may be found in slightly weathered clay-sized fractions. A *secondary mineral* is the result of the weathering of a primary mineral, either through alteration in the structure or from reprecipitation of the products of weathering (dissolution) of a primary mineral. Secondary minerals include aluminosilicate minerals such as kaolinite and montmorillonite, oxides such as gibbsite, goethite and birnessite, amorphous materials such as allophane, and in sulfur and carbonate materials. They are primarily found in the clay fraction of the soil but can also be found in the silt fraction. B. [Organic Components of Soil] Soil organic matter (SOM), like the inorganic components of soil, play a vital role in the chemistry of soils. SOM (also called humus) includes the total organic compounds in soils, excluding undecayed plant and animal tissues, their "partial decomposition" products, and soil biomass. SOM is also defined as a "mixture of plant and animal residues in different stages of decomposition, substances synthesized microbiologically and/or chemically from the breakdown products, and the bodies of live and dead microorganisms and their decomposing remains." -- -- -- -- -- -- Table 3.4.1 Definitions of Soil Organic Matter and Humic Substances -- -- -- -- -- -- Table 3.4.2 General Properties of Soil Organic Matter and Associated Effects in the Soil \*\*CEC (Cation Exchange Capacity) of soil humus is the maximum number of moles of proton charge dissociable from unit mass of solid-phase humus under given conditions of temperature, pressure, and aqueous solution composition, including the humus concentration. [Soil Decontamination] Two techniques are used for decontamination of soils: the *in situ* and *non-in-situ* techniques. *In situ* methods are used at the contamination site itself. Here, the soil does not need to be excavated and therefore exposure pathways are minimized. SEVERAL *In situ* TECHNIQUES A. [Volatilization] This low-cost method causes mechanical drawing or air venting through the soil. A draft fan is injected which causes an air flow through the soil, via a slotted or screened pipe, so that air can flow while preventing the entrainment of soil particles. This method removes compounds which are resistant to biodegradation. However, its application is only limited to volatile organic carbons. B. [Biodegradation] This method is effective on some non-volatile compounds. It involves the enhancement of naturally occurring microorganisms by boosting their numbers and activity. These microbes assist in the degradation of soil contaminants. However, it has a long-term timeframe. C. [Phytoremediation] This method makes use of plants to decontaminate soils and water. It is effective with several inorganic and organic chemicals. Common examples would be sunflowers used to absorb uranium, certain ferns used to absorb arsenic and clovers which take up oil. D. [Leaching] This method involves leaching the soil with water and a surfactant. The surfactant lowers the surface tension of water, thus removing the contaminants. The leachate, found downstream of the site, is then collected for treatment or disposal. The method is not commonly practiced due to large volumes of waste water produced and with disposal costs high. E. [Vitrification] In this method, contaminants are solidified with an electric current, resulting to contaminant immobilization. This method can immobilize pollutants for as long as 10,000 years. However, this process uses a large amount of electricity, thus it is very costly. SEVERAL *Non-In-situ* TECHNIQUES A. [Land Treatment] In this method, the contaminated soil is excavated and spread over land for natural processes such as biodegradation to occur to decontaminate the soil. The soil pH is then adjusted to 7.0 to immobilize heavy metals and enhance the activity of soil microbes. B. [Thermal Treatment] In this method, the excavated soil is subjected to extreme heat using a thermal incinerator. The high temperature breaks down the pollutants, and the volatiles released are then collected and are either burned or recovered as solvents. However, this is a costly method. C. [Asphalt Incorporation] Contaminated soil in this method added to hot asphalt mixes which are then used for paving roads. The heating process during mixing cause the contaminants to be volatilized or decomposed, with the remaining pollutants immobilized in the asphalt. However, heavier compounds can be incompletely removed. D. [Solidification/Stabilization] The method involves the incorporation of an additive to the excavated, contaminated soil so that the contaminants are encapsulated. The mixture is then landfilled, thus rendering the contaminants immobilized, yet not destroyed. **SUMMARY** Our environment is a hugely complex system that includes the air we breathe, the land we live on, the water we drink and the climate around us. Chemistry can help us to understand, monitor, protect and improve the environment around us. - The atmosphere is defined as the thick mixture of gases surrounding our planet and serves as a shield used to protect life on Earth. Atmospheric gases are generally classified by their amount and residence time. - Four and a half billion years ago, the Earth was formed as a hot molten rock, and with it the first atmosphere or primitive atmosphere. - As the Earth cooled, the secondary or reducing atmosphere of the Earth, similar to the atmospheres that Mars and Venus have today, was formed. - Through the photochemical dissociation of water vapor by strong ultraviolet radiation, oxygen was formed in the atmosphere.The formation of the ozone layer made sustainability of life on Earth possible. - Most of the first produced oxygen were released as a by-product by organisms known as cyanobacteria which were to the first to undergo photosynthesis. - Water is a chemical compound of hydrogen and oxygen. - The bonds between oxygen and each hydrogen atom are polar bonds with a 40% partial ionic character. This means that the electrons are unequally shared between the oxygen and hydrogen atoms, with more electrons attracted to the oxygen atom than each hydrogen atom. - Seventy-five percent (75%) of our planet's surface is covered with water. However, about 97% of that water is present in the seas and oceans, making it unusable for drinking, agriculture, and industrial purposes. - The usable fresh water comes down from two sources: surface water & ground water. - Substances which can induce physical, chemical, or biological changes to a body of water are referred to as water pollutants. - Sources that emit pollutants which directly influence different bodies of water are called point sources.On the other hand, sources of water pollution that indirectly affect bodies of water through environmental changes are called non-point sources. - Soils are heterogeneous mixtures of air, water, inorganic and organic solids, and microorganisms. The branch science that deals with the chemical composition, properties and reactions of soils is called soil chemistry. - Inorganic sand, silt, clay and organic compose the solid portion of soil. - Soil organic matters (also called humus) include the total organic compounds in soils, excluding undecayed plant and animal tissues, their "partial decomposition" products, and soil biomass. - Two techniques used for decontamination of soils are the in situ and non-in-situ techniques.