Ch 15Environmental Chemistry — Class 11 Chemistry, concept-first.

Bio-degradable pollutants are pollutants that can be easily decomposed by natural biological processes.

Non-biodegradable pollutants are pollutants that natural biological processes cannot decompose. Examples: metal wastes (mainly mercury and lead), D.D.T, plastics, and nuclear wastes.

The troposphere is the lowest layer of the atmosphere, extending from earth's surface up to about 10 km, and it holds roughly 80% of the total mass of the atmosphere.

The hydrosphere includes every type of water source on earth -- oceans, seas, rivers, lakes, streams, underground water, polar icecaps, clouds and so on.

The lithosphere is the solid component of earth -- it includes the soil, rocks and mountains that make up earth's crust.

The biosphere is the lithosphere, hydrosphere and atmosphere considered together, integrating the living organisms present within all three -- in short, it is the zone of earth (land, water and air) t…

Oxides of sulphur -- sulphur dioxide (SO₂) and sulphur trioxide (SO₃) -- are produced by burning sulphur-containing fossil fuels and by roasting sulphide ores.

Oxides of nitrogen are produced during high-temperature combustion processes, by oxidation of atmospheric nitrogen, and from the combustion of fuels such as coal, diesel and petrol: These oxides are c…

The major pollutants among the oxides of carbon are carbon monoxide and carbon dioxide -- each has quite different sources and health effects, discussed in the two sub-sections below.

Carbon monoxide (CO) is a poisonous gas produced by the incomplete combustion of coal or firewood; it is released into the air mainly by automobile exhaust.

Carbon dioxide (CO₂) is released into the atmosphere mainly by respiration, the burning of fossil fuels, forest fires, and the decomposition of limestone in the cement industry.

Hydrocarbons are compounds composed of carbon and hydrogen only. They are produced mainly naturally (as marsh gas) and also by the incomplete combustion of automobile fuel.

Smoke particulate consists of solid particles, or a mixture of solid and liquid particles, formed by the combustion of organic matter.

Dust is composed of fine solid particles produced during the crushing and grinding of solid materials.

Mists are formed by particles of spray liquids and the condensation of vapours in air. Examples: sulphuric-acid mist, and the mists formed by herbicide and insecticide sprays.

Fumes are obtained by the condensation of vapours released during sublimation, distillation, boiling and calcination, and by several other chemical reactions.

Classical smog, also known as London smog, was first observed in London in December 1952. It consists of coal smoke and fog, and occurs in cool, humid climate; this atmospheric smog is found in many l…

Photochemical smog, also known as Los Angeles smog, was first observed in Los Angeles in 1950. It occurs in warm, dry and sunny climate, forming from the combination of smoke, dust and fog with air po…

Oxides of nitrogen are introduced directly into the stratosphere by the exhaust gases of supersonic jet aircraft engines.

The chlorofluoro derivatives of methane and ethane are referred to by the trade name Freons. These chlorofluorocarbon (CFC) compounds are stable, non-toxic, non-corrosive and non-inflammable, easily l…

Microbiological (pathogen) pollution. Disease-causing microorganisms -- bacteria, viruses and protozoa -- are among the most serious water pollutants.

Organic wastes. Organic matter such as leaves, grass and trash can also pollute water, and water pollution is caused by excessive phytoplankton growth within water bodies too.

Eutrophication is a process by which water bodies receive excess nutrients that stimulate excessive plant growth (algae and other plant weeds).

Biochemical Oxygen Demand (BOD) is the total amount of oxygen, in milligrams, consumed by micro-organisms in decomposing the waste present in one litre of water, at 20°C, over a period of 5 days; its…

Because a BOD measurement takes 5 days to obtain, another parameter, Chemical Oxygen Demand (COD), is also measured.

Chemical wastes. A whole variety of chemicals from industries, such as metals and solvents, are poisonous to fish and other aquatic life.

Fluoride ion deficiency in drinking water causes tooth decay. Water-soluble fluorides are added to drinking water to increase the fluoride-ion concentration up to 1 ppm.

Drinking water containing lead contamination above 50 ppb can cause damage to the liver, kidney and reproductive systems.

A moderate level of sulphate is harmless. But an excessive concentration -- above 500 ppm -- of sulphates in drinking water causes a laxative effect.

Use of drinking water having a nitrate concentration higher than 45 ppm may cause methemoglobinemia (blue baby syndrome), a disease that affects children.

Total dissolved solids (TDS). Most salts are soluble in water. TDS includes cations like calcium, magnesium, sodium, potassium and iron, and anions like carbonate, bicarbonate, chloride, sulphate, pho…

Artificial fertilizers. Soil nutrients are useful for the growth of plants. Plants obtain carbon, hydrogen and oxygen from air or water, whereas other essential nutrients -- like nitrogen, phosphorous…

Pesticides are chemicals used to kill, or stop the growth of, unwanted organisms. But these pesticides can also affect the health of human beings.

Insecticides like DDT, BHC and aldrin can stay in soil for a long period of time and are absorbed by the soil. They contaminate root crops like carrot and radish.

Fungicide. Organo-mercury compounds are used as the most common fungicide. They dissociate in soil to produce mercury, which is highly toxic.

Herbicides are chemical compounds used to control unwanted plants -- they are otherwise known as weed killers. Examples: sodium chlorate (NaClO₃) and sodium arsenite (Na₃AsO₃).

Industrial wastes. Industrial activity has been the biggest contributor to soil pollution, especially mining and manufacturing activities.