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Environmental Chemistry

 We and our surroundings makes environment. For survival, clean environment is very essential. Many diseases are spreading through water, air, soil due to pollution. In 2005 Y. Chauvin, R.H. Grubbs, R.R. Schrock won the noble prize for their remarkable work on ''metathesis'', a great stepforward for ''Green Chemistry'' in which they created new Chemicals that reduces hazardous waste. It is an important application of basic Science to benefit man, society and environment. Environmental Chemistry deals with the study of the origin, transport, reactions, effects of chemical species in the environment.
          Pollution means "to spoil". Addition of any substance (organic/ inorganic/ biological/ nuclear) that harm badly the living organism slowly or immediately or directly or indirectly is called pollution. To understand environmental chemistry, one must know the meaning of the following terms.
Pollutant: A substance which is already present in nature and its concentration increases in the environment due to natural or human activity and adversely effects the environment.

e.g.:  SO2,  CO2.
Pollutant can be classified as primary pollutant (Pollutant which are emitted directly into environment and remaining there. e.g.: SO2, NO, NO2) and secondary pollutant (Pollutant which are formed by the Chemical reactions of primary pollutant.
e.g.:  PAN,  PBN,  SO3,  O3,  H2SO4,  HNO3,  acid rain).
Contaminant: A substance which is not present in nature, enters newly into environment and adversely effects the environment. e.g.: MIC,  DDT,  BHC.

 

Receptor: The medium which is badly effected by the pollutant. e.g.: eyes are receptor during traffic jam.
 

Sink: The medium which is not only effected by the pollutant but also remains there. e.g.: Sea water, trees are big sinks for CO2.
 

Speciation: The Chemical form of pollutant. e.g.: Alkylated mercury is more toxic than mercury.
 

Dissolved Oxygen (D.O.): The amount of Oxygen dissolved in water. The optimum value for good water quality is 4 - 6 mg/lit.
 

Threshold Limit Value (T.L.V.): The permissible level of a toxic pollutant in atmosphere where a healthy person works in that atmosphere for 8 hours per day without any adverse affect. e.g.: TLV for Zn = 1 mg/m3.
 

Chemical Oxygen demand (C.O.D.): The amount of Oxygen required to Oxidise organic substances present in polluted water. COD is determined by 50% acidified (H2SO4) KMnO4 solution. COD for pure sample of water is 4 ppm.
 

Bio Chemical Oxygen demand (B.O.D.): The amount of oxygen consumed by micro organisms present in polluted water during 5 days at 20°C.  Pure water has BOD less than 5 ppm where as untreated municipal water has 100 - 400 ppm. Highly polluted water has BOD more than 17 ppm. COD, BOD values determine the extent of pollution of water.
 

Environmental Segments
Biosphere: Plants, animals, human beings belong to biosphere.
Lithosphere: Earth, soil, minerals, mountains, hills belong to lithosphere.

 

Hydrosphere: Seas, rivers, lakes, streams, reservoirs, glaciers, polarise caps, ground water belong to Hydrosphere.
Atmosphere: The blanket of gases around the earth is called atmosphere. It maintains heat balance on earth. Atmosphere can be divided into 4 parts.

Environment is getting polluted due to modern living, deforestation, urbanization, industrialization, increase in population. Important types of pollution are soil, water, air pollution.

Water Pollution: It is due to domestic, industrial wastes, blue revolution and green revolution.
 

Effects of water pollution are: Vanishing of aquatic life, spreading of diseases like cholera, jaundice, typhoid, diarrhoea, uncontrolled growth of weeds, drying of lakes, salinity of water. Heavy metals like Pb, Hg can damage liver, kidney, reproductive system. If nitrates concentration is more than 50 ppm, causes "blue baby syndrome” (methemoglobinemia). Detergents disturb the 'symbiotic living' on the earth. If the concentration of fluorides exceeds 3 ppm, causes mottling of teeth and bones  become weak due to CaF2 formation. The presence and concentration of fluorides can be detected by Zirconium Alizarin- s dye. The deficiency of fluorides causes tooth decay. Upto 1 ppm fluorides is essential to make enamel on teeth much harder by converting hydroxy apatite [3Ca3(PO4)2 Ca (OH)2] into fluorapatite [3Ca3(PO4)2CaF2]. Excess of fluorides can be removed by activated carbon method, Ion exchange method (by defluoron-1, defluoron-2 resins), and by most popular Nalgonda technique.
 

Nalgonda technique: This harmless, cheap method is developed by National Environmental Engineering and Research Institute, Nagpur in Nalgonda. In this method fluorides are removed by adding required quantities of bleaching powder, lime, alum and the water is kept for some time. Fluoride ions are removed as Calcium aluminium fluoride complex.
 

Bioamplification: The process of increase of concentration of poisonous pollutant like DDT, BHC, Malathion from lower animals to higher animals through food chain is called 'Bioamplification'.
 

Eutrophication: When ponds and lakes become over nutritious due to the release of Phosphates, Organic Wastes from industry and agriculture, support overgrowth & decay of algae, causes sedimentation. This makes lake dry. This process is called "Eutrophication".
 

Air pollution: For all humans clean air, water, food are essential. Air pollution leads to global warming (green house effect), acid rains, ozone depletion, causes many diseases.
 

CO pollution: Due to decomposition of organic compounds, degradation of methane (2 CH4 + 3 O2 → 2 CO + 4 H2O), incomplete combustion of fuels (2 C + O2 → 2 CO) release CO into atmosphere. CO is poisonous as it binds to haemoglobin to form a stable complex (300 times more stable than Oxy haemoglobin).
Oxygen carrying capacity is reduced if the concentration level of carboxy haemoglobin reaches 3-4 percent. Oxygen deficiency in blood results into headache, nervousness, weak eyesight, cardiovascular disorders, may induce premature birth, spontaneous abortions and deformed babies, fatigue, unconsciousness and immediate death (if CO is more than 1000 ppm in atmosphere or 66% CO - Hb).

 

Acid Rains: The term acid rain was first used by Robert Angus in 1872. Rain water has pH of 5.6. Rain water when mixed with acids like H2CO3, HNO3, H2SO4 its pH drops below 5.6 and is called "acid rain". Oxides of Nitrogen (NO, NO2) are produced during combustion of fossil fuels in automobiles, jet planes destroy ozone layer, cause lung, respiratory disorders, effects photosynthesis in plants, causes acid rains. SO2 is released by burning fuels containing S, sulphideores, sulphur cause acid rain, bleaches green colour of the leaf apexes in plants to yellow colour, damage respiratory track, mucus membrane of nose.

Reactions involving in acid rains:
                                     H2O  +  CO2  →   H2CO3
                                     NO  +  O3  →   NO2  +  O2
                                     NO2  +  O3  →   NO3  +  O2
                                     NO2  +  NO3  →   N2O5
                                     N2O5  +  H2O  →   2 HNO3
                                     SO2  +  1/2 O2  →   SO3
                                     SO3  +  H2O     H2SO4
Oxides SO3 & N2O5 finally forms H2SO4 & HNO3 to cause acid rains. Ill affects of acid rains are affecting fertility of soil, reduction in life of building historical monuments like Tajmahal, formation of atmospheric haze (with NH4 + salts & acid rains).

 

Depletion of Ozone: Compounds formed from Cl, F, C are called freons ( or Chloro Fluoro Carbons). They are cheap, colourless, non reactive, odourless, lighter, non toxic organic molecules used as refrigerants in air conditioners, refrigerators.When C.F.C's released into air, they destroy ozone layer. NO, Cl2, NO2 are the other gases of ozone depletion.
They cause holes in ozone layer and leads to ageing of skin, cataract, sunburn, skin cancer, damage of paints, fibres, decrease the moisture in soil, damage of fish productivity, killing of phytoplanktons. The reactions involve in ozone depletion are

Global Warming (Green House Effect) : 75% of solar energy reaching and absorbed by the earth's surface. The remaining heat radiates back to the atmosphere. Some of this heat is trapped by CO2, CH4, O3, water vapour, CFC's and causes gradual rise of temperature in atmosphere is known as global warming.
 

Ill affects of Global warming are: Dengue, malaria, yellow fever, sleeping sickness, unseasonal rains, cyclones, decrease in ground water, melting of ice caps.
Global warming may be controlled by using bicycles, afforestation, non usage of C.F.C's, using solar, wind energies.
Smog: This word is coined from smoke and fog. There are two types of smog.
1) Reducing (Classical) Smog: It is a mixture of smoke, fog and SOhas reducing nature.
2) Photo Chemical Smog: Main Components of this kind of smog are sunlight, oxides of nitrogen, unsaturated hydrocarbons (acrolein, HCHO, PAN), O3 has oxidising nature. So it is also called as "oxidising smog". Ill affects of this smog are irritation of nose, throat, headache, chestpain, cough, cracking of rubber, corrosion of metals, stones, painted surfaces.

It can be prevented by using catalytic converters in automobiles (to prevent release of NO & hydrocarbons), Plantation of pinus, pyrus, ulitis, jumiparus plants (to metabolise NO).
Green Chemistry: A way of thinking and utilising the existing knowledge and principles of chemistry and other sciences to minimise pollution by using minimum chemicals, consumption of minimum energy and minimising waste generation.
           By using biogas, gobar gas, wind, solar energies, biodegradable, ecofriendly materials, bio fertilizers, bio pesticides, growing trees, controlling population, polluting industries, bringing awareness of pollution among people, by keeping environment clean & green we can expect healthy environment.

Posted Date : 04-08-2021

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

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