Environmental chemistry

Major Causes of water pollution are:

Pathogens: Pathogens include bacteria and other microorganisms that enter water from domestic sewage and animal excreta.
Human excreta contain bacteria such as Escherichia coli and Streptococcus faecalis, which cause gastrointestinal diseases.

Organic wastes: Organic wastes, when added to water, are decomposed by bacteria, which consume dissolved oxygen in water. When the concentration of dissolved oxygen in water decreases below 6 ppm, the growth of fish is inhibited. The breakdown of organic wastes by anaerobic bacteria produces chemicals that have a foul smell and are harmful to human health.

Chemical pollutants: Some inorganic chemicals as an industrial wastes dissolve in water like cadmium, mercury nickel etc. These metals are dangerous to humans and other animals. These metals can damage kidneys and central nervous system, liver etc. Petroleum products pollute many sources of water.

Depletion of ozone layer creates some sort of holes in the blanket of ozone which surrounds us, this is known as ozone hole.

The consequences are:

1. With the depletion of ozone layer, more UV radiation filters into troposphere. UV radiations lead to ageing of skin, cataract, sunburn, skin cancer, killing of many phytoplanktons, damage to fish productivity etc.
2. It has also been reported that plant proteins get easily affected by UV radiations which leads to the harmful mutation of cells.
3. It also increases evaporation of surface water through the stomata of the leaves and decreases the moisture content of the soil.

     4. Increase in UV radiations damage paints and fibres, causing them to fade faster.

Harmful effects of photochemical smog: Photochemical smog causes serious health problems. Both ozone and PAN (peroxyacetyl nitrate) act as powerful eye irritants. Ozone and nitric oxide irritate the nose and throat and their high concentration causes headache, chest pain, dryness of the throat, cough and difficulty in breathing. Photochemical smog leads to cracking of rubber and extensive damage to plant life. It also causes corrosion of metals, stones, building materials, rubber and painted surfaces.

Control:

• Control of primary precursors of photochemical smog, such as NO2 and hydrocarbons, the secondary precursors such as ozone and PAN, the photochemical smog will automatically be reduced.
• Use of catalytic converter in automobiles prevents the release of nitrogen oxide and hydrocarbons to the atmosphere.

Plants like Pinus, juniparus, quercus, pyrus etc. can metabolise nitrogen oxide thus their plantation could help in this matter.

Carbon monoxide binds to haemoglobin to form carboxyhaemoglobin, which is about 300 times more stable than the oxygen-haemoglobin complex. In blood, when the concentration of carboxyhaemoglobin reaches about 3–4 per cent, the oxygen-carrying capacity of blood is greatly reduced. This oxygen deficiency results into headache, weak eyesight, nervousness and cardiovascular disorder. This is the reason why people are advised not to smoke. In pregnant women who have the habit of smoking the increased CO level in blood may induce premature birth, spontaneous abortions and deformed babies. On the other hand, CO₂ does not combine with haemoglobin and hence is less harmful than CO.