The addition of certain pollutants like the carbon dioxide gases increases the temperature of the earth. These gases remain close to the surface of earth, forming an insulating layer. The surface becomes hot due to the solar radiations. This radiation is normally reflected back into the space. However, due to the presence of the insulating layer the heat remains within the earth's atmosphere and increases its temperature. The reduction in the forest cover also contributes to the heating of earth. This is called global warming.
Global warming results in the melting of polar ice caps. This inturn results in the rise in the level of ocean waters. It is also called the greenhouse effect. Greenhouses are the covered areas where the temperature is artificially kept higher than the surrounding cold environment for the growth of plants. This is done by preventing the radiation from going out by having glass covers for the greenhouse. The gases that contribute to global warming are also called the greenhouse gases.
Ozone Depletion
Ozone (O3) is a molecule formed by three atoms of oxygen while oxygen (O2), is essential for all aerobic forms of life. Ozone is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. UV radiation causes skin cancer, damage to eyes, immune system. It can also affect global rainfall and cause ecological disturbances.
Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown in the equations below.
The decline of ozone content in the atmosphere began in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.
Biological Magnification
Extensive usage of several pesticides and other chemicals to protect our crops from diseases and pests has resulted in the entry of these harmful chemicals into our bodies through the food chain. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, they get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in our bodies. This phenomenon is known as biological magnification. This is the reason why our food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues. They cannot always be removed by washing or other means.
Did U Know?
PERSISTENT ORGANIC POLLUTANTS [POP] OR PESTICIDES enter our food chain through various methods. DDT, a very harmful pesticide has been banned from use. Almost all ready made foods contain two or more pesticides. Among fruits and vegetables peaches, apples, spinach and lettuce have the highest amount of pesticide content. Onions have the least followed by papaya. Dieldrin and DDE are the most commonly used pesticides. DDE is a break down product of DDT. Dieldrin is an organochlorine pesticide.
Use of organically grown food items is one way of reducing pesticide intake.
