Biochemical oxygen demand is the amount of oxygen required by bacteria to decompose organic matter in a certain volume of sample of water. Clean water would have a BO value of less than 5 ppm, whereas highly polluted water has a BOD value of 17 ppm or more.
Q: 14. Do you observe any soil pollution in your Neighbourhood? What efforts will you make for controlling the soil pollution?
Major sources of soil pollution are industrial wastes and agricultural pollutants such as pesticides, fertilizers, etc.
It is very important to maintain the quality and fertility of soil to ensure and sustain the growth of plants and food crops.
Insecticides like DDT are not soluble in water. For this reason, they remain in soil for a long time, contaminating the root crops. Pesticides like Aldrin and Dieldrin are non- biodegradable and highly toxic in nature. They can enter the higher trophic levels through food chains, causing metabolic and physiological disorders. The same is true for industrial wastes that comprises of several toxic metals like , etc.
Hence, the best way to check soil pollution is to avoid direct addition of pollutants to the soil. Also, wastes should undergo proper treatment. They should be recycled and only then, allowed to be dumped.
Q: 15. What are pesticides and herbicides? Explain giving examples.
Pesticides are a mixture of two or more substances. They are used for killing pests. Pest include insects, plant pathogens, weeds, mollusks, etc., that destroy the plant crop an spread diseases. Aldrin and Dieldrin are the names of some common pesticides Herbicides are pesticides specially meant for killing weeds. For example, sodium chlorate sodium arsenite , etc.
Q: 16. What do you mean by green chemistry? How will it help decrease environmental pollution?
Green chemistry is a production process that aims at using the existing knowledge and principles of chemistry for developing and implementing chemical products and processes to reduce the use and generation of substances hazardous to the environmental, The release of different harmful chemicals (particulates, gases, organic and inorganic wastes) causes environmental pollution. In green chemistry, the reactants to be used in chemical reactions are chosen in such a way that the yield of the end products is up to . This prevents or limits chemical pollutants from being introduced into the environment. Through the efforts of green chemists, has replaced tetrachlorethane and chlorine gas in drying and bleaching of paper.