The physical and biological world where we live is called our environment. The environment includes our physical surroundings like air (or atmosphere), water bodies, soil (land) and all the organisms such as plants, animals, human beings and micro-organisms like bacteria and fungi (called decomposers).
All these constituents of the environment are dependent on one another. So, all the constituents of environment interact with one another and maintain a balance in the environment in a natural way.
Human beings are the only organisms who change the natural environment to fulfil their needs of food, clothing, housing, transport and industry, etc. In fact, the uncontrolled activities of human beings are damaging the balanced and healthy environment more and more.
All the waste materials produced by the various activities of man and animals are poisonous to some extent and can be divided into two main groups:
1. Biodegradable wastes, and
2. Non-biodegradable wastes.
Those waste materials which can be broken down to non-poisonous substances in nature in due course of time by the action of micro-organisms like certain bacteria, are called biodegradable wastes. A biodegradable waste decays (decomposes) naturally and becomes harmless after some time.
Cattle dung and compost are common examples of biodegradable wastes. [Compost is the manure made from decayed vegetable-stuff (plants)]. Other examples of biodegradable materials are: Animal bones; Leather; Tea- leaves Wool; Paper; Wheat; Wood; Hay; Cotton; Jute; Grass; Fruit and Vegetable peels; Leaves, Flowers, and Cake, etc.
Biodegradable wastes usually do not pollute the environment. Biodegradable wastes pollute the environment only when their amount is large which cannot be degraded (or decomposed) into harmless substances in nature at the right time.
The waste materials which cannot be broken down into non-poisonous or harmless substances in nature are called non-biodegradable wastes. The examples of non-biodegradable wastes are: D.D.T, (Dichloro Diphenyl Trichloroethane); Plastics; Polythene bags; Ball-point pen refill; Synthetic fibres; Glass objects; Metal articles like Aluminium cans; Iron nails; Silver foil and Radioactive wastes.
All these non-biodegradable wastes cannot be made less toxic (less poisonous) easily and hence they are major pollutants of the environment. The non-biodegradable wastes cannot be decomposed by micro-organisms like bacteria. D.D.T. is a non-biodegradable waste so it can be passed along the food chain from crops to man or other animals and birds and harms them.
For this reason, D.D.T. has been banned from use in most countries. Non-biodegradable wastes are the major pollutants of the environment. For example, the discarded plastic articles, glass articles and metal objects are the non-biodegradable waste materials which cause a lot of pollution in our surroundings. We will now describe a simple experiment to find out whether a given material is biodegradable or non-biodegradable.
We take a piece of paper, a piece of an old cotton cloth and a plastic bag (polythene bag). Dig the ground to about 15 centimetres depth and place the pieces of paper, cotton cloth and plastic bag in the dug up ground separately. We cover them with soil.
Leave these buried materials in the ground for about a month. After a month, we dig up the buried materials and observe them. We will find that the piece of paper and the piece of cotton cloth have been partially eaten up (or decomposed) but the plastic bag has remained unaffected, it has not been eaten up (or decomposed).
This means that paper and cotton cloth have been decomposed by the micro-organisms present in the soil. So, paper and cotton cloth are biodegradable. On the other hand, the plastic bag has not been decomposed by the micro-organisms present in the soil, therefore, plastic is non-biodegradable. So, the decomposer organisms are not able to decompose plastic into simpler harmless substances.
We will now explain why some materials are biodegradable whereas others are non-biodegradable. The micro-organisms like bacteria and other decomposer organisms (called saprophytes) present in our environment are ‘specific’ in their action.
They break down the natural materials or products made from natural materials (say, paper) but do not break down man-made materials such as plastics. So, it is due to the property of decomposer organisms of being specific in their action that some waste materials are biodegradable whereas others are non-biodegradable.
We should use the shopping bags (or carry bags) made of paper, cotton cloth or jute because these are biodegradable materials. On the other hand, plastic bags (or polythene bags) should be avoided because plastic is a non-biodegradable material.