The waste materials which cannot be broken down into non-poisonous or harmless substances in nature are called non-biodegradable waste. Examples are plastics, polythene bags, ball-point pen refills, synthetic fibres, and glass objects, metal articles like aluminium cans, iron nails, silver foil and radioactive 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 waste. A biodegradable waste decomposes naturally and becomes harmless after sometime. Animal bones, nails, hair ,leather, tea leaves, wool, paper and wheat are all examples of this.