All the waste materials are produced by the various activities of human and animals are poisonous to some extent, which can be divided into two main types

1. Biodegradable wastes – Those waste materials, which can be broken down into non-poisonous substances in nature of time by the action of microorganisms is called as biodegradable wastes. A biodegradable waste decomposes naturally and becomes harmless after sometime. Cattle dung and compost are common examples of biodegradable wastes. Other examples of biodegradable wastes are paper, leather, wheat, tealeaves, wool, animal bones, hay, and wood. Some of the industrial wastes are also biodegradable wastes. Some of the biodegradable wastes can be recycled in nature. The recycling of biodegradable wastes materials in nature helps to maintain ecological balance. This is because during the recycling process, various nutrients elements are returned to the nutrient pool of Earth such as water, air, and soil where they can be re-used for the growth and development of newer life forms.
2. Non-biodegradable wastes – The waste materials, which cannot be broken down into non-poisonous or harmless substances is known as non-biodegradable wastes. The examples of non-biodegradable wastes such as polythene bags, D.D.T, glass objects, plastics, ball-point pen, synthetic fibers, refill, and metal articles like silver foils, aluminum cans, iron snails, and radioactive wastes. All these non-biodegradable wastes cannot be made less poisonous easily and hence they are major pollutants of the environment. The non-biodegradable wastes cannot be decomposed by the micro-organisms such as D.D.T is a non-biodegradable wastes so it can be passed along the food chain from crops to man or several other animals and birds which harm them. That’s why D.D.T has been banned from use in most  countries. The radioactive wastes can pollute the soil and water of Earth to dangerous level of toxicity. Radioactive waste materials are produced during enrichment of nuclear fuels. They are produced in nuclear reactors.