1. Use of toxic materials such as pesticides, herbicides and fungicides creates new problems in the ecosystem. 

2. As these toxic materials are often indiscriminate in their action and vast numbers of other animals may be destroyed. 

3. Some of them may be predators which naturally feed on these pests, others may be the food for other animals. 

4. Thus causing unpredictable changes in food chains and upsetting the balance within the ecosystem. 

5. Some toxic substances have a cumulative effect. 

6. Some of them are degradable, can be broken down into harmless substances in a comparatively short time usually a year. 

7. Others are non-degradable which are potentially dangerous as they accumulate in the bodies of animals and pass right through food web. 

8. This process of entering of pollutants in a food chain is known as “Bioaccumulation”. 

9. The tendency of pollutants to concentrate as they move from one tropic level to the next is known as “Biomagnifications”.