Our food grains such as wheat, rice, vegetables, fruits, and even meat are found to contain varying amount of pesticide residues. State the reason to explain how and why this happens?

During cultivation of crops, harmful pesticides are applied to protect crops from various pests. Pesticides contain harmful chemicals that cannot be decomposed. Various food materials contain some amount of pesticide sticking to them. If the fruits and vegetables are not washed properly before consumption, these pesticides enter our body. Animals feeding on plants consume harmful pesticides along with the crops. The concentration of pesticides keeps on increasing at each tropic level. Due to rains, these chemicals are washed off the soil and enter into water bodies, from where they are taken up by aquatic animals. This is the reason why meat of animals also contains traces of pesticides.