Pesticides are chemical compounds that are used to kill all sorts of pests that damage crops, including insects, rodents, fungi and weeds (unwanted plants). In public health, pesticides are used to kill vectors of disease, such as mosquitoes.  Pesticides need to be used wisely, safely and disposed properly due to by nature, its potentially toxic to other organisms, including humans. It can cause acute and chronic health effects. Those who come into contact with pesticides at work regularly are face the greatest health risks from exposure.

While it may seem good to kill pests, these organisms will strive to survive. When farmers expose pests to a chemical compound that is designed to kill them, a few will survive to reproduce. This will then result in next generation of pests that is likely to be resistant to deadly chemical. Thus, creating a never-ending cycle of pesticide, due to the fact that pests will continue to reproduce with its next generation more chemical resistant.

In addition, some of the older and cheaper pesticides can remain for years in soil and water.  Pesticides that cannot be decomposed will be carried out by water flow and ended up in the sea.  It will endanger the water biota system.  High concentrations of pesticides in the sea can kill marine organisms such as fish and shrimp.  In the low levels, it can poison small organisms such as plankton. When the plankton is consumed by the fish then it will accumulate in the fish body and it would be very dangerous for birds or humans when they consume it.

Therefore, in order to reduce the damage to the environment, it would be better to replace non-biodegradable pesticides with biodegradable pesticides so that the remnants of pesticides will be easily neutralized into simpler elements that are easily absorbed by plants.

Source:

http://www.dummies.com/education/science/environmental-science/the-dangers-of-pesticides-in-the-environment/

https://www.scribd.com/document/356885764/Pencemaran-Pestisida-Pada-Perairan-Laut-dan-Dampaknya-Terhadap-Ekosistem

http://www.who.int/topics/pesticides/en/