Pesticides can present danger to consumers, bystanders, or workers during manufacture, transport, or during and after use. There is concern that pesticides used to control pests on food crops are dangerous to the consumer. These concerns are one reason for the organic food movement. Food crops, including many fruits and vegetables such as apples, celery, cherries, grapes, nectarines, peaches, pears, peppers, potatoes, red raspberries, spinach and strawberries, may contain pesticide residues after being washed or peeled.

 Residues, permitted by US government safety standards, are limited to tolerance levels that are considered safe, based on average daily consumption of these foods by adults and children. Tolerance levels are derived from scientifically-based risk assessments that pesticide manufacturers are required to support by producing toxicological studies, exposure modeling and residue studies prior to a product's registration for use on a particular food crop. Other exposure routes, particularly pesticide drift, may be significant to the general public as well. Risk of exposure to pesticide applicators, or other workers in the field after pesticide application, may also be significant and is regulated as part of the pesticide registration process.

Besides human health risks, pesticides also pose dangers to the environment. Non-target organisms can be severely impacted. In some cases, where a pest insect has some controls from a beneficial predator or parasite, an insecticide application can kill both pest and beneficial populations. The beneficial almost always takes longer to recover than the pest. Applications performed to control adult mosquitoes, for example, may temporarily depress mosquito populations but result in a larger population in the long run by damaging controlling factors.

Misuse of pesticides can cause pollinator decline which is a food supply issue.

An early discovery relating to pesticide use, is that pests may eventually evolve to become resistant to chemicals. When sprayed with a pesticides, many pests will initially be very susceptible. However, not all pests are killed, and some with slight variations in their genetic make-up are resistant and therefore survive. Through natural selection, the pests may eventually become very resistant to the pesticide. Farmers may resort to increased use of pesticides, exacerbating the problem.

‘'Persistent Organic Pollutants’' (POPs) are another less-known problem the environment faces as a result of pesticides. POPs may continue to poison non-target organisms in the environment and increase risk to humans by disruption in the endocrine system, cancer, infertility and mutagenic effects, although very little is currently known about these ‘chronic effects’. A wide variety of these chemical are persistent soil contaminants, whose effects may endure for decades.

Cite: Wikipedia