There are more than 1,000 pesticides used around the world to ensure food is not damaged or destroyed by pests. And each pesticide has different properties and toxicological effects, says the World Health Organisation.

Many of the older, cheaper (off-patent) pesticides, such as dichlorodiphenyltrichloroethane (DDT) and lindane, can remain for years in soil and water. These chemicals have been banned by countries who signed the 2001 Stockholm Convention, an international treaty that aims to eliminate or restrict the production and use of persistent organic pollutants.

The toxicity of a pesticide depends on its function and other factors. For example, insecticides tend to be more toxic to humans than herbicides. The same chemical can have different effects at different doses (how much of the chemical a person is exposed to). It can also depend on the route by which the exposure occurs (such as swallowing, inhaling, or direct contact with the skin).

None of the pesticides that are authorised for use on food in international trade today are genotoxic (damaging to DNA, which can cause mutations or cancer). Adverse effects from these pesticides occur only above a certain safe level of exposure. When people come into contact with large quantities of pesticide, this may cause acute poisoning or long-term health effects.

Pesticides are among the leading causes of death by self-poisoning, in particular in low- and middle-income countries. As they are intrinsically toxic and deliberately spread in the environment, the production, distribution, and use of pesticides require strict regulation. Regular monitoring of residues in food and the environment is also required.

The WHO has two objectives in relation to pesticides: to ban pesticides that are most toxic to humans, as well as pesticides that remain for the longest time in the environment; and to protect public health by setting maximum limits for pesticide residues in food and water.

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