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Primary reference(s)

CDC, 2019. . Accessed 25 October 2020.

Additional scientific description

The term ‘pesticide’ is considered to embrace active ingredients in any form, irrespective of whether, or to what extent, they have been formulated for application. The term is usually associated with materials intended to kill or control pests (insecticides, fungicides, herbicides, etc.) (WHO and FAO, 2016). Pesticides are used in many different sectors (e.g., agriculture, forestry, food industry, domestic etc.).

Insecticides are classified based on their structure and function. They include:

• Carbamates/Organophosphates: Although carbamates and organophosphates are structurally distinct, they have a similar mechanism of action – they kill insects by inhibiting the enzyme cholinesterase, which is essential in the functioning of the nervous system. While highly effective insecticides, they are also toxic to non-target species, including humans. Humans may be exposed via inhalation, ingestion or through skin contamination; and acute and chronic exposure can produce varying levels of toxicity. Similar to the insects exposed, these pesticides disrupt the function of the human nervous system, mainly the brain. They have also been linked to cancer risk. Their toxicity to humans has led to bans and use restrictions in many countries (CDC, 2019).
• Organochlorines: These are a group of chlorinated compounds that typically affect the central nervous system. They are known for their high toxicity, slow degradation and bioaccumulation. Examples include dichlorodiphenyltrichlorethane (DDT), methoxychlor, chlordane, and lindane. Human exposure may occur via inhalation, ingestion or through skin contamination. Many organochlorines have been banned in many countries, although a few are still registered for use (CDC, 2019).
• Boric acid: This type of pesticide comes in many forms (most commonly in pellets or tablets or a finely ground powder) and has many uses. It is a combination of boron and other elements. Toxicity depends on the amount of boron in the product. In addition to controlling insects, boric acid can be used to control growth of moulds, fungi and weeds. Boric acid is low in toxicity, but can still cause irritation to the skin or eyes, and nausea, vomiting, stomach aches and diarrhoea if ingested (CDC, 2019).
• Pyrethroids/Pyrethrins: Pyrethrum is a naturally occurring mixture of chemicals found in certain chrysanthemum flowers. Pyrethrum was first recognised as having insecticidal properties around 1800 in Asia and was used to kill ticks and various insects such as fleas and mosquitos. From pyrethrum extract, individual chemicals called pyrethrins which have active insecticidal properties were developed. Pyrethroids are manufactured chemicals that are very similar in structure to the pyrethrins, but are often more toxic to insects, as well as to mammals, and last longer in the environment than pyrethrins (ATSDR, 2003). These insecticides are used widely in households, agriculture, on pets, and in mosquito control. While they are generally less toxic to mammals than some other insecticides, they can still have harmful health effects (CDC, 2019).

Metrics and numeric limits

Available data are too limited to estimate the overall global health impacts of pesticides including insecticides. However, the global impact of self-poisoning (suicides) from preventable pesticide ingestion was estimated to amount to 155,488 deaths and 7362,493 Disability Adjusted Life Years (DALYs) in 2016 (WHO, 2019a).

In a report on exposure to highly hazardous pesticides (WHO, 2019a), the World Health Organization (WHO) gave the following guidance values for pesticides:

Maximum residue limits (MRLs) in food: The Joint FAO / WHO Meeting on Pesticide Residues (JMPR) evaluates those pesticides likely to contaminate food. MRLs are published by the Codex Alimentarius Commission. Guidance is available for individual pesticides or pesticide components – including for a number of highly hazardous pesticides (FAO, no date).

Drinking-water: The WHO provides guidelines for drinking-water quality (WHO, 2011) and this includes guidance for various insecticides.

Examples of drivers, outcomes and risk management

Outcomes of exposure to pesticides including insecticides include:

• Unintentional and self-inflicted (suicides) acute poisonings by pesticides are a serious public health concern in many parts of the world (WHO, 2019a).
• The acute hazard is highly variable depending on the pesticide and includes peripheral and central neurotoxicity and reduced blood clotting capacity. The specific pesticide formulation can significantly affect both exposure and toxicity. Short-term exposure can cause harmful effects on the liver, kidneys, blood, lungs, nervous system, immune system and gastrointestinal tract (WHO, 2019a).
• Chronic exposure to pesticides including insecticides can result in effects on the skin, eyes, nervous system, cardiovascular system, gastrointestinal tract, liver, kidneys, reproductive system, endocrine system, immune system and blood. Some pesticides, including insecticides, may cause cancer, including childhood cancer (WHO, 2019a).
• Toddlers and children are considered more vulnerable to exposure to pesticides, including insecticides, due to their smaller size, hand to mouth activity, different metabolism, and still developing internal organs (WHO, 2019a).

Risk mitigation measures are critical. In 2015, the Strategic Approach to International Chemicals Management (SAICM) International Conference on Chemicals Management adopted a resolution that recognised highly hazardous pesticides as an issue of concern and called for concerted action among countries to address these substances, with emphasis on promoting agro-ecologically based alternatives and strengthening national regulatory capacity to conduct risk assessment and risk management (WHO, 2019a).

Several initiatives undertaken by international organisations, including WHO/FAO, support this resolution. These include the publication of several guidelines to support the International Code of Conduct on Pesticide Management, including those on highly hazardous pesticides, good labelling practice for pesticides, pesticide legislation and numerous other resources and guidance documentation to assist in the implementation of best practices, which have been brought together in a toolkit (FAO, 2015).

Pesticide, including insecticide, risk reduction processes comprise three main consecutive steps: identification of the pesticide by checking registered pesticides against the FAO/WHO criteria; mitigation of pesticide risks by determining for each product whether risk mitigation measures are required, and if so, which options would be most appropriate (WHO, 2019a).

To reduce exposure to pesticides, including insecticides and their health impacts, the WHO summarises actions required in the following areas: handling, storage, use and disposal; elimination and replacement of pesticide use; education; and regulation, monitoring and surveillance (WHO, 2019a).

For example, fungicide classification and labelling, as with all pesticides, is an essential part of control (WHO, 2019b). The report describes the principles and content that aim to generate uniformity in the statement on the nature of the risk (by phrase and/or symbol) on the label of the product, irrespective of the country of origin or use. Labels of products classified in classes Ia (extremely hazardous) and Ib (highly hazardous), should bear a symbol indicating a high degree of hazard (usually a type of skull and crossbones) and a signal word or phrase, such as POISON or TOXIC. The presentation of the symbol and word or phrase, in terms of colour, size and shape should ensure that they are given sufficient prominence on the label. The text should be in the local language and for all formulations should include the approved name of the active ingredient or ingredients, the method of use, and precautions to be taken in use. For classes Ia and Ib, symptoms and immediate treatment of poisoning should also be included. The detailed precautions necessary for the use of a pesticide depend on the nature of the formulation and the pattern of use, and are best decided by a pesticide registration authority when accepting a commercial label. There are international agreements on symbols to denote hazards from materials which are inflammable, corrosive, explosive, etc., and these should be consulted and used where appropriate (WHO, 2019b).