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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).

Fungicides are pesticides that kill or slow the growth of fungi and their spores. They can be used to control fungi that damage plants, including rusts, mildews and blights. They might also be used to control mould and mildew in other settings. Fungicides work in a variety of ways, but most of them damage fungal cell membranes or interfere with energy production within fungal cells (NPIC, 2019).

Fungi are the primary cause of crop loss worldwide. Diseases are a common occurrence on plants, often having a significant economic impact on yield and quality, thus managing diseases is an essential component of production for most crops. Broadly, there are three main reasons that fungicides are used: (i) to control a disease during the establishment and development of a crop; (ii) to increase productivity of a crop and to reduce blemishes. Diseased food crops may produce less because their leaves, which are needed for photosynthesis, are affected by the disease; and (iii) to improve the storage life and quality of harvested plants and produce. Some of the greatest disease losses occur post-harvest (APS, no date).

As an example, banana and plantain (Musa spp.) are grown throughout the tropical and subtropical regions of the world. They are a key staple food in many developing countries and a source of income for subsistence farmers. Banana and plantain are attacked by different pathogens that affect plant development, cause yield losses and reduce fruit quality. From an economic point of view, banana and plantain leaf spots caused by Mycosphaerella fijiensis Morelet (black Sigatoka/black leaf streak) and by M. musicola Leach ex Mulder (yellow Sigatoka), can be considered the two most serious diseases of Musa spp. Fungicides (as a xenobiotic) help to reduce the impact but fungal resistance to fungicide usage is now being recognised (FAO, 2013).

People may be exposed to fungicides by breathing in, eating, or drinking the product, or by touching plants or surfaces that have recently been treated (CDC, 2019). A recent peer-reviewed paper summarised toxicologically harmful fungicides (Lopez and Sudakin, 2017). A summary of these compounds and some of the chemical incidents associated with the use of these fungicides follows.

Organomercury compounds (methylmercury, phenylmercuric acetate) are a class of fungicide formulated as dusts and aqueous solutions that are used primarily as seed protectants. Although their use has been banned or greatly restricted in many countries, they are of historical importance owing to their severe toxicity in humans. Lopez and Sudakin (2017) reported that a poisoning epidemic in rural Iraq in 1971 was the result of people ingesting bread prepared from wheat treated with methylmercury – acting as a fungicide. The outbreak resulted in 50,000 exposures and at least 439 deaths.

Chlorinated phenols, particularly pentachlorophenol, continue to have wide industrial application as fungicides and wood preservatives. There have been several historical accounts of acute poisoning caused by pentachlorophenol exposures. Lopez and Sudakin (2017) reported that in 1967, a cluster of cases of critical illness in a newborn nursery occurred through the misuse of sodium pentachlorophenate as an anti-mildew agent in the hospital laundry; nine poisoning cases and two fatalities were reported.

Substituted benzenes including hexachlorobenzene. Lopez and Sudakin (2017) reported that although the acute toxicity from ingestion or inhalation exposure is low with hexachlorobenzene, the systemic effects from chronic exposure are well documented. They reported that an epidemic of 5000 cases of porphyria cutanea tarda was described in Turkey between 1955 and 1959, where the cause was traced to the consumption of wheat treated with a seed protectant containing 10% hexachlorobenzene.

Dithiocarbamates (metam sodium, thiram, ethylene bisdithiocarbamate compounds). As a class of general- and restricted-use fungicides, the dithiocarbamates are available in a variety of formulations, including water suspensions, wettable powders, and dusts. They have many agricultural applications, including the protection of seedlings, turf, vegetables, fruits, and ornamentals from fungal growth. Compared with the known toxicity of several of the classes of fungicides described above, dithiocarbamates have considerably lower acute toxicity due to their rapid metabolism and lack of persistence in mammalian systems but have the potential to cause acute illness. Of note was the report of the clean-up of an accidental metam sodium spill into the Sacramento River where workers developed erythema, rash, itching, and scaling of the lower extremities (the areas that had come into contact with contaminated water). The same chemical spill resulted in the emergency triage of 360 individuals, most of whom had mild irritant upper airway symptoms that did not require hospitalisation.

A follow-up study of adults living within 0.5 miles of the site of the accident identified 20 cases of persistent irritant-induced asthma and 10 cases of persistent asthma exacerbations (Lopez and Sudakin, 2017).

Copper compounds (copper sulphate). Several copper compounds are available as fungicides for commercial use. Intentional and accidental ingestion of copper compounds has historically been a common cause of morbidity and mortality (Lopez and Sudakin, 2017).

Organotin compounds are formulated as wettable and flowable powders and used throughout the world as fungicides in a variety of agricultural and industrial settings. Tributyltin oxide had been registered for use as an anti-mildew control agent in interior and exterior paints, but is now severely restricted in many countries due to its potent irritant properties. Tributyltin oxide continues to be used as an antifouling agent in marine paints, due to its ability to prevent the growth of barnacles, algae, and marine organisms (Lopez and Sudakin, 2017).

Metrics and numeric limits

Available data are too limited to estimate the overall global health impacts of pesticides including fungicides; however, the global impact of self-poisoning (suicides) from preventable pesticide ingestion was estimated to be 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 fungicides including hexachlorobenzene and copper.

Examples of drivers, outcomes and risk management

Fungicides are a diverse group of structurally unrelated compounds that are widely used for agricultural, industrial, and domestic purposes. As with all pesticides, risk management is critical to reducing harm.

In 2015, the 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 bodies, including the WHO and the Food and Agriculture Organization of the United Nations (FAO), support this resolution. These include the publication of 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).

The highly hazardous pesticides risk reduction process consists of three main consecutive steps: identification of highly hazardous pesticides by checking registered pesticides against the FAO/WHO criteria; mitigation of highly hazardous 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 highly hazardous pesticides and their health impacts, the WHO summarised 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 have a 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).