1 Pesticides An enormous number of chemicals exist in trichogramma. The management of pests nature, which are used as pesticides, for actually disturbs the balance of nature, agricultural and non-agricultural purposes. thereby affecting biodiversity on Earth. Pesticides are introduced to manage popula- Pesticides can adversely affect non-target tions of living organisms, called pests, which organisms as well as affecting other ecologi- are deleterious to crops or the health of the cal components of the environment, which human race. A literal meaning of pesticide is they are not intended to do. ‘a substance used to kill undesired living organisms’. However the Food and Agricul- ture Organization (FAO, 2013) has defined 1.1 History pesticide as: any substance or mixture of substances Until the 1940s, during World War Two, intended for preventing, destroying, or pesticides were widely used for pest control controlling any pest, including vectors of to ensure food security by the introduction human or animal disease, unwanted species of inorganic chemicals such as calcium, lead of plants or animals, causing harm during arsenate and sulfur, and the use of common or otherwise interfering with the produc- salt and sodium chlorate as herbicides. The tion, processing, storage, transport, or organic molecules of this period were natu- marketing of food, agricultural commodi- ral products such as nicotine (extracted from ties, wood and wood products or animal tobacco) and rotenone (extracted from der- feedstuffs, or substances that may be administered to animals for the control of ris roots). These were named first-generation insects, arachnids, or other pests in or on pesticides. These pesticides, including heavy their bodies. The term includes substances metals, were toxic to humans and agricul- intended for use as a plant growth regula- tural plants. The growth in synthetic pesti- tor, defoliant, desiccant, or agent for cides accelerated in the 1940s with the thinning fruit or preventing the premature discovery of the effects of organochlorines, fall of fruit. Also used as substances applied known as second- generation pesticides, such to crops either before or after harvest to as dichlorodiphenyltrichloroethane (DDT), protect the commodity from deterioration b-hexachlorocyclohexane (BHC), aldrin, during storage and transport. dieldrin, endrin, chlordane, parathion, cap- Pest management is also achieved by the use tan and 2,4-dichlor ophenoxyacetic acid (2,4- of other biological active agents, such as D). The discovery of DDT by Dr Paul Muller, CAB International 2019. Pesticide Risk Assessment (S. Arora) 3 4 Chapter 1 in 1939 was a turning point that revolution- During the 1970s and 1980s, a herbi- ized agricultural production. DDT was popu- cide, ‘glyphosate’, currently the world’s best- lar because of its broad-spectrum activity selling herbicide product, was introduced, (Unsworth, 2008) and was widely used. It followed by sulfonylurea and imidazolinone appeared to have low toxicity to mammals, products. The insecticide industry marked and reduced the incidence of insect-borne the era of the third generation of pesticides, diseases, such as malaria, yellow fever and with the introduction of avermectins, ben- typhus. Consequently, in 1949, Dr Paul zoylureas and Bt (Bacillus thuringiensis). The Muller won the Nobel Prize in Medicine for triazole, morpholine, imidazole, pyrimidine discovering its insecticidal properties. How- and dicarboxamide families of fungicides ever, in 1946, resistance to DDT in house were also introduced during this period. flies was reported and, because of its wide- The massive use of pesticides during the spread use, there were reports of harm to 1960s significantly increased agricultural non-target plants and animals and problems productivity leading to the ‘Green Revolu- with residues (Unsworth, 2008). These tion’ and a safe and secure food supply, along insecticides were observed to be toxic to with other secondary benefits. However, humans and agricultural plants, due to some of the first-generation pesticides had their bioaccumulation and biomagnification the drawback of persistence in soils and properties. aquatic sediments, bioconcentration in the Throughout the 1950s, consumers and tissues of invertebrates, moving up trophic most policy makers were not overly con- chains and affecting top predators. Many cerned about the potential health risks asso- chemicals that have been identified as endo- ciated with using these pesticides, as these crine disruptors are pesticides. Of these, were considered safer than the forms of 46% are insecticides, 21% herbicides and arsenic that were used and had killed people 31% fungicides; some of them were with- in the 1920s and 1930s (Wessel’s Living drawn from general use many years ago but History Farm, 1930). However, the indis- are still found in the environment (e.g. DDT criminate use of these highly persistent and atrazine) (Mnif et al., 2011). Endocrine organochlorines could generate a lot of disruptor compounds (EDCs) have been problems as highlighted by Rachel Carson in defined in 2002 by the World Health Organi- her 1962 book Silent Spring (Carson, 2002 zation (WHO): ‘An endocrine disruptor is an [1962]). The problems necessitated a search exogenous substance or mixture that alters for safer and more environmentally friendly the function(s) of the endocrine system and products, which ushered in the era of consequently causes adverse health effects smarter pesticides. Organophosphates and in an intact organism, or its progeny, or carbamates replaced the highly persistent (sub)populations’ (Combarnous, 2017). organochlorines (Table 1.1). In the 1930s, Pesticides with common modes of a German chemist Gerhard Schrader at IG action become more selective and generally Farben experimented with nerve poison lead to resistance problems. During the insecticides, organophosphates, which were 1990s research continued to find new mole- meant to be used as chemical warfare agents cules with greater selectivity and better during World War II (López-Muñoz et al., environmental and toxicological profiles. 2009). After World War II, the organophos- New families like strobilurins and azolone phate pesticides were synthesized in large were introduced as fungicides, as well as fip- quantities. Parathion was among the first roles and spinosyn as insecticides with lower marketed, followed by malathion and dosages in grams instead of kilograms per azinphosmethyl. These insecticides became hectare. The introduction of user-friendly more popular after many of the organochlo- and environmentally safer formulations has rine insecticides like DDT, dieldrin and hep- helped to combat the problem of resistance tachlor were banned in the 1970s. Although management. The integrated pest manage- less persistent in the environment, they are ment (IPM) approach has led to a reduction more lethal even at low dosages. in the load of synthetic pesticides because of Table 1.1. History of pesticides according to their generation. Category Example Period of marketing Group of pesticides Benefits Drawbacks Reference First Heavy metals such World War I; prior to Inorganic and organic Pest management Toxic to humans and agricultural Hummel, generation as As, Cu and Pb 1940 botanical compounds plants 1983 Second DDT, methoxychlor, Post-World War I; 1940 Organochlorines Highly effective for Highly persistent due to their Hummel, generation lindane onwards (widespread malaria control bioaccumulation and 1983 (synthetic) use, 1940–1960) biomagnification properties Dimethoate, Early 1950s Organophosphates and Less persistent in Acutely potent nerve toxins and Hummel, malathion; (widespread use, carbamates environment more lethal even at low dosages 1983 aldicarb, carbaryl post-1970s) Permethrin, 1970s Synthetic pyrethroids Knock-down activity They are axonic excitotoxins; can Hummel, cypermethrin and be combined with the synergist 1983 deltamethrin piperonyl butoxide (PBO) Third Insect growth By 1975 Juvenile hormones, chitin Disrupt and impede the Selective, less harmful to the Hummel, generation regulator synthesis inhibitors, life cycle of insects environment, compatible with 1983 moulting hormones, pest management systems Pesticides precocenes, and compounds that mimic their effects Microbials Late 1970s Bacillus thuringiensis (Bt) Toxins produced following No human health or Gaalaas Bt protein in 1990s ingestion environmental hazards Mullaney, 2018 Fourth Behaviour modifiers Late 1990s Sex attractants, mating Interfere with normal Volatile, specific, potent, and Metcalf and generation (Antifeedants, disruptors behaviour patterns, non-toxic Metcalf, pheromones) delay or prevent mating 1994 and producing offspring Fifth Promising leads Late 1990s Nereistoxin (a neurotoxic Model compound tor the Sensitive to sunlight, should be Hummel, generation (natural products, substance isolated synthesis of the kept in dark (Fourouzan and 1983 brain hormone from the marine insecticide cartap Farrokh-Eslamlu, 2017) antagonist) annelid Lumbriconereis heteropoda) Endocrine Initiated from first Man-made Target a critical life cycle Alter the normal functioning of the Mnif et al., disruptors generation until date stage of insects endocrine system of both 2011 wildlife and humans DDT, dichlorodiphenyltrichloroethane. 5 6 Chapter 1 the other components for pest management pesticides tends to be more intense and that are involved. Resistant varieties, genet- unsafe. The regulatory, health and education ically engineered