EJBR2018v8i2art70 ISSN 2449-8955 European Journal of Biological Research Review Article European Journal of Biological Research 2018; 8 (2): 70-83 Pesticides and food safety in Africa Annabella A. Adewunmi, Stephen O. Fapohunda* Department of Microbiology, Babcock University, Ilishanremo, Ogun State, Nigeria *Corresponding author: Stephen O. Fapohunda; E-mail: oystak@yahoo.co.uk ABSTRACT African countries have experienced nonconformance in the levels of pesticides for local consumption and export. Sometimes this leads to rejects and other forms of embarrassment from the importing countries. Economic challenge and lack of awareness heighten the overall cost of interventions in pesticide-related food safety management. For example, not a few of the infractions were a result of incorrect ways of pesticide application. The hazard accompanying chemical pesticide application has left open a window of biological alternatives which this review article seems to explore. The bio- alternatives, including green pesticides cancel out the adverse effect of residual chemicals on crops in farm and store and so make it more attractive. Keywords: Pesticides; Food security; Human health; Green-pesticide; Africa. 1. INTRODUCTION With an annual growth rate of 1.2%, the world population is estimated to reach 9 billion by 2050 [1, 2]. United Nations (UN) estimates, indicate that 95% of this increase in world population will occur in the developing countries and regions such as sub-Saharan Africa [3, 4], hence the need to step- up food production through increase in agricultural productivity. In Africa, crop losses caused by pests and diseases are two major barriers to increase in agricultural produce. This has led to the overzealous application of agrochemicals or pesticides to farm crops [2, 5], and this in turn has brought its own set of problems both to the farmers and the environment [6-10]. Pesticides are chemical substances used to kill, repel or control pests or used to prevent the damage the pests may cause. They are commonly used to control a variety of agricultural pests that are likely to damage farm crops and livestock, leading to a substantial reduction in farm productivity. Initially, with little insight into the long term effect, pesticides use seemed to be a success, until the incidence of resistance. Hitherto, easily controlled pests became uncontrollable due to adaptation leading to application of higher amounts to ensure effectiveness. The development of new chemicals resulted in undesirable side effects both to the farm produce and the environment [2]. 2. CLASSIFICATION OF PESTICIDES The level of toxicity by pesticides is classified by WHO [11] into 4 categories. These are; class I: very toxic, class II: toxic, class III: slightly toxic and class IV: unharmful. Some common categories of pesticides include insecticides, algicides, herbicides, biocides, fungicides, molluscicides, nematicides, and rodenticides. Pesticides are also grouped accor- ding to their chemical properties and these include the organophosphates, organochlorines (chlorinated hydrocarbons), carbamates and thiocarbamates, and pyrethroids (Table 1). Pesticides formulations and Received: 01 February 2018; Revised submission: 13 April 2018; Accepted: 30 April 2018 Copyright: © The Author(s) 2018. European Journal of Biological Research © T.M.Karpiński 2018. This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial 4.0 International License, which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited. DOI: http://dx.doi.org/10.5281/zenodo.1237542 71 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 presentation are in solid, liquid and gaseous forms. Just before the commencement of the current millennium, new techniques were introduced which are mainly biological (chemical free) and include microbial pesticides, biochemical pesticides and genetically modified organisms (GMOs) to salvage the situation of massive spread of agro-chemicals in agricultural fields. However, in the tropical regions of sub-Saharan Africa, the use of pesticides (agro- chemicals) is still the common practice. Chemical compounds such as DDT, HCH and Lindane that are environmentally recalcitrant are today banned from use in farms in developed countries of the world but tragically remains in popular use in developing countries [2]. The persistent pesticide residues therefore readily contaminate food and disperse in the environment. This is particularly prevalent in regions of lack of progress and economic challenge. Food quality becomes compro- mised and the environment adversely affected. Agbohessi [12] stated that the growing use of pesticide in agriculture contributes significantly to environmental pollution. Velisek [13] had viewed the role of pesticides to environmental pollution to be on par with emissions from industrial sources. Only about 0.1% of the farm sprayed pesticides reach the target pests, the excess is dispersed in the ecosystems where it contaminates the land, water, and air [14] thus endangering lives. Even at non- lethal doses, these chemicals disrupt the nervous system, liver, hormonal regulation, reproduction, embryonic development and growth in fish [15-20]. In South Africa, agricultural residue pesticides such as DDT, malathion, cypermethrin, aldrin, and endrin have been in the waters of Western Cape. They express bio-concentration and bio-magnification along the food value chain with possible dire health consequences to man and livestock [21]. In West Africa sub region, farmers use large quantities of pesticides, sometimes not appropriate in doses and efficacy [12]. The use of banned pesticides is not uncommon, for example, Endo- sulfanis still in use though it was banned in 2007 due to its ability to pollute the environment and poison human beings [22]. Endosulfan (6,7,8,9,10, 10-hexachloro 1,5,5a,6,9,9a-hexahydro-6,9-methano- 2,3,4-benzodioxathiepine-3-oxide, CAS No.115-29- 7) is an organochlorine pesticide rated as the most hazardous to the environment due to its non- biodegradable nature and possibility of bio- magnification as it migrates along the food chain [23]. Tihan, a milder and more environmental biodegradable pesticide has been developed to replace Endosulfan, however, the two are still in use simultaneously in West Africa [12] thereby putting not only the environment but also our food crop at perpetual risk. Sodium chlorate and sulphuric acid were in use in the 1940s and in the late 1940s synthetic pesticides such as DDT, BHC, Aldrin, Dieldrin, Endrin, Chlordane, Parathion, Captan, and 2,4-D were developed and widely used. These new pro- ducts were cheap, effective and generally accepted. However, in 1962, the problems and danger of the indiscriminate use of pesticides to the environment was highlighted. Even when many African countries are familiar with, and possibly signatories to many global initiatives like FAO code of conduct on distribution and use of pesticides, Codex, Cartagena Protocol, Montreal Protocol, Stockholm convention, needless application leading to environmental pollution and the concerns about health of living organisms still subsists. Reasons for these include inadequate expertise [24]; conscious use of obsolete pesticides [25] and different monitoring capacities that vary from one location to another [26]. In 1970s-1980s, many new products were born out of research including the popular and greatest selling herbicide ‘glyphosate’, third gene- ration insecticides and new spray treatments. From the 20th to the 21st century, an entirely new family of pesticides or agrochemicals has been birthed. Modern research and advances in chemistry has made these products safer, more selective and much more environmental friendly, with effective usage rate only requiring grams rather than kilograms per hectare [27]. These modern agrochemicals have helped farmers boost productivity significantly, particularly in regions like Sub-Saharan Africa (SSA) where crop yields have been low. In a Kenya survey, the commonly used insecticides on vege- tables included dimethoate (WHO II), used by 48% of farmers, lambda cyhalothrin (WHO II, 27%), cymoxanil (WHO II, 22%), cypermethrin (WHO II, 22%), cyfluthrin (WHO Ib, 20%), mancozeb (WHO U, 18%), and deltamethrin (WHO II, 14%). Lack of Personal Protective Equipment (PPE), reduced literacy level and geographical location contribute to 72 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 pesticide-related cost of illness (COI). When morbi- dities arise from such exposure, cultural therapists deploy milk, lemon juices, honey, and herbs [28]. 3. TYPES OF PESTICIDES There are various types of chemical pesticides. Their characteristics and mechanism of action are as shown in Table 1. 4. PESTICIDES AND FOOD SAFETY IN AFRICA Agriculture remains the major occupation in most African countries and dominated by small and medium holder farmers with minimal education. Pesticide use in Africa has therefore been reported as low compared to other continents. Agrow [30] reported a range of approximately 2-4% of global pesticide market of US$ 31. Similarly, Repetto and Baliga [31] reported average pesticide use in Africa per hectare as 1.23 kg/ha, while 7.17 kg/ha has been recorded in Latin America and 3.12 kg/ha in Asia. One conclusion could be that most farmers in Africa being small holder farmers, and their output in terms of food production is low, do not usually consider the use of pesticides [32]. Pesticides are preferably used on large scale, commercial farming of cash crops such as cotton, cocoa, oil palm, coffee and vegetables. The fact remains that whether pesticide use in Africa is low or not, the risk and impact arising from the toxicity of the chemicals where used, cannot be overemphasized. Previous studies have reported poor pesticide practices by African farmers [32-34] and these practices include use of unsuitable products, poor handling, wrong dosage, timing and targeting of application, non-calibrated equipment, and application equipment that is poorly maintained [35]. Others are the use of banned products, mixture of products, mixing with bare hands, splashing pesticides on crops using brushes or twigs, lack of minimal protective clothing and even tongue-testing to assess concentration strength has been reported [34, 36-38]. In 2018, South Sudan played host to a technical team from the UN due to the invasion of the farms in 8 states by army worm [39]. A cocktail of pesticides is being proposed which may go with the attendant consequences, if misapplied. This misuse of pesticide results not only in the control of the intended pests but also has serious impact on the operator, the farm crops and livestock, the health of the consumer, soil organisms, and contamination of the entire environment [40, 41]. United Nations report [42] has highlighted the growing health and environmental hazards from chemicals and stated that the potential cost of pesticide-related illnesses in sub-Saharan Africa between 2005-2020 could reach $90 billion. United Nations Environmental protection (UNEP) estima- ted the cost of lost work, medical treatment and hospitalization due to pesticide poisonings among small scale farmers in 37 African countries to be $4.4 billion. In 2010, Uganda's National Environ- ment Management Authority reported that each farmer loses 24.6 days per year due to pesticide poisoning, 9.4 days due to respiratory illnesses and 15.2 days due to skin infections [43]. In 2015, the EU banned some agricultural food items meant for export from Nigeria due to the presence of high levels of dichlorvos pesticide. The food items include beans, sesame seeds, melon seeds, dried fish and meat, peanut chips and palm oil [44]. The European Food Safety authority (EFSA) claimed that the rejected food items were found to contain between 0.03-4.6 mg/kg of dichlorvos pesticide while the acceptable Maximum Residue Limit (MRL) is 0.01 mg/kg. This pesticide is usually applied during storage while the products are being prepared for export. In 2013, EU issued fifty (50) notifications of border refusals to Nigerian beans exporters over high level of unauthorized pesticide. In 2015, EU issued thirteen (13) border rejections alert to the same beans exporters. Generally, between 2008 and 2013, there has been a significant number of border refusals of food imports by the EU due to non-compliance of exporting countries with its food safety standards, which amount to about 9233 rejections between 2008 and 2013 [45]. Fruits and vegetables are the most commonly affected product usually refused entry into EU markets as a result of the exporters failing to meet EU standards. The surveillance studies on vegetables in Ghana presented a mixed bag. While residues were found at concentrations not particularly considered a health problem with occasional exceedances in respect of chlorpyrifos, diazinon and permethrin [46], an earlier investigation by the Christian Aid [47] and 73 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 NPA [48] the use and misuse of pesticides indeed constituted a major threat to the lives of farmers because of exceedance of EU MRLs. Although raw agro produce are particularly primary targets, industrial products like soft drinks and fast foods are not spared [49, 50]. Table 1. Various types of pesticides (insecticides, fungicides and herbicides), examples, their characteristics and mechanism of action. S/No Type: Chemical Examples Characteristics Mechanism of action 1. Organophosphates • Chlorpyrifos • Dimethoate • Fenthion • Naled • Temephos • Trichlorfon - Made from phosphoric acid - Most are insecticides - They are highly toxic - It breaks down faster in the soil, food and feed These control pest by acting on the nervous system, interfering with the nerve impulse transmission, disrupting the enzyme cholinesterase that regulates acetylcholine (a neurotransmitter) 2. Organochlorines (chlorinated hydrocarbons) • Aldrin • Chlordane • Dieldrin • Endolsulfan • Endrin - Generally persistent in the soil, food and in human and animal bodies. - They can accumulate in fatty tissues - Traditionally used for insect control and mites. - They do not break down easily. - Some such as DDT and Chlordane are no longer in use because they stay in the environment for a long time They control pests by disrupting nerve impulse transmission 3. Carbamates and Thiocarbamates 1.Insecticides • Carbaryl (banned due to health risks) • Propoxur • Methomyl • Carbofuran • Thiodicarb 2. Herbicides • Barban • EPTC • Propham • Triallate 3. Fungicides • Nabam - They are made from carbamide acid - They are less persistent in the environment - Mild health hazards to human and animals especially the herbicide and fungicide range. However, health risk is higher with insecticides They control pest by acting on the nervous system, interfering with the nerve impulse transmission, disrupting the enzyme cholinesterase that regulates acetylcholine, with enzyme effect usually reversible 4. Pyrethrin (synthetic version of Pyrethrin, modified to increase stability in the environment) • Cyhalothrin • Cypermethrin • Deltamethrin • Esfenvalerate • Permethrin - Stable in sunlight (do not degrade quickly) Disrupts nerve impulse transmission (increases sodium flow into axon), which stimulates nerve cells and eventually causes paralysis Source [29]. 74 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 Acute or chronic exposure of humans to dichlorvos can have dire consequences. It inhibits an enzyme, acetylcholinesterase [51] with neurotoxic effects such as difficulty in breathing, diarrhea, abdominal cramps, vomiting, salivation, sweating, nausea, convulsions, dizziness, weakness, tightness in the chests, blurred vision, eye and skin irritation, eye pain, runny nose, wheezing, laryngospasm, cyanosis, and at high concentrations convulsion and coma. As at date, there is no conclusive information on the carcinogenic effects of dichlorvos on humans. Symptoms in animals include ataxia, salivation, dyspnea, tremors and diarrhea. Toxicological studies on animals showed an increase in the incidence of tumors of the pancreas, mammary glands and stomach. According to Varo [51], dichlorvos has been found to be a highly toxic pesticide. In a study to determine the residual levels of the commonly used dichlorvos on small and large scale vegetables farms in Lusaka, Zambia, it was reported that the levels of dichlorvos was significantly above the MRL [52]. Similarly, in Northeastern Nigeria, research showed that farmers and traders use locally formulated pesticide which contains high levels of dichlorvos (about 7.7% w/v) in trade [53]. Therefore, consu- mers of such vegetables and other commodities with such levels of dichlorvos residues in Zambia and Nigeria, and in Africa as a whole are at risk to the health issues outlined above in the long run, since they export to other African countries. 5. PESTICIDE STANDARDS REGULATION Just like drugs, pesticides are subject to regulation. The safety of pesticides is reviewed by the authorities before they are allowed to be used on crops. In Nigeria, the Standards Organization of Nigeria (SON) and NAFDAC are responsible for setting these standards, controls and enforcement. These standards are synchronized with the Codex Alimentarius (Codex Alimentarius Commission) which was established by FAO and WHO in 1963. The commission ensures coordination of all food standards work embarked upon by international governmental and non-governmental organizations. The use of pesticides is usually authorized only after a risk assessment has been done and checked that any residue remaining after correct use of the pesticide will not lead to any consumer concern. The potential residues on a harvested crop are regulated by a maximum residue level (MRL) which is set As Low As Reasonably Achievable; the ALARA principle [54]. MRL usually include wide safety margins that are well below the level that could pose any adverse effect on consumers’ health and safety. Maximum Residue Levels (MRLs) are part of Good Agricultural Practices (G.A.P). MRLs are primarily trading standards, which are applied to help ensure that residue levels do not pose unacceptable risks for consumers of such food. Pesticides regulation in the EU, is governed by Directives (EC) No 396/2005. This Directive which came into effect in 2008 establishes the MRLs of pesticides allowed in products of plants and animal origin intended for consumption, based on scientific evidence from risk assessments. This Directive replaced all pesticides standards among EU member states which existed prior to 2008. Figure 1 illustrates how residue levels are measured. The ADI and ARfD are obtained through animals such as mice testing. These are set based on the highest dose where no recognizable harmful effects are observed; the No Observable Adverse Effect Level (NOAEL). The international practice is that the NOAEL is divided by an uncertainty factor of at least 100 to compensate for potential differences between animals and humans; and for differences between individuals [54]. Since the NOAEL may differ for chronic (long term) and acute (short term) effects, the ADI and ARfD may be set at different levels. When MRLs are exceeded, it does not necessarily imply a risk to health but an indication that a pesticide has been incorrectly used. Food products which have residues exceeding MRL cannot be sold. When a farmer uses a pesticide according to the label instructions and Good Agricultural Practice (GAP), the residues in crop at harvest do not normally exceed the Maximum Residue Level established in the country of use. However, since MRLs are not harmonized world- wide, MRL exceedances can occur when products are exported to a country with a lower MRL for the specific pesticide and crop combination. In South Africa, according to Mutengwe [26] the implicated pesticides that exceeded established MRLs were imazalil (37.71%), prochloraz (28.69%), 75 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 and iprodione (5.74%). The unregistered pesticide residue most often found on grapes and avocados was also imazalil (62.23%) and, on nectarines diphenylamine (11.15%) and the exceedances of MRL values involved oranges (43.44%), avocados (27.87%), grapefruits (7.38%), and lemons (6.56%). This led to a change of mind and negative perception by the public and reconsideration by the government on how to control pesticide use globally. It is not in all cases that residues went as higher than the MRL set by regulating bodies as observed in the survey carried out in Sudan [55]; although high levels sometimes are controlled by biological means [56]. In Libya, organochlorines and other pesticides from the field, were detected in some fish at concentrations higher than the permissible limit, according to FAO where concen- trations were calculated in mg/kg BW of fish [57]. Figure 1. Measuring Residue levels [54]. Legend: NOAEL (No Observable Adverse Effect Level): the highest exposure level at which no adverse effects can be identified in tests. ARfD (Acute Reference Dose): a toxicological safety limit specifying the amount of a substance which can be ingested on a single day without any effects on the health of the consumer. ADI (Acceptable Daily Intake): a toxicological safety limit specifying the amount of a substance which can be ingested every day over an entire lifetime without any recognizable risks to the health of the consumer. MRL (Maximum Residue Level): a legally fixed maximum concentration for a particular active ingredient in a particular crop. A trade standard, intended primarily to check that a pesticide has been applied correctly. 76 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 6. HEALTH EFFECTS DUE TO CONSUMP- TION OF FOOD WITH PESTICIDE RESIDUES Pesticides are potentially toxic and hence are hazardous to humans and animals resulting in both acute and chronic health effects depending on the dosage and ways in which persons are exposed. Exposure can be through contact with the skin, ingestion or inhalation. When people consume food with large quantities of pesticides, above safe limits, it can lead to acute poisoning or long term health effects including cancers. Chronic toxicity occurs when subjected to small doses over a period of time. Imazalil is among the persistent pesticides on edible fruits such as grapes, with an allowed MRL of 5 mg/kg. When consumed over a long of time in concentrations above the MRL, it can cause morta- lity issues and significant brain enzyme depression [58]. The numerous suspected health effects that have been associated with chemical pesticides include dermatological, gastrointestinal, neurolo- gical, carcinogenic, respiratory, reproductive and endocrine effects [59-62]. In some cases can lead to hospitalization and death [59, 63]. Pesticide residues and food safety has also been an issue of concern from the consumers perspective, although the rating seemed to be far below food safety caused by bacterial pathogens. In 2011, a workshop organized by EU to capture opinions of stakeholders on food safety issues in fresh foods reported that consumers ranked bacterial pathogens as the first, followed by foodborne viruses, with Pesticides residues and mycotoxins taking the third and fourth positions respectively in the ranking [64]. This shows that though pesticide residues cause serious health effects on consumption of foods contaminated with them, other more serious causative agents such as bacterial pathogens and viruses are of more importance to the consumers and should as a matter of priority be the main focus. In the same workshop, these consumers proposed as control measures good agricultural practices, good hygiene practices and food safety management system certifications. 7. CURRENT TRENDS IN FOOD AND CROP PROTECTION In the last decade, there has been new development in food and crop protection. They are the genetic engineering of organisms, the organic- chemical-free agriculture and green pesticides. 1. Genetically modified organisms (GMOs) such as engineered soybeans, maize, and tomatoes came as a solution to food security and revolutionized agriculture [65]. These crops were modified to be tolerant to glyphosate, a common herbicide. South Africa in recent times delved into the development of alternative methods of pest control in order to reduce environmental levels of organic and inorganic pesticides. One of these developments is genetically modified (GM) crops, such as GM maize and cotton. More than 90% of farmers plant GM maize and cotton and South Africa is currently ranked 9th worldwide in planting GM crops [66]. There are many advantages of using GM crops for pest control. First, the crop is protected continuously in the field and the time used to detect pest infestation is reduced. Secondly, there is protection of the plant part that is difficult to reach with insecticide spraying. Thirdly, control is no longer affected by the weather. The crop is protected even if the field conditions are not suitable for aerial or ground application of insecticides [67]. Also, there is general reduction in insecticide use. Although GM crops have become a major component of insect control strategies, a proper perspective of its potential demands a close look at limitations and uncertainties that may reduce its future impact on agriculture such as development of resistance of target pest and effect on potential non-target organism [21]. Secondly, sprays of the bacteria, Bacillus thuringiensis, have been used to control pests. The crystalline protein produced by these bacteria kills certain insect species and have limited effects on most non-target species [68]. The use of commercial Bacillus thuringiensis sprays have, however, been limited due to their relatively high cost, poor crop coverage, rapid environmental inactivation, and less desirable level of pest control, when compared with less expensive conventional chemical insecticides [69]. Toxin-encoding genes from B. thuringiensis have been expressed in transgenic crop plants, providing protection from some key pests [68]. In South Africa two of these key pests of maize are the lepidopteran stem borers, Busseola fusca and Chilo partellus which are of economic 77 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 importance throughout Southern and Eastern Africa. Large-scale planting of Bacillus thuringiensis (Bt) crops to control these pests started in South Africa in 1998. Bt cotton for control of the boll worm complex, particularly the African bollworm, Heli- coverpa armigera was also introduced into South Africa during the same period. Generally, there is reduction in insecticide use. For example, reduced insecticide use was reported from the Makathini Flats region of Kwa-Zulu Natal, South Africa, where 95% of smallholder (1-3 hectares) cotton producers grew rain-fed Bt cotton. Farmers that adopted Bt cotton reported reduced insecticide use and a reduction in labour [70]. However, in India there have been reports of Bt cotton failures and claims of mass suicide due to significant financial losses by the farmers [71]. The government of India claims the pink bollworm, a major pest that attacks cotton crop has already developed resistance to the new technology, as observed in 2015/16 crop year, where most cotton crops were significantly damaged by the bollworm and whitefly in most of the farms in India [72]. In 2002, after field trials with Bt cotton became successful, Indian government officially approved the commercial release of Bt cotton to farmers and by 2010, almost all the farmers in India had migrated from non-Bt cotton to Bt cotton because of the advantages of high income gained through better pest management at lower cost. Expenditure on chemical pesticides was drastically reduced. Bt cotton technology gave a boast to Indian cotton business and helped India come to be the second largest producer of cotton in the world. The recent development of pest resistance to Bt cotton technology has become a serious threat to Indian cotton business. Burkina Faso in Africa, has completely rejected the intro- duction of Bt Cotton technology to its farmers both for political and economic reasons. Herring and Rao [71] in their study of Bt cotton failure reported that each hybrid of cotton consist of different germ plasm and the mechanism for obtaining the Bt transgene which confer insect resistance trait on them is not exactly the same, leading to variations in results in yields comparisons. 2. Organic agriculture: The development of organic agriculture which respects the normal functioning of the ecosystem, avoids the use of pesticides and leads to food free of synthetic chemicals and thus healthier. However organic agriculture is limited in scope and does not have potential for mass production needed to feed the world [73]. Organic agriculture thus improves food safety but cannot cope with food security. 3. Green pesticides: These are nature-oriented and beneficial pest control materials used to control pest populations thus increasing food production. Green pesticides are botanical and natural materials that are used to reduce pest population and increase food production. They are safe and eco-friendly, and are compatible with environmental components than synthetic pesticides. They include substances such as plant extracts, hormones, pheromones, and toxins of organic origin. It also includes many other aspects of pest control such as microbial, entomophagus nematodes, plant derived pesticides, secondary metabolites of microorganisms and mineral-based controls used to express resistance to pests. More recently, under this umbrella of green pesticides, are extremely biodegradable synthetic and semi- synthetic products in pest management. Green pesticides are attractive alternative to chemical pesticides because they reduce the negative impacts to human health and the envi- ronment, the reason it is now a contemporary issue [6]. However, their use in Nigeria and other parts of Africa is still hampered by some challenges. First, there is still no appropriate application technology particularly the use of oils and dust formula- tions [75]. Secondly, the residual effect of green insecticides is short-lived compared to synthetic chemicals, hence repeated applications are required to obtain reasonable crop protection. Thirdly, they are yet to be available to farmers in commercial quantities. Fourthly, there is the problem of farmers’ acceptability of this new technology in pest control [76] which calls for training and promotion of the use of these green pesticides in integrated pest management by the relevant authorities. Awareness campaigns and farmer-friendly capacity building can resolve most of these issues. 78 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 Table 2. Types of green pesticides (botanicals, biological and mineral-based controls). Types Description Target 1. Botanical pesticides i. Neem ii. Pyrethrium iii. Horticultural oils iv. Dormant & summer oils v. Traditionally used botanical insecticides e.g. Nicotine, Rotenone, Ryania, Sabadilla, and pyrethrum These are plant extracts used as insecticides to control insects. They are usually harvested by macerating plant tissues high in active ingredients and distilling the specific compound. The advantage of using botanical pesticides is their rapid degradation in the environment. Insecticidal extract (namely azadirachtin) from seed and bark of the Neem tree (widely found in India), which act as insect repellant, anti-feedant and interferes with growth. Neem can also be used as systemic insecticide when applied directly to the soil and taken up by the plant and transported to the shoots and leaves. Multiple applications are required as it degrades easily (with 3-7 days). Easily broken down by stomach acid of mammals, hence toxicity is very low except if application doze is increased above recommended on label. They work by disrupting insect feeding and egg laying. Egg covered with oil suffocates the developing pest. Have minimal phytotoxic effects on plants when used properly. They can be applied to plants during growing season. Nicotine and tobacco have long history of use and is very effective against insects but also has high toxicity against mammals. Hence being considered for regulatory phase out. Rotenone made from isoflavonoid, an extracts of the tropical legumes Derris and Lonchocarpus. It is highly toxic to insects and fish but also moderately toxic to mammals. Rotenone has been widely used on ornamental crops, but has been phased out in the US and Canada during regular re-evaluation. However, its use is being continued in other countries. Sabadilla is an extract from the seed of Schoenocaulon officinale, a neo-tropical lilywhich contains veratridine alkaloids with a neurotoxic mode of action. It high toxicity as contact insecticide and low mammalian toxicity. Ryania is an extract from Ryania sp., a South American shrub. It contains the active ingredient di- terpene alkaloid ryanodine, which is a contact and ingested insecticide against horticultural and ornamental crop pests. Pyrethrum is an extract of Chrysanthenum cinerariaefolium plant. It is toxic to both mammals e.g. cats, fish and also insects Effective against caterpillars, flies, whitefly, scales, and aphids. Effective against soft bodied garden pest such as scales, whitefly, mealybugs and thrips but ineffective against mites. All insects Effective against eggs, nymph, larva, and adult leaf rollers, aphids, mites, and scales. Effective against agricultural insects such as lepidoptera, leafhoppers, and thrips. Also mosquitoes, fleas, flies, moths ants bees, 79 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 Types Description Target 2. Natural (biological) products i. Bacillus thuringiensis (Bt) ii. Beauveria bassiana iii. Nematodes iv. Nosema v. Fermented microbes e.g. abermectin These are living organisms used to control pests and are called biological controls or biological agents. When a microorganism is packaged and sold to control a pest, it is legally considered a bio pesticide and is regulated as such [74]. However, Nematodes are not regulated pesticides though equally used as bio pesticides. Bt is a naturally-occurring bacterium. Commercial Bt products are formulations of the bacterial toxin and are non-living. Bt can be sensitive to ultraviolet light (sunlight) and is most effective when applied in overcast conditions or late in the day. Most Bt products degrade within 24 hours regardless of sunlight conditions or temperature, giving them a very short period of effectiveness once they have been applied. Multiple applications are thus needed for sufficient management of pests. Beauveria bassiana is a soil borne fungus. It is applied to the target pest as a spore. Once the spores have contact with the insect exoskeleton, they grow hyphae that secrete enzymes, which in turn dissolve the cuticle. These fungal hyphae then grow into the insect, feed on its body tissue, produce toxins, and reproduce. It takes up to seven days for the insect to die. If moist conditions (92 percent humidity or greater) are present during this time, B. bassiana will “bloom” and release more spores into the environment to repeat the cycle on other pest insects. Nematodes are multi cellular organisms commonly referred to as microscopic worms. Nosema are protozoans. Abermectin, is a fermented product of Streptomyces avermitilis Feeds on the larval stages of insect pests such as mosquitoes, Colorado potato beetles, and cabbage loopers. Bt. var. kurstakifeeds on caterpillars, commonly found on vegetables and fruits. Effective against thrips, aphids, whitefly, caterpillars, beetles, and subterranean insects like ants and termites Effective against soil-dwelling insect pests such as root weevils and cutworms, and can also control pests that pupate or hibernate in the soil such as codling moth larvae Nosema locustae is used to manage grasshoppers Used in baits for household insect pests. The fermented product is very toxic to caterpillar pests such as cabbageworm, cabbage looper, diamondback moth, armyworm, and cutworm, as well as fruit flies such as spotted wing drosophila. 3. Mineral Controls Insecticides developed from mineral resources mined from the earth. The toxicity of mineral-based insecticides depends on the chemical properties of the mined elements. Some, such as sulfur are registered for organic use and have relatively low toxic effects on people and non-target organisms. In 80 | Adewunmi & Fapohunda Pesticides and food safety in Africa European Journal of Biological Research 2018; 8 (2): 70-83 Types Description Target i. Diatomaceous earth ii. Elemental Sulphur iii. Iron phosphate iv. Kaolin v. Soap contrast, lead arsenate is a natural mineral product that was cancelled as a pesticide in 1988 due to its toxicity and persistence in the environment. Fine particle dust comprised of fossilized diatoms. Elemental sulfur is a finely ground powder that can be applied either as a dust or a spray. This mineral is one of the oldest pesticides known, and reported pest resistance is rare. Sulfur acts as a metabolic disruptor on insects. They come in pellets and liquid formulations. Kaolin is fine clay that is sprayed on plant foliage or fruit to deter feeding and egg laying of insects. Natural soaps are derived from plants or animal fat. Effective against slugs and soil-dwelling insects Effective against aphids, thrips, and spider mites Effective against slugs and snails when combined with baits. Effective against apple maggot, codling moth, and leafhoppers. Effective against aphids, scales, whitefly, mealy bugs, thrips, and spider mites. Source: [6]. 8. CONCLUSION From the fore-going, there are several evidences that green pesticides are generally safe and effective, although they come with their challenges as already highlighted above. In spite of the seeming shortcomings, green pesticides still remain the attractive option and an alternative for the future. Vendors, consumers and policymakers need to be made aware of the higher quality and safety of products treated with green pesticides. 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