Smart Agrochemicals for Sustainable Agriculture

Smart Agrochemicals for Sustainable Agriculture proposes products that fulfill the need for chemicals that provide a sustainable delivery system for nutrients necessary to maximize the production of agricultural animals and plants while producing the smallest possible environmental footprint. This book addresses all aspects related to the production process, including chemical formulas, stability of formulations, and the application of the effect of its utilization. Over the past decade, biobased chemicals have received significant attention as candidate resource materials in fertilizers and agrochemicals production due to their renewability.

Substitution of conventional raw materials with biobased requires a new approach towards the development of technology. On the other hand, the use of biobased chemicals, such as biostimulants, bioregulators and biofertilizers offers a new palette of products that are natural, thus their application does not pose an impact on the environment (residues) or cultivated plants.

• Presents ideas for new products that provide appropriate nutrition while limiting environmental footprints
• Includes a full range of the production process, from chemical formulas to establishing the stability of formulations, applications and effects
• Offers a host of new products that are natural and whose applications do not negatively impact the environment nor cultivated plants

• Language: English
• Publisher: Academic Press
• Release date: Dec 1, 2021
• ISBN: 9780128170373

Book preview

Chapter 1

Conventional agrochemicals: Pros and cons

Magdalena Jastrzębskaa, Marta Kostrzewskaa, Agnieszka Saeidb

aUniversity of Warmia and Mazury in Olsztyn, Olsztyn, Poland

bDepartment of Engineering and Technology of Chemical Processes, Faculty of Chemistry, Wrocław University of Science and Technology, Wrocław, Poland

Abstract

This chapter introduces to conventional agrochemicals that have played a remarkable role in modern agriculture. It starts by defining them as commercially produced, usually synthetic, chemical compounds used in farming and recalling their contribution to the increase in agricultural productivity since the middle of the 20th century. It then emphasizes fertilizers and pesticides as key types of conventional agrochemicals and presents their advantages and disadvantages, and benefits and risks connected with their use, including health and environmental problems. By the end of the chapter, future prospects for conventional agrochemicals are presented, as well as recommendations for minimizing hazards arising from their use.

Keywords

Conventional agrochemicals; synthetic fertilizers; pesticides; food supply; human health disorders; environment contamination; biodiversity harm

1.1 Introduction

The term agrochemical is evolved by the contraction and combination of words agricultural and chemical, and is a generic term used for the various chemical products typically used in agriculture (Gupta and Hussain, 2014). The definition by Organization for Economic Cooperation and Development (OECD) specifies agrochemicals as commercially produced, usually synthetic, chemical compounds used in farming (OECD, 2000). These substances essentially help in intensifying crop production and to reduce the effects of pests and parasites on farm animals. Agrochemicals refer to the broad range of mineral fertilizers and pesticides, but they can also include soil conditioners, antibiotics, hormones, and other chemical substance used to help manage an agricultural ecosystem, or the community of organisms in a farming area (Lokesh Babu et al., 2017).

At present, in juxtaposition with bio-based agrochemicals of the new generation (biofertilizers, biopesticides, biostimulants), the abovementioned synthetic-based products are understood as conventional agrochemicals (Chojnacka, 2015).

There is no denying that conventional agrochemicals have played a remarkable role in modern agriculture (Baweja et al., 2020). In combination with genetically improved varieties of crop species, they have made important contributions to the successes of the green revolution started at mid of 20th century. The usage of agrochemicals became a great leap in agricultural productivity and has helped to increase the food supply for the rapidly increasing population of humans on Earth (Majeed, 2018; Nyamangara et al., 2020; Xiang et al., 2020). Now the times have been changed and the green revolution is not as green as it was earlier (Baweja et al., 2020). Although the significance of conventional agrochemicals in enhancing the agricultural yield is still self-evident, the harmful effect of these products on the environment and health is also carefully considered and treated as the major limitation on their use.

A key question appears: whether the hazards/risks of using conventional agrochemicals overtake the benefits? The answer is possible only after contrasting the expected gains with the potential losses. This paper focuses on such a confrontation for the key types of conventional agrochemicals, that is, fertilizers and pesticides.

1.2 Fertilizers

Most of nutrients essential for plant growth and development have to be uptaken from the soil. Soil nutrient abundance or nutrient availability does not always meet the nutritional needs of plants, especially those of high production potential. In such cases, a replenishment of nutrients from the external sources is necessary (Aziz et al., 2019). It is usually carried out by applying fertilizers. A fertilizer is any material, organic or inorganic, natural or synthetic, that supplies plants with the necessary nutrients for plant growth and optimum yield (Hati and Bandyoopadhay, 2011). Organic fertilizers are natural materials of either plant or animal origin, including livestock manure, green manures, crop residues, household waste, compost, and woodland litter (Gupta and Hussain, 2014). Inorganic fertilizers are compounds mined from mineral deposits with little processing (e.g., Chilean sodium nitrate, mined potash, or phosphate rock), or industrially manufactured through chemical processes (e.g., diammonium phosphate, ammonium nitrate, ammonium sulfate, single super phosphate, muriate of potash) (Gupta and Hussain, 2014). Urea is a synthetic organic fertilizer, an organic substance manufactured from inorganic materials but it is generally categorized as an inorganic fertilizer because of its rapid hydrolysis to form ammonium ions in soils (Hati and Bandyoopadhay, 2011).

Although some authors classify organic/natural fertilizers as conventional fertilizers (Mishra et al., 2013), however, according to the OECD definition of agrochemicals, conventional fertilizer agrochemicals are understood as commercial synthetic fertilizers, mainly inorganic. They are also called chemical, artificial, or mineral fertilizers (Jaja and Barber, 2017).

Organic and mined inorganic fertilizers have been used for many centuries, whereas chemically synthesized fertilizers made an entrance at the end of the 19th century and paved the way for modern agricultural production (Sabry, 2015), while significantly supporting global population growth (Gupta and Hussain, 2014).

Commercial fertilizers are used in modern agriculture to correct known plant-nutrient deficiencies, to maintain optimum soil fertility conditions, to provide nutrition, which aid plants in withstanding stress conditions, and to improve crop quality (Hati and Bandyoopadhay, 2011). The main nutrients supplied to agricultural soils are nitrogen (N), phosphorus (P), and potassium (P). In addition to this, fertilizers containing secondary nutrients (Ca, Mg, S) and micronutrients (Fe, Mn, Zn, Cu, Mo, B) are also applied per the deficiency of these nutrients in soil and crop requirement. Inorganic fertilizers vary in appearance depending on the process of manufacture. The fertilizer particles are available in many different sizes and shapes (crystals, pellets, granules, or dust), and the fertilizer grades can include straight fertilizers (containing one nutrient element only, e.g., urea, single super phosphate, muriate of potash), compound fertilizers (containing two or more nutrients usually combined in a homogeneous mixture by chemical interaction, e.g., diammonium phosphate, ammonium sulfate), and fertilizer blends (formed by physically blending mineral fertilizers to obtain desired nutrient ratios). Nutrients can be applied to the soil, foliar sprayed, added as a seed treatment, or through fertigation (fertilization + irrigation) (Saeid and Jastrzębska, 2017). Inorganic fertilizers dissolve fully or sparingly in water or in the soil–water system and release the nutrient(s) in the ionic form, which is absorbed by the plants (Hati and Bandyoopadhay, 2011). Some fertilizers like urea, after application to soil undergo a chemical transformation before releasing the nutrients in plant available form.

Current world fertilizer nutrient (N + P2O5 + K2O) agricultural use is 188.2 (108.7 + 40.6 + 38.9, respectively) million tons (FAO, 2018). Asia has the largest share of this quantity (55.2%), followed by the Americas (27.1%), Europe (12.3%), Africa (3.5%), and Oceania (1.9%). The global use of fertilizers is highly unbalanced. On average worldwide, per 1 hectare of cropland 69.71 kg N, 26.04 kg P2O5, and 24.92 kg K2O are used in the relevant mineral fertilizers. However, in many African countries, such as Central African Republic, Niger, Congo, the Democratic Republic of the Congo, and Uganda, less than 1 kg/ha of nitrogen is applied annually, while the use over 300 kg N/ha in Egypt and over 200 kg N/ha in China (mainland), United Arab Emirates, Luxemburg, and Belgium was noted in 2018. Both overfertilization and fertilizer underutilization cause specific problems in the regions of occurrence. It has been estimated earlier that the overfertilization with N in China, could potentially double yields if used on more than a million ha of cropland in sub-Saharan Africa (Bindraban et al., 2015).

1.2.1 Advantages and benefits

The main advantage of using conventional synthetic fertilizers is that they dissolve readily in water and nutrients are immediately available to plants. This immediate efficacy is especially beneficial to dying or severely malnourished plants (Sabry, 2015). What is more, these fertilizers contain precise and guaranteed levels of nutrients, in forms that are easy to uptake and assimilate by the plants, so it is possible to calculate and provide the plants with the exact amount of the element (Hati and Bandyoopadhay, 2011). The core benefit attributed to the use of conventional fertilizers, that is, obtaining a high yield of good quality, is rooted in this advantage. Emphasis should be placed on the facts that the application of synthetic fertilizers must comply with the recommendations (right source, right rate, right time, right place), and that these products are easy and efficient (Sabry, 2015), but not the only/exclusive way to achieve production and quality purposes.

However, it is commonly generalized that at least 30–50% of crop yield is attributable to commercial fertilizer nutrient inputs, which some find a conservative estimate (Stewart et al., 2005; Aziz et al., 2019). According to other estimates, almost 50% of the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use (Gupta and Hussain, 2014). Furthermore, meeting the expected future food demand (population growth) without a significant increase in food prices is believed to be possible only through the use of chemical fertilizers (Aziz et al., 2019). The use of synthetic fertilizers, especially nitrogen ones, is also encouraged by the fact that it usually brings a quick economic response (Alem et al., 2018).

Good plant nutrition guaranteed by chemical fertilizers enhances the nutritional value of crops and, in turn, improves animal and human health (Bindraban et al., 2015). For example, reasonable use of N, P, K, and S fertilizers increased protein concentration in cereals and pulses, oil concentration in oilseed crops, starch concentration in tubers, and concentration of essential amino acids and vitamins in vegetables (Wang et al., 2008). A mineral fertilizer strategy represents a rapid and effective way for the biofortification of food crops in micronutrients (Saeid and Jastrzębska, 2017).

Synthetic fertilizers are also an easy measure to quickly replenish the soil nutrient reserves (Mafongoya et al., 2006). Their depletion due to the removal along with the harvest of high-yielding crop varieties is one of the components of so-called soil fatigue (Wolińska et al., 2018) or soil sickness (Cesarano et al., 2017).

The use of synthetic fertilizers is seen as a remedy for nutrient mining and consequent land degradation in smallholder cropping systems in developing countries, where fertilizers are not or hardly used at all. Here, the role of synthetic fertilizers in the coming decades will be to help increase food production to feed a growing population without significantly increasing the area under agricultural production (Nyamangara et al., 2020).

The indirect positive effect of mineral fertilizers on soil structure has also been mentioned. The aggregating action from enhanced root proliferation and greater amount of decaying residues from well fertilized crops makes soil more friable, easier to cultivate and more receptive to water (Isherwood, 1998). In effect, the larger amount of plant residues remaining in the field after harvest also has a fertilizing effect and supports carbon sequestration in the soil (Ge et al., 2018).

The advantages of conventional fertilizers also include the fact that they are a concentrated source of nutrients on a weight basis, which reduces product bulk, and thus reduces transportation costs per weight unit of nutrient and facilitates storage (Hati and Bandyoopadhay, 2011). The incorporation of inorganic fertilizers into the soil is easy, making their application less labor-intensive, which gives farmers extra time for other tasks (Gupta and Hussain, 2014).

1.2.2 Disadvantages and risks

Although chemical fertilizers are very important for agriculture, there are several negatives to their use. They are, however, mainly connected with the excessive, imbalanced and prolonged application.

The rapid nutrient release from synthetic fertilizers considered their primary advantage, can lead to plant desiccation (burning) by the chemical salts they contain when too heavy doses of fertilizers are applied close to the plant roots or on the leaves (Hati and Bandyoopadhay, 2011). Excessive and imbalanced fertilization may affect all elements of the environment.

When the N supply exceeds the crop demand, several physiological responses occur that result in crop yield reduction and poor quality of the products. Nitrogen overfertilization causes changes in the anatomical structure of plant cells. A large part of the produced carbohydrates is converted to the protoplasm, and less is left to build cell walls (reduced synthesis of cellulose, hemicellulose, lignin, etc.). The cells formed are elongated with thin walls and a large amount of protoplasm. Increased vegetative growth is followed by reduced number of inflorescences, reduced flower bud initiation, and reduced fruit set (Albornoz, 2016). Such plants are more susceptible to pests (especially aphids) and pathogens (especially rust pathogens), and they also lodge more easily, which makes harvest more difficult. Deterioration of the product quality can be manifested in reduced organoleptic attributes (color, flavor, aroma, appearance), reduced content of other mineral nutrients (e.g., Cu), reduced synthesis of secondary metabolites (anthocyanin, vitamins), and increased nitrate content in the tissues. The latter poses a threat to the health of people and animals consuming overfertilized plants. In the presence of amines in the digestive tract, nitrates are converted to carcinogenic nitrosamines (van Maanen et al., 1998). What is more, the nitrites coming from the reduction of nitrates are absorbed into the blood where they react with the hemoglobin to cause methemoglobinemia, which damages the vascular and respiratory systems, causing suffocation and even death in extreme cases (when blood methemoglobin level is 80% or more) (Sabry, 2015). Infants under 6 months of age are particularly susceptible to methemoglobinemia (Viršilas et al., 2019).

Negative effects of phosphorus fertilization on crops and their yields are mentioned as the possibility of binding some microelements (e.g., Zn) by phosphates, which limits the possibility of their uptake by crops (Mandal and Mandal, 1990). Potassium (K) from fertilizers is commonly taken up by crops in excess (luxury consumption) (Moterle et al., 2016). This results in lower absorption of other metallic elements, such as Na, Ca, and Mg (ionic antagonism) (Daliparthy et al., 1994). A decrease in the magnesium content of fodder plants is one of the most adverse effects of overfertilization with potassium, as it leads to the occurrence of a metabolic disease called grass tetany in ruminant livestock (Penrose et al., 2020).

Excessive use of single-component N, P, and K fertilizers may induce secondary nutrient and micronutrient deficiency in the soil (Bindraban et al., 2015), unsustainable crop yields (Hati and Bandyoopadhay, 2011), and finally result in nutrient malnutrition, commonly known as hidden hunger (Saeid et al., 2019). Hidden hunger is defined as alarming high across several countries in sub-Saharan Africa and South Asia (Ritchie and Roser, 2017).

An important limitation of synthetic fertilizer use is that in reality nutrients do not all end up in the plant (Bindraban et al., 2015). According to estimates up to 70% nitrogen, 90% phosphorus, 70% potash, and 10% micronutrients (Fe and Zn) of applied conventional mineral fertilizers are lost to the environment or temporarily accumulate in the soil due to different soil dynamics (Aziz et al., 2019). This is followed by potentially lower yields, financial losses and negative environmental consequences.

Excessive or imbalanced application of fertilizers to the soil can have some negative effect on soil properties (Hati and Bandyoopadhay, 2011). Some studies have shown that the continued use of fertilizers, especially N fertilizers, can accelerate soil acidification and reduce base saturation, cation exchange capacity, soil aggregation, water-holding capacity, hydraulic conductivity, total porosity, and resistance to water, but increase soil bulk density and compaction (Cai et al., 2015; Ge et al., 2018; McLaughlin et al., 2011).

Overuse of chemical N fertilizers, such as ammonium sulfate, ammonium nitrate, and urea, is one of the main reasons for soil acidification (Cai et al., 2015; Conyers et al., 2011; Zhou et al., 2014). The generation of protons from the oxidation of NH4+ to NO3− (nitrification) and through urea hydrolysis is well summarized in the literature (Barak et al., 1997; De Vries and Breeuwsma, 1987). The form of P fertilizer added to the soil can affect soil acidity, principally through the release or gain of H+ ions by the phosphate molecule depending on soil pH (McLaughlin et al., 2011). Single superphosphate and triple superphosphate are declared to cause soil acidification due to reaction products being very acidic. The form of S fertilizer added to soil can affect the soil acidity, principally through the release of H+ ions by the addition of elemental S (S⁰) or thiosulfate (S₂O3²−, in ammonium thiosulfate).

When fertilizer N is applied at rates more than the optimum, increased residual inorganic N accelerates the loss of soil organic matter through its mineralization (Singh, 2018). Dramatic loss of inorganic carbon by N‐induced soil acidification was reported from China (Raza et al., 2020). This phenomenon is explained by the fact that soil acidification is neutralized by soil inorganic carbon and carbon dioxide (CO2) is released into the atmosphere.

Overly heavy applications of commercial fertilizers can build up to toxic concentrations of salts in the soil, thus creating chemical imbalances (Hati and Bandyoopadhay, 2011). When the monovalent NH4+ ion from ammonium containing or forming fertilizers accumulates in soils in large amount it becomes a dominant exchangeable cation and like Na+ it favors dispersion of soil colloids (Haynes and Naidu, 1998). In many cases, the application of K fertilizer alone particularly in humid temperate region decreases the aggregate stability of the soil owing to an increase in the proportion of exchangeable cations present in monovalent form and leaching of Ca and Mg. The use of fertilizers more than the recommended amounts may cause formation and accumulation of mineral salts of fertilizers that lead to the compaction layer and soil degradation in the long-term (Massah and Azadegan, 2016). High compaction decreases porosity and aeration while increasing bulk density and soil penetration resistance. Furthermore, root development and plant growth will be limited by reducing water and nutrient uptake.

Some chemical fertilizers may contain heavy metals or other toxic elements. In general, N and K fertilizers contain very low levels of contaminants, whereas P fertilizers often contain significant amounts of Cd, Hg, Pb (McLaughlin et al., 2000), and high concentrations of radionuclides (Savci, 2012). Although the permissible contents of these elements in fertilizers are nowadays legislated, they can accumulate in the soil when fertilizers are used for a long time and then can enter the food chains (Savci, 2012). The chemical studies show that high N rates of fertilization result in the formation of carcinogenic nitrosamines in soil environments (Barabasz et al., 2002).

The addition of synthetic fertilizers and changes in physical and chemical soil properties they cause may affect the amounts, activity, and diversity of soil organisms (Bünemann et al., 2006; Massah and Azadegan, 2016; McLaughlin et al., 2000; Tripathi et al., 2020). When applied at high rates, ammonium and urea fertilizers can inhibit soil microorganisms due to ammonia toxicity and increase in ionic strength (de Graaff et al., 2019; Omar and Ismail, 1999). A negative effect of N additions on microbial biomass was reported, and the reduction of microbial and fungal biomass became more evident as N load and duration of fertilization increased (Treseder, 2008). Some research has found that synthetic N fertilizer application decreases soil’s microbiological diversity or alters its natural microbiological composition in favor of more pathological strains (Paungfoo-Lonhienne et al., 2015; Zhou et al., 2017). According to Barabasz et al. (2002), high N rates reduced the number of bacteria and actinomycete species, but the change in the number of fungal species was negligible. It was also demonstrated that high mineral N fertilizer rates evoked recession of bacteria of the genera Arthrobacter and Streptomyces by 50% on average and complete eradication of bacterial genera Azotobacter, Rhizobium, and Bradyrhzobium, that is, nitrogen-fixing bacteria. On the other hand, a rise in the number of microorganisms and biomass of the genera Eubacterium, Pseudomonas, and Bacillus, and fungi of the genera Aspergillus, Fusarium, Penicillium, Verticillium, and others was noted. Moreover, a considerable reduction of arbuscular mycorrhizal fungi infectivity potential caused by high levels of N and P provided by mineral fertilization has been reported (de Souza and Freitas, 2018).

Chemical fertilizer use can result in a reduction in some larger soil organisms abundance, but these effects are relatively short-lived and occur only at the site of the fertilizer application band. The researchers have presented the toxic effects of urea (Abbiramy et al., 2013a; Dash and Mohapatra, 2018), superphosphate (Abbiramy et al., 2013b; Shruthi et al., 2017), and NPK fertilizer (Bhattacharya and Sahu, 2014) on earthworms upon direct contact. Inorganic fertilizers can also reduce species richness and abundance of microarthropods and earthworms due to acidification (Betancur Corredor et al., 2020). The abundance and diversity of soil microarthropods have been reported to decline following the application of nitrogenous fertilizer to soil (Gardi et al., 2008; Siepel and Van de Bund, 1988). Significant decreases in nematode abundance were reported after the application of phosphate fertilizer (Ikoyi et al., 2018; Zhao et al., 2014).

High doses of mineral NPK fertilization may lead to changes in the species composition of plant communities, mainly toward the impoverishment of biodiversity. In meadows, the increase in green mass and hay yield due to chemical fertilizers is followed by its relatively low feeding value (Barabasz et al., 2002). In croplands, high rates of mineral fertilizers, especially N ones, usually favor the expansion of nitrophilous competitive weeds while promoting the eradication of oligotrophic species from the communities (Andreasen and Streibig, 2011; Arslan, 2018; Fried et al., 2009).

Synthetic N, P, and K fertilizers easily leach into groundwater and increase their toxicity, causing potable water contamination (mainly by nitrates and nitrites) (Sabry, 2015). Fertilizer nutrients that leach into streams, rivers, lakes and other bodies of water facilitate eutrophication of these aquatic ecosystems (Barabasz et al., 2002; Hati and Bandyoopadhay, 2011). This process is well recognized and described in the literature (Yang et al., 2008). Excessive development of certain types of algae (including cyanobacteria) not only disturbs the aquatic ecosystems but also becomes a threat to animal and human health (Barabasz et al., 2002; Zanchett and Oliveira-Filho, 2013). There have also been economic impacts through damage to fisheries, and impacts on the value of real estate and tourism in affected areas (Pretty et al., 2003).

Improper use of N fertilizers can lead to volatilization loss of ammonia under high soil pH and also emission of nitrous oxide because of denitrification under anaerobic conditions (Jiang et al., 2017). Globally, up to 64% (an average of 18%) of N applied in synthetic fertilizers was lost as ammonia (NH3) (Pan et al., 2016). NH3 plays an important role in acid deposition and contributes to the indirect emission of nitrous oxide (N2O). Nitrous oxide (N2O) is one of three main greenhouse gases emitted through anthropogenic activity, and more than half of global N2O emissions are from agricultural soil management, include applications of synthetic mineral N (Ogle et al., 2020).

When excessive doses of fertilizers are used, the economic return decreases, so farmers can make losses (Huang et al., 2008). In addition, damage to water quality and aquatic ecosystems and changes in atmospheric composition due to fertilizer overuse are at the cost of the government, the environment and the health of the people (Chen et al., 2011).

To close the list of mineral fertilizer limitations, it should be noted that their production often requires large amounts of energy (especially for N fertilizers) and raw materials, which can be limited (especially P primary resources) (Dawson and Hilton, 2011). These factors may raise the price of fertilizers, which in turn may be a barrier to their use in some regions (Cedrez et al., 2020). In remote areas access to fertilizer can be a substantial obstacle (Jaja and Barber, 2017). Explosion hazard is associated with ammonium nitrate fertilizer (Laboureur et al., 2016).

1.3 Pesticides

The term pesticide covers a wide range of chemical substances (or their mixtures) and biological agents used to eliminate (kill, destroy) or mitigate (regulate) organisms that are considered to be pests (any insects, rodents, nematodes, fungi, plants/weeds, or any other life-forms unwanted by humans), as well as substances intended for use as plant regulators, defoliants, or desiccants, and organism repellents or attractants. Several formal definitions have been announced (EP, 2009; USC, 2012; WHO, 2010). However, conventional pesticides mean only pesticides synthesized by chemical companies and produced primarily or only for use as pesticides, excluding biological pesticides and antimicrobial pesticides, as well as miscellaneous chemicals used as pesticides but produced largely for nonpesticidal purposes (e.g., sulfur, petroleum oil, petroleum distillate, sulfuric acid, phosphoric acid, zinc sulfate, hydrated lime) (Grube et al., 2011; Lamichhane et al., 2016). Most of the currently used pesticides are synthetic organic or inorganic chemicals (Madariaga-Mazón et al., 2019; Tripathi et al., 2020).

Pesticides have been already used by ancient civilizations, but it is only in the last century that the synthetic ones have been applied extensively worldwide (Sharma et al., 2019). The growth in synthetic pesticides accelerated in the 1940s with the discovery of the effects of dichlorodiphenyltrichloroethane (DDT), beta-hexachlorocyclohexane (BHC), aldrin, dieldrin, endrin, and 2,4-dichlorophenoxyacetic acid (2,4-D) (Arora, 2019). These products were effective and inexpensive with DDT being the most popular, because of its broad-spectrum activity. DDT was widely used, appeared to have low toxicity to mammals, and reduced insect-borne diseases, like malaria, yellow fever and typhus. In 1962 Rachel Carson wrote the book Silent Spring, in which she alerted the world to the dangers of pesticide misuse and highlighted both immediate and long-term environmental consequences (Carson, 1962).

Nowadays, pesticides are widely used in various sectors of the human economy and activities (agriculture, forestry, trade, transport, storage, sport, recreation, household, and others) for controlling agricultural pests, human and livestock disease vectors and nuisance organisms, and preventing or controlling organisms that harm other human activities and structures (Cooper and Dobson, 2007). However, their largest user is agriculture, mostly applying them for plant/crop protection (plant protection products) (EP, 2009). Without diminishing the nonagricultural use of pesticides, yet following the scope of the book, in this chapter we focus on the significance of pesticides used in agriculture.

Agriculturally important pesticides can be classified based on various criteria such as target organism (e.g., herbicides, fungicides, insecticides, nematocides, rodenticides, and others), chemical composition (organophosphates, organochlorines, carbamates, pyrethroids), soil persistency (nonpersistent, moderately persistent, persistent), spectrum of activity (broad spectrum, selective), mode of entry in target organism (contact, systemic, stomach poisons, repellents), mode of formulation (emulsifiable concentrates, wettable or soluble powders, fumigants, dusts, granules, baits), toxicity of the active ingredient (from unlikely to present acute hazard in normal use to extremely hazardous), volatilization behavior (high, medium and low volatile) (Prashar and Shah, 2016). However, classification based on the chemical composition gives an outline of the nature, properties, and behavior of the pesticide.

Currently, the global amount of agricultural pesticide (total) use is 4.1 million tons, of which 52.5% is used in Asia (43.1% in China), 32.3% in total in the Americas (9.9% in the United States, 9.2% in Brazil), 11.6% in Europe, 1.9% in Africa, and 1.7% in Oceania (FAO, 2017). The current world average pesticide use per area of cropland is 2.63 kg/ha, however, there are great disparities between regions/countries. Generally, the least pesticides per hectare are used in African countries. For example, in Niger, the United Republic of Tanzania and Comoros no pesticide use has been noted since 1990. In contrast, in numerous world economies the average annual amount of pesticides exceeds 10 kg/ha, for example, in Saint Lucia (19.6 kg/ha in 2017), Japan, the Republic of Korea, Israel, China, Belize, Belgium-Luxemburg, and Netherlands.

1.3.1 Advantages and benefits

Although conventional pesticides do not have a good press nowadays, it is possible to find several articles presenting their benefits or advantages (Aktar et al., 2009; Casida, 2017; Cooper and Dobson, 2007; Damalas, 2009). However, it should be clearly stated that the benefits announced not accrue from pesticides themselves but the pest control through their use (Edwards-Jones, 2008). Worldwide an estimated 67,000 different pest species (including 9000 species of insects and mites, 50,000 species of plant pathogens and 8000 weeds) attack crops. From 30% to 80% of the pests in any geographic region are native to that region. In most instances the pests, which are specific to a particular region, have moved from feeding on native vegetation to feeding on crops which were introduced into the region (Pimentel, 1995).

According to estimations, approximately one-third of potential crop yield is lost to preharvest pests, pathogens and weeds (Oerke, 2006), but specific crop losses can range from zero to nearly 100% (Pimentel et al., 1992). What is more, yields of crops infested by fungal pathogens (e.g., Fusarium) contain their secondary metabolites, that is, mycotoxins (Ismaiel and Papenbrock, 2015; Wachowska et al., 2017). These compounds, particularly aflatoxins, ochratoxins, fumonisins, trichothecenes, and zearalenone, are known to pose a serious risk to human and animal health worldwide (Ismaiel and Papenbrock, 2015).

Using synthetic pesticides is only one solution for crop protection, but there are many reasons why farmers choose this option. Conventional plant protection products are usually seen as very efficient with fast visible effects, readily available and very easy to use (McCoy and Frank, 2020; Patyka et al., 2016). Due to their high structural, toxicological and functional diversity, pesticides offer a wide range of performance (Prashar and Shah, 2016; Yadav and Devi, 2017). When pest control over large areas of land is needed, pesticides prove to be very cost effective, including saving human labor and time, and have a high return on investment (McCoy and Frank, 2020). It was estimated earlier that each dollar spent on pesticide control returns approximately four dollars in crops saved (Pimentel et al., 1992). Synthetic pesticides assure quite a long period of protection which results with less frequent and lower volumes of chemical applied. They also have a quite long shelf life that guarantees a long-term storage (McCoy and Frank, 2020; Patyka et al., 2016).

Thus, the main benefit of pesticides (assuming the acceptability of such an expression) used in agriculture is primarily related to the effectiveness of achieving the purpose of their application, that is, pest control (Dhananjayan et al., 2020). Cooper and Dobson (2007) adopted a chain model of potential benefits of pesticides. They identified lists of primary and secondary benefits. Primary benefits of conventional pesticides in controlling agricultural pests are immediately apparent effects or the direct gains, and include: improved crop/livestock yields and quality, reduced fungal toxins, improved shelf life of produce, retailer networks established, reduced drudgery and fuel use for weeding, reduced soil disturbance, reduced pest epidemics, pests contained geographically, controlled invasive species.

Secondary benefits of pesticides arise from the primary ones. Being the less immediate, less intuitively obvious, or longer term consequences, they are linked to the primary benefits by a shorter or longer cause–effect chain. According to Cooper and Dobson (2007), secondary benefits can have their economic, social and environmental aspects and operate at community, national or global scales. The economic aspect concerns farm and agribusiness revenues, national agricultural economy, export revenues, wider range of viable crops, labor freed for other tasks, workforce productivity, and agronomic advice improve cropping. The social aspect goes into nutrition and health improved, food safety and security, quality of life improved, life expectancy increased, migration to cities reduced. The environmental aspect is about reduced soil erosion and moisture loss, less pressure on uncropped land, less greenhouse gas, and biodiversity conserved.

1.3.2 Disadvantages and risks

Most active ingredients of synthetic pesticides are hazardous substances. They are xenobiotics, that is, foreign substances, to all living beings, including humans, and their use involves theoretical risks to them. Many pesticides are nonspecific in their mode of action (e.g., atrazine, chlorosulfuron, chlorpyrifos, 2,4-D, diuron, ethion and phorate, endosulfan, parathion, malathion, and monochrotophos; some already banned in many countries) and can harm both pest and nonpest biota (Gill and Garg,