**4. Pesticide pollution**

Since the middle of the 19th century, pesticides have been commonly used to control pests [31,32] causing a widespread release of these xenobiotics into the environment [51]. The intensive use of pesticide leads to an increased risk of contamination of the environment and harmful effects on biodiversity, food security, and water resources [52,53].

Pests, such as insects, weeds, and plant diseases, are an ongoing challenge to agricultural producers. Oerke [54] reported that, globally, an average of 35% of potential crop yield is lost to preharvest pests. With the expected 30% increase of world population to 9.2 billion by 2050, there is a projected demand to increase food production by 70% according to Popp et al. [55]. Although nonpesticidal tools have a vital role, there will be a continuing need for pesticidebased solutions to pest control and food security in the future [55,56]. **Figure 1** shows the average pesticide use intensity (kg ha-1 yr-1) on the cultivable and permanent cropland worldwide. High use intensity countries above 10 kg ha-1 yr-1 include Surinam, Malta, Colum‐ bia, Palestinian, Japan, Korea, Chile, and China [57]. **Figure 2** presents that pesticide sales are increasing in Europe, Asia, and Latin America [58,59].

**Figure 1.** Average annual pesticide use intensity (kg ha-1 yr-1) on arable and permanent cropland from 2005 to 2009. Data are from FAO [57].

**Figure 2.** Annual pesticide sales by geographic regions. Data are from FAO [58].

More than 500 different pesticide formulations are being used in our environment, mostly in agriculture [60]. In the past five decades, pesticide usages increased the quantity and improved the quality of food. However, due to their usage with increasing amounts, the concern about their harmful effects on nontarget organisms, including human beings, has also been growing. Nontarget pesticide poisoning has been reported from fish, birds, and humans [61]. Although it is estimated that less than 0.1% of pesticide applied to crops actually reaches the target, the rest of it enters the environment [62]. Additionally, many pesticides can persist for long periods in an ecosystem; organochlorine insecticides, for instance, are still detectable in surface waters 30 years after their use and had been banned [63]. In the food chain, they meet with nontarget organisms, including mankind. They accumulate in the body tissues of organisms and cause a number of health problems [64,65].

Pesticides and herbicides are heterogeneous chemicals used widely in agriculture. Their design as bioactive molecules to exterminate different animal, vegetal, or fungal species implies that they are toxic by definition. Due to this toxicity, their use is regulated in the European Union. Depending on the water solubility and polarity of each specific pesticide, they can follow different pathways to reach water bodies once applied in the crop fields. In the case of surface waters, the most common entry pathway for these pollutants is runoff from agriculture lands after precipitation or irrigation [66]. Pesticides could influence biological communities in lakes, forcing changes from a clear-water, macrophyte-dominated state to a turbid state due to their effect on zooplankton or macrophytes [67,68].

As explained above, both point and diffuse pollution sources of pesticides, herbicides, and polycyclic aromatic hydrocarbons (PAHs) are usually anthropogenic. Therefore, it is expected that the concentration of some of these compounds in surface water is related to human activities that take place in the surroundings. The proportion of cultivated lands around the lake and the agricultural pressure and intensity are especially relevant, as certain substances such as herbicides and pesticides have a close relationship with agriculture. In fact, it has been observed that land uses are strongly related to nutrient concentrations in surface waters [69] and PAH concentrations in wetland sediments [70]. On the contrary, the distance between lakes and point or diffuse pollution sources such as urban areas, thermal power plants, industries and roads could also be related to the amount of these chemical compounds detected in aquatic ecosystems [68].

Pesticide fate in the environment is characterized by a number of complex processes occurring in different environmental compartments, such as air [71], soil [72], plant [73], and surface and groundwater [53,74].

Pollution due to the uncontrolled use of pesticides has become one of the most alarming challenges when pursuing sustainable development. Although pesticides are directly applied in soils and plants, only 1% of pesticide sprayed is delivered to the intended target. An accidental release of pesticides due to leaking pipes, spills, waste dumps, underground storage tanks, and groundwater may lead to their persistence in the environment for a long time (due to long half-lives). For proper management of pesticides, one needs to accurately assess the status of their contamination in soil, water, and air [75,76].

Soil is a major reservoir for a variety of pollutants [77] and is a secondary emission source of contaminants to surface water, groundwater, and air [78]. Multiclass environmental endocrine disruptor compounds (EDCs), such as organochlorine pesticides (OCPs) phthalate esters (PAEs), and polybrominated diphenyl ethers (PBDEs) may coexist in soils and accumulate in crops and human bodies through food chains, posing risks to human health and the ecosystem [79]. In addition, soil plays an important role in pesticide residue in plants. There are two pathways for pesticide transfer between the plants and their planted soils. First, most of pesticides could shift or fall onto the soil when pesticide is applied onto plants. Next, most of the deposited pesticides on the plant could be washed off by rainfall to the soil. Second, the residues of adsorbed pesticides in soil, especially for organochlorine pollutants, remain as contaminants in the environment because of their long-term persistence and mobility, and they could enter into food again via the plant uptake effect [10,80,81].

Persistent organic pollutants (POPs), such as OCPs, are ubiquitous contaminants in different compartments of the environment [82,83]. Although a number of countries have been removed from the circulation of the usage of POPs for nearly 30 years, these synthetic chemicals are found in nature at considerable levels worldwide due to their persistence. These substances are mainly generated by anthropogenic processes and can be introduced into the environment through various routes. These pesticides are toxic, carcinogenic, and mutagenic features. They are extremely hazardous for the both biota and environment [84]. Hence, the investigation of POPs in aquatic environments is needed to provide relevant information on the anthropogenic impact on the environment, and concentrations serve as an indicator of contaminant load [85, 86].

Pesticides are major components of the modern agricultural production because of their reliability and high capability for crop protection against pests [87]. Approximately 5 billion kilograms of pesticides are applied worldwide per year, which can have serious effects on biodiversity, nontarget organisms, and the food chain, posing high risks to the environment and human health [88]. In rural areas of developing countries, 3 million farmers suffer annually from serious pesticide poisoning and 25 million farmers suffer from mild poisoning, resulting in approximately 180,000 fatalities among agricultural workers annually [89] because of incorrect perceptions, lack of knowledge, regulation, and education among farmers [90,91].

Unsafe pesticide use or misuse in developing countries includes the use of pesticides banned by the local government [92], lack of self-protection [93], incorrect pesticide storage [94], overspraying [95], improper handling of pesticide containers [96], and, in extreme cases, reuse of washed pesticide containers as containers for food and drinking water (as reported by 35.4% and 77.2% of farmers in Nigeria and Ethiopia, respectively) [97]. The local authorities, the WHO, the Food and Agriculture Organization (FAO), and various nongovernment organiza‐ tions that focus on low- and middle-income countries (e.g. China, India, Vietnam, and African countries) have taken initiatives to improve the protective behaviors of farmers in pesticide use, including personal and environmental protection through education [98] and legislation and community intervention [99], although the results were often unsatisfactory [100]. The factors that affect farmers' behavior in pesticide use are far more complex than expected. Pesticide use can be influenced by age [101], gender [102], perceptions [90,91], level of knowledge, pesticide retailers [103], and even cultural or planting differences [92].

The chemical pesticide provides a necessary guarantee for the output increase, but pesticide abuse has led to daily worsening of the ecosystem of agricultural lands [104,105]. The use of large amount of pesticide is the main reason for agricultural pollution [106].
