**2.1 Air**

For over 12 days, pesticides may thoroughly orbit the globe and particles will abide in the air for around seven days; at a height of 6 km, for 30 days; at a height of 30 km, for two years [16]. The purpose of pesticide application is to control a pest population. Ideally, pesticide application should impact only the target organism and have little or no impact on other organisms in the environment. However, many pesticide applications have the potential to affect non-target organisms and move beyond the application site. The potential for a pesticide to contaminate the environment depends in large part on the nature of the pesticide, its ability to break down in a given substrate, type of formulation, application rate, frequency of application and environmental conditions [17, 18]. A pesticide can change its nature from liquid form to a vapor by a process called Volatilization. Pesticides become airborne in many ways, including volatilization, drift or through movement as dust borne particles. Volatility increases with increase in temperature, wind speed and humidity. Applying pesticides in cooler temperatures (below 29°C), or above wind speeds of (10 m/hour) or when the humidity is less high, it's likely for pesticides to volatilize and move off the target sites. After application, volatilized pesticides such as Methyl-bromide drift off the application site and locomote into the atmosphere and taking advantage of air currents can relocate to longer distances as highly volatile compounds vaporize or evaporate at low temperatures [19]. On the other hand, volatility is a useful property in the application of pesticides which aids a pesticide to disperse across the farm field or application site or target area and therefore increase the exposure of pests to the pesticide however, it also can lead to exposure for non-target organisms. Environmental conditions such as air movement, relative humidity and temperature also influence volatilization. A number of pesticides, such as emulsifiable concentrate formulations and all of the fumigants, are classified as volatile organic compounds (VOCs) because they readily volatilize into the atmosphere. With the help of Sunlight, VOCs react with nitrogen oxides to produce ozone can which can contribute to smog and cause respiratory and plant injuries. Drift, on the other hand, refers to the airborne movement of pesticides away from the treatment site during application. Drift can damage plants away from the application site, reduce the effectiveness of a pesticide and cause environmental contamination such as water pollution. Drift is most serious when applications are made in windy conditions. Low relative humidity and high temperatures increase the potential for drift by causing spray droplets to evaporate faster [20]. Air temperature also contributes to pesticide drift by creating inversion layers near the soil surface; as a result of which warmer air layers trap cool air layers. At the time of pesticide application, fine spray droplets and pesticide vapors can be trapped by the inversion layers which can form a concentrated cloud with the ability to move from the treatment site. During pesticide application, droplet size also plays an important role in the movement of spray particles away from the application site. Small droplets fall through the air slowly and have a great potential to drift therefore while large droplets fall faster and are more likely to fall to the ground. Applications that release the pesticide as close to the target site as possible reduce drift. Spray pressure also affects drift by influencing the size of spray droplets; higher pressure decreases droplet size and increases drift. After application, fine particles of pesticides may drift off while splashing dust formulations and liquid droplets may stick to the soil particles and later be transported by the wind into the atmosphere [21].

#### **2.2 Soil**

Pesticide characteristics like water solubility, tendency to adsorb to the soil, pesticide persistence and soil characteristics like clay, sand and organic matter are important in determining the fate of the chemicals in the environment. Pesticides may be directly applied to the soil surface, incorporated into the top few inches of soil, or applied through chemigation (**Figure 4**). Once pesticides are present, the soil acts as a reservoir from which persistent pesticides can move into the bodies of invertebrates, be taken up by plants, pass into air or water or break down. After contact with the soil, pesticides are influenced by many factors, including adsorption rate, soil texture, organic matter content in the soil, microorganisms and the presence of water. The soil type influences pesticide persistence and leaching as the tendency for pesticides to be adsorbed vary with the proportion of clay and organic matter in the soil: the higher the percentage of clay and organic matter in the soil, the greater the number of adsorption sites as clay and inorganic matter increase the binding because they have more positive and negative charge sites. It also decreases the potential of a pesticide to move down through the soil, therefore the residues stay in the soil for longer periods of time without moving [22]. Pesticides tend to stay

**Figure 4.** *Wet soil due to fresh pesticide application in a farm field. (Photo Muzafar Riyaz 2021).*

longer in soils with high clay content and organic matter. The amount of water in the soil affects the persistence of pesticides, when more water is added there is a high chance of pesticide release from the soil particle as the water can and force it onto a solution. Usually, the half-life of the pesticide is a used parameter by which the persistence of a pesticide can be measured. A half-life of a pesticide is the period that takes 50% of the pesticide to break down in the environment; the longer the halflife, the greater the possibility for movement of a pesticide before it degrades [23]. On contrary, adsorption refers to the tendency of pesticides to become attached to soil particles. After their release into the environment, pesticides undergo a series of reactions that transform the original compound into various degradation products. Comparing the parent compound, the breakdown products of pesticides may be more toxic, less toxic or equally. Chemically induced transformations of pesticides occur through hydrolysis, photodegradation, microbial degradation and oxidation– reduction. The beneficial soil microorganisms and their associated biotransformation in the soils have been adversely affected by the pesticide residues. The pesticides have also resulted in inactivation of nitrogen-fixing and phosphorus-solubilizing microorganisms soils. A number of studies have shown that some pesticides disturb molecular interactions between plants and N-fixing rhizobacteria and consequently inhibit the vital process of biological nitrogen fixation. Pesticide residue can also reduce activities of soil enzymes that are key indicators of soil health [24–26].

### **2.3 Water**

Water is the basis of life and only a tiny share of all the water on earth is fresh and renewed by the water cycle. Less than 1% of the water is left for drinking,

agriculture, industry and nature. Another potential fate of the pesticide residues in the environment is moving into the water. The potential for movement is greater for pesticides that have a long persistence rate while other factors may include the tendency to adsorb to soil and high-water solubility. Lower adsorption can be a potential cause for pesticides to leach or move in the water. However, some pesticides that adsorb to soil particles, such as pyrethroid insecticides can be washed into surface water when soil and sediment erode. The water solubility of a pesticide affects the ease with which it leaches into soil or moves with surface runoff water [27]. Surface water and groundwater contamination can be closely connected and water-soluble pesticides by a problem in both. Surface water contamination occurs through a direct application (usually by accident) or through drift or runoff. Runoff is one of the most common ways that surface water can become contaminated. During pesticide application from a particular area, the movement of water and dissolved or suspended matter move into surface water or onto neighboring land. However, it's likely to occur when heavy rainfall or irrigation takes place after an application. Groundwater contamination can happen in several ways. Pesticides contaminate groundwater through direct entry and by leaching through the soil. Any opening in the soil will be the cause of direct entry of pesticides into groundwater, as it allows water (or contaminants) to detour the soil's natural filtration agents such as plant roots, burrows, abandoned wells etc. Spilling pesticides while mixing them near a well, pumping water into pesticide application equipment without using air gaps or backflow prevention devices and injecting pesticides into an irrigation system without a backflow prevention device can cause groundwater contamination [28]. Ground water has more possible chances to get contaminated than surface water by the pesticide residues as most surface waters (except deep lakes) have a rapid turnover rate, which means that fresh water dilutes the concentration of the contaminant quickly. On contrary, most surface waters contain free oxygen, which enhances the rate at which pesticides are broken down by microorganisms [29]. Another cause of the movement of pesticides is leaching, which makes a passage for a pesticide to move in water descending through the soil as a result of rainwater or irrigation water which percolates between the soil particles, carrying water-soluble pesticides with it. Nonpoint source pollution, as a result of normal applications on a farm field, orchard, or other wide areas over time, occurs when a small amount of pesticide enters groundwater from any location. Point source pollution, due to pesticide mishandling or from improperly constructed disposal sites or holding facilities, would include large quantities of contaminants entering groundwater at small defined locations. Pesticides that are more mobile in the soil and are resistant to degradation can easily settle down in the groundwater. Shallow water tables beneath treated areas are more susceptible to contamination because pesticides pass through less soil and therefore do not degrade much.

#### **2.4 Food**

Pesticides are considered important for protecting harvests and ensuring our food supply. All pesticides contain active substances which are essential ingredients that enable them to function. This can be a chemical or a microorganism such as a bacterium or a virus. In some cases, the chemical works by making the crop less palatable for pests. However, the pesticides work by simply killing or damaging the insect pests, weeds, fungi and so on. In some cases, small amounts called residues can find their way into food that humans eat [30]. These residues could be harmful if they exceed certain levels. There are many ways in which pesticide residues can get into our food [31]. Residues in treated crops can be carried from the field into the food by direct application of pesticides on crops till the time of

#### *Pesticide Residues: Impacts on Fauna and the Environment DOI: http://dx.doi.org/10.5772/intechopen.98379*

harvest. Pesticide residues can get into the water supply or they can contaminate soil and animal feed, therefore, find their way into our food indirectly. The human food chain is also affected by the pesticide residues left in crops soil and water. Intake of pesticide residues in the body has been connected to birth imperfection, danger to the embryo, disease, hereditary deformities, neurotoxicity and endocrine disruption [32].

Pesticide residues can pose a risk to the heath of end consumers, if residue levels are too high. This is maintained by through Maximum residue levels (MRLs) which are the highest amounts of an individual pesticide that is permitted to be present. Pesticide residues are identified and quantified by comparing the sample extract to a calibration standard solution and analyzing them by liquid or gas chromatography coupled with mass spectroscopy. Once pesticides are demonstrated to be safe for the consumers, they have MRLs set for them which are determined based on rigorous evaluations. A maximum residue level is the maximum amount of residue that is legally permitted in food measured in milligrams of substance per kilogram of food based on good agricultural practices. MRLs are set far below levels that could possibly pose a risk to human health. Since MRLs are not safety limits but trading standards, these are not determined by the industry. However, MRLs are determined by independent government agencies which fully review each active substance present in pesticides. A number of reasons by which MRLs can surpass their limit of 3–5% which include; the incorrect way of pesticide application or exceptional climatic or crop conditions have occurred [33–35].
