Abstract
Since the industrial revolution, several new chemicals were discovered and introduced in society, and soon after the green revolution, pesticides were also introduced to strengthen food security. However, limited education on their application, handling, and usage resulted in them making their way into the aquatic ecosystem. This chapter defines the different sources of pesticides, based on their point of origin and the way it transports pesticides to the aquatic systems. After this, the pesticide interaction in an aquatic environment with various organic and inorganic substances is described. Each interaction is supported with the recent researches and examples. Following pesticides sources and interactions, its fate in the aquatic system has been defined through various physical and chemical processes. Ultimately, its impact on aquatic organisms is discussed. This chapter is concluded with recommended management practices and future research directions. Some terms are also defined at the end of this chapter.
TopIntroduction
Since 1960s pesticides helped farmers to expand agricultural production and support the growing population globally. Food security with an increasing global population intensifies pesticides application in the agricultural fields. USEPA reported (USEPA, 2016) world pesticide expenditure at the producer level nearly $56 billion in 2012, out of which $9 billion was spent by the USA alone. Due to the high application, pesticides can be easily detected in surface waters. They may enter into aquatic systems from the point or non-point sources of pollution. After entry, they may affect biota individually or in a mixture form defined further in this chapter. The fate is decided by the type of aquatic system they enter and interaction with different organic and inorganic substances in the ecosystem.
Pesticides are natural and artificially synthesized chemical products used to limit, inhibit, and prevent the growth of harmful organisms, insects, invasive plants, weeds, and fungi. Pesticides can be classified as herbicide, insecticide, and fungicide (based on targeted pests) and organophosphate (OP), carbamate, organochloride (OC) and pyrethroid (based on their chemical structure) (Figure 1). Out of the three major subclasses of pesticides, herbicides are the most frequently detected compounds in surface waters of Europe and USA (Gustavsson, Kreuger, Bundschuh, & Backhaus, 2017) due to generally higher hydrophobicity, shorter application duration, and lower quantity mass application. Herbicides were accounted for nearly $25,000 million expenditure worldwide in 2012 (Figure 2) and mostly used by agriculture with some percentage by home and garden (Figure 3). In contrast, the largest share of insecticides was used in households as compared to other areas (Figure 3).
Figure 1. Schematic classification of pesticides on the basis of mode of action and chemical structure
Figure 2. Graphical representation of world pesticide expenditure at producer level (A) from 2008-2012; (B) in 2012
Figure 3. Individual user expenditure on conventional pesticides in the USA by pesticide type and market sector - 2012 estimates
Pesticides are found at varying concentrations in the environment depending upon their uses. They enter into the environment through their application in public health (e.g. control of Mosquitoes and flies), large structure preservation and maintenance (e.g. Monuments and historic buildings), green area maintenance (e.g. public parks and community gardens), maintenance of water reserves especially use for recreational activities (e.g. fountains and lakes), livestock farming, aquaculture, industrial application (e.g. food preservation) and homes (e.g. insect repellent) (Figure 4). Once a pesticide applied in the field, it enters into the aquatic environment and undergoes one or more transformation product depending upon their physicochemical property. From there pesticides are known to affect aquatic organisms even at trace level concentrations. The severity and duration of toxicity decided by several chemicals and physical factors, including the insecticide chemical structure. The toxicity of a particular insecticide increases with higher concentrations in tissue and its affinity for acetylcholinesterase.
Key Terms in this Chapter
No Observation Effect Concentration (NOEC): In toxicology, it is specifically the highest tested dose or concentration of a chemical, at which no such adverse effect is found in exposed test organisms where higher doses or concentrations resulted in an adverse effect.
Oxidative Stress: A biological phenomenon includes various stress enzymes that can cause health issues in organisms.
Drift: A process of slow movement of chemical particles by a current of air and water.
Aquaculture: The culture of fishes and other aquatic organisms in man-made ponds, ditches, and floating cages.
Environmental Quality Standard (EQS): An environmental quality standard is a value, generally defined by regulation, which specifies the maximum permissible concentration of a potentially hazardous chemical in an environmental sample, generally of air or water.
Runoff: A process of draining water due to rainfall, snow, or any other precipitation event from land to surface water.
Absorption: The process by which one thing absorbs or is absorbed by another.
Storm Flow: The runoff of land surface water from rainfall.
Vitalization: Refers to the vaporization or sublimation of a volatile herbicide.
Adsorption: Adsorption is the adhesion of molecules of gas, liquid, or dissolved solids to a surface.
Leaching: A process in which certain material extract or move from a carrier material extract or move from a carrier to liquid. For example, pesticides get washed off from soil to groundwater through percolation.