**1. Introduction**

#### **1.1 Definition of ecology**

At a community level, ecology can be defined as complex interactions that exist among interdependent organisms that cohabitate the same geographical area and with their environment (Johnson and Strinchcombe, 2007). At individual level, it entails the relationships that exist between that particular individual with numerous physical and biological factors. The physical environment along with organisms (biota) inhabiting a particular space make up an ecosystem. Some typical examples of ecosystems include a farm pond, a mountain meadow and rain forest. In a natural environment, an ecosystem follows a certain sequence of processes and events through the days, seasons and years. The processes include not only the birth, growth, reproduction and death of biota in that particular ecosystem, but also the interactions between species and physical characteristics of the geological environment. From these processes and interactions, the ecosystem gains a recognizable structure and function, and matter and energy are exchanged and cycled through the ecosystem. Over time, better adapted species come to dominate; entirely new species may change, perhaps in a new or altered ecosystem.

#### **1.2 The organisation in ecosystems**

The basic level of ecological organisation is with the individual such as a single plant, insect or bird. The definition of ecology is based on the interactions of organisms with their environment. In the case of an individual, it would entail the relationships between that individual and numerous physical (rain, sun, wind, temperature, nutrients, etc.) and biological (other plants, insects, diseases, animals, etc.) factors. The next level of organization is the population. Populations are no more than a collection of individuals of the same species within an area or region. We can see populations of humans, birch trees, or sunfish in a pond. Population ecology is concerned with the interaction of the individuals with each other and with their environment.

The next, more complex, level of organization is the community. Communities are made up of different populations of interacting plants, animals, and microorganisms also within some defined geographic area. Different populations within a community interact more among themselves than with populations of the same species in other communities, therefore, there are often genetic differences between members of two different communities. The populations in a community have evolved together, so that members of that community provide resources (nutrition, shelter) for each other.

Ecological Effects of Pesticides 131

over long distances. The worldwide distribution of DDT and the presence of pesticides in bodies of water such as the Great Lakes far from their primary use areas are good examples

Fig. 2.1 Distribution of pesticides in different environmental compartments

important reason for the current strict regulations on the judicial use of pesticides.

In this chapter, a closer and detailed look on the major ecological effects of pesticides are described based on contemporary accumulated knowledge on the behavior of pesticides and the damage they cause to the ecosystem and the environment at large as a result of excessive use and/or injudicious use of pesticides. The effects may range from minor deviation on the normal functioning of the ecosystem to the loss of species diversity in the ecosystem. Since organisms in the ecosystem live in a complex interdependent association with each other, the loss one key species may result in the collapse of the particular ecosystem. These effects are an

The primary objective of using pesticides in the fields and the environment in general is to achieve a control of crop pests and disease vectors. This has been a deliberate human effort in a search for increasing agricultural yields and improving public health (Helweg, 2003). Pesticides applied to the environment have shown to have long term residual effects while others have shown to have acute fatal effects when not properly handled. Organochlorine pesticides for example have shown to be persistent in the environment, the result of which find their way to contaminate ground water, surface water, food products, air, soil and may affect human being through direct contact. Pesticides exposure to humans have been well documented to be the route cause of some diseases such as cancer, respiratory diseases, skin diseases, endocrine disruption, and reproduction disorders. It is this aspect of pesticide in the environment that has raised concern among environmental scientists to study their behaviour in the environment and then come out with a sound alternative so as to rescue

Fifty years (half a century) after Rachel Carson's eloquent warning to the world about the devastating effect pesticides have on birds and beneficial insects, pesticides continue to be

of the vast potential of such movement.

**2. Ecological effects of pesticides** 

the human population from their adverse effects.

The next level of organization is the ecosystem. An ecosystem consists of different communities of organisms associated within a physically defined space. For example, a forest ecosystem consists of animal and plant communities in the soil, forest floor, and forest canopy, along the stream bank and bottom, and in the stream. A stream bottom community, for example, will have various fungi and bacteria living on dead leaves and animal wastes, protozoans and microscopic invertebrates feeding on these microbes, and larger invertebrates (worms, crayfish) and vertebrates (turtles, catfish). Each community functions somewhat separately, but are also linked to others by the forest, rainfall, and other interactions. For example, the stream community is heavily dependent upon leaves produced in the surrounding trees falling into the stream, feeding the microbes and other invertebrates. Terrestrial ecosystems can be grouped into units of similar nature, termed biomes (such as a "deciduous forest," "grassland," "coniferous forest," etc.), or into a geographic unit, termed landscapes, containing several different types of ecosystems. Aquatic ecosystems are commonly categorized on the basis of whether the water is moving (streams, river basins) or still (ponds, lakes, large lakes) and whether the water is fresh, salty (oceans), or brackish (estuaries). Landscapes and biomes (and large lakes, river basins, and oceans) are subject to

greenhouse effect) and human activities (soil erosion, deforestation, pesticides use).

**1.3 Why pesticides are unique among environmental contaminants**  Pesticides released into the environment may have several adverse ecological effects ranging from long-term effects to short-lived changes in the normal functioning of an ecosystem. Despite the good results of using pesticides in agriculture and public health, their use is usually accompanied with deleterious environmental and public health effects. Pesticides hold a unique position among environmental contaminants due to their high biological toxicity (acute and chronic). Pesticides by definition are toxic chemical agents. A pesticide is usually capable of harming all forms of life other than the targeted pest species. On account of this behavior then, they can best be described as biocides (capable of killing all forms of life). Although some pesticides are described to be selective in their mode of action, their range of selectivity is only limited to the test animals.

global threats of pollution (acid deposition, stratospheric ozone depletion, air pollution, the

#### **1.4 The vast potentials of pesticides distribution and fate in the environment**

The term chemodynamics of pesticides refers to the study of the movement and transformation of pesticides as well as their fate in various compartments of the environment. The environment can be divided into four major compartments, namely; air, water, soil and biota (Fig.2. 1).

The widespread use and disposal of pesticides by farmers, institutions and the general public provide many possible sources of pesticides in the environment. Pesticides once released into the environment may have many different fates. Pesticides that are sprayed can move through the air and may eventually end up in other parts of the environment, such as in soil or water. Pesticides that are applied directly to the soil may be washed off the soil into nearby bodies of surface water or may percolate through the soil to lower soil layers and groundwater (Harrison, 1990). This incomplete list of possibilities suggests that the movement of pesticides in the environment is very complex with transfers occurring continually among different environmental compartments. In some cases, these exchanges occur not only between areas that are close together (such as a local pond receiving some of the herbicides applied on adjacent land) but also may involve transportation of pesticides

The next level of organization is the ecosystem. An ecosystem consists of different communities of organisms associated within a physically defined space. For example, a forest ecosystem consists of animal and plant communities in the soil, forest floor, and forest canopy, along the stream bank and bottom, and in the stream. A stream bottom community, for example, will have various fungi and bacteria living on dead leaves and animal wastes, protozoans and microscopic invertebrates feeding on these microbes, and larger invertebrates (worms, crayfish) and vertebrates (turtles, catfish). Each community functions somewhat separately, but are also linked to others by the forest, rainfall, and other interactions. For example, the stream community is heavily dependent upon leaves produced in the

surrounding trees falling into the stream, feeding the microbes and other invertebrates.

greenhouse effect) and human activities (soil erosion, deforestation, pesticides use).

**1.4 The vast potentials of pesticides distribution and fate in the environment** 

The term chemodynamics of pesticides refers to the study of the movement and transformation of pesticides as well as their fate in various compartments of the environment. The environment can be divided into four major compartments, namely; air,

The widespread use and disposal of pesticides by farmers, institutions and the general public provide many possible sources of pesticides in the environment. Pesticides once released into the environment may have many different fates. Pesticides that are sprayed can move through the air and may eventually end up in other parts of the environment, such as in soil or water. Pesticides that are applied directly to the soil may be washed off the soil into nearby bodies of surface water or may percolate through the soil to lower soil layers and groundwater (Harrison, 1990). This incomplete list of possibilities suggests that the movement of pesticides in the environment is very complex with transfers occurring continually among different environmental compartments. In some cases, these exchanges occur not only between areas that are close together (such as a local pond receiving some of the herbicides applied on adjacent land) but also may involve transportation of pesticides

**1.3 Why pesticides are unique among environmental contaminants** 

range of selectivity is only limited to the test animals.

water, soil and biota (Fig.2. 1).

Terrestrial ecosystems can be grouped into units of similar nature, termed biomes (such as a "deciduous forest," "grassland," "coniferous forest," etc.), or into a geographic unit, termed landscapes, containing several different types of ecosystems. Aquatic ecosystems are commonly categorized on the basis of whether the water is moving (streams, river basins) or still (ponds, lakes, large lakes) and whether the water is fresh, salty (oceans), or brackish (estuaries). Landscapes and biomes (and large lakes, river basins, and oceans) are subject to global threats of pollution (acid deposition, stratospheric ozone depletion, air pollution, the

Pesticides released into the environment may have several adverse ecological effects ranging from long-term effects to short-lived changes in the normal functioning of an ecosystem. Despite the good results of using pesticides in agriculture and public health, their use is usually accompanied with deleterious environmental and public health effects. Pesticides hold a unique position among environmental contaminants due to their high biological toxicity (acute and chronic). Pesticides by definition are toxic chemical agents. A pesticide is usually capable of harming all forms of life other than the targeted pest species. On account of this behavior then, they can best be described as biocides (capable of killing all forms of life). Although some pesticides are described to be selective in their mode of action, their over long distances. The worldwide distribution of DDT and the presence of pesticides in bodies of water such as the Great Lakes far from their primary use areas are good examples of the vast potential of such movement.

Fig. 2.1 Distribution of pesticides in different environmental compartments

In this chapter, a closer and detailed look on the major ecological effects of pesticides are described based on contemporary accumulated knowledge on the behavior of pesticides and the damage they cause to the ecosystem and the environment at large as a result of excessive use and/or injudicious use of pesticides. The effects may range from minor deviation on the normal functioning of the ecosystem to the loss of species diversity in the ecosystem. Since organisms in the ecosystem live in a complex interdependent association with each other, the loss one key species may result in the collapse of the particular ecosystem. These effects are an important reason for the current strict regulations on the judicial use of pesticides.
