2.5. Pesticides

They are the toxic chemical substances which are released intentionally into our environment to kill living organisms (insects, herbs, fungus, bacteria, etc.). Pesticides control or kill organism through a variety of mechanism, including the inhibition of biological processes such as photosynthesis, mitosis, cell division, enzyme function, growth; interference with the synthesis of pigments, proteins or deoxyribonucleic acid (DNA); destruction of cell membranes; or the promotion of uncontrolled growth. The use of pesticide is as old as human civilization. The first intentional use of a pesticide is 2500BC by Sumerians. They used the sulfur compounds to kill insects. Pesticides cause contamination in the environment mainly through air, soil, water and wildlife. Pesticides not only kill target pests but also damage many other organisms that are also present in the air, soil and water. Therefore, it decreases biodiversity. Safe alternate methods like development of relatively cheaper biopesticide should be encouraged.

2.5.1. Insecticides

They are toxic chemicals designed to be deliberately released into the environment to kill insects. They can also cause negative effect on the ecosystem. Insecticides easily contaminate the air, soil and water by spraying.

2.5.2. Herbicides

These chemicals are used to kill undesirable plants or “weeds”. Most of them will kill all the plants they touch, while some of them are designed to target one species. It is well known that herbicide application can pose a risk for the vegetation surrounding an arable field. Herbicides can cause environmental contamination such as air, soil and water. These herbicides can enter aquatic ecosystems as a result of terrestrial runoff, and to a lesser extent, of direct application and aerial spraying. Microbial communities in freshwater ecosystems are not directly targeted, but these communities are exposed to herbicides and can be directly or indirectly affected by these compounds.

2.5.3. Fungicides

These chemicals are used to kill fungi. Using fungicides causes air, water and soil pollutions. Fungicides get in to environment by agricultural or hospital usage. For example, areas of intensive agriculture, aquatic environments and etc. are exposed to agricultural pesticides, which are regularly detected in surface waters in these areas. As another example, after application of azole fungicides to treat fungal infection in human, these chemicals may reach to the receiving environment via direct or indirect discharge of wastewaters, thus posing potential risks to non-target organisms. But, most of fungicides have relatively low mammalian toxicities, and except for carbamates such as benomyl, a relatively narrow spectrum of toxicity to soil-inhabiting and aquatic organisms. Their greatest environmental impact is toxicity to soil and water microorganisms.

2.5.4. Bactericides

This chemical agent prevents the formation of bacteria. Bactericides are often used as coatings and corrosion inhibitors in oil wells and connecting pipelines in intermediate storage to the refinery for crude oil. These chemicals are increasingly added to antimicrobial surfaces and other products to kill bacteria or inhibit their growth. These are also intensively used in animal husbandry and in veterinary medicines for the purposes of caring for and rearing food-producing animals. Another important use of bactericides is in cooling tower systems to control the growth of some harmful bacteria such as Legionella that might otherwise be released from cooling towers in aerosols.