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Pesticides in General
The chemicals used to control all kinds of pests are known as pesticides. The word pest is an all embracing general term but in the current context includes insects, fungi, bacteria, viruses, nematodes that damage crops or incite diseases on crops; weeds in cultivators plots that rob Ute nutrients from soils; snails, birds and rodents that destroy seedlings at sowing time and grains at harvest time; and finally insects, microorganisms and rodents that consume stored grains and fruits in the post harvest stage. The word pesticides is again a general term that includes insecticides, fungicides, nematocides, rodenticides, herbicides and algicides.
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There are other chemicals which do not directly kill or mitigate pests but are nevertheless classed as pesticides. They are growth regulators, chemosterilants (sterilize insects, birds, rodents), defoliants (remove leaves), pheromones (attract insects) and repellents (repel insects, dogs, rabbits, birds). These chemicals, however, do not form part of the writing here which confines only to insecticides, herbicides and fungicides.
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Pesticides include one or more elements such as arsenic (As), boron, (B), bromine (Br), cadmium (cd), carbon (C), chlorine (Cl), copper (Cu), fluorine (F), hydrogen (H), iron (Fe), lead, (Pb), magnesium (Mg), manganese (Mn), nitrogen (N), oxygen (0), phosphorus (P), sodium (Na), sulphur (5), tin (5n) and zinc (Zn). The benzene ring is quite frequently found in pesticide publications. It is a six carbon ring with six hydrogen atoms. For ease of presentation it is usually indicated as a hexagon with double bonds. When other groups have replaced one or more of the hydrogens, the ring is referred to as the phenyl radical rather than a benzene radical.
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For example, DDT contains the words diphenyl which refers to the two benzene rings with other groups attached (see under DDT).
The original pure form of a pesticide is formulated to technical grade materials that can be directly used effectively and safely and are amenable to storage, handling and application. They come in the form of sprays that are emulsions, water soluble concentrates, wettable powders, water soluble powders, oil solutions, soluble pellets, suspensions, dusts with active or
inert diluents, aerosols; granulars; fumigants; impregnates either volatile or non-volatile; fertilizer combinations; baits and slow-release materials.
Benzene |
Hexagon |
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Apart from pesticides, oil-spills from many sources constitute another aspect of hazard for plant growth and this chapter also focuses problems and solutions faced by such pollutants
Residues of pesticides persist in soil water and food and have posed problems all over the world, especially in the U.S.A. where in 1988, global sales of pesticides produced by some top 10 companies of the world amounted to 20 million US dollars, of which herbicides alone constituted 5 billion dollars. During the subsequent decade, bewildering amounts of a variety of organic compounds have been used in diverse human activities.
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An approximate estimate made in 1992 shows that the following organic chemicals were produced in the U.S.A the quantities of the chemicals indicated in parenthesis as Kg x 109: ethylene (18.33), propylene (10.25), ethylene dichloride (7.23), vinyl chloride (6.00), benzene (5.45), ethylbenzene (4.99), methyl t-butyl ether (4.93). Styrene (4.06), methanol (3.96), Formaldehyde (3.17), Xylene (2.89), Toluene (2.74), p-xylene (2.57), terephthalic acid (2.56), ethylene oxide (2.52), ethylene glycol (2 32), cumene (2.07), phenol (1.68), butadiene (1.44), acrylonitrile (1.28), propylene oxide (1.22), vinyl acetate (1.21), acetone (1.08), cyclo-hexane (1.00), totalling to 9495 kg x 109. The residues of these chemicals remain hazardous to living beings. In recent years, oil spills have been considered as prime pollutants to the detriment of life in aquatic habitats.
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