PESTICIDES KILL INSECTS, WEEDS, AND FUNGI

Most species of insects are beneficial or even essential to agriculture. Honeybees, for example, are responsible for the pollination of 10 billion worth of produce in the United States. Countless other species take part in nutrient recycling and help maintain soil quality. A small minority of insect species, however, has continually threatened our capacity to grow, harvest, and store crops, and it is against these species that insecticides are used. The most widely used insecticides are chlorinated hydrocarbons, organophosphorus compounds, and carbamates. 

The chlorinated hydrocarbons have a remarkable persistence, killing insects for months and years on treated surfaces. There are at least two reasons for this persistence. First, chlorinated hydrocarbons tend to be nonbiodegradable, which means there are no natural pathways to break them down chemically. Second, they are nonpolar compounds, which means they are insoluble in water and so are not washed away by rainwater. 

Insect populations began to develop a resistance to DDT within a few years of its first application. Furthermore, DDT was found to be toxic to wildlife, including the natural predators of insects, such as birds. With fewer natural predators, DDT-resistant insects were able to thrive. The early increased crop yields resulting from DDT use were therefore not sustainable. 

Rachel Carson was a pioneer in the fight against excessive use of pesticides. 

The CIDT concentration in a food chain can be magnified from 0.000003 parts per million (ppm) as a pollutant in the water to 25 ppm in a bird ar the top of the chain. 

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Pesticide Any substance or agent employed to destroy a pest organism. Common pesticides include insecticides (to kill insects), herbicides (to kill weeds), fungicides to kill (fungi), and nematicides (to kill nematodes). 

Pesticides are chemicals that kill pests, and are categorized by the types of pests they kill. For example, insecticides kill insects, herbicides kill weeds, bactericides kill bacteria, fungicides kill fungi, and algicides kill algae. 

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