Pesticide

A pesticide is a material used for the mitigation, control, or elimination of plants or animals detrimental to human health or economy. Specifically, a pesticide is a chemical—liquid, granule, or gas—used to kill or control pests such as insects, weeds, bacteria, fungi, rodents, and worms. Pesticides play significant roles in increasing food production and [Page 352]eliminating diseases. However, only a few environmental issues have aroused the concern of the public as much as pesticides because exposure to them can be harmful to humans. The ill effects experienced may result from short- or long-term exposure or low- or high-level exposure through dermal absorption, inhalation, and oral ingestion. Frequent application of pesticides has led to the development of resistance to them. Scientists thus face the challenge of developing new environmentally friendly pesticides that overcome the rapid development of resistance by pests. Pesticides can be classified according to chemical class (e.g., organochlorine, carbamate, organophosphorus, and chlorophenoxy compounds) or according to their intended use (e.g., insecticide, herbicide, rodenticide, fungicide, fumigant, and acaricide). Insecticides act by poisoning the nervous system of target harmful insects. They include organochlo-rines, organophosphates, carbamate esters, pyrethroids, and botanical insecticides. Herbicides target weeds and include chlorophenoxy compounds and bipyridyl derivatives. Rodenticides target rodents and include zinc phosphide, fluoroacetic acid and derivatives, Naphthyl Thiourea, and anticoagulants. Fungicides target fungi, and they include hexachlorobenzene, organomercurials, pentachlorophenol, phthalimides, and dithiocarbamates. Examples of fumigants are phosphine, ethylene dibromide, and dibromochloropropane. Acaricides target acarose (a mite).

This agronomist is collecting broccoli samples from a test plot in Salinas, California, to test them for pesticide residue.

Source: U.S. Department of Agriculture Agricultural Research Service/Scott Bauer

When a pesticide is introduced into the environment by application, disposal, or spill, it is influenced by many processes. These processes determine a pesticide's persistence, its movement, and its ultimate fate. The fate processes can have both positive and negative influences on a pesticide's effectiveness or its effect on the environment. The fate processes can be beneficial. They can move a pesticide to the target area or destroy its potentially harmful residues. Sometimes they can be detrimental, leading to reduced control of a target pest, injury of nontarget plants and animals, and environmental damage. Different soil and climatic factors and different handling practices can promote or prevent each process. An understanding of the fate processes ensures that applications are not only effective but also environmentally safe. Fate processes could be grouped into four major types: degradation, transfer, adsorption, and bio-accumulation/bio-magnification. These physical and chemical properties of pesticides influence their environmental risk.