Pesticides natural chemicals

Wolfe. N.L. Abiotic transformations of pesticides in natural waters and sediments, in Fate of Pesticides and Chemicals in the Environment, Schnoor, J.L., Ed. (New York John Wiley Sons, Inc., 1992), pp. 93-104. 

One approach to the discovery of new insecticides which fulfill the criteria of efficacy, safety, selectivity, etc., is through the study of the natural chemical defenses of plants. Extracts of plants have been used as Insecticides by humans since before the time of the ancient Romans, a practice that continues today with many of the 2000 species of plants known to have insecticidal properties (4-5). The use of insecticidal" plants is especially prevalent among subsistence farmers since plants grown locally are cheaper, and sometimes more accessible, than synthetic chemical pesticides. Commercially, however, only a few of these plants. Including those containing pyrethrins, rotenoids, and alkaloids, have been used to any extent in the United States as sources of insecticides (6-8). 

About 99.9 percent of the chemicals humans ingest are natural, and the amounts of synthetic pesticide residues in foods are insignificant compared to the amount of natural pesticides that are always in our diet because of the plants we eat.13 Of all dietary pesticides that humans eat, 99.99 percent are natural chemicals produced by plants to defend themselves against fungi, insects, and other animal predators. The natural pesticides come in great variety because each plant produces a different array of such chemicals. 

Only a small proportion of natural pesticides have been tested for carcinogenicity, but 38 of the 72 tested are rodent carcinogens. As shown in Table 2, naturally occurring pesticides that are rodent carcinogens are ubiquitous in common fruits, vegetables, herbs, and spices. The widespread distribution of such chemicals means that no diet can be free of natural chemicals that are rodent carcinogens. 

Overall, our analyses have shown that HERP values for some historically high exposures in the workplace—to butadiene and tetrachloroethylene—and to some pharmaceuticals—clolibrate —rank high, and that there is an enormous background of naturally occurring rodent carcinogens in typical portions of common foods. The background of natural exposures casts doubt on the relative importance of low-dose exposures to residues of synthetic chemicals such as pesticides. (A committee of the National Research Council of the National Academy of Sciences reached similar conclusions about natural vs. synthetic chemicals in the diet, and called for further research on natural chemicals.) 16... 

The possible carcinogenic hazards from synthetic pesticides are minimal compared to the background of nature s pesticides, though neither may be a hazard at the low doses consumed. Analysis also indicates that many ordinary foods would not pass the regulatory criteria used for synthetic chemicals. Caution is necessary in drawing conclusions about the occurrence in the diet of natural chemicals that are rodent carcinogens. These di-... 

Dr. Bruce Ames, who received the National Science Medal from President Clinton, documented that we get 100000 times as much cancer risk from the natural chemicals in the foods we eat as from the tiny traces of pesticide on our foods and in our drinking water. 

Despite the diverse chemical types represented by forest pesticides, the variety of their formulations, and the many rates and routes of application, two factors remain consistently present in their environment—sunlight and powerful reagents. Quite apparently, these forces are active and acting. The well-known "blue haze" observed over forests in many parts of the world remote from man s chemical wastes is a result of photooxidation reactions of volatile natural chemicals similar to those which generate manmade smog. 

Benzene found in the environment is from both human activities and natural processes. Benzene was first discovered and isolated from coal tar in the 1800s. Today, benzene is made mostly from petroleum sources. Because of its wide use, benzene ranks in the top 20 in production volume for chemicals produced in the United States. Various industries use benzene to make other chemicals, such as styrene (for Styrofoam and other plastics), cumene (for various resins), and cyclohexane (for nylon and synthetic fibers). Benzene is also used for the manufacturing of some types of rubbers, lubricants, dyes, detergents, drugs, and pesticides. Natural sources of benzene, which include volcanoes and forest fires, also contribute to the presence of benzene in the environment. Benzene is also a part of crude oil and gasoline and cigarette smoke. For more information on the nature and uses of benzene, see Chapters 3 and 4. 

In addition to natural food contaminants that may be present in food, there are also man-made contaminants that can inadvertently enter food, such as pesticides, industrial chemicals hke dioxin, or substances fed to animals hke antibiotics or anabofic steroids. Some of these are discussed in Chapter 5. 

Pesticides are chemicals or biological substances used to kill or control pests. They fall into three major classes insecticides, fungicides, and herbicides (or weed killers). There are also rodenticides (for control of vertebrate pests), nematicides (to kill eelworms, etc.), molluscicides (to kill slugs and snails), and acaricides (to kill mites). These chemicals are typically manmade synthetic organic compounds, but there are exceptions which occur naturally that are plant derivatives or naturally occurring inorganic minerals. 

The words natural and organic are quite appealing to the consumer. Synthetic is often considered less desirable. Many believe that natural is better, safer, or not foreign to the body, but quite the opposite may exist. Native is identical to what is produced by or present in the body. Natural products refers to substances that are use to promote health or treat illness derived from plant, mineral, or animal sources. Organic refers to the level of pesticides or chemicals used in the growing process. For example, insulin from pork or beef sources is natural, but not native. Recombinant insulin is synthetic, but native. Thus, synthetic, as in synthetic insulin or estrogen, does not necessarily mean foreign or less desirable. 

Although originated for DHHS, the approach has potential for use throughout government when it is necessary to communicate risks to an interested public. This is especially true for pesticides. These chemicals, which are an important part of the armamentarium against that aspect of nature which would take the very bread from our mouths, have acquired a somewhat unsavory reputation because of the potential risk associated with some of their chronic effects. The method chosen to explain the context of a pesticide risk (health hazards, etc.) to the public is a vital part of effective pesticide use management. 

---