Pesticides


Pesticides, though not commonly used before the 1940s, are now in widespread use throughout the world. We will define pesticides as chemicals that control or kill pests or affect plant or animal life. Herbicides therefore will be included under the general term of pesticide. Pesticides are commonly used in your home to control pests and weeds. Their presence permeates many areas other than the home; they are used in agriculture, horticulture, public parks, and gardens, among others. Table 11.1 is a partial list of different types of pesticides and their functions.




THE HISTORY OF PESTICIDE DEVELOPMENT

Pesticides have been in use for centuries. In 470 B.C., the Greek philosopher Democrates used olive extracts on plants to prevent blight. Vine pests were destroyed with sulfur fumes by Cato in Italy in 200 B.C. Biological control was found effective by the ancient Chinese who used ants to protect their trees from insect pests.


Pesticide use in the early twentieth century brought with it some problems. Many of the so-called “natural” chemical pesticides in use before 1940 were extremely toxic. They included sulfur, copper, oil, nicotine, arsenates, formaldehyde, and micurate bichloride. These were all sprayed on crops, and little was mentioned of their hazards at that time.


The world market for pesticides has exploded since the 1940s. Approximately $13 billion worth of pesticides were being used every year by 1986. The breakdown of pesticide use in 1984 was as follows: herbicides, 43 percent; fungicides, 18 percent; and other pesticides, 39 percent. The United States uses more pesticides than any other country. In 1984 we used 34 percent of all pesticides; Eastern Europe and Russia used 8 percent; Latin America, 10 percent; the Far East, 16 percent; and Western Europe, 19 percent. The rest of the world used the remaining 13 percent.


Pesticides have made an important contribution to both food production and disease control. It is estimated that 45 percent of the world’s potential food supply is lost to pests: 30 percent to weeds, pests, and diseases before harvest, and another 15 percent between harvest and use. Some estimate that at least one third of the crops in Third World countries are lost to pests.)


Despite the fact that pesticides have aided in the control of malaria, schistosomiasis, and filariasis in tropical countries, there are still 150 million cases of malaria and about 250 million cases of schistosomiasis and filariasis each year in the world. There is no way of knowing and no way to calculate how many lives will be saved or improved by the use of pesticides to control diseases and increase our food production. Likewise there is no way to calculate how many lives will be lost from pesticide use either. Some dangerous pesticides that are banned or restricted in North ,America and Europe have been unloaded on Third World countries.


There were about 1,200 pesticide chemical compounds, combined in 30,000 different formulations and brands in the United States in 1981. The United States used about 900 million pounds of pesticides in that year. Approximately 334 million pounds of pesticides or 5-10 percent of the entire world’s supply was used by California alone in 1977. (2)


The High Cost of Pesticides

Companies that develop pesticides become committed to marketing them early in development for a number of reasons. First, they must test thousands of new compounds each year, among which only a few make it through the screening process. It usually takes about seven years for a pesticide to be put through the screening process and granted registration by the U.S. Department of Agriculture and the Environmental Protection Agency (EPA). Naturally, pesticide manufacturers are eager to advertise their products before they appear on the shelves because of their large out-of-pocket expense. For example, in 1987, one company invested approximately $45 million to develop one pesticide that required the screening of at least 20,000 chemical compounds before it could be identified as effective.


D. Pimentel has looked at the cost effectiveness of pesticides in the United States. (3,4) It cost approximately $2.8 billion each year to apply pesticides that prevent pest losses totaling about $10.9 billion a year. Hence, there is a return of about three dollars for every dollar invested in pesticide application. The indirect costs of pesticides are estimated to be about $1 billion and stem from human exposure to pesticides, an increase in the number of pests when the chemicals kill off the natural predator, pest resistance, pollination problems from destroying the bee population, and other problems. Pimentel’s estimate for the cost of cancers in the United States is about $125 million per year. About $58 million a year is ascribed to human pesticide poisonings.


Pesticides enter your body by inhalation, absorption through the skin, or ingestion. And unlike industrial chemicals, which are used in a very controlled manner, pesticides are sprayed, powdered, or dropped as pellets or granules in and around places where the general public may walk or play. In fact, pesticide residues are commonly found in human tissue in almost everyone in the United States, averaging six parts per million (ppm) in fatty tissue. (5) Pesticide residues have been found in breast milk and cow milk and have been found to cross the placental barrier to the human fetus. (6)


The Dangers of Pesticide Use

Because pesticides are soluble in oil or fatty tissue like that of the human breast and its milk, it is theorized that pesticides may be a contributing factor to breast cancer. (7) Incidental findings in experiments involving exposure of rats and mice to pesticides show a significant increase in breast cancer in the exposed animal group. Women are at greater risk than men when exposed to the same amount of pesticides because the Allowable Daily Intake for pes-ticides as determined by the federal government is calculated on the basis of a 70-kilogram man, not a 50-kilogram woman with larger breast tissue.


Some cases of Parkinson’s disease as well as other neurological diseases have been linked to various pesticides. (8) Hypertension, cardiovascular disease, and abnormal blood cholesterol and vitamin A levels have been linked to pesticide exposure. Pesticides are also associated with allergies, liver disease, skin diseases, fertility problems as manifested by changes in the egg and sperm (teratogenicity), and changes in the RNA and DNA (mutagenicity). Regular spraying of pesticides in homes and gardens was linked with the development of acute leukemia in young children in the Los Angeles area. (9) Other cancers have also been associated with pesticides. (10,11)


Pesticides also pose an environmental hazard. They pollute the rain water of many U.S. states when they are vaporized or when the wind blows soil particles treated with pesticides. (12)


If you were exposed to toxic amounts of pesticide, that is, if a large dose were inhaled or made contact with your skin, you would experience acute effects. These effects usually appear within minutes to hours after contact. However, the effects of low-level or prolonged pesticide exposure, particularly to those that may have carcinogenic potential, are very different. Cancer does not appear immediately after exposure to a pesticide; it may not be apparent until long after exposure has occurred. Unfortunately, by the time the medical and scientific community becomes aware that a particular pesticide causes cancer, a large number of persons could have been exposed without their knowledge. For example, R-11, which is a chemical found in insect repellents, has just been shown to cause cancer in animals.


Dioxin, otherwise known as Agent Orange, and one of its associated contaminants, TCDD, was extensively used toward the end of the United States’ conflict in Vietnam. (13) Hundreds of thousands of people were exposed to these agents, and serious allegations by Vietnam veterans and other persons have been raised that Agent Orange and TCDD (14) caused malignant tumors, sterility, spontaneous abortions, birth defects, disfiguring skin diseases, and other illnesses.


We do know that TCDD is very toxic and causes tumors in rats, in which it acts as a promoter of cancer. (15) It can also initiate carcinogenesis in animals. (l6,17) A number of human epidemiological and toxicological studies have suggested an association between TCDD or the chemicals it contaminates, and soft-tissue sarcoma, (18-20) Hodgkin’s, (21) non-Hodgkin’s lymphoma, (22-24) stomach cancer. (25,26) nasal cancer, (27) and liver cancer. (28,29) However, other studies did not show a correlation between TCDD and other cancers. (30-35) Most of these studies involved a short period of time between exposure and disease. It now appears that the longer the time from exposure to TCDD, the higher the risk for the development of cancer and the higher the incidence of cancer. (36,37)


Table 11.2 lists several different pesticides and their roles as human carcinogens. (38-41) Some are definitely associated with human cancer, some are probably associated with human cancer, and some are possibly associated with human cancer. You will recognize a number of them. Many other pesticides not included in this table, like malathion and Mirex, have been linked to cancers in animal studies. Some of them are also familiar to you because they are commonly used in household and garden settings. Currently there is no definite evidence that the pesticides causing animal cancer also cause human cancer. However, we should continue to be on the alert and await future studies for their possible link to human cancer.







Several human cancers are associated with pesticide use. They include the following:


  • Leukemia.
  • Multiple myeloma.
  • Lymphoma.
  • Soft-tissue sarcoma.
  • Prostate cancer.
  • Stomach cancer.
  • Melanoma.
  • Brain cancer.
  • Liver cancer.
  • Skin cancer.
  • Lung cancer.
  • Central nervous system tumors: gliomas.
  • Cancer of esophagus.
  • Ovarian cancers.


    There is a correlation between these cancers and a variety of pesticides and pesticide uses. This does not mean, however, that pesticides are the direct cause of these cancers.


    In this age of organic farming, the debate over pesticide use rages on. Othal Brand, who was recently appointed to the Texas Pesticide Regulatory Board, said of the termite killer Chlordane, “Sure, it’s going to kill a lot of people, but they may be dying of something else anyway.” (42) Farmer Clarence Hopmann of Dumas, Arkansas, decreased the use of agricultural pesticides because he developed an allergy to them. However, in order to qualify for bank loans, the bankers demanded that he use large doses of pesticides on his crops. He has resumed using them. (43 )


    There are several things that can and should be done to minimize the use of pesticides in our country and the world. Before the 1940s, pesticides were not used very much at all. Hence there have always been alternatives to the artificial chemical pesticides currently in use.


    Nature provides us with biological controls, that is, natural predators that can be introduced to control insects. For example, ladybugs can be used to fight off aphid predators. Beetles were used to control weeds in the western United States in the 1950s, parasites to control the citrus fly in Barbados in the 1960s. You can also minimize the number of pests by providing food and habitat for the pest’s natural enemies. Certain traditional farming practices may be employed as well. Crop residues may be removed by plowing or flooding. Pest deterrents, crop rotation, proper drainage methods, and physical controls like traps or blocking of insects and/or other pests can be used. These techniques, along with biological controls, have been used successfully by many countries, including China, Nicaragua, certain areas of England, and also some parts of America.


    While chemical pesticides certainly benefit populations by increasing food production and decreasing certain diseases, it is important to use them only when they must be used and to use the pesticides that cause the least toxicity in human beings and the least damage to the environment around us. Treat them all as hazardous and minimize their use in public areas and in and around your home. For example, since the pesticide 2,4,5-T is very hazardous, substitute the less hazardous Amcide or Krenite. Silicon and soap can be used in gardens as a nontoxic insecticide rather than the other commonly used pesticides for the garden. Wasps have been controlled by parasites in greenhouses more effectively than with chemicals. And the bacteria called Bacillus thuringiensis has also been shown to be a good alternative to several toxic insecticides.


    WHAT CAN BE DONE

    The number of tons of pesticides has increased thirty-three times since 1940, and their toxicity has grown tenfold. However, crop losses to microorganisms, insects, and weeds have gone up 31-37 percent. There are a number of reasons for this. As new pesticides are developed, insects develop resistance to them. But even more importantly, the government supports prices of various crops, which encourages farmers to produce only a single crop instead of rotating crops to inhibit the pests.


    By using crop rotation and biological pest control, pesticide use could be cut in half. Food prices would rise by one percent-about $1 billion a year-but the benefits would be enormous. The United States would save $4-$10 billion per year from decreased damage to fish and water supplies, decreased costs of regulating pesticides, and decreased health-care costs for the 20,000 people poisoned each year from pesticides. (44)


    You should learn as much as you can about any pesticides you do use. Acquiring such information is not easy but neither is maintaining good health. Acquire information and use alternatives to the current pesticides. Exposure to pesticides can be controlled. This is yet another risk factor for disease over which you have control.



  • From Cancer and Nutrition by Charles Simone, © 1992. Published by Avery Publishing, New York. For personal use only; neither the digital nor printed copy may be copied or sold. Reproduced by permission.

    Avatar Written by Charles B. Simone MD

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