Years of Pesticides

Like metals and drugs, a third functional group of chemicals—pesticides—has a long-standing role in human history. The first recorded remediation of pests by humans occurred more than 70,000 years ago, predating metallurgy, the domestication of animals, and the cultivation of crops. 

In a cave in South Africa, layers of human bedding, primarily reeds and sedges, have been identified. Over time, the bedding material would have become infested with bedbugs and lice. To deter the bugs, the top lining of the bedding was layered with leaves from 

Alan S. Ko ak,ModemPoisons ABriefIntroduction to Contemporary Toxicology, DOI 10.5822/ 978-1-61091-609-7 12, 2016 Alan S. Kolok. 

Further evidence supporting the use of insecticides dates back to the Sumerians and the Chinese between 3,200 to 4,500 years ago. As with the leaves lining prehistoric beds, the original pesticides used by these civilizations were readily available animal, plant, and mineral compounds. Mercury, arsenic, and sulfur compounds were all used for insect control in these ancient civilizations. Generations later, approximately 2,000 years ago, a botanical pesticide, dried chrysanthemum flowers, was added to the list of ancient pesticides. 

The pesticide arsenal remained true to its humble origins until the twentieth century. Occasionally, botanicals or other mineral complexes would arrive on the agricultural scene and enter into use as pesticides however for the most part, their arrival was more by happenstance than by any specific, concerted effort. As an example, tobacco, a botanical from North America, was introduced to Europe 

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LifeLine Aggregate and cumulative stochastic Simulates daily pesticide exposures for periods from birth up to 85 years of pesticide applicators, residents of homes where pesticides are used, and the general population (dietary and tap water consumption) LifeLine Group (2005)... 

Results from the Formative Years of Pesticide Chemistry... 

Historically, the discovery of one effective herbicide has led quickly to the preparation and screening of a family of imitative chemicals (3). Herbicide developers have traditionally used combinations of experience, art-based approaches, and intuitive appHcations of classical stmcture—activity relationships to imitate, increase, or make more selective the activity of the parent compound. This trial-and-error process depends on the costs and availabiUties of appropriate starting materials, ease of synthesis of usually inactive intermediates, and alterations of parent compound chemical properties by stepwise addition of substituents that have been effective in the development of other pesticides, eg, halogens or substituted amino groups. The reason a particular imitative compound works is seldom understood, and other pesticidal appHcations are not readily predictable. Novices in this traditional, quite random, process requite several years of training and experience in order to function productively. 

Year Number of pesticides found Number of states where pesticides found... 

The rate and extent of pesticide metaboHsm can vary dramatically, depending on chemical stmcture, the number of specific pesticide-degrading microorganisms present and their affinity for the pesticide, and environmental parameters. The extent of metaboHsm can vary from relatively minor transformations which do not significantly alter the chemical or toxicological properties of the pesticide, to mineralisation, ie, degradation to CO2, H2O, NH" 4, Cf, etc. The rate of metaboHsm can vary from extremely slow (half-life of years) to rapid (half-life of days). 

Mono- and dichlorotoluenes ate used chiefly as chemical iatermediates ia the manufacture of pesticides, dyestuffs, pharmaceuticals, and peroxides, and as solvents. Total annual production was limited prior to 1960 but has expanded greatly siace that time. Chlorinated toluenes ate produced ia the United States, Germany, Japan, and Italy. Siace the number of manufacturers is small and much of the production is utilised captively, statistics covering production quantities ate not available. Worldwide annual production of o- and -chlorotoluene is estimated at several tens of thousands of metric tons. Yearly productions of polychlorotoluene ate ia the range of 100—1000 tons. 

Many very hazardous solvents, such as benzene and carbon tetrachloride, were widely used until the 1970s. The situation was very similar for the use of pesticides. Among the toxic pesticides that were still in wide use 20 years ago were chlorophenols, DDT, lindane, and arsenic salts, all of which are classified as human carcinogens as well as being acutely toxic. Fortunately, use of these kinds of very toxic chemicals is now limited in the industrialized world. However, because the number of chemicals used in various industries continues to increase, the risks of long-term health hazards due to long-term exposure to low concentrations of chemicals continues to be a problem in the workplace. 

Furthermore, significant amounts of food are lost to pests. Worldwide preharvest crop losses to pests (insects, diseases, and weeds) are estimated to be about 35% each year (10). These major pest losses are occurring despite the application of about 2.5 million metric tons of pesticide, at an annual cost of 18 billion (11). Even after crops are harvested, an additional 20% of the food is lost to pests (12). Overall about 48% of all potential world food supply for humans is lost to pests despite all efforts to protect it. 

Cosmetic Standards. Over the last two decades, the U.S. Food and Drug Administration (FDA) has been lowering the tolerance levels for Insects and insect parts allowed in and on fresh and processed foods (14). Concurrently consumers have sought "more perfect," pest-free produce. To achieve this, farmers have Increased the quantities of pesticide they applied to crops. Although the presence of small amounts of insect parts in such products as catsup and apple sauce, or blemishes on oranges pose no health risk, these stringent standards have stood for many years. 

Each year the use of pesticides in U.S. agriculture costs the nation about 4.1 billion (15). This cost Includes the cost of the chemical plus that of application. Approximately 16 billion worth of crops is saved through the application of pesticides. Thus, for every dollar invested in pesticides about 4 is returned in protected crops. 

A large number of domestic animals are poisoned each year by pesticides and must be destroyed. Additionally, significant amounts of meat and milk are contaminated with pesticides and must be removed from the market place (51). The yearly cost of these losses is estimated to be at least 30 million. 

From this analysis it is clear that in addition to their benefits, the use of pesticides in food production not only causes serious public health problems but also considerable damage to vital agricultural and natural ecosystems in the United States and world. A conservative estimate suggests that the environmental and social costs of pesticide use in the United States total about 4 billion each year. Worldwide the yearly environmental and public health costs are probably at least 100 billion. This is several times the 18 bllllon/yr spent on pesticides in the world. 

Future studies must focus on those specific agricultural technologies that have contributed to the increased use of pesticides during the past 40 years, and why crop losses to pests continue to Increase. Research needs not only to identify the detrimental technologies, but, more Important, develop ecologically sound practices that farmers can use as profitable substitutes (15). 

Methyl parathion is approved only for use on crops. The maximum amount of methyl parathion residue allowed by the Food and Drug Administration (FDA) and EPA on crops used as food is 0.1-1 ppm. The FDA has monitored the food supply for pesticides for a number of years. FDA purchases many kinds of foods through Market Basket Surveys and analyzes them for residue levels of pesticides. These FDA studies allow scientists to estimate the daily intake of pesticides. Generally, the FDA monitoring studies conclude that the U.S. food supply contains only very small amounts of pesticides that are not a concern. However, there have been some reports of the illegal use of methyl parathion inside homes. For more information, see Section 1.7 and Chapter 6. 

In a case-control study of pesticide factory workers in Brazil exposed to methyl parathion and formulating solvents, the incidence of chromosomal aberrations in lymphocytes was investigated (De Cassia Stocco et al. 1982). Though dichlorodiphenyltrichloroethane (DDT) was coformulated with methyl parathion, blood DDT levels in the methyl parathion-examined workers and "nonexposed" workers were not significantly different. These workers were presumably exposed to methyl parathion via both inhalation and dermal routes however, a dose level was not reported. The exposed workers showed blood cholinesterase depressions between 50 and 75%. However, the baseline blood cholinesterase levels in nonexposed workers were not reported. No increases in the percentage of lymphocytes with chromosome breaks were found in 15 of these workers who were exposed to methyl parathion from 1 week to up to 7 years as compared with controls. The controls consisted of 13 men who had not been occupationally exposed to any chemical and were of comparable age and socioeconomic level. This study is limited because of concomitant exposure to formulating solvents, the recent history of exposure for the workers was not reported, the selection of the control group was not described adequately, and the sample size was limited. 

Groundwater has also been surveyed for methyl parathion. In a study of well water in selected California communities, methyl parathion was not detected (detection limit of 5 ppb) in the 54 wells sampled (Maddy et al. 1982), even though the insecticide had been used in the areas studied for over 15 years. An analysis of 358 wells in Wisconsin produced the same negative results (Krill and Sonzogni 1986). In a sampling of California well water for pesticide residues, no methyl parathion was detected in any of the well water samples (California EPA 1995). In a study to determine the residue levels of pesticides in shallow groundwater of the United States, water samples from 1,012 wells and 22 springs were analyzed. Methyl parathion was not detected in any of the water samples (Kolpin et al. 1998). In a study of water from near-surface aquifers in the Midwest, methyl parathion was not detected in any of the water samples from 94 wells that were analyzed for pesticide levels (Kolpin et al. 1995). 

Samples of rainfall in Iowa have been analyzed for levels of pesticides (Nations and Hallberg 1992). Samples collected in April, May, and June of the three years in the study period of 1987-1990 had the highest levels of methyl parathion, corresponding to the application to crops. Methyl parathion was found in 4 of the 318 rain samples analyzed at a maximum concentration of 2.77 pg/L. In a study of... 

In a Food and Dmg Administration (FDA) summary of the levels of pesticides in ready-to-eat foods in the 10-year period from 1982 to 1991, methyl parathion was found 12 times in 8 kinds of food, at an average concentration of 0.0035 ppm (Kan-Do Office and Pesticides Team 1995). A 5-year analysis of domestic and imported foods and animal feeds for the years 1982-1986 detected 94 samples out of 19,851 total samples that contained methyl parathion (Hundley et al. 1988). Eighty-nine of the samples had concentrations in the range of 0.05-0.5 ppm, and five had levels ranging from 1.0 to 2.0 ppm. Methyl parathion was found in celery, citms, coriander, cantaloupe, Chinese peas, hay, alfalfa feed, Italian squash, lettuce, mustard greens, okra, parsley, peppers, spinach, strawberries, tomatillos, and tomatoes. 

Luke MA, Masiunoto HT, Cairns T, et al. 1988. Levels and incidence of pesticide residues in various foods and animal feeds analyzed by the luke multiresidue methodology for fiscal years 1982-1986. J Assoc Off Anal Chem 71 415-420. 

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