Chapter 1
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Perceptions in Chemical Exposure Assessment Robert I. Krieger Personal Chemical Exposure Program, Department of Entomology, University of California, Riverside, CA 92521
Chemicals used as pesticides are both a broad, vital catalyst for the support and advancement of all aspects of our lives, and at the same time targets of extensive suspicion and mistrust. Spectacular beneficial responses to chemical technologies in medicine, agriculture, nutrition, and manufacturing have occurred over long periods of time. Issues and common perceptions of the health and environmental significance of chemical exposure often dominate discussion of pesticide use indoors and in agriculture. As those technologies have been developed and used, adverse effects have been observed from time to time, but that reality is dwarfed by subjective feelings that often outweigh reason.
Chemicals We live in a chemical world! The Chemical Abstracts Service now lists more than 22 million entries. The number increases every day. Only a small number of the 50,000 to 100,000 of them are chemicals of commerce, and pesticide active ingredients represent a much smaller number—perhaps 1,000 to 2,000. A still smaller number via inhalation, ingestion, and dermal contact are likely to contact humans and become part of our chemical experience. As more chemicals are added to the list, others are retired in a dynamic cycle. When all is said and done there can be little doubt that natural chemicals, principally in our diets, far outnumber our other chemical exposures.
© 2007 American Chemical Society Krieger et al.; Assessing Exposures and Reducing Risks to People from the Use of Pesticides ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
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Pesticides No other group of chemicals known for their toxicity to pests is so extensively used as part of an attempt to maintain a balance of advantage over our competitors for food and fiber as well as vectors of disease. Pesticides as a group designate (a) any substance or mixture of substances intended for preventing, destroying, repelling, or mitigating any pest, and (b) any substance or mixture of substances intended for use as a plant growth regulator, defoliant, or desiccant. Pesticide use is associated with direct and indirect human exposure, however, when the amounts of exposure are well below those that might produce human effects it seems more appropriate to consider them chemical exposures rather than pesticide exposures since the exposure likely lacks either pesticide or toxicological activity (7). These exposures are measurable only with extremely sensitive analytical equipment, and they occur within an unnumbered and unmeasured chemical milieu. It was suggested that such detections be regarded as "trace ag(riculture) by-products, less than tolerance." At the present time, dose and time are often not distinguished in discussions of the occurrence and effects of chemicals used as pesticides, and as a result, unreasonable responses to chemical exposure can be expected, e.g. HAZMAT, drift, food. No commercial use of chemicals is as controversial as pesticides (2). Persons in the United States are often strongly divided on grounds that are not easily defined (Table 1).
Table 1. Chemical Risk Characterization Hazard Identification Dose-Response
Use Exposure Assessment
Risk Assessment Risk Mitigation Risk Communication A classification scheme derived from the risk assessment paradigm separates persons on whether their focus is "How much is too much?" or "How little is OK?" (Table 2). Hazard identification seems to be foremost among persons who forecast "all-or-none" responses with exposure, deny that dose is a determinant of response, and have little or no confidence in the scientific method as a means to predict human responses from animal studies. Other persons seem to integrate their feelings about pesticides with their general experiences with pharmaceuticals, food ingredients, beverages, and other chemicals of their daily lives. The Paracelsian truth that "Dose determines the
Krieger et al.; Assessing Exposures and Reducing Risks to People from the Use of Pesticides ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
3 Table 2. Views of Chemical Exposures How much is too much?
How little is OK? Response
"All-or-none" Amount Small exposures cause certain harm Safe levels of everything Laboratory Studies Little confidence in relevance of Awareness of limitations of toxicity toxicity testing testing in animals "Dose makes the poison"
poison" establishes a foundation for their chemical encounters, and the idea that there is a safe level of everything is also consistent with our collective experience. Out of this perspective emerges a confidence in the scientific method as a means to meaningfully study responses of animals to protect human health. It is unfortunate that the views held by persons who hold an "All-or-None" perspective are often very prominent in shaping public opinion about trace pesticide contaminants, especially when they occur in food and the public water supplies. These chemicals in tiny amounts could be considered to represent the chemical signature of the 21 Century but they are characterized as a "body burden." The following sections of this paper will overview some origins of the public's worrisome perception of pesticides. st
Origins of Concern About Food Purity and Chemicals Food Adulteration The earliest public concerns about food purity were spawned by Fredrick Accum (3), a 19 Century chemist who addressed the adulteration of food. Pesticides were not an issue at this time, but food purity concerns were widespread and emotionally charged. Accum worked during a period of the emergence of many new chemical industries, and the appearance of quacks and impostors who made unlawful uses of new discoveries in chemistry. The adulteration of food and other necessities began to be practiced to an almost unlimited degree and in ways so subtle as to escape detection (4). Accum was a teacher, tradesman, analyst, and technical chemist, but he is best remembered as an author of books about chemistry that appealed to the popular mind. The best known book of several written on foods was "Treatise th
Krieger et al.; Assessing Exposures and Reducing Risks to People from the Use of Pesticides ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
4 on Adulteration of Foods." Accum discussed foods, their adulterants, and methods of detecting them in bread, beer, wine, spirituous liquors, tea, coffee, cream, confectionary, vinegar, mustard, pepper, cheese, olive oil, pickles, and other articles (4). In his crusade against food adulteration, Accum went beyond description of the frauds and indication of methods for their detection; he published the names of individuals who had been guilty of the practice. The cover of Accum's treatise carried the inscription "There Is Death In The Pot" and this philosophy became the foundation for the pure food movement based upon a quest for purity rather than findings shown to threaten human health.
Early Pesticide Residues During the next 50 years (1850-1900) a larger national agriculture emerged, pesticide use became more common and concerns existed about possible health effects of fruit and vegetable pesticide residues. The chemicals of concern were primarily arsenicals. A. J. Cook of Michigan reported results of the first official tests of arsenicals that considered consumer exposure in 1880 (5). Cook concluded that Paris green and London purple did not represent a danger to health. Eleven years later C. P. Gillette at the Iowa Agricultural Experiment Station also studied arsenicals on food and concluded that an individual would have to eat 30 cabbages dusted with Paris green to get enough arsenic to cause illness. A more extensive residue survey was conducted 1915 to 1919 by the Bureau of Chemistry enforcing the Federal Foods and Drugs Act in response to intensified patterns of insecticide use. Hundreds of samples of peaches, cherries, plums, apples, pears, grapes, cranberries, tomatoes, celery, and cucumbers were tested for lead, arsenic, and copper. Little chemical residue remained on produce treated according to standard recommendations of the Department of Agriculture, but other samples treated with excessive amounts or too close to harvest had higher residues. The possibility of cumulative effects over a period of time also emerged in discussion of the significance of food residues at this time. English, Canadian, and American orchardists faced trade and health concerns about the occurrence of lead, copper, and arsenic. The results of a British Ministry of Agriculture analysis of apple skin, stem, and calyx in 1925 are reported in Table 3. Results are reported as parts per million parts fruit. Seizures of contaminated pears occurred prompting litigation concerning whether or not the fruit "might be harmful to health (tf)." The Royal Commission on Arsenical Poisoning offered 14 ppm (1/100 grain per pound) as all humans could tolerate. The Bureau of Chemistry adopted this "world tolerance" as a working standard for enforcement of the Food and Drugs Act.
Krieger et al.; Assessing Exposures and Reducing Risks to People from the Use of Pesticides ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
5 Table 3. Lead, Copper, and Arsenic Trioxide Residues on Apples circa 1925 and 2004 Origin of Apples England Canada USA Modern Total Diet Study 1
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Number of Samples 13 6 5
-
Lead (ppm) 0.06 0.9 0.4 0.002
Copper (ppm) 0.2 0.2 0.3 0.2
Arsenic Trioxide (ppm) trace 0.4 0.2 0.003
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Recalculated from de Forest Lamb, 1936 (6) USDA, 2004(7)
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Western growers complained that they could not meet the 14 ppm tolerance, and the Secretary of Agriculture did not perceive an imminent threat to health. Leading toxicologists and physiological chemists were convened and after considerable study raised the tolerance to 35 ppm arsenic. They further reported "-evidence as to the prevalence of lead and arsenic poisoningfromthe ingestion offruitsand vegetables sprayed with insecticides and fungicides is scanty and unconvincing, but inasmuch as the insidious character of accumulative poisoning by these substances causes such cases to be overlooked, the lack of evidence as to the prevalence of such poisoning must not be accepted as proof that instances do not exist." These actions took place in an energized political climate with prevailing strong regional and international trade issues. Recognition of chronic lead poisoning in the industrial sector probably contributed to concern about accumulative poisoning from lead and arsenic residues on fruit and vegetable consumption. Current levels of these elements are reported (7) where arsenic and lead levels in market basket surveys were more than 2 orders of magnitude less than those reported by Lamb (6). Although time, sampling and analytical details are lacking, there can be little doubt that pest control practices at that time resulted in residues that would be considered unacceptable today.
20 Century Findings and Dr. Wiley's Poison Squad Harvey Wiley (8) was a chemist and physician who served as Chief Chemist, U . S. Department of Agriculture. His famous Poison Squad of 12 employees who voluntarily lived in a boarding house where they were served meals containing what must have been maximum tolerated doses of food adulterants including boric acid, salicylic acid, sulphates, benzoates, and
Krieger et al.; Assessing Exposures and Reducing Risks to People from the Use of Pesticides ACS Symposium Series; American Chemical Society: Washington, DC, 2007.
6 formaldehyde. Foods and excreta were collected, analyzed, and medical judgments were made about the impact of exposures on health. The work was of profound regulatory importance—Wiley is known as the Father of the Pure Food and Drug Act of 1906. Pesticides were not included because they were present in small amounts and Wiley considered them a normal part of agricultural practice. However, one of the food adulterants studied by Wiley also has use as a residential insecticide. "It appears...that both boric acid and borax, when continuously administered in small doses for a long period of time...will create disturbances of appetite, digestion, and health." No further definition of "small doses" or "long periods" was made. It has been estimated that 500 mg/day was served up over 50 days to yield a daily dosage of 7 mg/kg-d. Wiley's work earned him the title "Old Borax." Recent concerns about toxicity of borate pesticides have resulted from developmental toxicity studies. NOAELs were each substantially greater in rats (
