Chemical Mutagenesis: An Emerging Issue For Public Health LARRY D. CLAXTON, MS, AND PATRICIA Z. BARRY, DRPH

Abstract: Chemical mutagens are recognized as prevalent in the environment and a potential threat to the health of future generations. This paper presents an overview of chemical mutagenesis as an issue for public health. Several problems in the determination of risk to human populations are discussed, including

difficulties of extrapolating scientific data to humans, the latency period between exposure and recognizable genetic damage, and the large number of chemicals which must be tested. Test systems are described. Possibilities of control through federal regulation are discussed. (Am. J. Public Health 67:1037-1042, 1977)

In the last decade we have become painfully aware that our burgeoning technology has produced some highly undesirable side effects. The increasing prevalence of toxic substances in the environment has become a matter of public interest as a complex public health problem. To date the federal government has been concerned primarily with toxicity and carcinogenicity as targets for regulation, but the recently passed Toxic Substances Control Act authorizes the regulation of mutagenic agents.' Regulatory decisions for the control of mutagenic substances are extraordinarily complex due to the difficulty of extrapolating the scientific data to humans, the long period of latency between exposure and adverse recognizable damage, the lack of public awareness of mutagenesis as a threat to health, and the huge number of chemicals in use whose mutagenic status is unknown. It is the purpose of this paper to summarize some information on mutagenesis in the context of public health, with the hope of stimulating discussion of this complex issue among public health professionals. Mutagenic agents cause changes in the existing genetic material. Because mutations in reproductive cells may be carried in the recessive state through several generations, effects of mutagenic agents are likely to be hidden for decades. Specific agents may never be associated with specific

genetic damage. However, there is widespread opinion that increasing rates of mutation may have devastating consequences for the health of future generations.

Address reprint requests to Dr. Patricia Z. Barry, Assistant Professor, Department of Health Administration, UNC School of Public Health, Chapel Hill, NC 27514. Mr. Claxton is a biologist at the National Institute of Environmental Health Sciences, Research Triangle Park, NC, and a doctoral student at North Carolina State University, Raleigh. This paper, submitted to the Journal July 29, 1976, was revised and accepted for publication April 5, 1977. AJPH November 1977, Vol. 67, No. 11

The effects of mutation for the organism run from inconsequential to lethal. Genetic diseases are not uncommon. One survey estimates that 7.1 per cent of all hospital admissions involve genetic disease and suggests that 31.5 per cent of all admissions involve genetically influenced disease.2 McKusick records nearly 2,000 different human conditions which are genetically determined.3 Many of these are defects involving gross anatomical malformations; others are biochemical changes which interfere with normal metabolism. While some conditions are manageable through surgical or pharmacological treatment, many present lifelong problems to those afflicted. Several studies link cancer and mutation.4 5 McCann and Ames report that among 300 chemicals tested for mutagenicity and carcinogenicity, 90 per cent of the known carcinogens are mutagenic in bacterial test systems.6 Genetic susceptibility to cancer is suggested by the fact that elevated rates of leukemia are associated with many genetic disorders including Down's syndrome, Trisomy D, Kleinfelter's syndrome, Falconi's syndrome, and Bloom's syndrome.5 Several tumors and tumor syndromes such as retinoblastoma, pheochromocytoma, and polyposis of the colon are inherited as though caused by dominant gene mutations.5 Increases in mutation rates would increase the incidence of these conditions. Although there has been considerable research on the identification of mutagenic compounds, most of the results are from non-mammalian test systems. A fundamental barrier to understanding the implication of human exposure to 1037

CLAXTON AND BARRY

mutagenic hazards is the lack of direct information. Basic research in molecular genetics has produced a voluminous literature on the effects of chemical mutagens on bacteria, viruses, fungi, insects, plants, and mammalian cells in tissue culture; many chemical compounds have been identified which are mutagenic in these systems. Whether a substance is judged to be mutagenic depends on three factors: 1) the manner of administration and the suitability of the test system; 2) the methods of cytological and genetic examination; and 3) the definition of "mutation" on which the analysis is based. In general, "mutation" is taken to mean every kind of unexpected change in the genetic material which is not due to Mendelian recombination or crossing over.7 Since the genetic material and hereditary processes are similar in all living organisms, it is reasonable to expect that chemicals found mutagenic in non-mammalian test systems could have genetic consequences for humans. Although mutation of somatic cells can have serious health consequences, the effect of mutation in germ cells is a more insidious and potentially more dangerous long-term problem. Whether or not a mutagenic substance actually causes mutation in human germ cells depends on a number of circumstances including the body's usual manner of assimilating the substance (i.e., route of administration, blood and tissue barriers, site of metabolism, etc.); the degree of exposure to the mutagen both in terms of total amount delivered and amount delivered per unit time; the possibility of metabolic alterations of benign substances to intermediates with mutagenic properties; and the synergistic effects of combinations of substances.7 Therefore, although variability in test systems, in experimental methods, and in analysis may yield ambiguous information, even clearly positive results are not easily extrapolated to humans.

Chemical Mutagens Compounds which have been demonstrated to be mutagenic in non-human test systems are in common use.7 Hycanthone, a drug which is highly effective against schistosomiasis and can be given as a one-time curative dose, is of great benefit in many African and Asian countries where schistosomiasis is a major health problem. Hycanthone is a mutagen in a tissue culture system using L5 178Y mouse lymphoma cells.8 Since 1965 Japan has used a food preservative known as AF-2 (a furylfuramide) in processing widely used food such as soybean curd and fish sausage. AF-2 has been shown to be mutagenic in several test systems,9 and longterm carcinogenesis experiments are presently in progress. Vinyl chloride was recognized as a carcinogen before being tested for mutagenic activity;'0 recent tests demonstrate its mutagenic properties." Vinyl chloride is an occupational hazard in the manufacture of polyvinyl chloride, which is used in a variety of products including phonograph records, floor tile, latex wall paints, and pipes.'2 Some dye components used in hair dyes have been demonstrated to be mutagenic in bacterial test systems.13 While the testing of the dyes is underway, millions of Americans continue to use hair dye regularly. 1 038

The occupational environment presents significant hazards to workers who are exposed to high concentrations of chemicals and dusts. Over 16,000 chemicals are recorded in the Registry of Toxic Effects of Chemical Substances, and mutagenic information has been recorded for less than one per cent of them.'4

Test Systems A number of methods have been developed to test chemical compounds and other agents for mutagenic activity. The simplest of these is to treat bacteria and fungi directly with the potential mutagen. These methods are very reliable and reproducible. Plant test systems are useful for testing gaseous agents and are especially good for the analysis of chromosomal mutation. '5 Tissue cultures of human cells and other mammalian cells may be used to detect both gene and chromosome mutations. Tissue culture results are not especially useful for determining hazardous levels of exposure, because anatomical barriers at the tissue and cellular level may screen out mutagenic compounds and reduce the concentrations which actually reach sensitive sites.'6 The specific locus mutation system in mice is considered the most reliable whole mammal test for gene mutations. I' However, whole mammal test systems are very expensive, often requiring thousands of animals for a single test. Few laboratories are equipped to handle such large scale experiments. Monitoring of human populations using epidemiological and clinical techniques may yield preliminary information regarding mutagenic hazards. Three approaches to monitoring human populations have been proposed by Neel:'7 1. Vital statistics may be analyzed for changes in birth rate, incidence of congenital defects, sex ratio, and rates of spontaneous abortion. However, since these statistics are subject to variation due to circumstances other than mutation, changes in rates are most useful as indicators that mutagens may be present. Further tests would be necessary for confirmation. 2. Specific populations may be monitored for changes in the incidence of congenital abnormalities due to dominant mutations. For example, under the suspicion that waste anesthetic gases may be hazardous to operating room personnel, a survey was conducted to determine the rates of spontaneous abortion and congenital malformation among infants born to women working in operating rooms who were exposed to waste gases during pregnancy. It was found that exposed women reported higher rates of birth defects aflmong their infants than unexposed women. Elevated rates of congenital defects also were reported among babies born to wives of men who were exposed to waste gases during the year before conception.18 It is difficult to distinguish between mutagenic and teratogenic mechanisms in the production of congenital abnormalities; therefore, the monitoring of populations for birth defects will not be sufficient to determine mutagenicity of suspected chemicals. Furthermore, since dominant mutations may lead to early abortion and consequent loss of data, monitoring of specific populations may be of limited usefulness. AJPH November 1977, Vol. 67, No. 11

CHEMICAL MUTAGENESIS

3. Mutations may be detected through biochemical and/ or cytological screening of human tissue for abnormal genetically determined reactions. A system under development would examine red blood cells of normal individuals for the presence of sickle cell hemoglobin, indicating that a somatic mutation had taken place. Collection of data on the presence of sickle cell hemoglobin in normal individuals should yield information on the mutation rate for this gene.'9 Another technique currently under exploration is the identification of genetically determined protein variants which may be detected by electrophoresis.'7 Systems for measuring and detecting increases in mutation rates in humans are not yet feasible for massive screening of suspected mutagens, and there is no consensus regarding which system shows the most promise for general screening. Bridges has suggested a three-tier protocol for mutagenicity screening based on three general principles: 1) no generally mutagenic chemical should be released into the environment or be permitted to be used if there exists a satisfactory non-mutagenic substitute; 2) the extent and rigour of the screening procedures should be related to the extent to which man is likely to be exposed to the agent; and 3) mutagenic substances may be used if the benefits are judged to be great enough to outweigh the hazards and if appropriate controls are exercised.20 Bridges proposes that the first tier of tests should be used for all suspected mutagens and would consist of treating various lower organisms with the chemicals in order to assay gene mutation and chromosomal damage. This rapid and inexpensive test would demonstrate whether or not the chemicals were mutagenic per se, and it is expected that the majority of chemicals tested would prove to be negative. Those chemicals found positive in tier one would be rejected for use if a suitable non-mutagenic chemical were available as a substitute. If no substitute were available, the chemical would pass to tier three for further testing and assessment of genetic risk. Those chemicals found negative in tier one would be approved for use if they were unlikely to be consumed or ingested by humans through food or drugs. On the other hand, if the exposure were expected to be high, chemicals found negative in tier one would pass to tier two for further testing. The second tier would use in vitro tests and in vivo tests in order to detect mutagenic intermediary metabolites which might be produced from the chemical. Substances which proved negative in these tests would be approved for use. Substances which were positive would be passed on to the third tier of evaluation. The third tier would be reserved for those chemicals which proved positive in one of the lower tiers and which, in accordance with the first general principle, have no satisfactory substitute in their use. Tier three would be used to evaluate those chemicals of demonstrated mutagenicity whose use would have great and irreplaceable economic or medicinal value. The question for this level of testing would not be the detection of mutagenic activity, but rather the quantitative assessment of the mutagenic risk to humans.20 Tier three tests would use whole mammals exposed to suspected mutagens in a manner similar to expected human AJPH November 1977, Vol. 67, No. 11

exposure. Because few laboratories are equipped to perform tier three tests and because they are very expensive and time consuming, it is anticipated that a backlog of chemicals would rapidly be accumulated, leading to lengthy postponement of regulatory decisions. Bridges' approach views tier one as a basis for regulation, but others have suggested that it would be more appropriate to view tier one as an indication of priority for further testing.2' 22 These modified schemes suggest that some regulatory decisions could be made on the basis of positive tier two results rather than insisting on tier three testing for all identified mutagens. The modifications which have been suggested would help to mitigate the delays inherent in tier three tests. Other non-hierarchical and semi-hierarchical testing schemes undoubtedly will be proposed. Figure 1 summarizes a modified scheme for three tier testing. Table I summarizes further information regarding costs and time requirements for each tier. The assessment of genetic risk for human populations is exceptionally problematic. In lower organisms dose-response curves relating exposure to genetic damage may be generated through experiments; such dose-response curves will not be generated for human populations. Some data may be obtained from those exposed through occupational or other unwitting contact, but in practice we will have to depend on extrapolations from whole mammal tests to estimate the risk posed by each mutagen. A basic unit of mutagenic activity would be useful to compare the risks of various chemical mutagens. Two units have been suggested, one based on the spontaneous mutation rate and one on radiation equivalents.'6 All test systems have a spontaneous mutation rate, which is a low-level background rate of mutation occurrring without the presence of a known mutagen. One proposed unit of chemical mutagenic

[lHighly control led use; IReject if possible

|Control led use | tqi

[Negative |

Tier Three

m

Testing Positive tier one and negative tier two; low consumption

Negative tier one

and tier two

Negative

Positive tier two; beneficial with no substitute but low consumption

-\ .

rier Two

* Positive tier two; substitute available

Testing

/Rejected for use] |Negative; high

Positive-,

consurption

substitute

exposure and/or

low exposure

Pstv

Positive tier two; beneficial; no substitute

Approved for use t

~

poor or no

One Positive; Tier TeUnjgreplocable wihfsubstitutJ

FIGURE 1-ModIfied Scheme for Tier Testing 1039

CLAXTON AND BARRY

TABLE 1-Description of the Tier System Concept Types of Screening Systems Used

Average Costs

Tier Three Complex mammalian > $50,000 per compound systems

Tier Two

Tier One

Simpler mammalian systems, some plant, animal, and tissue culture systems including cytogenetic screening Simple microbial, plant and animal systems

> 6 months

$5000 to $50,000 > 2 months per compound

< $5000 per compound

activity would be that concentration of mutagen which produces a doubling of the spontaneous mutation rate. For mammals, this could be expressed in milligrams per kilogram of body weight. Radiation biology has quantified doses of ionizing radiation of several types in terms of biological damage, thereby allowing comparisons between sources. The REM (radiation-equivalent-man) is a unit dose equivalence of radiation used to compare sources of ionizing radiation with respect to biological damage of a specified sort.23 The REC (remequivalent-chemical) has been proposed as a unit which would allow comparison between radiation and chemical mutagens. The REC would be that dose concentration multiplied by time which produces the same amount of genetic damage as one REM of chronic irradiation.20 23 Although the use of both the doubling concentration and the REC have serious technical drawbacks, the development of such a unit would provide a quantitative measure of mutagenic activity which would be useful in determining and comparing genetic risks of chemical mutagens.

Regulation of Mutagenic Hazards The technical problems which obscure understanding the nature of genetic risk may be resolved in the laboratory; however, appropriate regulation of mutagenic hazards also will require decisions on a number of issues which are not so much technical as political or ethical. These decisions will be made by federal regulatory agencies on the basis of opinions offered by scientists, industry, consumers, and other interested parties. It is vitally important that health professionals understand the issues and be prepared to participate in the public debate which will attend future vital regulatory decisions. Protection of the general public from hazardous chemicals is entrusted to several federal agencies including the Occupational Safety and Health Administration (OSHA), which has regulatory authority over the workplace; the Food and Drug Administration (FDA) which regulates foods, 1 040

Time Needed

< 2 months

Use

Testing of needed or beneficial chemicals under use-like conditions for good benefitrisk estimate Definitive testing of compounds

Pre-screen for other tier levels; definitive testing of some compounds

drugs, and cosmetics; the Consumer Product Safety Commission (CPSC) which has regulatory powers over most consumer products; and the Environmental Protection Agency (EPA) which regulates air and water pollution, the manufacture and use of pesticides, and will administer the Toxic Substances Control Act of 1976. Until the passage of the Toxic Substances Control Act, explicit regulatory authority over mutagenic agents was limited to the regulation of pesticides by EPA. However, it is worth noting that in August 1973 the Consumer Product Safety Commission banned several brands of spray adhesive on the basis of experimental evidence in mice that the adhesives or the propellant in the aerosol containers caused chromosomal damage leading to birth defects.24 The ban was reversed in January 1974 because of a lack of confirmative data;25 however, the incident set a precedent for regulation on the basis of mutagenicity by CPSC. The Occupational Safety and Health Administration has the regulatory authority to protect workers from hazardous dusts and chemicals in the work environment. Shortly after OSHA came into existence it adopted as standards the Threshold Limit Values (TLVs) suggested for industrial chemical exposures by the American Conference of Government Industrial Hygienists. The TLVs were directed primarily at substances which caused physiological reactions such as poisoning, irritation of eyes or respiratory tract, and skin rashes. The TLVs were not established on the basis of carcinogenic, teratogenic, or mutagenic properties, and synergistic effects of chemical mixtures were not included in tests used to determine the TLVs.26 Approximately 500 TLVs were adopted as OSHA standards, and 16 new standards for carcinogenic agents have been promulgated by OSHA.27 Within the proposed rules for pesticides set forth by EPA, the evaluation of the mutagenic potential of the active ingredients of a pesticide product can be ordered.28' 29 However, the proposed EPA regulations would require the use of in vivo mammalian test systems for regulatory decisions. The proposed regulations state that positive results in nonmammalian tests will not necessarily provide the basis for denying registration of a pesticide product. If in vivo mamAJPH November 1977, Vol. 67, No. 11

CHEMICAL MUTAGENESIS

malian tests are to provide the basis for decision making, the number of pesticides which can be screened for regulatory purposes will be quite small. The Toxic Substances Control Act of 1976 appears to have considerable potential for improving protection from chemical hazards, and it specifically refers to mutagenesis as a health effect for which testing standards may be prescribed.' The Act requires that adequate data be developed on the health and environmental effects of chemicals, and that this activity should be the responsibility of the chemical manufacturers and processors. EPA is required to establish standards for the testing of chemicals. A committee composed of eight federal officials with scientific and regulatory expertise will be established to prepare- a list of chemicals in current use to which EPA will give priority in issuing testing requirements. Companies are required to notify EPA 90 days before manufacturing any new chemical and to provide test data and other information about the safety of the product. EPA will have the authority to ban or regulate such chemicals if test information is insufficient and if the chemical would be produced in substantial quantities with wide distribution. EPA is required to ban or restrict the use of any chemical presenting an unreasonable risk of injury to health or the environment. I The term "unreasonable risk" is ambiguous and subject to varied interpretation. The definition of "unreasonable risk" will emerge from regulatory and administrative decisions of EPA, and there will be debate around the issue. Consumer advocates and environmentalists would prefer a definition leading to stringent and rigidly enforced control over hazardous chemicals; industry would prefer a definition which allows for individual discretion and voluntary compliance. The necessity of exposure will be a large factor in defining "unreasonable risk". The risks of a life-saving drug with mutagenic properties would be more acceptable than the use of mutagenic food coloring which adds eye-appeal and no other benefits. The Consumer Product Safety Commission, whose mandate is to ""protect the public against unreasonable risks of injury associated with consumer products,"30 moved swiftly to ban vinyl chloride as a propellant in aerosols when vinyl chloride was found through industrial exposure to be carcinogenic.3' Through this decision CPSC has identified the presence of carcinogenic agents in consumer products as an unreasonable risk, i.e., an unnecessary exposure.

Congress has deemed the addition of carcinogenic substances to food as an unreasonable risk through the 1958 Food Additives Amendment of the Food, Drug, and Cosmetic Act of 1938. This amendment, known as the Delaney clause, specifies that no food additives may be used which are "found to induce cancer when ingested by man or animal. "32 The Delaney clause not only declares that food additives present an unnecessary exposure, but it allows for results from animal tests to provide the basis for regulatory decisions. Similar legislation could be directed against food additives with mutagenic activity. The regulation of carcinogens has demonstrated that benefit to the general public is only one criterion for deterAJPH November 1977, Vol. 67, No. 11

mining the necessity of exposure. The economic impact of a proposed regulation on industry also is considered, often creating a tension between private and public interests. The food industry has resisted regulation under the Delaney clause when test results were weak or equivocal. For example, Red 2, a dye used to color foodstuffs to increase eye appeal, has long been suspected to be a weak carcinogen. Red 2 has been banned only since 1975 after many years of controversy.33 Other procedural questions will require decisions. What criteria should be used to determine which chemicals are tested first? Who will control the testing of compounds? Who has the responsibility for the dissemination of information about compounds demonstrated to be mutagenic but not yet assessed for degree of risk? How shall we assign costs in order to discuss risks and benefits in terms of economics? Chemicals whose health effects in human populations are not immediate pose special problems for regulatory agencies since it is difficult to establish causal relationships. In the case of carcinogens, onset of disease may follow exposure by decades. Cancer cases appear to be isolated events, unconnected to any occupational or other specific environmental hazard. Painstaking epidemiological detective work uncovered the connection between exposure to asbestos and mesothelioma, a form of cancer which is inevitably fatal.34 An alert occupational physician may discover associations through unusual circumstances. For example, the link between angiosarcoma, a rare form of liver cancer, and occupational exposure to vinyl chloride was discovered when B. F. Goodrich Company physicians were investigating an unusual number of liver ailments among workers in Goodrich's Louisville, Kentucky plant. Investigation of medical records revealed three deaths of workers from angiosarcoma between 1971 and 1974. Since angiosarcoma is very rare (the annual death toll in the U.S. is estimated to be around 20), three cases in one plant raised the specter of occupational exposure to vinyl chloride as the casual agent. 12 The problem of time lag between exposure and effect is particularly severe for mutagenic agents. Mutations will not show up until the next generation at the earliest, and may not appear for several generations. The long latency makes questionable the possibility of discovering the connection between hazard and genetic damage through epidemiology. The lag greatly reduces the visibility of mutagenic hazards as a threat to health. Although birth defects are perceived as a tragedy in the lives of individual families, the general public is largely unaware of the connection between mutagenic hazards and increased rates of congenital abnormalities. Furthermore, since birth defects are rare events, the public is not aroused through personal fear to support prevention efforts. Instead, public support has been through contributions for treatment and rehabilitation of those already afflicted. We have learned through experience with regulatory agencies to date that regulation is expensive, time consuming, and highly controversial. We may anticipate that the barriers to the regulation of mutagenic agents will be especially high. Health professionals must take the lead in recognition of the problem and must have a strong voice in the 1041

CLAXTON AND BARRY

debate surrounding regulatory decision making. Many believe that our genes constitute our tnost precious heritage.16 If increasing exposure to mutagenic hazards will degrade the gene pool by increasing the rates of deleterious mutations, then we must act now in a way which is responsible and just to protect the future of humanity.

15. 16. 17.

REFERENCES 1. U.S. Congress. Senate. Toxic Substances Control Act. P. L. 94-469, 94th Cong., 1976, S. 3149. 2. Childs, B., Miller, S. M., and Beam, A. G. Gene Mutation as a Cause of Human Disease. In: Mutagenic Effects of Environmental Contaminants. H. E. Sutton and M. I. Harris, Eds., New York: Academic Press, 1972. 3. McKusik, V. A. Mendelian Inheritance in Man, 3rd ed. Baltimore: Johns Hopkins Press, 1971. 4. Ames, B. N., Lee, F. D., and Durston, W. E. An improved bacterial test system for the detection and classification of mutagens and carcinogens. Proc. Natl. Acad. Sci. (U.S.A.) 70:782786, 1973. 5. Knudson, A. Mutation and human cancer. Adv. in Cancer Res. 17:317-352, 1973. 6. McCann, J. and Ames, B. N. Detection of carcinogens as mutagens in the Salmonella micrtsome test: Assay of 300 chemicals. Proc. Natl. Acad. Sci. (U.S.A.) 72(12):5135-5139, 1975. 7. Barthelmess, A. Mutagenic Substances in the Human Environment. In: Chemical Mutagenesis in Mammals and Man. F. Vogel and G. Rohrborn, Eds., New York: Springer-Verlag, 1970. 8. Clive, D. Mutagenicity of thioxanthenes (hycanthone, lucanthone, and four indazole derivatives) at the TK locus in cultured mammalian cells. Mutation Res. 26:307-318, 1974. 9. deSerres, F. J. AF-2: Food preservative or genetic hazard? Mutation Res. 26:1-2, 1974. 10. Creech, J. L., Jr. and Johnson, M. N. Angiosarcoma of the liver in the manufacture of polyvinyl chloride. J. Occ. Med. 16(3):150-151, 1974. 11. Rannug, U., Johansson, A., Ramel, C., and Wachtmeister, C. A. The mutagenicity of vinyl chloride after metabolic activation. Ambio 3(5):194-197, 1974. 12. Technology: Industry's latest cancer scare. Business Week, 23 Feb. 1974:100-101. 13. Ames, B. N., Kammen, H. O., and Yamasaki, E. Hair dyes are mutagenic: Identification of a variety of mutagenic ingredients. Proc. Natl. Acad. Sci. 72(6):2423-2427, 1975. 14. Christensen, H. E. and Luginbyhl, T. T. Registry of Toxic Effects of Chemical Substances, 1975 ed. U.S. Department of

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Health, Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, 1975. Malling, H. V. Mutation Testing Systems. In: Handbook of Teratology. J. G. Wilson and F. C. Fraser, Eds., New York: Plenum Press, In Press. Committee 17, Environmental Mutagen Society. Environmental mutagenic hazards. Science 187:503-514, 1975. Neel, J. V. The Detection of Increased Mutation Rates in Human Populations. In: Mutagenic Effects of Environmental Contaminants. H. E. Sutton and M. E. Harris, Eds., New York: Academic Press, 1972. American Society of Anesthesiologists Ad Hoc Committee, E. N. Cohen, Chairman. Occupational disease among operating room personnel. Anesthesiology 41(4):321-340, 1974. Papayannopoulou, T., et al. Identification of HbS in red cells and normoblasts, using fluorescent and anti-HbS antibodies. British Journal of Hematology, 34:25-31, 1976. Bridges, B. A. The three-tier approach to mutagenicity screening and the concept of radiation-equivalent dose. Mutation Res. 26:335-340, 1974. Flamm, W. G. A tier system approach to mutagen testing. Mutation Res. 26:329-333, 1974. Green, S. U.S. Food and Drug Administration. Personal Communication, November, 1976. Advisory Committee on the Biological Effects of Ionizing Radiation. The Effects on Populations of Exposure to Low Levels of Ionizing Radiation. Washington, D.C.: National Academy of Sciences, National Research Council, 1972. Swit, D., Ed. Product Safety Letter 2(35):3, 1973. Swit, D., Ed. Product Safety Letter 3(4):3, 1974. Stellman, J. M. and S. M. Daum. Work is Dangerous to Your Health. New York: Vintage, 1973. Employment Safety and Health Guide, Vol. 2. New York: Commerce Clearing House, 1974. Environmental Protection Agency. Pesticide program: Guidelines for registering pesticides in the United States. Federal Register 40(123):26801-26928, 1975. p. 26833. Environmental Protection Agency. Pesticide programs: Registration, reregistration and classification procedures. Federal Register 40(129):28241-28286, 1975. p. 28276. U.S. Congress. Senate. Consumer Product Safety Act. Pub. L. 92-573, 92nd Cong., 2d sess., 1972, S. 3419. Swit, D., Ed. Product Safety Letter 3(33):3, 1974. Turner, J. S. The Chemical Feast: The Ralph Nader Study Group Report on Food Protection and the Food and Drug Administration. New York: Crossman, 1970. Carper, J. Red (2) scare. New Republic 173:5, 1975. Brodeur, P. Expendable Americans. New York: Viking, 1974.

Understanding People fo write prescriptions is easy, but to come to an understanding with people is hard.

Franz Kafka: A Country Doctor, Oxford, England: Counterpoint Publications, 1945.

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