ba-1979-0172.ch003

3 Health Implications of Trace Metals in the Environment

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K E N N E T H B R I D B O R D and H A R V E Y P. STEIN National Institute for Occupational Safety and Health, Center for Disease Control, Public Health Service, U.S. Department of Health, Education, and Welfare, Rockville, M D 20857

The objective of this chapter is to put into perspective some of the current knowledge with respect to trace metals and their health implications. Potential adverse health effects of occupational exposures to trace metals are discussed: cancer (arsenic, beryllium, chromium, nickel, and perhaps cadmium); chronic lung disease (beryllium and cadmium); neurologic and reproductive disorders (lead and mercury); and kidney disorders (lead and cadmium). Also discussed are the National Institute for Occupational Safety and Health (NIOSH) recommended standards for occupational exposure to several trace metals, the difficulty of establishing "safe" levels of exposure (particularly for carcinogens), and problems involved in identifying toxic components of trade name products. Special attention is given to the role of chemists to help protect the public health.

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he presence of trace metals i n the environment, both i n the workplace and i n the community, has been the subject of considerable public health concern i n recent years (1-15). H u m a n exposure to trace metals occurs primarily through inhalation of air and ingestion of food and water. Concentrations of trace metals i n community air and i n the diet vary considerably depending upon a number of factors, including proximity to sources of trace metal emissions. The trace metals of greatest concern for the general population are those which are ubiquitous i n the environment. L e a d is a good example, being present i n substantial quantities in the ambient air and i n the diet. I n general, workers comprise the 0-8412-0416-0/79/33-172-027$05.00/0 © 1979 American Chemical Society

Risby; Ultratrace Metal Analysis in Biological Sciences and Environment Advances in Chemistry; American Chemical Society: Washington, DC, 1979.


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group most highly exposed to trace metals, and occupational exposure varies considerably i n magnitude depending on the job situation. Estimates of the number of workers exposed to lead and to arsenic exceed one million each (7,11). T h e highest exposures tend to concentrate i n a defined number of industries. F o r example, the highest exposures to lead occur i n primary and secondary smelting and i n lead storage battery manufacturing and involve approximately 25,000 workers. Health implications of low-level chronic exposure to trace metals are not clearly understood. However, the trend of scientific investigation is generally shifting from emphasis on acute toxic effects to a greater concern for the effects of long-term exposure. Although trace metals are essential nutrients, excessive exposure to trace metals has been associated with a variety of adverse effects including cancer (arsenic, beryllium, chromium, nickel, and perhaps cadmium), chronic lung disease (beryllium and cadmium), neurologic and reproductive disorders (lead and mercury), and anemia and kidney disorders (lead and cadmium) (7-15). The largest body of information concerning the health effects of trace metals has come from studies of exposed workers. Although frequently involving much higher exposure levels than encountered by the general population, adverse effects observed among workers do provide insight into effects w h i c h can occur among the general population. Data on the health effects of arsenic, beryllium, cadmium, chromium, lead, mercury, and nickel have been reviewed and summarized i n criteria documents prepared by the National Institute for Occupational Safety and Health ( N I O S H ) (7-13). Additional knowledge regarding these health effects also has come from community studies as well as from toxicologic studies involving experimental animals. In the case of lead, considerable knowledge has been derived from studies of children exposed to lead-based paint and to other lead sources. Safe Levels of Exposure As new knowledge is obtained, the perspective as to safe levels of exposure to trace metals has resulted i n increasingly more stringent exposure standards both i n the workplace and i n the general population. The Consumer Product Safety Commission has recently reduced the maximum concentration of lead permitted i n consumer paints from 0.5 to 0.06%. T h e Environmental Protection Agency ( E P A ) is currently in the process of estabhshing an ambient air quality standard for lead. Mercury and beryllium both have been declared "hazardous" pollutants by E P A and are regulated as such under "The Clean A i r A c t . " Perhaps the clearest example of how "new knowledge" has resulted i n reducing permissible exposure limits comes from studies of workers. W i t h i n the


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past two years, N I O S H has recommended the reduction of occupational exposure to a number of trace metals including arsenic, beryllium, cad mium, chromium, lead, and nickel. A n employee exposure ceiling of 2 μξ arsenic per m air (as deter mined by a 15 m i n sampling period) was recommended by N I O S H to replace the existing limit of 500 jug/m , largely because of the carcino genic effect of arsenic (7). N I O S H recommended an exposure limit of 1 μg/m for carcinogenic hexavalent chromium; the previous general recommendation for chromium had been 100 /ig/m (10). N I O S H has recommended that allowable exposure to nickel be reduced from a 1000 /Lig/m ,8 hr time-weighted average ( T W A ) to a level of 15 fig/m because of nickel's carcinogenic activity, including increased risk of lung, nasal, and kidney cancer among exposed workers (13). The recommendation that maximum occupational exposure to beryllium be reduced to 0.5 /xg/m was based on N I O S H ' s assessment of the carcinogenicity of beryl lium i n humans (14). I n these cases, for trace metals believed to be human carcinogens, N I O S H has recommended that occupational expo sure be reduced to the lowest levels w h i c h can be quantitatively measured by specified sampling and analytical procedures routinely applicable to employee exposure monitoring. 3

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A reduction i n the maximum permissible lead exposure from 200 /Ag/m , the Occupational Safety and Health Administration ( O S H A ) standard, to a T W A of 100 /ig/m was recommended by N I O S H largely because of evidence showing adverse neurologic, kidney, hematologic, and reproductive effects among workers (11,15). N I O S H also recom mended that the standard for occupational exposure to cadcium be reduced from 100 /xg/m to 40 ftg/m T W A because of the effect of cadmium upon kidney function (9). A t issue i n this recommendation was whether or not exposure to cadmium poses a carcinogenic risk to either the lungs or the prostrate. W h i l e N I O S H d i d not consider the available evidence sufficient to recommend the regulation of cadmium as a carcinogen, future studies might well confirm the carcinogenic poten tial of cadmium. If so, a major determinant of any future cadmium standard may be the capability of sampling and analytical techniques routinely applicable to employee exposure monitoring. 3

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Role for Chemists Chemists play an important role i n protecting the health of workers at risk of exposure to trace metals. Recommendations of exposure limits for a number of carcinogenic metals (i.e., arsenic, beryllium, chromium, and nickel) have been based upon the limitations of sampling and analyti-



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cal technology routinely applicable to employee exposure monitoring rather than upon specific health effects studies. This has occurred because "safe" levels of exposure to carcinogens cannot be defined currently. Although a substance can be shown to be carcinogenic by appropriate epidemiologic and/or toxicologic data, the available information has not permitted the calculation of "safe" exposure levels. Under these circumstances, to minimize occupational exposure to carcinogens, N I O S H has generally recommended that occupational exposure to human carcinogens be no greater than the lowest levels that can be reliably measured by specified sampling and analytical procedures routinely applicable to the workplace. (In many instances, laboratory techniques do exist that can measure exposure below the recommended standard, yet these techniques were not believed to be readily available for use as routine monitoring procedures in the workplace). If new practical analytical methods can be developed or if existing methods can be adapted for routine employee exposure monitoring, then it might be possible to recommend occupational standards w i t h greater margins of safety for protecting health. N I O S H therefore has participated in the development of promising new techniques, including graphite furnace (atomic absorption spectrophotometry) and inductively coupled plasma (optical emission spectroscopy), i n its own research laboratories as well as through external funding. The need for improved sampling and analytical techniques for monitoring employee exposure extends to substances other than the trace metals. The "no detectable limit" philosophy for occupational exposure to carcinogens dates back to the 1974 situation w i t h vinyl chloride i n which N I O S H recommended that airborne concentrations be reduced "to levels not detectable by the recommended method" (1 ppm) (16). Very low maximum permissible exposure levels are likely to be recommended in the future for substances which are determined to be potential human carcinogens. The issue of analytical techniques for exposure monitoring extends beyond the workplace. Stationary sampling equipment used for community air monitoring generally lends to the development of systems that have lower limits of detectability than those based on the personal samplers used i n the workplace. This has facilitated the recommendation of standards for community exposures which generally specify lower levels than those permitted i n the workplace. However, this difference reflects not only sampling and analytical technology, but also the fact that community exposure occurs 24 hours a day, seven days a week, as opposed to occupational exposure which is usually limited to 40 hours per week. Other factors, including the existence of more high-risk groups in the general population (e.g., the very old and the very young), also



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have tended to reduce the maximum levels of exposure permitted i n the community as compared with the workplace. As the recommended air standards for the workplace become more stringent, however, there might be demands to further reduce community exposures to a point at which the limitations of sampling and analytical technology become factors determining the levels at w h i c h standards are ultimately set. Arsenic and beryllium are two current examples where this situation might occur. The availability of adequate control technology to reduce emissions of hazardous materials into the workplace and into the general environment also has been a severe limiting factor i n reducing exposure. It is easier to design controls into the basic process than to retrofit controls once a chemical plant has been built. Arsenic and lead are examples of trace metals where the lack of adequate control technology severely hampers the ability to reduce both occupational and community exposure. It is unfortunate that both chemists and chemical engineers frequently do not receive formal training i n the health hazards of chemical processes and i n various control techniques. Chemists, working together with engineers and health scientists, could then better contribute to the development of control technology and to the modification of basic processes, thereby helping to contain fugitive emissions. Chemists also can play an important role i n helping resolve the trade name product issue. It is extremely difficult for workers to protect themselves unless they know what materials they are being exposed to. A particular problem has been the existence of trade name products that do not readily reveal the presence of toxic substances. The N I O S H National Occupational Hazard Survey, i n a two-year field survey of approximately 5,000 workplaces, identified 86,000 trade name products and has been successful to date in obtaining the formulations of approximately 50,000 of these products. W i t h i n this latter group, more than 20,000 trade name products contained federally regulated toxic substances and more than 400 contained known cancer-causing agents. The situation is complicated by trade secret designations claimed i n roughly one-third of all responses to the N I O S H survey, which further obscures the presence of toxic substances i n commercial products. This poses a special challenge to chemists i n helping identify toxic substances i n commercial products so that proper precautions can be taken to protect the worker and the general population. Analytical chemistry also plays a crucial role i n toxicologic and epidemiologic studies because of the importance of ascertaining the actual exposures of the subjects under investigation. W e are all certain to benefit from the continuing contributions of the chemist and chemical engineer i n elucidating the health effects of trace metals and i n controlling their adverse impact.


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Literature Cited 1. Horvath, D. J., "Trace Elements and Health," in "Trace Substances and Health—A Handbook," P. M. Newberne, Ed., Part I, Marcel Dekker, New York, 1976. 2. "Metallic Elements in Human Health," D. H. K. Lee, Ed., Academic, New York, 1972. 3. Schroeder, Η. Α., Darrow, D. K., "Relation of Trace Metals to Human Health," Environ. Affairs (1972) 2, 222. 4. Schroeder, Η. Α., Darrow, D. K., "Relation of Trace Metals to Human Health Effects," Prog.Anal.Chem. (1973) 5, 81. 5. Underwood, E . J., "Trace Elements in Human and Animal Nutrition," Academic, New York, 1971. 6. Woolrich, P. F., "Occurrence of Trace Metals in the Environment—An Overview," J. Am. Ind. Hyg. Assoc. (1973) 34, 217. 7. "Criteria for a Recommended Standard . . . Occupational Exposure to In organic Arsenic New Criteria—1975," HEW Publication No. (NIOSH) 75-149, U.S. Department of HEW, Public Health Service, Center for Disease Control, NIOSH, Ohio, 1975. 8. "Criteria for a Recommended Standard . . . Occupational Exposure to Beryllium," Publication Number HSM 72-10268, U.S. Department of HEW, Public Health Service, Health Services and Mental Health Ad ministration, NIOSH, Ohio, 1972. 9. "Criteria for a Recommended Standard . . . Occupational Exposure to Cadmium," HEW Publication Number (NIOSH) 76-192, U.S. Depart ment of HEW, Public Health Service, Center for Disease Control, NIOSH, Ohio, 1976. 10. "Criteria for a Recommended Standard . . . Occupational Exposure to Chromium (VI)," HEW Publication Number (NIOSH) 76-129, U.S. Department of HEW, Public Health Service, Center for Disease Control, NIOSH, Ohio, 1975. 11. "Criteria for a Recommended Standard . . . Occupational Exposure to Inorganic Lead," Publication Number HSM 73-11010, U.S. Department of HEW, Public Health Service, Health Services and Mental Health Administration, NIOSH, Ohio, 1972. 12. "Criteria for a Recommended Standard . . . Occupational Exposure to Inorganic Mercury," Publication Number HSM 73-11024, U.S. Depart ment of HEW, Public Health Service, Health Services and Mental Health Administration, NIOSH, Ohio, 1973. 13. "Criteria for a Recommended Standard . . . Occupational Exposure to Inorganic Nickel," DHEW (NIOSH) Publication Number 77-164, U.S. Department of HEW, Public Health Service, Center for Disease Control, NIOSH, Ohio, 1977. 14. Baier, E . J., Deputy Director, NIOSH, statement at public hearings on occupational standard for beryllium, Occupational Safety and Health Administration, Department of Labor, Washington, D.C., 1977. 15. Baier, E. J., Deputy Director, NIOSH, statement at public hearings on occupational standard for lead, Occupational Safety and Health Admin istration, Department of Labor, Washington, D.C., 1977. 16. "Recommended Standard for Occupational Exposure to Vinyl Chloride," U.S. Department of HEW, Public Health Service, Center for Disease Control, NIOSH, Ohio, 1974. RECEIVED December

12, 1977.


ba-1979-0172.ch003

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