This paper emphasizes the importance of guides for occupational exposure to health hazards based on human experience, as well as on animal experiments. SCREENING OF OCCUPATIONAL ENVIRONMENT: A CRITIQUE OF EXPOSURE LIMITS John A. Pendergrass, M.P.H. IT was once said that physicians should be concerned with sick people. not "sick air." That cannot be the philosophy of industrial physicians. Any occupational health program that is dedicated to a philosophy other than employee health maintenance is doomed to failure. To successfully achieve that goal requires the concerted efforts of not only the multidiscipline industrial health team, but the active cooperation of an enlightened management, willing to alter processes and facilities as needed to provide a safe environment and lending active support to the industrial health program. Background Process and facility alterations are often, if not usually, the result of some type of environmental screening. The industrial hygienist who evaluates the environment will be guided in his judgment, in part, by exposure limits. Although exposure limits are a useful and even essential part of environmental screening, understanding, use and development of them have been under much discussion and some criticism lately. In 1916, a quantitative air sampling device was invented. As a result, a value of 300 particles/cm3 (8.5 mppef) was tentatively adopted as the maximum allowable concentration of dust in the mines in South Africa. Rapid progress has been made since that exposure limit was proposed. The industrial hygienist, the industrial physician, and the plant manager now have TLVs, MACs, EELS, MPCs, short-term limits, emergency hazard codes, air quality standards, and the like, to aid or confuse in the evaluation of conditions in the work areas. All exposure limits depend upon the principle of dose-response relationship. In the introduction to "Industrial Hvgiene Highlights,"' Hatch stated two principles of industrial hygiene with regard to chemical and physical stress in industry: (1) "There exists a systematic dose-response relationship between the magnitude of exposure to the hazardous agent and the degree of response in the exposed individual; (2) there is a graded decrease in the risk of injury as the level of exposure goes down, which risk becomes negligible when exposure falls below a certain tolerable level." If these principles are accepted, then it is obvious that in most cases there is no need for-nor is it economically 1204 VOL. 59. NO. 7. A.J.P.H.
SCREENING OF OCCUPATIONAL ENVIRONMENT wise-to pursue a philosophy of zero tolerance. Consequently, it is imperative that the exposure limits be scientifically souind. Exposure limits must be viable. Dose-response experience is the only valid data that can be used to define and refine exposure limits. But what constitutes a response? A transient physiological response in an experimental animal to a chemical or physical stress should not, in itself, be justification for severely limiting the use of that agent. Neither can a percentage of the working population be expected to accept the risk of disease or early death, so that the general public can enjoy the product of a hazardous process. Professionals in occupational health must insist that hazard. not toxicity, be the controlling factor in determining acceptable levels of stress. No standard or limit can be substituted for hazard evaluation. Knowledge and experience lead to sound judgment and competent evaluation. Composite experience and scientifically compiled data can provide the guides, not standards, that health specialists can use to determine the hazard of a particular stress. There is a need for a central place where data from toxicity studies, analvtical methods, stress measurement techniques, and human experience can be continually reviewed and analyzed for the purpose of establishing exposure guides for use in health hazard evaluations-a place where experience can be composited and distributed for the benefit of all. The Frye Report recommended that the USPHS have responsibility for setting enforceable standards. The Occupational Safety and Health Act of 1968 would have given this responsibility to the Secretary of Labor. Sterner2 proposed that a National Council on Hazardous Physical and Chemical Agents, modeled after the National Council on Radiation Protection and Measurement, be created to perform this function. Fixing the Responsibility If there is general agreement that some one group should have the responsibility to determine exposure guides or standards, what group should this be? Who should be represented in the group? Will guides or legally enforceable standards best serve to assure the maintenance of worker health in the United States? What types of guides or standards are needed to evaluate an environment? Who will provide data for the group to use in establishing the guides or staindards? Should the guides or standards be restricted to the environment of the work place? As these questions are answered, it is my opinion that support for the National Council approach is strengthened. The necessity for an independent body of highly competent specialists of unquestionable integrity is absolute, if the results of their efforts are to be accepted. In order to obtain such a council, no segment of qualified individuals can be excluded because they may or may not be employed by a public agency. Neither can appointment to this body in any manner depend upon the political persuasion of public officials. Likewise. no single profession, professional society, trade or labor organization should have control of or undue influence over the membership of the body. No existing agency or organization meets these criteria. However, a National Council would. Should the council issue guides or legally enforceable standards? Since the council would have no governmental status, obviously it could only recommend guides of good practice. The advisability of a legal standard is questioned. The primary objective of occupational health programs is to prevent illness due to conditions in the work place. This is accomplished through hazard evaluation and environmental controls. Contaminant concentration or JULY, 1969 1 205
stress quantity is only one aspect of hazard evaluation. Matching numbers on analytical results can become a futile exercise, uneconomical in time and money, and result in an ineffective worker-health maintenance program. The different exposure limits existing today are an indication of the need for guides based on varying circumstances and types of physiological response. Some of the criticism of the TLVs has been the inconsistency of the physiological response criteria used to establish exposure values. It is sometimes difficult to determine, even with the documentation, whether a TLV is based on toxicity, irritation, narcosis, or just analogy to a similar compound. It seems obvious that what is needed are multiple level guides, based on dose and exposure time, along with a clear statement on the physiological criterion used to determine each. Difficulty of Obtaining Data Exposure guides can be developed only if data are available to the council for review and analysis. The necessary data can be very briefly summarized as extensive animal studies and carefully monitored human experience. These are not easily obtained. The opinion is often expressed that the files of industry are filled with data which, if only released, would provide the needed answers. This, unfortunately, is not the case. Inquiries for specific information regarding exposure-response experience from industry have met with essentially negative results. The reasons or excuses are many. Physicians in industry have not emphasized group health and its correlation with industrial exposure. This may be because some industrial medical directors do not understand what exposure-response studies are all about, or feel that "sick air" is the responsibility of the industrial hygienist, or that management will not sup- 1206 port "research" projects of this type, or there is no money, time, or inclination for "nonproductive" work. Industrial hygienists and physicians do not work together. Rightfully, the industrial hygienist is primarily interested in controlling the environment to reduce or eliminate exposure. The latter is seldom accomplished and the former may be based upon compliance with an existing TLV or other guide. The time is not taken to establish that no adverse physiological response occurs at a particular exposure level. The TLV is accepted and not critically examined. These attitudes and practices must change if adequate exposure-response data are to be obtained. It is the responsibility of health specialists in industry to exert pressure from within to bring about the needed change; otherwise, the pressure will come from the outside. The Occupational Safety and Health Act of 1968 is just one outside pressure. Increased public interest in ambient air quality will surely be followed by increased public interest in environmental control for the work place. More Studies Needed In the past, the official agencies were leaders in determining exposure-response relationships. The USPHS and the state agencies were principle sources of data for determining guides. Studies of working conditions in one industry after another were conducted. We see and hear very little of this activity today. The industry-oriented groups, such as the American Petroleum Institute, Chlorine Institute, Industrial Hygiene Foundation, and Manufacturing Chemists Association, have directed and coordinated a few specific studies among their members. Much more, however, should be done. The universities and foundations VOL. 59, NO. 7. A.J.P.H.
SCREENING OF OCCUPATIONAL ENVIRONMENT should be more active in encouraging cooperative studies with industry groups or individual industrial concerns. There is a need for information on the physiological effect of exposure to specific chemicals. As an example, isocyanates are widely used and it is known that overexposure can lead to acute symptoms, as well as a unique type of sensitization. There is a threshold limit value which appears to be adequate in preventing both types of adverse reaction; however, there is very little information as to the mechanism of the disease. It is not known if all isocyanates have the same potential for causing disease. There is no bioassay for isocyanates. There is no way to predict which person will be most likely to develop the condition. Some research group should propose a cooperative study that will answer these questions. Silicosis is one of the oldest occupational diseases known. The techniques used to screen the environment for hazardous dust concentrations, and supposedly correlate these with disease, are essentially the same now as those developed 30 to 40 years ago. The advantages of electronic dust counting are just now beginning to be compared with microscopic methods. The work started at Saranac Lake and continued by the Industrial Hygiene Foundation should be renewed to develop a correlation between dust evaluation using modern techniques and pneumoconiosis. The enumeration of examples is almost limitless. In this area, the universities and foundations should stimulate and initiate interest, and industry should provide support. The final question of whether guides should be restricted to the in-plant environment can be answered in the negative. It is inconceivable that ambient air standards can be divorced completely from the work environment. Likewise it is inconceivable that the expertise of the proposed council would not be used to consider the health aspects of ambient air quality standards. Summary It has been the purpose of this presentation to emphasize the importance of occupational health exposure guides, based upon knowledge of human experience as well as on animal experiments. Over the years, it has become evident that a single value is not satisfactory for health hazard evaluation in industry. It is also important that guides provide the user with the physiological basis for the values, as well as the analytical techniques used to determine them quantitatively. There have been a number of organizations proposing exposure limits in the past. Most have done an outstanding job in one or more aspects of limit definition, but none have been completely satisfactory. It has been proposed that federal agencies promulgate legally enforceable standards. It is not felt that this is the answer. A National Council on Hazardous Physical and Chemical Agents, as suggested by Sterner, seems to be the best solution to a difficult problem. The most pressing need now and in the future is the accumulation of acceptable exposure-response experience upon which a National Council can base exposure guides for chemical and physical stresses. Occupational health specialists, industrial management, and public officials must recognize their roles in obtaining the pertinent information. Industrial physicians and industrial hygienists must educate themselves to the long-term needs of occupational health and discipline themselves to satisfying those needs while they continue to perform their day-byday tasks of preventing occupational illness. Industrial management must be educated to the fact that epidemiologic JULY, 1969 1 207
studies are not an "ivory tower" waste of time and money. The occupational health specialists in public agencies have essentially the same tasks as their counterparts in private industry. Fire fighting is not enough. The challenges to the universities and private foundations are as great now as they were when men were concerned with preventing deaths from occupational disease. The emphasis has changed, the problem is more subtle, but the scientific challenge is just as great now when prevention of disease rather than death is the primary objective. REFERENCES 1. Cralley, L. V.; Cralley, L. J.; and Clayton, G. D. Industrial Hygiene Highlights. Pittsburgh, Pa.: Industrial Hygiene Foundation of America, 1968, vol. 1, p. 1. 2. Sterner, J. H. Currents. New York: Manufacturing Chemists Association (Nov.-Dec.), 1967. Mr. Pendergrass is Manager, Industrial Hygiene, The 3-M Company (2301 Hudson Road), St. Paul, Minn. 55119 This paper was presented before a Joint Session of the Industrial Medical Association and the Occupational Health Section of the American Public Health Association at the Ninety-Sixth Annual Meeting in Detroit, Mich., November 11, 1968. Computer-Based System for Toxicology Information The Toxicology Information Program at the National Library of Medicine is developing a computer-based system for handling toxicology information (chemical compounds having biological effects) along with informational products and services designed to meet the needs of the public health communities. Inquiries pertaining to the system and its products and services should be addressed to Toxicology Information Program, National Library of Medicine, 8600 Rockville Pike, Bethesda, Md. 20014. 1208 VOL. 59, NO. 7, A.J.P.H.