Since Ramazzini published the seminal text on occupational medicine (Ramazzini 1713), we have come to realize that working at certain jobs can cause specific illnesses. At first, only observational tools were available to survey the work environment. As technology developed, we began to be able to measure the environments in which workers plied their trades. Measuring the workers’ environment has helped identify the sources of workplace stresses. However, this improved knowledge brought with it a need to set exposure limits to protect workers’ health. Indeed, we have found ways to detect the presence of toxic substances at low levels, before they can create health problems. Now we often can predict the results of exposures without waiting for the effects to appear, and thus prevent disease and permanent injury. Good health in the workplace is no accident; it requires surveillance of workers and their environments.
Workplace Exposure Limits
Early workplace exposure limits were set to prevent acute illness and death. Today, with much better information, we try to meet much lower limits in order to prevent chronic illness and subclinical health effects. The most successful systematic attempt to develop occupational exposure limits was the effort of the Committee on Threshold Limits established by the American Conference of Governmental Industrial Hygienists (ACGIH) in 1943. (The ACGIH is a US organization with no formal ties to any government regulatory agency.) The success of this effort is shown by the fact that many countries around the world have adopted the threshold limit values (TLVs) published by ACGIH, which now number more than 600, as workplace exposure standards. Their wide use as enforceable standards has invited critical examination of TLVs and the process by which they were set. Despite their usefulness, TLVs have been criticized from three sectors of the decision-making process: scientific, political and ethical. A brief review of several criticisms follows:
Scientists criticized the fact that the TLVs set on the basis of substantial data are not distinguished from those based on considerably less data.
TLVs were never intended to be “safe” exposure levels for all workers. The TLV Committee recognized that the biological variations among workers, and other factors that could not be calculated, made it impossible to set limits that would guarantee safety for all workers in all environments. Adopting TLVs as enforceable standards creates a political problem, because part of the worker population is not protected. Only zero exposure can provide this guarantee, but zero exposure and zero risk are not practical alternatives.
The data that the TLV Committee worked with were often produced and paid for by industry, and were unavailable to the public. Those protected by this limit-setting process argue that they should have access to the data upon which the limits are based. Industry’s attempts to restrict access to their data, no matter what the reason, are seen by many as unethical and self-serving.
TLVs are still widely respected as guidelines for workers’ exposures to environmental stresses, to be used by professionals who can interpret them properly.
Community Exposure Standards
There is a link between occupational and community exposures. Any adverse health effects seen in workers are a result of their total exposure to environmental contaminants. Total dose is important in selecting appropriate exposure limits. This need is already recognized for poisons that accumulate in the body, such as lead and radioactive substances.
Present exposure limits differ for workers and for the community, in part, because workers’ exposures are intermittent, not continuous. TLVs were set for a five-day work week of eight-hour days, the norm in the United States. TLVs reflect the action of human repair mechanisms. However, many argue that community and occupational exposure limits should not be different.
Without specific information about synergistic or antagonistic effects, exposure limits for both workers and the public reflect only additive interactions between multiple environmental contaminants. When setting limits for a single substance, the complexities of the environments in which we live and work make it impossible to evaluate all potential interactions among environmental contaminants. Instead, we make the following simplifying assumptions: (1) the basic mix of chemicals in our environment has not changed materially; and (2) the epidemiological information and the environmental criteria used to set standards reflect our exposure to this mix of chemicals. By making these assumptions when setting community exposure limits for individual substances, interactions can be ignored. Although it would be useful to apply the same reasoning to setting workplace exposure limits, the logic is questionable because the mix of substances in the various work environments is not uniform when compared with that in our communities.
A part of the political debate is whether to adopt enforceable international exposure standards. Should an individual country set its own priorities, as reflected in its exposure limits, or should international standards be adopted, based on the best data available? Many governments of developing countries take the position that the developed countries should have stricter community exposure standards, because the latter’s industrial and agricultural pollution has created a less healthy environment.
Health Criteria Based on the Type of Risk
Currently, we rely heavily on toxicity testing of animals to set human exposure limits. Today’s sophisticated technology makes it possible to determine both the degree and kind of toxicity that a body will suffer after exposure to a substance. We measure a substance’s ability to cause cancer, to damage a foetus, to cause even benign tumours. We also measure the degree to which that substance can affect somatic systems. Many scientists assume that there is a safe level of exposure, and this has been validated by observations of mankind’s early diseases. However, such an assumption may not be justified today, especially for cancer. Experts still argue both for the existence and absence of a no-effect or “safe” level of exposure.
We co-exist with natural carcinogens in our environment. To deal with them, we must calculate the risk associated with exposure to these substances, and then use the best available technology to reduce that risk to an acceptable level. To think we can achieve zero risk is a misleading idea, and possibly the wrong path to take. Because of the cost and complexity of animal testing, we use mathematical models to predict the risks of exposures to substances at low doses. The best we can do is compute statistically reliable predictions of what are likely to be safe levels of exposure to environmental stresses, assuming a level of risk that the community accepts.
Monitoring the Working Environment
Monitoring of the working environment is the speciality of occupational hygienists. (In North America, they are called industrial hygienists.) These professionals practice the art and science of identification, evaluation and control of occupational stresses. They are schooled in the techniques of measuring the environment in which people work. Because of their obligation to protect the health and well-being of employees and the community, occupational hygienists have a deep concern for ethical issues. As a result, the principal industrial hygiene societies in the United States recently completed a revision to their Code of Ethics, which was originally drafted in 1978 (see also “Canons of Ethical Conduct and Interpretive Guidelines”).
Problems of Secrecy
Data developed from monitoring the work environment are critical to improving exposure limits both for workers and for the community. In order to come up with the best limits, which balance risk, cost and technical feasibility, all data from industry, labour and government must be available to those who set the limits. This consensus approach seems to be growing in popularity in a number of countries, and may become the procedure of choice for setting international standards.
Regarding trade secrets and other proprietary information, the new Code of Ethics provides guidelines for industrial hygienists. As professionals, they are obliged to make sure that all parties who need to know information regarding health risks and exposures are given that information. However, hygienists must keep key business information confidential, except when overriding health and safety considerations require them to reveal it.