Setting Risk-Based Occupational Exposure Limits for No-Threshold Carcinogens

ABSTRACT

Several regulators have recently issued so-called risk-based occupational exposure limits for carcinogenic substances, and also reported estimates of the risk of fatality that exposure to the limit value would give rise to. This practice provides an opportunity to study how differences in the exposure limits set by different regulators are influenced by differences in the scientific judgment (what is the risk at different levels?) and in the policy judgment (how should large risks be accepted?). Based on a broad search, a list was compiled of exposure limits for carcinogens that the respective regulator associates with a numerical risk estimate. For benzene, such data was available from six regulators. The differences in estimates of the risk/exposure relationship and in risk tolerance were about equal in size for benzene, while the range for acceptability was somewhat wider. A similar pattern was observed, although less clearly, for substances with data from only two or three regulators. It is concluded that the science factor and the policy factor both contribute to differences in exposure limits for carcinogens. It was not possible to judge which of these two factors has the larger influence.

Key Words:

• occupational exposure limits
• carcinogens
• chemicals regulation
• acceptable risk
• scientific uncertainty
• science–policy relation

Notes

Three cancers—lung cancer, leukemia, and malignant mesothelioma—were included in this study. Arsenic, asbestos, beryllium, cadmium, chromium, diesel exhaust, nickel, and silica accounted for lung cancer. Benzene, ethylene oxide, and ionizing radiation accounted for leukemia. Asbestos was considered as the main cause of malignant mesothelioma.

Different organizations use different terminologies for limits on workplace exposure. In this article, we use the term “occupational exposure limits,” or OELs.