A Quantitative Analysis of Factors Affecting PELs and TLVs for Carcinogens

For carcinogens, this paper provides a quantitative examination of the roles of potency and weight-of-evidence (WOE) in setting permissible exposure limits (PELs) at the U.S. Occupational Safety and Health Administration (OSHA) and threshold limit values (TLVs) at the private American Conference of Governmental Industrial Hygienists (ACGIH). On normative grounds, both of these factors should influence choices about the acceptable level of exposures. Our major objective is to examine whether and in what ways these factors have been considered by these organizations. A lesser objective is to identify outliers, which might be candidates for further regulatory scrutiny. Our sample (N=48) includes chemicals for which EPA has estimated a unit risk as a measure of carcinogenic potency and for which OSHA or the ACGIH has a PEL or TLV. Different assessments of the strength of the evidence of carcinogenicity were obtained from EPA, ACGIH, and the International Agency for Research on Cancer. We found that potency alone explains 49% of the variation in PELs and 62% of the variation in TLVs. For the ACGIH, WOE plays a much smaller role than potency. TLVs set by the ACGIH since 1989 appear to be stricter than earlier TLVs. We suggest that this change represents evidence that the ACGIH had responded to criticisms leveled at it in the late 1980s for failing to adopt sufficiently protective standards. The models developed here identify 2-nitropropane, ethylene dibromide, and chromium as having OSHA PELs significantly higher than predicted on the basis of potency and WOE.     

Are Large Differences in “Lifesaving” Costs Justified? A Psychometric Study of the Relative Value Placed on Preventing Deaths

Government actions to reduce risks to health have varied greatly in their cost per death prevented, frequently by 10-fold or even 100-fold. This research asks whether disparities of this magnitude are justified by citizens' preferences abut the relative value of reducing deaths from different hazards. Four samples were asked to rank the relative priority of preventing deaths through 8 realistic programs, each addressed to a different hazard, and then to rate how large the differences in spending should be. Subjects were not asked to give absolute values on preventing deaths and were asked only for their relative valuation of the benefits of preventing a death, not to weigh the benefits and costs or to determine an optimal spending level. We found that in all samples the median respondent valued his top-rated program 5 to 6 times more than his bottom-rated program. However, because individuals disagreed upon the relative priority for different programs, the aggregated rankings barely showed more than a 2-fold difference in the amounts that should be spent. Thus, for the important programs considered by these samples, a large variation in spending does not appear to be justified on the basis of differentials in the values placed on preventing different types of deaths. A more deliberative methodology like the one used here appears fruitful for providing insights to policymakers about preferences in this sensitive area.