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AN AIR QUALITY DATA ANALYSIS SYSTEM FOR INTERRELATING EFFECTS, STANDARDS, AND NEEDED SOURCE REDUCTIONS: PART 13. APPLYING THE EPA PROPOSED GUIDELINES FOR CARCINOGEN RISK ASSESSMENT TO A SET OF ASBESTOS LUNG CANCER MORTALITY DATA
Citation:
Larsen, R. I. AN AIR QUALITY DATA ANALYSIS SYSTEM FOR INTERRELATING EFFECTS, STANDARDS, AND NEEDED SOURCE REDUCTIONS: PART 13. APPLYING THE EPA PROPOSED GUIDELINES FOR CARCINOGEN RISK ASSESSMENT TO A SET OF ASBESTOS LUNG CANCER MORTALITY DATA. JOURNAL OF THE AIR AND WASTE MANAGEMENT ASSOCIATION 53(11):1326-1339, (2003).
Impact/Purpose:
The goal of this research to develop models and computational tools to improve understanding of the functional relationships underlying human exposure to air toxics, and to reduce uncertainty in estimates of exposure to individuals and populations of concern. This goal will be met by addressing a number of key objectives in this task and include:
Model Research and Development: develop a multiroute/pathway/media human exposure and dose model for air toxics.
Model Application: apply model to an urban area (Houston, TX) to estimate human population exposure and dose.
Model Performance Evaluation: compare and evaluate exposure and dose estimates with independent model estimates or personal exposure measurements
Description:
The Clean Air Act Amendments of 1990 (CAAA-90) list 189 hazardous air pollutants (HAPs) for which "safe" ambient concentrations are to be determined. For a carcinogen, such as asbestos, the amendments specify that the safe concentration shall allow one excess cancer case per million people. To calculate a safe ambient asbestos concentration from one set of data, the EPA Proposed Guidelines for Carcinogen Risk Assessment are applied here to lung cancer mortality data for a cohort of 820 men who were exposed to airborne asbestos while working in a New Jersey asbestos factory. Data on their excess lung cancer mortality, expressed as a function of asbestos exposure, are fitted to two separate mathematical models, lognormal and logarithmic. Both models fit the data well and give almost identical answers. Since both models fit the data well, these two models might also be tried for other asbestos data and data for other HAPs. Averaged together these two models suggest a "safe" lifetime-mean ambient air concentration of 0.085 asbestos fibers per cubic meter of air. But measurements suggest that background asbestos concentrations may be about 1000 times this "safe" concentration, suggesting that this calculated safe concentration cannot be achieved. A Letter to the Editor and a Response that immediately follow this paper cite data that suggest that the "safe" concentration should probably be about 730 times as high as calculated in this paper. The Response suggests that the major reason for this discrepancy is because this paper uses the default assumption that excess mortality is linearly proportional to asbestos exposure from the "Point of Departure" down to zero excess mortality at zero exposure. The Response continues by acknowledging that this is a very weak assumption and then uses a nonlinear default assumption together with the factor of 730 to calculate that the relationship, instead of being linear, could be expressed as the "safe" asbestos concentration being proportional to the desired mortality level raised to the 0.39 power. The importance of determining the correct nonlinear relationship for any carcinogenic HAP is suggested as possibly the most important problem in setting a future "safe" concentration for any HAP. The following caveats for this study need to be stated. A prime reason for selecting this particular asbestos data set was that it covered a 100-fold exposure range and the primary purpose of this paper was to develop the two mathematical models (lognormal and logarithmic) that covered this large range. Also, only two sets of asbestos data are discussed here. All available asbestos excess mortality data would be considered, studied, and analyzed to determine any "safe" asbestos concentration that would be issued by the EPA.
The United States Environmental Protection Agency through its Office of Research and Development funded and managed the research described here. It has been subjected to the Agency's administrative review and approved for publication.