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

Our plain-English summary of 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, by R.I. Larsen (Journal of the Air & Waste Management Association, 2003).

The study

• Author: R.I. Larsen
• Journal: Journal of the Air & Waste Management Association
• Published: 2003;53(11):1326-39
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The Clean Air Act Amendments of 1990 (CAAA-90) list 189 hazardous air pollutants (HAPs) for which "safe" ambient concentrations are to be determined. The primary purpose of this paper is to develop two mathematical models, lognormal and logarithmic, that effectively express excess lung cancer mortality as a function of asbestos concentration for an example set of data and also to suggest using these two models for additional HAPs. The secondary purpose of this paper is to calculate a "safe" asbestos concentration by first assuming a default linear extrapolation (to one excess death per million people, as specified for carcinogenic HAPs). The resulting "safe" concentration is an impossible-to-achieve 1/1000 of present background asbestos concentrations. A letter to the editor and a response in this Journal issue use additional asbestos data that suggest that the "safe" concentration should be about 730 times higher than first calculated here and that a default nonlinear extrapolation should be used instead, with the "safe" concentration proportional to the desired mortality level raised to the 0.39 power. These results suggest that the most important problem in setting a "safe" concentration for each carcinogenic HAP is to determine the correct nonlinear extrapolation to use for each HAP.

In plain English

This paper was a mathematical risk-assessment exercise, not a new study of workers. The author applied EPA's 1996 Proposed Guidelines for Carcinogen Risk Assessment to previously published lung cancer death data on 820 men who began work between 1941 and 1945 at an amosite asbestos factory in Paterson, New Jersey. The men were followed from 5 to 40 years after starting work. Their exposures had been estimated from fiber measurements at two other plants of the same company. Two models, logarithmic and lognormal, were fitted to excess lung cancer mortality across eight exposure classes. They explained 0.89 and 0.86 of the variance. The author assumed a default straight-line relationship down to one excess lung cancer death per million people. On that basis the author calculated a 'safe' lifetime average community level of 0.085 fibers per cubic meter of air. Background levels may be about 1000 times higher, and the author wrote that this suggests the level cannot be achieved. The author also reported that a letter and a response in the same journal issue suggested the safe level should be about 730 times higher. Limitations the author stated included estimated rather than measured exposures and possible differences in smoking.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Quantitative risk-assessment modeling (re-analysis by regression) of previously published cohort mortality data, following EPA's 1996 Proposed Guidelines for Carcinogen Risk Assessment
• Who was studied: 820 men who started work between 1941 and 1945 at an amosite asbestos factory in Paterson, New Jersey, observed from 5 to 40 years after starting work. The data come from an earlier published study (Seidman, Selikoff and Gelb, 1986). The comparison population was all white males living in New Jersey.
• Exposure: Amosite asbestos in a factory setting. Most men worked briefly (days, weeks or months) and some for several years. Cumulative exposure (fiber-years per mL) was estimated from measurements at two other plants of the same company, not measured at the Paterson plant. The men were divided into eight exposure classes covering a 100-fold range.
• Main results:
  • Both models fitted the excess lung cancer mortality data across exposure classes: the logarithmic model explained 0.89 of the variance and the lognormal model 0.86.
  • After linear extrapolation from a starting point at 0.05 excess mortality, the two models gave essentially the same occupational exposure for one excess lung cancer death per million people. That exposure was 0.0000158 and 0.0000175 fiber-years per mL, an average of 0.0000167. The article prints these numbers in scientific notation, with its symbols damaged by scanning.
  • The author converted this to community exposure (dividing by 2.8 for continuous rather than workday breathing) and assumed a 70-year lifetime. The resulting 'safe' lifetime average concentration was 0.085 asbestos fibers per cubic meter of air.
  • Published median asbestos concentrations in Canadian cities were 1000 times this calculated safe level. The author wrote that this suggests the safe level cannot be achieved.
  • Extended to higher exposures, the logarithmic model eventually predicted excess mortality above 100%, which is impossible. The lognormal model always stayed below 1.
  • The author reported that a letter to the editor and a response in the same issue cited data suggesting the safe concentration should be about 730 times higher than calculated here.
• The authors' conclusion: The author concluded that both the lognormal and logarithmic models fitted these asbestos data well and gave essentially the same safe concentration, and that both might be tried for other asbestos data and other hazardous air pollutants.
• Limitations the authors state:
  • Exposures were estimated rather than measured.
  • The fiber studied, amosite, is rarely encountered in the United States, and its relative potency probably differs from more common types.
  • The cohort may have had different smoking habits from the New Jersey white male comparison population.
  • Only two sets of asbestos data were discussed. Any safe level issued by EPA would consider all available data.
  • As reported from the accompanying Response, the default assumption that risk falls in a straight line to zero at zero exposure is very weak.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer.

Medical terms in this study, explained in our Lexicon: Lung Cancer, Carcinogenic.

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