Lung cancer and mesothelioma risk assessment for a population environmentally exposed to asbestos

Our plain-English summary of Lung cancer and mesothelioma risk assessment for a population environmentally exposed to asbestos, by M.H. Bourgault, M. Gagné, M. Valcke (International Journal of Hygiene and Environmental Health, 2014).

The study

• Authors: M.H. Bourgault, M. Gagné, M. Valcke
• Journal: International Journal of Hygiene and Environmental Health
• Published: 2014;217(2-3):340-6
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos-related cancer risk is usually a concern restricted to occupational settings. However, recent published data on asbestos environmental concentrations in Thetford Mines, a mining city in Quebec, Canada, provided an opportunity to undertake a prospective cancer risk assessment in the general population exposed to these concentrations. Using an updated Berman and Crump dose-response model for asbestos exposure, we selected population-specific potency factors for lung cancer and mesothelioma. These factors were evaluated on the basis of population-specific cancer data attributed to the studied area's past environmental levels of asbestos. We also used more recent population-specific mortality data along with the validated potency factors to generate corresponding inhalation unit risks. These unit risks were then combined with recent environmental measurements made in the mining town to calculate estimated lifetime risk of asbestos-induced lung cancer and mesothelioma. Depending on the chosen potency factors, the lifetime mortality risks varied between 0.7 and 2.6 per 100,000 for lung cancer and between 0.7 and 2.3 per 100,000 for mesothelioma. In conclusion, the estimated lifetime cancer risk for both cancers combined is close to Health Canada's threshold for "negligible" lifetime cancer risks. However, the risks estimated are subject to several uncertainties and should be confirmed by future mortality rates attributed to present day asbestos exposure.

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In plain English

This article was a mathematical risk assessment, not a study of patients. The authors estimated the future lifetime risk of lung cancer and mesothelioma from present-day environmental asbestos for the general population of Thetford Mines, a chrysotile mining town in Quebec, Canada. They used Berman and Crump's potency factors for the Quebec mining cohort. They first checked these factors against earlier data on women in the mining area. The predictions covered the observed excess lung cancer deaths and the 10 observed mesothelioma cases. The older Nicholson model predicted far more. From published measurements (125 outdoor samples, 26 homes), they estimated an average lifetime exposure of 0.0023 fibers per millilitre. For 80 years of continuous exposure, the estimated lifetime death risk per 100,000 people was 0.7 to 2.6 for lung cancer, 0.7 to 2.3 for mesothelioma, and 1.4 to 4.9 for both combined. The authors described this as close to, or slightly above, Health Canada's 1 per 100,000 'negligible' threshold. They noted several uncertainties, including missing smoking data and limited exposure measurements.

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: Prospective quantitative cancer risk assessment using the Berman and Crump dose-response model, with a check of the chosen potency factors against past mortality data
• Who was studied: General population of Thetford Mines, Quebec, Canada. Exposure data came from 125 outdoor air samples taken in 2004 and from indoor air in 26 residences sampled in 2003 to 2004. The potency factors were checked against data from Camus et al. on women in the mining area (Thetford Mines and Asbestos), 1970 to 1989.
• Exposure: Environmental (non-occupational) airborne asbestos from chrysotile mining, tailings and ore residues. The ore is contaminated with tremolite, an amphibole. The calculated average lifetime exposure concentration was 0.0023 f/ml, combining indoor and outdoor air and assuming 91.3% of time spent indoors.
• Main results:
  • Lung cancer check, women in the mining area: across the range of past exposure estimates, the ratio of predicted to observed excess deaths was 0.1 to 1.5 with the best-estimate factor and 0.2 to 5.7 with the upper-bound factor. Both ranges include 1.
  • Applying the older Nicholson potency factor to the same lung cancer data overestimated lung cancer risk by 2- to 52-fold.
  • Mesothelioma check: predicted incident cases were 2.1 to 52.5 with the best-estimate factor and 6.5 to 162.5 with the upper-bound factor. Both ranges include the 10 observed cases.
  • With Nicholson's mesothelioma factor, 100 to 2500 cases were predicted, compared with the 10 observed.
  • Lifetime unit risks (men and women combined) for lung cancer were 0.0030 (best estimate) and 0.011 (upper bound) per f/ml. For mesothelioma they were 0.0032 and 0.0099, and for both cancers combined 0.0061 and 0.021.
  • Estimated lifetime lung cancer death risk, for lifetime continuous exposure at Thetford Mines concentrations: 0.7 (best estimate) and 2.6 (upper bound) per 100,000 persons.
  • Estimated lifetime mesothelioma death risk: 0.7 (best estimate) and 2.3 (upper bound) per 100,000 persons.
  • Estimated lifetime death risk for both cancers combined: 1.4 (best estimate) and 4.9 (upper bound) per 100,000 persons.
  • The mean outdoor total fiber concentration in Thetford Mines (0.0059 f/ml) was 3 times the mean for urban Montreal and Quebec City (0.0019 f/ml). The authors' own tests found this difference statistically significant (p less than 0.01).
• The authors' conclusion: The authors concluded that their population-specific assessment gave a lung cancer and mesothelioma risk close to 1 per 100,000. In the Discussion they wrote that the combined figures slightly exceed Health Canada's 1 per 100,000 negligible-risk threshold. They added that the potency factors and risk estimates could warrant further study, for example by comparison with future cancer death rates in Thetford Mines.
• Limitations the authors state:
  • Smoking data were not available for the population, so unit risks could not be computed separately for smokers and non-smokers.
  • The worker data behind the unit risks are limited, including by the difficulty of characterizing past exposures.
  • The potency factors were checked against past exposures much higher than present levels. Risk would be overestimated if a threshold exists below which risk does not occur, and underestimated if the dose-response is supralinear (risk rising more steeply at low doses).
  • Exposure data were limited and may not be representative: most samples were taken downwind, most homes were within 2 km of tailings, and outdoor samplers were on rooftops.
  • The exposure estimates may be overestimated because they rely on total fiber counts rather than asbestos fiber counts.
  • The assessment assumes exposure does not change over time and does not consider acute exposure from accessing the mine tailings area.

Topics

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

Medical terms in this study, explained in our Lexicon: Lung Cancer, Mesothelioma, Thetford Mines, Dose-response relationship, Asbestos Exposure.

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