An approach to estimating the environmental burden of cancer from known and probable carcinogens: application to Ontario, Canada

Our plain-English summary of An approach to estimating the environmental burden of cancer from known and probable carcinogens: application to Ontario, Canada, by S.L. Greco, E. MacIntyre, S. Young, et al (BMC Public Health, 2020).

The study

• Authors: S.L. Greco, E. MacIntyre, S. Young, H. Warden, C. Drudge, J. Kim, E. Candido, P. Demers, R. Copes
• Journal: BMC Public Health
• Published: 2020;20(1):1017
• Cited by: 15 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Quantifying the potential cancer cases associated with environmental carcinogen exposure can help inform efforts to improve population health. This study developed an approach to estimate the environmental burden of cancer and applied it to Ontario, Canada. The purpose was to identify environmental carcinogens with the greatest impact on cancer burden to support evidence-based decision making.

Methods: We conducted a probabilistic assessment of the environmental burden of cancer in Ontario. We selected 23 carcinogens that we defined as "environmental" (e.g., pollutants) and were relevant to the province, based on select classifications provided by the International Agency for Research on Cancer. We evaluated population exposure to the carcinogens through inhalation of indoor/outdoor air; ingestion of food, water, and dust; and exposure to radiation. We obtained or calculated concentration-response functions relating carcinogen exposure and the risk of developing cancer. Using both human health risk assessment and population attributable fraction models in a Monte Carlo simulation, we estimated the annual cancer cases associated with each environmental carcinogen, reporting the simulation summary (e.g., mean and percentiles).

Results: We estimated between 3540 and 6510 annual cancer cases attributable to exposure to 23 environmental carcinogens in Ontario. Three carcinogens were responsible for over 90% of the environmental burden of cancer: solar ultraviolet (UV) radiation, radon in homes, and fine particulate matter (PM2.5) in outdoor air. Eight other carcinogens had an estimated mean burden of at least 10 annual cancer cases: acrylamide, arsenic, asbestos, chromium, diesel engine exhaust particulate matter, dioxins, formaldehyde, and second-hand smoke. The remaining 12 carcinogens had an estimated mean burden of less than 10 annual cancer cases in Ontario.

Conclusions: We found the environmental burden of cancer in Ontario to fall between previously estimated burdens of alcohol and tobacco use. These results allow for a comparative assessment across carcinogens and offer insights into strategies to reduce the environmental burden of cancer. Our analysis could be adopted by other jurisdictions and repeated in the future for Ontario to track progress in reducing cancer burden, assess newly classified environmental carcinogens, and identify top burden contributors.

In plain English

In this computer modeling study, the authors estimated annual cancer cases in Ontario, Canada, attributable to 23 environmental carcinogens that the International Agency for Research on Cancer classes as carcinogenic or probably carcinogenic to humans. For 19 carcinogens, they combined air, food, drinking water and dust concentrations with potency values, assuming current exposures would continue. For five, they applied population attributable fractions to Ontario's 2011 cancer counts. Using a Monte Carlo simulation, they reported a mean and a 90% prediction interval for each estimate. The total mean was 4790 annual cases, with lower and upper estimates of 3540 and 6510. Solar ultraviolet radiation, radon and fine particulate matter (PM2.5) together accounted for over 90%. Asbestos was modeled from indoor and outdoor air levels. Its mean was 40 annual cases, with lower and upper estimates of 0 and 130, rounded to the nearest 10. The article did not name a fiber type or a cancer type for asbestos. The authors concluded the total fell between earlier estimates for alcohol and tobacco. They noted limited exposure data and that potency values represent an upper bound on risk.

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: Probabilistic modeling study (Monte Carlo simulation). A risk assessment model was used for 19 carcinogens, combining exposure concentrations with potency values. A population attributable fraction model was used for 5 carcinogens, applying a fraction to annual cancer incidence. A mean and 90% prediction interval were reported for each burden estimate.
• Who was studied: The general population of Ontario, Canada. About 12.7 million people under age 80 in 2011. Ontario Cancer Registry incidence data for 2011 were used for the attributable fraction models.
• Exposure: 23 environmental carcinogens, including asbestos, through five routes: indoor air, outdoor air, food, drinking water and indoor dust (and solar radiation). Asbestos was modeled from outdoor and indoor air concentrations measured in fibers/mL. No fiber type was specified.
• Main results:
  • The risk assessment model, which combined exposure concentrations with potency values, was used for 19 of the 23 carcinogens.
  • The population attributable fraction model was used for 5 of the 23 carcinogens. It applied a fraction to cancer incidence data for Ontario in 2011.
  • The source of the incidence data was cancers recorded in Ontario.
  • The authors reported a mean and a 90% prediction interval for each burden estimate.
  • For all 23 carcinogens combined, the estimated burden was between 3540 and 6510 annual cancer cases in Ontario.
  • The total had a mean of 4790 annual cases, with lower and upper estimates of 3540 and 6510.
  • The figures in Table 5 are rounded to the nearest 10.
  • Solar UV radiation (mean 2540), radon (mean 1310) and PM2.5 (mean 560) each had mean estimates over 500 annual cases. Together they accounted for over 90% of the estimated environmental cancer burden.
  • For asbestos, the estimated mean was 40 annual cancer cases, with lower and upper estimates of 0 and 130 (rounded to nearest 10).
  • Asbestos ranked after arsenic and acrylamide, among the carcinogens above the reporting threshold of 10 mean annual cases.
  • The asbestos concentration used for outdoor air was a mean of 0.00021 fibers/mL (5th to 95th percentile 0.000017 to 0.00050).
  • The asbestos concentration used for indoor air was a mean of 0.00026 fibers/mL (5th to 95th percentile 0.000023 to 0.00062).
  • No carcinogen exceeded the reporting threshold for drinking water or for dust.
• The authors' conclusion: The authors concluded that the estimated environmental burden (3540 to 6510 annual cancer cases) fell between previous estimates for the burden of alcohol and tobacco use. They also stated that the analysis could be repeated to track trends or applied elsewhere.
• Limitations the authors state:
  • The characterization of population exposure was limited by available data.
  • The data sources reflected general population exposure, not highly exposed individuals.
  • The potency values used represent an upper bound on cancer risk rather than a central estimate.
  • The analysis assumed current exposures continue unchanged into the future.
  • The analysis could not account for one carcinogen affecting more than one cancer type.
  • Uncertainty and variability were not fully separated in the analysis.

Topics

Medical terms in this study, explained in our Lexicon: Population Attributable Fraction (PAF), Jurisdiction.

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