Risk-based indicators of Canadians' exposures to environmental carcinogens

Our plain-English summary of Risk-based indicators of Canadians' exposures to environmental carcinogens, by E. Setton, P. Hystad, K. Poplawski, et al (Environmental Health, 2013).

The study

• Authors: E. Setton, P. Hystad, K. Poplawski, R. Cheasley, A. Cervantes-Larios, C.P. Keller, P.A. Demers
• Journal: Environmental Health
• Published: 2013;12:15
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: Tools for estimating population exposures to environmental carcinogens are required to support evidence-based policies to reduce chronic exposures and associated cancers. Our objective was to develop indicators of population exposure to selected environmental carcinogens that can be easily updated over time, and allow comparisons and prioritization between different carcinogens and exposure pathways.

Methods: We employed a risk assessment-based approach to produce screening-level estimates of lifetime excess cancer risk for selected substances listed as known carcinogens by the International Agency for Research on Cancer. Estimates of lifetime average daily intake were calculated using population characteristics combined with concentrations (circa 2006) in outdoor air, indoor air, dust, drinking water, and food and beverages from existing monitoring databases or comprehensive literature reviews. Intake estimates were then multiplied by cancer potency factors from Health Canada, the United States Environmental Protection Agency, and the California Office of Environmental Health Hazard Assessment to estimate lifetime excess cancer risks associated with each substance and exposure pathway. Lifetime excess cancer risks in excess of 1 per million people are identified as potential priorities for further attention.

Results: Based on data representing average conditions circa 2006, a total of 18 carcinogen-exposure pathways had potential lifetime excess cancer risks greater than 1 per million, based on varying data quality. Carcinogens with moderate to high data quality and lifetime excess cancer risk greater than 1 per million included benzene, 1,3-butadiene and radon in outdoor air; benzene and radon in indoor air; and arsenic and hexavalent chromium in drinking water. Important data gaps were identified for asbestos, hexavalent chromium and diesel exhaust in outdoor and indoor air, while little data were available to assess risk for substances in dust, food and beverages.

Conclusions: The ability to track changes in potential population exposures to environmental carcinogens over time, as well as to compare between different substances and exposure pathways, is necessary to support comprehensive, evidence-based prevention policy. We used estimates of lifetime excess cancer risk as indicators that, although based on a number of simplifying assumptions, help to identify important data gaps and prioritize more detailed data collection and exposure assessment needs.

In plain English

This was a screening-level risk assessment within the CAREX Canada project. It did not study people with disease. The authors combined average levels of selected known carcinogens in Canada around 2006 with standard body-weight and intake assumptions and published cancer potency factors. The levels came from outdoor air, indoor air, indoor dust, drinking water, and food and beverages. From these the authors estimated lifetime excess cancer risk for the Canadian population. They calculated indicators for 27 carcinogen-exposure pathway combinations, and 18 exceeded 1 per million. The highest estimates were for radon indoors (23,655 per million) and formaldehyde indoors (487). The article does not name the asbestos fiber type. Using California potency factors, the estimated lifetime excess cancer risk for asbestos was 10.8 per million in indoor air and 2.5 in outdoor air. Using US EPA factors, the figures were 1.3 and 0.3. The asbestos data were rated very low quality, and the outdoor figure relied on a US measurement program from the 1980s and 1990s. The authors identified asbestos in air as a data gap. They stated that the estimates should not be interpreted as real cancer risks.

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: Screening-level risk assessment: estimated lifetime excess cancer risk calculated from existing monitoring data and published literature combined with cancer potency factors. No new data were collected.
• Who was studied: The general Canadian population, using standard characteristics for adults, teens, children, small children and infants, with environmental data representing conditions circa 2006
• Exposure: Selected carcinogens listed as known human carcinogens by IARC, including asbestos (fiber type not stated), benzene, radon, formaldehyde, arsenic, hexavalent chromium and diesel engine exhaust, in outdoor air, indoor air, dust, drinking water, and food and beverages. Asbestos risk was calculated by multiplying the lifetime average hourly concentration by an inhalation unit risk factor.
• Main results:
  • Indicators were calculated for 27 carcinogen-exposure pathway combinations. 18 had potential lifetime excess cancer risks greater than 1 per million, based on varying data quality.
  • The highest estimated lifetime excess cancer risks were radon indoors (23,655), formaldehyde indoors (487), radon outdoors (371), diesel engine exhaust indoors (300) and arsenic in drinking water (89).
  • Asbestos in indoor air: average concentration 8.5x10-5 fibres per millilitre, data quality very low. Lifetime excess cancer risk was 10.8 per million using the California OEHHA potency factor and 1.3 using the US EPA factor; no Health Canada value was given.
  • Asbestos in outdoor air: average concentration 2.0 x10-5 fibres per millilitre, data quality very low. Lifetime excess cancer risk was 2.5 per million using the California OEHHA potency factor and 0.3 using the US EPA factor. The outdoor value was the average of outdoor measurements taken at buildings in a US program from the 1980s and 1990s.
  • Carcinogens with moderate to high data quality and estimated risk above 1 per million included benzene, 1,3-butadiene and radon in outdoor air; benzene and radon in indoor air; and arsenic and hexavalent chromium in drinking water.
  • Asbestos, hexavalent chromium and diesel exhaust in outdoor and indoor air were identified as data gaps.
• The authors' conclusion: The authors concluded that lifetime excess cancer risk estimates, although based on simplifying assumptions, can serve as indicators that help identify data gaps and prioritize further data collection and exposure assessment.
• Limitations the authors state:
  • The estimates are general relative indicators and should not be interpreted as real cancer risks or estimates of future disease burden.
  • Cancer potency factors rely on extrapolating from animals given high doses to humans exposed to low doses, and assume a linear dose-response with no threshold.
  • Asbestos is not regularly measured in outdoor air in Canada. Different measurement methods can produce substantially different results.
  • The few Canadian outdoor asbestos studies were from communities affected by asbestos mines, so US data were used instead.
  • The indicators do not represent how common exposure is in the Canadian population, because nationally representative data are lacking.
  • Food consumption data came partly from a national dietary survey conducted in the early 1970s, and the authors do not know how well it represents the current diet.

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