CANCER PREVENTION INSTITUTE OF CANADA

Last updated: 15-Jan-2007

Environmental Exposures

As challenging as it is to track occupational carcinogens, it is even more difficult to quantify the impact of environmental pollution. The generally low level and widespread nature of the exposure causes the identification of population impacts to be elusive. Apart from environmental tobacco smoke (covered in a previous section of this report), general air pollution in and around urban centres has probably been the most harmful pollutant in the past, accounting for 1 out of 100 cancer deaths, and up to 5% of lung cancer mortality.[1]

There are several other obstacles to the aggressive pursuit of prevention in the arena of environmental carcinogens:

• the degree to which cancer and other disease can be traced to such agents remains a matter of scientific and political controversy[2]

• setting priorities within various environmental improvement goals (most of which are massive projects), and between environmental and other modifiable risk factors for chronic disease

• sorting out the plausible from the implausible sources of cancer: “no field of epidemiological research has seen so many new hypotheses as that of carcinogenesis from environmental pollution”[3]

• choosing intervention plans in the absence of complete research data

• finding the will to redirect or complement energies and resources involved with the treatment of cancer; a letter from several environmental and occupational medicine authorities in The Scientist noted that the premier American Association for Cancer Research meeting in 2002 featured no presentation on primary cancer prevention[4]

• · identifying the most critical outcome to target: reduced environmental carcinogen levels, evidence of decreased uptake in human populations, or, after several decades, proof of decreased health impacts and mortality

• the extreme difficulty of establishing the comparative effectiveness of any intervention

There are also some potential pathways on which to move forward. First, an alliance can be formed with those working to eliminate occupational carcinogens; most of the agents in the environment are the same and originate in the workplace anyway. Second, there is the very real possibility of sizeable and powerful coalitions with other organizations concerned with the environment and the ecological and more acute human harms created by pollution.

Regulatory Changes

Inevitably, with something as large as “the environment,” government resources and action will be required, as well as significant partnerships with industry. The minutes of the recent meeting of the Environmental and Occupational Exposures group identified the following potential targets for elimination or reduction (not prioritized):[5]

• consumer and downstream exposure to pesticides / herbicides

• clorination byproducts exposure in drinking water

• air pollution

• consumer exposure to carcinogens in products, including food

• hazardous waste sites

• other industrial pollution.

Again, the very scope of the initiatives required in each of these situations is what has probably precluded getting the concerns off of high-level agendas and into the hands of policy-makers.

Clinical Care

Although much harder to trace than occupational exposures, physicians should look for cases where cancer may have been caused or exacerbated by environmental agents. Possibly of little help to the patient, perspectives gained in the clinical care setting can add to the priority-setting and momentum for environmental action.

Synergies between risk factors are a concern, as they were in the occupational sphere. An instance is radon gas, which forms as a result of the breakdown of subsurface uranium. When it accumulates in homes it can be carcinogenic, and this impact becomes synergistic for tobacco smokers.[6] The US Environmental Protection Agency estimates that radon gas is the second-leading cause of lung cancer in that country.[7] Concerns over radon have actually been leveraged in some cases to motivate people towards smoking cessation.[8] A synergism between smoking and other environmental pollutants also is likely; smokers are at a higher risk when exposed to air-borne carcinogens, a fact that should be underlined by healthcare providers.[9]

[2] Gold LS, Slone TH, Manley NB et al. Misconceptions About the Causes of Cancer. Vancouver, BC: The Fraser Institute, 2002.

[3] Adami H, Day N, Trichopoulos D et al. Primary and secondary prevention in the reduction of cancer morbidity and mortality European Journal of Cancer 2001; 37: S118-S127.

[4] Huff J, Castelman B, LaDou J et al. Primary prevention of cancer. The Scientist 2002; 16(18). Available at http://www.the-scientist.com/yr2002/sep/let_020916.html (accessed December 2004).

[5] Canadian Strategy for Cancer Control. Report on Environmental and Occupational Exposures Meeting, January 14, 2003. Available at http://209.217.127.72/cscc/pdf/pprev/Env&OccupMtgReport_ an142003.pdf (accessed December 2004).

[6] Lee ME, Lichtenstein E, Andrews JA et al. Radon-smoking synergy: A population-based behavioral risk reduction approach Preventive Medicine 1999; 29(3): 222-7.

[7] See the EPA fact sheet at http://www.epa.gov/iaq/radon/myths.html (accessed December 2004).

[8] Lee ME, Lichtenstein E, Andrews JA et al. Radon-smoking synergy: A population-based behavioral risk reduction approach Preventive Medicine 1999; 29(3): 222-7.

[9] Levi F. Cancer prevention: epidemiology and perspectives European Journal of Cancer 1999; 35(7): 1046-58.