On October 17, the World Health Organization’s International Agency for Research on Cancer (IARC) announced that it has classified air pollution as a human carcinogen. Although the composition of air pollution and exposure levels vary widely from place to place, IARC says its assessment is applicable worldwide and notes that exposures in rapidly industrializing countries with large populations have increased significantly in recent years. According to the IARC review of the latest scientific studies, exposure to air pollution increases the risk for lung cancer and for bladder cancer. IARC also evaluated particulate matter, a major component of air pollution, and concluded that it too is a human carcinogen. This is the first time outdoor air pollution has been classified as a cause of cancer. IARC notes that in 2010 – the most recent annual data available – approximately 223,000 deaths worldwide resulted from lung cancer prompted by air pollution. Meanwhile air pollution-related respiratory and cardiovascular diseases continue to decrease life expectancy worldwide. “We now know that outdoor air pollution is not only a major risk to health in general, but also a leading environmental cause of cancer deaths,” said Dr Kurt Straif of the IARC in the organization’s announcement.

Major sources of this carcinogenic air pollution, said the IARC in its announcement, include industrial and agricultural emissions, power generation and transportation. This means that in addition to visible sources of outdoor air pollution like vehicle exhaust and emissions from factory smoke stacks, this air pollution includes industrial chemicals such as solvents, metals, and numerous different hydrocarbon compounds. A look at the US Environmental Protection Agency’s Toxics Release Inventory gives an indication of the many carcinogenic chemicals regularly released by industrial facilities. Among the additional pollutants are chemicals in pesticide drift and the invisible molecules of environmentally mobile persistent compounds emanating, not only from waste sites and industrial facilities, but also from finished products as they wear and weather. There is now ample evidence that many potentially carcinogenic individual chemicals can become airborne in all of these ways. The IARC assessment looked at air pollution’s whole mix of cancer-causing substances and decided that wherever air is polluted it is potentially carcinogenic.

The IARC announcement is deeply disturbing, particularly for residents of the world’s most polluted cities and for those who live where polluting industries are clustered. It also adds considerably to the health concerns for people whose work exposes them to chemicals identified as carcinogens – and raises questions about the health risks posed by exposure to multiple carcinogens and to pollutants that can compromise the ability to fight disease and infection. But the IARC assessment also suggests that significant improvements in public health could be made by curtailing the use and generation of carcinogens in industrial and agricultural processes, including power generation and vehicle operation. “There are effective ways to reduce air pollution, and given the scale of the exposure affecting people worldwide, this report should send a strong signal to the international community to take action without further delay,” said IARC director Dr. Christopher Wild in a statement.

Air pollution and occupational disease

One place to begin such action would be by reducing and eliminating carcinogens in industrial operations that produce large amounts of hazardous air pollutants. Not only would this would improve public health, but it could make much-needed improvements in occupational health. For despite the advances in workplace safety that have been made in recent decades, the US Occupational Health and Safety Administration estimates that more than 850,000 people in the United States develop new work-related illnesses each year and approximately 60,000 people die from such diseases in the US each year. Of these deaths, an estimated 10,000 to 20,000 are a result of cancers related to occupational chemical exposures. While precise data is lacking about all of these specific exposures, reports of chemicals used in US industrial facilities gives an idea of what kinds of emissions may be occurring.

Worldwide, these numbers are far worse. Globally, the International Labor Organization (ILO) estimates that approximately 80% of the 2.2 million people who die annually from occupational causes do so because of a work-related illness. The ILO also estimates that about 160 million people worldwide are diagnosed each year with a new work-related disease. Nearly a third of these work-related deaths result from cancers and about a quarter from other diseases associated with exposure to hazardous chemicals – some of the same substances the IARC cited as hazardous components of ambient air pollution: diesel engine exhaust, solvents, metals and dust.

Not included in these numbers – US or global – however, are the children whose health is compromised by their parents’ occupational chemical exposure. Also not included in these figures are the community members whose health is affected by exposure to hazardous substances used or generated by local industry that occurs in emissions not accounted for by routine environmental monitoring – second-hand exposure to toxic dusts or poorly accounted for accidental releases and waste, for example. And it is widely acknowledged that due to incomplete reporting of work-related illnesses, these figures likely underestimate the number of people with occupational diseases.

The Massachusetts Toxic Use Reduction Institute’s recent report on state cancer rates and state-based industry’s use of carcinogen’s suggests that policies designed specifically to encourage reduced use of industrial carcinogens may indeed be effective in achieving declines in airborne releases of chemicals associated with specific cancers, including bladder and lung cancer. While the report wasn’t designed to investigate if the releases of carcinogenic pollutants reduced cancer rates it does suggest that reductions in use and releases of such contaminants can be achieved.

IARC says air pollution is carcinogenic but scientific debate delaying action continues

Meanwhile, against this backdrop of evidence that the air we breathe – indoors and out – has the potential to make us seriously ill, is the ongoing debate being carried out in scientific journals and policy discussions over the carcinogenicity of various widely-used chemicals. These chemicals include asbestos, benzene, 1,3-butadiene, formaldehyde, methylene chloride, certain metals and phthalates, styrene and trichloroethylene. The details are complex and the history is long, going back many decades, but the gist of what’s being played out in scientific journals is a dispute between industry-affiliated researchers and those without such ties over how various chemicals’ carcinogenicity should be determined.

The results of this back-and-forth, which has been well documented by the books Doubt is Their Product, Merchants of Doubt and Is it Safe?, among other accounts, is a delay in making policy decisions that would begin to significantly reduce exposure to such substances. The impacts of this debate seem worth considering in the context of the IARC’s classification of air pollution as a human carcinogen.

One recent example of this exchange between industry-funded and non-industry-affiliated scientists comes in an editorial published in the International Journal of Occupational and Environmental Health. The authors say that industry-funded studies questioning the validity of applying the results of laboratory animal studies to human health effects have prevented “timely and appropriate health protective actions on many economically important yet carcinogenic chemicals.” The details of this particular argument focus on how certain chemicals prompt kidney tumors, a type of cancer that has been increasing over the past several decades. The industry-affiliated scientists’ research says that the lab rats’ tumors are prompted by a kidney disease common to these animals rather than by the chemicals. The scientists without industry affiliations say the evidence suggests otherwise: that the chemical exposure prompted tumors in a sufficient number of animals without the kidney disease to indicate that the chemicals are carcinogenic. This is but one example, write the editorial’s authors, of hypotheses being used to question experimental results that provide evidence of chemicals’ carcinogenicity with the goal of delaying determinations that would be used to regulate these substances.

It is impossible to resolve these debates here – but when the World Health Organization’s International Agency for Research on Cancer has determined that air pollution is a human carcinogen, it would seem imperative to begin acting to eliminate use and generation of substances contributing to this contamination. A good place to start would be with carcinogens used and generated in industrial operations. Such reductions could have significant benefits, both for the workers with the greatest exposure and for the rest of us, who encounter them in the outdoor air.


  1. #1 Elizabeth Grossman
    October 24, 2013

    This post has been revised to accurately reflect the conclusions of the Toxics Use Reduction Institute’s report on
    Trends in the Use and Release of Carcinogens in Massachusetts. The report is available at: http://www.turi.org/About/Library/TURI_Publications/TURI-Methods-Policy-Reports/Trends_in_the_Use_and_Release_of_Carcinogens_in_Massachusetts and my post on the report at:

  2. #2 Dick Clapp
    October 24, 2013

    This has been a long time coming, but it changes some of the “received truths” about the portion of cancer due to environmental exposures. 223,000 cancer deaths would be 3% of worldwide cancer deaths in 2010. That’s lots more than what the old Doll and Peto (1981) table attributed to “pollution,” and their table included things like water pollution, contaminated soil, etc.
    As Lizzie points out, we still don’t have a full accounting, but this IARC report is a step in the right direction.