Risk of human health by particulate matter as a source of air pollution--comparison with tobacco smoking

Our plain-English summary of Risk of human health by particulate matter as a source of air pollution--comparison with tobacco smoking, by M. Enomoto, W.J. Tierney, K. Nozaki (The Journal of Toxicological Sciences, 2008).

The study

• Authors: M. Enomoto, W.J. Tierney, K. Nozaki
• Journal: The Journal of Toxicological Sciences
• Published: 2008;33(3):251-67
• Type of article: Review
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Increased air pollution, containing carcinogenic particulate matter smaller than 2.5 microm (PM(2.5)), has gained particular attention in recent years as a causative factor in the increased incidence of respiratory diseases, including lung cancer. Extensive carcinogenicity studies conducted recently under Good Laboratory Practice conditions by National Toxicology Program in the USA, Ramazzini Foundation in Italy or Contract Research Organizations on numerous chemical compounds have demonstrated the importance of considering dose levels, times and duration of exposure in the safety evaluation of carcinogenic as well as classical toxic agents. Data on exposure levels to chemical carcinogens that produce tumor development have contributed to the evaluation of human carcinogens from extrapolation of animal data. A popular held misconception is that the risk from smoking is the result of inhaling assorted particulate matter and by products from burning tobacco rather than the very low ng levels of carcinogens present in smoke. Consider the fact that a piece of toasted bread contains ng levels of the carcinogen urethane (ethyl carbamate). Yet, no one has considered toast to be a human carcinogen. Future human carcinogenic risk assessment should emphasize consideration of inhalation exposure to higher levels of benzo (a) pyrene and other possible carcinogens and particulate matter present in polluted air derived from automobile exhaust, pitch and coal tar on paved roads and asbestos, in addition to other environmental contaminant exposure via the food and drinking water.

In plain English

This article was a review, not a new study. The authors discussed particulate matter in air pollution, including PM2.5, as a source of lung cancer risk and compared it with tobacco smoking. They drew on animal cancer-testing data from the US National Toxicology Program and the Biosafety Research Center in Japan, 1983 to 1999, and on published measurements of carcinogens in air and smoke. In the Japanese data, about 40% of non-genotoxic chemicals tested in rats and mice produced tumors in at least one sex-species experiment. Across the studies reviewed, the ratio between the lowest dose that caused tumors and the highest dose that did not was generally less than a hundred-fold. A table listed 20-40 ng of benzo(a)pyrene in mainstream smoke per cigarette. The authors stated that carcinogen levels in smoke are so low they are considered to have negligible carcinogenic potential. They concluded that future risk assessment should emphasize inhaled benzo(a)pyrene and particulate matter from automobile exhaust, from pitch and coal tar on paved roads, and from asbestos. Asbestos was named only as a pollution source, without any asbestos data.

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: narrative review
• Who was studied: No new study population. The review covered animal carcinogenicity data, including chemicals tested in rats and mice at the Biosafety Research Center, Japan, and chemicals from the NTP database, 1983 to 1999, plus published air pollution and tobacco smoke measurements.
• Exposure: Particulate matter (PM2.5) and carcinogens such as benzo(a)pyrene in polluted air from automobile exhaust, coal burning, pitch and coal tar on paved roads, and asbestos, compared with tobacco smoke. No fiber type or asbestos data were given.
• Main results:
  • In data from the Biosafety Research Center, Japan (cited as Enomoto et al., 1996), about 40% of non-genotoxic chemicals evaluated in both rats and mice showed positive tumor responses in one or more sex-species experiments, 1983 to 1999.
  • In the animal studies reviewed, the dose ratio between tumor-producing and non-tumor-producing doses was generally less than a hundred-fold. The tables define this ratio as the lowest dose that produced evident carcinogenicity divided by the highest dose that did not. Only a few strong carcinogens, such as aflatoxin B1 and some nitroso-compounds, showed a range of 100 to 1,000 fold.
  • Tables 2 and 3 define the dose ratio as the lowest evident carcinogenicity dose divided by the highest non-carcinogenicity dose.
  • Table 1 listed benzo(a)pyrene in mainstream smoke at 20-40 ng per cigarette.
  • Table 4 listed the carcinogen urethane (ethyl carbamate) at 312 ng per piece of whole wheat toast, a figure the text attributes to Zimmerli and Schlatter (1991).
  • The authors calculated that exposing animals in whole-body chambers to 250 mg particulate matter per cubic metre for 6 hours a day required at minimum 2,500 cigarettes per day.
• The authors' conclusion: The authors stated that carcinogen levels in tobacco smoke are considered to possess negligible carcinogenic potential. They concluded that future human cancer risk assessment should emphasize inhaled benzo(a)pyrene, other possible carcinogens and particulate matter in polluted air from automobile exhaust, pitch and coal tar on paved roads, and asbestos.
• Limitations the authors state:
  • The authors stated that more work is needed to understand what the available epidemiologic evidence means for a cancer dose-response in humans.
  • The authors noted that naturally occurring tumors in aged rodents make it difficult to extrapolate animal results to low doses.
  • The authors stated that discussion of animal inhalation data was outside the scope of the review.

Topics

Medical terms in this study, explained in our Lexicon: Carcinogenic, Lung Cancer.

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