Carcinogens and the workplace
Authors: R. Hawkins
Journal: CA A Cancer Journal for Clinicians (1996)

To the Editor: In the article on carcinogens and the workplace by Stellman and Stellman in the March/April issue,1 Table 2 simply lists asbestos as though all forms of asbestos were the same. Table 5 does identify chrysotile but does not give any data on the workers' smoking habits. The article should list all six geologic types of asbestos or at least the tree types that have been used in commerce. One of the three, known as “blue” asbestos (crocidolite), causes serious lung problems. It was imported and used during World War II in ship construction and as a filter in Kent cigarettes with disastrous results in both cases, but the US government has taken no action against either the US Navy or the Lorillard Tobacco Company. The other hazardous form of asbestos is the brown (amosite) asbestos, which was imported from Africa and used in a factory in Patterson, NJ, with unfortunate results. Soft “white” asbsestos (chrysotile) is the kind of asbestos the federal government has declared war on despite the documented fact that even lifetime exposure to concentrations as high as two fibers per cc of air have not been shown to produce any significant hazard in the absence of concomitant cigarette smoking. All but one of the references in the Stellmans' article refer to undifferentiat-ed asbestos and only one made the connection between cigarette smoking and shipyard work. Was this crocidolite? I can't tell from the text, the references, or the tables. It is interesting that no form of asbestos is listed in Tables 3 or 4. Authors' Reply: The evidence for carcinogenicity of asbestos as well as the other substances mentioned in the article “Cancer and the Workplace”1 was based on assessments published in the monographs of the International Agency for Research on Cancer (IARC). These assessments are made by consensus of international working groups of experts from academia, government, and industry. In the article, asbestos appropriately appears in Table 2 (IARC Group 1 -known human carcinogen) and not Tables 3 (probable human carcinogen) or 4 (broad occupational exposure circumstances) precisely because it is a specific substance with recognized carcinogenic potential by IARC. While some mineralogic forms of asbestos may be quantitatively more carcinogenic than others, none is “safe.” The hypothesis that chrysotile asbestos in particular is less hazardous than amphibole varieties (crocidolite, amosite, tremolite) has recently been critically reviewed by Staynor et al,1 who concluded that “mechanistic and lung burden studies do not provide convincing evidence for the amphibole hypothesis,” while toxicologic and epidemiologic studies provide “strong evidence” that chrysotile is associated with an increased risk of lung cancer and mesothelioma. Table 5 of the article1 documents a dose-response for lung cancer in both male and female textile workers exposed primarily to chrysotile asbestos2 in one of the studies that provides key results in analyzing the carcinogenic potential of chrysotile alone. While there is some evidence that the risk of mesothelioma associated with exposure to chrysotile may be less than that for other forms of asbestos, it is not zero. Moreover, there is “absolutely no epidemiogic or toxicologic evidence” that chrysotile asbestos is associated with a lower risk for lung cancer,1 which occurs far more frequently in asbestos workets than does mesothelioma. Workers in the United States and elsewhere are almost always exposed to mixtures of different types of asbestos, so that the amphibole theory, even if partly correct, is largely academic in occupational settings.