The article by Clin et al. (1) provides additional information for a
dose-response relationship with asbestos and cancer. Information where a
response curve changes effect as observed from background is critical in
establishing a safe exposure limit (threshold -exposure/concentration-
dose). Some investigators have reported this threshold is around 25
fiber/ml-years (2); although for some members of an exposed group this may
be lower (3). However, a cumulative no-effect value does not provide
information applicable for practical every day use when monitoring worker
exposure.
Recent studies (4,5,6) have suggested levels of exposure where there
was no excess increase in cancer, notably lung cancer and mesothelioma.
This is especially noted for non-smokers where risk does not exceed unity
(lung cancer), even for high asbestos exposure, while there is a
significant increased risk for smokers and former smokers (6,7). Thus, it
appears smoking is the primary contributor and confounder of disease for
historical and current asbestos workers (6). Compounding this issue is
the high number of smokers performing asbestos abatement work
(approximately 60% or greater depending on the population observed even at
the present time) (8,9). The high rate of smoking makes it difficult to
estimate a threshold and subsequently establish an exposure value from
this type of information. Certainly, for today's asbestos workers smoking
constitutes their greatest risk (6,9,10).
Recent studies with direct (4,5) and indirect (e.g. Job Exposure Matrix
and Job Specific Modules) (6,11) exposure information do allow an estimate
of a threshold exposure dose. Although, exposure can greatly vary over
time (4), it appears even with mixed fiber exposure (chrysotile and
amphibole) (5) a threshold of 1.0 f/ml-year is applicable, but at the
upper range. If chrysotile alone is used in this estimate, it appears a
higher value would be warranted (5). Taken together, with a safety margin
to include a lower reported value in causation of asbestosis (about 23
f//ml - years) (11), a threshold of 0.8 f/ml-year would appear applicable
(20 f/ml - years). From this, using a work time period of 25 years, which
is not likely for asbestos workers in the United States, due to physical
demands of the occupation and actual length of the "industry", allows
suggestion for a threshold of 0.8 f/ml-Time Weighted Average. When
present exposure levels are included in this evaluation (12), it is
unlikely workers in developed nations will exceed a cumulative exposure of
20 or 25 fiber/ml-years. Comparison of this proposed threshold with data
reported by Clin et al., for lung cancer and mesothelioma, with 25 years
or less of exposure (table 1 in Clin et al.), provides support for this
threshold value. However, any value will be controversial, especially in
establishing a threshold.
References
1. Clin B, Morlais F, Launoy G, Guizard AV, Dubois B, Bouvier V,
Desoubeaux N, Marquignon MF, Raffaelli C, Paris C, Galateau-Salle F,
Guittet L, Letourneux M. Environ Occup Med 2011; First online March 15,
2011.
2. Lange JH. Emergence of a New Policy for Asbestos: A Result of the
World Trade Center Tragedy. Indoor and Built Environment 2004; 12:21-33.
3. Pierce JS, McKinley MA, Paustenbach DJ, Finley BL. An evaluation
of reported no-effect chrysotile asbestos exposures for lung cancer and
mesothelioma. Crit Rev Toxicol. 2008;38:191-214.
4. Sichletidis L, Chloros D, Spyratos D, Haidich AB, Fourkiotou I,
Kakoura M, Patakas D. Mortality from occupational exposure to relatively
pure chrysotile: a 39-year study. Respiration. 2009;78:63-8.
5. Dodic Fikfak M, Kriebel D, Quinn MM, Eisen EA, Wegman DH. A case
control study of lung cancer and exposure to chrysotile and amphibole at a
slovenian asbestos-cement plant. Ann Occup Hyg. 2007 51:261-8.
6. Frost G. The joint effect of asbestos exposure and smoking on the
risk of lung cancer mortality for asbestos workers (1971-2005). 2011;
Health & Safety Executive (HSE);
(http://www.hse.gov.uk/research/rrhtm/rr730.htm)
7. Frost G, Darnton A, Harding AH. The effect of smoking on the risk
of lung cancer mortality for asbestos workers in Great Britain (1971-
2005). Ann Occup Hyg. 2011 55:239-47.
8. Frost G, Harding AH, Darnton A, McElvenny D, Morgan D.
Occupational exposure to asbestos and mortality among asbestos removal
workers: a Poisson regression analysis. Br J Cancer. 2008 99:822-9.
9. Lange JH, Mastrangelo G, Buja A. Smoking and alcohol use in
asbestos abatement workers. Bull Environ Contam Toxicol 2006 77:338-42.
10. Harding A-H, Darnton A, Wegerdt J, McElvenny D. Mortality among
British asbestos workers undergoing regular medical examinations (1971-
2005). Occup Environ Med 2009;66487-495.
11. Mastrangelo G, Ballarin MN, Bellini E, Bicciato F, Zannol F,
Gioffr? F, Zedde A, Tessadri G, Fedeli U, Valentini F, Scoizzato L,
Marangi G, Lange JH. Asbestos exposure and benign asbestos diseases in 772
formerly exposed workers: dose-response relationships. Am J Ind Med 2009
52:596-602.
12. Lange JH, Sites SL, Mastrangelo G, Thomulka KW. Exposure to
airborne asbestos during abatement of ceiling material, window caulking,
floor tile, and roofing material. Bull Environ Contam Toxicol 2006 77:718-
22.
Conflict of Interest:
None declared
The article by Clin et al. (1) provides additional information for a dose-response relationship with asbestos and cancer. Information where a response curve changes effect as observed from background is critical in establishing a safe exposure limit (threshold -exposure/concentration- dose). Some investigators have reported this threshold is around 25 fiber/ml-years (2); although for some members of an exposed group this may be lower (3). However, a cumulative no-effect value does not provide information applicable for practical every day use when monitoring worker exposure.
Recent studies (4,5,6) have suggested levels of exposure where there was no excess increase in cancer, notably lung cancer and mesothelioma. This is especially noted for non-smokers where risk does not exceed unity (lung cancer), even for high asbestos exposure, while there is a significant increased risk for smokers and former smokers (6,7). Thus, it appears smoking is the primary contributor and confounder of disease for historical and current asbestos workers (6). Compounding this issue is the high number of smokers performing asbestos abatement work (approximately 60% or greater depending on the population observed even at the present time) (8,9). The high rate of smoking makes it difficult to estimate a threshold and subsequently establish an exposure value from this type of information. Certainly, for today's asbestos workers smoking constitutes their greatest risk (6,9,10). Recent studies with direct (4,5) and indirect (e.g. Job Exposure Matrix and Job Specific Modules) (6,11) exposure information do allow an estimate of a threshold exposure dose. Although, exposure can greatly vary over time (4), it appears even with mixed fiber exposure (chrysotile and amphibole) (5) a threshold of 1.0 f/ml-year is applicable, but at the upper range. If chrysotile alone is used in this estimate, it appears a higher value would be warranted (5). Taken together, with a safety margin to include a lower reported value in causation of asbestosis (about 23 f//ml - years) (11), a threshold of 0.8 f/ml-year would appear applicable (20 f/ml - years). From this, using a work time period of 25 years, which is not likely for asbestos workers in the United States, due to physical demands of the occupation and actual length of the "industry", allows suggestion for a threshold of 0.8 f/ml-Time Weighted Average. When present exposure levels are included in this evaluation (12), it is unlikely workers in developed nations will exceed a cumulative exposure of 20 or 25 fiber/ml-years. Comparison of this proposed threshold with data reported by Clin et al., for lung cancer and mesothelioma, with 25 years or less of exposure (table 1 in Clin et al.), provides support for this threshold value. However, any value will be controversial, especially in establishing a threshold.
References
1. Clin B, Morlais F, Launoy G, Guizard AV, Dubois B, Bouvier V, Desoubeaux N, Marquignon MF, Raffaelli C, Paris C, Galateau-Salle F, Guittet L, Letourneux M. Environ Occup Med 2011; First online March 15, 2011.
2. Lange JH. Emergence of a New Policy for Asbestos: A Result of the World Trade Center Tragedy. Indoor and Built Environment 2004; 12:21-33.
3. Pierce JS, McKinley MA, Paustenbach DJ, Finley BL. An evaluation of reported no-effect chrysotile asbestos exposures for lung cancer and mesothelioma. Crit Rev Toxicol. 2008;38:191-214.
4. Sichletidis L, Chloros D, Spyratos D, Haidich AB, Fourkiotou I, Kakoura M, Patakas D. Mortality from occupational exposure to relatively pure chrysotile: a 39-year study. Respiration. 2009;78:63-8.
5. Dodic Fikfak M, Kriebel D, Quinn MM, Eisen EA, Wegman DH. A case control study of lung cancer and exposure to chrysotile and amphibole at a slovenian asbestos-cement plant. Ann Occup Hyg. 2007 51:261-8.
6. Frost G. The joint effect of asbestos exposure and smoking on the risk of lung cancer mortality for asbestos workers (1971-2005). 2011; Health & Safety Executive (HSE); (http://www.hse.gov.uk/research/rrhtm/rr730.htm)
7. Frost G, Darnton A, Harding AH. The effect of smoking on the risk of lung cancer mortality for asbestos workers in Great Britain (1971- 2005). Ann Occup Hyg. 2011 55:239-47.
8. Frost G, Harding AH, Darnton A, McElvenny D, Morgan D. Occupational exposure to asbestos and mortality among asbestos removal workers: a Poisson regression analysis. Br J Cancer. 2008 99:822-9.
9. Lange JH, Mastrangelo G, Buja A. Smoking and alcohol use in asbestos abatement workers. Bull Environ Contam Toxicol 2006 77:338-42.
10. Harding A-H, Darnton A, Wegerdt J, McElvenny D. Mortality among British asbestos workers undergoing regular medical examinations (1971- 2005). Occup Environ Med 2009;66487-495.
11. Mastrangelo G, Ballarin MN, Bellini E, Bicciato F, Zannol F, Gioffr? F, Zedde A, Tessadri G, Fedeli U, Valentini F, Scoizzato L, Marangi G, Lange JH. Asbestos exposure and benign asbestos diseases in 772 formerly exposed workers: dose-response relationships. Am J Ind Med 2009 52:596-602.
12. Lange JH, Sites SL, Mastrangelo G, Thomulka KW. Exposure to airborne asbestos during abatement of ceiling material, window caulking, floor tile, and roofing material. Bull Environ Contam Toxicol 2006 77:718- 22.
Conflict of Interest:
None declared