Asbestos contamination has been a prominent inhalation hazard in many occupational environments and, as a result, many studies have been undertaken to measure airborne asbestos concentrations associated with the manufacture and use of asbestos-containing products in hundreds of workplace settings. In addition to concerns about the workplace, exposure to asbestos has been reported for individuals living in the residences of workers who returned home wearing contaminated clothing. Concerns for this household population have also included the potential for bystander exposures due to the presence of contaminated clothing in the residence, as well as the exposure potential associated with the active handling of contaminated clothing prior to laundering. As reported in the article “Evaluation of Take-Home Exposure and Risk Associated with the Handling of Clothing Contaminated with Chrysotile Asbestos,” (J. Sahmel, C. A. Barlow, B. Simmons, S. H. Gaffney, H. J. Avens, A. K. Madl, J. Henshaw, R. J. Lee, D. Van Orden, M. Sanchez, M. Zock and D. J. Paustenbach), Risk Analysis, February 2014, a study was conducted to better characterize the take-home asbestos exposure pathway and to measure the relationship between airborne chrysotile concentrations in the workplace, the contamination of work clothing, and take-home exposures and risks.
Asbestos Analysis Methodology
Of the six asbestos mineral fiber types currently recognized by the U.S. Occupational Safety and Health Administration (OSHA) in its regulatory exposure standards, only chrysotile is in the serpentine mineral class while amosite, crocidolite, tremolite asbestos, actinolite asbestos, and anthophyllite asbestos are in the amphibole mineral class. Over the past several decades, evidence has accumulated in the published literature indicating that there are significant differences in cancer potency according to asbestos mineral fiber type, with chrysotile being the least potent of the common industrial mineral types for both lung cancer and mesothelioma induction, and crocidolite being the most potent of the fiber types used commercially. In 1969, the U.S. Bureau of Occupational Health first published a method describing the use of a new filter counting method for industrial dusts and fibers that allowed for the characterization of the sizes of the individual airborne fibers collected, and in 1971, OSHA specified the use of this type of filter membrane sampling method with phase contrast (PCM) illumination for counting fibers and estimating fiber exposure. The PCM method does not distinguish asbestos fibers from other fibers of similar dimension and so a more extensive analytical method such as transmission electron microscopy (TEM) must be used. Studies have shown that the asbestos fiber disease potency for both lung cancer and mesothelioma differ substantially according to asbestos mineralogy and to fiber length and width characteristics, with longer and thinner fibers being more potent for disease. Both of these counting methods (PCM and TEM) can be helpful for fully characterizing airborne concentrations of asbestos, particularly when a data set contains large numbers of non-detects (NDs).
Previous Studies and Background
Three studies from the 1970s and 1980s reported measured airborne fiber concentrations associated with the presence or handling of asbestos contaminated clothing. Because of the sampling and analytical methods used, the results from all three of these studies are difficult to interpret. For most of these studies, the reported airborne measurements of asbestos were very low or not detectable (ND) by TEM or PCM. Although these studies are insightful for the individual products and scenarios evaluated, they do not specifically address the proportional relationship between workplace concentrations and the corresponding potential household concentrations from handling work clothing. Since there have been virtually no quantitative data presented in the literature to characterize the take-home risk for asbestos, the authors of this study determined that actual field data were needed to understand the plausible exposure potential associated with specific take-home scenarios, particularly in light of epidemiological studies that show a potential for increased disease incidence in household members. They also recognized that it would be beneficial to evaluate exposures and associated risks for individual fiber types in light of the reported fiber potency differences between chrysotile, amosite, and crocidolite. In this initial study, the focus was on take-home exposure potential to chrysotile, since this fiber type was used to make many common commercial products such as brakes, gaskets, packing, roofing materials, and floor tiles.
How the Study Was Conducted
Prior to performing the study, a medical institutional review board (IRB) reviewed and approved the study design. The study was conducted in a sealed chamber and three different airborne concentration ranges were used during a total of six loading events, with the goal of generating concentrations that were broadly classified at the target loading levels of low (0–0.1 f/cc), medium (1–2 f/cc), and high (2–4 f/cc). These were targets that could be considered representative of a variety of workplaces in which chrysotile asbestos was present during worker activities. A total of six 30-minute clothes-handling and shake-out events were performed during the study. The clothing that was contaminated during each loading event was matched to a separate, subsequent clothes-handling and shake-out event so that the data for each of the six loading and shake-out event pairs could be quantitatively analyzed. A total of six personal airborne fiber samples were collected on the clothes handler during each shake-out event. Four area samples intended to reflect the exposure of bystanders were also collected for the duration of each 30-minute handling and shake-out event.
All air samples were collected in accordance with NIOSH sampling method criteria and analyzed by PCM (NIOSH 7400) and TEM (NIOSH 7402) at RJ Lee Group in Monroeville, PA, which is accredited under the American Industrial Hygiene Association Laboratory Accreditation Program (AIHA-LAP). Descriptive statistics were performed on the PCM and TEM concentrations of total airborne fibers and airborne chrysotile collected during both the loading and clothes-handling events and all three of these concentration metrics were used in order to fully characterize the results, since each sampling method has advantages and disadvantages.
This study quantitatively compared the measured airborne chrysotile concentrations in a simulated work environment with the corresponding concentrations generated during the handling of clothing (over a range of contamination concentrations) and also evaluated the non-occupational risks associated with cumulative chrysotile doses from handling clothing contaminated at the levels evaluated in the study. An important observation from this study was the extent to which clothing fibers released during the handling and shake-out events contributed to the total PCM measurements, clearly showing that many, or most, of the fibers detected by PCM were clothing fibers rather than chrysotile fibers. In summary, the quantitative airborne chrysotile concentration measurements for the simulated occupational settings evaluated in this study, and the corresponding take-home airborne concentrations associated with the handling and shake out of the clothing contaminated with chrysotile, give some quantitative insight into both exposure potential and risk to household members who historically conducted such activities.
Although this study systematically and carefully attempted to quantitatively address take-home exposure potential for the conditions tested, there are aspects of the study design that should be considered in future studies.
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