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FILE NAME Brakes BRK DATE 2006 DOC BRK154 DOCUMENT DESCRIPTION Letter to the Editor Response to Letter from File 153 - American Journal of Industrial Medicine AMERICAN JOURNAL OF INDUSTRIAL MEDICINE 62-64 2006 Letter to the Editor Response to Letter from Paustenbach et al To the Editor We appreciate the interest expressed by Paustebach and colleagues in our study entitled Evaluation of the size and type of free particulates collected from unused asbestoscontaining brake components as related to potential for respirability which was published last year in this Journal AJIM 545-533 We were somewhat surprised to note that Paustebach and colleagues expected to find measurable TEM asbestos fibers on an unused brake component We assume that they mean asbestos fibers that can be detected by analytical transmission electron microscopy TEM However we do disagree with a number of their comments and conclusions They reference their study Paustenbach et al 2003 in which a survey of the world's literature on the subject of exposure to asbestos in automotive service facilities was carried out and comment that the airborne levels of asbestos are very low and in some cases detectable We con- ducted our study because it was unclear to us from the published literature whether respirable asbestos fibers that were smaller than those which would be detected and inclu- ded in a standard NIOSH count were readily released from new brake components or if they were tightly bound in inert matrix material and consequently not readily released Their comment goes to the salient point of our study that is that the asbestos fibers that are not included in such a fiber count or which are excluded by the count scheme still have the potential to cause disease The use of phase contrast The University of Texas Health Center at Tyler Tyler Texas ZERI Consulting Inc Tyler Texas Mark AL Atkinson is the Director of Research and Professor of Biochemistry Ronald Dodson is an Executive Vice President Correspondence to Ronald F Dodson ERI Consulting Inc. 2026 Republic Drive Ste A TyleTrX 75701. mail ron @ enconsulting com Accepted 22 September 2005 DOI 10 1002 20237. Published online in Wiley InterScience www.interscience.wiley.com microscopy PCM which is used to establish a permissible exposure limit PEL is incapable of detecting small asbestos fibers that are nevertheless potentially capable of causing disease Our theoretical classification Table I Atkinson et al 2004 of which asbestos structures in each group indicate which would be included in a PCM count as well as what would be missing fibers From the beginning what we did realize was that the literature contains abundant data including data from our own studies which indicate that the detection of chrysotile fibrils most thinner bundles and individual fibers of many amphiboles require the use of an analytical transmission electron microscope ATEM applied at a sufficiently high magnification to permit their recogni- tion The inclusion of fibers shorter than 5 ...min a count scheme is also important if one is to obtain an accurate representation of the populations of fibers in environmental Asbestos Hazard Emergency Response Act AHERA Rohl et al 1976 Rood and Streeter 1984 Upton et al 1991 as well as tissue samples Langer et al 1971 Churg and Warnock 1980 Pooley and Ranson 1986 Dodson et al 2003 It was not our original intent to discuss at great length phase contrast microscopy and NIOSH counting schemes However since Paustenbach and colleagues have raised the issue of why we did not employ the PCM in counting fibers and have placed an appreciable emphasis on based data it seems reasonable for us to elaborate further on what one can and cannot see with the PCM as well as the reasons that dictated the choice of instrument ATEM used in our study As Paustenbach and colleagues point out historical data on air quality obtained by PCM analysis NIOSH in the work place of mechanics show that the PEL was often not exceeded The use of the PCM and determination of PEL obviously tie together The reader is recommended to review the article by Langer et al 1991 that included the statement the phase contrast microscope was both resolution limited and incapable of acquiring data useful in fiber identification a conclusion with which we are in complete agreement The authors furthermore discuss the basis for establishment of a definition of a fiber as per the NIOSH count scheme '2005 Wiley Inc. Letter to the Editor 63 by PCM Langer et al 1991 Langer et al 1971 in an earlier study pointed out the optical microscope delivers a Of course we could have analyzed our samples with PCM and then compared the results with ATEM data as select biased population First we can only study what the suggested although this would seem pointless for the reason microscope sees and it only sees large fibers those thicker stated by Pooley and Ranson 1986 that is possible using than 0.5 ...min diameter Rood and Streeter 1984 pointed out that the detection limit of a good correctly adjusted PCM may be 0.15 ...mRooker et al 1982 however under normal operating conditions the detection limit is not so low the electron microscope to predict the asbestos fiber count that would be obtained by light microscopy the reverse prediction cannot be made it is impossible to determine the proportion of the various asbestos mineral types using Ashcroft and Heppleston 1973 Hwang and Graham 1981 the light microscope Paustenbach et al also take issue with Hwang and Wang 1983 and we shall assume a limit of 0.3 ...mThus the resolution limit used in our study for the our methodology specifically citing the lack of control rinsates In the text we state that the water used was filtered PCM seems rather liberal and indeed lower than published through a 0.2 ...mNucleopore filter to remove any particulates detection limits as is standard in our lab We periodically do run quality If one reviews the diameters of fibrils and most bundles control on our reagents including prefiltered water and found in our study is evident that they would be invisible by these are uniformly negative PCM and consequently not be included in any count canied The authors also criticize the lack of a review of the out by PCM The exclusion of asbestos structures derived world's literature on exposure to brake dust as it relates to from brake dust would be even further reduced if one used a industrial hygiene and epidemiology and that our citations count scheme excluding fibers below 5 ...mbe it done by are biased We maintain that this is unfair Our study was a PCM scanning electron microscopy or TEM The point of research report not a review article and perhaps more to the our study and the reason for conducting this study was to determine if respirable asbestos structures were released point was a study designed to answer the question What can be rinsed from the face of new brake components not from new brake components in numbers that posed a an industrial hygiene or epidemiology study An potential health hazard irrespective of regulatory counting extensive literature review of published industrial hygiene schemes which in turn are not linked to the potential of a or epidemiology studies would in all probability have given fiber to cause disease If an asbestos fiber is respirable it been viewed as irrelevant by the referees of our manuscript has the potential to contribute to the development of disease We did include the article by Paustenbach et al 2003 which inespective of whether limitations of the instrument used we thought to be an extensive review of these subjects It is permit seeing it or not in a given air sample our position that we did quote the section from the Butnor The logic of using ATEM to obtain a real representation study exactly as written Butnor et al 2003 as do of asbestos in brake dust has been cited in the literature The Paustenbach and colleagues of the statement they have used Health Effects Asbestos Research document con- Since that study has been referenced it may be of interest to cluded the TEM provides the most complete analysis note the technique used for analyzing the tissue burden was currently available for airborne asbestos The very high scanning electron microscopy with a defined fiber being 5 ...m resolving power of the TEM and its ability to provide the or longer to be included into the count scheme For reference mineralogical identity of asbestos when combined with the reader may choose to read our tables and determine how selected area diffraction SAED and EDXA make the TEM many of the total chrysotile asbestos structures including the method of choice for analysis of airborne asbestos fibrils and bundles would have even been included in such a samples During evaluation of asbestos exposure during count In essence a count of fibers or structures of 5 ...mand brake lining maintenance and repair Rohl et al 1976 found longer will exclude most asbestos dust from brakes and in that most fibers are too small to be seen by optical tissue samples preferably favor the thicker and longer microscopy almost all of them shorter than 0.4 min length amphibole population no matter what the instrument of virtually all of respirable size -5 ...m Jacko et al 1973 choice We believe from a health standpoint that this exclu- made size distribution measurements of asbestos fibers in sion is arbitrary brake dusts generated during dynamometer tests using both Finally and perhaps of greatest importance while we optical and electron microscopy They found at magnifica- respect the position of Pausterbach et al concerning the issue tions of 22,000 that 30 of the fibers were from 0.25- of exposures to brake dust and the potential for induction of 0.5 um in length and that 60 were longer than 0.5 m diseases in man we respectfully believe that the potential for Rohl et al 1976 The data found in our study confirms that cumulative exposure to asbestos even short chrysotile using an instrument not capable of resolving most asbestos raises further concerns as to the potential for inducing structures based on diameter or excluding structures based on disease We are confused by their comment that on one hand a count scheme that included only those greater than 5 ...min one should expect to find free fibers on the surface of new length would provide data on only a limited population of the brakes but that our findings of easily removed asbestos dust and ignore a large amount of potentially injurious dust structures from the surface of new brakes carried no 64 Atkinson and Dodson implication as to the potential for asbestos release into the air We would suggest that the reader considers the numbers of asbestos structures constituting the respirable components of each group of structures that were rinsed free from the binding material of the brake components and then logically consider if additional ones could be produced by sanding grinding or other traumatic events during replacement much less asbestos dust introduced into the air following physical wiping of brake drums or blowing the area with compressed air It seems to us that we have actually identified only a small portion of the potential asbestos that could be made friable and thus become aerosolized during brake replace- ment or repair If you find free asbestos structures of respirable size the logic eludes us as to how they may not at least potentially be inhaled if aerosolized and once deposited in the terminal airways have the potential to induce pathological responses at those sites or to be relocated to extrapulmonary sites It should not be lost to our readers that data concerning tissue burden in extrapulmonary sites where asbestos induced diseases occur indicate that the populations of asbestos are often over whelmingly represented by short fibers < mSebastien et al 1980 Dodson et al 1990 Suzuki and Yuen 2001 2002 Mark A.L. Atkinson MA DPhil The University of Texas Health Center at Tyler Tyler Texas Ronald F. Dodson MA PhD FCCP faha ERI Consulting Inc. Tyler Texas REFERENCES Ashcroft T Heppleston AG 1973. The optical and electron microscopic determination of pulmonary asbestos fiber concentration and its relation to the human pathological reaction J Clin Path 224 234 Atkinson MAL O'Sullivan M Zuber S Dodson RF 2004. Evaluation of the size and type of free particulates collected from unused asbestoscontaining brake components as related to potential for respirability Am J Ind Med 46-545-553 Butnor KJ Sporn TA Roggli VL 2003. Exposure to brake dust and malignant mesothelioma A study of 10 cases with mineral fiber analysis Ann Occup Hyg 325-330 Churg A Warnock ML 1980. 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