Document b5rre17bkVMwx6EyvZO0q2em0

FILE NAME: Phenolic Resins (PHR) DATE: 1977 Jan DOC#: PHR003 DOCUMENT DESCRIPTION: Proceedings of the Royal Society of Medicine Asbestos Content of Dust Encountered in Brake Maintenance & Repair Volarne 70 Number 1 January 1977 Proceedings of the Royal Society of Medicine Management of Pulmonary Tuberculosis page 4 Medicine at the Crossroads page 16 3 Published by The Royal Society of Medicine 1 Wimpole Street London w I m 8 a e and Academic Press % London New York San Francisco n i; 32 Proc. roy. Soc. Med. Volume 70 January 1977 irregular or nodular interstitial opacities of limited extent and intensity on their films. Silica or asbestos exposure had occurred in 22% of the work force examined. Such exposures had occur red in various job categories in the titanium facility as well as in prior occupations. Eight of the 26 workers with abnormal X-rays had had silica or asbestos exposure. No clear pattern of restrictive disease in relation to X-ray findings could be seen. Summary and Conclusions Clinically significant or symptomatic pulmonary disease was infrequent in a survey of 207 currently employed production workers in a plant producing titanium dioxide from ilmenite ore. Evidence of airways obstruction was found in 47% of all workers (including 38 % of workers who had never smoked regularly). This abnormality was not freq uently accompanied by disabling shortness of breath. Despite the fact that approximately 90 % of the group of workers examined had worked for 20 years or more, radiological changes consistent with pneumoconiosis were relatively few, and unrelated to the respiratory abnormalities observed. We conclude (with the caveats inherent in a prevalence study in which only half of the eligible long-term workers were examined) that occu pational exposure associated with titanium pro duction by the sulphate process may commonly cause undesirable irritation of the upper and lower respiratory tract and functional abnormalities of the lung, but does not result in an important incidence of serious occupational lung disease. Individual workers may, however, suffer unwanted abnormalities. These findings, of course, do not speak to the presence or absence of increased risk of malignant pulmonary disease. This is being separately studied. Acknowledgment: This research study was sup ported in part by National Institute for Occu pational Safety and Health Contract CDC-99-74- 91. Asbestos Content of Dust Encountered in Brake Maintenance and Repair by A N Rohl PhD , A M Langer PhD , R Klimentidis ba,.M S Wolff PhD and I J Selikoff m d (Environmental Sciences Laboratory, Mount Sinai School o f Medicine o f the City University o f New York, New York, N Y 10029) Asbestos in Brake Linings The composition of automotive brake linings in cludes chrysotile asbestos fibre which comprises about 50 % of the friction material. The exposure of garage workers to asbestos during brake lining maintenance and repair has recently been in vestigated (Rohl et al. 1976). This important issue was studied because a large labour force is poten tially exposed (over one million people in the United States alone). Consequently it was thought essential to determine if chrysotile fibre survives braking, and to measure the amounts liberated as an aerosol during maintenance and repair oper ations. Investigators in the past have expressed doubt as to whether chrysotile fibres can survive the high temperatures generated during braking (Lynch 1968, Hickish & Knight 1970, Hatch 1970). Chry sotile is alleged to be subjected to temperatures in excess of 800C, which would cause its thermal transformation to forsterite or to an amorphous magnesium silicate phase. While 'hot spots' up to 1000C may be attained (Carroll 1962), the heat distribution is nonuniform, and other processes, in addition to thermal wear, contribute to de gradation of brake linings. For example, abrasion and macroshear may also cause physical break down (Burwell 1957, Mizutani et al. 1973). Ac cording^, brake lining disintegration by these mechanisms may liberate partially altered or even unaltered chrysotile fibres. REFERENCE Miller a , Chuang M & Selikoff 1 J (1976) American Retie- o f Respiratory Diseuses 113, Suppl., p 89 (abstract) Analysis o f Brake Drum Dust Initially, ten samples of automobile brake drum dusts from brake repair shops in New York City were collected and examined by optical micros copy, X-ray diffraction, transmission electron mic roscopy and energy dispersive X-ray spectroscopy, to determine the presence of chrysotile. Optical microscopy: The detection of chrysotile in brake drum dust by optical microscopy is hindered by the nature of the debris matrix, consisting largely of opaque pyrolyzed phenolic-type resin binders and road dust. Chrysotile, particularly small fibres, has low optical relief and low birefrin gence, which further hinder its identification. Only in rare instances have large fibres, with optical Section o f Occupational Medicine 33 Table 1 Chrysotile asbestos content of brake drum dusts X-ray diffraction (step-scan) Great Britain West Germany France United Slates of America Finland Western Australia So. of samples 8 8 1 So. positive 6 5* 1 10 10 5 3 7 4 39 29 Weight percent Mean Range 1.8 0.7-2.3 2.4 0.5-3.2 2.5 4.5 2.0-15.1 1.8 0.8-2.5 1.4 0.5-2.3 x =2.4 1.1 1 sample possibly positive Transmission electron microscopy So. positi! e 8 8 1 10 5 7 39 properties consistent with chrysotile, been obser ved with this technique. X-ray diffraciomeiry: The ten brake dust samples were analysed by X-ray diffractometry, in both continuous and step-scan mode. The diagnostic reflection selected for chrysotile (3.66 A; hkl=(0Q4)) was step-scanned in the fixed-count mode. By comparison with external standards, the amount of chrysotile present can be determined. Chrysotile reflections were observed in all samples, with weight percentages estimated to range from 2 to 15 (average 4.5). Lead compounds, quartz, carbonate minerals, clays, halite (NaCl), graphite, micas and alpha-iron were also identified in vari ous samples. Twenty-nine additional brake drum dust samp les were collected by colleagues in four European countries and Australia. The samples were ob tained from areas representing variable circum stances, such as driving conditions, friction material composition, type of automobile and climate. The results of X-ray diffraction analyses are presented in Table 1. Of the 39 total samples analysed (including 10 United States samples) chrysotile w-as found in 29, or about three-fourths. The mean chrysotile content varied from 1.4% in the seven Australian samples to 4.5% in the New York City samples. The thermal breakdown product of chrysotile, i.e., forsterite. which might be expected to form as a result of recrystallization, was not unambigu ously detected in any sample. Transmission electron microscopy (TEM): In order to verify the results of X-ray diffraction analysis, the brake dust samples were prepared for electron microscopic analysis by means of a technique which disperses the dust particles in a nitrocel lulose film without altering particle sizes. Both free chrysotile fibre bundles and fibrils were observed in all 39 samples. Most of the chrysotile retained its characteristic morphology without significant alteration, and selected area electron diffraction patterns obtained on representative fibres dem onstrated the preservation of crystal structure as well (Fig 1). * Fibre size distribution: In ten brake dusts sampled in New York City, free asbestos fibres were sized by TEM at magnification 42 000. The results showed that about 80 % of chrysotile is in free fibril form and is shorter than 0.4 pm in length. Over 57 % have lengths of about 0.2 pm. At magnifi cation 40 000, such a fibre would be about l.cm long. If lower magnification were used to scan for asbestos, significant numbers of fibres might not be detected. It is obvious that most fibres are too small to be seen by optical microscopy. The Asbestos Stan dard adopted by the Occupational Safety and Health Administration (OSHA) of the US Depart ment of Labour is limited to optical microscopy and neglects to count or control fibres less than 5 pm long. On the other hand, accumulating evidence suggests that such small asbestos fibres may produce disease (Holt el al. 1964, Davis 1965. Pott et al. 1972, Wagner et al. 1973, Hilscher et al. 1970, Bouhuys 1975). Air sampling: Eight personal air samples taken ' during brake repair work were selected for electron microscopic analysis. This was done in order to positively identify chrysotile in the samples and to determine whether a systematic relationship existed between optically and submicroscopically visible fibres for this type of exposure. The memb rane filters were ashed in plasma oxygen to elimin ate organic materials and the residue was prepared for electron microscopy by a `rubout' technique (Nicholson et al. 1971), which comminutes large chrysotile fibre bundles into individual fibres and fibrils. Large inorganic particles are likewise re duced in size, permitting all chrysotile to be seen and measured. Chrysotile was identified in the eight samples, in both fibre and fibril form (Fig 2). By measuring a large number of fibres at magnifi cation 42 000 and converting the volumetric data into mass, a concentration per volume of air is determined. Comparison of optical microscopic 34 Proc. roy. Soc. Med. Volume 70 January 977 fibre counts and the electron microscopic asbestos mass calculations indicates that a positive cor relation exists between the two sets of data. These results show that the standard (OSHA) optical fibre c o u n ts m ay be only indicative of the total asbestos exposure. Asbestos Exposure o f Workmen After the identification' of chrysotile in the brake drum dusts, asbestos fibre exposure during main tenance and repair was determined by personal air sampling carried out at automobile repair shops, taxi fleet repair shops and a municipal truck repair shop in New York City. Air sampling and analyti cal methods for the determination of fibre con centrations were in accordance with the OSHA techniques (Bayer ei al. 1975). Present regulations of OSHA prohibit asbestos concentrations of 5 fibres per millilitre (f ml) or greater, longer than 5 pm as a time-weighted average, and con centrations above 2 f ml will be illegal after July 1976. Peak concentrations or maximum excursions of 10 f/ml are permitted by the regulations. In brake lining inspection and repair, the wheel Fig 1 Electron photomicrographs o f brake drum dints, taken at carious magnifications, a. the numerous chrysolitefibrils have average lengths ot 0.4 gw: or less ( x 30 000). B. large numbers o f chrysolitefibres imbedded in. and protrudingJrom. opaque panicle, probably pyrolhed phenolic resin binder ( x SO 000). c . large chrysotilefibre bundle ( x 4} 000). D. large particle in lejt centre o fphotograph is the same as in C, but cannot he identified at tow magnification ( x 5400) Section o f Occupational Medicine 35 is removed from the axle and loose dust is com monly removed from the drum and back plates by means o f a jet o f compressed air. A survey o f 220 garages in Baltimore and Washington, DC has shown that this is the method of choice in 80 of the shops (Castleman et al. 1975). A similar situation exists in New York City. The data in Table 2 show that fibre concentrations are high in the breathing zone of the operator during com pressed air blowing. An asbestos concentration gradient, diminishing with time and distance away from the operation, appears to occur. Persons up to 22 m from such activity are exposed to measur able concentrations of asbestos. Personal air sampling was also conducted at New York City Department of Sanitation where truck brakes are repaired. Used linings are salvaged by machine grinding to remove dirt and grease from the surface. New linings are bevelled by grinding to reduce noise and improve break-in. Accordingly, these studies relate to levels of as bestos exposure which may be experienced by workers engaged in brake lining manufacturing. Table 2 shows that fibre concentrations experi enced during grinding ranged from 1.7 to 7.0 f/ml of air in the breathing zone of the operator. The background or area samples for this operation ranged from 1.2 to 0.2 f/ml, with a general decrease Fig 2 Electron photomicrographs o f personal air samples taken during brake repair work. Clumps o f ehrysotile are associated with opaque particles o f road (hot and resin binders. A, B. x 60 000. c, D, x 72 000 36 Proc, roy. Soc. Med. Volume 70 January 1977 Table 2 Personal air samples, automobile and truck brake repair___________ Peak fibre concentration S o. o f [fibres per ml) samples Mean Range Automobile brake repair Blowing dust from brake drums: Distance 1-1.5 m Distance 1.5-3 m Distance 3-6 m 4 150 3 3.3 2 1.6 Background (5 min after air jet blowing, distance 3.6-16 m) 2 0.2 Background (7-14 mm after air jet blowing, distance 19.6-22.6 m) 2 0.1 6.6-29.4 2.0-4.2 0.3-4.8 0.1-0.2 0.1 13 Truck brake repair Renewing used linings by grinding (distance 1-1.5 m) to 4.8 1.7-7.0 Background to grinding used linings: Distance 3.3 m 2 1.5 1.2-1.7 Distance 8.3 m 2 0.8 0.6-1.0 Distance 20.0 m 1 0.2 Bevelling new linings 4 37.3 23.7-72.0 Background to bevelling new linings: Distance 2.4 m 1 0.6 . Distance 3.6 m 2 0.4 0.3-0.5 Distance 9.1 m 1 0.3 23 away from the operator. From six to ten other ledge support under a grant from the National mechanics work within an area up to 20 m from Institute of Environmental Health Sciences, ES this operation are exposed to asbestos as well. 00928 and support by the Ford Motor Company. Since a person breathes about one cubic metre of MSW wishes to acknowledge support under a air an hour, multiplication of the fibre con post-doctoral fellowship from the NIEHS, centrations by one million gives the number of fibres inhaled during this period. Fibre con centrations measured during bevelling of truck linings were as high as 72 f/ml and averaged about 37 f/ml. Background counts were measured up to 9.1 m away from this operation (0.3 f/ml). Fibre concentrations measured during drilling holes for rivets and grinding ranged from 0.3 to 29.2 f/ml, as reported by Boillat & Lob (1973). Four of the nine values exceeded 5 f/ml. ES 02565. We are grateful to the following for assistance in obtaining brake dust samples: Professor Donald Bowes, University of Glasgow, Scotland: Mr L B Bowes, Department of Labour and Industry, Adel aide. South Australia; Dr Trevor Turner, Adel aide, South Australia: Professor Jean Bignon, Hospital Laennec, Paris, France; Munu Harme, Geological Survey of Finland, Otaniemi, Finland; Dr G. Gaal, Helsinki University of Technology, Helsinki, Finland; Dr K Robock and Dr W Conclusions . The existence of significant exposure during brake servicing operations necessitates the following Klsterkotter, Institut fr Hygiene und Arbeitsme dizin des Klinikum der Universitt Essen, West Germany. measures: (1) Implementation of industrial hygiene pro cedures to control exposure. (2) Clinical studies of garage mechanics to de termine evidence of asbestos-related disease. (3) Epidemiological studies of the mortality ex perience of exposed workers. In addition, the entire variety of dusts and other materials present in brake repair work should be characterized in order to determine its disease potential, especially silica and lead compounds. Acknowledgment: The authors wish to acknow REFERENCES Bayer S G, Brown T A & Zurawalde R D (1975) Document TR-84. US Public Health Service, Cincinnati, Ohio Boillat M A & Lob M (1973) Schweizerische medizinische Wochenschrift 103, 39 Bouhuys A (1975) Annals o f Internal Medicine 83, $98 Burwell J T (1957) Wear 1,119 Carroll W G (1962) British Plastics 35. 414 Castleman B. Camarota L A, Fritsch A J , Mazzocchi S & Crawle* R G (1975) Puhln Health Reports 90, 254 Davis J M J (1965) Annals o f the Hew York Academy o f Sciences 132, 9$ Section o f Occupational Medicine 37 Hatch D (1970) Annals o j 0 ( cupational Hygiene 13, 25 Hickish D E & Knight K L (1970) Annals o f Occupational Hygiene 13, 17 Hilscher W, Sethi S, Friedrichs K H & Pott F (1970) Haturwissenst haften 57, 356 Holt P F, Mills J & Young D K (1964) Journal o f Pathology and Bacteriology 87, 15 Lynch J R (1968) Journal o f the Air Pollution Control Association 18, 824 Mizuuni Y, O bara H & Nakajima K (1973) Wear 23, 387 Nicholson W J , Rob) A N & Ferraud E F (1971) la : ProccidiBgs of the Second International Clean Air Congress. Ed. H M England & W T Berry. Academic Press, New York; pp 136-^139 Pott F, Huth F at Friedrichs K H (1972) Zentralblattfu r Bakteriologie. Abt. I, Originale, 155,463 Rohl A N, Langer A M, Wolff M S & Weisman 1 (1976) Environmental Research 12,110 Wagner J C, Berry G & Timbreli V ( 1973) British Journal oj Cancer 28,173 Neurotoxic Properties of Certain Aliphatic Hexacarbons by Peter S Spencer PhD and Herbert H Schaumburg md (Departments o f Pathology and Neuroscience, Saul R Korey Department o f Neurology, Rose F Kennedy Center, Albert Einstein College o f Medicine, Bronx, New York 1046J, USA) several species of experimental animal (Duckett et al. 1974, Mendell et al. 1974, Spencer, Schaum burg, Raleigh & Terhaar 1975). These studies demonstrated that prolonged intoxication by in halation or subcutaneous injection caused the insidious development of symmetrical weakness first in the hindlimbs and later in the forelimbs. The first signs of peripheral neuropathy developed after 4 to 12 weeks of continuous inhalation of 200 600 parts/106 of MBK, and after 12 to 16 weeks of intermittent inhalation of 1300 parts/106 of MBK. The onset of MBK neuropathy was associated with a reduction in the sciatic nerve conduction velocity (Mendell et al. 1974), an indication of nerve damage also found in rats and monkeys inhaling 1000 or 100 parts/106MBK intermittently for periods of 3 and 8 months respectively (John son 1975), the figure of 100 parts/106 being the recommended Threshold Limit Value in the United States. Recent studies have suggested that concurrent exposure to MEK and MBK will produce neuropathy more rapidly than in animals exposed to MBK alone (Saida et al. 1976). Methyl ethylketone alone or MBK alone produce no neurotoxic effects (Spencer & Schaumburg 1976). The purpose of the present paper is to emphasize the importance of chronic testing of potentially neurotoxic compounds in experimental animals, to describe the range of hexacarbon compounds which have been identified as neurotoxic agents and, finally, to characterize and illustrate the pathological basis for the onset of the nervous system disease. A total of seven hexacarbon com pounds have been tested in this study (Table 1). During the summer of 1973 an outbreak of per ipheral neuropathy developed among a large group of employees of a fabric manufacturing plant in Ohio, USA (Billmaier et al. 1974). The disease was characterized by distal weakness and sensory loss symmetrically in both the hands and the feet (Allen et al. 1975). The most severely affected individuals worked in the printing depart ment where colouring inks, dissolved in volatile solvents, were applied to the surfaces of plastic coated fabrics. For several years the printing process required the use of a 9:1 solvent mixture containing methylethylketone (MEK) and methylisobutylketone (M1BK). Methyl--butylketone (MBK) was gradually introduced in the summer of 1972 to replace the MIBK. Methyl-n-butylketone was in its maximal use by December 1972 and the first case of peripheral neuropathy occurred shor tly thereafter. The recent introduction of MBK into the printing department of the plant, coupled with other isolated outbreaks of neuropathy in individuals chronically exposed to MBK, sug gested that this compound had neurotoxic proper ties. MBK produced peripheral neuropathy in Table 1 Hexacarbon compounds tested (1) n-hexaneC H jC H .C H iC H .C H .C H , (2) methv)-n-buiy!ketone C'H3COCH2C H ,C H 2C H 3 (3) 2.5-hexanedione CH3COCH;CH ,C O C H 3 (4) 2.5-hexanediol C H 3C H O H (C H ,),C H O H CH , (5) 2.4-hexanedione CH ,COCH:CCH2CH 2 (6) 2.3-hexaJlfdione CH 3COCOCH; C H ,C H 3 (7) 1,6-hexanediol i IOCH: CH_CH ;CH X 'H .C H 2OH The first compound, -hexane, an important sol vent and a minor component ofpetrol, was indicted in several reports as a possible neurotoxic agent (Herskowitz et al. 1971, Korobkin et al. 1975). Rats were exposed continuously to atmospheric levels of 400 to 600 parts/106 of -hexane for up to five months, 500 parts/106 being the US Threshold Limit Value for -hexane (see also Schaumburg & Spencer 1976). The second compound, methyl-butylketone, the solvent implicated in the outbreak of neuropathy, was administered to cats by sub cutaneous injection of 150mg/kg twice daily for periods up to six months (see also Spencer & Schaumburg 1976). The third compound, 2,5-