Document qmgakD36QjbVwqB0mEKxq5ed5

Respiratory Health in Workers Exposed to Man-made Vitreous Fibers1'1 ,{(t /t*"* FST00Q60H HANS WEILL, JANET M. HUGHES, YEHIA Y. HAMMAD, HENRY W. GLINDMEYER, III, GIL SHARON, and ROBERT N. JONES Introduction Man-made vitreous fibers (MMVF), which include fibrous glass, mineral wool (rock and slag), and ceramic fi bers, are manufactured from glass, from natural rocks and minerals, or from slags, the residues of smelting. They are used extensively in thermal, acoustical, and electrical insulation products as well as in reinforcing plas tics and resins. With many millions of tons of prod ucts with MMVF being manufactured annually in the United States and Eu rope, thousands of workers are ex posed to these fibers in the workplace. The U.S. National Institute for Occu pational Safety and Health (NIOSH) estimated that 200,000 U.S. workers experienced occupational exposure to fibrous glass in the early 1970s (1). Since that time the industry has had ad ditional growth, some of it because of the substitution of these fibers for asbestos. The most commonly recognized ef fects of contact with MMVF are acute irritation of the skin and, to a lesser ex tent, the eyes and upper respiratory tract, with symptoms abating after ces sation of exposure. Although acute ef fects on the lunp have not been ob served, the fibrous nature of these sub stances has resulted in concern about possible long-term respiratory effects. Moreover, at a time when there is an evolving consensus that biological ef fects of fiber exposure are related to di mension (with long, thin fibers appar ently posing the greatest risk), environ mental studio have shown that airborne dusts in all plants manufacturing MMVF contain fibers having a wide range of diameters and lengths, a high proportion being respirable. The rela tive frequency of fine fibers depends on the nominal diameter of the fiber being manufactured, with production of (nominally) small-diameter fibers resulting in the greatest airborne con- 104 SUWMANV A study el We rasglratory hsaHli tS worker, uto product man-msda vtVoom flbera (WWW) Inotudad IMS mm length at niralgyinent. IS yi) In 7 fibrous gUu and mineral Mi puma. Health ataeesmant >M by raspbatary qumtWnnaW**, ILOISSO CUssifkattan chest radiograph raadbiga, and pulmonary hmetlen tasting. Aeaidta tram m Millar environmental array arara combined with |ab Materia* la dwtw Individual exposure otUmates. Tha ktudy popw laden M found la be fanaralty haaltiy, <ei raaplralory lyingiomo net ralaiad la era fiber aa- poaura and m detected advene lune hanction ooneaquancoa at dial aipaawa. (Udlograpn raadlnga ravaclcd law catagary pratualon at araaS apacHlar at S41, SS(7%) In Mtagavy OH. SS (J%) bt 1A, and 4 h in, with none tat higher calogorloo. Praralonco at aman ogoettloo Incrataad arid age and Ngaratti (making. A graatar pratalanca at (mail ogedtlea waa tmd among cur rant amoker* In the torn plants producing both orOnary and flna libera (tor prafualen> 10,11% In thaaa plants, 2% bi ethereb Among ex-amokan and noaar amofcara, graatar praralanra an aW aorrad In only ona at thaaa plants (14% varaua l%b Ora plant haalng era higher airborne ceneaa tratlena at nban Iom lhan 1 *a In dUmatar. Among currant (maker*, pro,stance at aatad opact- bee at pralgalan > an Incraaiod arhh lengthening employment (beyond age and peck-yaan at amoklnd bi bath glanta producing atdbtary and tine tlbati and Bra Baa other pftnta combine*. W la eonchidad that aapoaut* la MUW artfi amal dUmatara may load la tear level prahraian at anraS cpacltlra. Menatar. artewul WgMaaat pratualon at than ogcctUaa In a peculation nidi eonaidaraWa range at axgaaura dwatiens, a dHtuae tlaaua reaction (eg. fibrosis) teams unllkaty but cannot be aadudai tit an aorta ora iraa isfciss.ua ccatrationa of long, thin fibers (2). Manufacture of fine MMVF accounts for less than 1W of production in the United States; total production, how ever, continues to increase in response to demand for special purpose insula tion, primarily for Aircraft and Aero space Applications. Although there are certain similari ties between MMVF sad asbestoe fi bers, there are important differences. Asbestos fibers split longitudinally, creating even thinner fibers, whereas MMVF break transversely, thus pro ducing shorter and, therefore, possibly less hazardous fibers. Overall exposure levels also differ, with measured levels of airborne fiber concentrations la plants manufacturing MMVF being very low compared with those known to occur in occupational exposures to In order to assess the respiratory health of workers in this industry, a cross-sectional survey of current em ployees wis begun in 1979. This study, in 7 plants manufacturing MMVF be longing to the sponsoring organiza tion, the Thermal Insulation Manufac- turns' Association (TIMA), was de signed to include long-term employees exposed to various dimensions of fi brous glass and mineral wool. The study did not include-workers manu facturing ceramic fibers or products containing those fibers. Methods Study Design end Plant Seketion la order to have the largest amount of ex posure data available to investigate possible exposure-response relationships, only the Id plants surveyed in an earlier environ mental characterization study were consid- Utecefrarf in ertgform Nommbm It. IM2 end in renmdform Mend 9,19U) 1 From the Tulane University School of Medi etas, Department of Mediant. Pulmonary Di*casas Section, Nr* Orleans. Louisiana. Sponaorad by tha Thermal Insulaiioa Manu facturin' Assoriatloa and supported in part by SGOX Grant No. HL-I5092-I2 from the Nation al Heart, Lung and Blood Institute. a--p--* for reprints should be addressed to Haas Weill, M.D.. Tulane University School of Mediant, Pulmonary Diseases Section. 1700 Perdido Suets. New Orleans, LA 70112. DOW 07515 r ST00060I5 hmutquy him.TM m humum wwm ran woaxiae nd for iacluslon in the present nudy (2); categories for the concentration of airborne that study htd included the 16 oldest U.S. fibers, as determined by both optical mi plants ensued in MMVF production. croscopy (OM) and electron microscopy Ei|ht plants were excluded for various (EM): 0.001 to 0.01,0.01 to 0.1,0.1 to 1.0, reasons: textile production, unavailability and greater than 1.0 fibers/ml. Areas were because plant was sold, past asbestos use, classified into these categories based on the and very targe size with complex exposures median measurement for that area; the requiring separate study. Seven of the re* level assigned to an area was the geometric maining 8 were selected by the investigators mean of that category: 0.0032,0.032,0.32, for inclusion: two fibrous glass plants or 1.3 fibers/ml, respectively (8). For sev (Plants I, 2) producing ordinary fibers eral production lines, median concentration (greater than 3 pm in diameter), 2 (Plants 3, levels differed from the beginning of the 4) producing both ordinary and fine fibers line to the end, but all jobs on the lines were (I to 3 um), 1 (Plant 3) producing only very labeled identically in the work histories; in fine fibers (less than 1 tan), and 2 mineral such cases, the median concentration for wool plants (fibers greater than 3 tan). the entire line wafused. Products of these plants were primarily These exposure estimates were used in insulation materials but also included such conjunction with individual job histories to items as roofing supplies, acoustical tiles calculate total accumulated exposure and and panels, automotive liners, and flexible average concentration of exposure for each and rigid fibrous glass ducts. eligible employee. Calculations were per formed scpvateiy for fibers identified by Exposure Estimation OM (I to 3 tan in diameter) and by EM (leu than 1 um), as well as their sums 3 tan). The glass commonly used for the manufac Total length of plant employment and time ture of fibrous glass is a borosilicate type; ^ent in jobs at or above several fiber con the batch usually contains silica, soda ash, centration levels were also calculated for boric oxide, fluorspar, rutile, and day. The both the OM-sized and EM-sizcd fibers. materials are conveyed pneumatically from storage silos to a mixer, and then arc fad into a furnace. Insulation wool is produced Employs* Eligibility by feeding the molten glass through a fore In order to maximize the likelihood of do- hearth to centrifugal spinners where the fi , testing adverse health effects resulting from ber is forced out of small orifices in the fiber exposure, a minimum of 10 years of spinner head. The fibers arc attenuated by employment was required for participants compressed air or steam, and the binder is from Plants I to 4. Because Plants 3 to 7 sprayed on the fibers. The fine and very were small, a minimum of only 5 yr was re fine fibers are produced by passing the mol quired in these plants. Male employees with ten glass through a bushing plate located at I month or more in the batch or binder the bottom of a forehearth where large di areas, as well as female employees (leu ameter fibers are formed. The fine fibers than 34k of the work force), were excluded. are produced from the primary fibers by Because the study wu designed include flame attenuation. approximately 200 workers from each In slag wool manufacturing, slag and plant, additional inclusion restrictions were coke are melted and allowed to flow in imposed at the larger plants; these excluded open channels to rotary spinners. Fiber at employees with lengthy work in clerical tenuation is achieved by blowing air under positions. In 8 plants, recruitment efforts high pressure around the spinners. were directed at all employees meeting the Because of free crystalline silica in the inclusion criteria; in the largest plant (Plant batch mixing areas and phenol-formalde I), a random sample from the eligible em hyde in the binder mixing area, workers in ployees wu selected for recruitment. those areas were excluded bom the study. Using official employee rosters from Estimation of workers' exposure to air each plant (e.g., state tax and social securi borne fibers was based oo a survey coo- ty reporting forms), job histories were ob ducted by the University of Pittsburgh dur tained for 373 randomly selected employees ing 1974 and 1973, in which approximately not originally identified by plant personnel 800 samples were collected in the 7 plants u eligible. Of these, only 4 (14k) qualified included in the present study (2). A similar for inclusion in the study. Thu, identifica survey, using the same sampling methods tion of the target population wu excellent, and sample analyses, collected 201 samples with few eligible employees having been in 1980 as pan of the present investigation; omitted from reouitmeat efforts. results showed that exposures had not changed significantly since the earlier study. The Pituburgh survey provided esti Respiratory Health Assessment mates of fiber concentration levels in all A modified version of the American areas of each plant for all time periods since Thoracic Society-Division of Lung Diseases opening of the plants; these were the same (ATS-DLD) questionnaire (7) wu adminis as those used by Enterline and Henderson tered in all 7 plants by the same trained (3) and Enterline and Marsh (4, 3). These interviewer. estimates were obtained by considering 4 Participants were judged to have lower respiratory symptoms if they reported hav. tag usual cough, phlegm, or wheezing, cur rent attacks of shortness of breath with wheezing, or breathlessness when walking with others; upper respiratory symptoms if current sinus trouble or postnasal drip; chronic bronchitis if usual cough and phlegm for more than 3 months in each of the last 2 yr. Dyspnea levels were defined u: Grade 1, shortness of breath when hurrying on level ground or walking up a slight hill; Grade 2, when walking with others one's own age; Grade 3. when walk ing at own pace on level ground; Grade 4, when washing or dressing. Chest roentgenograms were taken at local facilities and seat to our unit. After all films were received they were placed into random order and read independently by 3 outside readers experienced in the use of the 0.0 1980 Classification of Radiographs (. Films judged unreadable by 2 of the 3 readers were excluded from analysis. The median of the 3 readings wu used u the summary reading. For shape of small opacity (rounded or irregular), at least 2 readers had to agree on presence and shape in order for a summary reading to be determined. Pulmonary function testing wu con ducted at each plant site in a mobile labora tory using a Pulmolab (Model 3000; Cardio pulmonary Instruments, Houston, TX). This unit measures forced expiratory flows and volumes, lung volumes, and single breath carbon monoxide diffusing capacity (Dice). Calibration for all measured pa rameters wu performed at the beginning and middle of each testing day. Spirometry wu conducted standing; nosedips were used. At least 3 satisfactory forced expiratory maneuvers were re corded. A forced expiratory maneuver wu considered satisfactory if its curve had a sharp initial flow and showed smooth con tinuous effort extending until flow ceased or 7 s elapsed. At least 2 curves of satisfac tory shape with forced vital capacity (FVC) within 34k of the largest were required. The values of FVC, forced expiratory flow be tween 23 and 734k of FVC (FEFn->0. and forced expiratory volume in one second (FEVi) used in statistical analyses were averages from the 2 satisfactory maneuvers with the greatest total of percent of pre dicted for FEV,., and FEF.. Both FEV,., and FEV, sure computed using backward extrapolation from the steepest post of the curve. Residual volume (RV), measured by the ntarogea washout technique, wu consid ered satisfactory when 2 tests wen within 104k or 200 ml, whichever wu larger. The --,iw rv wu used in analysis. Total lung capacity (TLQ wu calculated u the sum of RV and the larger of FVC or a slow vital capacity. The Du:o wu taken u the aver age of 2 measurements within 104k of each other in which the alveolar volume (in spired volume plus multibreath residual DOW 07516 <* IN nu. Mwa hamhm. tuaMPn, snahon. am TABU 1 mjov bahticipants by bunt BMM* IBttwTypW 1 (OretMiy) a (Onjtnery) S (Ordlnery/fln*) 4 (Ordtn*ry/Pln*| s (very Fine) a (Mineral WooB ? (Mineral WooO Total Numeer am 244 Median AO* 40 taa-es)t 44 9 8 110 air ior 34 so vm sa pa-04) 40 po-oo 34 04-10) sa pr-ea a 04-03) 40 04-001 Median Year* employed in Plant ao (10--34)1 IT (10-34) 30 P-30 10 (11-31) 0 (4-38) 10 o-ao 14 P-40 10 (4-40 Black (H> 14 as t a 3 31 0 12 Current Cigarette Smoker* (%) 47 sa 37 30 so SO SO 47 j Ttieev pi*m am* numeeree. leeaectlvery, A, 1*. 4,1,1111,1 in th* xwtranmnnul atwey ft Never Clgarena Smoker* <%) 23 ao as 20 33 30 ao aa volume) (ALVOL) *u u least 85% of TLC and the breath-holding time was 10 to I4t Statistical Analysis Multiple logistic regressions were used to test for a relationship between possible ex planatory variables and dichotomous re sponse variables (e.g., presence of small opacities of a specified profusion level, pctKnce of symptoms); multiple linear re gressions were used in the case of contin uous response variables such u the pulmo nary function measurements. These regres sions were run on the smoking groups separately as well as on these groups com bined. allowing for smoking main effects and interaction terms. Tests for the signifi cance of the exposure variables were per formed after allowing for other factors such as age, height, race, and smoking. Response variables were examined for in fluence of all exposure variables: fiber type, plant, average and cumulative dust levels (by both optical and electron microscopy counts, as well as their sum), length of exposure, and time spent at or above spe cific fiber concentration levels. Logarithms of the exposure measurements were also used to allow for a possible exponential relationship. Result* Participation Of the 1,148 employees ssked, 1,028 (90%) participated in some phase of the study; participation rates were sim ilar in all 7 plants. Health response data were, for various reasons, not complete for all participants: of those eligible, interviews were obtained for 79%, function testing was done in 78%, and radiography was done in 83%. Of those who did not participate on-site, most (67%) were unavailable at the time of testing (e.g., vacation, skit leave). Of the 1,028 participants, 33 had been employed in a plant job with silica exposure, and an additional 36 may have had silica exposure in mainten ance jobs. Analyses comparing these 2 groups of workers with those with no silica exposure found no differences in any respiratory health measures and these workers were retained in the study. Population Description Median age of the 1,028 participants was 46.3 yr; 12% were black and 88% were white. Median length of employ ment in the plants was 18.0 yr; 21 par ticipants were found not to have the minimal required length of employ ment because of leaves of absence but were retained in the study. Among the eligible employees, those who participated in various study phases and those who did not had com parable ages and employment dura tions. For example, the radiography participants had mean age of 43.9 yr and mean employment of 19.0 yr, whereas these parameters for nonpar ticipants were 46.6 yr and 18.9 yr, respectively. Interviews with 912 employees found 48% cigarette smokers (currently smoking or stopped within the past year), 29% ex-smokers (stopped more than 1 yr before), and 24% never cig arette smokers. Of these 912 employees. 187 (21%) had been employed previ ously in jobs potentially harmful to re spiratory health (27 of these 187 had multiple previous exposures); 38 had worked for more than 1 yr in a foun dry, 29 for more than 1 yr in mining or quarrying, 120 had sandblasted, 12 had worked with asbestos, and 13 had worked in a cotton mill. There were considerable differences among the plants in age of workers and length of employment (table I). There was also a wide range in the percent ages reporting previous employment in TABU a PWfVAUHCS (H> OB SCUCTEO SYMPTOMS BY SMOKING CATtOOPY II M 9 I090001S j Ogaretta Smoking Category Never emeker. n>213 Bt-emokar, naSSI Current emokar, ns 430 lower Mery ao aa ao Upper ftaapt tMty 37 30 4a Cbtenle Brew cMtle Dyspnea (Grade Bit Dyepnaa (Grade >9 el Bream erttk witeaung Aatfene Altar Seine Hired 0 ao a* 10 aa 1 0 0 00 0 10 7 30 a 4 3 30* 40 r 30* s* SlgnnicaAfIterance* wo* HMumimnuLKMiyiillvUHa 7 30* 3 Dow 07517 MSMUTOIT NSALTN M MAJMIAM VffUIOVS WO WOftXOtS m an industry with potential respiratory risk: 11% in Plant 3. 31% in Plant 7. Most of those in Plant 7 indicated pre vious sandblasting exposure, although plant management reported no known abrasive blasting with sand in this rural area. Many workers reporting sand blasting possibly referred to plant clean-up jobs, which included blasting with ferrous shot or water (referred to as sandblasting although sand was never used). If sandblasting experience is ignored, the overall percentage re porting such employment is 10%, ranging from 8% (Plant 3) to 16% (Plant 6). Estimation of Worker Exposure The plant manufacturing very fine fi bers (Plant 3) exhibited the highest concentrations of airborne fibers for both OM-sized and EM-sized fibers. For fibers 1 to 3 pm in diameter, the median concentration was 0.210 fi bers/ml in Plant 3: all other medians were less than 0.032 fibers/ml. For fi bers less than 1 pm in diameter, the me dian concentrations were 0.928 fibers/ ml for Plant 3, 0.203 fibers/ml for Plant 3, and less than 0.040 fibers/ml for all other plants. Total accumulated dust exposures exhibited similar trends: median cumu lative EM-sized fiber exposures were 7.4 fibers/ml/yr for Plant 3, 4.3 fibers/ml/yr for Plant 3, and 0.8 fibers/mi/yr for all other plants. Symptoms dost respiratory symptoms were sig nificantly related to cigarette smoking (table 2), and among current smokers were significantly related to either years or pack-years of smoking. A high prevalence (36%) of Grade I + dyspnea was unexpected in this ac tively employed population. Puimonary function results showed that those without dyspnea had higher values for spirometry and lung volume measure ments than those with Grade I dyspnea only, thus validating the responses to this question. Overall, 4 persons re ported Grade 3 dyspnea; none reported Grade 4. Among current smokers, those with previous hazardous employment had greater prevalences of lower respira tory symptoms (63 versus 34%) and wheezing (40 versus 27%), but this in crease was not observed among ex smokers and never smokers. For current smokers, there were dif ferences across the plants for several TABU 3 PUCVALENCg (%) or SELECTED SYMPTOMS AMONG CURRENT SMOKERS BY PONT _____________ - Symptom______________________ Plant (Fiber Type) 1 (Ordinary! Lower Respiraiory Upper Respi ratory Chronic Bran. chltle Oyapnea (Grade >a ot Sraain whh Wheeling Wheattag Numoer ot Person* SI 4S IT 7 4 34 toe (Ordinary) 43 33 17 7 7 33 131 (Ordlna/yffine) a a 39 13 S 30 33 (Ordlnafrty/ftne) 31 S 3 4 3S 74 (Vy fa# a 10 a 4 39 97 (Mineral woo!) a a m IS IS 43 It (Mineral wool) Total St is ss* r is is 4 34 93 39 s r 30* 43S * SipMticaiN aMfwwwa Mian* Man at < OM (* WM * 0 mm* tagimc anaim. ana> aaivattn* tar symptom prevalences (table 3), which were significant after adjusting for pack-years and previous employment. For 3 symptoms (lower respiratory, wheezing, shortness of breath with wheezing), the elevated prevalences occurred in the mineral wool plants, primarily in Plant 7. By contrast. Plant 7 exhibited very low rates for upper re spiratory symptoms. There were no dose-response rela tionships for any symptoms with any of the quantitative measures of expo sure, either within the mineral wool plants or within the entire population. Moreover, symptom prevalences among ex-smokers and never smokers demon strated no differences between the plants, nor any relationship with ex posure dose. Holography Overall film quality was excellent, with only 7 of the 948 chat radiographs judged unreadable by 2 of the 3 read ers; these were excluded from all analysa. Nine films were judged unread able by 1 of the 3 readers; a total of 64 were classified by median judgment as poor quality but nevertheless readable. Using the majority opinion, few films exhibited pleural abnormalities: 13 had pleural thickening, 16 had oblit eration of the costophrenic angle, 1 had pleural calcification, and 1 had pleural plaques. These were not associ ated with previous asbestos exposure, and the low prevalenca of pleural changa tends to confirm that no sig nificant asbestos was used in these plants. None of the 941 readable films was judged to show large opatitks. For profusion of small oparitia, 847 (90%) were classified as category 0/0. Of the 94 films (10%) judged to show small opacitia, 63 were categorized as 0/1,23 as 1/0, and 6 as 1/1. None was higher than I/I. Of the 94 films with profusion > 0/1, 33 were categorized by at least 2 readers as having irregular opacitia a the primary shape and 13 as having rounded. For the remaining 24, the 2 readers indicating praence of small opacitia disagreed on shape. The probability of having small opacitia was significantly related to age and cigarette smoking category both for profusion of categoria h 0/1 and ) 1/0 (figure I). There was a significant relationship between presence of small opacities and fiber type category: 8% (22 of 292) M-* > m-mm.w--.r--.< Pig. 1. Percentage whh prahitaon at mail opacities >0ri. by eg* end cigareit* smoking caiegonaa ST00060 I 7 4 DOUI 07518 IN 4 Pig. 2. Pwcantage wttti potation el miwN opacities > On among cufrent unokere, by *0* and fiber type category. of the radiographs from the ordinary/ fine fiber category were read u profu sion > 1/0, with only 2* (8 of 478), 0* (0 of 86), and 1% (1 of 85) from the ordinary, very fine, and mineral wool categories, respectively, showing this profusion level. All 6 of the 1/1 films were from the ordinary/fine fiber category. These differences were not explained by gross defects in Him qual ity because exclusion of the 64 films of poor quality left the prevalences essen tially unchanged. For both profusion levels Qk 0/1, ) 1/0) these increased rates in the ordi nary/fine fiber category were observed in both plants in this category for cur rent smokers (for profusion ^ 1/0, 12* in Plant 3,15* in Plant 4,2* in other plants combined) but only in Plant 3 for ex-smokers and never smokers (12* in Plant 3, 1* in Plant 4,1* in the others). These differences were significant (p < 0.01) after adjust ing for age, and among smokers, packyears. See figure 2 for the effect among smokers within various age categories. The preceding analyses were also performed for prevalences of small ir regular opacities. Although prev alences were lower than when shape was ignored, exactly the same patterns across plants were obeerved. For current smokers, presence of small opacities, profusion ^ 0/1, was also related to several quantitative ex posure variables; these wen, la de creasing order of significance; time above the second OM-sizsd fiber level, duration of employment, cumulative EM-sized fiber exposure, and time above the lowest fiber level (all p values < 0.025). The results for length of em ployment are illustrated in figure 3. The relationships with these exposure variables were significant after adjust ment for age, pack-years, and ordinary/flne fiber type. Moreover, after adjusting for one or more of these ex posure variables, the ordinary/fine A- Flg. X Percentage with profusion of smaS opaeitlae OH among currant smokora, by ago and length of amployinenL her type continued to be significant (p < 0.01). Although there was an indication of a possible relationship between profu sion ^ 1/0 and employment duration among current smokers, this was not significant, possibly because of the small number (n-21) of cases. Among ex-smokers and never smok ers, after age and Plant 3 had been ac counted for, no other variables were found to be significantly related to presence of small opacities (only 33 cases )i 0/1). Because of the observed relationship between small opacities (^ 0/1) and length of employment among smokers, the 163 smokers with over 20 yr em ployment were analyzed separately. Several measures of exposure were sig nificantly related to presence of small opacities (^ 0/1): cumulative EM-sized fiber exposure, average EM-sized fiber concentration, average total fiber con centration, and time above the second OM-sized fiber level (table 4). Although all regressions allowed for a possible effect of previous hazardous employment (never clow to statistical significance), ail analyses were re peated excluding persons with such em ployment; no changes in the overall re sults were observed. Analyses of the smoking groups combined found that the interaction between cunent smoking and these several exposure variables was signifi cant but that the main effects of the ex posure variables were not. Thus, the dow-responw relationship among cur rent smokers was significantly differ ent from the lack of a relationship found among ex-smokers and never smokers. Pulmonary Function Of the 897 employees who participated in lung function testing, 836 had satis factory spirometry, 824 repeatable lung volume measurements, and 796 repeatable pulmonary diffusing capaci ty results. Percentages of predicted (based on nonsmoker values) were calculated for each person using published equations (9-12) that take into account age, height, and race. Mean percentages of predicted (table 5) were generally high, with significant differences binweea the cigarette smoking groups. Among cunent smokers, there was a signifi cant correlation with pack-yean of cigarette smoking. For all symptoms, thow with the symptom had significantly (p < 0.001) tower spirometric measurements and higher lung volumes than those with out the symptom, after adjusting for age, height, race, and smoking. To assess the relationship between lung function and profusion of small opacities, residuals were obtained from internal regression equations (using age, height, race, and 2 smoking cate* gory-by-age interaction terms); FEV,, FEFis.fi, FEV./FVC*, and Dtco exhibited a significant trend in mean residuals by profusion of small opaci ties (table 6). After adjusting for pro fusion, there were no significant diffef^ ences in pulmonary function by prP"* TABU 4 O PERCENTAGE WITH SMALL OPACITIES > OH SY AOS. FIBS* TYPE CATEGORY, AND CUMULATIVE ELECTRON MICROSCOPY (ELI) EXPOSURE; CURRENT SMOKERS WITH YEARS EXPOSURE Age On) <0.1 Or^lnary/Ptne Plants Exposure Level* 0.1-04 >04 <0.1 Otlwr Plants Eipmiifk Level* 0.1-04 Q ----cc >04 Jl "J > 9ft AH egee (* IS am u am a am a aaa am 40 000f) TO a 0*34) 0 (inn 0 ana 14 am 10 4M* 0 am 10 ana 10 ann IS 1*34) 0 <0M) 10 011) 40 (W1S) 27 1*30) CmuiiM SM W*r iurnw Wk--*W DOW 0751*9 UfMT MULTM --nuabo wioaou* Ttfll I PULMONARY FUNCTION (MEAN FERCEKT OF PREDICTED) BY CIGARETTE SMOK1NO CATEGORY Oearam Smoking Category Function n Navor Cl Currant FVC FEV. FEV./FVC, RV VC TLC Ol DUALVOL ass 110* tie KM ioe* ies ass ao* 77 ass sa* as 8S4 114* ISO as* iir 111 as* toe* 111 rsa itv tie 7se nr in 10S sa 7S 75 137 107 111 104 SO OMM/Hm t! rtxowww.- FVC Mm* Ntef c IK FIV, terca* ntaMfy maw la m acaW PtfM.it a foread axNrarary now Ouring Ow mo o ami oMDo FVC RV a rooMum mlwarn VC a aim coMtnr. 1LC a mm tua immitn Ok a mwumo oaeaciTT OUALVOl a rtsM m mtfumna twain is oamoim mums. * litfiNeaM mifwones maonf wnsmnf caMgsnm Mr mimvMt m isnwi.* < 0.001. 1 usmi mus m men imoamg uup*ry. 1 MomnemH mlferaneo emon* mnsaiao tnmw Of enoiymo m mnwwa. > < 001 miry type of smell opacities (rounded versus irregular). For current smokers, comparisons across plants revealed that after adjust ing for known factors (age, height, race, pack-years), there were significant dif ferences for some of the lung volumes (RV, TLC) and for diffusing capacity (Dl, Di/ALVOL), but that these dif ferences showed no consistent or meaningful pattern. For example, F and Dt/ALVOL were lower in Plant 3 than in the other plants, but none of the other functions were, whereas RV was high in Plants 5 and 7, but all other functions were comparable. There were no differences for the spirometric measurements, and similar analyses of ex-smokers and never smokers found no differences for any functions. These results do not support the hypothesis that Tiber type or plant variables are having important effects on pulmonary function among current smokers. Combining the smoking groups, FEVi, FEFij.ii, and FEV./FVC* were found to be significantly related to length of employment and time above the lowest fiber concentration level, after adjusting for known fac tors, including smoking effects. The coefficients of these variables, how ever, were positive, indicating increas ing function with_increasing exposure time (employment time coefficients: 0.009 L/yr for FEVi, 0.019 L/s/yr for FEFij.il. 0.140tt/yr for FEV,/ FVCft). Detailed analyses of residuals and weighted regressions faded to ac count for these findings. When these regressions were performed on the smoking categories separately, no sig nificant relationships (p values > 0.10) were found. Analyses for RV, RV/TLC, and TLC showed similar results: coefficients were negative, indicating a decrease in these functions with increasing expos ure time; these results were generally consistent for the smoking groups. No exposure relationships were found for the measures of diffusing capacity. Discussion Assessment of the respiratory health of 1,023 workers engaged in the produc tion of MMVF gave the impression of a generally healthy population experi encing no substantial lung disease. In all studies, large unexplained vari ability in symptom prevalences, as determined by standardized question naire, occurred both within and be tween surveyed populations. For this TABUS MEAN REStOUAU* FOR SSMBTED FUNCTIONS SY FNOFUSION OF SMALL OFACinCS FrofuWon of Small FVC Opacltloa OS 00 SS)t OlOB (n Tii)* an -ones n <0401) no 0014 am (oaa* in -OS7S <0 0J43I FCV, 0010 401*1) >OOB3 (047* -one ft -oass *5" ooss naan -OISS f07S7> .0174 wo* -ores nnca* FCV^FVC m 0117 <M0* -040* (MO* -0737 (10*7* -00*0 (0107)0 RV <U 0004 (BOOT) -O04S fUri) ooei (0707) 0070 (040* TLC (D 0014 |B?a* -oooo IMO* 0117 (140* -oaa (1401) (X-aa (RWmkV ooas (4JMJ -oaos (MO* -1401 (0417) -1433 (040*1 * OlMWM praMtH* (xHN Jtf. IWtft f--. MM I *> m te I Nuntar M CMtfOf W* (M Miramar JtMM MMIIW * Oprawtaru ydmw w w--mWM acraaa jrar.uaa unjam m 'Uamoos. reason it is impossible to firmly estab lish the "background" prevalences that can be expected in a working pop ulation not occupationally exposed to any respiratory risk. Despite this diffi culty, it is unlikely that any of the ob served symptom prevalences were sig nificantly elevated in this population. Indeed, the prevalence of bronchitis seemed low, particularly among never smokers and ex-smokers. The relation ship of symptom prevalences with pul monary function measurements and cigarette smoking, as well as with the level of smoking among current smok ers, supports the validity of the ques tionnaire responses. Although an increased prevalence of certain symptoms was detected among current smokers in the 2 mineral wool plants, statistical significance was at tained in only ! of these plants, and nodose-response relationships were found. Bronchitis rates were not elevated in these plants and the nonsmokers exhibited no increased symptoms. It is concluded that prevelmcfs of respiratory symptoms are not increased in this population and no coherent pattern of symptoms in relation to ex posure to MMVF emerges. Lung function testing also failed to detect any adverse effect of exposure, although measurements were related to age, height, race, cigarette smoking stilus, and level of smoking. Using published equations to provide exter nal comparisons, mean values for ail smoking groups were near or above 1009k of predicted. After taking into account other in fluencing factors, there was no adverse association between functional meas urements and any of the indexes of exposure to MMVF. In fact, after age and smoking were taken into account, the associations of RV and expiratory flow rates with length of exposure suggested a possible "healthy worker" effect. The negative findings concerning symptoms and pulmonary function testing in this study are consistent with the generally reassuring results of all reports published to date. Several sur veys of working populations failed to driest any chronic respiratory effects of exposure to MMVF (IJ-16). The single histologic study also reported negative results, with lungs of exposed workers exhibiting no differences from those of matched control subjects (17). Although some mortality studies showed r ST000601 9 r S y DOW 07520 u in?*--v1** risk of nonmalignant interstitial fibrosis and neoplasms in both plants. They have produced fine respiratory disease, there was no in the lung tissue of animals (29). Several fibers for a sufficiently long period to dication of increased lung cancer risk studies showed that pitting, corrosion, make the detection of an effect pos (3, 4, 18-20), and animal inhalation progressive shell formation, decreasing sible. Among ex-smokers and never studies produced adverse respiratory fiber diameter, fracturing, and dissolu smokers, this effect wu observed only effects only after either intratracheal tion of MMVF occur in vivo and in in the dustier plant. Thus, in the gener injection or direct installation of fibers vitro (28', 30, 32-34). These findings ally leu duty plant, an increased pre into the pleural space (21-23). concerning the durability of MMVF in valence occurred only among smokers, However, reported findings of new lung tissue may help to explain the dis whereas in the dustier plant, an in and updated studies presented at the crepancies reported La the literature creased prevalence wu observed in all WHO International Occupational between intrapleural injection and smoking categories. If the higher duR Health Conference on the Biological inhalation Rudies. levels contributed to the increased Effects of Man-Made Mineral Fibres A recent cross-sectional survey of prevalence of small opacities, then a (Copenhagen, 1982), while providing 340 employees of a U.K. fibrous glass fiber dose-response relationship should no cause for alarm concerning health plant reported that 139b of the cheR be demonstrable in this fiber type cate risks from MMVF, were not entirely radiographs of men exhibited small gory after smoking hu been taken into negative. opacities of category 1/0 or higher account. In fact, such a relationship In a U.S. mortality study, there was (33). Although this Rudy had consider wu found only among current smokers. no overall excess of lung cancer among able technical limitations, the presence This could be a result of the smaller 14,884 fibrous glass workers, but an of small opacities was related to previ number of ex-smokers and never increase was observed (47 observed, ous employment in dusty trades and smokers with small opacities, but it 36.0 expected) among those with over general environmental exposures, but may also reflect the recognized diffi 30 yr of follow.up from initial expo there was no relationship with expos culties of individual exposure recon sure (3). The 1,846 mineral wool ure to MMVF as measured either by struction. workers in this study exhibited an over length or intensity of exposure. Al If the increased probability of small all excess of lung cancer mortality (43 though FEVi and VC were low, neither opacities is attributable to exposure to versus 28 expected). Both groups of' functional measurements nor symp fibers with the smallest diameter, then workers were found to have an increased toms were related to exposure to the plant manufacturing very fine risk of death caused by nonmalignant MMVF. Two smaller studies of mineral fibers, whose average fiber concentre- j respiratory disease. A European study wool workers found no evidence of tion levels were considerably higher of 17,083 employees, although not adverse functional effects (36, 37). than all other plants, would be ex-/ completed, reported a significant ex The present Rudy, also presented at peeled to exhibit increased prevalence/, cess of lung cancer deaths (12 versus the Copenhagen Conference, while of small opacities. In fact, they were 3.6) among those followed over 30 finding no adverse exposure effects u very low in this plant. Because them3, yr (26). Similar results were reported measured by symptom prevalence and workers were the youngert (media from another U.S. study (4,394 work function testing, found that the pres age, 34 yr) and overall had the shone ers), which found an excess of lung ence of small opacities was related to employment duration (a median of' cancer deaths (11 versus 6.2 expected) some measures of exposure. yr; only 14 employed for more than I; among workers with over 20 yr of Classification of chest radiographs yr), longer follow-up is required t{| employment and 30 yr of follow-up demonstrated a low prevalence of fully assess radiographic outcome (27). No mesotheliomas were found in small opacities, with no large opacities. this exposure category. , the U.S. studies, but one wu found in Films considered to show small opaci The focus of environmental charac^" the European studies. ties were almoR exclusively in the teriiation, and therefore exposure It is difficult to interpret the results Iowcr profusion categories (0/1 or reconstruction, hu been on qualitative of these mortality studies with regard 1/0) on median reading. On individual and quantitative upects of airborne to exposure to MMVF because none readings, a choice of these ILO cate fibers in this Rudy. Although this ap found a dose-response relationship aaa\ gories indicates that the reader favored proach seems well based in prioritizing none had smoking information avail ' (0/1) or seriously considered (1/0) a,- concern about potential' respiratory able. The past use of asbestos in some negativc judgment. health effects, we recognize that of the U.S. mineral wool plants intro-/ Prevalence of small opacities rose as further exploration of nonfibrous par duces further uncertainty regarding' both age and smoking increased, find-t ticulates and gaseous inhalants in this these results. Recent animal experiments with MMVF confirmed the results of earlier logs that have been reported elsewhere industry is a logical next Rep. (38-40). Among current smokers, 1 Inevitably, attention will be directed probability of small opacities was pod-/ to the potential biologic significance of studies: MMVF injected intrapleuraQyi tivdy associated with exposure dura/ the correlations found in this Rudy or intraperitoneaHy produced mcsoth* tion; however, among ex-smokers and between low profusion of small opaci Uomas, but none was produced by never smokers, there was no uaodd- ties and some Indexes of exposures. halation. Inhalation Rudies with glam i don with exposure measures* Possibly there is minimal duR accumu fibers produced no or mild fibrosis;' With respect to fiber type, exposure lation, retention, and persistence of fewer lung tumors occurred in exposed to a mixture of ordinary and fine fibers MMVF with fine diameters in lung tis rats than in unexposed control animals significantly increased the probability sue. If so, these effects, in general, are (28-31). Inhalation of very high con of low-level small opacities among cur attaining the radiographic detection centrations of ceramic fibers produced rent smokers, an effect observed in limit only in current smokers, perhaps DOU) 07521 Ill because of leu effective clearance of 9. Eimea NA, Hammad YY. Log-normality of ( particulate. The absence of intermedi environmental sampling dau (abstract). J Envi ate or higher profusion of small opac ron Sd Health 1977; 1239-41. ities, in a population with a consid 7. Ferris BO. Epidemiotogy rtanrtardlration project. II. Recommended rtapiretory discaae erable rente of exposure durations, qucsboonaircs for use with adults and children ia susiesu that a progressive, diffuse cpidemiolofic nacarch. Am Rev kespir Ola tissue reaction (e.g., fibrosis) is un 1979; ltKSupp():7-51. likely, yet it cannot be excluded. Because interobserver variability is greatest at these lowest profusion levels (0/1, I/O) and because of the im g. Ouidcttaca for tha uaa of ILO iateraaiiooai daadflcatioa of radiographs of pneumoconioiea. Rav. ad. Genera: International Labor Offloa. 1990. Occupational Safety and Health Scrim, no. 22, (rev. 10). portant influences of age and smoking 9. Boren Ha Kory RC. Syoer JC The x--on the probability of detecting thesbs Vcuraaa Adminiuririoa-Anny cooperative f opacities, the presence of small opac ities at these levels has a low order of Rudy ef pulmonary function. Am J Mod 1994; Wl:99*ll4. -- specificity for an occupational expo W. Areugdi P, Cotas JE. Cotnaad A. ede. /formal valua far respiratory flmcdoa ia man. sure effect. Gearly, the findings re Aighcro, Hair Piamiaarva Medico, 1999:3)9. ported here should be considered pre 11. Arcaagdi P. Coua JE. Ooumaad A, ede. liminary, requiring replication and Normal valuaa for respiratory fuactioa in man. confirmation before firm conclusions can be drawn. The suggestion that fibers with fine diameters may be hav ing an effect on lung parenchyma makes it prudent to continue biologic surveillance of workers exposed to Aighcro, Italy: Paomiatrva Medfca, 1999:339. 12. Roaster CE. Wa H. Ethnic difTcmcu ia lung ftiacdoe: cvldcnu for proportional diffartoot, tat J Epidemiol 1774; 3:33-41. 13. Wright GW. Airborne flbroua glam partides: chaw roaatgeaograiaa of penooa with pro longed expoeurt. Arch Environ Health 1999; MMVF with small and very small 21:173-41. diameters. This approach is particu 14. Ubdjian HMW, daTreriDs RTF. 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