American Journal of Industrial Medicine 22-378

(1992)

Morbidity Among Municipal Waste I ncinerator Workers Eddy A. Bresnitz, MD, MS, Jerry Roseman, MSIH, Dan Becker, MD, and Edward Gracely, PhD

Incinerator workers are exposed to many toxic compounds, most notably heavy metals. We evaluated medical and exposure monitoring data of an actively employed cohort of Philadelphia incinerator workers following an Agency for Toxic Substances and Disease Registry site survey and National Institute for Occupational Safety and Health (NIOSH) health hazard evaluation (HHE).Of the many airborne samples taken by NIOSH, only four of the personal breathing zone samples were above OSHA or ACGIH standards: one for lead, one for phosphorous, and two for total particulates. Because samples were taken during limited operations (only one of the two incinerators were operating), the results may underestimate historical exposures at this site. We limited our medical analysis to the 86 male workers who participated in the HHE out of the 105 active employees. The 86 employees were divided into potential high and low exposure groups based on a work site analysis done by an independent industrial hygienist. Eight individuals had at least one elevated biological index indicating exposure to a heavy metal. These elevations, however, were unrelated to the workers’ exposure categories. Furthermore, no clinically significant mean blood or serum measurements were noted. Thirty-four percent of the workers had evidence of hypertension which increased the risk of significant proteinuria. Neither hypertension nor proteinuria were related to exposure group. Changes in pulmonary function related only to smoking status. Although there was some evidence of an increased risk of exposure to products of incinerator waste, we could not relate the few elevated biological tests to exposure classification. Additional studies are needed to assess the potential health effects of municipal waste incinerator by-products. 0 1992 Wiley-Liss. Inc. Key words: waste incineration, airborne emissions, air pollution, heavy metals, biological monitoring

INTRODUCTION

Over the last decade, beleaguered public health and municipal officials have experienced increasing pressures to find safe and economical ways of disposing of Division of Occupational and Environmental Medicine, Department of Community and Preventive Medicine, Medical College of Pennsylvania, Philadelphia, PA. Address reprint requests to Dr. Btesnitz, Div. of Occupational and Environmental Medicine, Dept. of Community and Preventive Medicine, Medical College of Pennsylvania, 3300 Henry Avenue, Philadelphia, PA 19129. This study was presented, in part, at the 118th Annual Meeting of American Public Health Association in New York, NY, October 1990. Accepted for publication February 3, 1992. 0 1992 Wiley-Liss, Inc.

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solid waste. As some landfills have closed, while others have become prohibitively expensive, advocates of solid waste incineration have vocalized their commitment to waste combustion (together with recycling) as a potentially safe and efficient solution to this difficult problem. As a reflection of this, a recent report by the Environmental Protection Agency (EPA) projected a significant growth in the number of incinerators in the next decade [Morrison et al., 19871. Several investigators have studied the potential exposures and adverse health effects that may ensue from exposure to the incineration by-products found in airborne emissions and the solid residues in ash and slag. Potential toxic substances include heavy metals (lead, cadmium, mercury, and arsenic), total respirable particulates, respirable quartz, dioxins, furans, polycyclic aromatic hydrocarbons, and solvents, including benzene [Mozzon et al., 1987; Lisk, 1988; Kellam et al., 1989; Denison and Silbergeld, 1989; Mumma et al., 19901. In March 1988, the EPA and the Agency for Toxic Substances and Disease Registry (ATSDR) announced the results of an ash pile and soil sampling survey at the Northwest Incinerator in Philadelphia (EPA, ATSDR, 19881. The study concluded that the levels of contaminants did ". . . not pose a significant risk to on-site workers (and community residents) provided the workers wear proper personal protective equipment (PPE) and exercise proper personal hygiene" [EPA, ATSDR, 19881. Because of the multiple exposure sources existing at the site, the relatively recent implementation of PPE use by plant workers, and previous data from the National Institute for Occupational Safety and Health (NIOSH) study of another incinerator indicating potential excessive exposures to refuse-derived toxic substances [Ahrenholz, 19861, ATSDR recommended that the plant undergo a Health Hazard Evaluation [Kinnes and Bryant, 19911, which is the subject of this report. The Northwest Incinerator was built in 1959 with two mass burning furnaces, each approximately 42 feet long. At the front of the building are two concrete hoppers which lead to inclined stokers and the horizontal conveyor belt inside each furnace. Each furnace burns 375 tons of trash per day for a total of 750 tons per day. Both furnaces operate at from 1,650 to 1,900"F. The only fuel used is the trash itself. The emission control system for each furnace consists of a cooling tower, drying tower, and an electrostatic precipitator that are fed by an induced draft. MATERIALS AND METHODS

One of the authors (E.B.) received a contract from the City of Philadelphia to analyze each worker's data to assess the presence of work-related disease. A certified industrial hygienist (J.R.) was hired to represent the union in its interaction with NIOSH representatives. Neither the primary data collectors nor the authors were requested to analyze the data on an aggregate basis. However, the authors performed an independent, cross-sectional analysis of this convenience sample of incinerator workers. Environmental Monitoring

Over a 5-day period in June 1988, NIOSH collected environmental, personal, and area samples. NIOSH representatives selected sampled workers on the basis of

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availability, but included those workers with high potential exposures to dust. Only one of the two furnaces at the plant was in operation at the time of sampling. The environmental evaluation consisted of determining potential inhalation exposures by collecting full-shift personal breathing zone and general area air samples for polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) expressed as 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD equivalents), total dust, respirable dust, crystalline silica, and metals. Employees were asked to wear two personal sampling pumps which were used to evaluate potential exposures to respirable dust and silica on one sample, and total dust and metals on the other sample. Six area samples were collected to be analyzed for PCDDs/PCDFs. Five of these area samples were collected side-by-side with the same sample types that the employees were asked to wear. A sixth PCDD/PCDF sample was collected as an area sample outside an incinerator door during the slagging (cleaning) operation. The remaining samples were collected in various areas for respirable silica, metals, and total and respirable dust. Also, to determine the potential for dermal exposure to PCDDs/PCDFs and metals, a number of wipe samples were obtained from various working surfaces. The air and surface samples for PCDD/PCDF were analyzed by a gas chromatograph/mass spectrometer equipped with a DB-5 (screening) column and by DB17 and SP 2331 columns in tandem (for isomer confirmation). Selected I3C and 37Cl labeled PCDD and PCDF isomers were included as internal standards and recovery (surrogate) standards. Analyses were performed to measure total tetra-, penta-, hexa-, hepta-, and octachlorinated dibenzofurans; total tetra-, penta-, hexa-, hepta-, and octachlorinated dibenzodioxins; and specific PCDD and PCDF isomers containing chlorine substitution in the 2, 3, 7, and 8 positions. The analytical limits of detection were variable and ranged between 0.001 and 0.468 ng per sample. Results were expressed using 1989 International Toxicity Equivalency Factors. Air samples for respirable and total particulate, silica, and metals were analyzed for total weight by gravimetric analysis according to a modified NIOSH method [Kinnes and Bryant, 19911. After analysis for total weight, the samples were analyzed for silica (quartz and cristobalite) using X-ray diffraction. Samples were analyzed for metals using NIOSH Method 7300 [NIOSH, 19841. Study Subjects

The subjects were limited to 89 of 105 Philadelphia incinerator plant workers who were working at the time of the study in late June 1988 and who agreed to participate in the study. The employer and union did not agree to locate and assess individuals previously employed by the City of Philadelphia who had worked in a similar capacity. Health and work-related environmental data on these individuals were gathered from several sources as negotiated by the union and the Streets and Sanitation Department of the City of Philadelphia. A questionnaire designed and administered by Weston Environmental Services (Chester, PA) provided information regarding job history and descriptions and tobacco and alcohol use. Job history information was cross-referenced with employment records from the Streets Department for individuals whose records were available. Medical histories, physical examinations, and basic laboratory tests were performed at a community hospital in Philadelphia. Tests

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for heavy metals were done by SmithKline Bio-Science Laboratories. The medical history also provided a cross-reference for each individual’s tobacco and alcohol use. Job exposure and classification were based on job descriptions contained within the Weston questionnaire, and on a report describing the Northwest Incinerator plant prepared under the supervision of one of the authors (J.R.) [Gostin, 19881. Although the latter report dealt exclusively with the Northwest Incinerator facility, we assumed similar conditions and job activities existed at the four other Philadelphia incinerator locations (Central, Northeast, Southeast, Southwest) and the ash dispersal locations. Consequently, workers who had been employed at other Philadelphia incinerator facilities prior to working at the Northwest facility had potential exposures at these facilities classified according to the conditions assessed at the Northwest plant. Three levels of exposure were initially used: high, middle, and low. Although the activities with the highest level of exposure to ash and incinerator waste (slagging the furnace, hosing down the cooling tower, shoveling ash in the klinker room, and cleaning the dustwork under the combustion chamber) were performed by workers with almost any job title, the primary responsibility for these tasks belonged to workers classified as plant helper I or 11, and laborers. Consequently, these jobs were coded as having the highest potential exposures. Based on their job descriptions, bridge crane operators and firemen were classified in the middle level of exposure to waste and ash. Although the industrial hygiene report indicated that mechanics had shorter but more concentrated periods of exposure to incinerator waste, the mechanics’ own occupational histories indicated a lower level of exposure. As a result, mechanics, along with tractor trailer operators, equipment operators, clerks, and the plant superintendent, were classified as having the lowest levels of exposure. For purposes of our analysis, this three level classification was simplified such that individuals without a history of a job in the high exposure category were classified into a low exposure group. Workers with at least one job in a high exposure category were categorized into the high exposure group. All of the latter had worked at least 7 months (total) in high exposure jobs at the time of the study, with a median of 15.9 years of high exposure. Furthermore, 31 of the 45 in this group were employed in a high exposure setting at the time of the study. Alcohol consumption was classified as a dichotomous variable due to a lack of data regarding the amount and type of alcohol consumed. Tobacco use information was obtained from smoking histories in the medical record and in the Weston questionnaire. Workers were classified as non-smokers, former smokers, or current smokers. For current and former smokers, the type of tobacco used (cigarette, cigar, pipe), the quantity smoked per day, and the length of time smoked were recorded. For former smokers, the number of years since quitting was also obtained. Each individual’s age was recorded to the nearest year, according to the information given in the medical history. For a few individuals without a known specific date of birth, the subject’s age was recorded as the mid-interval. Maximal expiratory flow-volume loops were obtained using the Gould 2100 spirometer (SensorMedics, Yorba Linda, CA). A minimum of three acceptable efforts was obtained [ATS, 19871. The maximal forced expiratory volume in 1 second (FEV,), forced vital capacity (FVC), and FEV,/FVC% were used. A restrictive defect was defined as an FVC less than 80% of an age, height, and gender-based

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predicted value and an FEV,/FVC of greater than 70%. An obstructive defect was defined as an FEV, less than 80% of the predicted value and an FEV,/FVC less than or equal to 70%. Small airway obstruction was defined as an FEV,/FVC greater than 70%, an FVC greater than 80%predicted, and an FEF,,-,,, less than 70% predicted. Predicted values were derived from the prediction equations of Crapo and coworkers [1981]. Predicted values for FEV, and FVC in African-Americans were adjusted downward by 10% [Schoenberg et al., 19781. Posterior-anterior and lateral chest radiographs (41 X 43 cm), obtained at full inspiration, 110 kVp, and a standard distance of 183 cm, were interpreted by a pulmonary physician (E.B.) who is a NIOSH “B” reader, according to the ILO-1980 Classification [ILO, 19801 and without knowledge of the worker’s exposure classification category. Statistical methods. As a first step in data analysis, all numeric variables were examined to determine their suitability for particular levels of analysis. Those that were roughly normally distributed were analyzed with parametric tests, e.g., t-tests to compare high and low exposure groups, ANOVAs to compare smoking groups. Those variables with non-normal data that nevertheless exhibited a reasonable spread across several values were analyzed with rank tests, notably the Mann-Whitney U. Finally, those numeric variables for which all but a few subjects fell into one or two categories were dichotomized and subjected to chi-square analyses. Nominal variables, such as alcohol usage and smoking status, were analyzed with chi-square as well. Statistical analyses were performed using the SPSS-X package. With about 45 subjects per group, one-tailed, unpaired t-tests have a power of around 73% to detect a .5 standard deviation difference in group means. If the true difference of means was .8 standard deviations, power would be over 95%. Chisquare analyses on dichotomized and nominal variables have substantially less power and would only have reasonable power (e.g., 80%) for fairly large percentage differences (e.g., 10%vs. 36%). The Mann-Whitney U test has slightly less power than the unpaired t-test. Multiple comparisons were performed as part of this study. No correction for multiple comparisons was employed because we wanted to be sure to uncover any differences that might exist. The failure to find differences in this population would be as important as finding them. Because evidence was found that the smoking groups (i.e., non-smokers, former smokers, and current smokers) differed on several pulmonary function tests (PITS), the comparison between high and low exposure groups on PITS was performed as a two-way ANOVA, with smoking status and exposure (high vs. low) as the two factors. Classification on categories of lung impairment (obstructive, restrictive, and small-airway) was compared between high and low exposure groups with MantelHaenszel pooled odds ratios, using smoking status as the stratification factor. RESULTS Environmental Monitoring Five surface wipe samples were collected for tetra- through octa-chlorinated PCDD and PCDF homologs and the 2,3,7,8-tetra isomers. The calculated concentrations of TCDD-equivalents ranged from 0 to 47.0 ng/m2, with one of the samples

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above the National Research Council (NRC) guideline of 25 ng/m2. These samples were collected from the main office, lunchroom, change room, and incinerator floor. The sample that was above the NRC guideline was collected from the center of the incinerator building floor, an area with the highest probability of PCDD/PCDF contamination. A background sample (0 ng/m2) was also collected from the investigator’s hotel. The remaining samples were collected from areas where PCDD/PCDF contamination should not be present if proper control measures were taken. The results for these samples indicated that PCDDdPCDFs were being transported to the office, lunchroom, and change room via air or on the clothes and shoes of employees. Presence of PCDDIPCDF contamination on a table top in the lunchroom indicates that there may have been a potential for ingestion of contaminants. Six general area air samples were collected for tetra- through octa-chlorinated PCDD and PCDF homologs and the 2,3,7,8-tetra isomers. The collection of personal samples was impractical due to the size of the sampling media. The calculated concentrations of TCDD-equivalents ranged from 0 to 24.2 pg/m3. The sample with the highest concentration was collected during furnace cleaning from outside an open incinerator door. This sample was collected over the entire shift (8 hr) and was above the NRC guideline of 10.0 pg/m’. However, employees performing this function were wearing airline respirators during the time that this sample was collected. Another sample, collected from the center of the incinerator area, had a concentration of 0.2 pg/rn3. The remaining samples had concentrations below 2.3 pg/m3, which included samples collected from the southside ash pile (2.3 pg/m3) and the east central incinerator (0 pg/m3). The ambient concentration was determined to be 0.06 pg/m3 from a sample collected in a nearby residential yard. Although all of the above samples had detectable levels of PCDDdPCDFs, expressed as TCDD-equivalents, no 2,3,7,8-TCDD was detected in any of these airborne samples. The results of the environmental sampling reveal that the airborne concentrations of respirable dust in the 15 personal samples ranged from 0.02 to 0.72 mg/m3, while the 12 general area samples ranged from 0.01 to 0.18 mg/m3 (Table I). The three highest personal airborne concentrations occurred during duct cleaning (0.63 mg/m3), furnace slagging (0.71 mg/m3), and cooling tower washing (0.72 mg/m3). These are tasks that employees performed as part of the weekly general maintenance. However, all the samples were below the OSHA PEL for respirable dust. These air samples were also analyzed for respirable silica content; however, only two of the samples had trace (0.018-0.036 mg/m3) levels detected. The results of surface wipe samples for metals indicate either that metals were present in the air (at some point in time) at those locations or that metals were being transported (on shoes and clothing surfaces, etc.) from one area to another. The results of these wipe samples indicated that the major constituents of the surface dust consisted of aluminum, calcium, iron, magnesium, phosphorous, sodium, and zinc. The surfaces with the most metal present were the incinerator floor and the bulldozer hand controls. These samples had significantly higher amounts of all the metals identified. The samples taken from these surfaces also had small amounts of cadmium and chromium. The incinerator floor sample also had a significant amount of lead and detected the presence of arsenic. Fifteen personal breathing zone and 12 general area air samples for total airborne particulates were collected from the same employees and areas as sampled for the respirable samples (Table 11). All the samples were weighed to obtain the total

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TABLE I. Airborne Concentrations of Respirable Dust and Respirable Silica Dust in Philadelphia Waste Incinerator Workers* Respirable dust (m~~m~)"

Type-locatiodjob June 23, 1988 PBZ, mechanic # I PBZ, furnace operator (plant helper #2) Area, main office Area, incinerator room PBZ, bulldozer operator PBZ, truck driver PBZ, plant helper # I PBZ, laborer Area, lunchroom (top of refrigerator) Area, northside ashpile (dioxin samplers) Area, southside ashpile (dioxin samplers) June 24, 1988 Area, overhead crane operator PBZ, plant helper # I PBZ, mechanic PBZ, plant helper #2 PBZ, truck driver PBZ, laborer PBZ, bulldozer operator Area, office Area, incinerator room Area, lunchroom (top of refrigerator) Area, ambient Area, east-central incinerator June 25, 1988 PBZ, plant helper #2 PBZ, slagging furnaces PBZ, cleaning ducts Area, between incinerators Evaluation criteria NIOSH ACGIH OSHA ~

~

Respirable silica (mg/m3)

0.09 0.02 0.06 0.06 0.17 0.19 0.09 0.05 0.07 0.18

ND ND ND ND Trace ND ND ND ND ND ND

0.08 0.07 0.10 0.12 0.09 0.32 0.07 0.08 0.06 0.05 0.01 0.04

ND ND ND ND ND ND ND ND ND ND ND ND

0.72 0.71 0.63 0.11

ND ND Trace ND

0.40

0.05 0.05-0.Ib 0.05-0.Ib

5.0 ~

*Adapted from Kinnes and Bryant [ 19911. "mg/m3 = milligrams of substance per cubic meter of air; ND = none detected; Trace = substances were present in trace quantities, between the LOD (0.015) and LOQ (0.03). Atmospheric concentration range of 0.018-0.036 mg/m3 with air sample volume of 816 liters; PBZ = personal breathing zone. bcristobalite (0.05), quartz (0.1).

amount of particulate and then analyzed for metal content. The airborne concentrations of total dust ranged from 0.04 to 24.34 mg/m3, which included one sample that was above the ACGIH TLV of 10 mg/m3 and one above both the OSHA PEL and ACGIH TLV. The sample that was above both criteria was collected from a laborer, and the sample above the ACGIH TLV was collected from a worker during furnace slagging. Another total dust sample (9.4 ~ n g / ~collected ), from a plant helper during the washing of a cooling tower, was near the TLV. None of the remaining samples had airborne concentrations greater than 3.3 mg/m3.

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Bresnitz et al. TABLE 11. Samples for Total Airborne Particulates in Philadelphia Waste Incinerator Workers, 1988* Total particulates weight

Personal breathing zones Laborer Slag furnace operator Cleaning ducts Bulldozer operator Plant helper #2 Other PBZ (10) Area samples (12) ~

24.34 10.8 3.3 3.11 2.08,9.4 current, p < .05.

?

p for ANOVA on % pred’s ,438 ,136 .014a

S.E.).

in the low exposure group who had urinary arsenic values of 360 and 370 pg/dl, respectively. All other heavy metal tests were normal in these two individuals. Exclusion of these two values from the analysis yielded mean urinary arsenic levels of 28.6 pg/dl and 36.3 yg/dl in the low and high exposure groups, respectively (p = .033). It should be noted that reports have indicated that, of all the heavy metal tests, only arsenic levels were shown to be affected by recent dietary habits (e.g., shellfish ingestion). We had no information on recent dietary intake of the workers in this study. The prevalence of current smokers in the study sample was 50%. Table VII compares spirometric tests between never, past, and current smokers. Past smokers, who were on the average 6 years older than workers in either of the other two groups, had FVC and FEV, values that were lower than the other two groups, even when considered as a percentage of predicted values for age, sex, race, and height. However, the ANOVAs on these two parameters were not statistically significant (p’s > .13). There was a significant difference between mid-expiratory flow rates among smoking categories for the percent predicted (p = .014, by ANOVA). Multiple comparisons indicated a decreased flow rate for current smokers compared to never smokers. Table VIII indicates that there were no statistically significant differences in pulmonary function between the high and low exposure groups, even after adjustment for smoking status. The prevalence of pulmonary function patterns were similar in both exposure groups, except that the high exposure group had almost twice as many workers with spirometric changes suggestive of small airway obstruction (SAO). When adjusted for smoking status, the odds ratio for SAO in the high versus low group was 1.19 (95%C.I. = 0.45 to 3.16). The odds ratio for SAO among never smokers in the high versus low exposure groups was 1.85 (95% C.I. = 0.27 to 13.1). Five workers, all in the low exposure group, had X-ray findings suggestive of pleural plaques/thickening. Three of these five workers were included in a group of eight workers who had pulmonary interstitial opacifications at the 21/0 level. Five of the eight were in the high exposure group and three were in the low exposure group. All eight were either current (5) or ex-smokers ( l ) , or obese (6). Obesity was defined as more than 20% over ideal body weight. There were no significant differences in symptoms between the two groups. However, 29 workers (34%) had a diagnosis of hypertension determined by history and/or physical examination. Sixteen were in the low exposure group, and 13 were in the high exposure group. Hypertension was associated with significant proteinuria in both low and high exposure groups. The Mantel-Haenszel pooled odds ratio for proteinuria in hypertensives was 5.62 (95% C.I. = 1.4-22.7). Twenty-three of the

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TABLE VIII. Respiratory Function by E x p u r e Category, Adjusted for Smoking Status in Philadelphia Waste Incinerator Workers* Spirometry

Fvc (J-) FEV, (L) FEFZs-758

FEV,/FvC (%) (f S.E.)

Low (41) 4.12 (88.7 3.28 (87.3 3.28 (80.6 79.5

2.01) 2.16) f 3.99) 2 .8

f f

High (45)

p for exposure from 2-way ANOVA'

3.97 (86.8 f 2.07) 3.17 (85.3 f 2.37) 3.20 (78.4 3.%) 79.3 f 1.0

.877 .%2 .574 .592

*

*Values are uncorrected means (mean % predicted f S.E.). 'Smoking status by exposure status, using a regression approach that adjusts all effects for the others. bNo race correction.

29 (79%) hypertensives were in an older age stratum of 45-64 years. Overall, 57.5% of the 40 subjects in this age stratum were hypertensive. The prevalence of hypertension was elevated for both white and African-American workers in this age range compared to the U.S.population [Schoenborn, 19881. DISCUSSION

In this morbidity study of incinerator workers, there were few adverse health effects that we could directly relate to potential exposures in the plant. Evaluation of mean levels of renal, hepatic, and hematopoietic function was normal in both the high and low exposure groups. Although the overall prevalence of urinary abnormalities was high, as evidenced by 31% of workers with significant proteinuria, there was no statistically significant difference between the two exposure groups. The prevalence of hypertension was excessive in the cohort when compared to the expected prevalence in the U.S.population [NCHS, 19881 even after adjustment for the higher proportions of African-Americans in the study sample. The higher prevalence of hypertension may explain the higher prevalence of proteinuria in the cohort. The excess prevalence of hypertension may also be related to the higher prevalence of alcohol consumption in the group [Anda et al., 19901and/or excessive noise levels that have been previously documented at other municipal incinerators [Sobeih, 19881. Other studies of blue collar workers have demonstrated a possible causal relationship between hypertension and noise-induced hearing loss [Talbott et al., 1990; Tarter and Robins, 19901. Less than 2% of 471 individual blood and urine tests for heavy metals were elevated above the expected range in an unexposed population. Elevated values were equally frequent in individuals classified into the low and high exposure groups. Changing the exposure classification to account for possible higher exposures in driverdtractor trailer operators did not significantly alter these findings, except for two workers who only had elevated arsenic levels, which may have been diet-related. Although pulmonary function status did not relate to potential exposure status, past and current smokers had significantly lower mean levels of the mid-expiratory flow rate compared to never-smokers. Moreover, past and current smokers had forced expiratory volumes in the 1st second that were near the lower limits of the predicted normals. The overall prevalence of obstructive disease (including small airway obstruction) was 221, not surprising with the overall ever-smoker prevalence of 63% or

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the current smoker prevalence of 50%. Nineteen percent of workers had spirometric evidence of a possible restrictive process. However, lung volumes were not performed to firmly establish this diagnosis. Only eight workers had radiographic evidence that may have supported a diagnosis of an interstitial process, such as asbestosis, to explain possible pulmonary restrictive impairment. A significant proportion of these workers were considered to be overweight which may explain some of the reductions in forced vital capacity. None had documented significant previous asbestos exposure. Sixteen workers employed at the time of the evaluation chose not to participate in the study despite repeated efforts to include them. There was no information available to compare these workers to those who were assessed. As a result, we could not determine whether there was a potential referral bias that may have affected the analysis. In addition, we were unable to obtain information about individuals who no longer worked at the incinerators. Clearly, an analysis limited to current workers may be biased by a healthy worker effect [Monson, 19901. We classified workers who worked at any time in a high exposure job into the high exposure group. As it turned out, this group had substantial high exposure work (minimum, 7 months; median 15.9 years) and more than two-thirds of them were employed in a high exposure setting at the time of data collection. Moreover, those in the high exposure group had worked an average of 5.5 years longer at the incinerator compared to the low exposure group. As a result, we feel confident that there was minimal misclassification of individuals on exposure. We did not seek to identify a cohort of non-exposed workers as an outside comparison group. Theoretically, an outside group could have biological measurements that were even lower than the values we noted in our cohort. Without an outside group, our comparisons may be biased toward the null. Nevertheless, we were able to compare the results to the expected laboratory range of normal values. As reported, the bulk of individual and mean blood and urine tests for both biologic measurements and heavy metal exposure indices were well within normal limits. It is unlikely that the use of an outside comparison group would have changed our conclusions, given the generally overwhelming normality of biologic tests. There have been few epidemiologic studies of the health effects of exposure to incinerator waste. A mortality study of municipal waste incinerator workers in Sweden suggested an excess of deaths due to lung cancer and ischemic heart disease [Gustavsson, 19891. In an editorial commenting on this study, Landrigan [1989] suggested additional studies to assess the health effects of exposure to incinerator waste. A study of 45 workers in a waste-combustion plant in Germany did not demonstrate any biological evidence of occupational exposure to heavy metals [Bloedner et al., 19861. Four Health Hazard Evaluations (HHEs) of waste incinerators were conducted by the NIOSH in the 1980s [Jannerfeldt and Ruhe, 1981; Williams and Hickey, 1982; Ahrenholz, 1986; Sobeih, 1988; Seitz and Kinnes, 19901. The first HHE [Jannerfeldt and Ruhe, 19811 was done in a waste water treatment plant where sludge was incinerated. Limited medical surveillance data of the respiratory effects in the workers evaluated in this plant did not detect impairment that could be related to the exposures assessed. The later NIOSH studies did not include any medical monitoring of workers. There have been no other published mortality or morbidity studies of municipal waste incinerator workers in the United States.

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Environmental monitoring from these NIOSH studies showed that airborne concentrations of most substances measured were either below 1) American Conference of Governmental Industrial Hygienists (ACGIH), Threshold Limit Value Committee, 8-hour Time Weighted Average (TWA) levels; 2) OSHA, 8-hour TWA standards; or 3) the lower detection limit of the analytical method. One HHE [Ahrenholz, 1986; Sobeih, 19881 detected lead and nuisance dust exposures above OSHA Permissible Exposure Levels (PELS) and crystalline silica exposures exceeding the NIOSH Recommended Exposure Level ( E L ) . The assessment of airborne levels of heavy metals/minerals yielded only an elevated personal breathing zone (PBZ) sample for lead and cadmium in one sample. Two other samples indicated high levels of nickel. All of the other area and PBZ samples for metals/minerals were either non-detectable or well below published standards. Similarly, samples (whether area of PBZ) or airborne concentrations of respirable dust or silica dust were detected at very low levels, if at all. However, two PBZ samples for total airborne particulates were elevated (compared to ACGIH standards) in two workers considered to be in the high exposure category. These results compare to data from previous NIOSH HHEs [Jannerfeldt and Ruhe, 1981; Ahrenholz, 19861. The only other measurements of note were elevated wipe and airborne samples of 2,3,7,8-TCDD equivalents from the vicinity of the incinerator floor. In general, it appeared that the team from NIOSH conducted a sampling plan that was representative of the job titles and job tasks where exposures were likely to occur. However, there were a few factors beyond NIOSH’s control, that may have affected sampling results. First, during the sampling period, only one of the two furnaces was in operation. Because this represents only one-half of the normal operating capacity, inside area and personal samples may have measured lower levels of exposure to silica, metals, and other dust than the workers would normally have experienced. Second, personal and environmental monitoring and sampling over brief periods of time may not represent conditions normally encountered in the incinerator plant. Third, the pool of available workers for personal sampling was somewhat limited, especially on the weekend when the heavy-exposure cleaning tasks were performed. In preparation for the shutdown of the burning operations, some personnel in the targeted job titles had already been transferred, thus reducing the workforce for sampling. On weekends, the incinerator usually operated with a skeleton crew, in this case reduced even further by the transfers. The result was that while all tasks were sampled, the workers performing them were not always the ones who normally did that particular job. Fourth, although bulldozer and truck loading activity took place for NIOSH sampling purposes, the activity was simulated and may not have disturbed the ash pile as much as it would normally have been. As a result, the two outside area samples set up to collect for dioxins, metals, silica, and other dust may have indicated lower levels of exposure than actually occurred historically. Finally, the worker who performed the task of cleaning the ducts under the combustion chamber was unable to wear the personal sampling pump for portions of the task. A length of the duct work narrows to such a small space that the pump could not be worn. Again, the concern is that the sampling results inadequately reflected the true exposures experienced by workers who have performed this task.

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In addition to the above factors which may affect sampling results, during the course of the NIOSH Health Hazard Evaluation it became clear that basic health and safety protections for the workers had been practically non-existent. Until the union made demands in the winter-spring of 1988, workers did not have protective clothing and respirators. Paper dust masks (of little or no use especially as protection against toxic materials) were available as of April 1988, but their use was optional. Nevertheless, we were unable to show substantial morbidity due to high exposure in spite of these historically largely unprotected conditions. Besides exposure to the substances assessed, heat stress was another potential health problem [Sobeih, 19881. Although the furnaces were cooled overnight before weekend cleaning began, it was still extremely warm in places where vigorous work had to be performed. Another potential health hazard might have been exposure to asbestos. Suspect asbestos pipe insulation and panels on the furnace walls were probable sources of exposure. Several workers had X-ray changes compatible with asbestos exposure, although their work histories did not indicate having worked with asbestos previously. Although noise levels were not assessed, another HHE in a municipal incinerator plant documented levels well above OSHA’s action level [Ahrenholz, 19861. In conclusion, this study did not consistently demonstrate significant environmental elevations in ash and airborne contaminants at a trash burning municipal incinerator. However, the working conditions during the sampling period most likely did not reflect the usual operations at the plant. Only a few biological tests for heavy metals were elevated, without an apparent relationship to exposure category. Pulmonary function tests, although generally within normal limits, appeared to be affected by smoking status. Overall, there was a high prevalence of hypertension and related proteinuria in this cohort. Increased efforts in reducing personal risk factors and potential occupational exposures are needed to reduce the documented morbidity among incinerator waste workers. ACKNOWLEDGMENTS

This work was supported in part by the Preventive Pulmonary Academic Award NO. 1KO7 HL02 100-01A2. The authors wish to thank Laura Welch, Mike Ross, Harriet Rubenstein, Gregory Kinnes, and Charles Bryant for their helpful comments and Roseann Bilardo for help with the manuscript preparation. REFERENCES Agency for Toxic Substances and Disease Registry (1989): Toxicological Profile for Arsenic. ATSDR, US Public Health Service, 1989. Ahrenholz SH (1986): for National Institute of Occupational Safety and Health. Health Hazard Evaluation Report. HETA 85-041-1709, City of Columbus Refuse Derived Fuel Power Plant. American Thoracic Society (1987): Standardization of spirometry-1987 update. Am Rev Respir Dis 136:1285-1298. Anda RF, Waller MN, Wooten KG, Mast EE, Escobedo LG, Sanderson LM (1990): “Behavioral Risk Factor Surveillance, 1988.” In CDC Surveillance Summaries. MMWR; 39 (No.SS-2):l-21. HHS Publication No. (CDC) 90-8017. Bloedner CD, Reimann DO, Schaller Kit, Weltle D (1986): Evaluation of internal cadmium, lead, and

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