Byssinosis

BYSSINOSIS is an occupational respiratory disease which causes a subjective feeling of chest tightness and acute respiratory impairment, most often exhibited by reduction in forced expiratory volume in 1 s (FE[V.sub.1.0]) at the end of the first working day after weekend rest. The disease has been commonly found among workers in cotton textile mills. The presence of endotoxin in dust induces inflammation and is responsible for the byssinotic symptoms of cotton dust exposure. Studies undertaken in cotton mills in India and abroad have reported that respirable dust in the preparation zone contained high levels of endotoxin, which is considered to be the etiological factor for byssinosis among workers exposed to cotton dust. (1-7) Besides cotton mills, various other occupational environments (e.g., flax mills, hemp mills, and areas of rice and grain handling) have shown evidence of bacterial endotoxins. (8,9) Endotoxin has also been demonstrated in other environments where organic dusts and decayed materials are present, such as in dried sludge, sewage water, compost, poultry and pig farms, and humidifiers. (10,11)

Chattopadhyay et al. (12,13) identified byssinotic symptoms among Indian jute mill workers on the basis of workers' clinical histories and pulmonary function changes; however, the presence of endotoxin in the mill air could not be correlated with these findings. Some investigators have found evidence of byssinosis among jute mill workers, others have found no evidence, and some results were inconclusive. (14-22) The occurrence of byssinotic syndrome has been evaluated by clinical symptomatic (work-related) studies and by patterns of pre- and postshift pulmonary function test results. The etiological factors responsible for the onset of the disease have also been reported. (3,4) Because the nature of the disease is similar in jute mill and cotton mill workers, the causative factors may be the same. Specifically, endotoxin contains the pyrogenic component lipopolysaccharide and is found on the structural cell wall of gram-negative bacteria. The hydrophobic nature of the lipid A portion of endotoxin is responsible for a nonspecific affinity for surfaces. Therefore, the surfaces of borosilicate glass test tubes, pipettes, and so forth, have an affinity for endotoxin, and its removal is essential before they are used for the dilution of endotoxin. (23)

As in cotton fibers, bacterial contamination in jute fibers probably begins at the early stage of its processing. Fibers are extracted from the jute plant in the field by the "retting" process, in which plants are deliberately subjected to microbial decay. The softened jute fibers also are stacked in rolls for 24-48 hr in the batching area of the mill (called the "piling process"), which may be conducive to bacterial growth because the mill environments are generally hot and humid.

Previous research has shown that jute mills in and around Calcutta have 2 distinct dust zones: high in the softening, carding, and preparing (or batching) areas, and low in the spinning, winding, and finishing areas. No significant variation in the nature of the dust was observed from mill to mill, but the dust levels within the mills differed from process to process and tended to decrease from batching to finishing stages. (24) Rylander and Morey (6) estimated bacterial endotoxin in jute carding dust to be 0.02-0.05 [micro]g/[m.sup.3]--lower than in cotton (0.02-2.2 [micro]g/[m.sup.3]) and flax (0.5-2.5 [micro]g/[m.sup.3]) mill dust. (6) Kennedy et al. (7) observed an exposure-response relationship in the etiology of lung diseases such as byssinosis and chronic bronchitis with endotoxin among cotton textile workers, and reported 2.0-550.0 ng/[m.sup.3] endotoxin in the total dust of area samples/In a study of Indian cotton textile mills, (25) researchers reported 6.9-6600.0 and 0.02-1110.0 ng/[m.sup.3] endotoxin, respectively, in the card room and opening room of a cotton mill. Chattopadhyay et al. (26) reported 8.7% byssinotic symptoms and significant acute changes of FE[V.sub.1.0] in 35.7% of jute mill workers in India.

Although the American Conference of Governmental Industrial Hygienists has promulgated no occupational exposure limit for airborne endotoxin, the Dutch expert committee on occupational standards recommends a health-based limit of 50 endotoxin units (EU)/[m.sup.3] (approximately 4.5 ng/[m.sup.3]) based on personal 8-hr time-weighted average inhalable dust exposure. (27) We found no reports regarding the level of gram-negative bacterial endotoxin in Indian jute mills. The present study was conducted to correlate pulmonary function tests and symptoms of byssinosis among exposed workers to levels of endotoxin in dust samples collected from 2 different processing areas of the jute mill environment (high- and low-dust zones).

Materials and Method

Study site. The study was conducted during September--October 1995 in a jute mill located in a southwest suburb of Kolkata, India. More than 3000 workers were employed at the mill in 3 shifts--(1) 6:00-11:00 AM and 2:00-5:00 PM; (2) 11:00 AM-2:00 PM and 5:00-10:00 PM; and (3) 10:00 PM-6:00 AM--manufacturing items such as jute cloth and bags. In a shady area outside the mill, the raw jute was first graded and separated manually. Inside the mill, the fiber was then subjected to a succession of processes: softening, carding, preparing, spinning, winding and beaming, and weaving and finishing. Each of these processes involved multiple pieces of machinery. Processes such as softening, carding, and preparing (batching) were performed in an area we designated the high-dust zone. The area in which spinning, winding and beaming, and weaving and finishing were performed was designated the low-dust zone.

Sample collection. Samples (n = 29) of airborne dust from different processing areas--softening (n = 3), carding (n = 4), and preparing (n = 5) in 'high' dust zone (total, n = 12), and spinning (n = 4), winding and beaming (n = 5), weaving (n = 5), and finishing (n = 3) in 'low' dust zone (total, n = 17)--were collected from the breathing zone (at an approximate height of 1.5 m from the shop floor) in the mill by standard high-volume samplers (Staplex [Brooklyn, New York]) on pretreated (pyrogen-free) glass fiber filter paper (20 x 20 cm) GF/A (Whatman Ltd [Maidstone, UK]). (23) Control area samples were collected from the shaded area outside the mill at the same height under similar conditions. The collected samples (n = 2) were sealed and transported to the laboratory, where they were carefully desiccated and weighed in a semi-micro analytical balance (Model AG 245 [Mettler-Toledo, Inc. {Greifensee, Switzerland}]) to determine the dust concentration. Dust concentration in mg/[m.sup.3] was calculated by dividing the weight of dust in mg by the volume of air drawn in [m.sup.3]). Of the total samples collected from the jute mill air (n = 29), and from outside the mill (n = 2), 8 samples--3 from the batching area (i.e., 1 from softening and 2 from carding), 2 from spinning, 2 from weaving, and 1 from outside the mill--were selected for estimation of endotoxin.

Estimation of endotoxin. Endotoxin was estimated by the Limulus amebocyte lysate (LAL) test following the standard gel-clot technique, in accordance with U.S. Pharmacopeia guidelines. (28) Although this technique is very simple, needs little equipment, and is quite sensitive in the nanogram range, the absolute concentration of endotoxin in a sample cannot be measured by this technique. It is, however, suitable for the estimation of endotoxin in occupational environments where even the control area concentrations are well within the sensitivity range of the method. The LAL manufacturer (Endosafe [Charles River, South Carolina]) states that the method is at least 10-fold more sensitive than the detection limit (1 ng/ml); therefore, it was well suited for use in our study.

The test was performed by mixing equal parts (0.1 ml) of LAL reagent (Endosafe [Charles River, South Carolina]) and test samples (in 10 x 75-mm test tubes), in serial dilutions. These were incubated in a heating block at 37[degrees] [+ or -] 1 [degrees]C and examined for gel formation after 60 min. Serial dilutions of control standard endotoxin (Endosafe) also were subjected to LAL testing in parallel with the samples to identify the endpoint of the test between positive and negative gel clot. The sensitivity of the LAL test, divided by the total dilution of the sample at the endpoint, gave the concentration of endotoxin in the original sample extract. Thus, the result of endotoxin concentration was calculated in EU and converted to ng/ml by dividing it by 10 (i.e., 10 EU = 1 ng). Finally, the endotoxin concentrations were expressed as [micro]g/[m.sup.3].

Pulmonary function tests. Workers who had been at the mill at least 7 yr were selected randomly (every 5th worker) for pulmonary function assessment. A total of 148 workers, all male, participated in the study. Informed consent was obtained from all participants. All subjects were interviewed at the beginning of the study by a trained interviewer, using a standard questionnaire. The questionnaire was based on Schilling's byssinosis study (29) and emphasized work-related symptoms such as chest tightness, cough, sputum production, breathlessness, day of occurrence, duration, and relationship with work. Smoking habits of subjects were not addressed on the questionnaire. The age distribution of subjects was as follows: <30 yr (n = 8), 30-39 yr (n = 25), 40-49 yr (n = 63), and 50+ yr (n = 52). The mean [+ or -] standard deviation (SD) for age was 44.5 [+ or -] 2.64 yr, for height was 163.34 [+ or -] 5.65 cm, and for weight was 53.20 [+ or -] 7.63 kg.

Pulmonary function tests consisted of recording subjects' vital capacity (VC) and forced vital capacity (FVC) using a Vitalograph S-Model spirometer (Vitalograph Ltd [Buckingham, UK]). Each individual performed the tests 3 times during pre- and postshift examinations for more than 1 day. The best of the 3 performances was used in our analyses. [FEV.sub.1.0] was calculated from the FVC curve. The equipment was standardized daily, and the instrument was calibrated at regular intervals.

The definition of acute changes in pulmonary function ([FEV.sub.1.0]) from exposure to vegetable dusts, resulting in byssinosis, was classified as recommended by a World Health Organization (WHO) study group (30) and in accordance with the system developed by Bouhys et al. (31) Acute changes of 5-10%, 11-20%, and >20% of [FEV.sub.1.0] were categorized according to duration of exposure (i.e., <9 yr, 10-19 yr, 20-29 yr, and 30+ yr).

Statistical analysis. Only [FEV.sub.1.0] was considered in our calculations, in accordance with both the WHO (30) and Bouhys et al. (31) classification schemes. Preshift and postshift [FEV.sub.1.0] was measured, and the decrement of values at postshift was calculated from the preshift values. The number and percentage of workers in the 3 [FEV.sub.1.0] decrement categories were: 5-10% decrement (n = 26, 17.6%); 11-20% decrement (n = 14, 9.5%), and >20% decrement (n = 7, 4.7%). Among all subjects, duration of exposure was distributed follows: <9 yr (n = 8), 10-19 yr (n = 35), 20-29 yr (n = 79), and 30+ yr (n = 26) and variable for measuring the acute changes, the [FEV.sub.1.0], as used by both WHO (30) and Bouhys et al. (31) (Table 3). A greater percentage of workers in the 10-19-yr exposure group exhibited [FEV.sub.1.0] decrement than in the 20-29 yr exposure group; however, chi-square testing showed no significant difference between the 2 groups.

Results

Table 1 shows the mean and range of concentrations of 'total dust' and 'endotoxin' in the 8 dust samples selected out of 29 total samples collected from the jute mill and 2 samples from outside the mill. The highest dust levels were found in the batching area (6.64-13.99 mg/[m.sup.3]), followed by the spinning (3.40-5.64 mg/[m.sup.3]) and weaving (0.77-0.85 mg/[m.sup.3]) areas. Endotoxin concentrations reflected a similar pattern, with 0.22-4.42 [micro]g/m3 in batching, 0.04-1.47 [micro]g/[m.sup.3] in spinning, and 0.01-0.07 [micro]g/[m.sup.3] in weaving.

More than 77% (n = 115) of the mill workers were above the age of 40 yr. More than 71% of the workers in the high dust exposure group (n = 42) and 64% in the low dust exposure group (n = 57) had more than 20 yr of working exposure (data not shown). Table 2 shows the prevalence of byssinosis-like symptoms among workers at the jute mill. A total of 21 (14.2%) workers had byssinotic-type respiratory symptoms (e.g., chest tightness, cough, breathlessness, and difficulty breathing) on Monday after the weekend break. Another 30 (20.3%) workers had work-related symptoms on any day of the work week, not necessarily following the weekend break. These symptoms, although closely resembling those of byssinosis, are not typical of byssinosis, in which the symptoms start on the first day of the work week after a break. Figure 1 presents the acute change in [FEV.sub.1.0] and prevalence of byssinosis according to dust and endotoxin concentration zones of the mill. Prevalence of byssinosis was observed to be low in the low-dust/low-endotoxin zone whereas it was high in the high-dust/high-endotoxin zone. Acute changes in worker [FEV.sub.1.0] were determined in accordance with the WHO classification. (30) (See Table 3.)

[FIGURE 1 OMITTED]

Although the differences were not statistically significant, the percentage of workers with acute decline in [FEV.sub.1.0] was greater among those exposed for 10-19 yr than among those exposed for 20-29 yr. Workers exposed for 30 yr or more had the highest percentage decline of all groups studied. A similar decline in [FEV.sub.1.0] was also observed among some jute mill workers who had no byssinotic symptoms.

Discussion

Environmental monitoring in this jute mill showed that the highest dust levels were in the batching area, with values decreasing as material proceeded toward the finishing area, as reported earlier. (24) A similar trend in endotoxin levels was observed, although there was no proportionate increase in endotoxin values with the dust concentrations of the batching area compared with those of spinning and weaving. This may be because dust in the batching area is coarser and contains a higher proportion of mineral matter and nonfibrous dust, whereas dust in the spinning and weaving areas is mostly fibrous and may be a more suitable carrier for bacterial contaminants.

The levels of endotoxin in different types of textile mills, as reported by various authors, are presented in Table 4. Endotoxin levels from a Swedish jute mill, reported in 1982 by Rylander and Morey, (6) were 0.02-0.05 [micro]g/[m.sup.3], whereas the values reported in the present study were 0.01-4.42 [micro]g/[m.sup.3]. Comparison of the endotoxin values in the present study with those of the cotton mill studied by Gokani et al. (25) shows a lower overall range of endotoxin; however, the values from the batching area of the jute mill are quite comparable. It was also reported that the endotoxin values of the card room and blow room of the Indian cotton mill were much higher than those for synthetic fiber processing. (25) The endotoxin levels of this jute mill were much higher than those reported in jute and cotton mills in Sweden and the United States. (6,8) It is also evident that the endotoxin concentration inside the mill is much higher than outside, which was considered the control area (results for the control area are given in Table 1).

The endotoxin values obtained in this study are many-fold higher than the recommended Dutch occupational health standard. (27) This is the first report available on levels of airborne endotoxin in an Indian jute mill environment. Our findings also provide evidence of byssinotic symptoms among the jute mill workers, as have been reported previously for Indian cotton textile mills by Gokani et al. (25) The present study documents that jute mill workers exhibit respiratory symptoms and acute pulmonary function changes similar to those of byssinosis. Byssinosis-like symptoms among Indian jute mill workers were also noted by Roy. (15) In China, Zhou et al. (18) reported a higher prevalence of chest tightness and cough in jute mill workers compared with controls. Bacterial endotoxin, which is associated with byssinosis in cotton workers, may produce similar symptoms in jute mill workers. (6,8) Our findings comport with the those of Gandevia and Milne, (32) and with 2 of our earlier studies. (12,13) A temporary decrease in [FEV.sub.1.0] in nonbyssinotic workers indicates the constricting effect of jute dust on the smooth muscles of the airways. (17)

We characterized the acute and chronic respiratory impairments of [FEV.sub.1.0] in accordance with the classification of Bouhys et al., (31) and also used a clinical grading system based on changes in [FEV.sub.1.0] and expressed in milliliters, as per Bouhys et al. (31) Acute pulmonary function changes were higher (41.8%) with the Bouhys et al. (31) classification (slight-to-moderate and definite acute changes were 29.7% and 12.1%, respectively) than with the WHO (30) classification (31.8%; where mild = 17.6%, moderate = 9.5%, and severe = 4.7%).

Although we did not know the smoking status of our subjects, earlier reports have established that there is no association of smoking habits with byssinosis. (33,34) Chattopadhyay et al. (13) reported more byssinotic symptoms among workers with long-term exposure to high dust levels than for other factors. The present study found that the prevalence of byssinotic symptoms and acute pulmonary function changes was higher among jute mill workers with high endotoxin exposures, confirming a relationship between endotoxin concentration and the occurrence of byssinosis.

Conclusions

Endotoxin--already proven to be strongly associated with byssinosis among workers exposed to cotton dust--was also present in the Indian jute mill studied. Inasmuch as the endotoxin in this mill exceeded the available Dutch recommended occupational standard, it likely was responsible for the byssinotic symptoms and pulmonary function changes observed among the workers. Thus, we conclude that byssinosis may occur in jute mill workers who are exposed to jute dust for a long time (>15 yr). Jute dust exposure leads to byssinotic symptoms, including a fall in [FEV.sub.1.0] on the first day of the work week. Endotoxin is the probable etiological factor for the occurrence of byssinosis in both cotton and jute mill workers.

The authors express their sincere thanks to technicians S. Ahmad, J. Alam, and S. K. Roy, and to laboratory assistant S. Thakur, for their technical assistance in the study. The authors are also thankful to the director of the Central Drug Laboratory, Kolkata, for providing the necessary guidance in the study.

Submitted for publication April 25, 2003; revised; accepted for publication June 8, 2004.

Requests for reprints should be sent to Dr. A. K. Mukherjee, Regional Occupational Health Center (Eastern), Block DP, Sector V, Salt Lake, Kolkata--700 091, India. E-mail: ashit_ mukherjee@yahoo.com or mukherjee@icmr.org.in

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ASHIT K. MUKHERJEE

BHAKAR P. CHATTOPADHYAY

SANAT K. BHATTACHARYA

Regional Occupational Health Center (Eastern)

Kolkata, India

HABIBULLAH N. SAIYED

National Institute of Occupational Health

Ahmedabad, India

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