The Effect of Exposure to Rubber Production Emissions and Physical Activity on Pulmonary Function Indices among Tyre Manufacturing Employees in Iran.

BACKGROUND: Exposure to rubber production emissions can cause respiratory problems. There is some evidence that physical activity might have protective effects against respiratory obstruction. AIMS: This study, was investigated the effect of physical activity on potential respiratory damages induced by the exposure to rubber production chemicals.
METHODS: This cross-sectional study was carried out during 2019 on the staff of a rubber manufacturing company in Khorasan, Iran. Employees of a rubber manufacturing company were recruited in this cross-sectional study (n = 385), and were classified into exposed (n = 266) and unexposed (n = 119) groups. Baecke Physical Activity Questionnaire (BPAQ) was used to assess the level of physical activity. Logistic regression was used to evaluate the effects of exposure, physical activity and confounding variables on pulmonary function test (PFT) results.
RESULTS: Work, leisure time and total physical activity scores were significantly higher in exposure group compared with control group subjects. Although no significant differences were observed between the exposure and control groups in most spirometric parameters, FEF25-75 was significantly lower in the exposure group (P = 0.035). Abnormal PFT was observed in 93 participants (24.2%) and in the multivariate model was significantly associated with exposure (OR = 1.80, CI95: 1.01-3.22) and age (OR = 1.08, CI95: 1.02-1.14) but not physical activity score.
CONCLUSION: Exposure to rubber manufacturing chemicals nearly doubles the odds of abnormal PFT, and the self-reported level of physical activity had no protective effect against these occupational hazards. Copyright:

INTRODUCTION

Rubber industry workers are exposed to several hazardous chemicals including organic hydrocarbons such as benzene, toluene and styrene, dust particles, such as talc, and other components.[1] Although the exposure conditions are complex and variable, sufficient data exists to link lung cancer and non-malignant lung diseases to rubber production chemicals.[12345]

On the other hand, physical activity have been shown to enhance the function of respiratory system.[67] However, the effects of exercise on reversing the hazardous effects of chemical exposure in rubber industry workers is unknown.

Here, we aimed to assess the effects of occupational exposure and exercise on respiratory function in rubber industry workers.

METHODS

This cross-sectional study was carried out during 2019 on the staff of a rubber manufacturing company in Khorasan, Iran. Employees of a rubber manufacturing company in the production and official units were recruited in this cross-sectional study. Participants unable to be physically active, including those with a history of cardiovascular, pulmonary, neurologic or musculoskeletal disorders were excluded. The rationale for exclusion of these employees was the potential effects that their disease may have on spirometry findings or physical activity. This study was approved by the Ethics Committee of the Mashhad University of Medical Sciences (No.IR.MUMS.MEDICAL.REC.1397.265), and adhered to the Helsinki Declaration of 1975. Mashhad University of Medical Science has approved the ethical principles and the national norms and standards for conducting this research on 6 Oct. 2018. (Approval ID: IR.MUMS.MEDICAL.REC.1397.265)

The baseline characteristics, including age, sex, unit of employment, years of work experience, height, weight and body mass index (BMI) were recorded. Subjects were classified into two groups: (1) exposed group consisting of employees in the production unit who were in direct contact with chemical substances, and (2) unexposed group consisting of employees in the non-production units.

The self-reported level of physical activity was assessed using the Persian version of the BPAQ. Test-retest variability of the total physical activity index has been previously estimated as 0.87 for the original BPAQ and 0.74 for its Persian translation.[89] Based on the total physical activity index, participants were classified into low (<7), medium (7-11) and high (≥11) physical activity groups.

Pulmonary function was assessed by a trained technician based on ATS standards using the MIR Π spirometer (made in Italy). The measured parameters included forced expiratory volume in one second (FEV1), forced vital capacity (FVC), the ratio of FEV1/FVC, forced expiratory flow at 25–75% of the pulmonary volume (FEF25-75) and the peak expiratory flow (PEF). The results of PFT were evaluated by an experienced occupational medicine specialist as normal pulmonary function, obstructive, restrictive or mixed pattern.

Air sampling and analysis of chemical hazards including total rubber particulates and organic solvents mixture was done according to the National Institute for occupational Safety and Health (NIOSH) Manual of Analytical Methods.[10] The sampling was performed for 8 hours shift with 0.5 liter per minute flow rate in different production units. Activated charcoal was used for collecting organic solvents. Sample analysis were done by gas chromatography for solvents and gravimetric for particulates.

Statistical analysis

The statistical analysis was performed using IBM Statistics SPSS 25.0 (IBM Corp., Armonk, NY, USA). Univariate logistic regression was used to investigate the effect of age, BMI, exposure, work experience, total physical activity index and its subcategories on having an abnormal PFT. Furthermore, to account for the confounding variables, multivariate logistic regression was performed using all the study variables except the subcategories of physical activity. Statistical significance was defined as P ≤ 0.05.

RESULTS

We identified 385 employees of a rubber manufacturing company eligible for the study. Female employees were minority (n = 3, 0.7%) and were excluded. The employees in the unexposed group were significantly older, but no other significant difference was observed between the two groups in their baseline characteristics. However, age showed a weak inverse correlation with the total level of physical activity, work index and sport index. Additionally, the level of total physical activity and in particular, the work and leisure-time indices, were significantly higher in the exposed group. Furthermore, FEF25-75 was significantly lower in the exposed group [Table 1].

Table 1

Characteristics of participants in exposed and unexposed groups

Variable	Total (n=385)	Exposed (n=266)	Unexposed (n=119)	P
Age (years) mean±SD	38.4±5.6	37.7±4.7	39.8±7.1	<0.001t
Work experience (years) mean±SD	13.0±6.1	13.1±5.1	12.4±7.7	0.281t
Weight (kg) mean±SD	78.9±11.9	79.1±12.5	78.4±10.5	0.577t
Height (m) mean±SD	173±5	173±5	174±5	0.251t
BMI (kg/m2) mean±SD	26.2±3.6	26.3±3.8	25.8±3.2	0.278t
Physical activity index (out of 15) mean±SD	8.6±1.2	8.8±1.1	8.2±1.4	<0.001t
Work index (out of 5)	3.6±0.7	3.9±0.6	3.1±0.6	<0.001t
Sport index (out of 5)	2.5±0.6	2.5±0.6	2.5±0.7	0.938t
Leisure-time index (out of 5)	2.4±0.5	2.4±0.5	2.5±0.5	0.014t
FEV1 mean±SD	87.0±11.3	86.5±11.3	88.4±11.3	0.130t
FVC mean±SD	89.9±10.7	89.7±10.4	90.4±11.1	0.543t
FEV1/FVC mean±SD	81.6±7.3	81.3±7.7	82.1±6.4	0.336t
PEF mean±SD	94.0±16.2	93.8±16.5	95.7±15.6	0.219t
FEF25-75 mean±SD	77.7±20.5	76.3±20.6	81.1±20.2	0.035t
Abnormal spirometry n (%)	93 (24.2%)	70 (26.3%)	23 (28.7%)	0.259f
Obstructive pattern	39 (10.1%)	31 (11.7%)	8 (6.7%)
Restrictive pattern	46 (11.9%)	32 (12.0%)	14 (11.8%)
Mixed pattern	8 (2.1%)	7 (2.6%)	1 (0.8%)

The study variables are reported for all the participants and separately for the exposed and unexposed group. Bold=significant p-value, t=Student’s independent samples t-test, f=Fischer’s exact test, BMI=body mass index, FEV1=forced expiratory volume in one second, FVC=forced vital capacity, PEF=peak expiratory flow, FEF25-75=forced expiratory flow at 25-75% of the pulmonary volume

The mean age was significantly higher in the participants with abnormal spirometry (P < 0.01). Furthermore, in the logistic regression, age was a significant predictor of abnormal spirometry, with a univariate OR of 1.05 and a multivariate OR of 1.08 with each year increase in age. In the univariate logistic regression, exposure was not a significant predictor of abnormal spirometry however, in the multivariate logistic regression, after accounting for confounding variables, exposure predicted abnormal spirometry with a statistically significant OR of 1.80 [Table 2].

Table 2

Logistic regression for abnormal spirometry

Variable	Univariate		Multivariate
	OR (CI95)	P	OR (CI95)	P
Age*	1.05 (1.01-1.10)	<0.01	1.08 (1.02-1.14)	<0.01
BMI*	1.03 (0.97-1.10)	0.30	1.01 (0.95-1.08)	0.62
Exposure (yes/no)	1.49 (0.87-2.53)	0.14	1.80 (1.01-3.22)	0.04
Work experience*	1.02 (0.98-1.06)	0.22	0.98 (0.93-1.02)	0.43
Total PA score	1.01 (0.84-1.22)	0.85	1.02 (0.84-1.24)	0.81
Work index	1.07 (0.77-1.49)	0.65	-	-
Sport index	0.88 (0.69-1.24)	0.48	-	-
Leisure-time index	1.15 (0.76-1.73)	0.48	-	-

*=with each unit increase, OR=odds ratio, BMI=body mass index, PA=physical activity

Although the absolute value of FEV1 volume showed a weak significant correlation with the sport index of physical activity (r = 0.11, P = 0.03), physical activity was not a significant predictor of abnormal spirometry in univariate and multivariate logistic regressions. In the multivariate analysis, only total physical activity was entered in the model which was not a significant predictor of abnormal spirometry. Within both exposed and unexposed groups, no significant difference was observed in total physical activity scores between individuals with normal and abnormal PFT results [Figure 1]. Furthermore, when we limited the logistic regression to the exposed group, no significant association was found between abnormal spirometry with the total level of physical activity and its subcategories (data not shown).

Figure 1

Association of total physical activity score with PFT results. The total physical activity score was not significantly different between individuals with normal and abnormal PFT result within both exposed (P = 0.86) and unexposed (P = 0.97) groups. PFT: Pulmonary function test

Finally, workplace air analysis results showed that there were a mixture of organic hydrocarbons including benzene, toluene and xylene and also rubber dust at different parts of production units. The mean of benzene exposure was 2.9 PPM in finishing and 2.63 PPM in tyre repairing units (Threshold limit value (TLV) = 0.5 PPM). For toluene the mean exposure was 80 PPM in painting tyre and 56.2 PPM in apex unit (TLV = 20 PPM). The highest exposure with rubber dust was in raw material weighing and carbon black units with 4.25 and 3.67 mg/m3 at workers respiratory zone, respectively (TLV = 3 mg/m3).

DISCUSSIONS

Our main finding in this study was that occupational exposure to chemicals in the rubber production industry was significantly associated with 80% increase in the odds of abnormal PFT. Furthermore, the retrospective self-reported level of physical activity, as assessed using BPAQ, was not significantly associated with a better pulmonary function, within neither exposed nor non-exposed groups.

The association of abnormal PFT with the exposure was evident only after taking confounding variables, including age, into account. In the absence of any known risk-factors, increased age alone can often lead to respiratory problems.[11] Although we showed no significant difference between most of the spirometric variables, including FVC% of predicted, FEV1% of predicted and FEV1/FVC ratio, we found significantly lower FEF25-75 values in the exposed group.

Our results are in agreement with several other reports that showed rubber manufacturing emissions are responsible for the abnormal pulmonary function of workers exposed to them.[1234] Studies have reported lowered FEV1 and FVC in rubber industry workers[23] however, the degree of pulmonary dysfunction in our study is lower than similar studies probably due to our sample population that were all non-smokers. Prior reports suggested a high synergism of smoking and rubber emissions in causing pulmonary dysfunction.[245] Thus, to overcome this confounding effect of smoking, we only included non-smoker participants in our study.

The effect of exposure to the rubber production materials, especially talc, on the PFT results had been a matter of controversy throughout the published literature. Some researchers reported that talc can cause obstructive lung disease,[1] while another group showed that talc decreases the vital and total lung capacity, thus leading to restrictive lung disease.[12] Moreover it was shown that talc inhalation leads to granuloma formation, interstitial fibrosis and emphysema.[13] Our results did not show a significant reduction in most spirometric variables in the exposed group, except for FEF25-75 which is suggestive of an obstructive pattern of pulmonary diseases.

Organic hydrocarbons, such as benzene and toluene, are mainly used as solvents in rubber industry and enter body through inhalation; therefore, they mostly affect the respiratory system. Hazardous effects of benzene have been mostly studied in petrol station workers, and an obstructive pattern of spirometry was found for workers chronically exposed to benzene.[1415] Our results also suggest a mild obstructive pattern for rubber industry workers exposed to benzene. On the other hand, effects of toluene exposure on respiratory system is still a matter of controversy as some studies reported worsening of respiratory function upon exposure to toluene while others shown no significant effect.[161718] Although our study showed a mild decline of FEF25-75 in exposure group this effect cannot be directly associated with toluene exposure and animal studies may be a better alternative to answer this controversy.

We found no significantly better spirometric results in exposed workers with a higher self-reported level of physical activity. In contrast, a meta-analysis on randomised controlled trial studies showed that within individuals with chronic lung diseases, exercise training can result in a small but significant improvement in PFT.[19] Occupational lung diseases were not studied in this meta-analysis, and to our knowledge, no study has investigated the effect of exercise training on spirometry within these individuals.

LIMITATIONS

Our study was a cross-sectional study, which by definition, is limited in detecting risks of environmental agents. A more suitable alternative is using a cohort design, and long-term follow-up of exposed and non-exposed individuals to detect the long-term effects of exposure to rubber manufacturing chemicals. Second, the control group was significantly older than the exposed group, and we showed that the risk of abnormal spirometry increases with age. However, we attempted to overcome this limitation by including age as a covariate in the model. Finally, another important limitation of our study was that we had measured the level of physical activity using a subjective self-report questionnaire, which is prone to recall bias and is not very accurate.

CONCLUSIONS

Exposure to rubber manufacturing chemicals was significantly associated with a nearly doubled odds of abnormal PFT, after controlling for age. Therefore, it is crucial for the rubber manufacturing companies to omit or reduce these hazards in the workplace. The level of physical activity showed no protective effect against the occupational pulmonary hazards of exposure to these chemicals however, given the self-reported measure of physical activity, this must be interpreted with caution. Future cohort studies and randomised controlled trials are needed to better investigate the effects of occupational exposure to rubber manufacturing chemicals and the potential protective effects of exercise against these damages.

Financial support and sponsorship

This project was funded by Mashhad University of Medical Sciences.

Conflicts of interest

There are no conflicts of interest.