A study on spirometry in petrol pump workers of Ahmedabad, India

Abstract

Background:

Lung reactions to exposure to dust, gases, and fumes at work places have been studied in different populations. The emission level of pollutants that emit particulate matter less than 10 micrometers in size (PM 10) has been found very high in Ahmedabad. Hence, petrol pump workers in Ahmedabad are likely to get exposed to a high level of air pollution along with petrol and diesel vapors. Both of these factors can affect the respiratory health of petrol pump workers.

Materials and Methods:

A cross-sectional observational study was conducted at 53 different petrol pumps of Ahmedabad. A total of 227 petrol pump workers underwent pulmonary function testing. Their spirometry parameters were compared with 227 age-matched, healthy controls.

Results:

A significant reduction (P < 0.001) was found in the spirometry parameters, such as, forced vital capacity (FVC), forced expiratory volume in the first second (FEV₁), forced expiratory flow (FEF_25-75), and peak expiratory flow rate (PEFR) in petrol pump workers, as compared to the controls. The mean values of FEV₁/FVC (%) were significantly increased (P < 0.001). A decline in FVC was not significantly different among the workers according to the duration of exposure. As the duration of exposure increased, there was a progressive decline in FEV₁/FVC (%) and FEF_25-75.

Conclusion:

The study concludes that the deleterious effects of air pollution and petrol/diesel vapor inhalation on the lung function of petrol pump workers results in a restrictive type of lung function abnormality. The pattern of respiratory impairment changes to a mixed type as the duration of exposure increases.

INTRODUCTION

Rapid industrial growth, globalization, and poor environmental conditions at work places have created a lot of health-related issues. There is a high prevalence of occupational diseases, such as, silicosis, asbestosis, and pneumoconiosis among workers working in different industrial environments in India.[1] Fast urbanization trends have resulted in a tremendous rise in the number of transportation vehicles, thereby, resulting in the increased need of petrol. This increase in demand of petrol has led to a steady rise in the number of petrol pumps in the country. On account of the lack of availability of sufficient international research on the occupational aspects of petrol pump workers, the present study focuses on the occupational health-related issues in this population.

The rising number of vehicles has sharply increased the level of air pollution in various cities of India. A Health Survey done by the Centre for Science and Environment (CSE), New Delhi, has shown that 141 (80%) cities in India exceed the PM 10 (pollutants that emit particulate matter of less than 10 micrometers in size) standard, 90 cities have a critical level of PM 10 and 26 cities have the most critical level, exceeding thrice the standards.[2] In a study involving six cities of India, the measured annual PM10 concentration in microgram per cubic meter (μg/m³) averaged 94.0 ± 20.4 in Ahmedabad, exceeding the annual standard of 60 μg/m³, along with other five cities.[3] It has been found that an increase of 10 μg/m³ of PM10 and NO₂ is associated with a decrease of about 3% and 0.7% in FEV₁ (forced expiratory volume in the first second), respectively.[4] The emission of pollutants from motor vehicles can be evaporative emission, exhaust emission or crankcase (running loss) emission, out of which 20 – 32% is due to evaporative emissions.[5] Owing to the volatile nature of petrol and the high environmental temperature in a city like Ahmedabad, hydrocarbon vapors from the petrol evaporate constantly into atmosphere, mainly from fuel lines, fuel tanks, and carburetors, depending upon the fuel composition, engine operating temperature, and ambient temperature. Hence, in addition to exhaust emission, petrol pump workers are also exposed to evaporative emission of pollutants. A detailed study conducted in Italy to determine the exposure of petrol pump workers to the benzene content of petrol has shown the highest benzene concentrations in the breathing zone of petrol station attendants.[6] The study also shows that in a single refueling operation that lasts for about one minute, the mean air concentration of benzene to which a petrol pump worker is exposed is 3709 μg/m³. In addition, most of the benzene (88%) is emitted while supplying fuel to the vehicle.[6] The toxic effects of the benzene content of petrol on the various hematological indices and liver have been studied in gasoline-filling workers,[7,8] with documented neurotoxicity.[9] Petrol pump workers work 10 hours/day and six days/week at most of the pumps. The high level of environmental pollution and exposure to petrol and diesel vapors can have an impact on the lung function of petrol pump workers. Chest radiographs and arterial blood gas (ABG) analysis are unable to detect any significant airway obstruction in the early stages of respiratory disease. Spirometry is a valuable tool to assess lung function in the initial asymptomatic stages of respiratory dysfunction, as compared to other tools. It has been documented that only spirometry enables the detection of chronic obstructive pulmonary disease (COPD) — five to ten years before shortness of breath develops.[10] Petrol pump workers, who are asymptomatic, may have abnormal lung function. Hence, the purpose of this study is to assess the lung function of petrol pump workers by means of spirometry.

MATERIALS AND METHODS

A total of 53 (out of 107) petrol pumps were randomly selected from five different zones of Ahmedabad city. From these 53 petrol pumps, a total of 227(out of 358) non-smoking petrol pump workers (working as petrol/diesel filling workers for >1 year, at least 8 hours/day), in the age group of 20–50 years, were selected as the study group. The petrol pump workers were matched with 227 non-smoker office employees for age, gender, height, and weight. The subjects with presence or history of any respiratory illness, abdominal or chest surgery, neuromuscular disease or musculoskeletal abnormalities involving the upper trunk or rib cage, and those who were smokers, were excluded from the study. The Ethical Committee clearance and an informed consent of the subjects were taken. The petrol pump workers were classified into three different groups according to their duration of work [Table 1].

Table 1.

Classification of petrol pump workers

All subjects were first interviewed using a questionnaire that included the demographic data, smoking habits, duration of exposure, surgical history, past medical history of any respiratory illness, and use of any personal protective equipment resembling a face mask. Subjects who fulfilled the inclusion criteria were explained the purpose of the study. Spirometry was done in a sitting position using the computerized pulmonary function testing (PFT) machine (RMS MED SPIRER, Helios 401) and the guidelines of the American Thoracic Society were strictly followed.[11] The subjects were instructed about the procedure of the FVC (forced vital capacity) maneuver and were asked to perform it thrice. Proper rest was given in between each trial. The best value of the three was recorded. The lung function parameters studied were FVC (forced vital capacity), FEV₁ (forced expiratory volume in 1 second), FEV₁/FVC, FEF_25-75 (average forced expiratory flow rate over the middle 50% of vital capacity), and PEFR (peak expiratory flow rate). The spirometry data of the study and control groups were compared using the student's t test using the computer software Microsoft Office Excel 2007. Within-group analysis of data was done for the petrol pump workers using the one-way analysis of variance (ANOVA) test and a Post-hoc test using the GraphPad PRISM 5.01 software.

RESULTS

A total of 227 petrol pump workers and 227 office workers participated in this study. The demographic details of all are shown in Table 2. The mean age and duration of exposure of the petrol pump workers are shown in Table 3. There was a moderately positive correlation between the age and duration of exposure [Table 3]. No personal protective equipment, such as a face mask, was used by any of the workers in the present study. Comparison of the predicted and observed lung function parameters in petrol pump workers showed a significant reduction (P < 0.001) in the observed mean values of FVC, FEV₁, FEF_25-75, and PEFR [Table 4]. The observed mean values of FEV₁/FVC (%) were significantly increased (P < 0.001), as compared to the predicted values [Table 4]. Comparison of the predicted and observed mean values of various spirometry parameters in the controls showed a significant (P < 0.001) increase in the observed mean values of FVC, FEV₁, and FEV₁/FVC, as compared to the predicted values [Table 5]. Table 5 also shows that the predicted and observed mean values of FEF_25-75 and PEFR among the controls were not significantly different (P > 0.05). Table 6 and Figure 1 show the comparison of the spirometry parameters between petrol pump workers and controls. Table 6 also shows a significant reduction (P < 0.001) in the mean values of FVC, FEV₁, FEF_25-75, and PEFR along with a significant increase (P < 0.001) in the mean value of FEV₁/FVC (%) in petrol pump workers, as compared to the controls [Figure 2]. Table 7 shows a comparison of the lung function parameters between controls and all three groups of petrol pump workers. Comparison of the lung function parameters among the three groups of petrol pump workers [Table 8] revealed no significant difference (P > 0.05) in the mean values of FVC, FEV₁, and PEFR, while there was a progressive decline in FEV₁/FVC(%) and FEF_25-75, as the duration of exposure increased. The mean values of FEV₁/FVC (%) and FEF_25-75 were significantly decreased (P < 0.05) in group 3 as compared to group 1 and group 2 [Table 9].

Table 2.

Demographic details of subjects

Table 3.

Age and duration of exposure

Table 4.

Spirometry parameters in petrol pump workers

Table 5.

Spirometry parameters in controls

Table 6.

Comparison of spirometry parameters between petrol pump workers and controls

Figure 1.

Comparison of the observed mean values of FVC, FEV₁, FEF25-75, and PEFR, between petrol pump workers and controls

Figure 2.

Comparison of the observed mean values of FEV₁/FVC (%), between the petrol pump workers and controls

Table 7.

Spirometry parameters of petrol pump workers according to duration of exposure

Table 8.

Comparison of spirometry parameters among petrol pump workers according to duration of exposure (One-way ANOVA for comparison between groups)

Table 9.

Tukey's multiple comparison test

DISCUSSION

The purpose of the present study was to assess impact of petrol/diesel vapors and environmental pollution on the lung function of petrol pump workers. The results showed a significant reduction in the spirometry parameters such as FVC, FEV₁, and FEF_25-75 in petrol pump workers, as compared to their predicted values and observed values in the control group. The mean value of FEV₁/FVC (%) was significantly increased in the study group as compared to the control group. Such findings suggest the restrictive nature of lung function abnormality in petrol pump workers.[12] Results in the control group showed that the predicted and observed mean values of PEFR and FEF_25-75 were quite similar (not significantly different), while the observed mean values of FEV₁ and FVC were significantly higher than the predicted (better than expected) values, in contrast to the study group. These findings indicate better lung function in the control group as compared to petrol pump workers, as the control group was not exposed to petrol/diesel vapors and high environmental pollution for a prolonged period of time. Similar findings have been observed in previous studies.[13,14] Studies involving short-term exposure to diesel exhaust in healthy subjects have found a marked systemic and pulmonary inflammatory response, with insignificant change in lung function parameters.[15] As petrol pump workers in the present study were exposed to petrol and diesel vapors for a longer period of time (10 hours/day, >1 year), they were likely to develop chronic respiratory impairment as indicated by the results of the present study.

Comparison of lung function parameters among the petrol pump workers according to the duration of exposure revealed that the mean values of FVC and FEV₁ were not significantly different between all three groups, but there was a significant decline in the mean values of FEV₁/FVC (%) and FEF_25-75 in group 3 (>10 years) as compared to group 1(<5 years), and group 2 (5 – 10 years). This type of picture indicates that the restrictive pattern of lung function abnormality was changed to a mixed pattern of respiratory impairment, as the duration of exposure increased to >10 years. These findings support the results of the previous studies.[16,17]

Petrol is a complex combination of hydrocarbons, which on emission generates particles with a diameter of 0.02 nm. These particles, due to their large surface area, can carry various toxic compounds that are likely to remain in atmospheric air for a longer period and can deposit them in the small airways on inhalation.[17] Long-term exposure to such particles can cause chronic respiratory impairment, which includes lung parenchyma and small airways. The ambient air concentration of carbon monoxide (CO) has been found to be maximum in areas surrounding petrol stations during peak hours (6 a.m. – 2 p.m.), as compared to residential areas, in a study done by Nazia Uzma et al.[16] Thus, a high level of environmental pollution in cities like Ahmedabad and in areas surrounding petrol pumps can have an additional deleterious impact on the respiratory health of petrol pump workers. In the present study, all smoking petrol pump workers were excluded. It has been found that an urban smoker, who works adjacent to a busy road for eight hours per day is exposed to a daily benzene dose of 819 μg/day, while that of an urban non smoker is 95 μg/day.[6] Hence, smoking petrol pump workers are at an even higher risk of developing lung function abnormalities, as compared to non-smoking petrol pump workers. In addition, the risk of lung function abnormalities in petrol pump workers also increases due to the neglect of using personal protective equipment, such as a face mask, by each worker, in the present study.

Change from restrictive to mixed variety of impairment

Studies involving distribution of particulate matter in human lung have shown a major site of impact and injury at the level of the terminal bronchioles and adjacent first generation respiratory bronchioles.[18] There was relative absence of the retained particulate matter in large conducting airways reflecting more rapid clearance of particles from these regions.[19] This may be the reason for a restrictive impairment in all three groups of petrol pump workers in the present study. Aging can be a contributing factor in the change from a restrictive to a mixed variety of impairment. Studies have shown that the estimated rate of decline in FEV₁ is 25–30 ml/year starting at the age of 35 – 40 years and can double to 60 ml/year after the age of 70 years.[19] Aging also causes a decrease in the small airway diameter. In the present study, the results show that as the duration of exposure (which is positively correlated with age) increases, there is a progressive decline in FEF_25-75 (a valuable measure for small airway obstruction) and FEV₁/FVC, pointing toward obstructive pathology and resulting in a mixed type of respiratory impairment. Such findings support a previous study done by Priyadarshini et al.[20]

Unlike in India, exposure of petrol pump workers to petrol/diesel vapors has been restricted in USA and United Kingdom by placing a rubber hood over the delivery pump and the use of self-service stations.[21] Installation of a petrol vapor recovery system has controlled occupational exposure to volatile organic compounds in many countries. The Department of Environment, Climate Change and Water, Government of New South Wales (a state of the commonwealth of Australia) has published standards and practice guidelines for vapor recovery at petrol pumps.[22] The stage-I (vapor recovery) system limits the emissions of volatile organic compounds that result from unloading petrol from a road tanker into petrol pump storage tanks. The stage-II (vapor recovery) system is designed to capture the vapor displaced when vehicles are refueled at petrol pumps. Countries like USA have had stage-I (vapor recovery) system for many years and have now graduated to stage-II. A study done by Agip Petroli (an Italian oil company) has estimated that introduction of the petrol vapor recovery system will be capable of reducing benzene emission by 80% during the ‘fuel in flow’ and by 50% during removal and replacement of the nozzle and closure of the vehicle tank.[6] Although some of the states like Delhi, in India, have a few petrol pumps with the vapor recovery system, its installation is not mandatory in any of the states of India.

In India, there is no standardization regarding the number of petrol pumps in a particular geographical area, the number of workers employed in a particular petrol pump; their duration of work or the use of personal protective measures. In addition, most of the petrol pump workers belong to the lower socioeconomic class. All these aspects need to be given due consideration for the occupational hygiene of petrol pump workers

CONCLUSION

We found lung function abnormalities in petrol pump workers. The pattern of respiratory impairment is restrictive, which changes to a mixed variety as the duration of exposure to petrol and diesel vapor increases to >10 years. Future studies are required to investigate the effects on the diffusion capacity of the lungs and other pulmonary markers in petrol pump workers.