Table 1 summarizes the socio demographic characteristics of the study population. Auto rickshaw drivers spend 47% of time at work while cab drivers spend 50% of the day at work and majority of respondents from both the groups (48% and 33%, respectively) perceived the air quality at workplace to be hazardous (Figure S3 a & b, SI, Section S3). Vehicles were considered to be the most significant pollution source as mentioned by 97% auto drivers and 88% cab drivers. Most auto rickshaw drivers perceived air quality in their residential areas to be unhealthy (26%) while majority (30%) of cab drivers perceived it to be hazardous (Figure S3 c & d, SI, Section S3. Further, it is also observed that more than 85% respondents from both the groups used Liquified Petroleum Gas (LPG) as the cooking fuel. It is important to highlight that almost 50% of the sampled group both auto rickshaw and cab drivers considered air quality had a severe impact on their health (Figure S3e-f, SI, Section S3). In addition, more than half the auto rickshaw drivers and cab drivers found extreme summers to be the most difficult season as compared to extreme winters and rains in terms of health impacts and ease of work. Auto rickshaw drivers complained of headaches (54%), rapid heartbeat (28%), muscle cramps (23%), while taxi drivers reported headache (33%) and muscle cramps (12%) during extreme summers.
Table 1: Summary statistics of socio demographic characteristics of the study population
Variables
|
Autorickshaw drivers (n=75)
|
Cab drivers (n=75)
|
Age (yrs.)
|
39± 10.52
|
38 ±8.15
|
Height (cm)
|
166.5± 6.64
|
168.4±6.39
|
Weight (kg)
|
64.8± 23.35
|
69.8±12.2
|
BMI
|
23.3± 4.06
|
24.63± 4.07
|
Smoking
|
35%
|
36%
|
Alcohol
|
33.3%
|
59%
|
Tobacco
|
41%
|
33.30%
|
Working hours/day
|
11.3±1.8
|
12.11±1.8
|
Working since
|
12.82± 9.28
|
7.9±7.6
|
Monthly income (INR)
|
|
|
1,000-5,000
|
0%
|
0%
|
5,000-10,000
|
13%
|
4%
|
10,000-15,000
|
37%
|
19%
|
15,000-25,000
|
40%
|
28%
|
>25,000
|
10%
|
49%
|
Vehicle ownership
|
|
|
Own
|
53%
|
63%
|
Rented
|
47%
|
37%
|
Education
|
|
|
None
|
23%
|
5%
|
Primary
|
15%
|
9%
|
Secondary
|
30%
|
39%
|
Higher secondary
|
23%
|
35%
|
Graduation and higher
|
9%
|
12%
|
Exposure cycle
|
|
|
Home
|
44%
|
42%
|
Work
|
47%
|
50%
|
Outdoors
|
6%
|
5%
|
Travel
|
3%
|
3%
|
3.1 In- vehicle PM concentration
The comparative results of in-vehicle PM10, PM2.5 and PM1 concentrations monitored in cabs (taxies) and auto rickshaws at different times of the day, during summers and winters are presented in Fig. 3. We found that both, auto rickshaw as well as cab drivers spent almost half of the day outdoors at work. Thus, they are exposed to high PM concentrations continuously for long durations, which is likely to cause severe health impacts over time. The average PM concentration was significantly higher (p = 0.000) inside auto rickshaws as compared to cabs. Similarly, Jain (2017) reported PM exposure in non- airconditioned cars and auto rickshaws in New Delhi, was similar and showed no significant difference; while, the exposure was significantly less in airconditioned cars. Further, Okokon et al. (2018) in a study conducted in China reported very high PM2.5 concentrations (256 µg/m3) inside cars with windows open and air conditioning unavailable or off compared to PM2.5 146 µg/m3 in cars with windows closed and air conditioning available. In a similar study, Goel et al. (2015) in New Delhi reported 30% higher PM2.5 exposures while travelling in auto rickshaws; whereas, 50% lower exposure while travelling in airconditioned cars. Also, the in- cabin PM concentration for auto rickshaws as well as cabs was significantly higher in winters as compared to summers (p = 0.000). In addition, problems of episodic air pollution events in Delhi increases in winters, which necessities that proper, timely interventions are made by the concerned authorities to ensure safety of these vulnerable groups to further avoid health inequalities among outdoor exposed groups. Thus, auto rickshaw drivers can be considered more vulnerable to health issues due to PM exposure. Globally, there are no standards for in-vehicle indoor air quality except South Korea for public transport (PM10 < 150 µg/m3). Therefore, there is a dare need to have indoor air quality standards to save guard the human beings in various micro-environments.
3.2 Prevalence of disease symptoms, relative risk and testing of hypotheses
Auto rickshaw drivers had higher prevalence of all the disease symptoms as compared to cab drivers with breathlessness (~ 28%), eye redness (~ 44%), skin rashes (22%), joint pain (~ 39%), irregular heartbeat and chest discomfort (~ 9%) and general weakness (~ 44%) being the most prevalent respiratory, ophthalmic, dermatological, musculoskeletal, cardiovascular and general health symptoms, respectively (Fig. 4a-f). The value of relative risk greater than one for all symptoms, except common cold further suggests that auto rickshaw drivers are at relatively greater risk of developing health problems as compared to cab drivers who use airconditioned cars (Table 2). Overall, ophthalmic, musculoskeletal and general health symptoms were the most prevalent among both the groups. However, chi square test (p < 0.05), suggests that auto rickshaw drivers are significantly more susceptible to health issues may be attributed to higher exposure to transport microenvironment for all categories of disease symptoms except cardiovascular and musculoskeletal symptoms (Table 3). The p-value > 0.05 for musculoskeletal symptoms may be because these symptoms are related to ergonomic factors and long working hours and both the group of workers are involved in driving for long hours (Sekkay et al. 2018). Further, PM monitoring results as explained in Sect. 3.1 showed that auto rickshaw drivers are exposed to significantly greater PM concentrations than cab drivers. In addition, vehicular emissions also contribute to VOCs, benzene, and NOx (Nagpure et al. 2017). Such traffic emissions have been associated with chronic as well as acute respiratory problems like asthma, COPD, nasal and throat irritation as well as cardiovascular health issues (Hansell et al. 2018; Lin et al. 2018; Kumar and Mishra 2018; Fisher et al. 2016). Kisku et al. (2013) reported the prevalence of eye watering (~ 51%), redness and irritation (~ 33%) and burning in eyes (20%) among auto rickshaw drivers in Lucknow, owing to high exposure to vehicular fumes. Further, Liu et al. (2015) in Taipei, Taiwan, reported associations between exposure to traffic related PM2.5 and cardiovascular health of young adults and the effects were found to vary with the mode of commute. Exposure to PM, PAHs and black carbon is also known to aggravate various skin problems like aging, acne and skin cancer (Kim et al. 2016).
Table 2
Relative risk of disease symptoms
Symptoms
|
Relative risk
|
Sneezing
|
1.82
|
Chronic cough
|
1.75
|
Breathlessness
|
1.46
|
Wheezing
|
3.65
|
Phlegm
|
2.70
|
Common cold
|
0.73
|
Congestion
|
1.46
|
Sore throat
|
2.19
|
Eye Redness
|
3.54
|
Eye irritation
|
2.04
|
Blurred vision
|
2.19
|
Eye burning
|
2.04
|
Watering
|
1.46
|
Skin rashes
|
2.48
|
Skin redness
|
1.82
|
Itching
|
4.75
|
Chest Pain
|
1.09
|
Irregular heartbeat
|
5.10
|
Chest discomfort
|
5.11
|
Back ache
|
1.24
|
Shoulder Pain
|
1.75
|
Joint pain
|
1.46
|
Table 3
Results of hypothesis testing
Population
|
Hypothesis
|
p value- Chi square test
|
p- value Fisher Exact test
|
Test of null hypothesis
|
Auto rickshaw drivers and cab drivers
|
H1
|
0.002
|
0.0027
|
Reject
|
H2
|
0.00004
|
0.00005
|
Reject
|
H3
|
0.008
|
0.010
|
Reject
|
H4
|
0.065
|
0.09
|
Accept
|
H5
|
0.11
|
0.12
|
Accept
|
H6
|
0.00001
|
0.00002
|
Reject
|
3.3 Spirometry
The results of pulmonary function tests indicated that 48% of respondents among auto rickshaw drivers as well as 33% cab drivers had restrictive lung function, while obstructive lung function was reported only for 6% of the auto rickshaw drivers and none of the cab drivers (Fig. 5a & b). This could be because the auto rickshaw drivers had higher exposure to PM than cab drivers and obstructive lung function is known to be associated with exposure to pollutants like NO2 and PM2.5 and diseases such as asthma, chronic obstructive pulmonary disease and cystic fibrosis (Hansell et al. 2018; Lin et al. 2018; Fisher et al. 2016; Caronia, 2017). Restrictive pulmonary defect is associated with problems such as systemic inflammation, pulmonary fibrosis, interstitial lung disease (Johnson and Threuer 2014). Rice et al. (2015) reported significant association of chronic exposure to PM2.5 and other traffic emissions with decline in FVC and FEV1 values for those residing nearby major roads. Binary logistic regression (BLR) was used to test the association of lung function impairment with various factors such as age, smoking, tobacco consumption and number of years employed as auto rickshaw/ cab drivers. BLR test showed that age was significantly associated with respiratory impairment (p = 0.002).
3.4 Use of protective measures
Nearly 54% of the auto rickshaw drivers use cloth/ handkerchief to cover their face as a remedial measure while only 5% of cab drivers do so (Fig. 5a & b, SI, Section S4). These are not formal measures such as protective face masks that are specifically designed to prevent inhalation of PM and comply to standards such as the European standards, National Institute for Occupational Safety and Health standards (BS ENIOSH Guide to the Selection and Use of Particulate Respirators, 1996). Thus, such measures do not offer ample protection against PM (Noomnual and Shendell 2017; Chaschin et al. 2014; Jung et al. 2014; Langrish et al. 2012). Further, 25% auto rickshaw drivers were unaware about which mask to be used to prevent PM exposure, from a wide range of masks such as surgical masks, quarantine masks, general masks etc. Further, nearly 19% could not afford buying proper masks owing to high cost and 10% had discomfort wearing the masks while driving. This suggests the need of government interventions to make appropriate safety masks economically viable and available to all. This would also help reduce health inequalities. The lesser number of cab drivers covering their face while driving was because of their perception that they are not exposed to air pollution within their vehicles.