Inequalities in occupational exposures among people using popular commute modes☆
Graphical abstract
Introduction
Air pollution, being one of the top ten factors to affect public health (Smith & Mehta, 2003; Brauer et al., 2016), is of prime importance for identifying the most exposed groups. Particulate matter (PM), has been linked to increased rate of morbidities and mortalities in all over the world. National and international agencies are coming up with several policies to curb emissions, reduce exposure and the related burden of diseases (Wang et al., 2014). However, due to limited land availability and per capita income, inequality in environmental exposures is highlighted in middle and low-income countries (Chen et al., 2020; Newell, 2005). People living or spending maximum time near the busy roads, or inside different traffic environments are disproportionately exposed to several air pollutants (Gao et al., 2019).
Researchers have reported significant differences in air pollutant exposures within commute modes (Sanchez et al., 2020; Chaney et al., 2017; Ma et al., 2020; Pant et al., 2017; de Nazelle et al., 2012). A West-African study has observed that carbon monoxide (CO) levels inside cars (28.8 ± 6.5 ppm) were ∼2–4 times higher (p < 0.05) than other modes of travel (Odekanle et al., 2017). Studies have also reported that the relative differences in particulate matters are more inconsistent, and also dependent on sizes of the particles (Kumar et al., 2018; Rivas et al., 2017) and/or air exchange rates (AERs). There are studies to associate the in-cabin pollutants with several traffic-dependent and independent factors like fuel type (Zuurbier et al., 2010), ventilation efficiencies (Tong et al., 2019; Hudda and Fruin, 2018), body position (Kolluru et al., 2019), traffic lane (Tiwari and Kumar, 2020; Saleh et al., 2009), and diurnal variation (de Nazelle et al., 2012; Ragettli et al., 2013). AER, another important modifier of in-cabin ultra-fine particles (UFPs), was also reported to vary with speed, age and mileage of the vehicles (Hudda et al., 2011).
The size of the PM has critical toxicological and regulatory relevance. Epidemiological studies have shown that exposure to PM with an aerodynamic diameter of less than 10 (PM10) and 2.5 μm (PM2.5) induces oxidative stress reactions and inflammation, potentially resulting in deleterious cardiovascular and pulmonary health outcomes (Bates et al., 2019; Abrams et al., 2017, Yang et al., 2016). The studies focusing on fine particles (PM2.5) produced by combustion processes have found significant associations between higher exposure and increased all-cause mortality or the prevalence of many cardiopulmonary disorders (Yang et al., 2016). Also, there is evidence linking the health impacts of air pollution with coarse particles (PM2.5–10) produced by crustal metals or mechanical processes (Nitter et al., 2021; Yang et al., 2017). A recent study has investigated the blood coagulability among healthy adults exposed to non-exhaust sources on Norwegian roads. They reported a limited association between higher blood coagulability (p = 0.09) and exposure to quartz diorite (Nitter et al., 2021). Some studies have found that as particle sizes go smaller, the severity gets worse (Kwon et al., 2020). Because of their greater penetration efficiencies, propensity for translocating from the lungs to the bloodstream, and higher surface areas to absorb toxic chemicals, smaller particles are more harmful than bigger particles (Kwon et al., 2020; Leikauf et al., 2020). Although there is still a fundamental lack of knowledge in the underlying mechanism of the toxicity to humans, one of the widely accepted hypotheses is that the toxicity of PM depends on both their size and composition (Yang et al., 2017; Bates et al., 2019). Hence, estimating the internal doses of particles is critical for evaluating the health impacts. Further, the inconsistencies in the toxicological consequences of airborne particles call for more research.
Several case-controlled studies have investigated the causal association between disproportionate exposure and related allergic diseases (Davis et al., 2007; Laurent et al., 2013; Zietsman et al., 2018; Gupta & Elumalai, 2019). For example, a cohort study in Canada has estimated that people living near roads are at ∼20% higher risk of developing neurological disorders than those are away from the roads (Yuchi et al., 2020). Studies have found that policemen (Tan et al., 2018; Wang et al., 2020), cab drivers (Chen et al., 2005; Hachem et al., 2020), and professional motorcyclists (Carvalho et al., 2018) are among the most vulnerable working groups to air pollution. A study has reported that the policemen, exposed to traffic related pollution, have been detected by induced sputum (Dragonieri et al., 2006). Many studies have demonstrated that professionals exposed to air pollution tend to have a significant decrease in lung functions and mucociliary clearance, higher risk of developing cardiovascular and infectious diseases, and the presence of airway acidification (Ekpenyong et al., 2012; Lawin et al., 2016). However, the studies estimating the exposure of the professionals inside cars or near roads are mutually exclusive.
The contribution of this study to the existing literature is of two-folds. Primarily, the present study aims to quantify the variation in both the gaseous and size-segregated PMs inside five popular commute modes. During rapid urbanization, several commute modes are being promoted in developing nations without a prior check on air qualities inside those modes. Hence, there is a scarcity of data on pollutant levels inside those modes. Secondly, we have estimated the differences in exposures among the people who are spending significant durations near roads due to their occupational obligations. A thorough assessment of the inhaled doses of pollutants for major occupational groups were done and further compared with daily office commuters. To our best knowledge, monitoring of both particulate and gaseous pollutants inside vehicles, and utilizing the observations to explore the inequalities in exposure among the working groups has been done for the first time.
Section snippets
Study design
Gaseous pollutants and particulates were measured inside five popular commute modes in Mumbai. Ninety-eight trips were repeated on a fixed predefined route (∼8.5 km) with buses (without air conditioning), auto-rickshaws, cars, sub-urban trains and motorbikes. People with different socio-economic backgrounds and different parts of the city were asked about their daily work-related trips, personal and demographic information through household surveys. Further, daily exposures were estimated based
Particulate matter
The particulate number and mass concentrations inside the vehicles are shown in Fig. 2. The pollutant levels inside the roadway transportation modes were significantly higher (p < 0.05) than those inside suburban trains. It was due to the lack of exhaust sources near the railway tracks. PNC was the maximum inside auto-rickshaws (8.9 ± 3.6 × 104 cm−3) and least inside suburban trains ((1.2 ± 0.6) × 104 cm−3). However, there was no significant difference in PNC within the on-road vehicles
Conclusion
The present study has measured the in-cabin particulate matters of different sizes and gaseous pollutants inside popular commute modes in Mumbai, India. Out of the five commute modes, the sub-urban trains offer the lowest exposures to air pollutants to the commuters. While buses had the lowest concentrations, among the on-road vehicles, due to longer trip-time and frequent traffic congestions, commuters are highly exposed. Due to the increased concentrations inside vehicles and their lengthy
Funding
This project is supported by the seed grant from IRCC, IIT Bombay (Grant no. RD/0516-IRCCSH0-008) as well as partial support from MHRD, Govt. of India (Grant no. RD/0114-IMHPC06-003).
Data availability
Available upon request.
Author contributions
Harish C. Phuleria contributed to the study conception and design. Material preparation, data collection and analysis were performed by Arpan Patra. The first draft of the manuscript was written by Arpan Patra. Harish C. Phuleria reviewed and edited previous versions of the manuscript. Both authors read and approved the final manuscript.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
We acknowledge the partial financial support received from the IRCC, IIT Bombay under the seed grant no. RD/0516-IRCCSH0-008, and MHRD, Govt. of India, grant no. RD/0114-IMHPC06-003, towards conducting these measurements. We would like to thank the survey participants for their active interests while participating in the commute surveys.
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This paper has been recommended for acceptance by Pavlos Kassomenos.