Personal exposure to fine particulate matter (PM2.5) of pregnant women during three trimesters in rural Yunnan of China☆
Graphical abstract
Introduction
Fine particulate matter (PM2.5) is considered one of the most significant ambient air pollutants in terms of potential health impact. The World Health Organization (WHO) estimated that in 2013, 87% of the world's population lived in communities where the mean ambient PM2.5 level exceeded the WHO air quality guideline of no greater than 10 μg/m3 (annual exposure) (Brauer et al., 2016). The Lancet reported the ambient PM2.5 as the fifth-ranking mortality risk factor in the Global Burden of Disease Study (GBD) (Cohen et al., 2017). Due to rapid economic development, industrial expansion, urbanization, and the increasingly frequent occurrence of smog episodes characterized by PM2.5 in the eastern regions of China, scientists and the Chinese government have raised increasing concerns about the impact of air pollution on the health of urban populations. However, less attention has been given to populations in rural areas where indoor air quality may be compromised by the use of coal and biomass fuel, exposure to tobacco smoke, and poorly ventilated living conditions (Zhang & Smith, 2007; Lim et al., 2012). In rural China, many households continue to rely on biomass fuels including wood, animal wastes, and crop residues (World Bank, 2013). A national survey in China showed that 47.6% of rural population still used biomass as predominant fuel for cooking, and 21.4% of them mainly used coal for heating (Duan et al., 2014). The combustion of biomass and coal (collectively called solid fuels) is the main source of indoor air pollution. Additionally, this combustion contributes significantly to poor health outcomes and mortality (Barone-Adesi et al., 2012). The Global Burden of Disease Study in 2017 estimated indoor air pollution contributed to 1.6 million premature deaths and 59 million DALYs annually (DALY & Collaborators, 2018). Effects of indoor air pollution to human health should be investigated in rural areas especially among women who spend a considerable portion of their time indoors engaged in household activities such as cooking and cleaning.
Xuanwei is a county-level city located in the mountainous area of northeast Yunnan Province, China where coal is widely accessible; most residents live in houses with poor ventilation and use smoky coal as their daily fuel (Seow et al., 2014). In addition, tobacco smoking is highly prevalent in rural China (the current smoking prevalence is 56.1% among rural adult men) (World Health Organization, 2010). A previous study (T. Li et al., 2016) reported that the level of PM2.5 in local residences using coal as domestic fuel averages 132.58ug/m3 which is almost twice as high as the ambient air pollution standard of 75ug/m3 (daily exposure) issued by Chinese Ministry of Environment Protection in 2012 (Ministry of Ecology and Environment of People's Repubic of China, 2012). This suggests that household use of solid fuel may be a major source of indoor air pollution in Xuanwei.
The high levels of indoor air pollution from coal burning in Xuanwei have contributed to increased risk of lung cancer, which is characterized by high mortality especially among women (Jedrychowski et al., 2007) (Lin et al., 2015). Xuanwei has one of the highest prevalence of lung cancer in the country (Lin et al., 2015). While the effects of indoor air pollution on lung cancer are well documented, their effects on pregnant women and birth outcomes have been studied less. Pregnant women spend much of their time indoors and may be more susceptible to the adverse health effects of indoor air pollution.
The “developmental origins of health and disease” (DOHaD) is a concept and research framework linking the health state and risk from disease in later childhood and adult life with environmental factors in early life including pre-conceptional, prenatal, and early postnatal periods (Gluckman et al., 2016). Initial work in this field focused on how early life nutrition may shape the developing fetus by disrupting the fetal metabolic homeostasis and causing certain epigenetic changes. This process, “fetal programming”, may predispose the fetus in higher risk of chronic diseases in adult life (Goodman et al., 2018). More recently, exposure to PM2.5 has also been regarded as one of the environmental factors associated with epigenetic changes and adverse outcomes among offspring exposed in utero (Olden et al., 2015; Nachman et al., 2016; Manners et al., 2014). An increasing number of studies have attempted to determine possible linkages between prenatal exposure to ambient fine particulate matter and effects on the developing human fetus, including adverse birth outcomes such as premature birth (DeFranco et al., 2016), term low birth weights (Dadvand et al., 2013), small for gestational age (Rich et al., 2009), birth defects (Tanner et al., 2015), and stillbirths (Siddika et al., 2016). However, findings are not consistent (X. Li et al., 2017). These inconsistent findings may be due to differences in the measures and timing of measurement of air quality, as well as the timing of exposure during pregnancy. Many of the initial studies used data collected by air pollution monitoring devices that are location-specific and do not measure personal exposure to air pollutants. Measuring exposure to air pollutants at the personal level may be necessary for accurately investigating the effects of exposure to PM2.5 at various stages of pregnancy on birth outcomes.
The goal of this longitudinal study is to follow the women exposed to high levels of PM2.5 throughout pregnancy. The specific aims are to (1) characterize personal exposure to PM2.5 at various stages of pregnancy using portable monitors, and (2) identify risk factors for PM2.5 exposure, among pregnant women living in rural China. We hypothesize that pregnant women from lower socioeconomic households, poor ventilation dwelling, using solid fuel for cooking and heating, engaging in food preparing and sweeping work, and exposed to second hand smoke are at risk of higher exposure to PM2.5 throughout pregnancy.
Section snippets
Study site
The study site is shown in Fig. 1 (Wkipedia, n.d.). The study was conducted in two townships (Township 1 and Township 2) in Xuanwei.
Participants
Between 2014 and 2017, pregnant women who registered in Township 1 and 2 hospitals were recruited to participate in this study if they met the following eligibility criteria: (1) resided in the area for ≥ 2 years; (2) had rural occupation; (3) is in their first trimester at time of study enrollment; (4) no plans for relocation post pregnancy; and (5) not using
Characteristics of participants
A total of 606 pregnant women were recruited. Twelve had spontaneous abortions, one had stillbirth, two withdrew from the study, and 67 had invalid PM2.5 data for at least one of the three trimesters, and were excluded from the analytic sample (Fig. 3). Therefore, a total of 524 women were included in the analytic sample.
The characteristics of participants and their households are summarized in Table 1. Participants were predominantly majority Han, and about 85% of them have a middle school
Discussion
Traditional methods to quantify personal PM2.5 have relied on the measure from monitors placed in fixed locations (Steinle et al., 2013). However, air quality may vary by season and time of day, and is influenced by the use of biomass fuels and ventilation. People usually live in different microenvironments and are exposed to varying levels of PM2.5 spatially and temporally. Previous studies have indicated that the PM2.5 concentration measures from monitors placed in fixed locations do not
Strengths and limitations
To our knowledge, our study is the first to focus on pregnant women in rural China and characterize personal exposure to PM2.5 during each trimester and to investigate risk factors of exposure. However, some limitations should be noted. Since ambient PM2.5 data from the environmental monitoring station was not accessible at the time our study was conducted, we did not have a chance to assess the impact of outdoor air pollution.
Conclusions
The daily exposure to PM2.5 of pregnant women living in Xuanwei in this study exceeded the WHO guideline for PM2.5. Personal exposure to PM2.5 among pregnant women studied was significantly higher in winter and during the day time and food preparation hours. Seasonality, low family income and individual characteristics such as the use of solid fuel, cooking, heating and secondhand smoke exposure were independent risk factors for higher PM2.5 exposure. These findings suggest an urgent concern
Conflicts of interest
The authors declare no conflicts of interest.
Author contributions
Y. L. and J.W.: conceptualization.
J.W., X.X., F.Y., S.Y., L.S. and R.M: field work and investigation.
J.W. and X.X.: data curation and formal analysis.
Y. L.: supervision.
J.W.: original draft writing.
M.W. and Y. L.: Methodology; Writing - review & editing.
All authors read and approved the final manuscript.
Acknowledgement
This study was funded by National Natural Science Foundation of China (Grant Number: 81360432) and Talents Cultivating Plan of Second Affiliated Hospital of Kunming Medical University (KCPYXM2017-3-15). We thank Professor Edmund Seto and his team, at Department of Environmental and Occupational Health Services, University of Washington, for providing us with particulate monitors for measuring personal PM2.5 exposure. We are indebted to the participants for their time and effort in making this
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This paper has been recommended for acceptance by Dr. Da Chen.