An urban-rural and sex differences in cancer incidence and mortality and the relationship with PM_2.5 exposure: An ecological study in the southeastern side of Hu line

Highlights

• Increased risks for lung, ovarian, prostate cancers and leukemia are closely associated with increased PM_2.5 exposure (Short version: Lung/ovarian/prostate cancer and leukemia are closely related with increased PM_2.5).

• PM_2.5 significantly impacts the risks for lung cancer and leukemia in rural area.

• PM_2.5 significantly impacts the risks for prostate and ovarian cancers in urban area.

• Females are at higher risks for lung cancer and leukemia due to elevated PM_2.5

Abstract

This study investigates the urban-rural and sex differences in the increased risks of the ten most common cancers in China related to high PM_2.5 concentration in the southeastern side of Hu line. Pearson correlation coefficient is estimated to reveal how the cancers closely associated with PM_2.5 long-term exposure. Then linear regression is conducted to evaluate sex- and area-specific increased risks of those cancers from high level PM_2.5 long-term exposure. The major finding is with the increase of every 10 μg/m³ of annual mean PM_2.5 concentration, the increase of relative risks for lung cancer incidence and mortality are 15% and 23% for males, and 22% and 24% for females in rural area. For urban area, the increase of relative risk for ovarian cancer incidence is 9% for females, while that for prostatic cancer increases 17% for males. For leukemia, the increase of relative risks for incidence and mortality are 22% and 19% for females in rural area, while in urban area the increase of relative risk for mortality is 9% for males and for incidence is 6% for females. It is also found that with increased PM_2.5 exposure, the risks for ovarian and prostatic cancer rise significantly in urban area, while risks for lung cancer and leukemia rise significantly in rural area. The results demonstrate the higher risks for lung cancer and leukemia with increased PM_2.5 exposure are more significant for female. This study also suggests that the carcinogenic effects of PM_2.5 have obvious sex and urban-rural differences.

Introduction

The threat to the public health caused by the exposure to fine particulate matter and air pollution has attracted more and more attentions from the public, governments and health organizations worldwide (Pope et al., 1995, Katsouyanni et al., 2001, Yim and Barrett, 2012). Recent studies show that air pollution has become a major global health risk factor (Gu et al., 2018, Forouzanfar et al., 2016, Cohen et al., 2004, Oliveri Conti et al., 2017), particulate matter with aerodynamic diameter less than 2.5 μm (PM_2.5) shortens life expectancy due to its health impact on morbidity and mortality (Mazzi et al., 2017, Dai et al., 2014, Samet et al., 2000), especially for lung cancer (Dehghani et al., 2017, MacNaughton et al., 2017) and cardiovascular diseases (Gurgueira et al., 2002, Zhang et al., 2018; Lee et al., 2014). Cohen et al. (2017) indicated that 4.2 million deaths in 2015 were caused by the exposure to PM_2.5, and more than 1.1 million deaths were in China. WHO issued a PM_2.5 guideline value of annual mean 10 μg/m³, and interim targets (IT) level 1, 2 and 3 of 35, 25 and 15 μg/m³. At IT-1 level, a 15% higher long-term mortality risk is reported relative to the guideline level (World Health Organization, 2006). However, IT-1 level is not achieved at most of the areas of China, and population-weighted mean of PM_2.5 concentration in Chinese cities were 61 μg/m³ at the year of 2013 (Huang et al., 2014, Zhang and Cao, 2015). Therefore, the health impact caused by PM_2.5 exposure has become an urgent issue in China (Hu and Jiang, 2014, Li and Gao, 2014, Pui et al., 2014, Liu et al., 2016, Liu et al., 2017).

The studies in the developed areas revealed that air pollution caused by PM_2.5 was a serious threat to human health in various aspects, i.e. its enhancement of cardiopulmonary diseases (Yoshinaga et al., 2018, Ali et al., 2017, Wong et al., 2008, Pope et al., 2009, Oh et al., 2011, Madrigano et al., 2013, Cesaroni et al., 2014), premature birth and low birth weight (Han et al., 2018, Brauer et al., 2008, Aguilera et al., 2009, Kloog et al., 2012), and systemic diseases (O'Neill et al., 2005, Dubowsky et al., 2006, Zeka et al., 2006, Pope et al., 2016). In China, many studies showed that short-term exposure of PM_2.5 was also associated with the rise of hospital emergency-room visits, cardio-respiratory diseases and mortality in city areas (Chen et al., 2018, Guo et al., 2009, Li et al., 2010, Chen et al., 2011, Huang et al., 2012, Wang et al., 2013, Yang et al., 2012, Lu. et al., 2015, Qiao et al., 2014); while cohort studies show that ambient particulate matter can increase the risks of total, cardiovascular and respiratory mortality (Dong et al., 2012, Zhou et al., 2014, Zhang et al., 2014, Chen et al., 2016, Guo et al., 2016). There are two main causes of these health hazards: one is that the fine particles in PM_2.5 are small enough to arrive a large part of human organs (including the respiratory system, the circulatory system, and the reproductive system), and another is that there are numerous kinds of hazardous substances in the PM_2.5, i.e. carcinogenic polycyclic aromatic hydrocarbons (PAHs), heavy metals (such as lead, mercury, chromium and cadmium), and pathogenic microorganisms (such as bacteria, viruses and fungi) (Lee et al., 2007, Cao et al., 2014, Zhai et al., 2014). PAHs in PM_2.5 are suspected to be a predisposing factor of breast cancer because of its disruption of BRCA-1 gene expression in estrogen receptor (Jeffy et al., 2002). Parikh et al. (Parikh and Wei, 2016) also conclude that PAHs in PM_2.5 have a significant impact on the increased incidence of female breast cancer in urban areas. Further, BRCA-1 has been confirmed to be associated with ovarian cancer (Chen and Parmigiani, 2007). Therefore, it could be deduced that cancer is a manifestation of the health effects of PM_2.5 in the regions with large population density, since PAHs can almost always be detected in PM_2.5 in these regions (Yang et al., 2011).

The PM_2.5 concentration in China has been at the elevated level for a long time and the main hazardous substances in PM_2.5 such as PAHs and heavy metals have also been identified to have impacts on increased risks for some common disease (Martin et al., 2017, Leontief and Ford, 1971, Contoyannis and Jones, 2004, Huang et al., 2011). Thus, a screen on all most common disease is conducted in this study to understand the health effects of PM_2.5 exposure in China. Moreover, we need to consider the geographical and sex factors, because there are spatial differences in the PM_2.5 concentration and compositions (mainly between urban and rural area) as well as sex differences in the sensitivity to toxic substances. To assess the health effects caused by PM_2.5 in China, firstly, we need to find out which cancers closely associated with high PM_2.5 concentration; and then, we need to evaluate sex- and area-specific increased risks of those cancers from high level PM_2.5 long-term exposure.

In this study, we first investigated the association between the ten most common cancers in China (identified by the National Central Cancer Registry of China) incidence and mortality with PM_2.5 concentration to find out which cancers are closely relative to PM_2.5 by using the time series data of yearly incidence and mortality of the ten most common cancers and the annual mean PM_2.5 concentration in China from 2000 to 2011. Secondly, we estimated the sex- and area-specific increased cancer incidence/mortality risks from long-term exposure to high PM_2.5 concentration by using spatiotemporal series data of the southeastern side of Hu line from 2006 to 2009. Finally, we studied the urban-rural and sex differences in the increased risks of incidence and mortality for the ten most common cancers from long-term exposure to high PM_2.5 concentration. The southeastern side of Hu line (Hu, 1990) was selected as our research region, because this part of China has larger population density and more developed social economic level, which mean the air pollution caused by PM_2.5 is very serious and the data collected are also more consistent with the actual situation.