In the past 20 years, China has experienced rapid industrialization, urbanization and urban transport development, industrial emissions, urban construction and vehicle exhaust caused serious air pollution. In recent years, the studies on air pollution increased, and found that PM2.5 exposure associated with all-cause, lung cancer, and cardiopulmonary mortality. Fine particulate air pollution was associated with approximately a 4%, 6%, and 8% increased risk of all-cause, cardiopulmonary, and lung cancer mortality, respectively, the study areas involved Beijing, Shanghai, Guangzhou, Taiyuan, Shenyang and other large cities in China. Compared with developed countries, the type of air pollution in Chinese cities changed from traditional soot type to hybrid soot/vehicle exhaust type, which made the source of PM more complicated and diversified. As PM2.5 level increased, health effects and diseases burden had more attention. An increase of 10 μg/m3 of PM2.5 was associated with 12% increases in the risk of mortality from lung cancer, and the concentration response curve suggested a nonlinear relationship between PM2.5 and mortality in China, where the exposure is higher than exposure in developed countries. Therefore, research on the association between PM2.5 and lung cancer is very important and necessary, this is helpful to understand the impact of PM2.5 on lung cancer in China and formulate targeted measures.
In our study, from 1990 to 2017, for the lung cancer case attributable to PM2.5, the number of APE was 1.5 times that of HPE. In mortality rate, the ASMRs in APE increased significantly between 1990 and 2017, while that in the HPE decreased significantly, after 2006, the ASMRs in APE were significant higher than those in HPE. Both in APE and HPE, the ASMRs in male were higher than those in female, and after 2004, the ASMRs of APE in male were highest. At the same time, we also analyzed the other three indicators of disease burden, and found the similar changes. In the APCM, net drift represented the average annual percentage change of the indicators over the study period. For all the indicators of burden disease, the overall net drift were above zero in APE, while below zero in HPE. This suggested that the burden of lung cancer had shown a significant upward trend in APE, and a significant downward trend in HPE from 1990 to 2017. With the urbanization of China, it had gradually shifted from household air pollution to ambient air pollution, this is consistent with our results. Previous studies in China also showed a significant effect of outdoor PM2.5 exposure on lung-cancer mortality[20, 21].We further analyzed the local drifts of four indicators in each age group, which represented the average annual percentage changes in indicators over time across different age groups. We found that local drift values in APE and HPE increased by age groups, but the local drifts values in APE were above zero after 45-49 age group, all the local drifts values in HPE were below zero. In the longitudinal age curves, the indicators of lung cancer burden for younger in APE or HPE were in a low level, and significantly increased from 45-49 age group to 90-94 age group. So were the results of the male and female. It suggested that the Lung cancer burden attributable to APE or HPE for younger was low, and for older, the burden was high. It may be mainly related to immune system decline in older people. In China, policy action to reduce PM2.5 concentrations could have a large potential to reduce lung cancer cases, especially in outdoor and elders.
In our results, period effects showed an opposite effect on four indicators of disease burden for APE and HPE; an elevated trend for APE, but a declined trend for HPE. China has always attached great importance to indoor and outdoor air pollution. Since the early 1980s, China introduced more than 180 million improved stoves to improve household energy use. All introduced stoves had chimneys and some had manual or electric blowers to promote more efficient combustion for reducing the concentration of indoor pollutants.Since the 20th century, with the serious ambient air pollution in China, the government had implemented emission-control policies that have been continuously tightened since 2005, and the overarching goal was to cut down the total emissions of air pollutants. In 2013, the government issued the “Air Pollution Prevention and Control Action Plan”, which was the most stringent policy on air pollution in Chinese history . In 2018, the government also issued the three-year action plan to win the blue sky defense war, proposing to effectively promote clean heating in the northern region, accelerate the upgrading and transformation of "coal to electricity" in rural area, carry out comprehensive renovation of coal-fired boilers, and strengthen the elimination of small coal-fired boilers. The related studies also found that the decrease in household solid-fuel consumption was mostly responsible for the reduced indoor PM2.5 pollution in China, and the whole society solid-fuel consumption, which mainly came from power, industrial, and transportation sources was responsible for the ambient PM2.5 pollution .In the cohort RRs, compared to the 1945 reference cohort, the related indicators of lung cancer in APE indicated an upward trend before 1965, and after from 1970 to 1990, the related indicators of lung cancer fluctuated, while the related indicators of lung cancer in HPE indicated a downward trend. The results were also similar to those of local drifts. The cohort RRs also indicated that lung cancer burden of younger generations in APE was higher than that in HPE. Compared with adults, due to small airway size, immature detoxification and metabolic system, children are more sensitive to ambient PM2.5 exposure.In order to prevent children from being affected by PM2.5 for a long time, we should pay attention to protection for them. For male, the APE levels of the related indicators exceed the HPE levels at earlier age (45-49). However, for female, the APE levels of the related indicators exceed the HPE levels at earlier age (55-59). The results showed that PM2.5 exposure had more harmful in male. Both the period and cohort RRs also confirmed that China had changed from household air pollution to ambient air pollution. Meanwhile, our study found that the changes of DALY rate was mainly dominated by YLL rate, due to the low 5-year survival rate of lung cancer .
Our study was the first to analyze the effects of age-period-cohort on the temporal trends of lung cancer mortality attributable to PM2.5 exposure and focus on a comprehensive comparison between APE and HPE. GBD 2017 could provide sufficient data, which contained age- and sex-specific all-cause and cause-specific indicators, to reduce the possibility of misclassification of outcomes. Our study found that the effect of APE on the related indicators of lung cancer burden were higher than those of HPE, and PM2.5 exposure had more harmful in male and older people. WHO recommended that public policies and interventions can improve air quality with consequently wide-ranging health benefits. Our study contributed to the importance of reducing PM2.5 exposure in the population. Based on the above findings, China should try our best to implement public policies and interventions to reduce the effect of PM2.5 exposure on lung cancer burden in the next few years, to achieve the goal of reducing the burden of lung cancer.