Pollution and Lung Cancer
Lung cancer is the leading cause of cancer deaths in both men and women causing more than 1.8 million deaths a year worldwide. Globally, the five-year net survival for lung cancer is 10% to 20%. The association between outdoor air pollution and lung cancer has been suspected for the past few decades, however, recent decades, many studies have explored the correlation between outdoor air pollution and the alarming rise in lung cancer cases. The process of developing cancer, or carcinogenesis, involves the inhalation of pollutants leading to oxidative stress and changes in the human epithelial cells lining the respiratory tract.
Significant associations between long-term exposure to PM2.5 air pollution has been indicated to be the trigger for lung cancers. PM2.5 refers to particulate matter, the mass of particles smaller than 2.5 µm. To put it into perspective, PM2.5 is approximately 1/30th the width of a human hair. PM is the mixture of solid and liquid particles consisting of diverse chemical compounds that include polycyclic aromatic hydrocarbons, nitrosamines, and other related compounds. The source of PMs could arise from construction, industry, transportation, and wildfires. They vary in physical size and will exhibit different aerodynamic properties. The International Agency for Research on Cancer (IARC) classified PM2.5 in outdoor air pollution as carcinogenic to humans (IARC group 1) and as a severe threat to contributing the escalating lung cancer worldwide. It has been found that a reduction in these PM2.5 air pollution concentrations will result in substantial reduction of lung cancer cases.
Other than air pollution, other forms of pollution are significant causes increasing the risk for lung cancers. These include active and passive smoking, second hand smoke, household air pollution from use of solid fuels for cooking, and occupational exposures to pollutants. The Global Burden of Disease 2019 study estimated that the percent of the global lung cancer deaths attributable to such potentially modifiable risk factors was 62% for smoking, 15% for PM2.5 in outdoor air, 5.8% for secondhand smoke, 4% for household air pollution with occupational exposures and possibly dietary factors (smoked and charred foods) contributing the remainder.
Gaseous pollutants that are potential health hazards include ground-level ozone (O3), volatile organic compounds (VOCs), sulfur dioxide, and nitrogen oxides (NOx) consisting of nitrogen oxide and nitrogen dioxide (NO2). Ground-level O3 is a major component of photochemical smog and is mainly formed by chemical reactions of NOx with VOCs particularly at warm temperatures. VOCs are compounds that have a high vapor pressure and low water solubility. They are emitted by different industrial sources: manufacture of paints, synthetic plastic materials, and pharmaceuticals and indoor sources, such as cooking methods. Sulfur dioxide and NOx are mainly derived from the combustion of fossil fuels, mainly from automobile exhaust. Epidemiologic and toxicology studies suggest that exposure to these gaseous pollutants can lead to respiratory symptoms and diseases including lung cancer.
Understanding the pivotal role of pollutants in the rise of lung cancer cases underscores the urgency for action within the healthcare community. Advocacy efforts must target both public health and policy levels to reduce the harmful effects of pollution. This means a collective commitment to addressing modifiable risk factors, enhancing air quality, and promoting healthier environments to curb the devastating impact of pollution on lung health including pollution-induced lung cancers.