Introduction:
Lung cancer has transitioned from a rare to a pressing global health concern. It now ranks the highest in cancer-related mortality worldwide. The causative factors behind this disease have become increasingly intricate, driven by the expansion of industrialization and environmental pollution. There has been a surge in lung cancer cases among non-smokers, attributed to their exposure to various hazardous substances in both their environments and workplaces.
Mutations targeting specific genes are more prevalent in non-smoking lung cancer cases compared to smokers. It is imperative to identify high-risk groups among non-smokers, factoring in environmental and occupational determinants as crucial risk factors. Efforts to prevent lung cancer related to environmental and occupational factors should be intensified through dedicated research initiatives to identify areas necessary for intervention.
What Is the Prevalence of Lung Cancer Occurrence?
Lung cancer stands as a major contributor to illness and death globally, with 2.094 million cases and 1.8 million fatalities annually. It has maintained its status as the most prevalent cancer worldwide for several decades, with incidence rates rising notably in developing nations. Unfortunately, lung cancer often remains undetectable until it reaches an advanced stage, with over 75 percent of cases diagnosed at such late stages.
Smoking accounts for 80 percent of lung cancer cases, while outdoor pollution and solid fuel usage contribute significantly to lung cancer-related deaths. Household air pollution has also been linked to increased lung cancer risk. Lung cancer stems from a complex interplay of genetic, environmental, and occupational factors, with preventable risk factors varying widely across countries. Various research has linked lung cancer occurrence to active and passive smoking, occupational exposures, and indoor and outdoor air pollution.
Environmental factors encompass physical and chemical exposures, including radiation, asbestos, metals, and industrial pollutants. In contrast, occupational exposures are strongly associated with lung cancer, often stemming from physical, chemical, and biological agents present in the work environment. Occupational health risks are closely tied to these exposures, with lung cancer being one of the most frequently cited outcomes.
What Are the Environmental Risk Factors Related to Lung Cancer?
Environmental risk factors for lung cancer are as follows:
1. Chemicals: Exposure to industrial and manufacturing chemicals. Also, harmful pesticides, like aflatoxin, are strongly linked to cancer development in both living and working environments. Agricultural and public health workers face significant exposure to these hazardous substances during various tasks such as handling, dilution, and application. While some studies have linked occupational pesticide usage to lung cancer, not all cases show this association.
The collective body of evidence, including various studies, supports the notion that pesticides play a significant role in lung cancer development. Additionally, pesticide groups such as chlorophenols (CPs), dioxin compounds, and related phenoxyacetic acids (PAs) have been identified as carcinogenic to the lungs. Despite various reports of lung cancer in workplace settings, meta-analyses have shown mixed results regarding the association between pesticide exposure duration, intensity, cumulative exposure, and lung cancer mortality in both smokers and nonsmokers.
2. Outdoor Pollution: Numerous air pollutants stem from mining, industrial activities, municipal waste sites, and inadequate domestic incineration. Motor vehicles, particularly in urban areas, significantly contribute to air pollution, with some emissions classified as carcinogenic or potentially carcinogenic. Urban dwellers face a higher risk of lung cancer compared to those in rural areas, attributed in part to air pollution. In developed countries, agricultural emissions are the primary contributors to particulate matter. Projections suggest outdoor air pollution’s impact on premature mortality could double. The risk of lung cancer rises with increased levels of particulate matter 2.5 in the atmosphere.
3. Indoor Pollution: Household combustion of coal for heating or cooking purposes emits particulate matter and gasses containing carcinogenic substances like benzene, carbon monoxide, formaldehyde, and polycyclic aromatic hydrocarbons (PAHs). This indoor air pollution is classified as carcinogenic to humans. Extensive evidence supports the carcinogenicity of household coal combustion in humans. Increased levels of indoor smoke are associated with a higher risk of lung cancer. Additionally, research suggests that individuals carrying the T-genotype of HID-1alpha rs2057482 are more susceptible to small-cell carcinoma.
4. Smoking: Tobacco and second-hand smoke are established human carcinogens. Tobacco smoking is a known cause of lung cancer, with the risk of death from lung cancer increasing with longer smoking duration and higher cigarette consumption. There is evidence supporting the link between environmental tobacco smoke (ETS), commonly known as secondhand smoke, and lung cancer.
Numerous epidemiological studies, including case-control investigations, have shown an increased risk of lung cancer associated with prolonged exposure to secondhand smoke, whether from traditional tobacco or electronic cigarettes. Childhood exposure to environmental tobacco smoke is particularly strongly linked to lung cancer risk, as indicated by one study.
5. Asbestos: Asbestos, naturally occurring fibrous silicates used for acoustical and thermal insulation, are divided into chrysolite and amphibole groups, including amosite, crocidolite, anthophyllite, actinolite, and tremolite fibers. All types of asbestos are carcinogenic. Amphiboles demonstrate stronger biological effects on the pleura and peritoneum compared to chrysolite. While many epidemiological studies focus on asbestos-exposed workers, fewer examine household exposures to asbestos.
Household exposure typically affects immediate family members of asbestos workers through dust brought home on clothing or from household sources like degradation, installation, removal, or repair of asbestos-containing products. Residential exposure stems from outdoor pollution related to asbestos mining or manufacturing nearby and natural exposure from erosion of asbestos or asbestiform rocks.
Non-occupational asbestos exposure assessment is challenging due to generally low levels and poorly defined duration, frequency, and type of exposure. Heavy asbestos exposure is associated with increased lung cancer risk, with long and intermediate fibers being more carcinogenic than short fibers. Despite the health risks, asbestos use continues in many regions.
6. Metals and Others: Arsenic, present in forms like arsenite and arsenate, is an environmental and occupational lung carcinogen commonly encountered in lead, gold, copper ore mines, and smelters. Inhalation of arsenic increases lung cancer risk, according to the International Agency for Research on Cancer (IARC). Beryllium compounds are classified as probable human carcinogens by both the Environmental Protection Agency (EPA) and IARC, with sufficient evidence linking them to lung cancer. Hexavalent chromium exposure is significantly associated with an increased risk of lung cancer, with cumulative exposure further amplifying this risk. While the EPA has not evaluated nickel compounds as potential carcinogens as a class, occupational exposure to nickel compounds is linked to lung cancer. In polyvinyl chloride workers, exposure to PVC dust and vinyl chloride is associated with a significant increase in lung cancer risk, although general population exposure levels are typically low.
Ionizing radiation, including natural sources like radon, is a known risk factor for lung cancer. Residential radon exposure has been directly linked to increased lung cancer risk, supported by findings from occupational studies on radon-exposed miners. The relationship between uranium contamination and lung cancer risk is complex, with limited studies on the dose-effect relationship and challenges in distinguishing between radiotoxicity, chemical toxicity, and the radiotoxicity of its progeny.
Conclusion:
Environmental exposures play a significant role in lung cancer risk. Substances such as asbestos, arsenic, tobacco, and vinyl chloride, along with ionizing radiation sources like radon, contribute to the development of lung cancer. Occupational exposures in industries such as mining, manufacturing, agriculture, and household and residential exposure to carcinogens further elevate this risk. Understanding and mitigating these exposures are crucial steps in reducing the burden of lung cancer and improving public health outcomes.
