Air pollution and cancer: Growing concern in low- and middle-income countries

Abhishek Shankar; Deepak Saini; Shubham Roy

doi:10.4103/aort.aort_31_22

REVIEW ARTICLE

Year : 2022 | Volume : 2 | Issue : 2 | Page : 66-70

Air pollution and cancer: Growing concern in low- and middle-income countries

Abhishek Shankar¹, Deepak Saini², Shubham Roy³
¹ Department of Radiation Oncology, All India Institute of Medical Sciences, Patna, Bihar, India
² Department of Materia Medica, Lal Bahadur Shastri Homoeopathic Medical College and Hospital, Prayagraj, India
³ Shining Stars Child Development Clinic, Delhi, India

Date of Submission	05-Nov-2022
Date of Acceptance	07-Nov-2022
Date of Web Publication	18-Nov-2022

Correspondence Address:
Dr. Abhishek Shankar
Department of Radiation Oncology, All India Institute of Medical Sciences, Patna, Bihar
India

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/aort.aort_31_22

Abstract

Air pollution has become a major health issue affecting billions of people and effects are more pronounced in low- and Middle-income countries (LMICs). Air pollution is a major contributor to the burden of disease worldwide. Most of the global population resides in places where air pollution levels exceed the WHO acceptable limits, caused by various industries, power generation, transportation, and domestic burning. More than 85% of total air pollution death are observed in LMICs. There are many carcinogens that are found in air pollution. There is substantial evidence from studies of humans and experimental animals as well as mechanistic evidence to support a causal link between outdoor (ambient) air pollution and cancer.

Keywords: Breast cancer, childhood cancer, low- and middle-income countries, lung cancer, pollution

How to cite this article:
Shankar A, Saini D, Roy S. Air pollution and cancer: Growing concern in low- and middle-income countries. Ann Oncol Res Ther 2022;2:66-70

How to cite this URL:
Shankar A, Saini D, Roy S. Air pollution and cancer: Growing concern in low- and middle-income countries. Ann Oncol Res Ther [serial online] 2022 [cited 2023 Mar 29];2:66-70. Available from: http://www.aort.info/text.asp?2022/2/2/66/361498

Introduction

There are 19.3 million cancer cases and 9.9 million deaths globally, of which 9.5 million cases and 5.8 million deaths are reported in Asia. Apart from tobacco, alcohol, infection, and obesity as major risk factors for cancer, air pollution has emerged as an important risk factor.^[1],[2] Globally, more than 6.5 million people die of air pollution and half of these deaths are attributed to outdoor air pollution.

Air pollution has become a major health issue affecting billions of people and its effects are more pronounced in low- and middle-income countries (LMICs). Air pollution is a major contributor to the burden of disease worldwide. Noncommunicable diseasess, including cancer, have been associated with different forms of air pollution, leading to the death of millions of people in LMICs. Most of the polluted places on earth belong to LMICs, with 63 out of 100 in India.^[3] Most of the global population resides in places where air pollution levels exceed the WHO acceptable limits, caused by various industries, power generation, transportation, and domestic burning. More than 85% of total air pollution death are observed in LMICs. India reports the death of near to 2 million people in India attributed to air pollution.^[4]

Air pollution is a combined result of various anthropogenic activities emitting pollutants such as particulate matter 2.5 and 10 (PM 2.5, PM 10), ozone, dioxide of sulfur and nitrogen, fossil fuel and biomass burning, and industrial emissions.^[5],[6] Many components of air pollution, which include benzene, engine exhaust, aromatic hydrocarbons, and involuntary smoking, have been categorized as carcinogenic and probably carcinogenic to humans (categorized in Group 1 and 2A) by International Agency for Research on Cancer (IARC).^[4]

There have been various studies that have proven the link between exposure to air pollution and the risk of different cancer types. Exposure to air pollution is linked with inflammation, immune and oxidative response, DNA damage, and alteration in gene expression and mutation.^[7],[8],[9]

Air Pollution and Carcinogenesis

Air pollutants have inhaled particles such as polycyclic aromatic hydrocarbons (PAH), volatile compounds, metals, and insoluble particles that get deposited in thoracic and alveolar regions. There is a nonlinear dose-response relationship between air pollution PAH and DNA adducts and it increases the chances of cancer. There is an enhanced frequency of chromosome aberrations and micronuclei in lymphocytes, along with changes in the expression of genes involved in DNA damage and repair, inflammation, immune and oxidative stress response, altered telomere length, and DNA methylation. These cascades of events turn on oncogenes and turn off tumor suppressor genes, leading to gene mutations and cancer.^[7] There are many carcinogens that are found in air pollution. Air pollution components and related risks of cancer types are described in [Table 1].

Table 1: Air pollution components and related risk of cancer type^[4]

Click here to view

Air Pollution and Lung Cancer

Lung cancer rank on the top among commonly diagnosed cancers at the advanced stage, along with poor survival, account nearly 20% of all cancer deaths.^[10] Nearly 62,000 lung cancer deaths are estimated to be due to air pollution. Air pollution is known, and probably carcinogens such as benzene, benzopyrene, butadiene, ozone, oxide of nitrogen, and sulfur are found in polluted air.^[11] Air pollution, commonly diagnosed as lung cancer, is associated with high fatality and low survival rates, with variations in incidence and mortality across the globe. Polynesia, Micronesia, part of Asia, and Europe have high age-standardized incidence rates of lung cancer in men, while parts of America and Europe have a high incidence of lung cancer among women.^[4],[6]

Although lung cancer is primarily associated with cigarette smoking, the incidence of lung cancer in nonsmokers is seeing upward trends. This increased incidence of lung cancer among nonsmokers is reported to be linked to air pollution. Exposure to smoke of burning of biomass and fossil fuel, engine exhaust, organic and inorganic chemical, second-hand smoke, along with exposure to carcinogens at the workplace have been reported to be linked with lung cancer.^[5],[6] Air pollution poses an elevated risk of lung cancer development in both smokers and nonsmokers.^[11] Studies have found a positive association in incidence and mortality of lung cancer and the concentration of PM 2.5 and PM 10.^{[12],[13],[14]}

Indoor air pollution also elevates the risk of lung cancer. Using biomass for cooking and heating release carcinogens such as PAHs, benzene, and formaldehyde, contributing to indoor air pollution along with the habit of smoking in a family member, increasing the risk of lung cancer in the household.^[5]

Lung cancer has been linked to long-term exposure to air pollution worldwide. In vitro experiments have reported genotoxicity and DNA damage in tissue by engine exhaust, PM matter even at low concentrations. Human biomarker data indicate genotoxicity as the principal mechanism, and studies on exposure to air pollution in various study settings and different age groups have shown genotoxicity by DNA and protein adducts, DNA break, and chromosomal aberration.^[4],[15] Damaged to lung tissue by air pollution is well established, but it also damages other organs and tissues of the body. Air pollution is majorly associated with lung cancer, but the risk of the development of other cancer has also been linked to air pollution. A positive correlation has been found between PM 2.5 and various cancer sites, including oral, urogenital, renal, and gastrointestinal.^[8],[16]

In Tehran, a high incidence of lung cancer was found in cities with a higher concentration of oxide of nitrogen, benzene, ethylbenzene, and xylene in air pollution indicating a positive linked between air pollution and lung cancer risk.^[17]

Air Pollution and Childhood Cancer

Exposure to air pollution among children is associated with adverse health outcomes affecting their overall development. High PM level was found to be associated with lower birth weight. The risk of cancer development in children increases with long exposure to air pollution during their outdoor activity and indoor air pollution.^{[18],[19],[20],[21]}

Studies suggest the role of air pollution in the development of neoplasm in children, especially hematological malignancies.^[21],[22] Exposure to second-hand smoke in the house due to the smoking habits of family members increase the risk of childhood cancer along with residing in the area with the unhygienic condition and polluted air.^[18] Air pollution due to engine exhaust and traffic was found to be associated with hematological cancer, retinoblastoma, and teratomas in childhood in California, USA, and Switzerland.^[23],[24] Finding suggests increased mortality in children with cancer exposed to PM 2.5.^[25]

Air Pollution and Urological Cancer

Exposure to air pollution, including cigarette smoking, chlorinated hydrocarbons, polycyclic amines, and aromatic amines, have associated with an increased risk of urological cancer, which includes prostate, renal, bladder, and testicular cancer. Studies have linked exposure to these carcinogens at the workplace in the development of these cancer types.^{[26],[27],[28],[29]}

Use of benzene-based dyes such as 2-naphthylamine and benzidine at the workplace are associated with increased risk of development of prostate, renal, and bladder cancer in industries such as rubber, paint, chemical, and metal.^{[30],[31],[32]} Hydrocarbons such as PAH emitted during biomass burning and industrial emission as categorized as carcinogens and posed an elevated risk of bladder and renal cancer development.^[4],[33] Second-hand smoke is one of the common causes of exposure to carcinogens, having elevated risk of bladder and renal cancer.^[34],[35] Air pollution containing oxide of nitrogen, generally a result of traffic, is associated with an elevated risk of prostate cancer.^[36]

There is limited evidence of the association of bladder cancer with PM as few studies found an association, and others did not.^{[6],[37],[38]} IARC report suggests exposure to air pollution, engine exhaust, and exposure in occupational settings to carcinogens may have an association with bladder cancer.^[6] Zare Sakhvidi et al., in the systemic review, reported link between air pollution and the risk of bladder and kidney cancer among the general public, with many gaps in studies conducted.^[26]

Air Pollution and Breast Cancer

Many Studies have linked the elevated risk of breast cancer and exposure to air pollution due to PM and oxides of nitrogen. Exposure to PAHs has been linked with breast cancer risk. Biomass burning is a major source of PAH in indoor air pollution, which has been found to be positively associated with an increased risk of breast cancer in long-term exposure. Exposure to ultrafine particles of size < 0.1 μm and NO₂ was found to be associated with an increased risk of postmenopausal breast cancer. The Sister Study among US women indicates a positive association between the risk of breast cancer and exposure to NO₂. Studies also suggest an association between second-hand smoke and breast cancer.^{[39],[40],[41],[42]}

California Teacher Study found higher concentrations of carcinogens such as benzenes, methylene chloride, CCl4, butadiene, and vinyl chloride, along with other mammary gland carcinogens. This study suggests a significant elevated risk of breast cancer on exposure to these carcinogens (P < 0.5). Exposure to higher concentrations of benzene was associated with an elevated risk of estrogen-receptor negative and progesterone-receptor negative subtype of breast cancer with a hazard ratio of 1.45.^[43]

Air Pollution and Other Types of Cancer

A strong association of risk of brain cancer was found with exposure to benzene, PM 10, and Ozone, with a hazard ratio in some exposure more than 3. Traffic-related air pollution responsible for increased concentration of oxides of nitrogen resultant of emission of engine exhaust was found associated with an elevated risk of cervical cancer and brain cancer.^[44],[45]

Air pollution may cause damage to the liver, increasing risk of the development of hepatocellular malignancy. Exposure to fine PM was found to be associated with an increased level of alanine aminotransferase (ALT), which is associated with liver cancer. Deng et al. suggest exposure to PM 2.5 after liver cancer diagnosis was associated with a lower survival period.^[46]

Toxic emission from engine exhaust, including benzene, butadiene, toluene, and ethyl benzene, was found to be associated with the risk of retinoblastoma.^[47] Dehghani et al. suggest exposure to PM and polluted air due to traffic are associated with an increased risk of ovarian cancer. Exposure to higher concentrations of PM2.5 and oxides of nitrogen also found to lower the survival period in ovarian cancer survival.^[48],[49]

Conclusion

Currently, there is substantial evidence from studies of humans and experimental animals as well as mechanistic evidence to support a causal link between outdoor (ambient) air pollution, especially PM in outdoor air, with lung cancer incidence and mortality. There is an increase in the percentage of lung cancer cases caused by risk factors other than cigarette smoking, and air pollution has emerged as an important risk factor. It has a risk for other cancer types, such as bladder cancer or breast cancer but in limited numbers. Outdoor air pollution may also be associated with poorer cancer survival, although further research is needed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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