Introduction: Coal is burned by electric utilities, about 10% remains as ash. The heavy ash settles, while the light coal fly ash (CFA) condenses and accumulates in the flue gases. In India and China CFA is usually allowed to exit smokestacks, but in Western nations it is trapped and sequestered for public health reasons. Epidemiological evidence indicates that aerosolized particulate pollution in the size range ≤ 2.5 µm is associated with numerous risks to health including, but not limited to lung cancer.

Aim: Coal fly ash (CFA) is a major contributor to ambient air pollution in China and India, but it is trapped and sequestered in Western nations. Members of the public chronically exposed to aerosolized CFA are likely to have an increased incidence of respiratory disease, including lung cancer. Our objective is to review the multiple carcinogenic constituents of aerosolized coal fly ash in connection with their potentiality to cause lung cancer.

Methods: We review the interdisciplinary scientific and medical literature.

Results: CFA contains a variety of potentially carcinogenic substances including aluminosilicates, an iron oxide-containing magnetic fraction, several toxic trace elements, nanoparticles, and alpha-particle-emitting radionuclides.  Silica, arsenic, cadmium, and hexavalent chromium are found in CFA and all have been associated with increased lung cancer risk.  Radical generation catalyzed by transition metals associated with the particulate matter in CFA can result in a cascade of cell signaling, transcription factor activation, and mediator release. Ferric iron in the aluminum-silicate glass phase of CFA is a source of bioavailable iron. There is emerging evidence that reactive iron induces cancer stem cells and aggressive phenotypes in lung cancer. The potential pulmonary toxicity and carcinogenicity of aerosolized CFA is suggested by studies of asbestos, a fibrous silicate that also contains iron oxide. CFA contains an abundance of ultrafine particles and nanoparticles, including magnetite (Fe3O4). These tiny particles are toxic to lung cells, capable of producing oxidative stress, cytotoxicity, and genotoxicity. Radioactive elements are concentrated in CFA. CFA can settle deep in the lungs where its alpha-particle-emitting radionuclides pose significant risk factors for lung cancer.

Conclusion: Considering the well-known and manifold toxicities of CFA, the public should be made aware of the potential risks for lung cancer and severe respiratory disease posed by aerosolized CFA including its use in climate alteration activities. CFA contains a plethora of potentially carcinogenic agents likely to have cumulative additive and/or synergistic interactions with long-term exposure. The CFA industry can be diligent about minimizing the likelihood of CFA aerosolization for sake of workers and those living in the proximity of CFA dumps. Jet-spraying of CFA into the regions where clouds form represents a potential global and previously unrecognized long-term risk factor for respiratory disease and lung cancer, especially in vulnerable populations.

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