Air pollution is responsible for 8 million deaths a year globally, which is as many as tobacco. And air pollution isn’t just causing lung cancer, it may cause other cancers too—including neck cancer and mesothelioma—and diseases such as cardiovascular disease, strokes, heart attacks, type 2 diabetes, and neurodegenerative disease. We urgently need public health measures to lower pollution levels.
In the lab, we’ve been studying how air pollution causes lung cancer. Recently, we’ve shown a close association between rising air pollution levels—specifically 2.5 micrometers particles (known as PM 2.5) from diesel exhaust and coal-fired power stations—and increasing incidence of lung cancer in patients who’ve never smoked. We were interested in understanding what the underlying mechanism is for this process. It’s become apparent that it’s very different from the way we normally understood how carcinogens—chemicals in the environment that cause cancer—usually act. Traditionally, we thought that chemicals in the environment caused cancer by mutating DNA. It turns out the air pollution doesn’t mutate DNA. Instead, it creates an inflammatory response in a white cell called a macrophage. This cell releases an inflammatory mediator that can turn certain cells (those with a particular cancer-causing mutation) in the breathing apparatus of the lung into a cancer stem cell. In other words, the cancer-causing mutation and the air pollution work together in the right cell at the wrong time to initiate a cancer.
How does air pollution cause so many different clinical diseases? We don’t yet know the answer to that. What we do know is that the macrophage takes up air pollutants. These particular particles are so large that they can’t be digested by the cell. Instead, they remain in the cell until it dies. Because of this, throughout its life, the cell releases a sort of SOS signal—inflammatory mediators that communicate with other cells. This causes chronic long-term inflammation, which we speculate may be the central cause for the underlying pathologies associated with pollution, leading to damage to the pancreas, for example, or type-two diabetes, or damage to blood vessels, which results in strokes and heart attacks.
In London, authorities are increasing stringent mechanisms to control and curb air pollution—the yellow Ultra Low Emissions Zone, for example, is being extended. There’s also an increasing move toward electric cars. That in itself won’t eliminate the problem, however, because the air pollution doesn’t just come from diesel and petrol exhausts. It also comes from car tires and brake dust. For instance, the levels of PM 2.5 particulates on the London Underground, which runs on electric trains, are particularly high. Also, in the winter, wood burners contribute to much higher levels of PM 2.5 particulates.
It’s estimated that over 90 percent of the world’s population lives in areas where the concentrations of PM 2.5 air pollutants are higher than the WHO recommended level of 5 micrograms per meter cubed. We need to make sure that individuals are aware of the risks to them by being exposed to high levels of pollution in urban areas. We need to walk more and we need to cycle more. And we need to redouble our efforts to try to control air pollution, limit exhaust fumes, and find cleaner fuels.
This article appears in the July/August 2023 edition of WIRED UK magazine.
