There is no safe level of air pollution.
That’s the finding of a 12-year study published in the New England Journal of Medicine looking at health records from nearly 61 million people on Medicare combined with a databank of pollution readings.
For every increase of 10 micrograms of a key type of pollutant known as PM2.5, death rates among seniors rose 7.3%. That’s the equivalent of 120,000 deaths, said Qian Di, a doctoral student at the Harvard T.H. Chan School of Public Health and one of the study authors. The effects were the strongest for low-income Americans and people of color.
To put that figure into perspective, the World Health Organization has recommended a guideline level of 20 micrograms worldwide, which is a massive reduction from many countries that regularly exceed levels of 70 micrograms or more. Over the course of the study, the average levels the researchers observed ranged from about 6 to 16 micrograms.
Even in years when the concentrations of that pollutant in an area were low and approached levels considered “safe,” the researchers saw a connection between exposure and death rates, Di and his colleagues wrote in their study.
“It is clear from this study that there is not really a safe level of air pollution,” said Brian Christman, who serves as vice chair of the department of medicine at Vanderbilt University Medical Center and was not directly involved in the research.
For years, researchers have known about the close ties between exposure to high levels of pollutants and an uptick in death rates. They’ve also known that when regions manage to slash pollution levels, fewer people die.
What they were less clear about, however, was how being exposed even to low levels of the particulates could have such drastic consequences over the long term.
“When you have a large study that shows that the current level of air pollution is toxic – I hope that’s something we can do something about,” Francesca Dominici, a professor of biostatistics at Harvard and another author on the study, told The New York Times.
In addition to studying the well-known pollutant PM2.5, which is known to be harmful because of its ability to penetrate and lodge deep inside the lungs, the researchers also looked at ozone concentrations, and found a similarly worrisome scenario. For every 10 part-per-billion rise in ozone concentration, the mortality rate among the elderly rose by 1.1%, which amounts to roughly 19,000 deaths.
To arrive at their conclusions, they drew from satellite and meteorological data, plus data gathered from close to 4,000 Environmental Protection Agency monitoring stations. Then, they followed their 60 million Medicare recipients and recorded nearly 23 million deaths over roughly a decade.
Average levels of the first pollutant – PM2.5 – ranged from 6 to 16 micrograms over the course of the study, while ozone concentrations ranged from about 36 to 56.
Given the stark findings they observed, the researchers concluded that current US policies are not strict enough to prevent pollution-related deaths. To make a bigger impact, policy makers need to further slash pollution.
“The data indicates that additional effort … would save lives,” said Christman.