Formaldehyde causes more cancer than any other toxic chemical in the air.
It’s emitted from cars, trucks, planes, industrial facilities and many other sources. It’s also formed in the atmosphere when other chemicals combine in the presence of sunlight. Even if you don’t live in a high-traffic or industrial area, the geography and climate of your area could increase your cancer risk from formaldehyde because of this so-called “secondary formation.”
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About Formaldehyde Cancer Risk and This Database
ProPublica analyzed formaldehyde concentrations modeled by the Environmental Protection Agency and released through the agency’s AirToxScreen database and found that, in every populated U.S. census block, formaldehyde in the air poses an incremental lifetime cancer risk greater than one incidence of cancer in every million people, the limit that the agency aims to stay below for toxic air pollutants. Some 320 million people live in areas where that risk is at least 10 times higher. In other areas, the cancer risk from formaldehyde is even worse.
We’re making that data searchable in this interactive database.
AirToxScreen works by modeling a year’s worth of emissions (in this case, emissions in 2020) along with weather data and natural sources to approximate what the concentrations of different chemicals are in each census block. Although emissions were likely lower than usual in 2020 because of the COVID-19 shutdowns, we used 2020 data because it’s the most recent and most detailed available. (Prior to 2020, AirToxScreen provided results by census tract, each of which contains many blocks.) The data does not include the risk from formaldehyde in indoor air, which studies show is much higher than outdoors.
The data includes two categories of modeled chemical concentrations: ambient concentrations and exposure concentrations. Ambient concentrations are the agency’s estimates for the amount of a chemical in the outdoor air in the tract, whereas exposure concentrations are the agency’s estimates for how much of a chemical a human in the area realistically inhales.
We calculated incremental lifetime cancer risks by multiplying AirToxScreen’s exposure concentrations of formaldehyde by a figure called an Inhalation Unit Risk, which is the EPA’s best scientific estimate of how carcinogenic a chemical is. We used the new Inhalation Unit Risk for formaldehyde, which was finalized in August.
However, even the new IUR is an underestimate. It is based solely on the risk of nasopharyngeal cancer, which is rare. It does not reflect the risk of myeloid leukemia, a blood cancer that the EPA acknowledged in August is also caused by formaldehyde. The agency calculated the risk of developing myeloid leukemia but ultimately decided not to use its estimate because it did not have confidence assigning a precise number to the amount of the chemical required to trigger a case of the disease. If the EPA had included the number it calculated, it would have shown that the cancer risk from formaldehyde is roughly four-fold higher. Since our analysis is based on the EPA’s IUR, this database also underestimates cancer risk from formaldehyde.
Certain census blocks contain caveats that the EPA published after the release of AirToxScreen. The EPA would not provide guidance on how to adjust our results to account for these caveats and said it is recalculating the cancer risk in these areas. Some blocks appear to have very high risks because wildfires occurred in or near them in 2020 and emissions in 2020 were used to calculate lifetime risks. These blocks may not necessarily have risks as high as indicated, but according to the EPA, “climate change has already led to an increase in wildfire season length, wildfire frequency and burned area. This could affect future risks.” Blocks with exceedingly high risks due to wildfire have EPA caveat notes on their results pages.
Sources: EPA AirToxScreen 2020, EPA Integrated Risk Information System
Jeff Frankl contributed design and development.