UCS Science: How Many Cancers Did Airlines Really Cause?

There is a lot of confusion about how many excess cancer deaths will likely result from exposure to radiation at low-dose and low-dose-rates. As we see below, 79,000 and 40,000 are reasonable estimates of the number of excess cancers and cancer deaths attributable to the flying in the past decade.

I was inspired to investigate this subject after reading an article in the socialist magazine Monthly Review by Lisbeth Gronlund, senior scientist at the Union of Concerned Scientists (UCS), which was entitled "How Many Cancers Did Chernobyl Really Cause?" In this article, she uses the "best possible risk estimates for exposure to low-dose, low-LET radiation in human subjects," which was proposed by the BEIR (Biological Effects of Ionizing Radiation) Committee of the National Academy of Sciences to estimate the number of additional cancers and cancer deaths (above the number of "naturally occurring" cancers) that could be attributed to the Chernobyl accident. It is interesting that Dr. Gronlund's numbers are strikingly different from those put forward by the United Nation's Chernobyl Forum (4000 to 9000 deaths), which used a similar methodology.

Therefore, I decided to apply Dr. Gronlund's methodology to something more familiar to the average person: commercial aviation. Each airline flight exposes its crew and passengers to an excess risk of cancer in the form of cosmic radiation. As the US EPA explains, exposure to cosmic radiation depends on altitude, latitude, and solar activity, but the EPA estimates that "a typical cross-country flight in a commercial airplane" results in "2 to 5 millirem (mrem)" of dose from radiation.

The statistics from the US Bureau of Transportation Statistics indicate that over 7 billion airline passengers (international and domestic) flew in the US between January 2001 and January 2011. Thus, if we assume a fairly low average value of 3 millirem per passenger, then aviation has resulted in a collective dose of 210,000 passenger-Sv over the past decade.

This is quite a large number already, but Dr. Gronlund did not consider the radiation exposure within just one country. She provided an estimate for the entire world. So we should follow suit.

The US aviation market comprises somewhere between 25 to 30 percent of the entire world's airline passengers (e.g., in 2009, passengers in the US comprised roughly 28% of the airline passengers worldwide, according to IATA statistics). Thus, if we conservatively assume that US passengers comprised 30% of the passengers worldwide during the past decade, then worldwide, the collective dose due to commercial aviation is 700,000 passenger-Sv.

Using Dr. Gronlund's methodology (which was taken from the BEIR VII report), we should assume that "the expected incidence and mortality of solid cancers and leukemia are 0.1135 cancer cases and 0.057 cancer deaths per Sv." Thus, because of radiation exposure due to the airline industry, the expected number of cancer cases is 79,000, of which some 40,000 should result in death.

Note however that, because exposure only increases the probability of developing cancer, we should keep in mind that no given cancer can be attributed to flying. Moreover, because these additional cancers will be distributed among hundreds of millions of people, it is practically impossible to discern them among all the other cancer cases. (About 42% of the general population have cancer at some point in their lives, and about 20% of the population die because of cancer or complications that result from cancer.)

It is somewhat illustrative to compare these numbers to the numbers presented by Dr. Gronlund for the Chernobyl accident: 68,000 cancer cases with 34,000 deaths. Given these numbers, one can scientifically conclude that the airline industry is far more dangerous -- in terms of deaths due to low-dose exposure to radiation -- than old, Soviet-era nuclear reactors.

In light of these numbers, I expect that the UCS will be setting itself up as an "aviation watchdog" any day now.