The Impact of PM2.5 and Lead Aviation Pollution on Declining Fertility Rates
"Our findings suggest that even minimal exposure to PM2.5 and lead from airplane emissions can have significant health impacts, evidenced by lower birth weights and reduced fertility rates. Combined with the growing body of evidence on the high cost of air pollution, this paper underscores the need for policies to mitigate aviation-related pollution." (Pg. 39)
Airlines, Pollution and Fertility by Xinming Du and Charles Taylor, first published on March 14, 2024, was updated in July 2024.
Most airport studies to date have focused on emission levels of aircraft in proximity to airports. This article, by contrast, looks at emissions released during the cruise phase of flight. As explained by the authors, aviation accounts for 4% of global warming when CO2, nitrogen oxides and water vapors are factored in. "Much of this pollution is emitted during the cruising phase, which accounts for over two-thirds of fuel consumption, as opposed to the takeoff and landing phases. But unlike takeoff and landing, which occur near population centers, cruising emissions are largely unregulated and unmonitored. We show that air pollution is persistently elevated among populations beneath overhead flight routes across the world." (Pg. 2-3)
The authors also point out that, "While some particulate matter from cruising aircraft will be disbursed broadly via atmospheric currents and weather conditions, on average, much will land in the vicinity directly beneath the flight path, especially due to wet deposition (i.e., binding to rain and falling to the ground). (Pg. 2 - footnote)
Excerpts from the paper appear below.
Abstract
This paper demonstrates a large but little-known negative externality of the aviation industry. Using a new instrument for air pollution from aircraft cruising, we show that pollution is higher beneath overhead flight routes in ways uncorrelated with local pollution. We combine this cross-sectional variation with the launch of new flight routes to establish several findings. First, aircraft cruising persistently elevates local PM2.5 by 1-3 μg/m3. Second, PM2.5 has adverse impacts on infant health via lower birth weights, including in 44 developing countries where data are scarce. Third, we leverage the fact that propeller planes still use leaded fuel to show that 1 ng/m3 ambient lead reduces fertility rates by 0.19%. Fourth, we generalize this in relation to the historical phase-out of leaded fuel in vehicles, which our analysis suggests added over 2 million people per year to the global population—making it among the most material public health interventions. We provide this global gridded airline data product for use in future research.
On the Global Decline in Fertility Rates
"Over the past 250 years since the Industrial Revolution, fertility, together with economic outputs, has increased rapidly worldwide. However, in the past 50 years, the global fertility rate has halved. In 2000, the world's fertility rate was 2.7 births per woman, comfortably above the "replacement rate" of 2.1, at which a population remains stable. Today it has decreased to 2.3 and continues to decline, with over half of the global population residing in regions with fertility rates below replacement level." (Pg. 7)
"Environmental factors such as pollution are increasingly recognized as potential contributors to fertility patterns." (Pg. 8)
PM2.5
We find that an increase in PM2.5 by 1μg/m3 (2.3% over the DHS sample mean) increases the incidence of low birth weight by one percentage point, which is 40% above the baseline incidence of 2.3%. We confirm that this effect is not driven by potential confounders such as noise pollution from overhead cruising aircraft. (Pg. 4)
"How big is the air pollution impact from the launch of a new airline route? Over each year between 2000 and 2014, a total of 5,497 new airline routes (origin-destination pairs) were established...The increase due to each new airline [route] is equivalent to 0.9% of the average PM2.5 levels in areas located beneath the flight path. Our findings underscore the substantial externality associated with airline operations." (Pg. 26)
"Our results demonstrate a robust link between overhead airline routes and local air pollution that extends beyond areas near airports." (Pg. 26)
Lead
Given that ambient lead eventually falls to the ground through deposition, we assess whether propeller planes also contribute to increased soil lead levels...our findings...suggest the number of leaded routes operated by propeller planes results in high soil lead levels. Specifically, for every increase of 1,000 in leaded route count, the soil lead collected by the surrounding laboratory rises by 473.9 wt%. The consistency between air and soil results concludes that emissions from propeller planes have a substantial and statistically significant impact on environmental lead levels. (Pg. 30)
...we find female respondents are less likely to give birth in areas with a high intensity of propeller planes...an increase in leaded route intensity from 0 to 1 causes a 0.07 decrease in the probability of giving birth. (Pg. 30)
We also study the fertility response in the US... Leaded airline routes are associated with decreased birth rates, while unleaded routes show no effect. Specifically, a 1-unit increase in propeller airline intensity leads to a decline in the birth rate by 2.2 percentage points, representing a 3.2% decrease relative to the mean birth rate.
In terms of fertility, the Flint water crisis, which was characterized by lead exposure, reduced the number of births by 7.5 per 1,000 women, constituting 12% of the average fertility rate (Grossman and Slusky, 2019). The elimination of lead from gasoline has been linked to increased fertility in the US: the observed reduction in airborne lead corresponded with four additional births per 1,000 women, accounting for 6% of the mean fertility rate (Clay et al., 2021). Furthermore, lead exposure affects birth outcomes. The Flint water crisis is associated with a reduction in birth weights by 32 to 49 grams (Abouk and Adams, 2018; Wang et al., 2021). Airborne lead pollution, leading to the relocation of lead battery recycling from the US to Mexico, resulted in a 24-gram decrease in birth weight for infants born within two miles of Mexican recycling plants (Tanaka et al., 2022). (Pg. 9-10)
Our analysis focuses on the detect rate of high blood lead, defined as the number or proportion of cases with confirmed blood lead levels exceeding 10μg/dL. (Pg. 13)
To access the entire article click here.
Oregon's Declining Birthrate
In keeping with global trends, Oregon's fertility rates are also on the decline.
According to a 5/24/2024 Oregon/Live article by Mike Rogaway, Oregon's Birth Rate Is Among Nation's Lowest, and It Keeps Falling, "Already deaths outnumber births in Oregon."
A 10/16/2023 Axios Portland article, How Oregon's Falling Birth Rate Could Shape Its Future, provides additional detail.
- The state's birth rate is now below replacement level – meaning Oregon's economy is "fully reliant upon migration for any population growth," according to Josh Lerner, an economist with the Office of Economic Analysis...
- By the numbers: Since 2007, the number of births has fallen from 13.3 per 1,000 residents to 9.3 in 2022, according to new data from the Centers for Disease Control and Prevention.
- That's a nearly 30% decline overall and it mirrors a national trend as well as a global one.
- Oregon has the 5th lowest birth rate nationwide.
Population data specific to Hillsboro, the 5th largest city in Oregon, reveals an increase in population from 92,000 in 2010 to its peak population year of 108,743 in 2018. By 2024 the population count had declined to 107,730 compared to 6 years ago. Part of the decline in recent years is attributed to the pandemic but a review of the numbers indicates the drop off in birth rates began well before Covid.
Hillsboro Airport (HIO), the largest general aviation airport in Oregon, is located in Hillsboro. According to the Environmental Protection Agency (EPA), out of 20,000 airports nationwide, HIO ranks 8th in lead pollution. HIO releases 0.6 tons of lead into the air each year during the landing and take-off phase of flight. Additional lead, not accounted for in the EPA National Emissions Inventory, is emitted during ground run-up procedures and the cruise phase. The EPA also ranks HIO as one of the top facility sources of PM2.5 in Washington County.
There are two primary zip codes in Hillsboro: 97123 and 97124. Both are subjected to heavy levels of aviation activity and both experienced a 16% decline in number of births during a 13 year period between 2010 and 2022. During this same timeframe the population in Hillsboro increased by more than 15,000.
HIO is located in 97124. In 2010 the birth count in this zip code was 733. By 2022 that number had dropped to 617.
The 97123 zip code, located to the south of HIO, is subjected to heavy aviation activity produced by flight students and private pilots. In addition, Twin Oaks Airport, the second largest facility source of lead pollution in Washington County, is located here. In this zip code birth count dropped from 679 in 2010 to 569 in 2022.
Communities bordering Hillsboro including Forest Grove, Cornelius, and Banks that are frequently subjected to repetitive flight training and recreational flying also experienced declines in birth counts between 2010 and 2022.
For additional information on Oregon zip code data click here.
U.S. Declining Fertility Rates
The illustration below is from a 12/5/2022 Pew Charitable Trust article, The Long-Term Decline in Fertility–and What It Means for State Budgets.
Nationwide, 20,000 airports serve the 177,000 piston-engine aircraft that use leaded aviation fuel. It is worth noting that seventy-seven of the top 100 lead polluting airports in the U.S. are located in the 17 states that have experienced the greatest decline in fertility rates.
Concluding Remarks
The Airlines, Pollution and Fertility study adds to the growing body of evidence attesting to the link between aviation emissions and adverse health impacts. It is imperative that public officials, health experts, and politicians take immediate steps to protect current and future generations from these toxic pollutants.
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