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Findings of County-Commissioned Airborne Lead Study Published Online in the Proceedings of the National Academy of Sciences

SANTA CLARA COUNTY, Calif. – The results of an airborne lead contamination study commissioned by the County of Santa Clara, which found that children living near Reid-Hillview Airport had increased blood lead levels due to airport operations, have been published in the prestigious, peer-reviewed online version of the scientific journal – the Proceedings of the National Academy of Sciences.

The abbreviated version of the 113-page report appeared online in the PNAS Nexus on January 10 for inclusion in the March 2023 issue. The PNAS Nexus is an open-access scientific journal that is “committed to the timely dissemination of scientifically rigorous research from across the biological, medical, physical, social and political sciences, engineering and mathematics.”

It is a sibling journal to the Proceedings of the National Academy of Sciences, the flagship journal of the National Academy of Sciences, with an editorial board that includes members of the NAS, the National Academy of Engineering and the National Academy of Medicine.

The County-commissioned study on lead exposure risks for children found that leaded aviation fuel from airport operations contributed to significantly increased blood lead levels for those within a half-mile of Reid-Hillview Airport. For context, the lead levels during peak hours were double the levels seen during the height of the Flint Water Crisis in Michigan.

After the report was released, the County took a number of immediate measures to prevent continued lead exposure from Reid-Hillview Airport, including prohibiting the sale and distribution of leaded avgas at County airports in January 2022 and petitioning the EPA to take action to eliminate lead pollution at the nationwide level.

The County also sought publication of the report in a scientific journal to further disseminate this vital information and to ensure that its findings are considered by the EPA as it undertakes a process to issue emission standards applicable to the emission of any air pollutant that may reasonably be anticipated to endanger public health or welfare, including emissions from aircraft fueled with avgas. Leaded gas remains in use by more than 170,000 aircraft in the United States, with 4 million people and 600 K-12 schools within 500 meters of an airport used by these planes. In January 2022, the U.S. Environmental Protection Agency launched an evaluation of whether lead emissions from aircraft contribute to pollution that endangers public health. According to a Significance Statement included in the PNAS article, the study supports such an endangerment finding: “An ensemble of evidence is presented indicating that the deposition of leaded aviation gasoline significantly elevates the blood lead levels of at-risk children.”

“Publication by the National Academy of Sciences puts this important and groundbreaking study on the official scientific record and in the national dialogue regarding the continued use of leaded fuel at airports throughout the nation,” said Supervisor Cindy Chavez, who originally requested that County staff conduct a study. “It’s important to recognize and document the results of this study, which clearly show that lead presents an immediate hazard to all those in the vicinity of these airfields, and particularly children.”

The peer-reviewed study found that children living downwind from the airport had higher blood lead levels, with increases of .40 micrograms per deciliter, over children living upwind from the airport. For context, lead levels detected during the peak of the Flint Water Crisis were between .35 and .45 micrograms per deciliter over baseline.

The study also examined levels during times of maximum exposure to air traffic for children within a half-mile of the airport and estimated an increase of .83 micrograms per deciliter at peak times – significantly higher than the levels seen in Flint.

Children who live within a half-mile of the airport had blood lead levels 20% higher than children living between half-mile to 1.5 miles from the airport. The study also correlated blood lead levels with the proximity of a child’s home and school to Reid-Hillview Airport. Children who commute toward Reid-Hillview to attend school present substantially higher blood lead levels than children who commute away from the airport.

Health organizations agree that there is no known safe level of lead in a child’s blood, and exposure to even a small amount of lead has a negative effect on cognitive ability, particularly in developing children who absorb lead more efficiently than older children and adults.

The PNAS study was conducted by Dr. Sammy Zahran, Dr. Christopher Keyes, and Dr. Bruce Lanphear. It incorporated three main tests of exposure risk and was controlled for other sources of lead exposure.


The County of Santa Clara government serves a diverse, multi-cultural population of 1.9 million residents in Santa Clara County, California, making it more populous than 14 states in the U.S. The County provides essential services to its residents, including public health protection, environmental stewardship, medical services through the County of Santa Clara Health System, child and adult protection services, homelessness prevention and solutions, roads, park services, libraries, emergency response to disasters, protection of minority communities and those under threat, access to a fair criminal justice system, and many other public benefits.