Scientists say there is growing evidence of the threat to health to those living close to fossil fuel facilities.

Boston University researchers found that more than 14% of people in the contiguous United States reside within a mile of at least one piece of fossil fuel infrastructure, the majority in cities.

The team added fossil fuels release pollutants into the air when extracted and burned, but there’s more to their production than massive oil rigs diving deep into the Earth and smoky power plants. Those processes are examples of only the first and last—and generally most visible—moments in a fossil fuel’s five-stage journey.

Between the initial extraction site and the final power-generating facility, oil and gas are also refined to remove impurities, held in storage facilities, and transported from place to place. These mid-supply chain steps occur in a sprawling fossil fuel infrastructure network that spans the United States and is often hidden from plain sight.

The study examined populations living within 1.6 km (roughly a mile) of fossil fuel infrastructure across all stages of the supply chain. It estimated that 46.6 million people in the contiguous US live within about a mile of at least one piece of fossil fuel infrastructure. This represents 14.1% of the population.

“While a growing body of research confirms that communities residing near extraction and end-use facilities face a higher risk of adverse birth outcomes and asthma – and research on other health outcomes, including leukaemia, is emerging – much less is known about the health effects of living near mid-supply chain infrastructure. Harmful pollutants such as volatile organic compounds have been detected near some of these facilities.

“This study helps us get a general size of the potential problem and really starts the process of doing a better job of understanding exactly what the hazards are and how many people are potentially exposed,” said Jonathan Buonocore, the paper’s first author, an assistant professor of environmental health at BU’s School of Public Health (SPH), and core faculty at BU’s Institute for Global Sustainability (IGS). “Especially for these more obscure pieces of energy infrastructure, this is the first step to tracking what emissions and stressors those are imposing on the communities.”

Breaking down that 46.6 million figure, the team estimated how many people live near each type of infrastructure nationwide. Almost 21 million Americans live near end-use facilities, including power plants. More than 20 million are within a mile of extraction sites, like oil and gas wells. Storage facilities – like peak shaving facilities, underground gas storage facilities, and petroleum product terminals – have more than 6 million nearby residents. Fewer people live near refining and transportation. Many Americans, about 9 million, are counted toward several of those totals, as their homes are in proximity to multiple types of infrastructure.

“There is reason to believe that there could be air pollution coming from each of these stages, from consistent pollution, gas leaks, or blowouts, when gas or oil flows from a well uncontrollably,” said Mary Willis, the study’s senior author, an assistant professor of epidemiology at SPH, and core faculty at IGS. “All of these stages can reasonably impact a range of population health outcomes, yet the basic information of who is even near the infrastructure components has not been examined to date.”