The Harvard scientists said this could damage the health of people living in nearby communities and that further research was needed to understand how to stop the release of the radioactive elements from under the ground.
The radioactivity rose by 40% compared with the background level in the most affected sites. The increase will be higher for people living closer than 20km to the fracking sites, which was the closest distance that could be assessed with the available data.
The scientists used data collected from 157 radiation-monitoring stations across the US between 2001 and 2017. The stations were built during the cold war when nuclear war was a threat. They compared data with the position and production records of 120,000 fracking wells.
“Our results suggest that an increase in particle radioactivity due to the extensive [fracking development] may cause adverse health outcomes in nearby communities,” the team concluded.
Petros Koutrakis at the Harvard TH Chan School of Public Health in Boston, who led the study, said: “If you asked me to go and live downwind [of fracking sites], I would not go. People should not go crazy, but I think it’s a significant risk that needs to be addressed.”
Previous work has shown that chemicals released during fracking could pose a health risk to children and the process has contaminated groundwater in some places. Fracking is also an issue in the forthcoming presidential election, particularly in swing states such as Pennsylvania. Donald Trump has falsely claimed Joe Biden will ban fracking but the Democratic presidential candidate is largely supportive of fracking and only backs a ban on federal lands and offshore.
The researchers found that fracking resulted in a far bigger increase in particle radioactivity than conventional oil and gas operations. This is because the initial source of the radioactivity is a uranium isotope in the rocks. Tapping a conventional oil and gas reservoir barely disturbs the rock. But in the shale formations targeted by frackers the oil and gas is trapped within the rock, which is blasted apart with high-pressure water and releases the uranium.
The uranium isotope decays to the gas radon, which itself decays to ultrafine radioactive particles containing polonium and lead. These are thought to become attached to particles already in the air and are then carried by the wind.
“The polonium isotopes are the ones which are very toxic,” said Koutrakis. The element was used as a poison to kill the former Russian spy Alexander Litvinenko in London in 2006. Koutrakis said previous studies have shown that increases in particle radioactivity of the scale seen in his work can have harmful effects on people.