SAN FRANCISCO (AP) — Some of the chemicals used in California’s fracking boom likely pose a risk to public health, and the state for years has failed to track and deal with those potential threats, a state-commissioned study concluded Thursday.

The fracking study, required by state lawmakers and carried out by the California Council on Science and Technology and the Lawrence Berkeley National Laboratory, urged greater oversight of hydraulic fracturing and other intensive oil field production methods.

“We found practices that we do not think are inherently safe that we think should be made safer,” Jane Long, an author of the study and researcher at Lawrence Livermore National Laboratory, told reporters.

“Although air and water quality studies suggest public health hazards exist, many data gaps remain,” the report concluded.

Public-health science nationwide and in California in particular is “playing catch up” with the surge in fracking and other intensive oil field production, the study added.

Hydraulic fracturing injects chemicals and liquids at high pressure to force oil and gas out of underground formations. California is the country’s third-largest oil-and-gas-producing state. Fracking accounted for one-fifth of the state’s petroleum production in the last decade, and for roughly half of the 300 wells installed monthly in the same period.

All but 5 percent of all fracking in the state occurs in central California’s San Joaquin Valley. The report also noted Los Angeles, however, where a half-million people live, go to school or play within a mile of a well that has been fracked or otherwise produced by intensive drilling methods, researchers said.

No one knows whether more than 50 percent of the chemicals used in fracking are fully safe for humans and the environment, the study said.

Scientists in the study urged the state to disallow use of any chemicals that had unknown environmental risks, and limit the risk of chemicals with known hazards.

The report also urged better management of wastewater from fracking and other intensive oil production. Currently, the report said, oil field operators dump more than half of the wastewater into pits, which can allow the contaminants to seep into groundwater.

And the report urged quake-vulnerable California to do more to study whether oil companies’ injection of oil field wastewater underground is linked to quakes here, as scientists believe is the case in Oklahoma.

New state legislation focusing in part on fracking transparency and monitoring will deal with some of the data gaps identified in the report, officials said.

Some oil-industry figures said Thursday’s study simply underscored that there is no proof of public harm from fracking and other intensive forms of oil production.

“The extensive research confirms what regulators and scientists have said previously: there is no evidence of ground water contamination or induced earthquakes to date in California, after many decades of the routine use of hydraulic fracturing in the state,” Dave Quast, the California director of Energy in Depth, a project of Independent Petroleum Association of America, said in a statement.