Several Democratic senators said Tuesday that the Environmental Protection Agency should step up regulation of the natural gas industry because they are concerned that toxic chemicals used in drilling could enter the public water supply.

In a Senate hearing, Democrats pressed the agency about the consequences of a fast-growing drilling technique called hydraulic fracturing, or hydrofracking, that involves pumping chemicals and water deep underground to release gas deposits.

“The industry has failed to meet minimal acceptable performance levels for protecting human health and the environment,” said Senator Benjamin L. Cardin, Democrat of Maryland and chairman of the Water and Wildlife Subcommittee of the environment committee. “The question is, What is E.P.A. doing about this?”

A recent article by The New York Times reported that these drilling fluids, which are often processed at sewage treatment plants, contain radioactivity at levels far higher than federal regulators say is safe for these plants to handle.