When Pennsylvania's new natural gas law, which takes effect Saturday, was being debated, the focus was on high-profile issues such as the new impact fee.

But just before it passed, medical provisions were added that now have some physicians worried it will compromise public health.

Except in an emergency, a physician who needs proprietary information about chemicals used in natural gas drilling to assess a patient must provide "a written statement" to a company, according to the act, and must sign a confidentiality agreement.

Some doctors are calling it a "gag law" because, as they read the act, the confidentiality agreement could limit them from sharing information about the chemicals with colleagues and perhaps even patients.

They also say the law's chemical-disclosure requirements are weak, giving the industry too many loopholes.

The law's proponents disagree, saying that rather than putting up roadblocks, the law removes them.

Adam M. Finkel, who directs the University of Pennsylvania's Program on Regulation, called the bill an "ominous piece of work."

From his initial reading, Finkel, who headed rule-making at the federal Occupational Safety and Health Administration during the Clinton administration, said that "it's really not at all clear" what a physician could tell a patient. If "not much" is the answer, "obviously, as a regulator and public health advocate, I would be appalled."

The head of the Pennsylvania Medical Society and the medical director of the Poison Control Center at Children's Hospital of Philadelphia expressed similar concerns.

The law, known as Act 13, "retains some of the worst aspects of industry secrecy about proprietary hydrofracking chemicals while making unethical demands on physicians," wrote Bernard Goldstein, emeritus professor in the University of Pittsburgh Graduate School of Public Health, and a colleague in an analysis.

However, Gov. Corbett's top energy official, Patrick Henderson, said that the law "specifically provides for medical professionals to access confidential and proprietary information in a timely manner" and that nothing prohibits "free sharing of information with the patient, other health professionals providing care to the patient, and the health-care regulators."

If so, why doesn't the act say that? critics ask.

"In an ideal world, I'd rather be clear," said Goldstein's co-author, Jill Kriesky of Pitt's Center for Healthy Environments and Communities. "Our reading is that doctors perhaps cannot share this information."

Proponents say the provision is standard language, pretty much copied from similar legislation in Colorado and other states.

Colorado's legislation, passed in December, does read similarly, as do federal OSHA provisions regarding the disclosure of materials deemed to be trade secrets.

But both are more specific about the confidentiality agreement, stipulating that the health professional won't use the information "for any purpose other than the health need(s) asserted."

Pennsylvania's law doesn't say what confidentiality means, critics argue. Does it mean a physician can't consult with a colleague? What about the insurer?

Or what if a physician is treating a child who was exposed to a chemical while playing in a field? What can the doctor tell families of other children playing in the same field?

"It looks as if this would prohibit you from sharing with a government agency or publishing in scientific journals," said the Children's Hospital physician, Kevin Osterhoudt. "So you wouldn't be able to prevent anyone else from getting hurt."

Medical officials are especially concerned about the possibility that confidentiality agreements will hamper studies because the law's final version also cut $2 million a year for a health registry to track symptoms and illnesses that could be linked to drilling.

Little is known about the long-term fate of many of these chemicals, Osterhoudt said. If, in five years, health professionals wanted to investigate a cluster of illnesses, the confidentiality agreement could mean "there would be no way to share information between scientists, to study it and discover patterns that could link cause and effect."

Corbett's own Marcellus Shale Advisory Commission recommended over the summer that the state Health Department create a health registry to follow residents who live within a mile of gas drilling and production sites.

The funding was killed because GOP senators from the Marcellus region felt the department didn't have a good grasp of what it would do with the money, said the lead Senate negotiator.

"There wasn't a plan, a detailed plan in place for how the money was going to be utilized," said Drew Crompton, chief counsel for Senate President Pro Tempore Joe Scarnati (R., Jefferson).

Public health experts ridiculed that assertion, noting that the agency had a track record of maintaining similar registries. Pennsylvania has collected data on new cancer cases since 1985.

Marilyn J. Heine, who practices in Langhorne and Norristown and who is president of the Pennsylvania Medical Society, said she hoped to work with state officials to sort things out. "There needs to be a lot of clarifying."

Though the Pennsylvania Environmental Council and others agree the act is an improvement in chemical disclosure, critics say it has too many loopholes. It requires companies to disclose what's in the fluid they use to frack a well, but it also allows them to keep secret the other chemicals, some toxic, that come out of a well in flowback water.

Also, companies are not responsible for verifying information given to them about chemicals - from, say, a chemical supplier to a subcontractor to an operator.

"It lets them off the hook," said George Jugovic Jr., president of PennFuture and former southwest regional director of the state Department of Environmental Protection.

After concerns started coming out, Corbett officials sent responses to the editors of several newspapers.

"I do not believe Act 13 prohibits a physician from sharing information with their patient or other necessary health-care professionals for the purposes of diagnosis or treatment," wrote Elia N. Avila, secretary of the state Department of Health.

Michael Krancer, secretary of the DEP, wrote that "the assertion that physicians are 'gagged' is nonsense."

The Marcellus Shale Coalition, an industry group, called concerns "blatantly false." "What I really want to get across is that doctors and medical professionals have complete and unfettered access to any and all additives . . . in the event they need that for patient care," said Patrick Creighton, a spokesman.

The medical provisions of the act were added late in the process - after the bill went to conference committee - and State Sen. Daylin Leach (D., Montgomery) said legislators were focused on other things. "There were a couple big issues that were sucking the oxygen out of the room."

"This provision really didn't get any attention," Leach said. "However," he added, "now that the dust has settled . . . it raises an obvious huge problem."

Leach did not find the assurances of Corbett officials comforting. "I do not believe the wording of the statute supports their position."

He plans to introduce new legislation to add specifics.

If the intention of state officials "is not to create these problems," he said, "maybe they'll support the wording of my legislation."

Contact Sandy Bauers at 215-854-5147, sbauers@phillynews.com, or follow @sbauers on Twitter. Read her blog, "GreenSpace," at www.philly.com/greenspace

This article contains information from the Associated Press.