PITTSBURGH - In the debate over natural gas drilling, the companies are often the ones accused of twisting the facts. But scientists say opponents sometimes mislead the public, too.
Critics of fracking often raise alarms about groundwater pollution, air pollution, and cancer risks, and there are still many uncertainties. But some of the claims have little - or nothing- to back them.
For example, reports that breast cancer rates rose in a region with heavy gas drilling are false, researchers said.
Fears that natural radioactivity in drilling waste could contaminate drinking water aren't being confirmed by monitoring, either.
And concerns about air pollution from the industry often don't acknowledge that natural gas is a far cleaner burning fuel than coal.
"The debate is becoming very emotional. And basically not using science" on either side, said Avner Vengosh, a Duke University professor studying groundwater contamination who has been praised and criticized by both sides.
One of the clearest examples of a misleading claim comes from north Texas, where gas drilling began in the Barnett Shale about 10 years ago.
Opponents of fracking say breast cancer rates have spiked exactly where intensive drilling is taking place - and nowhere else in the state. The claim is used in a letter that was sent to New York's Gov. Andrew Cuomo by environmental groups and by Josh Fox, the director of "Gasland," a film that criticizes the industry. Fox, who lives in Brooklyn, has a new short film called "The Sky is Pink."
But researchers haven't seen a spike in breast cancer rates in the area, said Simon Craddock Lee, a professor of medical anthropology at the University of Texas Southwestern Medical Center.
David Risser, an epidemiologist with the Texas Cancer Registry, said researchers checked state health data and found no evidence of an increase in the counties where the spike supposedly occurred.
And Susan G. Komen for the Cure, a major cancer advocacy group based in Dallas, said it sees no evidence of a spike, either.
"We don't," said Chandini Portteus, Komen's vice president of research, adding that they sympathize with people's fears and concerns, but "what we do know is a little bit, and what we don't know is a lot" about breast cancer and the environment.
Yet Fox tells viewers in an ominous voice that "In Texas, as throughout the United States, cancer rates fell - except in one place - in the Barnett Shale."
Lee called the claims of an increase "a classic case of the ecological fallacy" because they falsely suggest that breast cancer is linked to just one factor.
Fox responded to questions by citing a press release from the Centers for Disease Control and Prevention that doesn't support his claim, and a newspaper story that Risser said is "not based on a careful statistical analysis of the data."
When Fox was told that Texas cancer researchers said rates didn't increase, he said the claim of unusually high breast cancer rates was "widely reported" and said there is "more than enough evidence to warrant much deeper study."
Another instance where fears haven't been confirmed by science is the concern that radioactivity in drilling fluids could threaten drinking water supplies.
Critics of fracking note the deep underground water that comes up along with gas has high levels of natural radioactivity. Since much of that water, called flowback, was once being discharged into municipal sewage treatment plants and then rivers in Pennsylvania, there was concern about public water supplies.
But in western Pennsylvania, the Pittsburgh Water and Sewer Authority did extensive tests and didn't find a problem in area rivers. State environmental officials said monitoring at public water supply intakes across the state showed non-detectable levels of radiation, and the two cases that showed anything were at background levels.
Critics also repeat claims of air pollution threats, even as evidence mounts that the natural gas boom is contributing to cleaner air.
Marcellus air pollution "will cause a massive public health crisis," claims a section of the Marcellus Shale Protest website.
Yet data from the U.S. Energy Information Administration show that the shale gas boom is helping to turn many large power plants away from coal, which emits far more pollution. And the U.S. Environmental Protection Agency passed new rules to force drillers to limit releases of methane from wells and pumping stations.