A new study released Wednesday by Austin officials and the U.S. Geological Survey blames a common chemical for significantly more pollution, particularly in waterways, than was previously believed. Such a finding could have implications not only for Austin's efforts to protect its creeks and streams, but for anyone, anywhere, who walks or plays on a parking lot.

The culprits are sealants that protect parking lots, according to the study that will appear in Environmental Science & Technology, the journal of the American Chemical Society.

"We're surrounded, in the areas that we live and work, by parking lots. This is not a contamination issue that is limited to industrial areas or densely urbanized downtown areas," said Barbara Mahler, a research hydrologist for the Geological Survey and the report's lead author. "This is a potential contamination issue that affects all of us."

State and federal environmental officials said they want to review the study, and possibly conduct new ones, to ascertain the risk to people and the environment and to determine whether policymakers need to take action.

The contamination in question comes from a family of chemicals known as polycyclic aromatic hydrocarbons, or PAHs. Such chemicals can, with sufficient concentrations and exposure levels, cause cancer in humans and kill aquatic life.

Health officials said PAH levels in the parking lot sealants are almost certainly too low to make people sick. The biggest concern, city officials say, is for aquatic ecosystems. According to Wednesday's report, parking lot sealants may contribute about 90 percent — perhaps even 95 percent — of the PAH pollution in urban watersheds.

Because of the findings, city officials are contemplating a ban on sealants deemed harmful to the environment. But they also plan discussions through the summer with state and federal counterparts, other scientists and companies that make or sell parking lot sealants.

PAHs are primary components of many common parking lot sealants, particularly those with coal tar, a toxic byproduct of coke, a fuel derived from coal that's used in the production of steel.

Though the report and the city have singled out coal-tar sealants, the Geological Survey's Mahler said it's not clear whether other types are substantially better for the environment.

Austin officials pointed to parking lot sealants as a likely source of PAHs in 2003, in the midst of a series of American-Statesman stories about pollution in and around Barton Springs Pool. The series speculated that the intense concentrations of pollutants may have come from buried hazardous waste.

After a three-month review, during which the city kept the pool closed, health and environmental officials from the state and federal governments declared that the pollution did not threaten the health of swimmers.

The city and the Geological Survey continued studying the source of the pollution. High levels of PAHs have also been found in parts of Waller Creek through the University of Texas campus, the ponds in the Central Market area north of UT, Walnut Creek around Metric Boulevard in North Austin and other areas.

The city also has tested parking lots across Austin, including at the Texas Commission on Environmental Quality offices on North Interstate 35 and the American-Statesman building just south of downtown. All showed high levels of PAH contamination, officials said.

As part of the study released Wednesday, the Geological Survey and the city extensively tested parking lots at the former Robert Mueller Municipal Airport, and they studied parking lots and watersheds in Austin and Fort Worth. Initial findings, reported a year ago, showed that PAH concentrations in the particles washing off coal-tar-treated parking lots were 65 times higher than those in the runoff from untreated lots.

The conclusions, Mahler said, were reviewed by other scientists before Environmental Science & Technology agreed to publish them.

"I think it's a big, big piece of the puzzle," Mahler said of the report's findings. "As soon as you recognize the problem and you start looking around, it's right in front of your face. I don't know why it hasn't been figured out."

Indeed, some environmental experts and sealant industry leaders were skeptical of the report's findings.

A spokesman for Gardner-Gibson Inc., a Tampa, Fla.-company that makes pavement sealants, told Bloomberg News that components of sealants are present in numerous other products.

"It's going to be tough to narrow it down and say it's specifically driveway sealers," Gordon Blickle, the spokesman, told Bloomberg.

David Palmerton, who heads a Syracuse, N.Y.-based environmental consulting firm that's worked with a number of Fortune 500 companies, said he doubted that sealants could be such a significant pollutant without being dumped en masse into a waterway. What helps sealants protect asphalt — the strong chemical bonds they form with pavement — also keeps them from running off with rainwater during storms, he said.

Asked whether sealants could represent such an overwhelming share of a watershed's PAH pollution, Palmerton said, "I find it difficult to imagine."

Mahler said the report is far from the last word on parking lot sealants and the environment. The report, she said, raises questions of which sealants are friendlier to the environment, whether alternatives to them exist and whether different solutions would be better in different parts of the country.

"I think really what this study does is open our eyes to this as a source and hopefully spur some more research," Mahler said.

An apartment complex atop a hill upstream of Barton Springs Pool has already stopped using coal-tar sealants on its parking lot. City officials said such sealants were primarily responsible for a well-publicized hot spot of PAH contamination, though they said Wednesday that they still plan to build a sediment pond and take other actions to catch and treat runoff from the parking lot.

The city has also worked with sellers and contractors to curtail the use of coal-tar sealants, which are usually easy to find at home improvement stores.

Karen Cobb, a spokeswoman for Lowe's Cos. Inc., said the home improvement retailer has shared the city's information with its vendors and plans to look into the issue.

"Lowe's makes every effort to be a good steward of the environment," Cobb said. "We rely on our vendors to make certain that the products they are offering are safe and environmentally sound."