Getting ahead of the curve on water pollution has been a decades-long battle in the waterways around Chattanooga.

The problem, local environmental experts say, is that methods for controlling pollutants always play catch-up to their creation and production.

The recent discovery locally of pharmaceuticals in water is no exception, and learning more about the effects of new contaminants, as well as solutions, will take time — just as it has in previous decades when researchers and regulators tackled yesteryear’s “new” problems of raw sewage, industrial waste, PCBs and DDT, to name a few.

“This is going to follow the same scenario of other problems. We’ll start tracking and measuring, which will result in new controls and criteria (water quality standards,)” said Dr. Richard Urban, manager of the Tennessee Department of Environment and Conservation’s Water Pollution Control Division in the Chattanooga field office.

But until there’s more evidence and science about the pharmaceuticals’ effects, it is difficult to know what further limits might be needed after a 2 1/2 study by the University of Tennessee found small amounts of at least 13 common drugs in the Tennessee River, Chattanooga’s drinking supply. The drugs include several antibiotics, antidepressants and substances designed to lower human cholesterol levels.

Pharmaceuticals are excreted by humans through urine, sweat, saliva and other waste products, then sent into the water system through the sewers, experts say. Levels of the drugs in the Tennessee River are measured in parts per trillion — minuscule amounts when it comes to humans — but experts say they don’t know how the drugs will affect wildlife, and there’s also the danger of the amounts building up over time, perhaps to a point where humans are affected.

Chattanooga, like other communities across the nation, had no water pollution regulation until the mid 1900s, and the federal Clean Water Act was not enacted until 1972.

Population and industry were booming here long before then, but the 652-mile Tennessee River could handle most of the polluted matter, along with that of other towns and cities, until 1933, when the Tennessee Valley Authority began building dams and restricting the river’s free flow, according to officials.

When Congress passed the Clean Water Act, another evolution of sampling and treatment began, Dr. Urban said. Testing resulted in the discoveries of PCBs and DDT — leftovers from years of unregulated industrial dumping and agricultural runoff — in the fish and birds living in and on the water.

“From a standpoint of traditional pollutants, the waters are better than they were, and there’s more controls. We’re seeing less effect in the natural environments,” Dr. Urban said. “With the pharmaceuticals, what you don’t know raises a lot of questions about risks.”

Discoveries and questions about new pollutants aren’t restricted to the Tennessee River.

In 2007, University of Georgia researchers announced that the man-made chemical PFOA was found in the Conasauga River below the wastewater treatment plant of Dalton, Ga.. The chemical was used for years in the carpet industry to make stain-resistant carpet.

Perfluoroctanoic acid, also called PFOA or C8, is used to manufacture nonstick cookware and outdoor clothing. In 2006, a U.S. Environmental Protection Agency advisory board had labeled the chemical a “likely carcinogen,” and EPA reports state the substance has been linked to problems such as low-weight babies.

Other Tennessee clean-water advocates said they hope to see more research on the discovery of pharmaceuticals.

“It’s a complicated chemistry question,” said Larry Cook, executive director of the North Chickamauga Creek Conservancy. “Perhaps there needs to be new innovation for disposal.”

As the population increases and brings more people and businesses, the potential for pollution, including new kinds, goes up, Mr. Cook said.

“I guess it’s always going to be a game of catch-up, and regulations may need to be reviewed to match the emerging science. But it’s almost always more expensive to clean up a mistake,” he said.