The U.S. Environmental Protection Agency found Iodine-131 in the city's drinking water April 4 and in August. The presence of the substance before the accident at Japan's Fukushima power plant suggests that was not the source, scientists said.
The EPA found Iodine-131 at three sites in Philadelphia, and the amount found at the Queen Lane water-treatment plant was the highest of 69 sites tested nationally. But even the amount found at Queen Lane falls within safety standards the EPA sets for acceptable drinking water.
Even so, the agency, the Philadelphia Water Department, and the Pennsylvania Department of Environmental Protection are trying to identify possible sources.
Katy Gresh, a spokeswoman for the state DEP, said the department hoped to start sampling in the next few weeks, focusing on treatment plants that accept wastewater from hospitals.
Philadelphia is downstream from about 100 wastewater treatment plants, said Joanne Dahme, general manager, public affairs, Philadelphia Water Department.
That large number is "what sort of makes the detective piece of this very hard," Dahme said.
The EPA has been doing the testing, but the water department wants to do its own tests to get more data, she said. Philadelphia water officials are worried that it could take a while to find a lab to do the work because the Japan accident has driven up demand for testing.
There is also a good chance that there are multiple sources. It could be coming from patients who have been treated with radioactive iodine.
"Somebody will go in and they will get a massive dose of Iodine-131 and it doesn't all stay in the body," said Kathryn Higley, head of the department of nuclear engineering and radiation health physics at Oregon State University. "I suspect it's a summation of a lot of people - I don't know how to put this - peeing in their toilets all around the metropolitan area."
Other metropolitan areas also have high concentrations of cancer-treatment centers, but not all of them draw on local rivers for their water, which could explain why Iodine-131 shows up at higher levels here, Keklak said.
Contact staff writer Miriam Hill at 215-854-5520 or email@example.com.