U.S. hospitals and long-term care facilities annually flush millions of pounds of unused pharmaceuticals down the drain, pumping contaminants into America's drinking water, according to an ongoing Associated Press investigation.

These discarded medications are expired, spoiled, over-prescribed or unneeded. Some are simply unused because patients refuse to take them, can't tolerate them or die with nearly full 90-day supplies of multiple prescriptions on their nightstands.

Few of the country's 5,700 hospitals and 45,000 long-term care homes keep data on the pharmaceutical waste they generate. Based on a small sample, though, the AP was able to project an annual national estimate of at least 250 million pounds of pharmaceuticals and contaminated packaging, with no way to separate out the drug volume.

One thing is clear: The massive amount of pharmaceuticals being flushed by the health services industry is aggravating an emerging problem documented by a series of AP investigative stories — the commonplace presence of minute concentrations of pharmaceuticals in the nation's drinking water supplies, affecting at least 46 million Americans.

Researchers are finding evidence that even extremely diluted concentrations of pharmaceutical residues harm fish, frogs and other aquatic species in the wild. Also, researchers report that human cells fail to grow normally in the laboratory when exposed to trace concentrations of certain drugs.

The original AP series in March prompted federal and local legislative hearings, brought about calls for mandatory testing and disclosure, and led officials in more than two dozen additional metropolitan areas to analyze their drinking water.

And while most pharmaceutical waste is unmetabolized medicine that is flushed into sewers and waterways through human excretion, the AP examined institutional drug disposal and its dangers because unused drugs add another substantial dimension to the problem.

"Obviously, we're flushing them — which is not ideal," acknowledges Mary Ludlow at White Oak Pharmacy, a Spartanburg, S.C., firm that serves 15 nursing homes and assisted-living residences in the Carolinas.

Such facilities, along with hospitals and hospices, pose distinct challenges because they handle large quantities of powerful and toxic drugs — often more powerful and more toxic than the medications people use at home. Tests of sewage from several hospitals in Paris and Oslo uncovered hormones, antibiotics, heart and skin medicines and pain relievers.

Hospital waste is particularly laden with both germs and antibiotics, says microbiologist Thomas Schwartz at Karlsruhe Research Center in Germany.

The mix is a scary one.

In tests of wastewater retrieved near other European hospitals and one in Davis County, Utah, scientists were able to link drug dumping to virulent antibiotic-resistant germs and genetic mutations that may promote cancers, according to scientific studies reviewed by the AP.

Researchers have focused on cell-poisoning anticancer drugs and fluoroquinolone class antibiotics, like anthrax fighter ciprofloxacin.

At the University of Rouen Medical Center in France, 31 of 38 wastewater samples showed the ability to mutate genes. A Swiss study of hospital wastewater suggested that fluoroquinolone antibiotics also can disfigure bacterial DNA, raising the question of whether such drug concoctions can heighten the risk of cancer in humans.

Pharmacist Boris Jolibois, one of the French researchers at Compiegne Medical Center, believes hospitals should act quickly, even before the effects are well understood. "Something should be done now," he said. "It's just common sense."