Mar 23, 2015 12:09 AM EDT By Staff Reporter, UniversityHerald Reporter

Chlorine, a disinfectant commonly used in most wastewater treatment plants, may encourage the formation of new, unknown antibiotics that could also enter the environment, potentially contributing to the growing problem of antibiotic resistance.

Researchers found that chlorine treatment may be failing to completely eliminate pharmaceuticals from wastes.  As a result, trace levels of these substances get discharged from the plants to the nation's waterways. And now, scientists are reporting preliminary studies that show chlorine treatment.

These findings suggest that a re-evaluation of wastewater treatment and disinfection practices is needed.

"Pharmaceuticals that get out into the environment can harm aquatic life, making them react slowly in the wild and disrupting their hormone systems," notes researcher Olya Keen of the University of North Carolina at Charlotte.

According to Keen, increased antibiotic exposure, even at low levels in the environment, can lead to development of antibiotic-resistant microbes and a general weakening of antibiotics' abilities to fight bacterial infections in humans.

"Treated wastewater is one of the major sources of pharmaceuticals and antibiotics in the environment," she explained. "Wastewater treatment facilities were not designed to remove these drugs. The molecules are typically very stable and do not easily get biodegraded. Instead, most just pass through the treatment facility and into the aquatic environment."

But besides failing to remove all drugs from wastewater, sewage treatment facilities using chlorine may have the unintended consequences of encouraging the formation of other antibiotics in the discharged water.

For the study, Keen and her colleagues ran several lab experiments and found that exposing doxycycline, a common antibiotic, to chlorine in wastewater increased the antibiotic properties of their samples.

"Surprisingly, we found that the products formed in the lab sample were even stronger antibiotics than doxycycline, the parent and starting compound," she adds.

Keen has not yet identified all the properties of these "transformation products," and that research is now underway. She notes that these compounds could turn out to be previously unidentified antibiotics.

Keen explains that the best solution may be to decrease the amount of these drugs that reach a treatment plant in the first place. Currently, disposal of pharmaceuticals is not regulated, however. So she urges a greater emphasis on collecting and incinerating old pharmaceuticals, rather than dumping them down the drain or placing them in the trash, which can lead to harmful environmental exposures.

The findings were presented  at the 249th National Meeting & Exposition of the American Chemical Society (ACS).

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