It turns out that chlorine, a common disinfectant that is a staple in most water treatment plants, may be doing as much harm as good.

According to a new study presented today at the 249th National Meeting & Exposition of the American Chemical Society in Denver, chlorine may not be eliminating all the pharmaceutical drugs that wind up in wastewater.

In fact, as the remnants of those drugs break down, they may bond with the chlorine in new and unpredictable ways. Thus superbugs, a scourge of modern medicine, may be getting a boost from wastewater treatment plants meant to protect us from dangerous contamination.


A re-evaluation of wastewater treatment and disinfection practices may be in order.

“Treated wastewater is one of the major sources of pharmaceuticals and antibiotics in the environment,” according to Olya Keen, Ph.D., of the University of North Carolina at Charlotte and the lead scientist on the new study.

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How the Biological Breakdown Happens

Here’s what happens, Keen says: Drugs get into the environment when your body does not metabolize all of your prescribed dose, so the excess is flushed out in urine. They also make it into wastewater when unused pharmaceuticals are thrown away improperly.

“Pharmaceuticals that get out into the environment can harm aquatic life, making them react slowly in the wild and disrupting their hormone systems,” she said.

The increased antibiotic exposure, even at low levels in the environment, can also lead to the development of antibiotic-resistant bacteria, called “superbugs.” The end result is that these antibiotics are less able to fight bacterial infections in humans.

“Wastewater treatment facilities were not designed to remove these drugs,” Keen said. “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.”

From there the water goes … everywhere. Downstream, it could become someone’s drinking water. Or have an industrial use. Or flow into the ocean.

Moreover, chlorine treatment appears to allow for the creation of new and unknown antibiotics that also enter the environment.

In her study, Keen exposed doxycycline, a common antibiotic, to chlorine in wastewater. Her team found that the products formed in the lab sample were even stronger antibiotics than the doxycycline.

“We don’t know much about the effect [of these new antibiotics] on humans,” she says, “but we have seen the effects on aquatic life.”

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Proper Drug Disposal Is Crucial

Keen first looked at the issue of pharmaceuticals in wastewater while working on her degree in environmental engineering. She says proper disposal of pharmaceuticals would help combat the problem.

“We don’t know if we can reverse these effects,” she said.

At present, disposal of pharmaceuticals is not regulated. Keen has no figures on what percentage of the pharmaceuticals found in wastewater comes from excretion and what percentage comes from drug disposal.

She suspects it’s easier to keep pharmaceuticals out of water treatment plants in the first place than to figure out how to fight the problems they create. Keen says that collecting and incinerating old pharmaceuticals would be more beneficial than dumping them down the drain or tossing them in the trash. Although Keen’s research looked at wastewater systems, it applies as well to drinking water treatment systems. Most drinking water treatment systems also use chlorine as a disinfectant.

The process of purifying drinking water requires that chlorine remain in the distribution piping system for hours, which blocks microbes from growing. But the longer it stays in the system, the more time the chlorine has to interact with pharmaceuticals that may be in the water, encouraging development of new antibiotic compounds.

Keen says research is ongoing to identify all the properties of these “transformation products.” These compounds could turn out to be totally new antibiotics.

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