Acetaminophen forms toxics during wastewater chlorination

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November 30, 2005

Acetaminophen forms toxics during wastewater chlorination

Disinfection of wastewater can lead to the formation of unwelcome

byproducts from pharmaceuticals.

http://pubs.acs.org/subscribe/journals/esthag-w/2005/nov/science/as_acetaminophe\

n.html

Acetaminophen, the most widely used painkiller in the world and the

active ingredient in over-the-counter drugs like Tylenol, may be

transformed into toxic compounds during chlorination in wastewater

treatment plants, according to research posted today on /ES & T/'s

Research ASAP website (10.1021/es0509073

<http://dx.doi.org/10.1021/es0509073>). The research suggests that the

scientists need to look more carefully at what happens when the

pharmaceuticals being found in waterbodies throughout the world are

subjected to wastewater treatment.

The occurrence of pharmaceuticals in the environment has received a lot

of interest following a study by the U.S. Geological Survey

<http://www.usgs.gov> (USGS) (/Environ. Sci. Technol./ *2002*, /36/,

1202-1211 <http://dx.doi.org/10.1021/es011055j>), but little is known

about their potential transformation during wastewater and

drinking-water treatment. According to the USGS study, acetaminophen,

which is also known as paracetamol, is one of the most frequently

detected anthropogenic compounds in streams in the U.S.

Chlorination is the most common chemical method for wastewater and

drinking-water disinfection in the U.S. Under conditions simulating

wastewater disinfection, acetaminophen reacted with hypochlorite to form

a variety of products, two of which were identified as toxic

compounds--1,4-benzoquinone and N-acetyl-/p/-benzoquinone imine

(NAPQI)--by authors Bedner and MacCrehan

<http://www.cstl.nist.gov/nist839/839.04/maccrehan.htm> of the U.S.

National Institute of Standards and Technology <http://www.nist.gov/>.

After a 1-hour treatment with 4 milligrams per liter (mg/L) of chlorine,

these byproducts comprised 25% and 1.5% of the initial acetaminophen

concentration, respectively. Typical chlorine concentrations used in

wastewater chlorination range from 2 to 10 mg/L, with a usual contact

time of 5 minutes to 1 hour.

" This is one of the first papers that details the products of chlorine

reaction of a pharmaceutical, " says Sedlak

<http://www.ce.berkeley.edu/%7Esedlak/> of the civil and environmental

engineering department at the University of California, Berkeley. He

stresses the importance of studying the reaction products of

pharmaceuticals more closely, because they can be more toxic or more

stable than the parent compounds. " Otherwise, when looking at

pharmaceuticals in the environment, we may simply not be looking at the

right compounds, " Sedlak says. He predicts that this type of reaction

will also play a role in other disinfection techniques, such as

ozonation or reaction with chloramines.

It would be interesting to see whether 1,4-benzoquinone and NAPQI can be

measured in real wastewater treatment plants, says Bedner, who

acknowledges that these compounds are not very stable and, therefore,

are unlikely to persist in the environment. They could nonetheless have

an ecological impact downstream of the treatment area in

effluent-dominated environments, Sedlak says. In addition, changes in

the dose of chlorine (which can be caused by variations in the volume of

the wastewater influent) may lead to a buildup of these compounds in the

treatment plant, he says.

NAPQI is a known liver toxin. It is also generated in the human body

during acetaminophen metabolism and can be responsible for lethality in

overdoses of the drug. 1,4-Benzoquinone, a hydrolysis product of NAPQI,

is a benzene metabolite suspected of causing genotoxic and mutagenic

effects. In fact, acetominophen's potential transformation to toxic

products triggered Bedner's interest in the drug's behavior during

wastewater treatment. " Acetaminophen is so common these days, since it

is added to all sorts of sinus and cold medicines, " she says, " but it

also has this dark side to its oxidation chemistry that we don't usually

acknowledge. "

" This paper provides a good example of why we should consider

disinfection chemistry when we evaluate pollutant fate during municipal

wastewater treatment, " says environmental chemist Dodd, who is

with the Swiss Federal Institute of Aquatic Science and Technology

<http://www.eawag.ch/e_welcome.html> (Eawag) and has investigated the

reactions of chlorine and ozone with a number of antibacterial agents.

" Municipal wastewater oxidation will only lead to small changes in most

reactive pollutant molecules, " says Dodd, " but even minor structural

modifications can dramatically alter some compounds' biochemical or

physicochemical properties. "

We are just beginning the second phase in the study of pharmaceuticals,

says Sedlak, who draws parallels to the history of pesticide research.

Now that researchers have determined the occurrence of the parent

compounds, they can begin to investigate potential reaction products,

especially those that could be more toxic or stable than the parent

compounds. Dodd agrees, adding that parent compounds should be

prioritized by some basic considerations such as modes of action,

reported concentrations, or expected reactivities with the active

compounds used for different wastewater treatment technologies. " Many

different pharmaceuticals have been detected in wastewaters, " he says,

" so it's important to keep the focus on the compounds likely to be most

significant. " --ANKE SCHAEFER

<http://pubs.acs.org/journals/esthag/bios.html>

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