[Pharmwaste] Sunlight turns antiepileptic drug into harmful compound

Laurie.Tenace at dep.state.fl.us Laurie.Tenace at dep.state.fl.us
Fri Sep 1 17:43:22 EDT 2006


http://pubs.acs.org/subscribe/journals/esthag-w/2006/aug/science/nl_sunlight.
html

Sunlight turns antiepileptic drug into harmful compound

In estuarine-like settings, carbamazepine photodegrades into the toxic
acridine.
When researchers first looked for pharmaceuticals in the environment in
Europe and elsewhere, some of the highest concentrations they found were for
residues of the antiepileptic drug carbamazepine, which showed up in a
variety of places, including drinking-water treatment plants and sewage
effluent. The drug, which is sold as Tegretol and under other commercial
names, treats seizures as well as bipolar disorder. New research published
today on ES&T's Research ASAP website (DOI: 10.1021/es060502y) shows that
when carbamazepine is exposed to sunlight in an estuary-like setting, it
breaks down into a more toxic compound, acridine.

Carbamazepine's structure-three rings of carbon with an amine attached-makes
it susceptible to fracturing under certain conditions. That quality led
researchers to target the drug for further study with regard to its
photochemistry. Previous research has shown that in the presence of hydrogen
peroxide and UV light, carbamazepine breaks down to acridine, which is both
mutagenic and carcinogenic.

Although obtaining information about carbamazepine's use is difficult, the
drug's widespread consumption is reflected in its high concentrations in the
environment. It has been found at levels up to several micrograms per liter
in sewage treatment plants, first measured by Thomas Ternes of the Federal
Institute of Hydrology (Germany) in 1998. Scientists at the U.S. Geological
Survey later measured it at parts-per-billion levels in U.S. streams, and
researchers from Environment Canada recently added to those North American
data (publishing in Environmental Toxicology and Chemistry).

A team of researchers led by Serge Chiron at the University of Provence
(France) has now taken a closer look at the photodegradation of
carbamazepine. They created a laboratory setting to mimic the natural estuary
waters of the Rhône delta in southern France. By adding humic acids, Fe(III),
and nitrate to tap water, they created "artificial" river water.

The researchers then subjected carbamazepine to irradiation experiments that
simulated natural light with a mercury lamp emitting at UV and visible
wavelengths. They documented the resulting photodegradation of the drug into
a dozen intermediate forms, paying particular attention to its behavior in
the presence of chlorine.

Among the breakdown products, the researchers detected acridine, which
occurred as the 4th of 12 intermediates. The compound is relatively stable,
and after 8 h, its concentrations accounted for 10% of the carbamazepine in
the initial samples. The final three degradation products were chlorinated.

The study "reinforces the idea that photochemistry transforms compounds [and]
doesn't completely destroy them," says Kristopher McNeill of the University
of Minnesota, but it "sometimes turns them into other organic contaminants,
sometimes more toxic than the original."

Researchers comment that the results cannot be scaled up to estimate the
amount of the potential mutagen produced in the environment. "Both the light
source and the carbamazepine levels were very different than they would be in
the natural environment," says Mihaela Stefan, a research scientist at Trojan
Technologies (Canada). She points out that the experiments had much higher
concentrations of the drug than those reported for natural waters and used a
different spectral distribution and intensity of UV light than what is
present in natural sunlight.

The work "still is a bench-scale kind of experimental system," says Chris
Metcalfe of Trent University (Canada). "The next step would be obviously to
look at it in natural conditions."

Real estuarine environments with iron, dissolved organic matter, and other
materials that promote photodegradation would also have chlorine present.
"Generally speaking, chlorinated compounds are more toxic than nonchlorinated
ones, and chlorination potentially contributes to greater bioaccumulation,"
McNeill says. He agrees with the authors that further studies of the
chlorinated forms are necessary. -NAOMI LUBICK


Laurie J. Tenace
Environmental Specialist
Florida Department of Environmental Protection
2600 Blair Stone Road, MS 4555
Tallahassee, Florida 32399-2400
PH: (850) 245-8759
FAX: (850) 245-8811
Laurie.Tenace at dep.state.fl.us  
 
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