Speaker
Ms
Erzsebet Takacs
(Centre for Energy Research, Hungary)
Description
Background of the study
Wide varieties of toxic organic compounds are entering the aquatic
environment. The main sources of these impurities are the waste water
treatment plants for domestic sewage. The co-occurrence of sublethal
antibiotic concentration and high density of microbial population
provides ideal condition for facilitating the selection and
propagation of resistant bacteria in sewage treatment plants. To
reduce the amount of harmful organic compounds entering into the
receiving bodies of waste water a family of new technologies with the
name advanced oxidation processes (AOP) is under development. In
these technologies highly reactive, oxidizing radical intermediates
(mainly OH radicals) are produced by various techniques, e.g. , by
ionizing radiation. Radiolysis provides the benefit to produce
reactive oxidizing ($^{\bullet}$OH and H$_2$O$_2$) and reduce
(O$_2^{\bullet}$, $\mathrm{e}_{\mathrm{aq}}^-$ and $^{\bullet}$H)
species (or from a kinetic point of view highly reactive electrophile
and nucleophile species) in situ from water
Methodology
Electron pulse radiolysis experiments were conducted using a Tesla
Linac LPR-4 accelerator with kinetic spectrophotometric detection.
A $^{60}$Co facility with $11.5$ kGy/h dose rate was used for
$\gamma$-irradiation. LC/ESI-MS was used for final product analysis.
The samples were also characterized by COD, TOC, TN and pH
measurements and by complex toxicological analysis.
Results
The oxidative and reductive decomposition of penicillin derivatives
was studied, the change in the antimicrobial activity of the drugs was
followed. The reaction mechanism of $^{\bullet}$OH induced oxidation
of penicillins indicates the existence of a short-living and a
stabilized long-living $^{\bullet}$OH adduct to the sulfur.
The $\mathrm{e}_{\mathrm{aq}}^-$ is accommodated on the carbonyl groups of
the penicillin skeleton yielding ketyl radicals. Penicillins react
with the hydrated electron somewhat similarly to a tripeptide. It
appeared that excessive or insufficient absorbed dose is deleterious
in relation to elimination of antibacterial activity. At low radical
exposure the forming products exhibit enhanced toxicity and
antimicrobial potency. The adverse effect at high radical exposure
presumably arises from the forming polyhydroxylated phenolic
compounds.
The $^{\bullet}$OH induced decomposition of sulfonamide antibiotics in
dilute solutions was also studied by a wide variety of analytical
techniques. The degradation was shown to start with $^{\bullet}$OH
addition to the aromatic ring, the cyclohexadienyl type radical thus
formed reacts with dissolved oxygen transforming to peroxy radical.
This radical yields hydroxylated molecules by HO$_2^{\bullet}$
elimination, or it undergoes ring opening to aliphatic compounds.
Conclusion
It was shown that $\mathrm{e}_{\mathrm{aq}}^-$ and $^{\bullet}$OH are
able to demolish the penicillin’s $\beta$-lactam system responsible
for their antimicrobial activity. However, careful optimization of
the advanced oxidation process, determination of the dose necessary
for decreasing the toxicity and improving the biodegradability is
necessary. Based on complex investigations for both types of
antibiotics the degradation with the formation of inorganic ions is
multistep process, the molecules first are step-by-step oxidized and
then mineralized.
| Country/Organization invited to participate | Hungary |
|---|
Primary author
Ms
Erzsebet Takacs
(Centre for Energy Research, Hungary)
