12 research outputs found
Photodegradation of Veterinary Ionophore Antibiotics under UV and Solar Irradiation
The veterinary ionophore antibiotics
(IPAs) are extensively used
as coccidiostats and growth promoters and are released to the environment
via land application of animal waste. Due to their propensity to be
transported with runoff, IPAs likely end up in surface waters where
they are subject to photodegradation. This study is among the first
to investigate the photodegradation of three commonly used IPAs, monensin
(MON), salinomycin (SAL) and narasin (NAR), under UV and solar irradiation.
Results showed that MON was persistent in a deionized (DI) water matrix
when exposed to UV and sunlight, whereas SAL and NAR could undergo
direct photolysis with a high quantum yield. Water components including
nitrate and dissolved organic matter had a great impact on the photodegradation
of IPAs. A pseudosteady state kinetic model was successfully applied
to predict IPAs’ photodegradation rates in real water matrices.
Applying LC/MS/MS, multiple photolytic transformation products of
IPAs were observed and their structures were proposed. The direct
photolysis of SAL and NAR occurred via cleavage on the ketone moiety
and self-sensitized photolysis. With the presence of nitrate, MON
was primarily degraded by hydroxyl radicals, whereas SAL showed reactivity
toward both hydroxyl and nitrogen-dioxide radicals. Additionally,
toxicity tests showed that photodegradation of SAL eliminated its
antibiotic properties against <i>Bacillus subtilis</i>
UV/Peracetic Acid for Degradation of Pharmaceuticals and Reactive Species Evaluation
Peracetic acid (PAA) is a widely
used disinfectant, and combined
UV light with PAA (i.e., UV/PAA) can be a novel advanced oxidation
process for elimination of water contaminants. This study is among
the first to evaluate the photolysis of PAA under UV irradiation (254
nm) and degradation of pharmaceuticals by UV/PAA. PAA exhibited high
quantum yields (Φ<sub>254 nm</sub> = 1.20 and 2.09 mol·Einstein<sup>–1</sup> for the neutral (PAA<sup>0</sup>) and anionic (PAA<sup>–</sup>) species, respectively) and also showed scavenging
effects on hydroxyl radicals (<i>k</i><sub><i><sup>•</sup></i>OH/PAA<sup>0</sup></sub> = (9.33 ± 0.3)
× 10<sup>8</sup> M<sup>–1</sup>·s<sup>–1</sup> and <i>k</i><sub><sup><i>•</i></sup>OH/PAA<sup>–</sup></sub> = (9.97 ± 2.3) × 10<sup>9</sup> M<sup>–1</sup>·s<sup>–1</sup>). The pharmaceuticals
were persistent with PAA alone but degraded rapidly by UV/PAA. The
contributions of direct photolysis, hydroxyl radicals, and other radicals
to pharmaceutical degradation under UV/PAA were systematically evaluated.
Results revealed that <sup>•</sup>OH was the primary radical
responsible for the degradation of carbamazepine and ibuprofen by
UV/PAA, whereas CH<sub>3</sub>CÂ(î—»O)ÂO<sup>•</sup> and/or
CH<sub>3</sub>CÂ(î—»O)ÂO<sub>2</sub><sup>•</sup> contributed
significantly to the degradation of naproxen and 2-naphthoxyacetic
acid by UV/PAA in addition to <sup>•</sup>OH. The carbon-centered
radicals generated from UV/PAA showed strong reactivity to oxidize
certain naphthyl compounds. The new knowledge obtained in this study
will facilitate further research and development of UV/PAA as a new
degradation strategy for water contaminants
Degradation of DEET and Caffeine under UV/Chlorine and Simulated Sunlight/Chlorine Conditions
Photoactivation
of aqueous chlorine could promote degradation of
chlorine-resistant and photochemically stable chemicals accumulated
in swimming pools. This study investigated the degradation of two
such chemicals, <i>N</i>,<i>N</i>-diethyl-3-methylbenzamide
(DEET) and caffeine, by low pressure ultraviolet (UV) light and simulated
sunlight (SS) activated free chlorine (FC) in different water matrices.
Both DEET and caffeine were rapidly degraded by UV/FC and SS/FC but
exhibited different kinetic behaviors. The degradation of DEET followed
pseudo-first-order kinetics, whereas the degradation of caffeine accelerated
with reaction. Mechanistic study revealed that, under UV/FC, ·OH
and Cl· were responsible for degradation of DEET, whereas ClO·
related reactive species (ClOrrs), generated by the reaction between
FC and ·OH/Cl·, played a major role in addition to ·OH
and Cl· in degrading caffeine. Reaction rate constants of DEET
and caffeine with the respective radical species were estimated. The
imidazole moiety of caffeine was critical for the special reactivity
with ClOrrs. Water matrix such as pH had a stronger impact on the
UV/FC process than the SS/FC process. In saltwater matrix under UV/FC
and SS/FC, the degradation of DEET was significantly inhibited, but
the degradation of caffeine was much faster than that in nonsalty
solutions. The interaction between Br<sup>–</sup> and Cl<sup>–</sup> may play an important role in the degradation of caffeine
by UV/FC in saltwater. Reaction product analysis showed similar product
patterns by UV/FC and SS/FC and minimal formation of chlorinated intermediates
and disinfection byproducts
Biodegradation of Veterinary Ionophore Antibiotics in Broiler Litter and Soil Microcosms
Ionophore
antibiotics (IPAs) are polyether compounds used in broiler
feed to promote growth and control coccidiosis. Most of the ingested
IPAs are excreted into broiler litter (BL), a mixture of excreta and
bedding material. BL is considered a major source of IPAs released
into the environment as BL is commonly used to fertilize agricultural
fields. This study investigated IPA biodegradation in BL and soil
microcosms, as a process affecting the fate of IPAs in the environment.
The study focused on the most widely used IPAs, monensin (MON), salinomycin
(SAL), and narasin (NAR). MON was stable in BL microcosms at 24–72%
water content (water/wet litter, w/w) and 35–60 °C, whereas
SAL and NAR degraded under certain conditions. Factor analysis was
conducted to delineate the interaction of water and temperature on
SAL and NAR degradation in the BL. A major transformation product
of SAL and NAR was identified. Abiotic reaction(s) were primarily
responsible for the degradation of MON and SAL in nonfertilized soil
microcosms, whereas biodegradation contributed significantly in BL-fertilized
soil microcosms. SAL biotransformation in soil microcosms yielded
the same product as in the BL microcosms. A new primary biotransformation
product of MON was identified in soil microcosms. A field study showed
that MON and SAL were stable during BL stacking, whereas MON degraded
after BL was applied to grassland. The biotransformation product of
MON was also detected in the top soil layer where BL was applied
Transformation of Tetracycline Antibiotics and Fe(II) and Fe(III) Species Induced by Their Complexation
Tetracycline antibiotics (TCs) are
frequently detected micropollutants
and are known to have a strong tendency to complex with metal ions
such as FeÂ(II) and FeÂ(III) in aquatic environments. Experiments with
FeÂ(II) and TCs showed that the complexation of FeÂ(II) with tetracycline
(TTC), oxytetracycline (OTC), or chlorotetracycline (CTC) could lead
to the accelerated oxidation of FeÂ(II) and the promoted degradation
of TCs simultaneously. The reaction started with complexation of FeÂ(II)
with TC followed by oxidation of the FeÂ(II)–TC complex by dissolved
oxygen to generate a FeÂ(III)–TC complex and reactive oxygen
species (ROS). The ROS (primarily ·OH) then degraded TC. The
oxidation rate constants of FeÂ(II) in the Fe<sup>II</sup>–H<sub>2</sub>L and Fe<sup>II</sup>–HL complexes were 0.269 and 1.511
min<sup>–1</sup>, respectively, at ambient conditions (pH 7,
22 °C, and <i>P</i><sub>O<sub>2</sub></sub> of 0.21
atm), which were about 60 and 350 times of the oxidation rate of uncomplexed
FeÂ(II). Humic acids (HA) compete with TCs for FeÂ(II), but the effect
was negligible at moderate HA concentrations (≤10 mg·L<sup>–1</sup>). Experiments with FeÂ(III) and TCs showed that the
complexation of FeÂ(III) with TC could generate oxidized TC and FeÂ(II)
without the need of oxygen at a relatively slower rate compared to
the reaction involving FeÂ(II), O<sub>2</sub>, and TCs. These findings
indicate the mutually influenced environmental transformation of TCs
and FeÂ(II) and FeÂ(III) induced by their complexation. These newly
identified reactions could play an important role in affecting the
environmental fate of TCs and cycling of FeÂ(II) and FeÂ(III) in TCs-contaminated
water and soil systems
Degradation of Pharmaceuticals and Metabolite in Synthetic Human Urine by UV, UV/H<sub>2</sub>O<sub>2</sub>, and UV/PDS
To
minimize environmental pharmaceutical micropollutants, treatment
of human urine could be an efficient approach due to the high pharmaceutical
concentration and toxic potential excreted in urine. This study investigated
the degradation kinetics and mechanisms of sulfamethoxazole (SMX),
trimethoprim (TMP) and N<sub>4</sub>-acetyl-sulfamethoxazole (acetyl-SMX)
in synthetic fresh and hydrolyzed human urines by low-pressure UV,
and UV combined with H<sub>2</sub>O<sub>2</sub> and peroxydisulfate
(PDS). The objective was to compare the two advanced oxidation processes
(AOPs) and assess the impact of urine matrices. All three compounds
reacted quickly in the AOPs, exhibiting rate constants of (6.09–8.53)
× 10<sup>9</sup> M<sup>–1</sup>·s<sup>–1</sup> with hydroxyl radical, and (2.35–16.1) × 10<sup>9</sup> M<sup>–1</sup>·s<sup>–1</sup> with sulfate radical.
In fresh urine matrix, the pharmaceuticals’ indirect photolysis
was significantly suppressed by the scavenging effect of urine citrate
and urea. In hydrolyzed urine matrix, the indirect photolysis was
strongly affected by inorganic urine constituents. Chloride had no
apparent impact on UV/H<sub>2</sub>O<sub>2</sub>, but significantly
raised the hydroxyl radical concentration in UV/PDS. Carbonate species
reacted with hydroxyl or sulfate radical to generate carbonate radical,
which degraded SMX and TMP, primarily due to the presence of aromatic
amino group(s) (<i>k</i> = 2.68 × 10<sup>8</sup> and
3.45 × 10<sup>7</sup> M<sup>–1</sup>·s<sup>–1</sup>) but reacted slowly with acetyl-SMX. Ammonia reacted with hydroxyl
or sulfate radical to generate reactive nitrogen species that could
react appreciably only with SMX. Kinetic simulation of radical concentrations,
along with products analysis, helped elucidate the major reactive
species in the pharmaceuticals’ degradation. Overall, the AOPs’
performance was higher in the hydrolyzed urine than fresh urine matrix
with UV/PDS better than UV/H<sub>2</sub>O<sub>2</sub>, and varied
significantly depending on pharmaceutical’s structure
Kinetics and Modeling of Degradation of Ionophore Antibiotics by UV and UV/H<sub>2</sub>O<sub>2</sub>
Ionophore antibiotics
(IPAs), one of the major groups of pharmaceuticals
used in livestock industry, have been found to contaminate agricultural
runoff and surface waters via land application of animal manures as
fertilizers. However, limited research has investigated the means
to remove IPAs from water sources. This study investigates the degradation
of IPAs by using ultraviolet (UV) photolysis and UV combined with
hydrogen peroxide (UV/H<sub>2</sub>O<sub>2</sub>) advanced oxidation
process (AOP) under low-pressure (LP) UV lamps in various water matrices.
Three widely used (monensin, salinomycin, and narasin) and one model
(nigericin) IPAs exhibit low light absorption in the UV range and
degrade slowly at the light intensity of 3.36 × 10<sup>–6</sup> Einstein·L<sup>–1</sup>·s<sup>–1</sup> under
UV photolysis conditions. However, IPAs react with hydroxyl radicals
produced by UV/H<sub>2</sub>O<sub>2</sub> at fast reaction rates,
with second-order reaction rate constants at (3.49–4.00) ×
10<sup>9</sup> M<sup>–1</sup>·s<sup>–1</sup>. Water
matrix constituents enhanced the removal of IPAs by UV photolysis
but inhibited UV/H<sub>2</sub>O<sub>2</sub> process. A steady-state
kinetic model successfully predicts the impact of water constituents
on IPA degradation by UV/H<sub>2</sub>O<sub>2</sub> and determines
the optimal H<sub>2</sub>O<sub>2</sub> dose by considering both energy
consumption and IPA removal. LC/MS analysis of reaction products reveals
the initial transformation pathways of IPAs via hydrogen atom abstraction
and peroxidation during UV/H<sub>2</sub>O<sub>2</sub>. This study
is among the first to provide a comprehensive understanding of the
degradation of IPAs via UV/H<sub>2</sub>O<sub>2</sub> AOP
Rapid Disinfection by Peracetic Acid Combined with UV Irradiation
This study proposes a novel disinfection
process by sequential
application of peracetic acid (PAA) and ultraviolet light (UV), on
the basis of elucidation of disinfection mechanisms under UV/PAA.
Results show that hydroxyl radicals, generated by UV-activated PAA,
contribute to the enhanced inactivation of Escherichia
coli under UV/PAA compared to PAA alone or UV alone.
Furthermore, the location of hydroxyl radical generation is a critical
factor. Unlike UV/H<sub>2</sub>O<sub>2</sub>, which generates hydroxyl
radicals mainly in the bulk solution, the hydroxyl radicals under
UV/PAA are produced close to or inside E. coli cells, due to PAA diffusion. Therefore, hydroxyl radicals exert
significantly stronger disinfection power under UV/PAA than under
UV/H<sub>2</sub>O<sub>2</sub> conditions. Pre-exposing E. coli to PAA in the dark followed by application
of UV (i.e., a PAA-UV/PAA process) promotes diffusion of PAA to the
cells and achieves excellent disinfection efficiency while saving
more than half of the energy cost associated with UV compared to simultaneous
application of UV and PAA. The effectiveness of this new disinfection
strategy has been demonstrated not only in lab water but also in wastewater
matrices
Acid-Catalyzed Transformation of Ionophore Veterinary Antibiotics: Reaction Mechanism and Product Implications
Ionophore
antibiotics (IPAs) are polyether antimicrobials widely
used in the livestock industry and may enter the environment via land
application of animal waste and agricultural runoff. Information is
scarce regarding potential transformation of IPAs under environmental
conditions. This study is among the first to identify the propensity
of IPAs to undergo acid-catalyzed transformation in mildly acidic
aquatic systems and characterize the reactions in depth. The study
focused on the most widely used monensin (MON) and salinomycin (SAL),
and also included narasin (NAR) in the investigation. All three IPAs
are susceptible to acid-catalyzed transformation. MON reacts much
more slowly than SAL and NAR and exhibits a different kinetic behavior
that is further evaluated by a reversible reaction kinetic model.
Extensive product characterization identifies that the spiro-ketal
group of IPAs is the reactive site for the acid-catalyzed hydrolytic
transformation, yielding predominantly isomeric and other products.
Toxicity evaluation of the transformation products shows that the
products retain some antimicrobial properties. The occurrence of IPAs
and isomeric transformation products is also observed in poultry litter
and agricultural runoff samples. Considering the common presence of
mildly acidic environments (pH 4–7) in soils and waters, the
acid-catalyzed transformation identified in this study likely plays
an important role in the environmental fate of IPAs
The Presence of Pharmaceuticals and Personal Care Products in Swimming Pools
The
introduction of pharmaceuticals and personal care products
(PPCPs) into the environment can be partially attributed to discharges
of human wastes, which is also relevant in swimming pool settings.
Little or no information exists to address this issue in the literature.
Therefore, experiments were conducted to examine the presence and
behavior of PPCPs in swimming pools. Among 32 PPCPs amenable to analysis
by an available method, <i>N</i>,<i>N</i>-diethyl-<i>m</i>-toluamide (DEET), caffeine, and triÂ(2-chloroethyl)Âphosphate
(TCEP) were found to be present in measurable concentrations in pool
water samples. Examination of the degradation of selected PPCPs by
chlorination illustrated differences in their stability in chlorinated
pools. These results, as well as literature information regarding
other attributes of PPCPs, indicate characteristics of these compounds
that could allow for their accumulation in pools, including slow reaction
with chlorine, little potential for liquid → gas transfer,
and slow metabolism by humans (among orally ingested PPCPs). The findings
of this study also suggest the potential for accumulation of topically
applied PPCP compounds in pools. More generally, the results of this
study point to the importance of proper hygiene habits of swimmers.
The potential for the accumulation of PPCPs in pools raises questions
about their fate and the risks to swimming pool patrons