12 research outputs found

    Photodegradation of Veterinary Ionophore Antibiotics under UV and Solar Irradiation

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    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

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    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>C­(O)­O<sup>•</sup> and/or CH<sub>3</sub>C­(O)­O<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

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    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

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    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

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    Tetracycline antibiotics (TCs) are frequently detected micropollutants and are known to have a strong tendency to complex with metal ions such as Fe­(II) and Fe­(III) in aquatic environments. Experiments with Fe­(II) and TCs showed that the complexation of Fe­(II) with tetracycline (TTC), oxytetracycline (OTC), or chlorotetracycline (CTC) could lead to the accelerated oxidation of Fe­(II) and the promoted degradation of TCs simultaneously. The reaction started with complexation of Fe­(II) with TC followed by oxidation of the Fe­(II)–TC complex by dissolved oxygen to generate a Fe­(III)–TC complex and reactive oxygen species (ROS). The ROS (primarily ·OH) then degraded TC. The oxidation rate constants of Fe­(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 Fe­(II). Humic acids (HA) compete with TCs for Fe­(II), but the effect was negligible at moderate HA concentrations (≤10 mg·L<sup>–1</sup>). Experiments with Fe­(III) and TCs showed that the complexation of Fe­(III) with TC could generate oxidized TC and Fe­(II) without the need of oxygen at a relatively slower rate compared to the reaction involving Fe­(II), O<sub>2</sub>, and TCs. These findings indicate the mutually influenced environmental transformation of TCs and Fe­(II) and Fe­(III) induced by their complexation. These newly identified reactions could play an important role in affecting the environmental fate of TCs and cycling of Fe­(II) and Fe­(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

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    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>

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    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

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    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

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    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

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    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 tri­(2-chloroethyl)­phosphate (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
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