INTRODUCTION
Recently a variety of antibiotics have been detected in the environments (Roobberson et al. 2006; Kosutic et al. 2007). Antibiotics used for humans and animals can be introduced to the various environment by an excretion, disposal of unused or expired drug, and accidental spills (Jorgensen and Halling-sorensen, 2000; Diaz-Cruz et al. 2003; Reyes et al. 2006). These antibiotics are incom-pletely removed by the conventional biological processes, and finally released from µg l-1 to ng l-1 into aquatic environment (Ternes et al. 2002; Balcioglu and Otker 2003; Drillia et al. 2005; Hernando et al. 2006; Bautitz and Nogueira 2007). The continual exposure of antibiotics may lead to the resistance in bacterial strains and the unknown adverse effects on human and ecosystem (Diaz-Cruz et al. 2003; Brown et al. 2006; Cabello 2006; Hernando et al.
2006).
Recently, many researches have been conducted on the treatments of antibiotics found in ground-water, surface-water and wastesurface-water. Gartiser et al. (2007) reported that percent removal of amoxicillin by the biological treatment was observed between 11% and 63% in 28 days. TOC removal was reported as 14 to 24% after 3 hours. Also, Batt et al. (2006) showed that sulfamethoxazole, tetracycline, and trimethoprim antibiotics in conventional wastewater treatment plants were not completely removed by the bio-logical processes. Due to the poor treatment efficiencies of biological processes, advanced oxidation processes (AOPs) are evaluated as a suitable alternative for the removal of antibiotics. AOPs using free radicals such as the hydroxyl radical enhance the removal efficiency for refractory toxic organic pollutants in aquatic environment (Balcioglu and Otker 2003; Arslan-Alaton and Gurses 2004; Reyes et al. 2006). Andreozzi et al. (2005) reported the removal effici-ency more than 90% of amoxicillin by ozone at pH 5.5. However, Alaton et al. (2004) reported that ozonation and
Journal of Radiation Industry 1 (1) : 21~24 (2007)
─ ─ 21 ──
Decomposition and Mineralization of Amoxicillin by
High Ionizing Energy
Dongkyu Choi1,2, Seungho Yu1,*, Myunjoo Lee1and Seung-Woo Jeong2
1Advanced Radiation Technology Institute, Korea Atomic Energy Research Institute, Jeongeup 580-185, Korea 2Department of Environmental Engineering, Kunsan National University, Kunsan 573-701, Korea
Abstract -- The presence of antibiotics in aquatic environment has been concerning as a new
environment pollutant problem. The aim of this study was to evaluate the degradation of antibio-tics by gamma irradiation. Amoxicillin as one of ββ-lactam antibiotics is widely used for both human and animals. To compare the removal efficiencies of amoxicillin, amoxicillin solutions were saturated or purged with three difference gases; N2O, O2and N2separately. The amoxicillin
solutions were irradiated at up to 100 kGy. Amoxicillin was completely degraded between 20 and 40 kGy. Especially, amoxicillin saturated with N2O showed the highest degradation rate, and 90%
TOC removal efficiency. The enhanced radiolytic decomposition of amoxicillin can be explained by the reactions with oxidizing radicals such as ∙∙OH and O2∙∙-/HO2∙∙ radicals.
Key words : Antibiotics, Amoxicillin, Gamma radiation, Radical
* Corresponding author: Seungho Yu, Tel. +82-63-570-3341, Fax. +82-63-570-3348, E-mail. [email protected]
the photo-Fenton showed the removal efficiencies of 49-66% and 42~52% for COD and TOC, respectively. To the
best of our knowledge, however, none of the AOPs is able to obtain complete removal efficiencies of TOC or COD.
This study was designed to investigate radiolytic degra-dation of amoxicillin (Fig. 1). The purposes of this study were: 1) to evaluate degradation efficiencies of amoxicillin by gamma radiation; 2) to investigate influence of N2O and O2gases as radical scavengers on the removal of total organic carbon (TOC).
MATERIALS AND METHODS
1. Chemicals
Amoxicillin (C16H19N3O5, FW; 365.4) was obtained from Sigma-Aldrich, Co. (St Louis, MO, USA). Aqueous solu-tions of amoxicillin were prepared with purified water (SAMBO SCIENTIFIC CO.,LTD). N2(99.9%), O2(99.9%), and N2O (99.9%) gases (Korea Special Gas Co., Iksan, Korea) were used to saturated or purge the batch bottles prior to gamma irradiation.
2. Analytical methods
After gamma irradiation, amoxicillin concentrations in the aqueous solutions were measured by using a high performance liquid chromatography (HPLC). An Agilent 1200 Series HPLC (Agilent Technologies, USA) equipped with an UV detector was operated at 230 nm. A Pheno-menex Luna 5µ C8 (2) 100A column (150×4.6 mm) was
used for the separation of amoxicillin, and the injection sample volume was 50µl. 20 mM potassium phosphate adjusted to pH 4.6/methanol (55 : 45 ratio) at a flow rate of
2.0 ml min-1was used as a Mobile phase. The analysis of total organic carbon (TOC) in the aqueous samples was carried out by using a Shimadzu TOC-VCSN analyzer (Shimadzu Co., Japan).
3. Irradiation
Gamma irradiations were conducted in a high-level 60CO source (Nordion Inc., Canada) at the Korea Atomic Energy Research Institute (Jeongeup, Korea). The aqueous solu-tions of amoxicillin were placed into 50 ml tube screw cap bottles without a headspace prior to gamma irradiation. All the samples were in equilibrium with an atmospheric pre-ssure and room temperature (22�C±2) before irradiation
and were sealed with screw caps to avoid the contact with air. For the radical scavenger experiments, the aqueous solutions were purged with high-purity (99.99%) N2, O2, and N2O gases for 30 min just before irradiation, respec-tively, and were sealed with caps.
RESULTS AND DISCUSSION
1. Decomposition of amoxicillin by gamma irradiation
Fig. 2 shows a decomposition curve of amoxicillin by gamma irradiation. The aqueous concentration of amoxi-cillin irradiated was 30 mg l-1in each of the batch bottles and the irradiation doses ranged from 0 to 100 kGy. As shown in Fig. 2, the decomposition degree of amoxicillin was increased along with increases of the absorbed doses. As shown in Fig. 2, amoxicillin in aqueous solutions satu-rated by N2O and O2gases achieved the complete removal at 10 kGy. Also, complete degradation of amoxicillin in the control (atmospheric) and N2 saturated solutions was observed at the absorbed dose of 20 kGy and 40 kGy, res-pectively. Thus, amoxicillin was decomposed easily by gamma irradiation under every experiment condition. De-composition of amoxicillin is explained by the reaction between solute molecules and oxidizing species produced from a water radiolysis. It is well known that water radioly-sis produces the primary species (∙OH, eaq-, and ∙H) and molecular products (H2, H2O2) (Equation 1) (Getoff 1996).
γ
H2O mmmmmmmmmm→∙H; eaq-∙OH; H2; H2O2 (1) (G-value) (0.6) (2.7) (2.8) (0.45) (0.72)
Especially, N2O and O2saturated solutions showed high-Dongkyu Choi, Seungho Yu, Myunjoo Lee and Seung-Woo Jeong
22
Fig. 1. Chemical structure of amoxicillin.
NH2 H N H N S O OH HO O O
er removal efficiencies than the other solutions (Fig. 2). As shown in Table 1, N2O gas converts generated eaq-and ∙H into ∙OH radicals which are strong oxidative to
amoxi-cillin. Enhanced degradation of amoxicillin saturated with O2is explained by the reaction with oxidizing species such as O2∙-and HO2∙ radicals generated through a fast reac-tions of∙H radicals and eaq-(Buxton et al. 1988; Getoff 1996; Mú ˇcka et al. 2003). In N2-purged solutions the degradation efficiency of amoxicillin was lower than the control (atmospheric) condition. As the results of experi-ment, oxidizing species such as ∙OH, and O2∙-/HO2∙ radicals were closely associated with a radiolysis decom-position of amoxicillin.
2. Mineralization of amoxicillin by using scavenger gases
Batch experiments were performed to study the radical scavenger effects on an enhancement of amoxicillin mine-ralization under four different conditions; 1) control
(atmo-spheric) 2) N2gas bubbled 3) O2saturation 4) N2O satura-tion. The initial TOC concentrations of the aqueous amoxi-cillin solutions ranged from 13 mg l-1 to 15 mg l-1. As shown in Fig. 3, the control and O2saturated solutions achieved 30% and 60% TOC removal efficiencies, respec-tively, at 20 kGy. The N2O saturated solutions showed the highest TOC removal of 94% at 40 kGy. However, only 12% mineralization was observed at 60 kGy with N2purge, which was much lower than the other experimental condi-tions. As demonstrated previously, the enhanced TOC re-moval efficiencies were attributed to the oxidizing radicals (∙OH, O2∙- and HO2∙) produced from the reaction of eaq-and ∙H with N2O and O2. However, TOC increased with the control, O2, N2O conditions after 40 kGy. It can be tentatively concluded from our visual observations that increases in TOC are due to polymerization reactions of intermediate by-products as the absorbed doses increase.
CONCLUSIONS
This study used gamma radiation for the treatment of amoxicillin in aqueous solution. The results of this study showed that gamma irradiation was very effective on the removal of amoxicillin in an aqueous solution. Moreover, the radiolytic decomposition of amoxicillin showed much enhanced TOC removal with radical scavengers such as O2 and N2O. These results suggest that the use of radical
Decomposition of Amoxicillin by Radiation 23
0.0 0.2 0.4 0.6 0.8 1.0 0 10 20 30 40 50 60
Radiation dose (kGy)
C/Co
Fig. 2. Radiolysis degradation of amoxicillin in an aqueous solu-tion (==30 mg l-1) by using radical scavenger gases. (◇) atmospheric; (□) N2; (△) O2; (○) N2O.
Table 1. Chemical reactions and rate constants for the radical scavengers during the radiolysis of water (Buxton et al. 1988; Getoff 1996)
Scavengers Reaction k (l mol-1s-1) O2 ∙H+O 2→HO2∙ 2.1×1010 eaq-++O2→O2∙- 1.9×1010 N2O ∙H + +N2O →∙OH++N2 2.1×106 eaq-++N2O →OH-++∙OH++N2 9.1×109 0.0 0.2 0.4 0.6 0.8 1.0 0 10 20 30 40 50 60
Radiation dose (kGy)
TOC
(C/Co)
Fig. 3. TOC removal efficiency of amoxicillin by using radical scavenger gases. (◇) atmospheric; (□) N2; (△) O2; (○)
scavengers with radiation is very effective for enhancing TOC or COD removal efficiencies in a pharmaceutical wa-stewater containing antibiotics.
ACKNOWLEDGEMENT
The research was supported by the Nuclear R&D pro-gram of the Ministry of Science and Technology and the Environmental Core Technology R&D project for the Next Generation of the Ministry of Environment of Korea. This article has not been reviewed by the ministry, and no offi-cial endorsement should be inferred.
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Manuscript Received: April 16, 2007 Revision Accepted: May 29, 2007
Dongkyu Choi, Seungho Yu, Myunjoo Lee and Seung-Woo Jeong 24
