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药用活性化合物(PhACs)包括抗生素、消炎止痛药、β-阻滞剂、抗菌药和雌激素类,广泛用于疾病治疗,常通过固体废物和废水进入环境中,成为一类新兴环境污染物[1]。卡马西平(carbamazepine,CBZ)是一种常见药用活性化合物,主要用于治疗癫痫、精神运动性发作和三叉神经痛等疾病[2]。据报道全球CBZ年均消耗量高达1014t[3],但人体对CBZ的吸收只有78%[4],剩余部分则直接排出体外,从而导致自然环境中存在CBZ药物残留,在污水处理厂出水、地表水、地下水、土壤和污泥中广泛检出[5]。当前传统水处理工艺很难去除CBZ[6],使得CBZ可能对生态系统和人类健康构成潜在威胁,因此需要一种有效去除水中CBZ的方法。
已有研究者使用O3[7]、UV/TiO2[8]、UV/H2O2[9]和UV/H2O2/Fe2+[10]等高级氧化工艺(AOPs)进行卡马西平的控制与去除。UV/氯是一种新型的高级氧化工艺,它通过紫外线激发游离氯(HClO/ClOˉ)产生高氧化能力的羟基自由基·OH(2.8 V)和氯自由基·Cl(2.4 V)[11],能有效去除水中有机污染物和病原微生物,应用前景广阔。研究表明,UV/氯工艺对布洛芬、双氯芬酸和莠去津等有良好的去除效果[12-13]。然而UV/氯降解过程中可能会生成含氯副产物[14],表现出比母物质更强的潜在毒性。因此UV/氯工艺降解副产物的潜在危害亟待引起重视。
本研究以CBZ为目标污染物,考察UV光强、余氯初始浓度、溶液初始pH值和氨氮浓度等因素对UV/氯工艺降解效果的影响。利用高分辨率质谱HRMS Orbitrap(Q-E Plus)对CBZ降解中间产物进行鉴定,探讨CBZ降解机制,提出降解路径,评估降解过程中的毒性变化,为水中PhACs新兴污染物的去除与控制、水质安全保障提供理论依据和技术支撑。
卡马西平在UV/氯高级氧化工艺中的去除、转化与毒性评价
Removal, transformation and toxicity evaluation of carbamazepine by the UV/chlorine advanced oxidation process
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摘要: UV/氯作为一种新型高级氧化工艺在新兴污染物控制领域引起了广泛关注。采用UV/氯工艺对典型抗癫痫药物卡马西平(CBZ)进行降解研究。比较单一UV、单一氯和UV/氯对CBZ的降解效果,考察了UV光强、余氯初始浓度、溶液初始pH值和氨氮浓度等因素的影响,解析CBZ在降解过程中的中间产物,提出降解机理,并评估生态风险。结果表明,UV/氯工艺的降解效果明显优于单一UV和单一氯。降解过程遵循准一级反应动力学。降解速率常数随UV光强和余氯初始浓度增大而增大,随氨氮浓度增加而减小,酸性条件更有利于降解过程。采用HRMS Orbitrap和GC-MS鉴定出10种CBZ降解中间产物,CBZ降解主要通过羟基化、氯取代和电子转移等反应实现。发光细菌毒性实验和ECOSAR预测均表明,CBZ在UV/氯工艺中会产生毒性高于母体的中间产物,对水质安全保障造成潜在风险。Abstract: The UV/chlorine process has attracted wide attention as a new advanced oxidation process for emerging pollutant control. In this study, the degradation of the typical anti-epileptic drug carbamazepine (CBZ) was investigated by UV/chlorine process. The degradation of CBZ by single UV, single chlorine and UV/chlorine process was compared. Besides, the effects of UV light intensity, concentration of residual chlorine, pH of solution and ammonia nitrogen concentration on the degradation were also investigated. Built on the identification of degradation products, the degradation mechanism of carbamazepine (CBZ) in the UV/chlorine process was proposed. The ecological risk during the process was also evaluated. The results showed that the UV/chlorine process was more efficient than single UV and single chlorine. The whole process followed pseudo-first-order reaction kinetics. The degradation rate constants increased with the increase of UV light intensity and residual chlorine concentration, while decreased with the increasing ammonia nitrogen concentration. The acidic condition was in favor of the degradation process. Ten CBZ degradation intermediates were identified by HRMS Orbitrap and GC-MS. CBZ degradation was mainly achieved through hydroxylation, chlorine substitution and electron transfer. Both luminescent bacteria toxicity test and ECOSAR prediction indicated that the intermediates with higher toxicity than the parent could be generated during the UV/chlorine process, which may process the potential ecological risk for the water quality security.
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表 1 不同工况下CBZ的准一级反应动力学模型参数
Table 1. Parameters of pseudo-first-order kinetics at different conditions of CBZ degradation
工况 Operating condition /min−1$k_{{\text{app}}}'$ R2 t1/2/min 单一UV 0.0084 0.7320 77.8 单一氯 0.0056 0.8794 154.3 UV/氯 0.2601 0.9898 3.8 表 2 不同UV光强下CBZ的准一级反应动力学模型参数
Table 2. Parameters of pseudo-first-order kinetics of CBZ degradation at different UV intensities
UV光强/(μW·cm-2) UV intensity /min−1$k_{{\text{app}}}'$ R2 t1/2/min 500 0.0416 0.9518 19.9 1000 0.0882 0.9956 8.4 2000 0.1326 0.9899 4.7 3000 0.1609 0.9757 3.4 表 3 不同余氯初始浓度下准一级反应动力学模型参数
Table 3. Parameters of pseudo-first-order kinetics of CBZ degradation at various initial residual chlorine dose
余氯初始浓度 /(mmol·L−1)
Initial concentration of residual chlorine /min−1$k_{{\text{app}}}'$ R2 t1/2/min 0.085 0.0252 0.9768 29.0 0.170 0.0491 0.9872 14.4 0.255 0.0823 0.9957 9.0 0.340 0.1019 0.9866 8.2 0.425 0.1574 0.9639 6.2 表 4 溶液不同初始pH值下CBZ的准一级反应动力学模型参数
Table 4. Parameters of pseudo-first-order kinetics of CBZ degradation at different pH values
pH /min−1$k_{{\text{app}}}'$ R2 t1/2/min 3 4.2991 0.9998 0.16 5 0.0510 0.9934 12.5 7 0.0501 0.8919 9.4 9 0.0681 0.8990 6.9 11 0.0210 0.9411 29.9 表 5 不同氨氮浓度下CBZ的准一级反应动力学参数
Table 5. Parameters of pseudo-first-order kinetics of CBZ degradation at different ammonia concentrations
氨氮浓度(/mmol·L−1 ) Ammonia concentration /min−1$k_{{\text{app}}}'$ R2 t1/2/min 0 0.1315 0.9932 4.4 0.05 0.0728 0.9581 6.4 0.10 0.0647 0.9548 7.5 0.20 0.0444 0.9945 14.9 0.40 0.0319 0.9900 21.4 表 6 通过HRMS检出的CBZ及中间产物
Table 6. CBZ and its intermediates detected by HRMS
序号
Serial
number化合物
Compound分子式
Molecular
formula结构式
Structural
formula保留时间/min
Retention
time[M+H]+ 理论质荷比
Theoretical mass-
charge ratio(m/z)实际质荷比
Actual mass-
charge ratio(m/z)Δ(×10−6) 1 CBZ C15H12N2O 8.17 237.1022 237.1022 0 2 Pr287 C15H11ClN2O2 7.75 287.0582 287.0587 1.7 3 Pr271 C15H14N2O3 4.83 271.1077 271.1080 1.1 4 CBZ-Cl C15H11ClN2O 9.18 271.0633 271.0632 −0.3 5 CBZ-OH C15H12N2O2 7.11 253.0972 253.0970 −0.8 6 Pr240 C15H13NO2 7.36 240.1019 240.1021 0.8 表 7 通过GC-MS检出的降解产物
Table 7. Degradation products detected by GC-MS
序号
Serial
number产物
Product分子量
Molecular
weightCAS号
CAS
number保留时间/min
Retention
time匹配度/%
Degree of
match分子式
Molecular
formula分子结构
Molecular
structure1 乳酸(2TMS) 90 79-33-4 10.6 87.2 C3H6O3 2 乙醇酸(2TMS) 76 79-14-1 11.1 83.4 C2H4O3 3 草酸(2TMS) 89 144-62-7 12.9 80.5 C2H2O4 4 苯甲酸(TMS) 122 65-85-0 15.9 88.2 C7H6O2 5 丁二酸(2TMS) 118 110-15-6 18.5 83.1 C4H6O4 注:TMS表明为小分子酸硅烷化物质.
Note: TMS stands for silylated small molecule acid.表 8 利用ECOSAR预测CBZ及其中间产物的急性毒性(mg·L−1)
Table 8. Estimated acute toxicity of CBZ and its intermediates by ECOSAR software
鱼 Fish 水蚤 Daphnid 绿藻 Green Algae 96 h-LC50 48 h-LC50 96 h-EC50 CBZ 116.13 64.40 59.82 CBZ-Cl 36.59 22.84 21.29 CBZ-OH 1317.45 588.22 542.75 Pr271 0.24 0.24 0.22 Pr240 43.68 26.53 24.71 Pr287 120.87 67.99 63.17 -
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