水體中布洛芬的間接光降解作用機(jī)理研究

白 瑩,崔正國*,蘇榮國,曲克明

水體中布洛芬的間接光降解作用機(jī)理研究

白 瑩1,崔正國1*,蘇榮國2,曲克明1

(1.中國水產(chǎn)科學(xué)研究院黃海水產(chǎn)研究所,農(nóng)業(yè)農(nóng)村部海洋漁業(yè)可持續(xù)發(fā)展重點(diǎn)實(shí)驗(yàn)室,青島海洋科學(xué)與技術(shù)試點(diǎn)國家實(shí)驗(yàn)室,海洋漁業(yè)科學(xué)與食物產(chǎn)出過程功能實(shí)驗(yàn)室,山東 青島 266071；2.中國海洋大學(xué)化學(xué)化工學(xué)院,海洋化學(xué)理論與工程技術(shù)教育部重點(diǎn)實(shí)驗(yàn)室,山東 青島 266100)

為闡明布洛芬(IBP)在海水中的間接光降解機(jī)理,研究了4種不同來源的溶解有機(jī)物(DOM)以及溶液初始pH值、鹽度、NO3-和HCO3-對IBP間接光降解的影響.結(jié)果表明,4種DOM均可促進(jìn)IBP的間接光降解作用,降解過程符合準(zhǔn)一級反應(yīng)動(dòng)力學(xué), 4種DOM對IBP間接光降解的促進(jìn)效果從大到小為:腐殖酸(JKHA)> Suwannee 河腐殖酸(SRHA)> Suwannee 河富里酸(SRFA)> Suwannee 河天然有機(jī)物(SRNOM). DOM主要通過產(chǎn)生活性自由基促進(jìn)IBP的間接光降解過程,其中1O2和?OH的作用較顯著.在初始pH5~11的范圍內(nèi),IBP的光降解速率先降低后增加,在pH5時(shí)最快.鹽度、NO3-和HCO3-初始濃度的增加均會(huì)促進(jìn)IBP的間接光降解.

布洛芬；間接光降解；溶解有機(jī)物；活性自由基

藥品和個(gè)人護(hù)理用品(PPCPs)是與人類生活密切相關(guān)的一類新型化學(xué)物質(zhì)[1-2].大多數(shù)PPCPs是水溶性的,有的還帶有酸性或堿性官能團(tuán),半衰期短,其活性官能團(tuán)在自然環(huán)境中易發(fā)生光降解、水解和微生物降解等,但由于人類的大量使用,導(dǎo)致PPCPs形成“假持續(xù)現(xiàn)象”,從而對人類和環(huán)境造成潛在危害[3-4].PPCPs的大量使用污染了近海的水體環(huán)境,破壞了海洋養(yǎng)殖業(yè)良好的水體狀態(tài),嚴(yán)重危害了海洋漁業(yè)資源.

布洛芬(IBP)是一種非甾體類抗炎藥,療效確切,不良反應(yīng)少,具有解熱、鎮(zhèn)痛的作用.常用于減輕感冒發(fā)燒、偏頭痛、肌肉疼痛、關(guān)節(jié)炎、肩周炎和牙疼等,是應(yīng)用最廣泛的藥物之一[5].IBP產(chǎn)量世界第3,每年約為15000t[6].IBP可以在生物體內(nèi)累計(jì),對人類的健康和生態(tài)系統(tǒng)的平衡造成危害,例如長期攝入IBP會(huì)導(dǎo)致生物畸形和產(chǎn)生抗藥性[7].

間接光降解主要是指光敏劑吸收光子激發(fā)后與污染物分子發(fā)生反應(yīng),或者通過生成的活性含氧自由基氧化污染物使其降解的過程.間接光降解過程中的光敏劑主要是指溶解有機(jī)物(DOM).DOM是分布最為廣泛的天然有機(jī)質(zhì),作為一種重要的光敏化劑,其光降解生成的活性自由基主要有:激發(fā)三線態(tài)DOM(3DOM*)、單線態(tài)氧(1O2)、羥基自由基(?OH)和有機(jī)過氧化物其中3DOM*、1O2和?OH被認(rèn)為是參與外源性物質(zhì)降解的主要自由基[8-9].通過研究Suwannee河、Pony湖和Old Woman溪的富里酸對IBP光降解的影響發(fā)現(xiàn),富里酸促進(jìn)了IBP的間接光降解,?OH在IBP的光降解過程中起著一定的作用,IBP的光降解速率與DOM的組成有重要的關(guān)系[10].間接光降解是IBP在環(huán)境中的重要消失途徑之一,不僅是決定IBP環(huán)境歸趨的重要方式,而且還會(huì)影響其生態(tài)效應(yīng)[11-12].雖然國內(nèi)外對IBP的光降解開展了部分研究,但是目前對海水中IBP的間接光降解作用及其機(jī)理的認(rèn)識(shí)尚不明確.本文研究了4種DOM產(chǎn)生的活性自由基以及溶液初始pH值、鹽度、NO3-和HCO3-對IBP間接光降解的影響,為預(yù)測IBP在海水中的光化學(xué)歸趨和評價(jià)其生態(tài)風(fēng)險(xiǎn)提供科學(xué)依據(jù).

1 材料與方法

1.1 實(shí)驗(yàn)試劑與儀器

實(shí)驗(yàn)儀器: XPA-7多試管攪拌式光化學(xué)反應(yīng)儀(南京胥江機(jī)電廠),UV-2550紫外可見分光光度計(jì)(日本島津公司),Agilent 1260 高效液相色譜儀(安捷倫科技有限公司),C18液相色譜柱(Agilent PLRP-S,5μm, 150mm′4.60mm),FE28pH計(jì)(梅特勒-托利多),KQ2200超聲波清洗器(昆山市超聲儀器有限公司).

實(shí)驗(yàn)試劑:IBP(399%,Sigma-Aldrich), Suwannee 河腐殖酸(SRHA)(2S101H, 國際腐殖酸協(xié)會(huì)), Suwannee河天然有機(jī)物(SRNOM)(2S101N, 國際腐殖酸協(xié)會(huì)),Suwannee 河富里酸(SRFA)(2S101F,國際腐殖酸協(xié)會(huì)),異丙醇(99.9%,Sigma-Aldrich),糠醇(FFA,98%,Sigma-Aldrich),腐殖酸(JKHA)(百靈威科技有限公司),硫酸奎寧(399%,百靈威科技有限公司),標(biāo)準(zhǔn)海水(OSIL, Environmental Instruments and Systems),甲醇(色譜純,德國默克股份兩合公司),乙腈(色譜純,德國默克股份兩合公司),磷酸(色譜純,國藥集團(tuán)化學(xué)試劑有限公司),濃硫酸(分析純,煙臺(tái)三和化學(xué)試劑有限公司),鹽酸(優(yōu)級純,國藥集團(tuán)化學(xué)試劑有限公司),氫氧化鈉(優(yōu)級純,國藥集團(tuán)化學(xué)試劑有限公司).

1.2 溶液的配置

用乙腈配制2mmol/L的IBP儲(chǔ)備液,放于冰箱4℃冷藏保存.用Milli-Q 超純水分別配制2,5,10mg C/L的SRHA、SRFA、SRNOM和JKHA溶液,以0.1mol/L的鹽酸和氫氧化鈉調(diào)節(jié)溶液pH值至(8.0±0.1),放于冰箱冷藏備用.

1.3 光降解實(shí)驗(yàn)

光降解實(shí)驗(yàn)在XPA-7多試管攪拌式光化學(xué)反應(yīng)儀中進(jìn)行,光源為1000W氙燈,用濾光膜濾去320nm以下的紫外光避免直接光降解反應(yīng)[13],控制反應(yīng)溫度為(25±1)℃.在光照條件下,研究DOM、(溶液)初始pH值、鹽度、NO3-和HCO3-對IBP間接光降解的影響.同時(shí),以未添加DOM的IBP溶液為對照,分析IBP的直接光降解作用.光降解溶液用0.1mol/L的鹽酸和氫氧化鈉調(diào)節(jié)pH值至(8.0±0.1),每組實(shí)驗(yàn)做3個(gè)平行樣品,最終結(jié)果取平均值.

1.4 分析方法

采用Agilent 1260高效液相色譜儀分析測定IBP的濃度,色譜條件為:安捷倫C18液相色譜柱(5μm,150mm′4.60mm),流動(dòng)相是乙腈:磷酸水溶液(pH=2.9)=60:40(體積比),檢測器檢測波長為230nm,流速為1.0mL/min,進(jìn)樣量為20μL.

2 結(jié)果與討論

2.1 IBP在不同DOM溶液中的間接光降解作用

分別移取40mL濃度為2,5,10mg C/L的DOM溶液和200μL濃度為2mmol/L的IBP溶液到50mL的石英試管中,然后將反應(yīng)溶液置于光化學(xué)反應(yīng)儀中照射24h,結(jié)果如圖1所示.光照24h后,IBP在Milli-Q超純水中的降解率為4.5%. IBP在波長>290nm時(shí)基本沒有光吸收(圖2),說明在波長>320nm的光照條件下IBP幾乎不能進(jìn)行直接光降解.

在4種DOM溶液中,IBP的間接光降解均符合準(zhǔn)一級反應(yīng)動(dòng)力學(xué)方程.溶液中添加DOM后,IBP的間接光降解速率明顯增加,4種DOM均對IBP的間接光降解具有促進(jìn)作用,但I(xiàn)BP的間接光降解速率隨著DOM初始濃度的增加呈現(xiàn)非線性增加的趨勢.DOM對PPCPs的間接光降解既有促進(jìn)作用也有抑制作用:(1)DOM光敏化作用產(chǎn)生的活性自由基,如3DOM*,1O2,?OH和有機(jī)過氧化物等,可促進(jìn)PPCPs的間接光降解[13-14],(2)DOM可以與活性自由基反應(yīng),通過與PPCPs競爭活性自由基來抑制其間接光降解作用,DOM還可以通過猝滅光降解過程中產(chǎn)生的活性自由基來抑制PPCPs的間接光降解[9]. DOM對IBP光降解的這種促進(jìn)或抑制作用的相對強(qiáng)弱變化,是導(dǎo)致IBP的間接光降解速率隨DOM的濃度表現(xiàn)出非線性變化的主要原因.4種DOM對IBP間接光降解的促進(jìn)效果從大到小為:JKHA> SRHA>SRFA>SRNOM,這種差異主要是由不同組成的DOM產(chǎn)生活性自由基的效率不同導(dǎo)致的[14-15]. Batista等[16]研究發(fā)現(xiàn),3DOM*和?OH的穩(wěn)態(tài)濃度與DOM的芳香性有良好的正相關(guān)關(guān)系.Timko等[17]發(fā)現(xiàn),1O2和?OH穩(wěn)態(tài)濃度的變化與DOM的性質(zhì)有關(guān),陸源類腐殖質(zhì)能夠產(chǎn)生較多的1O2和?OH.

圖1 不同DOM溶液中IBP的光降解作用

圖2 IBP的紫外可見吸收光譜圖

2.2 DOM產(chǎn)生的活性自由基對IBP間接光降解的影響

DOM吸收光子后產(chǎn)生的3DOM*、1O2和?OH等活性自由基可促進(jìn)藥物的間接光降解.本文通過自由基猝滅實(shí)驗(yàn)探討了活性自由基在IBP間接光降解中的作用,異丙醇為?OH的猝滅劑,對?OH的猝滅率高達(dá)98.4%~99.6%[8], FFA為1O2的猝滅劑,結(jié)果如圖3a和3c所示.光降解溶液中添加異丙醇后IBP的間接光降解速率明顯降低,說明?OH的減少對IBP的間接光降解有顯著影響.Jacobs等[10]也證實(shí)?OH參與了IBP的間接光降解.添加FFA的反應(yīng)溶液中,IBP的間接光降解速率比未添加FFA體系低,但程度不如添加異丙醇的明顯,說明?OH和1O2都對IBP的間接光降解有重要影響,且?OH的影響較顯著.

O2是3DOM*的猝滅劑,能獲得1DOM*的能量產(chǎn)生1O2,從而減少3DOM*的生成[18].在充滿O2的溶液中,1O2的穩(wěn)態(tài)濃度會(huì)得到顯著性的提高,與此同時(shí),3DOM*的穩(wěn)態(tài)濃度會(huì)降低到最小值.在去氧的溶液中,3DOM*的穩(wěn)態(tài)濃度會(huì)得到顯著性的提高,而1O2的穩(wěn)態(tài)濃度會(huì)降低到極小值[19].本研究分別以O(shè)2和N2作為3DOM*和1O2的猝滅劑來研究3DOM*對IBP間接光降解的影響,實(shí)驗(yàn)結(jié)果如圖3b和3d所示.在充N2的條件下,IBP的間接光降解速率沒有顯著變化但是在充O2的條件下,IBP的間接降解速率明顯加快,說明1O2在IBP的間接光降解過程中起著重要的作用,而3DOM*的作用不顯著.

圖3 猝滅劑存在條件下IBP的光降解動(dòng)力學(xué)

2.3 pH值對IBP間接光降解的影響

水體中pH值的變化既能夠改變藥物和DOM的存在形態(tài),又能夠影響活性自由基的生成速率[20],因此對水體中IBP的間接光降解有著顯著影響.為了研究pH值對IBP間接光降解的影響,以10mg C/L的SRHA和SRFA溶液配制初始pH值為5,7,9,11的10μmol/L的IBP溶液進(jìn)行光降解實(shí)驗(yàn),結(jié)果如圖4所示.在初始pH值為5時(shí),IBP的光降解速率最快,當(dāng)pH>7時(shí),IBP的光降解速率隨著pH值的增加而增大.IBP的pa=4.8,在pH值為5時(shí),IBP在溶液中幾乎不帶電[21],以分子的形式存在腐殖酸和富里酸的結(jié)構(gòu)中除含有大量的苯環(huán)外,還有羧基、羰基和酚羥基等官能團(tuán),使得腐殖酸和富里酸具有酸性[22].在酸性條件下,腐殖酸和富里酸也主要以分子的形式存在,這使得IBP容易吸附在DOM的表面,增加了IBP與?OH和1O2的接觸機(jī)率,從而提高了IBP的光降解速率.在中性和堿性條件下,IBP和DOM在水溶液中電離均帶負(fù)電荷,隨著pH值的增加,DOM與IBP的排斥增強(qiáng)、吸附減弱,這樣會(huì)抑制IBP的光降解速率,但I(xiàn)BP的間接光降解主要是IBP與?OH和1O2反應(yīng),而?OH和1O2的穩(wěn)態(tài)濃度會(huì)隨著pH值的增大逐漸增加[14],這種促進(jìn)作用強(qiáng)于抑制作用,所以IBP的間接光降解速率呈現(xiàn)出隨pH值的增大逐漸加快的趨勢.

圖4 pH值對IBP間接光降解的影響

2.4 鹽度對IBP間接光降解的影響

近海水體中的鹽度是影響藥物光降解的重要因素之一.鹽度的增加可促進(jìn)磺胺類抗生素的光催化降解,但對噁唑烷酮類抗生素和菲的光降解無顯著影響[23-25].為了研究鹽度對IBP間接光降解的影響,以Milli-Q超純水和標(biāo)準(zhǔn)海水配制鹽度分別為0,5,15,25,35的10mg C/L的JKHA溶液,加入一定量的IBP儲(chǔ)備液,使其初始濃度為10μmol/L,進(jìn)行光降解實(shí)驗(yàn),結(jié)果如圖5所示.IBP的間接光降解速率隨著鹽度的增大而增加,這主要有2方面的原因:(1)鹽度能夠大幅度的增加水體中DOM光解產(chǎn)生的水合電子[26],促進(jìn)H2O2的生成[27],最終導(dǎo)致水體中?OH穩(wěn)態(tài)濃度的增加;(2)高鹽海水中的Cl-和Br-能夠與3DOM*發(fā)生反應(yīng)生成Cl-?和Br-?,從而與IBP發(fā)生電子轉(zhuǎn)移或抽氫反應(yīng)等促進(jìn)其光降解[28].

圖5 鹽度對IBP間接光降解的影響

2.5 NO3-對IBP間接光降解的影響

圖6 NO3-對IBP間接光降解的影響

NO3-是海水中普遍存在的陰離子,同時(shí)也是?OH的重要來源,濃度在1~80μmol/L之間.為了研究NO3-對IBP間接光降解的影響,以10mg C/L的JKHA溶液配制不同NO3-濃度(0,10,20,30,40μmol/L)的10μmol/L的IBP溶液進(jìn)行光降解實(shí)驗(yàn),結(jié)果如圖6所示.在不同NO3-濃度的條件下,IBP的間接光降解均符合準(zhǔn)一級反應(yīng)動(dòng)力學(xué)方程,且間接光降解速率隨著NO3-濃度的增加而加快,NO3-促進(jìn)了IBP的間接光降解.在波長大于280nm的光照條件下,NO3-有兩個(gè)主要的光致降解過程[29-30]:

NO3-吸收B段的紫外光變?yōu)閇NO3-]*(式1),然后通過2個(gè)途徑進(jìn)行分解:一個(gè)過程是生成NO2-和O(3P)(式2),NO2-能夠光解形成?OH(式4~6);另一個(gè)過程是[NO3-]*快速的質(zhì)子化形成?OH(式3).所以NO3-的光解可以產(chǎn)生?OH,從而促進(jìn)IBP的間接光降解.

2.6 HCO3-對IBP間接光降解的影響

HCO3-也是海水中最常見的陰離子之一[31],其在水環(huán)境中的濃度一般不超過4mmol/L.HCO3-既是水環(huán)境中?OH的清除劑又是?CO3-的主要來源(式7),對藥物的光降解既有促進(jìn)作用也有抑制作用[32-33].為了研究HCO3-對IBP間接光降解的影響,以10mg C/L的JKHA溶液配制不同HCO3-濃度(0,1,2,3, 4mmol/L)的10μmol/L的IBP溶液進(jìn)行光降解實(shí)驗(yàn),結(jié)果如圖7所示.在不同HCO3-濃度的條件下,IBP的間接光降解均符合準(zhǔn)一級反應(yīng)動(dòng)力學(xué)方程,且間接光降解速率都隨著HCO3-濃度的增加而增大, HCO3-對IBP的間接光降解有促進(jìn)作用.HCO3-與?OH反應(yīng)生成的?CO3-是一種選擇性自由基,可以通過電子轉(zhuǎn)移或抽氫反應(yīng)與富電子的化合物,如含N、S的化合物和酚類化合物等發(fā)生反應(yīng)[34].HCO3-也可與激發(fā)態(tài)的IBP或3DOM*發(fā)生反應(yīng)生成?CO3-;同時(shí)?CO3-較穩(wěn)定,不易被DOM掩蔽,導(dǎo)致較高濃度的?CO3-參與IBP的光降解.

3 結(jié)論

3.1 4種DOM均可促進(jìn)IBP的間接光降解作用,降解過程符合準(zhǔn)一級反應(yīng)動(dòng)力學(xué).4種DOM對IBP間接光降解的促進(jìn)效果從大到小為:JKHA>SRHA> SRFA>SRNOM,這種差異主要是由DOM的來源不同導(dǎo)致.

3.2 DOM主要通過產(chǎn)生活性自由基促進(jìn)IBP的間接光降解作用,其中1O2和?OH的作用較顯著,3DOM*基本不起作用.

3.3 在初始pH值為5~11的范圍內(nèi),IBP的光降解速率先降低后增加,在pH=5時(shí)最快,這與不同pH值條件下IBP和DOM的存在形態(tài)及?OH和1O2穩(wěn)態(tài)濃度有關(guān).

3.4 鹽度和NO3-的增加對IBP間接光降解的促進(jìn)作用主要是由于它們使活性自由基的穩(wěn)態(tài)濃度增加.HCO3-的增加對IBP間接光降解的促進(jìn)作用主要與生成的?CO3-有關(guān).

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The indirect photodegradation mechanism of ibuprofen in simulated seawater.

BAI Ying1, CUI Zheng-guo1*, SU Rong-guo2, QU Ke-ming1

(1.Laboratory for Marine Fisheries Science and Food Production Processes, Pilot National Laboratory for Marine Science and Technology (Qingdao), Key Laboratory of Sustainable Development of Marine Fisheries, Ministry of Agriculture and Rural Affairs, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China；2.Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China)., 2019,39(7)：2831~2837

To clarify the indirect photodegradation mechanism of IBP, the indirect photodegradation behaviors of IBP were investigated in the presence of four kinds of dissolved organic matter (DOM) and were also assessed in the presence of seawater components and conditions such as salinity, pH, nitrate and bicarbonate. Firstly, the indirect photodegradation of IBP could be accelerated by the four different sources of DOM and followed pseudo-first-order kinetics, the photodegradation rate constants of APAP were found to decrease in the following order: JKHA> SRHA> SRFA> SRNOM. DOM promoted the indirect photodegradation of IBP through the formation of various reactive intermediates, ?OH and1O2were the main contributors. Secondly, in the range of pH 5~11, the photodegradation rate of IBP was firstly decreased and then increased, the highest photodegradation rate of IBP was found at pH 5.0. Lastly, the photodegradation rate constants of IBP increased with increasing salinity, nitrate and bicarbonate.

ibuprofen；indirect photodegradation；dissolved organic matter；reactive intermediates

X703

A

1000-6923(2019)07-2831-07

白 瑩(1988-),女,山東聊城人,博士后,主要從事水體中抗生素的光降解機(jī)理研究.發(fā)表論文6篇.

2018-11-30

中國博士后科學(xué)基金資助項(xiàng)目(2018M632750);山東省支持青島海洋科學(xué)與技術(shù)試點(diǎn)國家實(shí)驗(yàn)室重大科技專項(xiàng)(2018SDKJ05);青島市博士后研究人員應(yīng)用研究項(xiàng)目資助(喹諾酮類抗生素的間接光降解機(jī)理研究-以萊州灣為例)

*責(zé)任作者, 副研究員, cuizg@ysfri.ac.cn