全氟辛烷磺酰胺在小麥和蚯蚓中的富集與轉(zhuǎn)化

吳思寒,吳雨濛,王雙杰,陳 萌,劉 青,祝凌燕

全氟辛烷磺酰胺在小麥和蚯蚓中的富集與轉(zhuǎn)化

吳思寒,吳雨濛,王雙杰,陳 萌,劉 青,祝凌燕*

(南開(kāi)大學(xué)環(huán)境科學(xué)與工程學(xué)院,環(huán)境污染過(guò)程與基準(zhǔn)教育部重點(diǎn)實(shí)驗(yàn)室,天津城市生態(tài)環(huán)境修復(fù)與污染防治重點(diǎn)實(shí)驗(yàn)室,天津 300350)

研究了不同培養(yǎng)介質(zhì)和培養(yǎng)方式下全氟辛烷磺酰胺(PFOSA)在小麥、蚯蚓體內(nèi)的生物富集和轉(zhuǎn)化.結(jié)果表明:小麥根系可以從培養(yǎng)介質(zhì)中吸收PFOSA并向上轉(zhuǎn)運(yùn)至莖葉.土壤中PFOSA生物有效性受總有機(jī)碳(TOC)的影響顯著,高TOC含量土壤中PFOSA的生物有效性降低,導(dǎo)致其在小麥和蚯蚓中的生物富集因子分別由(61.24±8.42)和(21347.91±208.86)降至(5.61±0.23)和(1404.92±108.21).PFOSA在小麥的根和莖葉以及蚯蚓中都可以轉(zhuǎn)化為PFOS,但在蚯蚓中的轉(zhuǎn)化率((3.87±1.71)%)顯著低于小麥((26.39±3.02)%).小麥根中PFOS的支鏈異構(gòu)體(-PFOS)比例在低、高TOC含量時(shí)分別為(14.8±2.0)%、(66.1±26.2)%,低于莖葉(分別為(63.0±21.3)%、(85.2±2.4)%)),可能是由于根部轉(zhuǎn)化生成的-PFOS更容易向莖葉轉(zhuǎn)運(yùn).小麥特別是小麥莖葉中的-PFOS比例((85.2±2.4)%)顯著高于蚯蚓((16.5±4.0)%).小麥的存在可以提高土壤中PFOSA的生物有效性,從而促進(jìn)蚯蚓對(duì)PFOSA的富集,但對(duì)其轉(zhuǎn)化影響不大.本文為小麥和蚯蚓中PFOSA的富集和轉(zhuǎn)化提供了證據(jù),有助于探索環(huán)境中PFOS的間接來(lái)源.

全氟辛烷磺酰胺(PFOSA)；小麥；蚯蚓；生物富集；生物轉(zhuǎn)化

全氟和多氟化合物(PFASs)因其優(yōu)異性質(zhì)已在日常生活中被廣泛使用,如食品包裝材料、消防泡沫、表面活性劑、紡織品等[1].PFASs結(jié)構(gòu)中的C-F鍵是最強(qiáng)的共價(jià)單鍵,因此PFASs極為穩(wěn)定,難以發(fā)生生物和非生物降解(如水解、光解),可在環(huán)境中長(zhǎng)期存在,并發(fā)生生物富集、生物放大效應(yīng)[2-3].全氟辛烷磺酸(PFOS)是研究最多、環(huán)境中最常見(jiàn)的一種PFASs[4],已在環(huán)境介質(zhì)和人體中[5-10]廣泛檢出,并對(duì)生殖、免疫、內(nèi)分泌和神經(jīng)系統(tǒng)以及肝臟均具有毒害作用[11-12],因此于2009年列入斯德哥爾摩公約,被逐步禁用[13].除直接排放外,環(huán)境中PFOS的另一主要來(lái)源是環(huán)境中前體物(PreFOS)的轉(zhuǎn)化[14].據(jù)報(bào)道,1970～2002年間,PreFOS的最大歷史排放量(6800 ～45250t)要遠(yuǎn)高于PFOS(450～2700t)[15].全氟辛烷磺酰胺(PFOSA)是一種在環(huán)境中廣泛檢出的典型PreFOS[16-19].它是許多其他大分子PreFOS轉(zhuǎn)化為PFOS的中間物質(zhì),且是限速步驟[20-26].工業(yè)生產(chǎn)的PFOSA中,支鏈異構(gòu)體(-PFOSA)比例為24.7%[27]. PFOSA的轉(zhuǎn)化存在異構(gòu)體選擇性,其異構(gòu)體轉(zhuǎn)化特征會(huì)對(duì)環(huán)境中PFOS的異構(gòu)體分布特征產(chǎn)生影響,有助于追溯環(huán)境中PFOS的來(lái)源[28].但目前關(guān)于PFOSA在陸生動(dòng)植物中的特異性轉(zhuǎn)化研究較少,因此對(duì)其進(jìn)行研究十分必要.

土壤是PFASs在環(huán)境中的重要?dú)w屬地之一[6], PFASs能通過(guò)點(diǎn)源污染、大氣沉降、地面徑流等進(jìn)入土壤系統(tǒng)[29].例如,在美國(guó)空軍設(shè)施附近的土壤中PFOSA最高濃度甚至已達(dá)到20000ng/g[6].土壤中PFASs可以通過(guò)植物或動(dòng)物進(jìn)入食物鏈,經(jīng)食物鏈的富集產(chǎn)生生物放大效應(yīng),對(duì)人體健康產(chǎn)生危害.小麥(L.)是一種世界各地都廣泛種植的禾本科農(nóng)作物,是人類食物的重要來(lái)源之一[12].蚯蚓()是土壤中生物量最大的無(wú)脊椎動(dòng)物,其生命活動(dòng)會(huì)直接或間接地對(duì)有機(jī)污染物在土壤中的遷移和轉(zhuǎn)化產(chǎn)生影響[30].土壤的性質(zhì)、生物種類等都會(huì)影響PFOSA的生物富集和生物轉(zhuǎn)化,因此本文以小麥、蚯蚓為受試生物,PFOSA為目標(biāo)污染物,研究不同培養(yǎng)介質(zhì)和培養(yǎng)方式下PFOSA在小麥、蚯蚓體內(nèi)的生物富集和轉(zhuǎn)化,為探索環(huán)境中PFOS的間接來(lái)源、評(píng)價(jià)PFOSA的人類健康和生態(tài)風(fēng)險(xiǎn)以及環(huán)境修復(fù)提供理論參考.

1 材料與方法

1.1 實(shí)驗(yàn)材料

實(shí)驗(yàn)所用試劑如下:全氟辛烷磺酰胺工業(yè)品(PFOSA,>90%,北京百靈威科技有限公司),全氟辛烷磺酸標(biāo)準(zhǔn)品及其內(nèi)標(biāo)(PFOS和13C-PFOS,>99%)、全氟辛烷磺酰胺標(biāo)準(zhǔn)品及其內(nèi)標(biāo)(PFOSA和13C- PFOSA, >99%)購(gòu)自加拿大惠靈頓實(shí)驗(yàn)室.甲醇(色譜純)、過(guò)氧化氫30%(H2O2,質(zhì)量分?jǐn)?shù),分析純)均購(gòu)自天津市化學(xué)試劑供銷公司,甲基叔丁基醚(分析純,天津市康科德科技有限公司),氫氧化鈉(NaOH,優(yōu)級(jí)純)、四丁基硫酸氫銨(TBAHS,分析純)、無(wú)水碳酸鈉(Na2CO3,優(yōu)級(jí)純)均購(gòu)自天津市津科精細(xì)化工研究所.甲酸(色譜純,上海安譜實(shí)驗(yàn)科技股份有限公司)、氨水(色譜純,阿拉丁)、甲醇(HPLC級(jí))和乙腈(HPLC級(jí))購(gòu)自美國(guó)Fisher公司.

實(shí)驗(yàn)所用小麥種子(L.)購(gòu)自天津農(nóng)科院,所用赤子愛(ài)勝蚓()購(gòu)于天津當(dāng)?shù)仞B(yǎng)殖場(chǎng).

1.2 暴露實(shí)驗(yàn)

1.2.1 小麥在土壤和石英砂介質(zhì)中的暴露實(shí)驗(yàn) 首先將小麥種子于3% H2O2(質(zhì)量分?jǐn)?shù))中浸泡30min消毒,用Milli-Q水沖洗5次后,用Milli-Q水浸泡一夜,之后在鋪有濕濾紙的底部未全封閉的透氣托盤架上均勻鋪開(kāi),使之于22～27℃下發(fā)芽,托盤架上部鋪一層鋁箔以保證含水率,防止水分蒸發(fā)過(guò)快.為了研究土壤中TOC對(duì)PFOSA生物有效性的影響,實(shí)驗(yàn)采用2種培養(yǎng)介質(zhì)種植小麥,分別為土壤和石英砂,設(shè)立4組實(shí)驗(yàn):有毒有植物、無(wú)毒有植物、有毒無(wú)植物和無(wú)毒無(wú)植物,染毒濃度為200ng/g,每組設(shè)置3個(gè)平行.將發(fā)芽3d、大小均一的小麥幼苗移植到1L塑料花盆中,每盆裝有650g培養(yǎng)介質(zhì),種植7株小麥.將花盆放置于采光較好的天臺(tái)處培養(yǎng),每天隨機(jī)更換盆的位置以保證小麥?zhǔn)荜?yáng)光照射條件良好,每天澆水使土壤含水率保持在30%左右,14d后收獲小麥.收獲時(shí)用蒸餾水沖洗小麥根部,之后用濾紙擦干,將小麥根和莖葉分離,棄去根莖連接處,于-20℃冰箱中儲(chǔ)存.

1.2.2 蚯蚓在不同TOC含量土壤中的暴露實(shí)驗(yàn) 將蚯蚓于未染毒土壤中避光馴養(yǎng)14d.實(shí)驗(yàn)采用土壤和土壤/石英砂(8:2,質(zhì)量比)兩種培養(yǎng)介質(zhì),染毒濃度為0, 200ng/g,設(shè)置3個(gè)平行.將馴養(yǎng)好的蚯蚓放入250mL燒杯,每杯裝有100g培養(yǎng)介質(zhì),放入10條蚯蚓.將燒杯用鋁箔包裹,避光培養(yǎng),每天加水保持土壤濕度在30%左右,分別培養(yǎng)7和14d后收獲蚯蚓.收獲時(shí)從土壤中取出蚯蚓并用水清洗,在裝有潮濕脫脂棉的玻璃杯中放置24h清腸后用水沖洗,再用濾紙吸去水分,于-20℃冰箱中儲(chǔ)存.

1.2.3 蚯蚓-小麥聯(lián)合暴露實(shí)驗(yàn) 小麥種子的培育見(jiàn)1.2.1,蚯蚓馴養(yǎng)見(jiàn)1.2.2.將赤子愛(ài)勝蚓與小麥聯(lián)合培養(yǎng),采用土壤和土壤/石英砂(8:2)兩種培養(yǎng)介質(zhì),染毒濃度為0, 200ng/g,設(shè)置3個(gè)平行.將發(fā)芽3d的小麥和馴養(yǎng)完成的蚯蚓放入1L塑料花盆中,每盆裝有650g培養(yǎng)介質(zhì),加入7株小麥和10條蚯蚓.用鋁箔包裹花盆邊緣并高出邊緣3cm,以防蚯蚓在實(shí)驗(yàn)期間爬出.每天加水保持土壤濕度在30%左右,14d后收獲小麥和蚯蚓.小麥和蚯蚓的取樣方式同1.2.1和1.2.2.

1.3 樣品前處理

生物樣前處理采用Chen等[31]的方法并稍作改進(jìn).將生物樣置于冷凍干燥機(jī)中-50℃下干燥48h,剪碎.稱取一定質(zhì)量干重樣品(根取0.01g,莖葉取0.05g,蚯蚓取0.1g)于10mL PP 離心管中,加入2ng內(nèi)標(biāo)(包括M4-PFOS和M8-PFOSA),渦旋振蕩,使其充分混勻,平衡至少2h.依次加入1mL 0.5mol/L的TBAHS 溶液(pH值用氫氧化鈉溶液調(diào)至10)和2mL 0.25mol/L的Na2CO3緩沖液,充分混勻后,加入4mL甲基叔丁基醚,混合液于250r/min下震蕩20min,然后在4℃、6000r/min下離心10min使有機(jī)相與水相分離,將上層有機(jī)相轉(zhuǎn)移至新10mL離心管中.萃取過(guò)程重復(fù)2次,萃取液氮吹至干.用2mL甲醇復(fù)溶,加入50mg Carb填料以去除色素等雜質(zhì),混勻后在4℃,11000r/min下離心15min.取上清液至新離心管中氮吹干.用1mL甲醇復(fù)溶,過(guò)0.22μm尼龍濾膜后轉(zhuǎn)移到進(jìn)樣小瓶中,放在凍存盒中于-20℃冰箱中保存,以待分析.

培養(yǎng)介質(zhì)前處理采用Zhao等[30]的方法并稍作改進(jìn).將培養(yǎng)介質(zhì)置于冷凍干燥機(jī)中-50℃下干燥48h,將1g干燥的介質(zhì)置于10mL PP離心管中,加入2ng內(nèi)標(biāo)(包括M4-PFOS和M8-PFOSA),渦旋振蕩,使其充分混勻,平衡至少2h.加入5mL甲醇,然后于250r/min下震蕩10min.將離心管于40℃超聲10min.將該混合物在3000r/min下離心10min.重復(fù)提取3遍,并將上清液合并到另一個(gè)新的離心管中.萃取液氮吹至2mL.加入50mg Carb填料以去除色素等雜質(zhì),混勻后在4℃,11000r/min下離心15min.取上清液至新離心管中氮吹干.用1mL甲醇復(fù)溶,過(guò)0.22μm尼龍濾膜后轉(zhuǎn)移到進(jìn)樣小瓶中,放在凍存盒中于-20℃冰箱中保存,以待分析.

1.4 儀器分析

在負(fù)電噴霧電離模式下,使用Waters超高效液相色譜-質(zhì)譜聯(lián)用儀(ACQUITY-UPLC/XEVO-TQS)分析樣品中各物質(zhì)含量.色譜柱采用FluoroSep-RP Octyl柱(150mm′2.1mm,3μm粒徑; ES Industries, West Berlin,NJ).柱溫為38℃,進(jìn)樣體積為10μL,流動(dòng)相流速為0.15mL/min.對(duì)于PFOSA異構(gòu)體,流動(dòng)相A、B分別為3mmol/L甲酸的水溶液(pH值用氨水調(diào)至4.15)和乙腈溶液.流動(dòng)相初始比例為60%A、40%B,保持1min,在3min變?yōu)?4%B,在35min變?yōu)?0%B,在35.1min變?yōu)?00%B并保持至40min,在45min回到初始比例.對(duì)于PFOS異構(gòu)體,流動(dòng)相A、B分別為3mmol/L甲酸的水溶液(pH值用氨水調(diào)至4.15)和甲醇溶液.流動(dòng)相初始比例為60%A、40%B,保持0.3min,在1.9min變?yōu)?4%B,在5.9min變?yōu)?6%B,在7.9min變?yōu)?0%B,在26min變?yōu)?4%B,在30min變?yōu)?00%B并保持至33min,在35min回到初始比例并保持至40min.質(zhì)譜條件為:毛細(xì)管電壓2700V;離子源溫度150℃;去溶劑溫度350℃;錐孔氣流速150L/Hr;去溶劑氣流速800L/Hr;霧化氣流速7bar.目標(biāo)化合物的定量離子、錐孔電壓及碰撞能參數(shù)如表1所示.

表1 目標(biāo)化合物的定量離子、錐孔電壓、碰撞能

注:a3-和5-PFOS異構(gòu)體無(wú)法進(jìn)行基線分離,因此被合并為3+5-PFOS.

1.5 質(zhì)量保證與質(zhì)量控制

回收率實(shí)驗(yàn)通過(guò)向空白基質(zhì)中加入標(biāo)準(zhǔn)品進(jìn)行.在樣品前處理過(guò)程中添加過(guò)程空白以校正背景污染.根據(jù)樣品峰面積與內(nèi)標(biāo)峰面積之比對(duì)物質(zhì)濃度進(jìn)行定量.方法檢出限(MDL)定義為信噪比為3:1時(shí)物質(zhì)濃度.各物質(zhì)的回收率和檢出限如表2所示.本實(shí)驗(yàn)中,各基質(zhì)中PFOSA和PFOS的回收率均在80%～100%范圍內(nèi),因此不使用回收率對(duì)測(cè)得的各物質(zhì)濃度進(jìn)行校正.

在暴露實(shí)驗(yàn)開(kāi)始前,小麥中就檢測(cè)到一定濃度的PFOSA(根(11.71±0.93) ng/g,莖葉(2.64±0.44) ng/g)和PFOS(根(16.89±4.25) ng/g,莖葉(4.20±2.56) ng/g).在暴露14d后,空白小麥中檢測(cè)到相似水平的PFOSA(根(9.53±1.74)～(10.38±1.60) ng/g,莖葉(2.56±0.59)～(3.34±1.64) ng/g )和PFOS(根(15.31±1.31)～(16.24±1.96) ng/g,莖葉(1.64±0.54)～(1.71±0.47) ng/g).空白蚯蚓體內(nèi)PFOSA和PFOS的濃度遠(yuǎn)低于實(shí)驗(yàn)組蚯蚓(相差103～105個(gè)數(shù)量級(jí)).由此判斷,空白組小麥和蚯蚓中PFOSA和PFOS來(lái)源于背景污染.本文所用暴露組濃度均扣除了空白組濃度.

表2 目標(biāo)化合物的回收率和方法檢出限(MDL)

1.6 數(shù)據(jù)分析

對(duì)小麥的根富集因子(RCF)、蚯蚓的生物富集因子(BSAF)和轉(zhuǎn)化率(TR)進(jìn)行計(jì)算,公式如下:

式中:m為培養(yǎng)介質(zhì)中PFOSA的濃度, ng/g;root為小麥根中PFOSA濃度, ng/g dw;e為蚯蚓中PFOSA濃度, ng/g dw;PFOS為小麥或蚯蚓中PFOS濃度, ng/g dw;PFOSA為小麥或蚯蚓中PFOSA濃度, ng/g dw.

使用IBM SPSS Statistics 22進(jìn)行數(shù)據(jù)分析.使用配對(duì)檢驗(yàn)評(píng)估各組間RCF、TR和-PFOS比例的差異,當(dāng)< 0.05時(shí)認(rèn)為存在顯著性差異,當(dāng)< 0.01時(shí)認(rèn)為差異極顯著.

2 結(jié)果與討論

2.1 小麥和蚯蚓的生理狀況

在整個(gè)實(shí)驗(yàn)周期內(nèi),小麥和蚯蚓生理狀況良好,沒(méi)有不良反應(yīng)、死亡等現(xiàn)象,空白對(duì)照組和實(shí)驗(yàn)組小麥和蚯蚓生物量無(wú)顯著性差異(> 0.05).

2.2 小麥對(duì)PFOSA的富集和轉(zhuǎn)化

通過(guò)公式(1)計(jì)算小麥的RCF,發(fā)現(xiàn)PFOSA在石英砂培養(yǎng)小麥中的RCF((61.24±8.42))遠(yuǎn)大于土壤中培養(yǎng)的小麥((5.61±0.23)),存在顯著性差異(<0.01),說(shuō)明培養(yǎng)基質(zhì)中的總有機(jī)碳含量(TOC)會(huì)顯著影響其生物有效性.Liu等[32]研究表明土壤TOC含量與所吸附的PFOS量之間存在顯著的線性關(guān)系(< 0.01).土壤中TOC含量高于石英砂,對(duì)PFOSA具有較強(qiáng)的吸附能力,使得土壤中可生物利用的PFOSA減少,導(dǎo)致在土壤中生長(zhǎng)的小麥的RCF較低.

在小麥的根和莖葉中均測(cè)得轉(zhuǎn)化產(chǎn)物PFOS.通過(guò)公式(3)計(jì)算了小麥中PFOSA的轉(zhuǎn)化率,發(fā)現(xiàn)莖葉中轉(zhuǎn)化率遠(yuǎn)高于根中(<0.01,圖1).有實(shí)驗(yàn)表明,當(dāng)辛醇-水分配系數(shù)(logow)>4時(shí),疏水性有機(jī)化合物會(huì)強(qiáng)烈吸附于根的上表皮,難以轉(zhuǎn)運(yùn)到莖葉[33].Zhao等[34]研究也表明當(dāng)有機(jī)化合物logow>4時(shí),該物質(zhì)從根到莖葉轉(zhuǎn)運(yùn)因子(TF)隨logow的增加而指數(shù)遞減.PFOSA的logow(5.62)小于PFOS(logow= 6.43)[35],表明PFOS較PFOSA更難從根轉(zhuǎn)運(yùn)至莖葉,因此莖葉中較高的轉(zhuǎn)化率表明葉中PFOS不僅來(lái)源于根部轉(zhuǎn)運(yùn),還來(lái)源于莖葉的生物轉(zhuǎn)化.此外還發(fā)現(xiàn)PFOSA在土壤培養(yǎng)的小麥根(<0.05)和莖葉(< 0.01)的轉(zhuǎn)化率均大于石英砂中小麥(圖1).這可能是由于PFOSA被土壤中微生物轉(zhuǎn)化為PFOS[36],生成的PFOS被小麥富集.土壤中有機(jī)碳可以為微生物的生長(zhǎng)提供充足的碳源,從而提高微生物數(shù)量和活性[37].Bizkarguenaga等[38]也觀察到在高TOC的土壤中生菜對(duì)PFOSA降解更強(qiáng).

圖1 生長(zhǎng)在不同培養(yǎng)基質(zhì)中的小麥對(duì)PFOSA的轉(zhuǎn)化率

**、*分別表示差異極顯著(<0.01)和顯著(<0.05)

除石英砂培養(yǎng)的小麥根外((14.8±2.0)%),小麥中-PFOS比例均顯著高于24.7%(土壤中小麥根:(66.1±26.2)%,土壤中小麥葉:(85.2±2.4)%,石英砂中小麥葉:(63.0±21.3)%,圖2),說(shuō)明小麥中-PFOSA比-PFOSA優(yōu)先發(fā)生轉(zhuǎn)化.小麥中-PFOS比例呈現(xiàn)以下趨勢(shì):根中-PFOS比例小于莖葉,石英砂培養(yǎng)的小麥中-PFOS比例小于土壤.小麥根中- PFOS比例要小于莖葉,這是因?yàn)橹辨湲悩?gòu)體比相應(yīng)的支鏈異構(gòu)體具有更高的疏水性[18],導(dǎo)致-PFOS比-PFOS更易從根轉(zhuǎn)運(yùn)至莖葉.石英砂介質(zhì)培養(yǎng)的小麥根中-PFOS比例低于24.7%,可能也是由于根中生成的-PFOS部分轉(zhuǎn)運(yùn)至莖葉.已有研究表明,PFOSA是N-EtFOSE生物轉(zhuǎn)化過(guò)程的中間產(chǎn)物[21,39].Liu等[25]在好氧土壤中觀察到N-EtFOSE的異構(gòu)體特異性生物轉(zhuǎn)化并檢測(cè)到-PFOS的生成.Chen等[31]表明,-PFOSA在生物體內(nèi)會(huì)優(yōu)先轉(zhuǎn)化為-PFOS.因此可以推測(cè),土壤中微生物對(duì)-PFOSA進(jìn)行優(yōu)先轉(zhuǎn)化,生成更多的-PFOS并被小麥吸收,從而導(dǎo)致土壤中培養(yǎng)的小麥中-PFOS比例高于石英砂中培養(yǎng)的小麥.

圖2 小麥根和莖葉中br-PFOS比例

2.3 蚯蚓對(duì)PFOSA的富集和轉(zhuǎn)化

通過(guò)計(jì)算蚯蚓對(duì)PFOSA的生物富集因子(BSAF),發(fā)現(xiàn)隨培養(yǎng)時(shí)間增加,PFOSA在蚯蚓體內(nèi)的BSAF增加(圖3).培養(yǎng)14d后,土壤/石英砂(8:2)介質(zhì)中PFOSA在蚯蚓體內(nèi)的BSAF值(21347.91±208.86)遠(yuǎn)高于土壤中(1404.92±108.21),是土壤中的15.20倍(圖3),該趨勢(shì)與PFOSA在小麥體內(nèi)富集的結(jié)果相同,進(jìn)一步說(shuō)明土壤中TOC對(duì)PFOSA具有較強(qiáng)的吸附能力,降低了土壤中PFOSA的生物有效性.

圖3 不同培養(yǎng)時(shí)間和培養(yǎng)介質(zhì)下蚯蚓中PFOSA的BSAF

在蚯蚓中同樣檢測(cè)到PFOSA轉(zhuǎn)化產(chǎn)物PFOS的生成,但其TR相對(duì)較低.在土壤中培養(yǎng)了14d的蚯蚓中PFOSA的TR((3.87±1.71)%)顯著低于小麥中((26.39±3.02)%),表明不同生物對(duì)PFOSA的轉(zhuǎn)化能力存在很大差異[40].

圖4 不同培養(yǎng)時(shí)間和培養(yǎng)介質(zhì)下蚯蚓中br-PFOS比例

不同培養(yǎng)介質(zhì)對(duì)蚯蚓中-PFOS比例會(huì)產(chǎn)生影響,土壤/石英砂(8:2)介質(zhì)中,-PFOS比例更高(圖4,<0.05).這可能是由于土壤/石英砂(8:2)介質(zhì)加入了石英砂,土壤黏性降低,孔隙度高,通氣透水性強(qiáng),更適宜蚯蚓生存,其中蚯蚓的活性更高.在生物體內(nèi)-PFOSA異構(gòu)體會(huì)優(yōu)先代謝[31,41],生成-PFOS.土壤/石英砂(8:2)介質(zhì)僅加入20%的石英砂,TOC含量與土壤差距不大,所以推測(cè)其微生物數(shù)量和活性差異較小,對(duì)PFOSA轉(zhuǎn)化的影響也差別不大.因此土壤/石英砂(8:2)介質(zhì)中蚯蚓體內(nèi)-PFOS比例高.與小麥特別是莖葉中較高的-PFOS比例不同,在土壤中培養(yǎng)了14d的蚯蚓中-PFOS比例為(16.5±4.0)%,小于24.7%.這可能是由于蚯蚓通過(guò)大量排出糞便向外排出污染,而-PFOS比-PFOS更易從體內(nèi)排出[31].

2.4 小麥共同生長(zhǎng)對(duì)蚯蚓中PFOSA的富集和轉(zhuǎn)化的影響

蚯蚓和小麥聯(lián)合培養(yǎng)時(shí),土壤/石英砂(8:2)介質(zhì)中PFOSA在蚯蚓體內(nèi)的BSAF(32176.65±844.49)高于土壤中(26743.14±11311.21)(圖5),進(jìn)一步說(shuō)明土壤TOC會(huì)顯著影響其中PFOSA的生物有效性.由圖5可知,聯(lián)合培養(yǎng)時(shí)PFOSA在蚯蚓體內(nèi)的BSAF顯著高于蚯蚓單獨(dú)培養(yǎng)時(shí)的結(jié)果(<0.05).Kelsey等[42]、Zhao等[34]也發(fā)現(xiàn)南瓜和小麥會(huì)促進(jìn)蚯蚓對(duì)p,p'-DDE和PFASs的富集.這主要是由于植物根系分泌物會(huì)提高PFOSA從土壤中的解吸,提高其生物有效性.小麥存在時(shí),蚯蚓中PFOSA轉(zhuǎn)化率與單獨(dú)培養(yǎng)時(shí)無(wú)顯著性差異(>0.05),表明小麥的存在對(duì)蚯蚓中PFOSA轉(zhuǎn)化率無(wú)影響.

圖5 不同培養(yǎng)方式和培養(yǎng)介質(zhì)下蚯蚓中PFOSA的BSAF

E:蚯蚓單獨(dú)培養(yǎng); E+W:蚯蚓和小麥聯(lián)合培養(yǎng)

3 結(jié)論

3.1 小麥根能從土壤溶液中吸收PFOSA并轉(zhuǎn)運(yùn)至莖葉.土壤TOC含量顯著影響其中PFOSA的生物有效性,TOC含量高,其生物有效性降低.PFOSA在小麥的根和莖葉中都可以轉(zhuǎn)化為PFOS,且土壤培養(yǎng)的小麥中PFOSA的轉(zhuǎn)化率更高.小麥中-PFOS比例關(guān)系為根<莖葉,石英砂<土壤.

3.2 蚯蚓能有效從土壤中富集PFOSA并將其轉(zhuǎn)化為PFOS.土壤/石英砂(8:2)介質(zhì)培養(yǎng)的蚯蚓-PFOS比例更高.蚯蚓中PFOSA轉(zhuǎn)化率和-PFOS比例均低于小麥.

3.3 小麥提高了蚯蚓對(duì)PFOSA的富集,但對(duì)蚯蚓中PFOSA轉(zhuǎn)化率影響不大.

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Bioaccumulation and biotransformation of perfluorooctane sulfonamide in wheat and earthworms.

WU Si-han, WU Yu-meng, WANG Shuang-jie, CHEN Meng, LIU Qing, ZHU Ling-yan*

(Key Laboratory of Pollution Processes and Environmental Criteria of Ministry of Education, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China)., 2021,41(5)：2434～2440

The bioaccumulation and biotransformation of perfluorooctane sulfonamide (PFOSA) in wheat and earthworms was investigated in different culture media by different culture methods. The results indicated that PFOSA was effectively absorbed by wheat roots from the culture media and translocated from roots to shoots. The bioavailability of PFOSA in soil was significantly affected by the soil total organic carbon (TOC) content. The bioavailability of PFOSA in the soil with higher TOC content was reduced, resulting in the bioaccumulation factors in wheat and earthworms decreased from (61.24±8.42) and (21347.91±208.86) to (5.61±0.23) and (1404.92±108.21), respectively. PFOSA could be transformed into PFOS in the earthworms as well as in the roots and shoots of wheat, but the transformation rate of PFOSA in the earthworms ((3.87±1.71)%) was significantly lower than that in the wheat ((26.39±3.02)%). The ratio of branched PFOS isomers (-PFOS) in the wheat roots was (14.8±2.0)% and (66.1±26.2)% at low and high TOC content, respectively, lower than those in the shoots ((63.0±21.3)% and (85.2±2.4)%), respectively), which might be because it was easier to translocate-PFOS formed in roots to shoots. The ratio of-PFOS in wheat, especially in wheat shoots ((85.2±2.4)%), was significantly higher than that in earthworms ((16.5±4.0)%). The presence of wheat enhanced the bioavailability of PFOSA in the soil, thereby promoted the accumulation of PFOSA in earthworms, but had little effect on the transformation of PFOSA. The results provided evidence for the bioaccumulation and biotransformation of PFOSA in wheat and earthworms, and were helpful to explore the indirect sources of PFOS in the environment.

PFOSA；wheat；earthworm；bioaccumulation；biotransformation

X131

A

1000-6923(2021)05-2434-07

吳思寒(1998-),女,河南安陽(yáng)人,南開(kāi)大學(xué)碩士研究生,主要從事全氟和多氟化合物環(huán)境行為研究.

2020-10-08

國(guó)家重點(diǎn)研發(fā)計(jì)劃(2018YFC1801003,2019YFC1804203),國(guó)家自然科學(xué)基金資助項(xiàng)目(41991313,21737003)

* 責(zé)任作者, 教授, zhuly@nankai.edu.cn