楊夢(mèng)茹,徐 雄,王東紅,劉權(quán)震,呂 婧,林利華,王殿常,陳永柏,梁文艷

長江典型江段水體PAHs的分布特征、來源及其生態(tài)風(fēng)險(xiǎn)

楊夢(mèng)茹1,2,徐 雄2*,王東紅2,劉權(quán)震2,呂 婧2,林利華2,王殿常3,陳永柏3,梁文艷1**

(1.北京林業(yè)大學(xué)環(huán)境科學(xué)與工程學(xué)院,北京 100083；2.中國科學(xué)院生態(tài)環(huán)境研究中心,中國科學(xué)院飲用水科學(xué)與技術(shù)重點(diǎn)實(shí)驗(yàn)室,北京 100085；3.中國長江三峽集團(tuán)有限公司,湖北 武漢 430014)

針對(duì)我國長江典型江段豐、平、枯不同時(shí)期的地表水,采用了固相萃取—?dú)庀嗌V質(zhì)譜聯(lián)用(GC-MS)的分析技術(shù),調(diào)查了16種優(yōu)先控制多環(huán)芳烴(PAHs)的污染狀況.研究了長江干流PAHs的污染水平和分布特征,并在定量分析的基礎(chǔ)上評(píng)估了長江干流PAHs的來源和生態(tài)風(fēng)險(xiǎn).結(jié)果顯示,Σ16PAHs濃度范圍為2.22～1450.91ng/L,均值為107.04ng/L,其中,平水期武漢江段Σ16PAHs濃度最高,均值為1050.64ng/L,長江干流PAHs污染狀況與近5a國內(nèi)其他水體相比處于中等偏低水平.空間分布上長江典型江段地表水中Σ16PAHs從上游攀枝花江段到下游南京江段呈現(xiàn)出先上升后下降的趨勢(shì);時(shí)間分布上Σ16PAHs的變化趨勢(shì)為平水期(187.78ng/L)>豐水期(73.30ng/L)>枯水期(38.02ng/L).由同分異構(gòu)比值法分析表明:在枯水期和平水期中,煤炭、生物質(zhì)燃燒和石油源是長江干流PAHs的主要來源,而豐水期PAHs主要源于煤炭、生物質(zhì)燃燒,其中南京江段PAHs的來源較為復(fù)雜.采用物種敏感性分布評(píng)估法對(duì)PAHs進(jìn)行生態(tài)風(fēng)險(xiǎn)評(píng)估,結(jié)果顯示長江典型江段地表水中PAHs尚未對(duì)水生生物造成顯著的負(fù)面影響,與歷史數(shù)據(jù)比對(duì)表明現(xiàn)階段長江干流PAHs生態(tài)風(fēng)險(xiǎn)低于長江大保護(hù)政策實(shí)施前的生態(tài)風(fēng)險(xiǎn).

長江干流；多環(huán)芳烴；生態(tài)風(fēng)險(xiǎn)評(píng)價(jià)

多環(huán)芳烴被聯(lián)合國環(huán)境規(guī)劃署(UNEP)列為管控類的持久性有機(jī)污染物.由于人類活動(dòng)過程中燃料的不完全燃燒、車輛和船舶尾氣排放以及工業(yè)廢料的排放,使得大量的PAHs進(jìn)入到各種環(huán)境介質(zhì)中,不論在大氣[1-2]還是土壤[3]、沉積物[4]等介質(zhì)中均有PAHs被檢出的研究報(bào)道,進(jìn)而PAHs通過地表徑流、大氣沉降[5]、廢水排放以及石油泄漏等方式最終進(jìn)入到河流生態(tài)系統(tǒng)中,進(jìn)入到河流生態(tài)系統(tǒng)中的PAHs一部分會(huì)溶解在水體中,另外一部分PAHs由于其高疏水性極易吸附于懸浮顆粒物表面并隨著水流的遷移沉于底泥中[6],而處于底泥表層的PAHs隨著水文等因素的擾動(dòng),PAHs會(huì)重新進(jìn)入河流水體中,從而對(duì)水生態(tài)系統(tǒng)和人類健康造成潛在危害[7].

長江是中國的第一長河,城市經(jīng)濟(jì)的快速發(fā)展給長江帶來了巨大的環(huán)境壓力,在過去幾十年里長江沿岸建設(shè)了30多家石油化工廠,導(dǎo)致大量的PAHs排放到河流中[8-10].因此人們對(duì)長江流域中PAHs的賦存特征進(jìn)行了長期的監(jiān)測(cè)和研究.Yang等[8]調(diào)查了2006～2017年長江地表水PAHs的污染狀況,發(fā)現(xiàn)PAHs為長江主要的風(fēng)險(xiǎn)微污染物.由于水體受到嚴(yán)重污染,長江已被列入世界十大瀕危河流名單中[9],因此引起了社會(huì)各階層的廣泛關(guān)注.2016年通過的《長江經(jīng)濟(jì)帶發(fā)展規(guī)劃綱要》[12]以及2017年開展的長江干流岸線保護(hù)和利用專項(xiàng)檢查行動(dòng)[13],堅(jiān)持生態(tài)優(yōu)先,綠色發(fā)展,共抓大保護(hù)、不搞大發(fā)展,督促各地推進(jìn)涉嫌違法違規(guī)項(xiàng)目的整改.長江大保護(hù)政策實(shí)施期間,長江中游岸線PAHs污染狀況(58.17ng/L)[14]低于長江大保護(hù)政策實(shí)施前的狀況(2006年:2095.00ng/L[15];2007年:247.45ng/L[16]),同樣南京江段也發(fā)現(xiàn)相同規(guī)律,2018年南京江段PAHs的濃度(208ng/L)[4]低于2004年和2015年南京PAHs的濃度(2004年:1511ng/L;2015年:12826ng/L)[17-18].這一系列的研究結(jié)果表明國家出臺(tái)的一系列長江大保護(hù)政策和各種有效的控制手段,使得長江流域PAHs的污染程度有下降的趨勢(shì).

目前對(duì)于長江干流地表水中PAHs的濃度水平和分布狀況的研究大都集中于部分江段,如重慶江段[19]、三峽江段[20]、武漢江段[21]、下游江段[22]等江段,而PAHs污染往往受到當(dāng)?shù)毓I(yè)模式和人口密度的影響,長江大保護(hù)行動(dòng)期間,PAHs在長江干流上的整體污染情況目前研究較少.盡管已有研究報(bào)道了2021年枯水期和豐水期長江流域重點(diǎn)江段PAHs的污染情況并評(píng)估了長江流域地表水中PAHs的健康風(fēng)險(xiǎn)[23],然而地表水中PAHs對(duì)水生生物的危害同樣不容忽視,近年來長江流域干流地表水中PAHs對(duì)水生生物造成的生態(tài)風(fēng)險(xiǎn)狀況不清.

因此,本研究針對(duì)長江干流典型江段地表水,包括攀枝花、宜賓、重慶、三峽庫區(qū)、武漢以及南京江段,從2019～2020年在豐水期、平水期和枯水期進(jìn)行樣品采集,以16種優(yōu)控PAHs為研究對(duì)象,分析PAHs在長江干流的濃度以及時(shí)空分布特征,識(shí)別長江典型江段地表水中PAHs的來源,并對(duì)長江干流PAHs進(jìn)行生態(tài)風(fēng)險(xiǎn)評(píng)價(jià).

1 材料與方法

1.1 實(shí)驗(yàn)材料與試劑

1.2 樣品采集與前處理

根據(jù)長江沿岸城市的工農(nóng)業(yè)發(fā)展程度以及人口密度的不同,選取長江干流6個(gè)受人類活動(dòng)影響較大的典型江段作為本次的研究區(qū)域,共設(shè)置了51個(gè)采樣點(diǎn):包括攀枝花江段(P1～P6),宜賓江段(YB1～YB6),重慶江段(C1～C11),三峽庫區(qū)江段(SX1～SX12),武漢江段(WH1～WH6),以及南京江段(N1～N10).每個(gè)典型江段采樣點(diǎn)均囊括城市上下游區(qū)域,整體地反映城市不同功能區(qū)對(duì)長江地表水中PAHs的影響.采樣點(diǎn)示意見圖1.于2019年12月(枯水期)、2020年6月(豐水期)以及2020年10月(平水期)分3次在以上采樣點(diǎn)對(duì)長江干流地表水進(jìn)行樣品采集,共計(jì)采集了127個(gè)樣品.2020年6月(豐水期)武漢江段由于疫情的原因未進(jìn)行樣品采集.在長江中弘線的垂直方向上使用不銹鋼盛水器直接采集水面下約0.5m處的表層水,水樣采集時(shí)均避開了明顯的污染源,采集的2L地表水樣存儲(chǔ)于預(yù)先清洗的避光棕色玻璃瓶中,水樣在4℃條件下保存和運(yùn)輸,且在48h內(nèi)完成過濾和固相萃取等前處理操作.

圖1 采樣點(diǎn)示意

樣品前處理方法參照文獻(xiàn)[24],采集到的2L水樣首先使用0.7μm孔徑的玻璃纖維濾膜去除水體中的懸浮顆粒物.加入回收率指示物氘代菲100ng,混勻后使用C18固相萃取柱對(duì)水樣進(jìn)行富集:富集前固相萃取小柱依次用5mL二氯甲烷、甲醇和超純水進(jìn)行淋洗和活化,在負(fù)壓條件下使水樣通過固相萃取小柱富集.富集好的小柱使用10mL二氯甲烷進(jìn)行洗脫,洗脫液使用無水硫酸鈉進(jìn)行脫水處理,氮吹并置換溶液為正己烷,定容至0.5mL后于-20℃條件下保存以供后續(xù)儀器分析.

1.3 儀器分析與質(zhì)量控制

PAHs的定性和定量分析使用安捷倫6890N氣相色譜以及安捷倫5975B質(zhì)譜聯(lián)用儀.色譜柱為安捷倫DB-5MS柱(30m×0.25mm×0.25μm),柱溫箱升溫程序?yàn)?初始溫度為60℃,保持2min,然后以10℃/min的速率升至300℃,保持10min.高純氦氣為載氣,恒流模式下載氣流速為1mL/min,采用不分流進(jìn)樣模式,進(jìn)樣量為1μL.質(zhì)譜儀在選擇離子模式(SIM)下進(jìn)行定量分析,16種PAHs以及氘代菲的保留時(shí)間、特征離子、標(biāo)準(zhǔn)曲線等信息列于表1.

本研究采取了嚴(yán)格的質(zhì)量控制過程,使用2L超純水作為實(shí)驗(yàn)室空白,16種PAHs的實(shí)驗(yàn)室空白在n.d.～14.31ng/L間,除了萘的空白最高為14.31ng/L,其余15種PAHs濃度均在4.12ng/L以下,其中高環(huán)PAHs(>4環(huán))在空白樣品中均未檢出,該實(shí)驗(yàn)空白對(duì)后續(xù)數(shù)據(jù)的解讀和分析影響不大;在所有樣品中加入回收率指示物氘代菲,結(jié)果表明氘代菲的回收率為(107%±12.13%) (=130,包括127個(gè)實(shí)際樣品和3個(gè)空白樣品);PAHs的檢出限使用儀器自帶的信噪比(/)工具進(jìn)行估算,以/≈3時(shí)的進(jìn)樣濃度為儀器檢出限(LOD),16種目標(biāo)PAHs的LOD在0.05～ 0.2μg/L間;目標(biāo)化合物的回收率通過實(shí)驗(yàn)室空白加標(biāo)來測(cè)定,PAHs的回收率為65%～118%.

表1 16種PAHs以及氘代菲的保留時(shí)間,特征離子以及標(biāo)準(zhǔn)曲線

1.4 生態(tài)風(fēng)險(xiǎn)評(píng)價(jià)

采用物種敏感性分布評(píng)估法(SSD)對(duì)PAHs的生態(tài)風(fēng)險(xiǎn)進(jìn)行評(píng)價(jià),該方法描述了在一定污染物暴露濃度下預(yù)計(jì)受影響的物種比例,被廣泛應(yīng)用于評(píng)價(jià)某一污染物或多種污染物對(duì)生物的生態(tài)風(fēng)險(xiǎn)[25].SSD構(gòu)建和應(yīng)用的步驟如下:(1)毒性數(shù)據(jù)的獲取;(2)SSD曲線擬合;(3)計(jì)算可能受影響的物種比例(PAF);(4)單一PAHs的生態(tài)風(fēng)險(xiǎn)評(píng)估.

生物毒性數(shù)據(jù)由美國環(huán)保署EPA ECOTOX數(shù)據(jù)庫提供.毒性數(shù)據(jù)優(yōu)先選擇慢性毒性數(shù)據(jù),當(dāng)慢性數(shù)據(jù)量不足以構(gòu)建SSD曲線時(shí),可采用急性數(shù)據(jù),并通過急/慢性毒性比率(ACR)來預(yù)測(cè)化合物相應(yīng)的慢性值[25-26].本研究使用急性毒性數(shù)據(jù)來構(gòu)建PAHs的SSD曲線,急/慢性毒性比率選用10[27]并選擇暴露終點(diǎn)為半數(shù)致死濃度(LC50)及半數(shù)有效濃度(EC50),暴露時(shí)間小于4d的標(biāo)準(zhǔn)測(cè)試品種的毒理數(shù)據(jù).所選物種的信息列于表2中.

表2 構(gòu)建SSD曲線的物種信息

注:物種信息均來自EPA ECOTOX數(shù)據(jù)庫.

Log-Normal, Log-logistic和Burr III型分布(包括Burr III、ReWeibull和Weibull)是構(gòu)建SSD常用的擬合方法[26].與其他兩個(gè)方法相比,Burr III型分布通?？梢暂^好的擬合SSD曲線,本研究采用Burr III型分布擬合SSD曲線,并通過Burrli OZ軟件構(gòu)建SSD曲線[28].Burr III型分布可有公式(1)表示:

式中:為環(huán)境濃度,μg/L;、、為函數(shù)3個(gè)參數(shù);當(dāng)趨于無窮大時(shí),Burr III分布函數(shù)變?yōu)镽epareto 分布函數(shù);當(dāng)趨于無窮大時(shí),可變成ReWeibull分布函數(shù).

在SSD模型中,水生態(tài)風(fēng)險(xiǎn)以PAF值表征,PAF值越大,則污染物帶來的水生態(tài)風(fēng)險(xiǎn)越高.當(dāng)PAF值小于5%時(shí),認(rèn)為生態(tài)風(fēng)險(xiǎn)低或不顯著;大于等于5%時(shí)生態(tài)風(fēng)險(xiǎn)被定義為高風(fēng)險(xiǎn)[29].PAF值的計(jì)算方法以公式(1)為例說明:取為污染物的濃度值帶入式中,計(jì)算得到()值,即為PAF值.

2 結(jié)果與討論

2.1 長江典型江段PAHs污染水平及時(shí)空分布特征

2.1.1 長江典型江段PAHs污染水平 水生態(tài)系統(tǒng)中低分子量PAHs因其高溶解性更傾向存在于水體中,而高分子量PAHs由于其對(duì)顆粒具有較強(qiáng)的親和力更容易積聚于沉積物中[30-31],因此水體中16種PAHs的濃度以及檢出率可能存在差異.如表3所示,從PAHs的組成上來看,2環(huán)和3環(huán)PAHs濃度在總量中占很大比例(中位數(shù)占比:82.54%;均值占比: 91.53%),其中Nap、Phe以及Flu是主要的組分,4環(huán)和5～6環(huán)PAHs濃度中位數(shù)分別占總量的15.69%和1.77%,濃度均值占總量的比值分別為6.97%及1.5%,可以看出2～4環(huán)PAHs濃度(中位數(shù)占比:98.23%;均值占比:98.50%)占比最大.Σ16PAHs濃度范圍為2.22～1450.91ng/L,平均濃度為107.04ng/L.從長江典型江段PAHs的檢出率來看,2～4環(huán)PAHs檢出率較高,其中Nap、Flu、Flt以及Pyr的檢出率均為100%,5～6環(huán)的PAHs除了BbF的檢出率為98.43%外,其他PAHs的檢出率均較低.研究發(fā)現(xiàn)平水期長江干流地表水中Nap以及豐水期3環(huán)和4環(huán)PAHs在上游江段存在累積現(xiàn)象,而枯水期和平水期PAHs幾乎不存在累積.

本研究長江干流地表水中PAHs污染水平與近5a內(nèi)(2017～2021年)報(bào)道的我國其他水體地表水中PAHs濃度相比(圖2),長江干流的Σ16PAHs平均值與黃河[32]、豐水期海河[33]及潮白河[34]水體相似,高于丹水河流域、鄱陽湖等水體[33,35-38],低于松花江、臺(tái)灣鹽河以及觀瀾河等水體[39-44].可以看出近5a內(nèi)長江干流PAHs污染在我國地表水中處于中等偏低水平.

表3 16種PAHs在長江干流地表水中濃度統(tǒng)計(jì)(ng/L)

注:Min、Max、Aver以及Median分別為濃度最小值、最大值、平均值以及中位數(shù); n.d.為未檢出.

圖2 近5a內(nèi)(2017～2021)中國不同水體地表水中PAHs的濃度范圍和均值

2.1.2 長江典型江段PAHs的時(shí)空分布特征 長江流域水系眾多,支流、湖泊的匯入以及沿岸城市人文活動(dòng)導(dǎo)致長江干流ΣPAHs在時(shí)空分布上可能存在明顯的差異.圖3顯示了不同時(shí)期典型江段Σ16PAHs的分布特征,首先從空間分布上看,平水期PAHs的濃度從上游攀枝花江段(Σ16PAHs均值為43.61ng/L)到中下游武漢江段(1050.64ng/L)有上升趨勢(shì),下游的南京江段(94.61ng/L)較武漢江段濃度有所降低,但其濃度高于三峽江段(71.33ng/L);豐水期PAHs的濃度上游從攀枝花江段(23.59ng/L)到三峽庫區(qū)江段(122.86ng/L)有上升趨勢(shì),下游的南京江段濃度較低(33.67ng/L),該江段濃度值僅高于上游的攀枝花江段濃度值;枯水期PAHs的濃度從上游到下游沒有明顯的變化趨勢(shì).總體上長江地表水中Σ16PAHs含量從上游攀枝花到下游南京江段呈現(xiàn)先上升后下降的趨勢(shì),下游南京江段Σ16PAHs含量(51.11ng/L)高于上游攀枝花(39.41ng/L)和宜賓江段(44.71ng/L). Nguyen等人研究表明工業(yè)區(qū)地表水中PAHs含量高于居民區(qū)[45],另外三峽[46]以及中下游[4,8]的工業(yè)較上游其他地區(qū)發(fā)達(dá),可能是造成長江三峽庫區(qū)以及中下游地區(qū)PAHs含量高于上游的攀枝花和宜賓江段的原因.

圖3 長江典型江段PAHs在不同時(shí)期的變化特征

人類活動(dòng)是地表水和沉積物中PAHs的主要來源.平水期武漢段與同時(shí)期其他城市的PAHs濃度有顯著性差異(<0.05),該現(xiàn)象可能因?yàn)橐咔榈玫娇刂坪蟮奈錆h為滿足經(jīng)濟(jì)的快速發(fā)展,排放大量工業(yè)廢水以及頻繁航運(yùn)所排放的廢棄物造成武漢江段PAHs污染嚴(yán)重.受疫情影響,2020年初武漢港一度貨運(yùn)需求下降,但是2020年全年武漢港集裝箱年吞吐量達(dá)到193.25萬,同2019年比增長了14.4%[47],并從武漢新港管理委員會(huì)得到武漢港2020年4～10月的集裝箱吞吐量數(shù)據(jù),發(fā)現(xiàn)2020年9月和10月集裝箱吞吐量均高于同年4～8月的數(shù)據(jù);頻繁航運(yùn)排放的廢棄物可能是導(dǎo)致PAHs污染量劇增的原因.

從時(shí)間分布上看,枯水期16種PAHs的總濃度范圍為4.05～87.65ng/L,均值為38.02ng/L;豐水期濃度范圍2.22～184.51ng/L,均值為73.30ng/L;平水期濃度范圍為25.3～1450.91ng/L,均值為187.78ng/L.枯水期攀枝花江段的Σ16PAHs濃度最高,為51.02ng/L;豐水期三峽庫區(qū)的Σ16PAHs濃度最高,為122.86ng/L;而平水期武漢Σ16PAHs濃度最高,為1050.64ng/L.總的PAHs變化趨勢(shì)為平水期>豐水期>枯水期.若忽略平水期武漢江段濃度,豐水期Σ16PAHs濃度均值略高于平水期Σ16PAHs濃度均值(70.12ng/L).本研究長江干流枯水期PAHs濃度低于其他時(shí)期的分布特征與太子河[48]、太湖[44]、長江重慶段[19]的分布特征相似.該現(xiàn)象的原因可能是豐水期和平水期降雨會(huì)增加地表水中PAHs濕沉降和地表徑流的輸入[44],另外,降雨引起沉積物擾動(dòng)可能會(huì)導(dǎo)致沉積物中PAHs再次進(jìn)入水環(huán)境[19].

豐水期的重慶和三峽庫區(qū)江段PAHs含量明顯高于其他時(shí)期(<0.05),該結(jié)果與Zhu等[19]研究的長江重慶江段PAHs時(shí)間變化趨勢(shì)一致.近年來有研究表明重慶市區(qū)ΣPAHs的大氣(氣態(tài)+顆粒態(tài))平均濃度為(79.9±40.5)ng/m3[49],以及大氣沉降物平均濃度為(457±375)ng/L[50],均處于較高的濃度水平,豐水期強(qiáng)降雨可能增加重慶段和三峽庫區(qū)段中PAHs濕沉降和地表徑流的輸入,三峽庫區(qū)PAHs含量高可能還因?yàn)榭菟诔练e物中PAHs大量累積,雨季三峽庫區(qū)開閘泄洪以及強(qiáng)降雨[19]導(dǎo)致底泥中的PAHs再次進(jìn)入水體中[51],造成豐水期該江段PAHs含量的增加.

隨著長江沿岸城市的快速發(fā)展,大量的污染物即工業(yè)污廢水和廢棄物、市政污水以及航運(yùn)產(chǎn)生的廢料不斷排入到長江干線中,城市江段內(nèi)S16PAHs的分布可能會(huì)受到PAHs排放影響,因此本研究就單個(gè)城市的上下游PAHs濃度進(jìn)行了研究,發(fā)現(xiàn)城市區(qū)域?qū)沃蠵AHs的含量有明顯影響,例如攀枝花江段(上游S16PAHs濃度均值:38.37ng/L、中游39.63ng/L、下游:40.68ng/L(下同))、重慶江段(54.48,73.94, 84.14ng/L)以及南京江段(55.06,68.32,76.50ng/L)總PAHs含量從城市上游到下游呈現(xiàn)出上升的趨勢(shì),另外宜賓江段和武漢江段在中心城區(qū)處PAHs濃度高于城市上中下游(宜賓江段: 31.94,52.71,40.43ng/L和武漢江段:538.02, 823.45, 486.48ng/L).對(duì)于單個(gè)采樣點(diǎn)而言,本研究發(fā)現(xiàn)C7采樣點(diǎn)的S16PAHs濃度較高(114.19ng/L),該值高于重慶S16PAHs濃度均值(67.84ng/L),并且發(fā)現(xiàn)該采樣點(diǎn)上游分布著化工廠、鋼鐵廠、碼頭以及污水處理廠,這些場所影響著該江段的水質(zhì).WH1(702.79ng/L)以及WH3(768.39ng/L) 采樣點(diǎn)S16PAHs濃度值高于武漢S16PAHs濃度均值(546.27ng/L),這是因?yàn)閃H1附近分布著眾多工業(yè)園區(qū),WH6采樣點(diǎn)附近為武漢港口,這些場所排放的廢水和廢料造成該江段PAHs污染嚴(yán)重.N1(82.50ng/L)、N5(154.19ng/L)以及N9采樣點(diǎn)(82.78ng/L)濃度值高于南京江段S16PAHs濃度均值(51.11ng/L),N1及N9為南京市工業(yè)園區(qū)、碼頭的下游區(qū)域,N5為南京市中心城區(qū)下游段,工業(yè)生產(chǎn)、航運(yùn)以及城市生活污水的排放造成長江江段水質(zhì)惡化.

2.2 來源分析

同分異構(gòu)體比值法通常被用于識(shí)別和評(píng)估PAHs來源[52-53].本研究采用Ant/(Ant+Phe)和Fla/(Fla+Pyr)2個(gè)同分異構(gòu)比值[52]對(duì)長江干流地表水中PAHs的來源進(jìn)行分析,分析結(jié)果見圖4.當(dāng)Flt/(Flt+Pyr)比值小于0.4時(shí)表示PAHs主要源于石油源(石油、石油物質(zhì)的泄漏),大于0.4但小于0.5時(shí)表示PAHs主要來源于石油燃燒、大于0.5時(shí)PAHs主要來源于煤炭、生物質(zhì)燃燒;Ant/(Ant+Phe)比值小于0.1和大于0.1分別表示PAHs來源于石油源和煤炭、生物質(zhì)燃燒[52,54].枯水期和平水期長江典型江段地表水的PAHs主要來源是煤炭、生物質(zhì)燃燒和石油源.豐水期地表水中PAHs主要來源于煤炭、生物質(zhì)燃燒.攀枝花江段PAHs來源在3個(gè)時(shí)期的比值基本未發(fā)生變化,均來源于煤炭、生物質(zhì)燃燒和石油源.不同時(shí)期南京江段和武漢江段PAHs的來源存在顯著性差異,枯水期南京江段以及武漢江段PAHs來源與其他江段PAHs來源一致,均來源于煤炭、生物質(zhì)的燃燒以及石油泄漏,豐水期南京江段PAHs主要源于石油泄漏以及石油燃燒,而平水期南京江段和武漢江段PAHs主要由煤炭、生物質(zhì)的燃燒.

圖4 長江典型江段PAHs在不同時(shí)期的來源特征

總的來說,長江PAHs主要源于煤炭、生物質(zhì)燃燒和石油源,Tang等[46]對(duì)三峽庫區(qū)PAHs進(jìn)行了來源分析,發(fā)現(xiàn)煤炭、生物質(zhì)燃燒與石油源為PAHs的主要來源,與本研究結(jié)果一致.長江干流地表水中PAHs污染來源與近5a內(nèi)(2017～2021年)國內(nèi)其他水體地表水中PAHs污染成因相比,長江干流PAHs污染成因僅與鄱陽湖[36]中PAHs的成因相同,均以石油源和煤炭、生物質(zhì)燃燒為主;其他河流大多以石油、煤炭以及生物質(zhì)混合燃燒為主[32,37-38,41]或者僅以煤炭、生物質(zhì)燃燒為主[33,35,40].不難發(fā)現(xiàn)國內(nèi)大多數(shù)河流中PAHs的來源均以煤炭、生物質(zhì)燃燒為主,僅有小清河[43]和太湖[44]以石油污染和石油燃燒為主.

2.3 生態(tài)風(fēng)險(xiǎn)評(píng)估

表4 長江干流地表水中8種PAHs的PAF值(%)

注: 0.00為PAF值較小接近無風(fēng)險(xiǎn);——為在化合物未檢出的情況下沒有進(jìn)行生態(tài)風(fēng)險(xiǎn)評(píng)估.

由于水生生物毒性數(shù)據(jù)的缺乏,本研究僅分析了8種PAHs的生態(tài)風(fēng)險(xiǎn).從表4可以看出,所有江段地表水中Flt和Pyr的PAF值均比其他PAHs的PAF值高,豐水期三峽庫區(qū)地表水中Flt和Pyr的PAF值高于枯水期和平水期,除此之外其他江段枯水期Flt和Pyr的風(fēng)險(xiǎn)均高于豐水期和平水期.長江典型江段PAHs的PAF值均低于5%,不存在明顯的生態(tài)風(fēng)險(xiǎn).為了解大保護(hù)政策的實(shí)施對(duì)長江地表水中PAHs生態(tài)風(fēng)險(xiǎn)的干預(yù)效果,本研究收集了大保護(hù)政策實(shí)施前長江流域水體中8種PAHs濃度均值的數(shù)據(jù),并通過本研究擬合的SSD曲線評(píng)估了以往報(bào)道的PAHs的生態(tài)風(fēng)險(xiǎn).結(jié)果如表5所示,大保護(hù)政策實(shí)施前攀枝花江段地表水的Pyr(PAF值為6.97%),武漢江段的Flt(7.62%)和南京江段的Ant(11.80%)、Flt(7.52%)以及Pyr(5.80%)均對(duì)地表水中水生生物構(gòu)成較高的生態(tài)風(fēng)險(xiǎn),并且在武漢江段地表水中Pyr(4.23%)以及Bap(3.63%)存在潛在的生態(tài)風(fēng)險(xiǎn),而本研究中攀枝花、武漢以及南京的江段的風(fēng)險(xiǎn)均低于1%,不存在明顯的生態(tài)風(fēng)險(xiǎn).該結(jié)果表明長江大保護(hù)政策的實(shí)施,有效的降低了長江干流中PAHs的生態(tài)風(fēng)險(xiǎn).

表5 以往長江地表水中PAHs濃度均值(μg/L)的報(bào)道及相應(yīng)的PAF值(%)

注: 0.00為PAF值較小接近無風(fēng)險(xiǎn);n.d.為化合物未檢出;——為化合物未報(bào)道或未檢出情況下沒有進(jìn)行生態(tài)風(fēng)險(xiǎn)評(píng)估.

3 結(jié)論

3.1 長江干流地表水中PAHs檢測(cè)結(jié)果顯示, Σ16PAHs濃度范圍為2.22～1450.91ng/L,均值為107.04ng/L,長江PAHs的污染水平與5a年國內(nèi)其他水體相比,總體處于中等偏低水平.

3.2 長江典型江段地表水中PAHs來源解析顯示,水體受到石油源(石油泄漏)及生物質(zhì)、煤燃燒共同污染,南京江段PAHs來源較為復(fù)雜.

3.3 生態(tài)風(fēng)險(xiǎn)評(píng)價(jià)結(jié)果顯示,長江典型江段地表水中PAHs對(duì)水生生物沒有造成明顯的生態(tài)風(fēng)險(xiǎn),其生態(tài)風(fēng)險(xiǎn)值低于2017年之前長江流域中PAHs的生態(tài)風(fēng)險(xiǎn)值,該結(jié)果與長江大保護(hù)政策的實(shí)施密不可分.

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Distribution characteristics, source and ecological risks assessment of PAHs in water bodies of typical sections of the Yangtze River.

YANG Meng-ru1,2, XU Xiong2*, WANG Dong-hong2, LIU Quan-zhen2, LV Jing2, LIN Li-hua2, WANG Dian-chang3, CHEN Yong-bo3, LIANG Wen-yan1**

(1.College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China；2.Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China；3.China Three Gorges Corporation, Wuhan 430014, China)., 2022,42(11)：5308～5317

Sixteen priority polycyclic aromatic hydrocarbons(PAHs) were investigated in water samples (wet, normal and dry periods) in the main stream of the Yangtze River using solid-phase extraction (SPE) -gas chromatography-mass spectrometry (GC-MS) analysis technique. The pollution levels and distribution characteristics of PAHs were studied, the sources and ecological risks of PAHs were evaluated based on quantitative analysis. The results showed that the concentration of Σ16PAHs was from 2.22 to 1450.91ng/L, the average concentrations of ΣPAHs was 107.04ng/L in the Yangtze River, among them, the concentration of Σ16PAHs in the Wuhan river section was the highest during the normal period, with an average value of 1050.64ng/L. Compared with other domestic water bodies in the past five years, the PAHs pollution in the main stream of the Yangtze River was at a moderately low level. In terms of spatial distribution, the Σ16PAHs in surface water of typical sections of the Yangtze River showed a trend of first rising and then falling from the Upstream Panzhihua section to the downstream Nanjing section, The variation trend of Σ16PAHs in temporal distribution: normal period (187.78ng/L)>wet period (73.30ng/L)> dry period (38.02ng/L). The analysis by isomeric ratio method showed that coal, biomass burning and petroleum sources were the main sources of PAHs in the main stream of the Yangtze River in dry and normal periods, In the wet season, PAHs mainly originated from coal and biomass combustion, among them, the sources of PAHs in the Nanjing River section were more complex. The ecological risk assessment of PAHs was carried out using the Species Sensitivity Distributions (SSD) assessment method. The results showed that the PAHs in the surface water of typical sections of the Yangtze River had not yet caused significant negative impacts on aquatic organisms. The comparison of the results with historical data showed that the current ecological risk of PAHs in the main stream of the Yangtze River is lower than the ecological risk before the implementation of the Yangtze River protection policy.

the main stream of the Yangtze River；polycyclic aromatic hydrocarbons；ecological risks assessment

X522

A

1000-6923(2022)11-5308-10

楊夢(mèng)茹(1997-),女,山西運(yùn)城人,北京林業(yè)大學(xué)碩士研究生,主要從事水體中風(fēng)險(xiǎn)污染物篩查研究.

2022-04-24

中國長江三峽集團(tuán)有限公司科研項(xiàng)目(201903139);廣東省基礎(chǔ)與應(yīng)用基礎(chǔ)研究基金資助項(xiàng)目(2020B1515120080);國家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(2021YFC3200802-02)

* 責(zé)任作者, 助理研究員, xuxiong@rcees.ac.cn;** 教授, lwy@bjfu.edu.cn