陳 明,李鳳果,師艷麗,陶美霞,胡蘭文

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贛南桃江河表層沉積物鎢賦存特征及風(fēng)險(xiǎn)分析

陳 明*,李鳳果,師艷麗,陶美霞,胡蘭文

(江西理工大學(xué)資源與環(huán)境工程學(xué)院,江西省礦冶環(huán)境污染控制重點(diǎn)實(shí)驗(yàn)室,江西 贛州 341000)

選擇贛南桃江河表層沉積物為研究對(duì)象,采用改進(jìn)的BCR提取法分析桃江上、中、下游及支流表層沉積物中鎢的含量及賦存形態(tài),并利用富集系數(shù)法(EF)和風(fēng)險(xiǎn)指數(shù)編碼法(RAC)對(duì)桃江河表層沉積物中鎢的富集程度與環(huán)境風(fēng)險(xiǎn)進(jìn)行評(píng)價(jià).結(jié)果表明,桃江河表層沉積物鎢的總量范圍為1.21~39.73mg/kg,均值為18.21mg/kg.研究區(qū)域58%的采樣點(diǎn)沉積物中鎢總量高于江西省土壤重金屬背景值;桃江河沉積物中鎢的主要賦存形態(tài)是殘?jiān)鼞B(tài)(B4態(tài)),沉積物中各形態(tài)鎢占總鎢的比例大小順序?yàn)闅堅(jiān)鼞B(tài)>可氧化態(tài)>可還原態(tài)>弱酸提取態(tài),空間上有效態(tài)鎢占總鎢的比例大小為支流>下游>上游>中游,平均比例分別為22.44%、21.03%、14.45%及10.91%.相關(guān)性分析顯示,pH值和陽離子交換與鎢的各形態(tài)及總量呈正相關(guān).EF法分析表明桃江河上游與支流沉積物中鎢富集嚴(yán)重;RAC法分析結(jié)果顯示采樣點(diǎn)沉積物中鎢含量呈低、中、高生態(tài)風(fēng)險(xiǎn)占比分別為33.33%、46.67%、17.78%.上述結(jié)果表明,桃江河表層沉積物鎢富集程度及環(huán)境風(fēng)險(xiǎn)較嚴(yán)重,應(yīng)引起重視并開展深入研究.

桃江河；沉積物；鎢；賦存形態(tài)；風(fēng)險(xiǎn)評(píng)估

鎢(W)是一種水不溶性金屬且呈化學(xué)惰性[1-2],相當(dāng)長的時(shí)期內(nèi)被認(rèn)為無顯著的生態(tài)毒性及環(huán)境效應(yīng),其生態(tài)環(huán)境安全性基本被忽視[3-5].與其他金屬物質(zhì)相比,確定鎢及鎢化合物可能對(duì)人類健康和毒性作用的動(dòng)物研究相當(dāng)有限.美國環(huán)保署(USEPA)于 2008 年正式將鎢列為新興環(huán)境污染物[6-7],俄羅斯也已經(jīng)將鎢列為一種水體污染物[8].雖然到目前為止尚未證實(shí)兒童白血病群發(fā)與該群體對(duì)鎢的攝入之間存在確切聯(lián)系,但實(shí)驗(yàn)室動(dòng)物實(shí)驗(yàn)研究確已表明鎢有毒性、可致癌[9-13],且在中性-偏堿性水環(huán)境中具有較強(qiáng)的遷移能力[14-15].

我國贛南分布著眾多鎢礦,鎢礦開采已有百年歷史,早先的鎢礦開采、冶煉、工業(yè)生產(chǎn)等,將大量鎢尾砂和廢棄渣質(zhì)等含大量重金屬的污染物直接排入河道,沉積物是是重金屬污染的源和匯[16],沉積物中重金屬含量能有效反映河流重金屬富集情況.重金屬污染的生態(tài)風(fēng)險(xiǎn)和生物毒性不僅與重金屬的總量有關(guān),與重金屬賦存形態(tài)也密切相關(guān)[17].不同形態(tài)的重金屬生物效應(yīng)不同,重金屬賦存形態(tài)可以有效判斷重金屬的來源、生物毒性、遷移轉(zhuǎn)化及環(huán)境行為[18-19].桃江河是贛江重要的支流之一,由于多年的工業(yè)生產(chǎn)、鎢礦開采、生產(chǎn)養(yǎng)殖等,造成河流污染.目前已有學(xué)者對(duì)桃江河沉積物中重金屬污染進(jìn)行調(diào)查分析[20],但缺少對(duì)河流積物中重金屬鎢的探究.本文對(duì)桃江河表層沉積物中鎢的含量及賦存形態(tài)進(jìn)行研究,期望為鎢污染的預(yù)防治理提供科學(xué)參考.

1 材料與方法

1.1 研究區(qū)域與樣品采集

桃江是贛江的二級(jí)支流,發(fā)源于贛州市全南縣飯池嶂,流經(jīng)龍南縣、信豐縣、贛縣,在贛縣大埠、大田鄉(xiāng)后匯入貢江.桃江河屬于亞熱帶丘陵山區(qū)濕潤季風(fēng)氣候,河流以雨水補(bǔ)給為主,徑流量隨降水變化而變化.近年來,由于養(yǎng)殖業(yè)、城鎮(zhèn)建設(shè)以及早期無序的礦山開采等大量的污染物排入水體,造成河流水體污染.本文充分考慮了桃江河段內(nèi)生產(chǎn)和生活取水口、廢水排放口及污染物排放的位置,采用宏觀控制重點(diǎn)布設(shè)法布設(shè)采樣點(diǎn)[21].在桃江干流和支流共選取了45個(gè)采樣點(diǎn)(圖1).

圖1 研究區(qū)域位置及采樣點(diǎn)分布

樣品于2017年6月采用GPS定位系統(tǒng)定位,并采用抓斗式采樣器采集1.5~2kg的表層沉積物(0~10cm)裝入自封袋中,放于4℃保溫冰箱中運(yùn)回實(shí)驗(yàn)室.

1.2 樣品預(yù)處理與測(cè)定

采集的樣品自然風(fēng)干后,剔除貝殼、樹枝、碎石等雜質(zhì),用瑪瑙缽碾碎過200目篩子,保存于聚乙烯袋中待測(cè).鎢總量的測(cè)定:稱取0.50g土樣在聚四氟乙烯坩堝中,然后加5mL體積比為 1:1硝酸和1mL濃縮磷酸在95℃下加熱30min后加濃縮硝酸2.5mL,再加熱30min,重復(fù)4次后95℃加熱2h,然后加3mL 30%過氧化氫95℃加熱15min,再加2mL 30%過氧化氫95℃加熱2h,鎢形態(tài)(弱酸提取態(tài)B1、可還原態(tài)B2、可氧化態(tài)B3、殘?jiān)鼞B(tài)B4)采用改進(jìn)BCR三步法提取[22],提取步驟見圖2.所有預(yù)處理后的鎢總量和各形態(tài)均用1%硝酸稀釋至50mL.

本實(shí)驗(yàn)所有提取液均送工程研究院采用電感耦合等離子體質(zhì)譜儀(ICP–MS,Agilent 8800)測(cè)定.實(shí)驗(yàn)過程均設(shè)置空白對(duì)照和3個(gè)平行樣以減小誤差,桃江表層沉積物鎢總量的回收率控制在93%~107%之間;鎢的形態(tài)分析標(biāo)準(zhǔn)物質(zhì)的回收率控制在89%~ 110%之間;Fe的回收率在91%~105%之間,測(cè)量誤差小于±10%.沉積物理化性質(zhì)包括pH值、土壤有機(jī)質(zhì)、陽離子交換、全氮等,具體測(cè)定方法見表1.

表1 沉積物理化性質(zhì)測(cè)定方法

1.3 評(píng)價(jià)方法

1.3.1 富集系數(shù)法(EF) 計(jì)算公式見文獻(xiàn)[23],其鎢背景值參照江西省土壤重金屬背景值為5.1mg/ kg[24].根據(jù)富集系數(shù)將污染程度分為5個(gè)等級(jí),當(dāng)富集系數(shù)介于0.5~1.5時(shí),表明沉積物中重金屬主要源自土壤和巖石圈的自然風(fēng)化的過程;如果大于1.5,表明沉積物中重金屬來源受人為影響.

1.3.2 風(fēng)險(xiǎn)指數(shù)編碼法(RAC) 沉積物中重金屬總量不能反映重金屬的潛在生態(tài)風(fēng)險(xiǎn)[25].風(fēng)險(xiǎn)評(píng)估編碼法是基于重金屬不同形態(tài)對(duì)環(huán)境有不同程度的威脅而提出的.B1態(tài)化學(xué)性質(zhì)不穩(wěn)定,易在上覆水-沉積物界面交換從而污染水體;B2態(tài)在沉積物中氧化電位較低的情況下會(huì)被釋放出來;B3態(tài)在強(qiáng)氧化條件下性質(zhì)活躍易污染水體環(huán)境.因此將B2、B3態(tài)視為潛在生物有效態(tài).B4態(tài)性質(zhì)比較穩(wěn)定生物可利用性低.利用這4種形態(tài)在沉積物重金屬總量中所占的比例來評(píng)價(jià)鎢的生態(tài)環(huán)境風(fēng)險(xiǎn)[26].RAC通過河流沉積物中鎢的B1、B2、B3態(tài)之和占重金屬總量的比例來評(píng)價(jià)鎢的生態(tài)風(fēng)險(xiǎn)[27-28].具體風(fēng)險(xiǎn)評(píng)價(jià)等級(jí)標(biāo)準(zhǔn)見表2.

2 結(jié)果分析

2.1 桃江河沉積物中鎢含量及形態(tài)分布

由表3可知,桃江河沉積物中鎢的總量在0.51~ 39.73mg/kg之間,均值為10.86mg/kg.從空間分布上,桃江上游沉積物中鎢總量在1.21~39.73mg/kg之間,均值為18.21mg/kg;桃江中游沉積物中鎢的總量在1.61~15.03mg/kg之間,均值為8.07mg/kg;下游沉積物中鎢含量在2.58~10.36mg/kg之間,均值為6.38mg/kg;支流表層沉積物中鎢總量均值為8.19mg/kg.結(jié)果顯示,桃江河表層沉積物中鎢總量大小順序?yàn)樯嫌?支流>中游>下游.沉積物中鎢總量均值均超過了江西省土壤背景值,其中,上游沉積物中鎢平均含量高出背景值3.57倍.總體上來看,桃江河表層沉積物鎢含量變異系數(shù)均高,表明桃江鎢為點(diǎn)源污染.

由圖3、4可知,桃江河沉積物中鎢的4種形態(tài)占比大小為B4態(tài)>B3態(tài)>B2態(tài)>B1態(tài),表明桃江河上流、中游、下游及支流沉積物中鎢主要以B4態(tài)形式賦存,其B4態(tài)均值占鎢總量比分別為89.72%、88.05%、82.66%和83.50%,平均百分比為85.98%;B3態(tài)均值所占總量比例分別為15.55%、10.55%、9.67%和16.11%.平均百分比 12.97%;B2態(tài)、B1態(tài)均值占總量比相對(duì)較低,平均百分比分別為0.07%、0.98%,表明桃江河沉積物中鎢的生物可利用性低.但是B3態(tài)、B2態(tài)、B1態(tài)在外界環(huán)境條件發(fā)生變化時(shí),隨時(shí)有可能被釋放出來,從而對(duì)水體造成污染.從潛在生物有效態(tài)考慮,鎢的生物有效態(tài)在桃江上游、中游、下游和支流的占比范圍分別為5.42%~39.67%、4.88%~20.36%、9.87%~45.09%和2.5%~52.94%.桃江河中上游沉積物中鎢的生物有效態(tài)占比較低,平均比例分別為14.45%、10.91%;但下游與支流沉積物中鎢的生物有效態(tài)相對(duì)較高,平均比例分別為21.03% 和22.44%;支流和下游B3態(tài)鎢含量較高,可能與竹制品廠、養(yǎng)殖場、礦產(chǎn)冶煉等向河流排入廢水有關(guān).

表3 桃江表層沉積物中鎢各形態(tài)含量

續(xù)表3

圖3 桃江支流沉積物中形態(tài)分布比例

圖4 桃江干流沉積物中形態(tài)分布比例

2.2 桃江河沉積物中鎢形態(tài)相關(guān)性分析

為了研究桃江河沉積物中理化指標(biāo)對(duì)鎢形態(tài)的影響,將鎢的各形態(tài)含量與有機(jī)質(zhì)、全磷、全氮、pH值和陽離子交換量進(jìn)行Pearson相關(guān)性分析結(jié)果見表4.在桃江表層沉積物中,鎢的B2態(tài)與pH值呈顯著正相關(guān),B3態(tài)與陽離子交換呈顯著正相關(guān)(￡0.05),其他形態(tài)與pH值和陽離子交換量均有一定的相關(guān)性.自然界中鎢常以鎢酸鹽形式存在,但隨著pH值的酸化在偏酸性-中性條件時(shí)水中大量形成硫代鎢酸鹽.在偏堿性條件下,鎢仍以鎢酸鹽的形式存在,水中可檢出的硫代鎢酸鹽含量極低.離子強(qiáng)度的增加在酸性條件下會(huì)抑制硫代鎢酸鹽形成[29].鎢的B3態(tài)與B4態(tài)呈顯著正相關(guān)(￡0.01),B3態(tài)、B4態(tài)與B1態(tài)、B2態(tài)有一定的相關(guān)性但不明顯,表明B3態(tài)、B4態(tài)在外界條件改變時(shí)可能相互轉(zhuǎn)化[30]. 4種形態(tài)與陽離子交換具有一定相關(guān)性,說明水體中離子強(qiáng)度不同會(huì)影響水體酸堿度從而對(duì)水中硫化物、微生物等產(chǎn)生影響,進(jìn)一步影響鎢的遷移轉(zhuǎn)化. B1態(tài)、B3態(tài)和B4態(tài)與有機(jī)質(zhì)呈正相關(guān),可能隨著有機(jī)質(zhì)含量提高,微生物的活躍度相應(yīng)提高,對(duì)鎢形態(tài)之間的轉(zhuǎn)化也將產(chǎn)生一定的影響.全氮與pH值、B1態(tài)、B2態(tài)呈正相關(guān),表明水中氨氮會(huì)影響水體pH值的變化,從而進(jìn)一步改變鎢的存在形態(tài).B1態(tài)是對(duì)生態(tài)環(huán)境和水體生物最具危險(xiǎn)性的形態(tài),總磷與其呈負(fù)相關(guān),可能說明總磷對(duì)鎢造成的生態(tài)風(fēng)險(xiǎn)影響較小.

表4 桃江沉積物中理化性質(zhì)與各種形態(tài)相關(guān)分析

注:**.在0.01水平(雙尾)相關(guān)性顯著;*. 在0.05水平(雙尾)相關(guān)性顯著.

2.3 桃江河沉積物中鎢的富集與評(píng)價(jià)

2.3.1 EF法富集程度評(píng)價(jià) 本研究參考江西省土壤重金屬背景值,以Fe作為參比元素.對(duì)桃江河各采樣點(diǎn)沉積物中鎢含量與Fe的含量進(jìn)行標(biāo)準(zhǔn)化比值計(jì)算[31],得到45個(gè)采樣點(diǎn)鎢的富集系數(shù).鎢的富集系數(shù)可以有效反映鎢的富集程度[32].由圖5可知,桃江河上游與支流沉積物中鎢出現(xiàn)較強(qiáng)富集,按空間分布來看,桃江上游沉積物中鎢富集最明顯,平均富集系數(shù)為8.42,可能與上游存有贛南兩大鎢礦區(qū)的鎢礦開采有關(guān).與中上游相比下游鎢的富集量最少,平均富集系數(shù)為3.07,表明桃江沉積物中鎢含量較高與人為影響有關(guān).

2.3.2 RAC風(fēng)險(xiǎn)評(píng)價(jià) 與富集系數(shù)法相比,RAC風(fēng)險(xiǎn)評(píng)價(jià)著重考慮了易被生物利用的鎢對(duì)環(huán)境的污染風(fēng)險(xiǎn)[33].根據(jù)風(fēng)險(xiǎn)指數(shù)編碼法,以桃江河表層沉積物中B1、B2、B3態(tài)鎢之和占總鎢的百分比為基礎(chǔ),評(píng)價(jià)桃江河沉積物中鎢的風(fēng)險(xiǎn)程度,結(jié)果如圖6所示.從空間分布上,桃江河沉積物有效態(tài)鎢占總鎢比例基本在30%以下;其中桃江上游沉積物中有效態(tài)鎢占總鎢的比例均值為14.45%,呈中度風(fēng)險(xiǎn);桃江中游沉積物中有效態(tài)鎢占總鎢的比例均值為10.91%,呈中度生態(tài)風(fēng)險(xiǎn);桃江下游沉積物中有效態(tài)鎢占總鎢的比例均值為21.03%,呈中度生態(tài)風(fēng)險(xiǎn);支流沉積物中有效態(tài)鎢占總鎢的比例均值為22.44%,呈中度生態(tài)風(fēng)險(xiǎn).數(shù)據(jù)表明,桃江河支流表層沉積物中鎢的風(fēng)險(xiǎn)程度高于干流,結(jié)合實(shí)地考察,表明支流受人為影響較大,同時(shí)桃江支流富營養(yǎng)化比較嚴(yán)重,對(duì)有效態(tài)鎢的釋放風(fēng)險(xiǎn)有一定影響[34].根據(jù)圖6數(shù)據(jù)分析發(fā)現(xiàn)有82.22%的采樣點(diǎn)屬于低中等風(fēng)險(xiǎn),只有17.78%的采樣點(diǎn)呈高風(fēng)險(xiǎn).

通過富集系數(shù)法和風(fēng)險(xiǎn)指數(shù)編碼法對(duì)桃江河標(biāo)稱沉積物中鎢的富集及風(fēng)險(xiǎn)等級(jí)的評(píng)價(jià)可知桃江支流沉積物中鎢富集程度和風(fēng)險(xiǎn)等級(jí)均高于干流.對(duì)比2種評(píng)價(jià)方法, EF法能夠有效反映河沉積物中鎢的富集程度,但是忽略了鎢的生物可利用性,容易造成污染評(píng)價(jià)的夸大或低估.相反,RAC法根據(jù)不同形態(tài)鎢在沉積物中的風(fēng)險(xiǎn)等級(jí)進(jìn)行評(píng)價(jià),能夠更精確反映鎢在沉積物中的賦存形態(tài)及潛在風(fēng)險(xiǎn).富集系數(shù)法得出研究區(qū)域40%采樣點(diǎn)沉積物中鎢含量呈較強(qiáng)富集,37.78%的采樣點(diǎn)呈中度富集,26.67%的采樣點(diǎn)呈輕富集或無富集;RAC法可知桃江河33.33%的采樣點(diǎn)沉積物中鎢含量呈低風(fēng)險(xiǎn),46.67%的采樣點(diǎn)呈中等風(fēng)險(xiǎn),17.78%的采樣點(diǎn)屬于高風(fēng)險(xiǎn).桃江表層沉積物中70%以上的區(qū)域存在鎢的富集,全河段有效態(tài)鎢含量存在不同等級(jí)的風(fēng)險(xiǎn),因此吸取21世紀(jì)已發(fā)生鎢污染事件的教訓(xùn),我國也應(yīng)將河流沉積物中鎢存在的風(fēng)險(xiǎn)考慮到沉積物重金屬污染修復(fù)中.

圖5 桃江河沉積物中鎢的富集系數(shù)

圖6 桃江河沉積物中鎢RAC風(fēng)險(xiǎn)指數(shù)

3 結(jié)論

3.1 桃江河沉積物中鎢的形態(tài)分析表明,鎢的主要賦存形態(tài)為殘?jiān)鼞B(tài),且鎢各形態(tài)含量占比為殘?jiān)鼞B(tài)>可氧化態(tài)>可還原態(tài)>弱酸提取態(tài),桃江支流有效態(tài)含量普遍高于干流,中游與下游個(gè)別采樣點(diǎn)可氧化態(tài)鎢含量較高.

3.2 相關(guān)性分析顯示,弱酸提取態(tài)、可還原態(tài)、可氧化態(tài)、殘?jiān)鼞B(tài)與pH和陽離子交換呈正相關(guān),表明pH和陽離子交換是鎢富集的影響因子;可氧化態(tài)與殘?jiān)鼞B(tài)顯著相關(guān).

3.3 富集系數(shù)法分析結(jié)果顯示,桃江河40%的采樣點(diǎn)沉積物中鎢含量呈較強(qiáng)富集,風(fēng)險(xiǎn)指數(shù)編碼法分析表明,46.67%的采樣點(diǎn)沉積物中鎢含量呈中等風(fēng)險(xiǎn),17.78%的采樣點(diǎn)表層沉積物中鎢含量呈高生態(tài)風(fēng)險(xiǎn),表明桃江表層沉積物中鎢的富集與生態(tài)風(fēng)險(xiǎn)相對(duì)較高.

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Occurrence characteristics and risk assessment of tungsten in surface sediments of Taojiang River in Southern Jiangxi Province.

CHEN Ming*, LI Feng-guo, SHI Yan-li, TAO Mei-xia, HU Lan-wen

(Jiangxi Key Laboratory of Mining & Metallurgy Enviromental Pollution Control, Jiangxi University of Science and Technology, Ganzhou 341000, China)., 2019,39(4)：1715~1723

Total concentrations and forms of tungsten in surface sediments from Taojiang river were determined and the methods of enrichment coefficient (EF) and risk index coding (RAC) were applied to assess the accumulative degree and environmental risks. The results showed that the tungsten concentrations ranged from 1.21 to 39.73mg/kg, with an average of 18.21mg/kg, while 58% of sampling sites were greater than the background values of the soil in Jiangxi Province. The species of tungsten were presented dominantly in the residual fraction, followed by the oxidizable, reducible and weak acid extraction fraction. Spatially, the effective tungsten in tributary is maximal with a mean value of 22.44%, followed by downstream (21.03%), upstream (14.45%) and midstream (10.91%). Correlation analysisshowed that total concentrations and species of tungsten were positively correlated with the pH and cation exchange, respectively. The EF analysissuggested that the tungsten enrichment was seriously accumulated in the upper reaches and tributaries of the Taojiang River. The RAC analysis demonstrated the ecological risk in different sampling sites was low, medium and high, with a proportion of 33.33%, 46.67% and 17.78%, respectively. Altogether, this study indicated that the tungsten were accumulated in sediments of Taojiang River with seriously environmental risks, which deserve to be additional more extensive researches.

Taojiang River；sediment；tumgsten；occurrence form；risk assessment

X142

A

1000-6923(2019)04-1715-09

2018-09-10

國家自然科學(xué)基金資助項(xiàng)目(51664025)

*責(zé)任作者, 教授, jxlgdx@qq.com

陳 明(1976-),男,江西贛州人,教授,主要研究方向?yàn)橹亟饘傥廴究刂?發(fā)表論文30余篇.