某焦化企業(yè)周邊兒童重金屬經(jīng)口綜合暴露健康風(fēng)險(xiǎn)

陳月芳,許錦榮,段小麗,曹素珍*,孫善偉,康藝瑾

某焦化企業(yè)周邊兒童重金屬經(jīng)口綜合暴露健康風(fēng)險(xiǎn)

陳月芳1,2,許錦榮1,段小麗1,2,曹素珍1,2*,孫善偉1,康藝瑾1

(1.北京科技大學(xué)能源與環(huán)境工程學(xué)院,北京 100083；2.工業(yè)典型污染物資源化處理北京市重點(diǎn)實(shí)驗(yàn)室,北京 100083)

針對(duì)焦化企業(yè)開展的研究多關(guān)于企業(yè)工藝流程、污染物排放特征、周邊環(huán)境有機(jī)物污染特征等方面,鮮有關(guān)注企業(yè)周邊人群的重金屬暴露及其健康風(fēng)險(xiǎn)的問(wèn)題,本研究以我國(guó)北方某焦化企業(yè)為案例區(qū),以當(dāng)?shù)貎和癁檠芯繉?duì)象,基于環(huán)境暴露行為模式問(wèn)卷調(diào)查和現(xiàn)場(chǎng)實(shí)地樣品的采集分析,探討飲用水、土壤和食物介質(zhì)中5種重金屬(Pb、Cd、Cr、Ni和As)的污染特征,并分析兒童經(jīng)口途徑對(duì)飲用水?土壤和食物中重金屬的暴露和健康風(fēng)險(xiǎn)水平.研究結(jié)果表明,焦化企業(yè)周邊環(huán)境污染尚不突出,但兒童經(jīng)口綜合暴露的非致癌風(fēng)險(xiǎn)水平為0.74~6.30,是可接受風(fēng)險(xiǎn)水平的1~6倍,非致癌風(fēng)險(xiǎn)主要來(lái)自食物As暴露.兒童致癌風(fēng)險(xiǎn)水平為1.76×10-4~7.75×10-3,是可接受最高風(fēng)險(xiǎn)水平(1.0×10-4)的幾倍至幾十倍,且主要?dú)w因于Cr經(jīng)食物的暴露.本研究表明食物的經(jīng)口暴露是各重金屬經(jīng)口綜合暴露的主要途徑,占經(jīng)口綜合暴露量的90%以上;焦化企業(yè)周邊環(huán)境重金屬污染雖不嚴(yán)峻,但可能會(huì)當(dāng)?shù)貎和瘞?lái)嚴(yán)重的健康風(fēng)險(xiǎn),需引起重視.

兒童；重金屬；焦化企業(yè)；暴露評(píng)價(jià)；健康風(fēng)險(xiǎn)評(píng)價(jià)

焦化過(guò)程產(chǎn)生的大量重金屬可通過(guò)干濕沉降或地表徑流等過(guò)程進(jìn)入土壤、水體和食品等環(huán)境介質(zhì)中,最終經(jīng)過(guò)食物鏈富集進(jìn)入人體從而對(duì)人體健康帶來(lái)危害.識(shí)別并評(píng)價(jià)焦化企業(yè)周邊人群重金屬暴露的健康風(fēng)險(xiǎn)及主要風(fēng)險(xiǎn)來(lái)源,對(duì)于防范人體暴露的健康危害具有十分重要的現(xiàn)實(shí)意義.中國(guó)是世界上最大的煤炭生產(chǎn)和消費(fèi)國(guó),而山西作為我國(guó)煤炭重要存貯和開采基地,其煤炭產(chǎn)量占中國(guó)煤炭產(chǎn)量的24.46%[1].煤炭相關(guān)工業(yè)活動(dòng)的發(fā)展,在帶動(dòng)經(jīng)濟(jì)社會(huì)發(fā)展的同時(shí),也給水體、空氣、土壤等環(huán)境帶來(lái)嚴(yán)重的污染和考驗(yàn).Qian等[2]研究表明,2000年以后我國(guó)大氣環(huán)境鉛主要來(lái)自煤炭的燃燒使用.山西省焦化企業(yè)的生產(chǎn)排放是華北地區(qū)空氣揮發(fā)性有機(jī)污染物污染的重要來(lái)源[3].Cao等[4]對(duì)北京市某廢棄焦化廠周邊土壤多環(huán)芳烴的研究表明,土壤中16種多環(huán)芳烴含量高達(dá)314.7~1618.3mg/kg,處于中度污染水平.Li等[5]發(fā)現(xiàn),在無(wú)控制條件下我國(guó)焦化廠揮發(fā)性有機(jī)化合物的排放因子為3.065g/kg焦炭,焦化行業(yè)揮發(fā)性有機(jī)化合物的年排放量由1949年的3.38Gg增加到2016年的1376.54Gg.總體來(lái)看,以往對(duì)焦化企業(yè)的研究多關(guān)注于多環(huán)芳烴、苯系物等有機(jī)污染及其人體暴露的健康風(fēng)險(xiǎn)評(píng)估[6-10],鮮少關(guān)注重金屬的污染及人體暴露健康風(fēng)險(xiǎn).雖然煤炭中重金屬含量相比礦石等較低,但是與其他國(guó)家或地區(qū)煤炭中元素含量相比,中國(guó)煤炭尤其是山西煤炭中重金屬的含量更高[11],焦化企業(yè)在焦化期間可使煤炭中重金屬大量釋放[12],有研究表明焦化廠煤場(chǎng)土壤由于長(zhǎng)年直接裸露于煤堆下,在雨水淋濾、土壤吸附阻滯等綜合作用下,其表層重金屬As、Cr、Cd和Pb等含量均高于底層土壤[13].同樣有研究表明,焦化廠周圍降塵中As、Pb、Ni 等重金屬污染物的含量遠(yuǎn)高于對(duì)照區(qū)和其他城市大氣降塵中金屬含量,焦化廠對(duì)周圍大氣降塵中的金屬含量貢獻(xiàn)較大[14],在對(duì)蘇南某焦化廠研究中也發(fā)現(xiàn)焦化廠附近土壤和地下水受到了不同程度Pb、As等重金屬污染[15].且相比于有機(jī)污染物及一般重金屬類污染物,重金屬和類金屬Pb,Cd,Cr、Ni和As的長(zhǎng)期低劑量暴露,可對(duì)人體帶來(lái)如肺癌,腎功能不全,認(rèn)知障礙,慢性支氣管炎,神經(jīng)系統(tǒng)損傷等影響[16-18].因此,開展焦化企業(yè)周邊人群Pb,Cd,Cr、Ni和As等重金屬暴露的健康風(fēng)險(xiǎn)具有重要的現(xiàn)實(shí)意義,可為其健康風(fēng)險(xiǎn)的防范提供參考依據(jù).

環(huán)境中的重金屬主要通過(guò)土壤、飲用水、空氣和食物四種環(huán)境介質(zhì)經(jīng)口、經(jīng)呼吸和經(jīng)皮膚的暴露途徑進(jìn)入人體[19-20].近年來(lái)隨著對(duì)人體暴露健康風(fēng)險(xiǎn)認(rèn)識(shí)的不斷提高,污染物人體多介質(zhì)多途徑暴露的研究成為熱點(diǎn),針對(duì)鉛鋅冶煉區(qū)、鉛酸蓄電池企業(yè)、污水灌溉區(qū)等典型重金屬污染企業(yè)周邊人群多介質(zhì)多暴露途徑研究表明,經(jīng)口暴露對(duì)總暴露健康風(fēng)險(xiǎn)的貢獻(xiàn)達(dá)80%以上,說(shuō)明經(jīng)口暴露是人群重金屬暴露健康風(fēng)險(xiǎn)的主要途徑[7,21-23],因此,準(zhǔn)確評(píng)估重金屬等污染企業(yè)周邊人群經(jīng)口暴露的健康風(fēng)險(xiǎn)一定程度上可為了解其重金屬暴露總暴露的健康風(fēng)險(xiǎn)提供重要的依據(jù).那么,對(duì)于焦化企業(yè)而言,重金屬經(jīng)不同介質(zhì)的經(jīng)口暴露水平如何,經(jīng)多介質(zhì)的綜合暴露風(fēng)險(xiǎn)又如何,優(yōu)先控制哪種暴露途徑以防范健康風(fēng)險(xiǎn),目前仍缺乏有說(shuō)服力的數(shù)據(jù)支撐.鑒于兒童手-口接觸行為較多[24],且兒童因其較高的吸收率,低排出率,是重金屬和類金屬暴露的敏感人群[25-26],開展兒童重金屬經(jīng)口綜合暴露的研究有重要意義[27].基于此,亟需針對(duì)焦化企業(yè)周邊兒童重金屬經(jīng)口綜合暴露的健康風(fēng)險(xiǎn)開展深入研究.

綜上,本研究以我國(guó)北方某焦化企業(yè)所在地為研究案例區(qū),以當(dāng)?shù)貎和癁槟繕?biāo)人群,系統(tǒng)分析兒童外暴露的環(huán)境介質(zhì),如飲用水、食物、土壤中典型有毒有害重金屬Pb,Cd,Cr、Ni污染特征.考慮到As是煤非常重要的特征污染物,且對(duì)人體健康可造成嚴(yán)重危害,故本研究也將類金屬As作為重要的金屬污染物質(zhì)開展研究.基于兒童環(huán)境暴露行為模式特征,利用美國(guó)環(huán)境署(USEPA)推薦的暴露評(píng)估模型和健康風(fēng)險(xiǎn)評(píng)價(jià)模型探討焦化企業(yè)周邊兒童經(jīng)口途徑對(duì)環(huán)境重金屬的暴露水平及其健康風(fēng)險(xiǎn).通過(guò)本研究的開展,以期(1)量化中國(guó)典型焦化企業(yè)周邊兒童外暴露的飲用水,食物和土壤中5種典型重金屬的污染水平;(2)量化人群經(jīng)口途徑的多介質(zhì)重金屬綜合暴露量,以及每種介質(zhì)對(duì)經(jīng)口多介質(zhì)重金屬綜合暴露的貢獻(xiàn);(3)評(píng)估重金屬經(jīng)多介質(zhì)經(jīng)口暴露的致癌和非致癌健康風(fēng)險(xiǎn),從而為環(huán)境風(fēng)險(xiǎn)管理、企業(yè)周邊兒童健康風(fēng)險(xiǎn)防范提供依據(jù).

1 材料和方法

1.1 研究區(qū)域

本研究所選焦化企業(yè)是中國(guó)最大的焦化廠之一,位于山西省某鎮(zhèn),焦化廠周圍有住宅區(qū)、小學(xué)和農(nóng)田.受當(dāng)?shù)爻Ｄ昶憋L(fēng)向的影響,住宅區(qū)、小學(xué)和商業(yè)活動(dòng)區(qū)位于該焦化廠10km范圍內(nèi)下風(fēng)向.除該焦化廠外,該地區(qū)無(wú)其他大型企業(yè),無(wú)高速公路且車流量較少.

1.2 環(huán)境暴露行為模式問(wèn)卷調(diào)查

考慮到相較高齡兒童,低齡兒童的手-口行為更為頻繁;且兒童早期環(huán)境暴露的健康危害對(duì)其終生的健康影響更為突出[28-30],同時(shí)兼顧兒童對(duì)其行為模式的認(rèn)知能力,本研究關(guān)注小學(xué)一年級(jí)的7~8歲兒童.在獲取知情同意的前提下,在焦化企業(yè)所在鎮(zhèn)唯一的小學(xué)里根據(jù)學(xué)生人數(shù)采用電腦隨機(jī)抽樣的方式隨機(jī)選15人(占班級(jí)總?cè)藬?shù)1/2),結(jié)合調(diào)查對(duì)象的入戶意愿、時(shí)間安排等因素,最終于當(dāng)?shù)卣心剂?~8歲兒童10名開展環(huán)境暴露行為模式問(wèn)卷調(diào)查.問(wèn)卷調(diào)查內(nèi)容包括飲食行為,日?；顒?dòng)模式和生活方式等,以獲取相關(guān)暴露參數(shù)信息和關(guān)鍵風(fēng)險(xiǎn)因素.飲食行為調(diào)查內(nèi)容包括日常攝入的食物和飲用水的類型?攝入頻次和攝入量等;日?；顒?dòng)模式調(diào)查內(nèi)容包括活動(dòng)場(chǎng)所,活動(dòng)范圍和活動(dòng)時(shí)間等;生活方式調(diào)查內(nèi)容包括土壤的攝入行為和頻次等信息.環(huán)境暴露行為模式問(wèn)卷調(diào)查通過(guò)一對(duì)一,面對(duì)面詢問(wèn)兒童家長(zhǎng)或監(jiān)護(hù)人的形式開展.

1.3 樣品采集和分析

1.3.1 現(xiàn)場(chǎng)取樣 在獲取知情同意的前提下,入戶開展兒童環(huán)境暴露行為模式調(diào)查時(shí),采集兒童外暴露的飲用水?食物和家庭庭院土壤樣品,以評(píng)估兒童經(jīng)多介質(zhì)經(jīng)口暴露途徑的重金屬攝入量和健康風(fēng)險(xiǎn).

水樣:現(xiàn)場(chǎng)預(yù)調(diào)查表明,當(dāng)?shù)鼐用竦娘嬘盟鶠樽詠?lái)水,因此本研究現(xiàn)場(chǎng)樣品采集時(shí)通過(guò)入戶的方式采集兒童家庭的飲用水樣品.采集時(shí),每個(gè)家庭將直接飲用的水裝入預(yù)先清洗過(guò)的100mL聚四氟乙烯采樣瓶中.每個(gè)家庭采集1個(gè)飲用水樣,考慮質(zhì)量控制等因素共采集13個(gè)飲用水樣.每個(gè)樣品采集后立即滴加兩滴65%的濃HNO3后,冷藏運(yùn)輸至實(shí)驗(yàn)室并于-4℃冰箱保存,盡快完成分析.

土樣:入戶采集每個(gè)兒童家庭庭院的表層土(0~20cm).采集時(shí),根據(jù)家庭庭院的布局并結(jié)合兒童的日?；顒?dòng)模式,按S型或梅花型等布設(shè)3~5個(gè)子采樣點(diǎn),每個(gè)子采樣點(diǎn)等量采集并混合為1個(gè)土壤樣品(約1kg).去除沙石、根系等雜質(zhì)后,混勻,用四分法取約500g裝入潔凈自封袋中.

食物樣:基于環(huán)境暴露行為模式問(wèn)卷調(diào)查結(jié)果,同時(shí)結(jié)合入戶時(shí)膳食來(lái)源調(diào)研結(jié)果,從當(dāng)?shù)夭杉?8種兒童攝入頻次較高的新鮮蔬菜:韭菜?歐芹?生菜?蒜?白菜?大白菜?菊花?菠菜?番茄?南瓜?西葫蘆?黃瓜?辣椒?茄子?菜豆?白蘿卜?土豆?蘆筍.每個(gè)食物樣品均從3~5個(gè)售賣店等量采集后混勻而成,即每個(gè)蔬菜樣品都經(jīng)過(guò)3~5個(gè)子樣本整合.預(yù)調(diào)查發(fā)現(xiàn),當(dāng)?shù)厝酥魇骋孕←溂捌渲破窞橹?因此為了反映人群食物的實(shí)際暴露特征,入戶時(shí)從每家收集小麥樣品(約50g).考慮到入戶的兒童以蔬菜攝入為主,本研究未考慮肉及其制品.

同時(shí),為了減少樣品采集帶來(lái)的誤差,各種介質(zhì)樣品采集時(shí)均設(shè)置現(xiàn)場(chǎng)空白樣品,平行樣品及全程序質(zhì)量控制樣品.

1.3.2 樣品前處理 飲用水樣:為減少外來(lái)污染,本研究飲用水樣品過(guò)0.45μm濾膜后,于4℃冷藏保存,待分析.

土樣:土壤樣品于室溫下風(fēng)干,經(jīng)瑪瑙研缽研磨后分別過(guò)20目和100目尼龍篩,用于土壤樣品pH值和重金屬的分析.將過(guò)100目的篩分樣品取0.1000g于聚四氟乙烯消煮管,用HNO3-HF-KClO4酸體系于微波消解儀(MARS 5, CEM)消化制備土壤樣品[31],可重復(fù)執(zhí)行消解程序,直到消解管無(wú)深色顆粒.然后用超純水將消解液少量多次轉(zhuǎn)移至趕酸管,于90℃趕酸儀趕酸直至最后一滴,用2%稀硝酸溶液溶解并稀釋至50mL,過(guò)0.45μm濾膜后,于4℃冷藏保存,待分析.

食物樣:徹底清洗后,將食物樣品的可食部分切成小塊,于-75℃下真空冷凍干燥后,將凍干樣經(jīng)木制研缽研磨并過(guò)100目尼龍篩.取0.5000g粉末樣于聚四氟乙烯消煮管,加入2mL 65%濃HNO3冷消化30min;再加入1mL H2O2進(jìn)一步冷消解10min;用以下程序消解食物樣品:階段Ⅰ,50%功率,升溫至150℃,保持10min;階段II,80%功率,升溫至180℃,保持10min;階段III,40%功率,降溫至100℃, 10min.消解程序可重復(fù)執(zhí)行,直至無(wú)深色殘?jiān)?然后用超純水將消解液少量多次地轉(zhuǎn)移至趕酸管,于90℃趕酸儀趕酸直至最后一滴,用2%稀硝酸溶液溶解并稀釋至50mL過(guò)0.45μm濾膜后,于4℃冷藏保存,待分析.

質(zhì)量控制:為減少樣品前處理過(guò)程的誤差,每種介質(zhì)樣品前處理時(shí),均同時(shí)設(shè)置10%平行處理樣品、試劑空白樣品、10%標(biāo)準(zhǔn)物質(zhì)處理樣品(水體成分分析標(biāo)準(zhǔn)物質(zhì)GBW08607和GBW080255,潮褐土標(biāo)準(zhǔn)物質(zhì)CSZ-ZWY-1,小麥成分標(biāo)準(zhǔn)物質(zhì)GBW10011,白菜成分標(biāo)準(zhǔn)物質(zhì)GBW10014,白蘿卜成分分析標(biāo)準(zhǔn)物質(zhì)GBW10047等).

1.3.3 樣品檢測(cè) 前處理制備好的土壤等樣品用超純水稀釋至適當(dāng)濃度后,用電感藕合等離子體質(zhì)譜儀(ICP-MS, Agilent, 7500a)和原子熒光分光光度計(jì)(吉天,AFS-8230)分別測(cè)定Pb、Cd、Cr、Ni和As.ICP-MS測(cè)量前,在優(yōu)化條件下[32]使用多元素標(biāo)準(zhǔn)品校準(zhǔn)液來(lái)調(diào)節(jié)儀器,并量化測(cè)定的結(jié)果.環(huán)境外暴露樣品測(cè)試的相對(duì)標(biāo)準(zhǔn)差RSD￡5%,標(biāo)準(zhǔn)物質(zhì)質(zhì)控樣品的回收率為91%~103%,說(shuō)明本研究測(cè)量方法和數(shù)據(jù)的準(zhǔn)確性和可靠性較好.

1.4 重金屬暴露量評(píng)估

不同介質(zhì)暴露于人體的途徑不同,但主要暴露途徑包括經(jīng)口暴露、經(jīng)呼吸暴露和經(jīng)皮膚的暴露.飲水、食物、土壤環(huán)境介質(zhì)是重金屬經(jīng)口暴露的主要路徑[33].本研究根據(jù)USEPA推薦的污染物暴露評(píng)價(jià)模型,對(duì)人體經(jīng)飲用水?食物和土壤介質(zhì)經(jīng)口暴露途徑的日均暴露劑量進(jìn)行估算后,通過(guò)各介質(zhì)暴露量與多介質(zhì)經(jīng)口綜合暴露量的分析可揭示不同環(huán)境介質(zhì)對(duì)兒童經(jīng)口綜合暴露的貢獻(xiàn).

根據(jù)USEPA推薦的暴露評(píng)價(jià)方法[34],可用如下模型估算化學(xué)物經(jīng)口暴露途徑的日平均暴露劑量(ADD)[mg/(kg?d)].

式中:為化學(xué)物濃度, mg/kg或μg/L; Ing為攝入量, mg/d或mL/d,EF為暴露頻率, d/a; ED是暴露持續(xù)時(shí)間, a; BW是以kg為單位的體重; AT為平均暴露時(shí)間,d.食物和水的攝入量Ing、暴露持續(xù)時(shí)間和體重等參數(shù)基于現(xiàn)場(chǎng)行為模式問(wèn)卷調(diào)查獲取;平均暴露時(shí)間參數(shù)取自美國(guó)環(huán)保署EPA參數(shù)手冊(cè)[34],其他參數(shù)如土壤攝入量等取自中國(guó)人群暴露參數(shù)手冊(cè)兒童卷[35].相關(guān)暴露參數(shù)的具體取值如下表1所示.

表1 經(jīng)口暴露評(píng)估相關(guān)暴露參數(shù)

在進(jìn)行食物經(jīng)口暴露評(píng)價(jià)時(shí),基于問(wèn)卷調(diào)查獲取兒童對(duì)主要食物的攝入量信息,即日常攝入的各種類型食物的攝入量信息,結(jié)合不同食物中污染物的水平以評(píng)價(jià)其食物的累積綜合暴露量.食物的累積暴露量用如下評(píng)價(jià)模型:

本研究主要考慮蔬菜和主食類食物,故綜合考慮小麥、白菜、土豆、黃瓜等19種食物類型.

1.5 健康風(fēng)險(xiǎn)評(píng)估

化學(xué)物質(zhì)的健康風(fēng)險(xiǎn)根據(jù)其毒理學(xué)性質(zhì)分為有閾(即非致癌性)和無(wú)閾(即致癌性)兩類,污染物的非致癌風(fēng)險(xiǎn)用危險(xiǎn)熵(Hazzard Quotient, HQ)表示,可通過(guò)每個(gè)暴露途徑的日均暴露劑量(Average Daily Dose, ADD)除以特定經(jīng)口暴露參考劑量(Reference Dose, RfD)來(lái)計(jì)算[36].評(píng)價(jià)模型如下:

式中:RfD為某種污染物某種暴露途徑下的參考劑量(mg/(kg×d)).當(dāng)HQ<1時(shí),表明污染物經(jīng)該暴露途徑的非致癌風(fēng)險(xiǎn)可接受,可能帶來(lái)的健康風(fēng)險(xiǎn)較小;而當(dāng)HQ31時(shí),認(rèn)為可能存在潛在的非致癌風(fēng)險(xiǎn)[37].此外,為獲得所有種類化學(xué)物質(zhì)的潛在非致癌風(fēng)險(xiǎn),需要將不同化學(xué)物質(zhì)HQ相加得到總非致癌風(fēng)險(xiǎn)危險(xiǎn)指數(shù)[38](Harzard Index,HI).

如果有多種暴露途徑,可用綜合暴露危險(xiǎn)指數(shù)(HIt)來(lái)表示不同介質(zhì)的綜合非癌癥風(fēng)險(xiǎn),表示如下[36]:

當(dāng)HIt<1時(shí),表明污染物經(jīng)多介質(zhì)綜合暴露途徑的非致癌風(fēng)險(xiǎn)可接受,可能帶來(lái)的健康風(fēng)險(xiǎn)較小;而當(dāng)HIt31時(shí),認(rèn)為可能存在潛在的綜合非致癌風(fēng)險(xiǎn),則需再細(xì)分每種介質(zhì)暴露的風(fēng)險(xiǎn),分別評(píng)價(jià)其潛在危害[37].

終生增量癌癥風(fēng)險(xiǎn)(Lifetime Incremental Cancer Risk,ILCR)是評(píng)估個(gè)體因接觸潛在致癌物而在一生中患癌的增量概率[36].對(duì)于化學(xué)物質(zhì)的癌癥健康風(fēng)險(xiǎn),用ILCR評(píng)價(jià):

式中:SF為某致癌物質(zhì)的癌癥斜率因子(kg×d)/mg.若評(píng)價(jià)多種無(wú)閾化學(xué)物質(zhì)的綜合致癌風(fēng)險(xiǎn),可不考慮化合物之間的相互作用,將每種無(wú)閾化合物的致癌風(fēng)險(xiǎn)相加即可評(píng)價(jià)其綜合致癌風(fēng)險(xiǎn).綜合USEPA及其他機(jī)構(gòu)對(duì)無(wú)閾化合物致癌風(fēng)險(xiǎn)閾值的限定,本研究將1.0×10-6~1.0×10-4設(shè)為可接受的致癌風(fēng)險(xiǎn)水平.

根據(jù)國(guó)際癌癥研究機(jī)構(gòu)(IARC)對(duì)化合物毒性的定義和分類[39],本研究將Pb,Cr,Cd,Ni和As視為可經(jīng)口暴露途徑產(chǎn)生非致癌健康效應(yīng)的化合物,同時(shí)考慮Cr和As經(jīng)口暴露產(chǎn)生的潛在致癌風(fēng)險(xiǎn).各化合物相應(yīng)的RfD和SF值見表2[40].

表2 各金屬的參考劑量和癌癥斜率因子

注:NA為不適用.

1.6 統(tǒng)計(jì)分析

為反映人群重金屬暴露的分布特征及不確定性,本研究使用Crystal Ball軟件(16.0)進(jìn)行蒙特卡羅模型的演算,模擬計(jì)算10,000次迭代.相關(guān)統(tǒng)計(jì)分析和多元回歸分析采用SPSS(20.0)軟件進(jìn)行.

2 結(jié)果與討論

2.1 重金屬污染特征

由表3可見,家庭庭院土壤中Pb、Cr、Ni和Cd的水平與山西省土壤自然背景值相比均略高[42],但均低于國(guó)家土壤環(huán)境第一類用地質(zhì)量標(biāo)準(zhǔn)(GB 36600-2018)[43]限值.土壤中As含量較高,均值不僅超過(guò)山西省土壤背景值,而且是國(guó)家土壤環(huán)境第一類用地質(zhì)量標(biāo)準(zhǔn)(GB 36600-2018)限值20mg/kg[43]的2.58倍,這與其他焦化廠周邊土壤污染特征相似[44],可能由于焦化廠在生產(chǎn)過(guò)程中使煤炭及燃煤飛灰中的As大量釋放,進(jìn)入土壤環(huán)境后在雨水淋濾、土壤吸附阻滯等綜合作用下導(dǎo)致土壤重金屬污染.

表3 各環(huán)境介質(zhì)重金屬濃度

表4 蔬菜中重金屬的含量

飲用水中所有重金屬的濃度均低于國(guó)家生活飲用水衛(wèi)生標(biāo)準(zhǔn)(GB 5749-2006)中相應(yīng)的限值[45],表明本研究案例區(qū)飲用水的重金屬污染尚不突出.然而,蔬菜Cr和As污染較重,是國(guó)家食品標(biāo)準(zhǔn)(GB 2762-2017)污染物相應(yīng)限值[46]的2.68和3.82倍.相比之下,小麥中Pb的污染更為突出,其平均濃度為相應(yīng)限值的1.45倍,由于國(guó)家食品標(biāo)準(zhǔn)(GB 2762-2017)缺少Ni污染物食品限值,故在本研究中暫不討論其污染情況.結(jié)果表明,盡管土壤中Cr和As的含量不高,但蔬菜易通過(guò)根系吸收等途徑累積土壤Cr和As從而造成污染[47],并通過(guò)食物鏈富集導(dǎo)致兒童重金屬暴露的風(fēng)險(xiǎn)[48-49].此外,蔬菜中Pb和As有較高的相關(guān)性(Spearman= 0.713,<0.05),表明食物中Pb和As可能具有相同的污染源.

為深入研究每種食物的重金屬污染及富集特征,表4列出了所有當(dāng)?shù)夭杉卟朔N類重金屬的濃度.不同種類蔬菜表現(xiàn)出不同的土壤重金屬富集性,有研究發(fā)現(xiàn)葉菜類重金屬積累量最高,其次是莖類蔬菜,而果類蔬菜累積量最低,不同類型蔬菜重金屬的積累與土壤中重金屬含量呈顯著正相關(guān)[50].本研究中,與莖類蔬菜(白蘿卜和大蒜)和果類蔬菜(南瓜,黃瓜,辣椒,茄子和青豆)相比,葉類蔬菜(卷心菜,菠菜,生菜,歐芹等)積累了更多的鉛,但土壤和蔬菜中的重金屬含量之間無(wú)顯著相關(guān)性.這一結(jié)果可能由于本研究關(guān)注的是家庭庭院土壤而非農(nóng)耕土壤,農(nóng)耕土壤和家庭庭院土壤的重金屬來(lái)源存在差異所致.

2.2 兒童重金屬日均暴露劑量

人體經(jīng)口暴露途徑的介質(zhì)主要包括飲用水、食物和土壤[34].根據(jù)每種環(huán)境介質(zhì)中重金屬的含量,以及基于現(xiàn)場(chǎng)人群行為模式調(diào)查問(wèn)卷和中國(guó)人群暴露參數(shù)手冊(cè)(兒童卷)獲取的兒童飲用水,食物和土壤的攝入量以及相關(guān)暴露參數(shù),利用暴露評(píng)價(jià)模型評(píng)估兒童經(jīng)不同介質(zhì)對(duì)重金屬的日均暴露劑量,綜合暴露量如圖1a所示.結(jié)果表明,不同重金屬的日均暴露劑量為Ni>Cr>Pb>As>Cd. Ni的日均暴露劑量最高,達(dá)22.08μg/(kg?d),遠(yuǎn)高于其他四種重金屬[0.73~ 4.58μg/(kg?d)],綜合環(huán)境介質(zhì)的污染特征及人群攝入特征,主要是由于兒童攝入的食物中Ni含量相對(duì)較高所致.該焦化企業(yè)周邊兒童Pb、As和Cd的日均暴露特征與某典型礦區(qū)周邊兒童和成人重金屬的暴露量相似[51-52],其中As的日均暴露劑量[1.89μg/(kg·d)]遠(yuǎn)低于某燃煤型砷污染區(qū)人群的暴露劑量[50~70μg/(kg·d)][53],可能與本研究相對(duì)較低的環(huán)境砷污染特征有關(guān).此外,本研究?jī)和瘜?duì)鉛的日均暴露劑量較低為3.35μg/(kg·d),可能由于兒童鉛暴露外環(huán)境的差異和本研究?jī)H關(guān)注有限暴露介質(zhì)和暴露途徑的原因,其暴露量遠(yuǎn)低于某涉鉛企業(yè)周邊兒童的鉛暴露量[44.8μg/(kg·d)][54].

圖1 兒童經(jīng)不同介質(zhì)的經(jīng)口綜合日均暴露量及其相對(duì)貢獻(xiàn)

a:暴露量; b:貢獻(xiàn)率

每種暴露介質(zhì)對(duì)兒童多介質(zhì)經(jīng)口日均綜合暴露劑量的貢獻(xiàn)如圖1b所示.結(jié)果表明,不同重金屬經(jīng)飲用水途徑占經(jīng)口綜合暴露劑量的貢獻(xiàn)整體較小;相比其他重金屬,Cr經(jīng)飲用水暴露的貢獻(xiàn)最高,占6.04%.不同重金屬經(jīng)土壤暴露的貢獻(xiàn)水平與飲用水相似,相比其他重金屬,As經(jīng)土壤暴露的貢獻(xiàn)最高(4.9%).對(duì)所有重金屬而言,兒童經(jīng)食物途徑的暴露量占其經(jīng)口綜合暴露劑量的90%以上,是重金屬經(jīng)口日均暴露劑量的主要來(lái)源.特別是Ni和Cd,經(jīng)食物的暴露量分別占綜合暴露量的99.48%和99.75%.由此表明,相比其他環(huán)境介質(zhì)而言,食物是兒童經(jīng)口暴露重金屬的主要途徑,也可能是兒童重金屬暴露健康風(fēng)險(xiǎn)的主要來(lái)源,需重點(diǎn)關(guān)注.

2.3 健康風(fēng)險(xiǎn)特征

2.3.1 非致癌風(fēng)險(xiǎn) 根據(jù)每種污染物的ADD和RfD,評(píng)估當(dāng)?shù)貎和?jīng)多介質(zhì)經(jīng)口暴露重金屬的非致癌風(fēng)險(xiǎn).不同重金屬經(jīng)不同介質(zhì)暴露的綜合非致癌風(fēng)險(xiǎn)見表5,各介質(zhì)兒童經(jīng)口非致癌健康風(fēng)險(xiǎn)如圖2所示.

兒童經(jīng)多介質(zhì)經(jīng)口途徑對(duì)重金屬的綜合暴露非致癌風(fēng)險(xiǎn)HIt為12.06,遠(yuǎn)遠(yuǎn)超過(guò)可接受的非致癌風(fēng)險(xiǎn)水平(1),且主要來(lái)源于As和Pb的暴露,二者分別貢獻(xiàn)50%和20%.不同重金屬經(jīng)口綜合暴露的非致癌風(fēng)險(xiǎn)水平為As>Pb>Cr>Ni>Cd,其中As、Pb、Cr和Ni經(jīng)口暴露非致癌風(fēng)險(xiǎn)均高于可接受風(fēng)險(xiǎn)水平(1),該結(jié)果與典型礦區(qū)周邊兒童重金屬非致癌風(fēng)險(xiǎn)結(jié)果一致[51].考慮到該焦化企業(yè)是當(dāng)?shù)匚ㄒ粷撛诘奈廴驹?周圍環(huán)境中的As污染可主要?dú)w因于該企業(yè)煤的焦化處理[55].因此,推測(cè)該企業(yè)在焦化過(guò)程中燃煤引起的As和Cr等重金屬污染可對(duì)當(dāng)?shù)貎和瘞?lái)潛在的重金屬暴露健康風(fēng)險(xiǎn).但是,當(dāng)?shù)貎和亟饘俦┞督】碉L(fēng)險(xiǎn)的增加有多少歸因于該企業(yè),有待借助其他方法進(jìn)一步深入研究.

表5 兒童經(jīng)多介質(zhì)經(jīng)口綜合暴露非致癌風(fēng)險(xiǎn)

圖2 兒童經(jīng)多介質(zhì)經(jīng)口重金屬暴露的非致癌健康風(fēng)險(xiǎn)

從圖2來(lái)看,總體上飲用水和土壤經(jīng)口暴露途徑的非致癌風(fēng)險(xiǎn)較小,不同重金屬經(jīng)土壤和飲用水暴露的非致癌健康風(fēng)險(xiǎn)分別占經(jīng)口綜合非致癌風(fēng)險(xiǎn)的0.07%~4.90%和0.22%~6.00%.不同介質(zhì)對(duì)兒童經(jīng)口綜合暴露非致癌風(fēng)險(xiǎn)相對(duì)貢獻(xiàn)的分布與其日均暴露量貢獻(xiàn)的分布相同.兒童經(jīng)口非致癌風(fēng)險(xiǎn)主要來(lái)自食物攝入途徑.各重金屬經(jīng)食物暴露的非致癌風(fēng)險(xiǎn)占經(jīng)口綜合暴露非致癌風(fēng)險(xiǎn)的90%以上.根據(jù)兒童環(huán)境暴露行為模式問(wèn)卷調(diào)查發(fā)現(xiàn),當(dāng)?shù)貎和疽允秤卯?dāng)?shù)刈援a(chǎn)食物為主.這意味著當(dāng)?shù)厥称分兄亟饘傥廴緦⒊蔀閮和┞吨亟饘俚闹饕緩胶椭苯拥娘L(fēng)險(xiǎn)來(lái)源,防范該焦化企業(yè)周邊兒童經(jīng)口暴露重金屬的風(fēng)險(xiǎn)需從當(dāng)?shù)厥称分兄亟饘傥廴镜墓芾碇?

此外,本研究表明雖然焦化企業(yè)周邊環(huán)境未受到重金屬的嚴(yán)重污染,且兒童未暴露于嚴(yán)重污染的環(huán)境中,但是受污染物毒性及兒童行為活動(dòng)特征的影響,其外暴露的生活環(huán)境仍可給當(dāng)?shù)貎和瘞?lái)潛在的重金屬暴露非致癌健康風(fēng)險(xiǎn).

2.3.2 致癌風(fēng)險(xiǎn) 兒童經(jīng)多介質(zhì)經(jīng)口重金屬暴露的綜合致癌風(fēng)險(xiǎn)如表6所示,不同介質(zhì)對(duì)經(jīng)口綜合暴露致癌風(fēng)險(xiǎn)的貢獻(xiàn)如圖3所示.

表6 兒童經(jīng)口多介質(zhì)暴露致癌風(fēng)險(xiǎn)

圖3 兒童經(jīng)不同介質(zhì)對(duì)重金屬綜合暴露致癌風(fēng)險(xiǎn)的貢獻(xiàn)

Table 3 Contribution of each medium to the cumulative carcinogenic risks of children to metals

a:Cr; b:As

結(jié)果表明,Cr和As經(jīng)多介質(zhì)經(jīng)口暴露的致癌風(fēng)險(xiǎn)均高于可接受的風(fēng)險(xiǎn)水平,分別為最大可接受風(fēng)險(xiǎn)水平(10-4)的77.53倍和1.75倍.不同重金屬來(lái)看,Cr暴露的致癌風(fēng)險(xiǎn)遠(yuǎn)高于As,約為As的44倍,經(jīng)口暴露途徑的致癌風(fēng)險(xiǎn)主要?dú)w因于Cr的暴露.從不同暴露途徑來(lái)看(圖3),重金屬Cr經(jīng)食物暴露的致癌風(fēng)險(xiǎn)占經(jīng)口綜合暴露致癌風(fēng)險(xiǎn)的73%以上.同樣有研究表明,某煤礦區(qū)周邊重金屬Cr經(jīng)食物暴露的風(fēng)險(xiǎn)最大[56],可能由于當(dāng)?shù)匦←満褪卟说仁澄锔繉?duì)土壤中Cr的吸收能力較強(qiáng),且兒童經(jīng)食物途徑的暴露量較高等原因造成.此外,As也對(duì)兒童構(gòu)成潛在的致癌風(fēng)險(xiǎn),食物途徑對(duì)經(jīng)口綜合暴露的貢獻(xiàn)達(dá)90%以上.有其他類似研究報(bào)道,盡管As健康風(fēng)險(xiǎn)并不高,但風(fēng)險(xiǎn)水平高低與當(dāng)?shù)鼐用袷秤玫氖称酚嘘P(guān)[57].因此,本研究表明該焦化企業(yè)周邊兒童可能存在較高的Cr暴露致癌風(fēng)險(xiǎn)(>1.0×10-4)和一定的As暴露致癌風(fēng)險(xiǎn),兩種污染物的防治對(duì)降低致癌風(fēng)險(xiǎn)至關(guān)重要.且食物中重金屬的暴露會(huì)對(duì)當(dāng)?shù)貎和瘞?lái)較高的致癌風(fēng)險(xiǎn),關(guān)注食品重金屬風(fēng)險(xiǎn)管理對(duì)防范兒童重金屬暴露的健康風(fēng)險(xiǎn)起重要作用.

2.4 不確定性分析

理想情況下,人群環(huán)境重金屬暴露的健康風(fēng)險(xiǎn)評(píng)估需基于一定數(shù)量的群體開展,且其健康風(fēng)險(xiǎn)評(píng)價(jià)結(jié)果的準(zhǔn)確性受樣品的分布?樣品的均質(zhì)性?人群代表性?暴露參數(shù)的準(zhǔn)確性?模型穩(wěn)定性等因素的影響.受抽樣過(guò)程人群合作意愿等局限,本研究只調(diào)查了一定數(shù)量的個(gè)體及其外暴露的環(huán)境樣本,可能造成本研究的風(fēng)險(xiǎn)評(píng)價(jià)結(jié)果受樣品均質(zhì)性的影響.此外,使用生物可利用濃度或生物可獲取濃度進(jìn)行人體非致癌和致癌風(fēng)險(xiǎn)評(píng)估被認(rèn)為是最可靠和最準(zhǔn)確的方法[58],然而,受動(dòng)物實(shí)驗(yàn)所限,本研究只關(guān)注污染物的總含量并用于評(píng)估兒童的致癌和非致癌風(fēng)險(xiǎn),因此,本研究的健康風(fēng)險(xiǎn)評(píng)估結(jié)果可能存在偏高的不確定性.但通過(guò)本研究的開展,可初步了解焦化企業(yè)周邊兒童經(jīng)口途徑對(duì)重金屬的綜合暴露及其健康風(fēng)險(xiǎn)特征,對(duì)于防范兒童重金屬暴露的健康風(fēng)險(xiǎn)及環(huán)境風(fēng)險(xiǎn)的優(yōu)先管理可補(bǔ)充重要的依據(jù).

為評(píng)估樣本分布及暴露參數(shù)等因素對(duì)本研究結(jié)果造成的不確定性,以食物經(jīng)口砷暴露為例, 使用Crystal ball 軟件的蒙特卡羅模型對(duì)其進(jìn)行分析,描述個(gè)體食物砷暴露的非致癌風(fēng)險(xiǎn)分布,模擬表征兒童食物經(jīng)口暴露的非致癌健康風(fēng)險(xiǎn).其中,食物中污染物濃度?人體重量和食物攝入量這三個(gè)不確定因素分布中獨(dú)立抽取樣本,分別服從對(duì)數(shù)正態(tài)分布表征?正態(tài)分布表征和三角分布來(lái)表征.結(jié)合各暴露因子的分布特征?標(biāo)準(zhǔn)差和均值等參數(shù)設(shè)定,進(jìn)行了10000次迭代計(jì)算,結(jié)果如圖4所示.食物砷經(jīng)口暴露的HQ模擬值為5.96,接近計(jì)算值5.98(圖2),表明本研究食物砷暴露的非致癌風(fēng)險(xiǎn)評(píng)估基本不存在偏差,說(shuō)明當(dāng)?shù)貎和_實(shí)存在較高的食物暴露健康風(fēng)險(xiǎn),需引起高度重視.

圖4 兒童經(jīng)食物途徑砷暴露非致癌風(fēng)險(xiǎn)累計(jì)概率分布

3 結(jié)論

3.1 本研究家庭庭院土壤中Pb、Cr、Ni和Cd污染程度較低,As污染相對(duì)較重,一定程度受焦化廠的排污影響;飲用水重金屬濃度均較低;食物Cr和As污染嚴(yán)重,分別為相應(yīng)標(biāo)準(zhǔn)閾值的2.68和3.82倍.

3.2 不同重金屬經(jīng)口多介質(zhì)綜合暴露量為Ni>Cr> Pb>As>Cd, Ni的日均暴露劑量達(dá)22.08μg/(kg·d),遠(yuǎn)高于其他四種重金屬[0.73~4.58μg/(kg·d)].當(dāng)?shù)刈援a(chǎn)食物是各重金屬經(jīng)多介質(zhì)經(jīng)口綜合暴露量的主要途徑,占經(jīng)口綜合暴露量的90%以上.

3.3 非致癌健康風(fēng)險(xiǎn)研究表明,當(dāng)?shù)貎和?jīng)多介質(zhì)經(jīng)口暴露的綜合非致癌風(fēng)險(xiǎn)水平為12.06,主要來(lái)源于As和Pb的暴露,二者分別貢獻(xiàn)50%和20%;食物途徑對(duì)綜合非致癌風(fēng)險(xiǎn)的貢獻(xiàn)90%以上.

3.4 Cr和As經(jīng)口暴露的致癌風(fēng)險(xiǎn)水平為77.53和1.75,主要來(lái)自當(dāng)?shù)刈援a(chǎn)食物的暴露.說(shuō)明焦化企業(yè)周邊兒童存在較高的重金屬暴露健康風(fēng)險(xiǎn),需引起重視,亟需重點(diǎn)關(guān)注食物As?Cr和Pb污染的管理和防控.

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Health risks of cumulative oral exposure to heavy metals for children living around a coking enterprise.

CHEN Yue-fang1,2, XU Jin-rong1, DUAN Xiao-li1,2, CAO Su-zhen1,2*, SUN Shan-wei1, KANG Yi-jin1

(1.School of Energy and Environmental Engineering, University of Science and Technology Beijing, Beijing 100083, China；2.Beijing Key Laboratory of Resource-oriented Treatment of Industrial Pollutants, Beijing 100083, China)., 2019,39(11)：4865~4874

At present, the researches on coking enterprise are mostly focused on technological process, emission characteristics of pollutants, organic pollution in surrounding environment and so on. However, few studies concerned on the exposure and health risks to heavy metals for the population living in the vicinity of coking enterprise. Thus, this study selected a typical coking plant in north China as a model and recruited the local children as subjects. On the basis of environmental related exposure behavior patterns questionnaire survey and field investigation on sample collection and analysis, it explored the pollution status of five heavy metals (Pb、Cd、Cr、Ni and As) in environmental media including drinking water, soil and food, as well as the exposure dose and health risk to the metals via the environmental media through oral exposure. The results showed that the surrounding environment was not heavily polluted by heavy metals. However, the children’s cumulative non-carcinogenic risks from various exposure pathways were in the range of 0.74 to 6.30, which was up to 6 times higher than the acceptable level (1), and was attributable to As exposure from food ingestion. The carcinogenic risks was 1.76×10-4~7.75×10-3, which was several to dozens of times higher than the acceptable level (1.0×10-4), and mainly from Cr exposure due to food ingestion. This study indicated that food ingestion was the main pathway for total oral exposure dose, accounting for more than 90% to the total oral exposure dose. It highlighted that although the surrounding environment of coking plant was not heavily contaminated by heavy metals, it would cause severe potential health risks to local children, which need to be paid more attention.

children；heavy metal；coking enterprise；exposure assessment；health risk assessment

X503.1

A

1000-6923(2019)11-4865-10

陳月芳(1973-),女,河北石家莊人,副教授,博士,主要從事水污染控制與治理技術(shù)研究.

2019-04-15

國(guó)家水體污染控制與治理科技重大專項(xiàng)(2017ZX07301005- 003);中央高?；究蒲袠I(yè)務(wù)費(fèi)專項(xiàng)(FRF-TP-17-064A1)

* 責(zé)任作者, 講師, love-lmd@163.com