鄭順安,韓允壘,袁宇志,倪潤祥,吳澤嬴,黃宏坤,師榮光

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鹽漬化環(huán)境下秸稈還田對稻米汞及甲基汞累積的影響

鄭順安1,2,3,韓允壘4,袁宇志5,倪潤祥1,2,吳澤嬴1,2,黃宏坤1,2,師榮光3*

(1.農(nóng)業(yè)農(nóng)村部農(nóng)業(yè)生態(tài)與資源保護(hù)總站,北京 100125；2.農(nóng)業(yè)農(nóng)村部資源循環(huán)利用技術(shù)與模式重點(diǎn)實(shí)驗(yàn)室,北京 100125；3.農(nóng)業(yè)農(nóng)村部環(huán)境保護(hù)科研監(jiān)測所,天津 300191；4.中國農(nóng)學(xué)會(huì),北京 100125；5.廣東省生態(tài)環(huán)境技術(shù)研究所,廣東 廣州 510650)

通過盆栽試驗(yàn)探討了鹽漬化環(huán)境下秸稈還田對土壤中總汞(THg)、甲基汞(MeHg)含量和轉(zhuǎn)化以及對水稻吸收汞的影響.試驗(yàn)用土采集自天津典型污灌地區(qū),人為添加不同梯度的鹽分(0、0.2%、0.5% NaCl)及外源汞(0、5mg/kg~Hg(NO3)2),秸稈還田按照0.1%進(jìn)行處理.結(jié)果顯示:1.秸稈還田促進(jìn)稻田系統(tǒng)中無機(jī)汞的甲基化.與未添加秸稈的處理相比,秸稈還田后土壤MeHg含量提高了56.8%~76.8%,水稻MeHg含量增加了127%~171.6%.2.在輕度鹽漬化稻田開展秸稈還田,會(huì)進(jìn)一步提高稻田土壤中汞的甲基化水平,進(jìn)而增加水稻籽粒中甲基汞含量.與不添加鹽分處理相比,輕度鹽漬化環(huán)境中(0.2% NaCl),秸稈還田處理導(dǎo)致土壤MeHg含量提高了92.2%~101.2%,水稻籽粒MeHg含量增長了52.8%~132.1%.更高的鹽漬化水平會(huì)抑制土壤汞甲基化趨勢,水稻籽粒中甲基汞含量降低.在中度鹽漬化環(huán)境中(0.5% NaCl),秸稈還田導(dǎo)致土壤MeHg含量降低了57.9%~88.6%,水稻籽粒MeHg含量降低了72.9%~86.8%.以上研究結(jié)果表明,在鹽漬化且汞污染稻田開展秸稈還田可能大幅度增加該地區(qū)汞食物鏈暴露風(fēng)險(xiǎn),因此在中輕度鹽漬化的污灌區(qū),對秸稈還田等農(nóng)藝措施需要格外慎重.

鹽分；汞；甲基汞；水稻；秸稈還田

天津污灌區(qū)是我國北方最大的污灌區(qū)[1],也是汞(Hg)污染重災(zāi)區(qū).王祖?zhèn)サ萚2]對天津污灌區(qū)水田和菜田調(diào)查顯示,灌區(qū)內(nèi)土壤-作物系統(tǒng)中汞的污染等級達(dá)到了重度污染,部分農(nóng)作物中汞的質(zhì)量分?jǐn)?shù)遠(yuǎn)超國家食品衛(wèi)生標(biāo)準(zhǔn).王婷等[3]調(diào)查顯示,天津污灌區(qū)內(nèi)采樣的22個(gè)蔬菜樣品100%都受到Hg污染,且都處于重污染的情況.濕地土壤中,隨著濕度增加,充滿水的土壤微孔增加,有利于形成硫酸鹽還原菌和鐵還原菌等甲基化微生物需要的還原環(huán)境.稻田生態(tài)系統(tǒng)是濕地的一種類型,水稻在生長期內(nèi)因季節(jié)性灌溉,使其也成為一種特殊的濕地生態(tài)系統(tǒng),為硫酸鹽還原菌和鐵還原細(xì)菌等提供理想的生存條件,因此稻田也存在較強(qiáng)的汞甲基化能力,而成為陸地生態(tài)系統(tǒng)的甲基汞“源”[4-5],這在之前的研究中已有報(bào)道[6],甚至有研究者認(rèn)為,食用大米而非水產(chǎn)品已經(jīng)成為汞污染嚴(yán)重地區(qū)人體甲基汞暴露的主要途徑[5, 7-8].2013~2014年,本課題組對天津污灌區(qū)內(nèi)的稻田汞污染狀況進(jìn)行了調(diào)查,在29個(gè)稻田中,土壤甲基汞(MeHg)平均含量為(0.87±0.77)μg/kg,占總汞(THg)的比例為0.12%~0.38%,個(gè)別汞污染較嚴(yán)重地塊存在甲基汞暴露風(fēng)險(xiǎn)[9].武超等[10]也對天津污灌區(qū)內(nèi)水稻土壤及農(nóng)產(chǎn)品汞污染狀況進(jìn)行了調(diào)查,結(jié)果顯示,北塘、大沽和北京污灌區(qū)稻田土壤THg和MeHg濃度顯著高于對照區(qū)海河土壤THg濃度,水稻籽粒MeHg富集系數(shù)為1.63-3.70,污灌區(qū)食用稻米MeHg暴露對居民健康存在較大風(fēng)險(xiǎn),人體MeHg每天攝入量超標(biāo)率達(dá)到20.83%.

秸稈還田是秸稈綜合利用的重要途徑之一.當(dāng)前,我國每年還田的作物秸稈超過1.5億t,且在快速增加.對農(nóng)業(yè)生產(chǎn)而言,秸稈還田具有增加土壤有機(jī)質(zhì)含量、為植物生長提供營養(yǎng)、使作物增產(chǎn)等多種良性效果,但秸稈還田對土壤中重金屬等污染物,特別是汞的環(huán)境化學(xué)行為的影響報(bào)道相對較少.南京大學(xué)的鐘寰課題組研究表明,秸稈還田總體會(huì)提高土壤中汞的甲基化水平[11-13],在稻麥輪作體系中,秸稈還田后會(huì)顯著提高產(chǎn)地土壤中甲基汞含量,同時(shí)水稻和小麥各部位甲基汞含量也會(huì)明顯升高[14].天津污灌區(qū)承受汞污染與鹽漬化的雙重壓力,在這種特殊生境條件下,秸稈還田后是否會(huì)提高稻田土壤-水稻籽粒中總汞和甲基汞含量,增加汞食物鏈暴露風(fēng)險(xiǎn),是人們迫切希望搞清楚的問題.綜上,本研究采集天津典型污灌地區(qū)土壤,通過盆栽試驗(yàn),添加不同梯度的鹽分及外源汞,探討秸稈還田對鹽漬化汞污染稻田土壤-作物系統(tǒng)Hg及MeHg含量的影響,為北方鹽漬化且汞污染風(fēng)險(xiǎn)較高地區(qū)合理開展秸稈還田提供支撐.

1 材料與方法

1.1 樣品準(zhǔn)備

土壤:盆栽試驗(yàn)所用土壤樣品采集自天津市郊東北方向李明莊的菜地(潮土,0~20cm).該菜地距離天津三大排污河之一的北(塘)排污河約400m,污灌歷史約30年,屬于間歇性清污混灌,污灌口位于菜地的西南角.土壤樣品經(jīng)自然風(fēng)干后過2mm尼龍篩冷凍儲(chǔ)存,基本理化性質(zhì)分析參照中國土壤學(xué)會(huì)的分析方法[15],結(jié)果如下:pH值為8.03,CaCO3含量為1.03g/kg,有機(jī)質(zhì)含量為12.43g/kg,CEC為16.27cmol/ kg,游離鐵含量為8.71g/kg,無定形鐵含量為0.88g/kg,黏粒(<0.002mm)含量為191.05g/kg.受長期污灌的影響,供試土壤的Hg含量(0.601mg/kg)顯著高于區(qū)域土壤Hg背景含量(0.073mg/kg),但未超過土壤環(huán)境質(zhì)量二級標(biāo)準(zhǔn)(pH>7.5為1.0mg/kg,GB 15618- 1995).鹽分總量為0.875g/kg(低于0.1%),按照鹽土重量比劃分標(biāo)準(zhǔn)[15],不屬于鹽漬化土壤.

供試秸稈:水稻秸稈采自未受汞污染的天津津南地區(qū).秸稈洗凈,30℃烘干至恒重,磨碎過2mm篩備用.水稻秸稈總汞含量為0.129mg/kg,甲基汞含量為0.017μg/kg.

水稻栽培品種:津原89(具有較強(qiáng)耐鹽漬化能力,經(jīng)預(yù)實(shí)驗(yàn),該品種在實(shí)驗(yàn)設(shè)置的鹽度梯度下可以生長).

1.2 實(shí)驗(yàn)設(shè)計(jì)

表1 實(shí)驗(yàn)處理設(shè)計(jì)方案

根據(jù)實(shí)驗(yàn)?zāi)繕?biāo),設(shè)置8個(gè)處理,每個(gè)處理設(shè)置6次重復(fù),具體設(shè)置見表1.

添加時(shí),將10kg原土按比例添加鹽分和外源汞,混勻采用逐級混勻的方法,先將鹽分和重金屬溶液與少量土壤混勻,再將少量土壤與大量土壤混勻,直到所有土壤.混勻后放置老化180d后(預(yù)備試驗(yàn)證明180d后污染土壤內(nèi)重金屬老化趨于穩(wěn)定)自然風(fēng)干,過2mm篩后保存.制備結(jié)束后,采用IonPac AS11- HC分析柱及30mmol/L氫氧化鉀溶液分離Cl-,測定鹽處理后土壤樣品中Cl-含量(Dionex ICS-3000型離子色譜儀),同時(shí)測定土壤總汞含量(方法見1.4),結(jié)果見表2.總體來看,外源加入的鹽分和總汞回收率在90.0%~110.5%之間.

表2 不同處理中土壤Cl-與總Hg含量

1.3 盆栽試驗(yàn)

供試土壤中按照總氮100mg/kg、總磷100mg/kg和總鉀150mg/kg施加底肥后混勻,根據(jù)表1實(shí)驗(yàn)方案開展水稻種植(16年6月到11月).具體方法為:每盆3.5kg土壤添加35.0g水稻秸稈(即土壤和秸稈質(zhì)量比為100:1,秸稈長度為0.2cm,Hg含量低于0.1 μg/kg),加入去離子水后淹水靜置14d插播水稻秧(在無汞污染土壤上培育秧苗).盆栽試驗(yàn)露天進(jìn)行,采用有機(jī)玻璃板遮擋防止雨水.作物生長期間,淹水層保留3cm,進(jìn)行常規(guī)蟲害和肥料管理.

水稻盆栽周期為(120±7)d.盆栽試驗(yàn)結(jié)束后采集根區(qū)土壤,測定總汞、甲基汞含量.水稻收獲后,采集植株地上部分,去離子水洗凈后,用0.8mmol/L半胱氨酸溶液浸泡20.0min,去除植株表面吸附的MeHg,測定水稻籽粒(脫殼后糙米)中總汞與甲基汞含量.土壤和水稻籽粒中總汞和甲基汞含量測定參考鄭順安等[9]的測定方法.

1.4 統(tǒng)計(jì)制圖

土壤和水稻籽粒中總汞和甲基汞含量變化采用單因素方差分析(One-way ANOVA,LSD法)進(jìn)行統(tǒng)計(jì)學(xué)檢驗(yàn).制圖采用Origin 8.6SR2軟件.

2 結(jié)果與討論

2.1 不同處理下根際土壤總汞與甲基汞含量

圖1 盆栽后各處理土壤總汞(THg)與土壤甲基汞(MeHg)含量

CK:對照,T1:添加0.1%水稻秸稈,T2:添加0.2% NaCl和0.1%水稻秸稈,T3:添加0.5% NaCl和0.1%水稻秸稈,T4:添加5mg/kg Hg,T5:添加5mg/kg Hg和0.1%水稻秸稈,T6:添加5mg/kg Hg、0.2% NaCl和0.1%水稻秸稈,T7:添加添加5mg/kg Hg、0.5% NaCl和0.1%水稻秸稈.不同小寫字母表示處理間差異達(dá)到顯著性水平(<0.05)

圖1為水稻收獲后不同處理根際土壤總汞與甲基汞含量.對于土壤總汞,未添加外源汞的處理——對照(CK)、秸稈(T1)、低鹽秸稈(T2)和中鹽秸稈(T3),土壤THg含量平均為0.655mg/kg,處理間無顯著性差別(<0.05,下同);添加外源汞的處理——高汞(H)、高汞低鹽秸稈(HLS)和高汞中鹽秸稈(HHS),土壤THg均值為5.62mg/kg.對于土壤甲基汞,不同處理之間差異顯著,土壤MeHg含量依次為:T6(高汞低鹽秸稈,102.37μg/kg)>T5(高汞秸稈,53.27μg/kg)> T4(高汞,30.13μg/kg)>T2(低鹽秸稈,8.55μg/kg)> T7(高汞中鹽秸稈,6.09μg/kg)>T1(秸稈,4.25μg/kg)> CK(對照,2.71μg/kg)>T3(中鹽秸稈,1.79μg/kg).可以看出,高汞低鹽秸稈處理的土壤MeHg含量最高,是高汞秸稈處理的1.92倍、高汞處理的3.4倍、高汞中鹽處理的16.8倍、對照的37.8倍;低鹽秸稈處理下土壤MeHg含量是秸稈處理的2.01倍、對照的3.2倍;中鹽秸稈處理下土壤MeHg含量最低,僅為對照的66.1%.

2.2 不同處理下水稻籽粒中總汞與甲基汞含量

圖2為水稻收獲后不同處理水稻籽粒中總汞與甲基汞含量.對于THg,不同處理間存在顯著差異,含量依次為:T7(高汞中鹽秸稈,56.44μg/kg)> T6(高汞低鹽秸稈,42.15μg/kg)>T5(高汞秸稈, 29.79μg/kg)、T4(高汞,29.33μg/kg)>T3(中鹽秸稈, 16.59μg/kg)>T2(低鹽秸稈,12.77μg/kg)>CK(對照, 10.35μg/kg)、T1(秸稈,9.48μg/kg).對于MeHg,不同處理間同樣差異顯著,含量依次為:T6(高汞低鹽秸稈,20.54μg/kg)>T5(高汞秸稈,13.44μg/kg)>T2(低鹽秸稈,6.43μg/kg)、T4(高汞,5.92μg/kg)>T1(秸稈, 2.77μg/kg)>T7(高汞中鹽秸稈,1.78μg/kg)>CK(對照,1.02μg/kg)>T3(中鹽秸稈,0.71μg/kg).總體來看,高汞中鹽秸稈處理下水稻籽粒中THg含量最高,是對照的5.45倍;高汞低鹽處理下水稻籽粒中MeHg含量最高,是對照的20.13倍.

圖2 盆栽后各處理稻米籽粒中總汞(THg)與甲基汞(MeHg)含量

CK:對照,T1:添加0.1%水稻秸稈,T2:添加0.2% NaCl和0.1%水稻秸稈,T3:添加0.5% NaCl和0.1%水稻秸稈,T4:添加5mg/kg Hg,T5:添加5mg/kg Hg和0.1%水稻秸稈,T6:添加5mg/kg Hg、0.2% NaCl和0.1%水稻秸稈,T7:添加添加5mg/kg Hg、0.5% NaCl和0.1%水稻秸稈.不同小寫字母表示處理間差異達(dá)到顯著性水平(<0.05)

3 討論

對于未發(fā)生鹽漬化的土壤,與未添加秸稈的對照相比,秸稈施入后,土壤和水稻總汞含量未出現(xiàn)顯著性變化,這與還田的秸稈本身汞含量較低,且還田量不高有關(guān).另一方面,秸稈還田后,土壤和水稻籽粒中甲基汞含量均顯著提高.低汞土壤中,加入秸稈的處理相比對照,土壤甲基汞含量提高了56.8%,水稻籽粒中甲基汞含量提高了171.6%;高汞土壤中,加入秸稈的處理與未加入秸稈的處理相比,土壤甲基汞含量提高了76.8%,水稻籽粒中甲基汞含量提高了127.0%.這種秸稈施入農(nóng)田后土壤和作物甲基汞升高的趨勢,與之前報(bào)道的研究結(jié)果基本一致.如Zhu[16]等報(bào)道,水稻秸稈和根施入萬山汞礦區(qū)污染的稻田土壤后,土壤中甲基汞的濃度提高了2~8倍.陳宗婭等[14]研究顯示,小麥秸稈還田后土壤甲基汞含量增加127.1%,水稻秸稈還田后土壤甲基汞含量增加25.1%.Liu等[17]研究表明,秸稈還田大幅度提高重度汞污染土壤(含量高于5mg/kg)中汞的甲基化,對于汞含量相對較低的土壤(0.5mg/kg),效果弱于高汞土壤,原因可能是由于兩種土壤中微生物群落特征不同.不同的土壤微生物群落組成影響秸稈的降解、溶解性有機(jī)碳含量及其與汞結(jié)合形態(tài),從而影響汞的微生物甲基化.這與本研究的結(jié)果也是相一致的,其他研究者[18-19]也有類似的結(jié)論.以往的報(bào)道[18,20-22]認(rèn)為秸稈還田促進(jìn)稻田生態(tài)系統(tǒng)汞甲基化,可能與秸稈還田后稻田土壤性質(zhì)發(fā)生變化有關(guān),如氧化還原電位的變化、土壤中有機(jī)質(zhì)含量的升高、S和Fe的還原、無機(jī)汞活性的變化、甲基化微生物數(shù)量和活性的變化等.這些因素中,溶解性有機(jī)質(zhì)比較關(guān)鍵,目前有4種解釋的機(jī)制,一是秸稈分解產(chǎn)生的活性有機(jī)碳直接作為速效碳源提高汞甲基化微生物的數(shù)量和活性,促進(jìn)無機(jī)汞的甲基化[19],二是溶解性有機(jī)質(zhì)與HgS絡(luò)合形成甲基化生物可利用態(tài)的復(fù)合物[23-24],三是溶解性有機(jī)質(zhì)與土壤有機(jī)質(zhì)競爭甲基汞的結(jié)合點(diǎn)位,促進(jìn)甲基汞溶出[25],四是孔隙水中的溶解性有機(jī)質(zhì)絡(luò)合汞,降低汞在土壤顆粒上的吸附量,附近土壤中固持的汞溶出,提高可甲基化的汞“原料”[26].

對于鹽漬化土壤,秸稈對土壤和作物中汞累積的影響更為復(fù)雜.含0.2% NaCl和0.1%秸稈的輕度鹽漬化土壤中,與不添加鹽分僅加入秸稈的處理相比,土壤總汞無顯著性變化,但土壤甲基汞和水稻籽粒中總汞、甲基汞含量有顯著增長,其中土壤MeHg含量提高了92.2%(低汞)~101.2%(高汞),水稻籽粒中THg含量增長了24.2%(低汞)~36.9%(高汞),水稻籽粒中MeHg含量增長了52.8%(高汞)~132.1%(低汞).含0.5% NaCl和0.1%秸稈的中度鹽漬化土壤中,與不添加鹽分僅加入秸稈的處理相比,土壤總汞仍無顯著性區(qū)別,但土壤甲基汞含量與水稻籽粒中甲基汞含量顯著降低,其中土壤MeHg含量降低了57.9% (低汞)~88.6%(高汞),水稻籽粒中MeHg含量降低了72.9%(低汞)~86.8%(高汞);水稻籽粒中總汞含量則有所上升,上升幅度為75%(低汞)~83.3%(高汞).綜合來看,在鹽漬化土壤中這些升高或降低的效應(yīng)不論在低汞或高汞土壤中均存在,這些效應(yīng)可能與鹽漬化土壤中Cl含量有關(guān).Cl-對于Hg(II)而言是最易移動(dòng)和常見的結(jié)合劑,與Hg(II)之間存在強(qiáng)烈的絡(luò)合作用,可形成HgCl20及HgCl3-等絡(luò)合離子,使帶負(fù)電荷的腐殖物質(zhì)和粘土礦物膠體對汞的專性吸附作用顯著降低,進(jìn)而使土壤對Hg(II)的固持量及吸附速率迅速下降[27].根據(jù)報(bào)道[28-29],體系Cl-含量增加后,易被植物吸收的土壤交換態(tài)(含水溶態(tài))、富里酸結(jié)合態(tài)汞顯著上升,增加了水稻總汞吸收風(fēng)險(xiǎn),這與本研究的結(jié)果是相一致的.但Cl-對土壤-水稻體系中汞甲基化的影響與其濃度相關(guān),根據(jù)之前的報(bào)道[30], NaCl處理下,隨著鹽度的增長,外源Hg進(jìn)入土壤后汞甲基化程度總體呈現(xiàn)先增長后降低的趨勢.低鹽度水平下(0.2%~0.6%),土壤汞甲基化程度提高,增加了土壤-水稻體系中甲基汞含量;高鹽度(1.0%~5.0%)則會(huì)抑制汞的甲基化,且高鹽度環(huán)境下生成的MeHg不穩(wěn)定,容易發(fā)生去甲基化,降低土壤-水稻體系中甲基汞水平.這是當(dāng)NaCl鹽度較低時(shí),Cl-與Hg(II)之間存在強(qiáng)烈的絡(luò)合作用,可形成HgCl3-和HgCl42-等多種負(fù)性絡(luò)合離子,使得帶負(fù)電荷的腐殖物質(zhì)和粘土礦物膠體對汞的專性吸附作用顯著降低,進(jìn)而使土壤對Hg(II)的固持量及吸附速率迅速下降,Hg在土壤中的移動(dòng)性及活性增強(qiáng),增加了汞甲基化的“供應(yīng)量”,甲基化率上升;但當(dāng)鹽度進(jìn)一步提高后,微生物可能通過溶液體系中滲透壓變化而影響其物質(zhì)運(yùn)輸過程,引起細(xì)胞質(zhì)壁分離,造成細(xì)胞死亡或活性下降,從而降低汞甲基化程度[31-32].這些報(bào)道與本研究結(jié)果總體一致,但在敏感鹽度水平區(qū)間上有所不同.在加入0.1%秸稈的基礎(chǔ)上,本研究在0.2% NaCl鹽度水平下出現(xiàn)稻田汞甲基化程度提高,在0.5%鹽度水平下就出現(xiàn)了顯著降低,再結(jié)合之前與僅加入秸稈的處理之間土壤-水稻體系汞含量的差異,表明鹽度和秸稈之間存在一些交互性作用.綜合來看,在鹽漬化環(huán)境中秸稈還田后的汞環(huán)境化學(xué)更加復(fù)雜,涉及到多環(huán)境因子的組合及眾多生物化學(xué)反應(yīng),對其機(jī)理機(jī)制有待更深入的研究.

4 結(jié)論

4.1 秸稈還田會(huì)促進(jìn)稻田土壤中無機(jī)汞的甲基化.在輕度鹽漬化稻田開展秸稈還田,會(huì)進(jìn)一步提高稻田土壤中汞的甲基化水平,進(jìn)而增加水稻籽粒中甲基汞含量.但更高的鹽漬化水平會(huì)抑制土壤汞甲基化趨勢,水稻籽粒中甲基汞含量降低.

4.2 在輕度鹽漬化稻田開展秸稈還田,會(huì)大幅度增加該地區(qū)汞食物鏈暴露風(fēng)險(xiǎn),因此在污灌區(qū)等存在鹽漬化問題的地區(qū),對秸稈還田等農(nóng)藝措施需要格外慎重.

[1] 農(nóng)業(yè)部環(huán)境監(jiān)測總站. 1996~1999第二次中國污水灌溉普查報(bào)告[R]. 北京:農(nóng)業(yè)部環(huán)境監(jiān)測總站, 1999:25-40. Agro-Envrionmental Protection Institute, Ministry of Agriculture. The 2nd Chinese sewage irrigation survey report in 1996~1999 [R]. Beijing: Agro-Envrionmental Protection Institute, Ministry of Agriculture, 1999:25-40.

[2] 王祖?zhèn)?張 輝.天津污灌區(qū)土壤重金屬污染環(huán)境質(zhì)量與環(huán)境效應(yīng)[J]. 生態(tài)環(huán)境, 2005,14(2):211-213. Wang Z W, Zhang H. Environmental quality and biological effects of heavy metals in soils in the regions of sewage irrigation in Tianjin [J]. Ecology and Environment, 2005,14(2):211-213.

[3] 王 婷,王 靜,孫紅文,等.天津農(nóng)田土壤鎘和汞污染及有效態(tài)提取劑篩選[J]. 農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào), 2012,31(1):119-124.Wang T, Wang J, Sun H W, et al. Comtamination of cadmium and mercury in farmland of Tianjin and extration methods for predicting their bioavailability [J]. Journal of Agro-Environment Science, 2012,31(1):119-124.

[4] Rothenberg S E, Windham-Myers L, Creswell J E. Rice methylmercury exposure and mitigation: A comprehensive review [J]. Environmental research, 2014,133:407-423.

[5] Zhang H, Feng X, Larssen T, et al. In inland China, rice, rather than fish, is the major pathway for methylmercury exposure [J]. Environmental health perspectives, 2010,118(9):1183-1188.

[6] Li B, Shi J B, Wang X, et al. Variations and constancy of mercury and methylmercury accumulation in rice grown at contaminated paddy field sites in three Provinces of China [J]. Environmental Pollution, 2013,181:91-97.

[7] Li P, Feng X, Yuan X, et al. Rice consumption contributes to low level methylmercury exposure in southern China [J]. Environment International. 2012,49(1):18-23.

[8] Meng B, Feng X, Qiu G, et al. Inorganic mercury accumulation in rice (Oryza sativa L.) [J]. Environmental Toxicology and Chemistry, 2012,31(9):2093-2098.

[9] 鄭順安,唐杰偉,鄭宏艷,等.污灌區(qū)稻田汞污染特征及健康風(fēng)險(xiǎn)評價(jià)[J]. 中國環(huán)境科學(xué), 2015,35(9):2729-2736. Zheng S A, Tang J W, Zheng H Y, et al. Pollution characteristics and risk assessments of mercury in wastewater-irrigated paddy fields [J]. China Environmental Science, 2015,35(9):2729-2736.

[10] 武 超,張兆吉,費(fèi)宇紅,等.天津污灌區(qū)水稻土壤汞形態(tài)特征及其食品安全評估[J]. 農(nóng)業(yè)工程學(xué)報(bào), 2016,32(18):207-212. Wu C, Zhang Z J, Fei Y H, et al. Characteristics of mercury form in soil-rice system and food security assessment in wastewater-irrigated paddy fields of Tianjin [J]. Transactions of the Chinese Society of Agricultural Engineering, 2016,32(18):207-212.

[11] Zhu H, Zhong H, Evans D, et al. Effects of rice residue incorporation on the speciation, potential bioavailability and risk of mercury in a contaminated paddy soil [J]. Journal of Hazardous Materials, 2015,293:64.

[12] Shu R, Fei D, Zhong H. Effects of incorporating differently-treated rice straw on phytoavailability of methylmercury in soil [J]. Chemosphere, 2016,145:457-463.

[13] Liu Y R, Dong J X, Han L L, et al. Influence of rice straw amendment on mercury methylation and nitrification in paddy soils. [J]. Environmental Pollution, 2016,209:53-59.

[14] 陳宗婭,王永杰,舒 瑞,等.秸稈覆蓋還田對稻麥輪作體系中土壤及作物甲基汞累積的影響[J]. 農(nóng)業(yè)環(huán)境科學(xué)學(xué)報(bào), 2016,35(10):1931-1936.Chen Z Y, WANG Y j, Shu R, et al. Effects of straw amendment on methylmercury accumulation in soil and crop plants under wheat-rice rotation [J]. Journal of Agro-Environment Science, 2016,35(10):1931-1936.

[15] 魯如坤.土壤農(nóng)業(yè)化學(xué)分析方法[M]. 北京:中國農(nóng)業(yè)科技出版社, 2000:15-20. LU R K. Soil argrochemistry analysis protocoes [M]. Beijing: China Agriculture Science Press, 2000:15-20.

[16] Zhu H, Zhong H, Evans D, et al. Effects of rice residue incorporation on the speciation, potential bioavailability and risk of mercury in a contaminated paddy soil. [J]. Journal of Hazardous Materials, 2015,293:64-71.

[17] Liu Y R, Dong J X, Han L L, et al. Influence of rice straw amendment on mercury methylation and nitrification in paddy soils [J]. Environmental Pollution, 2016,209:53-59.

[18] Windhammyers L, Marvindipasquale M, Kakouros E, et al. Mercury cycling in agricultural and managed wetlands of California, USA: seasonal influences of vegetation on mercury methylation, storage, and transport. [J]. Science of the Total Environment, 2014,484(24):308.

[19] Marvin-Dipasquale M, Windham-Myers L, Agee J L, et al. Methylmercury production in sediment from agricultural and non-agricultural wetlands in the Yolo Bypass, California, USA [J]. Science of the Total Environment, 2014,484(1):288-299.

[20] Jeong H Y, Klaue B, Blum J D, et al. Sorption of mercuric ion by synthetic nanocrystalline mackinawite (FeS). [J]. Environmental Science & Technology, 2007,41(22):7699-7705.

[21] Skyllberg U, Drott A. Competition between disordered iron sulfide and natural organic matter associated thiols for mercury(II)-an EXAFS study. [J]. Environmental Science & Technology, 2010,44(4):1254-1259.

[22] Yang Y, Li L, Wang D. Effect of dissolved organic matter on adsorption and desorption of mercury by soils [J]. Journal of Environmental Science-China, 2008,20(9):1097-1102.

[23] Graham A M, Aiken G R, Gilmour C C. Dissolved organic matter enhances microbial mercury methylation under sulfidic conditions [J]. Environmental Science & Technology, 2012,46(5):2715-2723.

[24] Zhang T, Kim B, Levard C, et al. Methylation of mercury by bacteria exposed to dissolved, nanoparticulate, and microparticulate mercuric sulfides [J]. Environmental Science & Technology, 2012,46(13):6950.

[25] Yang Y, Li L, Wang D. Effect of dissolved organic matter on adsorption and desorption of mercury by soils [J]. 環(huán)境科學(xué)學(xué)報(bào)(英文版), 2008,20(9):1097-1102.

[26] Peng J, Zhe L, Rui J, et al. Dynamics of the Methanogenic Archaeal Community during Plant Residue Decomposition in an Anoxic Rice Field Soil [J]. Applied & Environmental Microbiology, 2008,74(9):2894.

[27] Yang Y K, Zhang C, Shi X J, et al. Effect of organic matter and pH on mercury release from soils [J]. Journal of Environmental Sciences- China, 2007,19(11):1349-1354.

[28] Rogers R D. Methylation of mercury in agricultural soils [J]. Journal of Environmental Quality, 1976,5(4):454-458.

[29] de Vries W, Lofts S, Tipping E, et al. Impact of Soil Properties on Critical Concentrations of Cadmium, Lead, Copper, Zinc, and Mercury in Soil and Soil Solution in View of Ecotoxicological Effects [J]. Reviews of Environmental Contamination and Toxicology, 2007,191(4):47-89.

[30] 鄭順安,周 瑋,薛穎昊,等.污灌區(qū)鹽分累積對外源汞在土壤中甲基化的影響[J]. 中國環(huán)境科學(xué), 2017,37(11):4195-4201. Zheng S A, Zhou W, Xue Y H, et al. Investigating effect of salinity on methylation of exogenous mercury of soil in wastewater-irrigated area by labeling with stable isotopically enriched tracers [J]. China Environmental Science, 2017,37(11):4195-4201.

[31] Boyd E S, Yu R Q, Barkay T, et al. Effect of salinity on mercury methylating benthic microbes and their activities in Great Salt Lake, Utah. [J]. Science of the Total Environment, 2017.

[32] Laporte J M, Truchot J P, Ribeyre F, et al. Combined effects of water pH and salinity on the bioaccumulation of inorganic mercury and methylmercury in the shore crab Carcinus maenas [J]. Marine Pollution Bulletin, 1997,34(11):880-893.

Influence of rice straw amendment on mercury/methylmercury accumulation in rice grains in the saline soils.

ZHENG Shun-an1,2,3, HAN Yun-lei4, YUAN Yu-zhi5, NI Run-xiang1,2, WU Ze-ying1,2, HUANG Hong-kun1,2, SHI Rong-guang3*

(1.Rural Energy & Environment Agency, Ministry of Agriculture, Beijing 100125, China；2.Key Laboratory of Technologies and Models for Cyclic Utilization from Agricultural Resources, Ministry of Agriculture, Beijing 100125, China；3.Agro-Environmental Protection Institute, Ministry of Agriculture, Tianjin 300191, China；4.Chinese Association of Agricultural Science Society, Beijing 100125, China；5.Guangdong Institute of Eco-environment and Soil Science, Guangzhou 510650, China)., 2019,39(1)：243~248

A pot experiment was conducted to simulate a mercury-contaminated paddy fields irrigated with wastewater. Soil sample was collected from a typical wastewater-irrigated area of Tianjin, and exogenous salinity (0%, 0.2%, 0.5% NaCl), mercury (0, 5mg/kg Hg(NO3)2) and rice straw (0, 0.1%) were added into soil manually to discuss the influence of rice straw amendment on total mercury (THg)/methylmercury (MeHg) accumulation in rice grain. Results showed that, (1) Methylation of inorganic mercury in paddy soil-rice system was promoted by rice straw amendment. After rice straw amendment, MeHg concentration in soil and rice grain increased by 56.8%~76.8% and 127%~171.6% respectively. (2) Stimulation of methylation of inorganic mercury in mild salinized paddy soil by rice straw amendment was even more serious, and which lead to an additional increment of MeHg in rice grain. Compared with un-salinized soil, MeHg in soil and rice grain increased by 92.2%~101.2% and 52.8%~132.1% respectively after rice straw amendment. However, in a more serious salinized soil (0.5% NaCl), methylation of inorganic mercury in soil was suppressed and MeHg accumulation in rice grain decreased. MeHg concentration in soil and rice grain decreased by 57.9%~88.6% and 72.9%~86.8% respectively in moderate salinized soil (0.5% NaCl) after treated with rice straw amendment, compared with in un-salinized soil. These results indicated that the treatment of rice straw amendment in a medium or low level salinized soil with Hg contamination may lead to adverse effect to human health. Therefore, treatment of rice straw amendment in this kind of area should be cautious.

salinity；mercury；methylmercury；rice；rice straw amendment

X53

A

1000-6923(2019)01-0243-06

鄭順安(1981-),男,安徽合肥人,副研究員,博士,主要從事產(chǎn)業(yè)環(huán)境監(jiān)測與土壤污染防治工作研究.發(fā)表論文40余篇.

2018-06-08

國家重點(diǎn)研發(fā)計(jì)劃資助項(xiàng)目(2016YFD0201306,2016YFD0201200, 2017YFD0801401,2017YFD0801205);國家自然科學(xué)資助項(xiàng)目(41203084, 41371463)

* 責(zé)任作者, 研究員, shirongguang_aepi@126.com