吉林省中北部農(nóng)田土壤有機氯農(nóng)藥的殘留特征

劉寶林,李 明,董煒華,花修藝,董德明,王彬彬

(1.吉林大學 環(huán)境與資源學院,長春 130012;2.長春師范大學 化學學院,長春 130032)

Abstract:Typical farmland soil samples of Changchun,Dehui,Fuyu,Gongzhuling,Yongji were collected with grid method.The residues of organochlorine pesticides(OCPs) in soil and the distribution were measured and the composition and sources of organochlorine pesticide residues were discussed.The results show that HCHs and DDTs of the study areas had higher detection rate.The total OCPs content of the residues was in a range of 1.45～83.88 ng/g.HCHs and DDTs were found widely in all the samples with a range of 1.17～27.83 ng/g and 1.45～81.75 ng/g respectively.The residue levels in different lands were in the order as follows:Changchun>Gongzhuling>Yongji>Dehui>Fuyu.A significant positive correlation existed between the total amount of OCPs and that of TOC was showed.The source analysis shows that the average value ofα-HCH/γ-HCH of survey region was 0.37,indicating that there was a large number of lindane imported recently.The DDTs pesticide composition displays that P,P′-DDT/(P,P′-DDD+P,P′-DDE) values of each sampling site except Gongzhuling were less than 1,indicating the sources of DDTs were residues historically.Gongzhuling was likely contaminated by industrial DDTs.From the results of factor analysis and cluster analysis,we conclude that the content of organochlorine pesticides causing Changchun area pollution is significantly higher than those of other regions.From the analysis of pollutant factor,γ-HCH and P,P′-DDT are the major pollutants.

Keywords:soil of Jilin Province;organochlorine pesticides;residue;distribution character

有機氯農(nóng)藥(OCPs)是環(huán)境中廣泛存在的一種難降解有機物,具有高殘留性和高生物富集性,對生態(tài)系統(tǒng)和人類健康具有潛在的威脅[1-4].六六六類(HCHs)和滴滴涕類(DDTs)在一些區(qū)域的土壤環(huán)境中殘留較多[5-8],其危害已引起人們廣泛關注[9-13].本文通過分析HCHs和DDTs在吉林省典型區(qū)域農(nóng)田土壤中的分布特征,探討其來源及對人類可能帶來的環(huán)境風險,并研究其殘留特征,為土壤修復和治理提供一定的理論依據(jù).

圖1 采樣點位置分布Fig.1 Sampling sites position

1 材料與方法

1.1 樣品采集

土壤樣品的采集地點為長春(C)、德惠(D)、扶余(F)、公主嶺(G)和永吉(Y),采集時間為2012年4月.運用網(wǎng)格布點法,以網(wǎng)格中心點為中心確定50 m×50 m的采樣區(qū),每個區(qū)域采集5個表層土(0～15 cm)樣品進行混合.采集土壤樣品均為黑鈣土,土壤樣品采集后用鋁箔密封,在實驗室冷藏保存.采樣點位置如圖1所示.

1.2 土壤DDTs和HCHs的提取與凈化

將風干土樣去除雜質后置于清潔木板上,磨碎過60目篩,用四分法取足量樣品于棕色玻璃瓶中密封備用,在一定時間內完成提取DDTs和HCHs.準確稱量15 g土樣和3 g無水硫酸鈉置于40 mL玻璃離心管中,加入10 mL丙酮和10 mL正己烷,密封離心管,在50 ℃,400 W功率下超聲波萃取 20 min,靜置冷卻5 min后以3 000 r/min離心3 min,再靜置5 min后轉移有機相至100 mL的磨口玻璃瓶中,上述萃取過程重復提取2次,將所得溶液混合,在旋轉蒸發(fā)儀上(≤30 ℃)濃縮至約為1 mL后,分次加入正己烷10～15 mL置換溶劑,再濃縮至約為1 mL.將濃縮液通過硅膠氧化鋁柱進行凈化(6 cm氧化鋁和12 cm中性硅膠),先用5 mL正己烷淋洗層析柱,棄去,再用70 mL(V(正己烷)∶V(二氯甲烷)=7∶3)混合溶劑淋洗,收集并濃縮洗脫液至1 mL,將其置于2 mL樣品瓶中,待測.

1.3 DDTs和HCHs的測定

用具有電子捕獲檢測器的氣相色譜(GC-ECD)分析土壤中DDTs和HCHs,儀器控制條件及儀器參數(shù)如下：毛細管色譜柱AgilentDB-17MS(30 m×0.25 mm×0.25 μm),進樣口溫度為300 ℃,分流比為10進樣,進樣量2 μL,載氣為氮氣,恒流模式,流速為4.0 mL/min,檢測器的溫度為320 ℃.程序升溫：初始溫度80 ℃,保持1 min;以30 ℃/min升溫至180 ℃,保持1 min;再以3 ℃/min升溫至205 ℃,保持4 min;最后以20 ℃/min升溫至290 ℃,保持2 min.

1.4 分析質量控制方法

1) 加標樣：每個采樣區(qū)域樣品測試時需帶一個待測樣添加標樣；2) 空白樣：每個土壤樣品分析樣帶一個空白樣,以確定容器的清潔程度；3) 平行樣:每個采樣區(qū)域樣品測試時做2～3個平行樣,以保證測定結果的再現(xiàn)性.

2 結果與討論

2.1 土壤中有機氯農(nóng)藥殘留狀況及來源分析

研究區(qū)域土壤樣品的OCPs和TOC測定結果列于表1.

表1 各采樣點OCPs和TOC的質量比(ng/kg)*Table 1 Mass concentration (ng/kg) of OCPs and TOC at different sampling sites

*nd表示未檢出.

由表1可見:HCHs和DDTs在各采樣點土壤中的檢出率較高,其中α-HCH檢出率為48%,β-HCH檢出率為45%,γ-HCH檢出率為71%,表明γ-HCH為土壤中HCHs的主要殘留物;P,P′-DDD檢出率為90%,P,P′-DDE檢出率為81%,P,P′-DDT檢出率為58%,表明P,P′-DDD和P,P′-DDE為土壤中DDTs的主要殘留物;HCHs在長春采樣點土壤中的質量比為10 950 ng/kg,低于北京城市和郊區(qū)土壤中的38 200 ng/kg[14],HCHs在公主嶺和永吉采樣點土壤中質量比為5 198,5 003 ng/kg,與北京官廳水庫的5 100 ng/kg[15]相近,低于太湖流域的7 800 ng/kg[16],其在德惠和扶余采樣點土壤中質量比為3 438,2 024 ng/kg,低于上述區(qū)域,但遠高于香港市內與農(nóng)村土壤中的520 ng/kg[17];表1所列采樣點的DDTs質量比均符合《土壤環(huán)境質量標準》一級標準.北京城市與郊區(qū)土壤中DDTs的質量比為5 800 ng/kg[14],低于長春采樣點土壤中的10 950 ng/kg,德惠、扶余、公主嶺和永吉采樣點土壤中DDTs的質量比分別為3 437.96,2 024.26,5 198,5 002 ng/kg,高于北京和上海農(nóng)田土壤中DDTs的質量比[16,18],但遠小于國外的某些地區(qū)[19-21].長春、德惠、公主嶺和永吉采樣點土壤中α-HCH/γ-HCH的平均值為0.37,表明大部分采樣點可能有林丹輸入;若P,P′-DDT/(P,P′-DDD+P,P′-DDE)>1,則表明土壤中近期有新的DDTs輸入[22].由長春、德惠、扶余、公主嶺和永吉采樣點土壤中P,P′-DDT/(P,P′-DDD+P,P′-DDE)平均值分別為0.47,0.87,0.15,1.22和0.25可見,除公主嶺外,其他采樣點土壤中的DDTs類物質主要來自歷史殘留物.

圖2為3種HCHs異構體在不同采樣點的組成特征.由圖2可見,α-HCH,β-HCH和γ-HCH所占質量分數(shù)平均值分別為18.00%,31.05%和50.94%,即γ-HCH所占比例較高.圖3為3種DDTs異構體在不同采樣點的組成特征.由圖3可見,P,P′-DDD、P,P′-DDE和P,P′-DDT所占質量分數(shù)平均值分別為 35.54%,38.04%和26.42%,即P,P′-DDD和P,P′-DDE所占比例較高.

圖2 吉林省中北部土壤中HCHs的組成特征Fig.2 Isomer composition of HCHs in the soils of the north and centre of Jilin Province

圖3 吉林省中北部土壤中DDTs的組成特征Fig.3 Isomer composition of DDTs in the soils of the north and centre of Jilin Province

2.2 不同采樣點表層土壤有機氯農(nóng)藥分布特征

應用SPSS17.0軟件對5個區(qū)域采樣點表層土壤中有機氯農(nóng)藥的平均質量比進行因子分析和系統(tǒng)聚類分析,結果分別列于表2和表3.由表2可見,采樣區(qū)域的6種有機氯農(nóng)藥中六六六類以γ-HCH為主要污染物,滴滴涕類以P,P′-DDT為主要污染物.由表3可見:當劃分為3類時,長春為第一類,德惠、公主嶺和永吉為第二類,扶余為第三類；當劃分為2類時,長春為第一類,德惠、扶余、公主嶺和永吉為第二類.表明長春區(qū)域的土壤污染最重,明顯高于其他區(qū)域,這與長春區(qū)域曾大量施用有機氯農(nóng)藥有關.

表2 不同類型有機氯農(nóng)藥成分得分系數(shù)矩陣Table 2 Component score of coefficient matrix of different types of organochlorine pesticides

表3 聚類成員統(tǒng)計Table 3 Statistics of cluster members

圖4 土壤中OCPs與TOC的關系Fig.4 Relationship between OCPs and TOC in the soils

2.3 影響土壤中有機氯農(nóng)藥質量比的因素

有機氯農(nóng)藥屬于憎水性有機物,其辛醇-水分配系數(shù)較高,因而可以快速通過分配作用進入土壤的有機顆粒中[23].圖4為各采樣點土壤中OCPs與TOC的關系.由圖4可見,OCPs與TOC呈顯著的正相關(r=0.93,p<0.05),表明土壤中有機氯農(nóng)藥的質量比與土壤中的有機質質量比有關.

綜上,本文可得如下結論:

1) 在吉林省5個區(qū)域的31個表層土壤樣品中,OCPs的質量比為1.45～83.88 ng/g,HCHs的質量比為1.17～27.83 ng/g,DDTs的質量比為1.45～81.75 ng/g.OCPs總體分布為長春>公主嶺>永吉>德惠>扶余.OCPs與TOC呈顯著正相關.

2) 吉林省5個區(qū)域α-HCH/γ-HCH的平均值為0.37,表明大部分采樣點可能有林丹輸入；除公主嶺外,土壤P,P′-DDT/(P,P′-DDD+P,P′-DDE)的比值都小于1,表明土壤中的DDTs類物質主要來自歷史殘留物.公主嶺市農(nóng)田采樣點可能受到工業(yè)DDTs影響.

3) 因子分析和系統(tǒng)聚類分析表明,長春區(qū)域污染明顯高于其他區(qū)域,污染物因子分析表明,六六六類以γ-HCH為主要污染物,滴滴涕類以P,P′-DDT為主要污染物.

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