吉林省中北部农田土壤有机氯农药的残留特征

刘宝林,李 明,董炜华,花修艺,董德明,王彬彬

(1.吉林大学 环境与资源学院,长春 130012;2.长春师范大学 化学学院,长春 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

有机氯农药(OCPs)是环境中广泛存在的一种难降解有机物,具有高残留性和高生物富集性,对生态系统和人类健康具有潜在的威胁[1-4].六六六类(HCHs)和滴滴涕类(DDTs)在一些区域的土壤环境中残留较多[5-8],其危害已引起人们广泛关注[9-13].本文通过分析HCHs和DDTs在吉林省典型区域农田土壤中的分布特征,探讨其来源及对人类可能带来的环境风险,并研究其残留特征,为土壤修复和治理提供一定的理论依据.

图1 采样点位置分布Fig.1 Sampling sites position

1 材料与方法

1.1 样品采集

土壤样品的采集地点为长春(C)、德惠(D)、扶余(F)、公主岭(G)和永吉(Y),采集时间为2012年4月.运用网格布点法,以网格中心点为中心确定50 m×50 m的采样区,每个区域采集5个表层土(0～15 cm)样品进行混合.采集土壤样品均为黑钙土,土壤样品采集后用铝箔密封,在实验室冷藏保存.采样点位置如图1所示.

1.2 土壤DDTs和HCHs的提取与净化

将风干土样去除杂质后置于清洁木板上,磨碎过60目筛,用四分法取足量样品于棕色玻璃瓶中密封备用,在一定时间内完成提取DDTs和HCHs.准确称量15 g土样和3 g无水硫酸钠置于40 mL玻璃离心管中,加入10 mL丙酮和10 mL正己烷,密封离心管,在50 ℃,400 W功率下超声波萃取 20 min,静置冷却5 min后以3 000 r/min离心3 min,再静置5 min后转移有机相至100 mL的磨口玻璃瓶中,上述萃取过程重复提取2次,将所得溶液混合,在旋转蒸发仪上(≤30 ℃)浓缩至约为1 mL后,分次加入正己烷10～15 mL置换溶剂,再浓缩至约为1 mL.将浓缩液通过硅胶氧化铝柱进行净化(6 cm氧化铝和12 cm中性硅胶),先用5 mL正己烷淋洗层析柱,弃去,再用70 mL(V(正己烷)∶V(二氯甲烷)=7∶3)混合溶剂淋洗,收集并浓缩洗脱液至1 mL,将其置于2 mL样品瓶中,待测.

1.3 DDTs和HCHs的测定

用具有电子捕获检测器的气相色谱(GC-ECD)分析土壤中DDTs和HCHs,仪器控制条件及仪器参数如下：毛细管色谱柱AgilentDB-17MS(30 m×0.25 mm×0.25 μm),进样口温度为300 ℃,分流比为10进样,进样量2 μL,载气为氮气,恒流模式,流速为4.0 mL/min,检测器的温度为320 ℃.程序升温：初始温度80 ℃,保持1 min;以30 ℃/min升温至180 ℃,保持1 min;再以3 ℃/min升温至205 ℃,保持4 min;最后以20 ℃/min升温至290 ℃,保持2 min.

1.4 分析质量控制方法

1) 加标样：每个采样区域样品测试时需带一个待测样添加标样；2) 空白样：每个土壤样品分析样带一个空白样,以确定容器的清洁程度；3) 平行样:每个采样区域样品测试时做2～3个平行样,以保证测定结果的再现性.

2 结果与讨论

2.1 土壤中有机氯农药残留状况及来源分析

研究区域土壤样品的OCPs和TOC测定结果列于表1.

表1 各采样点OCPs和TOC的质量比(ng/kg)*Table 1 Mass concentration (ng/kg) of OCPs and TOC at different sampling sites

*nd表示未检出.

由表1可见:HCHs和DDTs在各采样点土壤中的检出率较高,其中α-HCH检出率为48%,β-HCH检出率为45%,γ-HCH检出率为71%,表明γ-HCH为土壤中HCHs的主要残留物;P,P′-DDD检出率为90%,P,P′-DDE检出率为81%,P,P′-DDT检出率为58%,表明P,P′-DDD和P,P′-DDE为土壤中DDTs的主要残留物;HCHs在长春采样点土壤中的质量比为10 950 ng/kg,低于北京城市和郊区土壤中的38 200 ng/kg[14],HCHs在公主岭和永吉采样点土壤中质量比为5 198,5 003 ng/kg,与北京官厅水库的5 100 ng/kg[15]相近,低于太湖流域的7 800 ng/kg[16],其在德惠和扶余采样点土壤中质量比为3 438,2 024 ng/kg,低于上述区域,但远高于香港市内与农村土壤中的520 ng/kg[17];表1所列采样点的DDTs质量比均符合《土壤环境质量标准》一级标准.北京城市与郊区土壤中DDTs的质量比为5 800 ng/kg[14],低于长春采样点土壤中的10 950 ng/kg,德惠、扶余、公主岭和永吉采样点土壤中DDTs的质量比分别为3 437.96,2 024.26,5 198,5 002 ng/kg,高于北京和上海农田土壤中DDTs的质量比[16,18],但远小于国外的某些地区[19-21].长春、德惠、公主岭和永吉采样点土壤中α-HCH/γ-HCH的平均值为0.37,表明大部分采样点可能有林丹输入;若P,P′-DDT/(P,P′-DDD+P,P′-DDE)>1,则表明土壤中近期有新的DDTs输入[22].由长春、德惠、扶余、公主岭和永吉采样点土壤中P,P′-DDT/(P,P′-DDD+P,P′-DDE)平均值分别为0.47,0.87,0.15,1.22和0.25可见,除公主岭外,其他采样点土壤中的DDTs类物质主要来自历史残留物.

图2为3种HCHs异构体在不同采样点的组成特征.由图2可见,α-HCH,β-HCH和γ-HCH所占质量分数平均值分别为18.00%,31.05%和50.94%,即γ-HCH所占比例较高.图3为3种DDTs异构体在不同采样点的组成特征.由图3可见,P,P′-DDD、P,P′-DDE和P,P′-DDT所占质量分数平均值分别为 35.54%,38.04%和26.42%,即P,P′-DDD和P,P′-DDE所占比例较高.

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

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

2.2 不同采样点表层土壤有机氯农药分布特征

应用SPSS17.0软件对5个区域采样点表层土壤中有机氯农药的平均质量比进行因子分析和系统聚类分析,结果分别列于表2和表3.由表2可见,采样区域的6种有机氯农药中六六六类以γ-HCH为主要污染物,滴滴涕类以P,P′-DDT为主要污染物.由表3可见:当划分为3类时,长春为第一类,德惠、公主岭和永吉为第二类,扶余为第三类；当划分为2类时,长春为第一类,德惠、扶余、公主岭和永吉为第二类.表明长春区域的土壤污染最重,明显高于其他区域,这与长春区域曾大量施用有机氯农药有关.

表2 不同类型有机氯农药成分得分系数矩阵Table 2 Component score of coefficient matrix of different types of organochlorine pesticides

表3 聚类成员统计Table 3 Statistics of cluster members

图4 土壤中OCPs与TOC的关系Fig.4 Relationship between OCPs and TOC in the soils

2.3 影响土壤中有机氯农药质量比的因素

有机氯农药属于憎水性有机物,其辛醇-水分配系数较高,因而可以快速通过分配作用进入土壤的有机颗粒中[23].图4为各采样点土壤中OCPs与TOC的关系.由图4可见,OCPs与TOC呈显著的正相关(r=0.93,p<0.05),表明土壤中有机氯农药的质量比与土壤中的有机质质量比有关.

综上,本文可得如下结论:

1) 在吉林省5个区域的31个表层土壤样品中,OCPs的质量比为1.45～83.88 ng/g,HCHs的质量比为1.17～27.83 ng/g,DDTs的质量比为1.45～81.75 ng/g.OCPs总体分布为长春>公主岭>永吉>德惠>扶余.OCPs与TOC呈显著正相关.

2) 吉林省5个区域α-HCH/γ-HCH的平均值为0.37,表明大部分采样点可能有林丹输入；除公主岭外,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类物质主要来自历史残留物.公主岭市农田采样点可能受到工业DDTs影响.

3) 因子分析和系统聚类分析表明,长春区域污染明显高于其他区域,污染物因子分析表明,六六六类以γ-HCH为主要污染物,滴滴涕类以P,P′-DDT为主要污染物.

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