零价铁的应用在水和土壤中甲草胺和甲霜灵系统的吸附行为的影响.docx

课后翻译内容 学院： 专业： 班级： 学号： 姓名：时间2016年4月25日1零价铁的应用在水和土壤中甲草胺和甲霜灵系统的吸附行为的影响摘要： 甲草胺和甲霜灵污染环境和农业水土系统对人类健康造成潜在威胁，然而，农药吸附量的信息（q）在水和土壤系统中的关系是有限的。因此，作甲草胺和甲霜灵在系统中受零价铁的应用影响吸附行为（ZVI，Fe0）和使用农药吸附Q/I关系研究。在系统处理铁后，甲草胺迅速下降，浓度消失约在57天；而甲霜灵的浓度在28天的实验期间约减少4045%。特别是，铁吸附更多的甲霜灵在水溶液体系中比在土壤溶液体系在水和土壤溶液随铁处理甲草胺浓度急剧下降，而在其减甲霜灵浓度相对缓慢。土壤中的农药溶液体系的吸附机理表现为多部位吸附Q /I拟合，缓冲能力（BC）的农药在所有吸附位点铁处理增加。在沙土中的BC值随ZVI升级应用率，砂质土壤比粘质土壤的值高。此外，在应用铁甲草胺浓度的变化是由于脱氯和吸附；而甲霜灵的浓度取决于吸附反应。因此，该农药吸附Q/I关系不同，系统被严重影响。简介： 农药可以成为一种主要的污染源，因为它们在农业中仍然被广泛使用，许多泄漏和农药及相关的事故发生在农场。因此，在土壤系统的农药污染的极大关注。甲草胺（2-chloro-20，60-diethyl-n -（甲氧基甲基）苯胺），一种酰胺类除草剂和内分泌干扰物，广泛用于控制阔叶杂草和禾本科杂草和农作物已被定性为“可能的人类致癌物（Nowell和雷塞克1994；李和本森2004；崔等人。2009年）。甲霜灵（甲基-（2，6 -二甲基-苯基）-（20methoxyacetyl）- DL丙氨酸），phenylamide杀菌剂以及残余和系统性活动，是用来治疗你的种子，叶面喷雾，和土壤的应用（沙龙和爱丁顿费尔南德斯等人1982年；2003年）。农药已广泛应用于农田、韩国高尔夫球场（刘某和郑2002；基姆等人。2006）。与专业C农药土壤和水的污染造成人体健康密切相关的环境和农业系统的潜在威胁。由于这些原因，科学家们的研究方法在有机基质的吸附去除农药、生物和化学降解（例如，零价铁（ZVI），联合应用。金等，2006；Bezbaruah等，2009年；汤普森等人，2010年），和植物修复（Wilson等。2001年）去了解他们的行为和命运在土壤和水环境（沙龙和爱丁顿费尔南德斯等人1982年；2003年和2004；李森. 卡等。2006年；Mamy和Barriuso；2007）。在土壤中的溶液体系，和甲草胺和甲霜灵生物吸附可与粘土含量、有机质、相关的表面积，和阳离子吸附容量（Peter和韦伯1985；夏尔马和Awasthi 1997；科斯基宁等人。2003剑鱼等。2005）。粘土和有机质含量的增加，增加其生物利用度和甲草胺的吸附降低（Peter和韦伯1985）；然而，对甲霜灵的吸附是依赖在粘土含量比土壤有机质含量（夏尔马和Awasthi 1997）。 在一般情况下，吸附解吸，缓冲能力退化和浪费，缓冲能力可以用来评价有机和无机化学物质在土壤溶液体系中的命运和行为。特别是，缓冲容量的概念用于对系统中使用的重要因素获得的污染物可能清晰，数量和强度（琳赛，1979）。然而，在影响铁的甲草胺和甲霜灵的吸附/脱附量强度中的应用（Q/I）在土壤和水系统的关系进行了评估。 因此，本研究的目的是探讨铁应用对甲草胺和水和土壤中甲霜灵浓度的变化并探讨使用农药的吸附等温线的Q /I在不同土壤溶液体系中甲草胺和甲霜灵行为的影响。材料与方法： 农药和零价铁 甲草胺的参考标准（2氯2，6二乙基N（甲氧基甲基）乙酰苯胺，纯度99.9%）和甲霜灵（甲基-N-（2-甲氧基乙酰基）-N-（2,6-二甲苯基）-DL-丙氨酸，纯度96.6%）从公司购买ehrenstorfer博士（奥格斯堡，德国）。所有的溶剂和化学品使用的高效液相色谱法和分析等级分别。 无双零价铁（ZVI；未底特律，MI，USA）进行。体积密度、粒子密度、孔隙率、规范表面积和平均粒径分布的铁2.43 g cm-3，7.15 g cm-3，66%，0.055 m2 g-1，195.73（杨等，2005）土壤 表面15厘米的两种不同的土壤，全北壤粘土（CCL）和全北壤质砂土（CLS）的土壤进行了研究。土壤是全北国立大学（韩国）从收全州收集实验的。土壤样品风干、粉碎通过2mm筛选定的土壤的物理和化学性质，如表1所示。通过改变程序的基础上的usda-scs和Tanner和杰克逊的方法测定粒度分布（- 1993）。测定（连二亚硫酸钠-柠檬酸提取）铁的方法由奥尔森和埃利斯所描述的决定（1982）。利用土壤和pH计测定水比1:5土壤pH（猎户座3星，热科学）。其他土壤性质进行了测定，使用的方法，建议由农村发展管理，韩国（2000）。用1 M醋酸铵测定阳离子交换（CH3COONH4，pH 7）由秋林滴定法测定土壤有机质的含量。程序确定甲草胺和甲霜灵含量的变化 一组样品的制备确定每天的变化，甲草胺或甲霜灵在水和土壤系统的内容。整整20毫升的10 mg L-1甲草胺或甲霜灵溶液放入50毫升离心管有或无0.5克铁（Fe0）。另外，10克（干基）覆土或无0.5克铁是重到50毫升离心管和治疗用20毫升的10 mg L-1甲草胺或甲霜灵溶液的混合物，搅拌的往复振动筛2小时，每一天在120转的速度，并在0，1，3，5，7，14，和28天采取的样品。 搅拌后，悬浮样品离心10 min，使铁/铁沉积物和土壤上清液450009g（清除农药溶液）。 样品的其他设置也准备研究在系统中甲草胺和甲霜灵含量的变化是由不同数量的铁应用的影响。整整20毫升的10 mg L-1甲草胺或甲霜灵溶液放入50毫升离心管有或没有0，0.1，0.25，0.5，和1克铁。另外，10克铜板的土壤样品（绝干基）被称为50毫升离心管中，用20毫升10毫克L-1甲草胺或甲霜灵溶液中添加0、0.1、0.25、0.5处理，和1克铁的混合物被放置在一个倒数的振动筛和24小时，在一个120转的速度，动摇。悬浮液离心10分钟，分离450009g之间的铁/土壤中铁和上清液，所有样品一式三份。 在确定分离的子样本的甲草胺和甲霜灵内容程序，铁/土壤中铁和上清液，在莫迪的农药研究所提出的方法（农村发展局、韩国1992）。确定农药浓度的气相色谱分析用的是休利特帕卡德4890和5890型气相色谱仪（GC）进行电子捕获检测器（ECD）甲草胺和氮磷检测器（NPD）分别为甲霜灵。休利特帕卡德4890型气相色谱仪，色谱柱为高性能（HP-1）毛细管柱（0.32毫米直径9长度25 m，0.52m厚度）。惠普5890气相色谱NPD模型，列为高性能（惠普-双毛细管柱（1）0.32毫米直径的长度LM 9 25 m，厚0.25）。 同时，用酸度计测定pH值和水系统含有甲草胺和氯离子浓度的铁（猎户座，热科学）和离子色谱（dionox，IC 1000）由Zvi验证甲草胺脱氯。甲草胺和甲霜灵在土壤中的吸附曲线 十克土，覆铜板和CLS，称重为50 mL聚丙烯离心管和20毫升的甲草胺、甲霜灵溶液（0，0.5，1，2.5，5，10，20，50，和100 mg L-1）和铁（0，0.5，1，和2克）。混合物放在往复式摇床孵育24 h的速度在每分钟120转。平衡后，混合液的上清液和沉淀物分离（土铁）由上述的离心。上清液中甲草胺、甲霜灵的浓度（土壤溶液）和沉积物进行强度（I）和量（Q）的因素，分别在土壤溶液体系中的农药的缓冲能力（公元前）进行了评价从农药的吸附曲线的斜率与选定的物理性质的土壤如下：BC是农药的缓冲能力，高压测量体积含水量（m3m-3），Q是容重（kgL-1，加入铁引起的差异被忽略），和分配系数KD系数（Lkg-1），是由下面的方程得到：其中Q是农药量因子（mgkg-1），我是农药的强度因子（毫克/升），和B是一个常数（安德森和克里斯坦森，1988；范雷斯等人。1990；党等。1994；李和杜利特2004，2006；李和安2010）。结果与讨论：零价铁对甲草胺和水和土壤系统甲霜灵浓度的影响 无铁应用甲或甲霜灵浓度日变化水系统示于图1。两种农药的浓度逐渐降低，约1520%的初始浓度在测试日（从0到28天）无铁处理。 然而，随着铁中的应用（0.5 g，1:20重量/体积比），农药浓度明显明显下降。甲草胺的总浓度在铁的应用第一天降低约40%，不断减少，并最终5天左右未检测到铁。另一方面，甲霜灵减少25%在第一天，然后略有下降，土壤溶液中的系统（图2）没有铁的应用，甲草胺和甲霜灵的浓度在前7天分别降低了45%和2530%，可以忽略实验期间休息期间。此外，在水系统，铁处理土壤溶液系统中甲草胺和甲霜灵的减少（0.5克，1:10:20 W / W /体积比）显示值的趋势非常相似，根据这些结果，土壤中主要反应初期一定量的甲草胺和甲霜灵（在第一天，2小时的平衡反应）和铁也不断减小直至完全消失。 吸附和脱氯甲草胺的影响不同数量的铁在系统中的应用进行了研究（图3）。水体系中重要的甲草胺浓度的铁增加量明显下降。甲草胺的减少主要是由脱氯，即使铁表面吸附的发生。在这个系统中，用了0.25克铁与高铁（ 0.25 g）处理甲草胺，逐渐增加，铁表面吸附（2500:1在绝对量W / W比）略有下降。 在土壤溶液体系中，甲草胺浓度显著随铁的应用明显减少，尤其是相对较低的零价铁（0.5 g）治疗水平。在这种情况下，在溶液中甲草胺含量的下降是由土壤表面的吸附作用增强。然而，随着铁处理甲草胺逐渐降低土壤铁表面的吸附。总甲草胺含量受土壤吸附的减少是由于增加铁量增加甲草胺脱氯。类似的结果在水及土壤，异丙甲草胺；异丙甲草胺氯，零价铁（舒适等。2001）。零价铁氧化物脱氯在水系统中甲草胺含量变化相关的额外的证据，如图4所示。溶液的pH值和氯离子（Cl-）浓度显著增加量铁在水溶液体系中明显增加因为在好氧或厌氧条件下产生的氢氧根离子（OH-）零价铁的氧化反应和甲草胺的还原脱氯发生反应（式3）与金属铁的氧化在铁的表面一组（公式4）如下（Eykholt和Davenport 1998）：然而，在溶液浓度的甲霜灵铁和/或土壤表面吸附的含量成反比（图3）。这些结果表明，在水或土壤溶液浓度的降低是甲霜灵的主要取决于铁和土壤表面的在水溶液体系中，甲霜灵含量的吸附在铁表面的比例增加与添加较高量的铁。在水溶液体系中，甲霜灵含量的吸附在铁表面的比例增加与添加较高量的铁。然而在土壤溶液中，吸附系统，甲霜灵的内容可能不严重受铁的补充，尤其是铁的应用量较低，由于甲霜灵铁表面吸附的内容会与土壤表面的吸附量相比是最小的。另外，在土壤中的解决方案，系统的解决方案，甲霜灵浓度下降低于水系统，即使有大量的铁的应用。此外，在水溶液体系中甲霜灵浓度接近或低于土壤溶液体系虽然铁表面的吸附量均低于土壤溶液中的铁含量和土壤吸附系统。低浓度甲霜灵在水系统是由较高的自然损耗和降解甲霜灵系统与土壤溶液的系统相比，由于甲霜灵水半衰期一般较短的土壤。此外，铁吸附反应是在水溶液体系中甲霜灵远高于土壤系统。零价铁对农药的吸附量的影响强度（Q/I）关系的土壤 农药的吸附量强度（Q/I）曲线装置在受不同数量的铁在土壤中的解决方案，系统的应用如图5。甲草胺和甲霜灵的装置出现多吸附曲线，这是由目标农药吸附密度差异引起的（农药浓度/特殊表面土壤和ZVI）异构平衡土壤吸附位点在土壤溶液体系。对农药吸附Q/I关系的铁在土壤系统中的应用影响参数见表2，系数测定系数（R2）为多点吸附Q /装置农药的范围从0.880到0.999在1区和0.953区的吸附位点在2到0.999。分配系数（Kd），有效的比例浓度的吸附和溶液相，对农药在土壤中的解决方案系统的变化与不同数量的铁的应用。甲草胺的Kd值范围从低到高的215 L G-1 3608 L G-1，而甲霜灵的Kd值介于110至2680升-1。thekd值的缓冲能力的价值观密切相关（BC），描述了使用Q的因素。计算值年甲草胺3383608和1734208的甲霜灵在土壤中的解决方案系统。农药的KD和BC值均显著显著高于区域1的吸附位点比区域2个站点。同时，BC农药值明显显著高于粘土（CCL）溶液体系中比在砂质土壤（CLS）-无铁应用系统解决方案。施瓦布等人。（2006）也报告了类似的结果，吸附系数分别为4甲草胺的20倍，壤土和沙壤土比含沙质的土壤。然而，BC值明显ZVI的吸附位点施用后明显增加，区域1和2，在土壤中的解决方案系统。在沙土中的BC值高（CLS）与粘土相比（CCL）系统，特别是在区域1的吸附位点。即，在沙质土壤系统BC农药值均大幅升级增加铁的应用率。因此，这些结果表明，联合应用严重影响农药的吸附Q/I关系土壤溶液中的系统。结论：在这项研究中，影响应用程序的行为作为水中甲草胺和甲霜灵和两个不同的土壤系统使用的农药吸附Q/I关系的评价。两种农药在水和土壤系统中的浓度下降，由于自然降解和/或吸附机理。当应用在零价铁系统，几乎检测不到5天的铁甲草胺溶液浓度。然而，甲霜灵的浓度逐渐降低在前7天，然后下降到可以忽略不计，实验期结束。此外，最初在土壤溶液系统的甲草胺和甲霜灵的浓度分别为45和25%，分别减少了，由于土壤表面吸附反应的第一天，因此，在水和土壤中的溶液与铁在系统应用相关的甲草胺浓度的降低都脱氯是铁土壤表面的吸附造成的。甲霜灵浓度发生的变化主要是由于只有铁土壤表面的吸附。另一方面，农药的吸附量强度（Q/I）装置出现多处的吸附曲线。分配系数（Kd）和有效缓冲能力（BC）在土壤系统的农药明显显著高于区域1的吸附位点比区域2和铁的应用及土壤性质的不同量的不同。农药BC值均显著高于粘质土壤系统，沙质土壤系统无铁的应用。然而，BC值在零价铁的吸附位点施用后明显增加。在这种情况下，BC值均显著高于沙质土壤，粘质土壤由于沙质土壤系统BC农药值均大幅升级，增加铁的应用率。即，铁严重影响土壤溶液系统中农药吸附Q/I的关系。参考文献：略原文：Impacts of zerovalent iron application on the adsorption behavior of alachlor and metalaxyl in water and soil systemsAbstract Alachlor and metalaxyl contaminations of environmental and agricultural water and soil systems cause potential threats to human health. However, information on the pesticide adsorption quantityintensity (Q/I) relationships in water and soil systems is limited. Therefore, adsorption behavior and the fate of alachlor and metalaxyl in the systems as inuenced by the application of zerovalent iron (ZVI, Fe0) were investigated using the pesticide adsorption Q/I relationships. After treating ZVI in the systems, the concentration of alachlor rapidly decreased within a few days and then it disappeared at approximately 57 experiment days; whereas metalaxyl concentration was reduced by approximately 4045% during the 28 day experimental period. In particular, ZVI adsorbed more metalaxyl in the aqueous system than in the soil-solution system. The alachlor concentration in the water and soil solution drastically decreased with increasing ZVI treatment, while metalaxyl concentration was relatively slow in its decrease. Adsorption mechanism of the pesticides in the soil-solution system was shown as multiple-site adsorption Q/I tting. Buffering capacity (BC) of the pesticides increased with ZVI treatment in all sorption sites. The BC values in sandy soil were escalated with increasing ZVI application rates, so that the values were rather higher in sandy soil than in clayey soil. In addition, changes in alachlor concentration with applying ZVI were due to both dechlorination and adsorption; whereas metalaxyl concentration was dependent upon adsorption reaction. Thus, thepesticide adsorption Q/I relationships in different soilsolution systems were critically affected by the ZVI treatment.Keywords Alachlor Metalaxyl Zerovalent iron Adsorption Buffering capacity Quantity-intensityIntroductionPesticides can be a major contamination source because they are still used extensively in agriculture. Many spills and accidents related to pesticides occur around and on farmsteads. Thus, the pesticide contamination in soilsolution systems is of great concern. Alachlor (2-Chloro-20, 60-diethyl-N-(methoxymethyl)acetanilide), a chloroacetanilide herbicide and endocrine disruptor, is widely used to control broadleaf and grass weeds in agricultural crops and has been characterized as probable human carcinogen (Nowell and Resek 1994; Lee and Benson 2004; Choi et al. 2009). Metalaxyl (Methyl N-(2,6-dimethyl-phenyl)-N-(20methoxyacetyl)-DL-alaninate), a phenylamide fungicide with residual and systemic activity, is used as seed treatment, foliar spray, and soil application (Sharom and Edgington 1982; Fernandes et al. 2003). Both pesticides have been widely used in farmlands and golf courses in Korea (Ryu and Jung 2002; Kim et al. 2006). The contaminations of soil and water with the specic pesticides cause potential threats to environmental and agricultural systems closely related to human health. For these reasons, scientists have studied methods to remove the pesticides using adsorption within the organic matrix, biological and chemical degradation (e.g., application of zerovalent iron (ZVI), Fe0; Kim et al. 2006; Bezbaruah et al. 2009; Thompson et al. 2010), and phytoremediation (Wilson et al. 2001) and tounderstand their behaviors and fates in soil and water environment (Sharom and Edgington 1982; Fernandes et al. 2003; Lee and Benson 2004; Khay et al. 2006; Mamy and Barriuso 2007). In the soil-solution system, the adsorption and bioavailability of alachlor and metalaxyl can be associated with clay content, organic matter, surface area, and cation adsorption capacity (Peter and Weber 1985; Sharma and Awasthi 1997; Koskinen et al. 2003; Dorado et al. 2005). As clay and organic matter content increase, the adsorption of alachlor increases and its bioavailability decreases (Peter and Weber 1985); however, the adsorption of metalaxyl was dependent more upon clay content than organic matter content of soil (Sharma and Awasthi 1997). In general, adsorption and desorption, degradation and dissipation, and buffering capacity can be used to evaluate the fate and behavior of organic and inorganic chemicals in soil-solution system. In particular, the concept of buffering capacity has been used to obtain the possible clearness of contaminants in the system using important factors, quantity and intensity (Lindsay 1979). However, the inuence of ZVI application on the alachlor and metalaxyl adsorption/desorption quantityintensity (Q/I) relationships in soil and water systems has not been evaluated. Therefore, the objectives of this study were to investigate the effects of ZVI application on the changes in alachlor and metalaxyl concentrations in water and soil and to examine the behavior of alachlor and metalaxyl in different soil-solution systems using the pesticide adsorption Q/I isotherms.Materials and methodsPesticides and zerovalent ironReference standards of alachlor (2-chlor-2,6-diethyl-N(methoxymethyl) acetanilide, purity 99.9%) and metalaxyl (methyl N-(2-methoxy acetyl)-N-(2,6-xylyl)-DL-alaninate, purity 96.6%) were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). All solvents and chemicals used were HPLC and analytical grades, respectively.Commercial peerless unannealed zerovalent iron (ZVI; Detroit, MI, USA) was used. Bulk density, particle density, porosity, specic surface area, and mean of particle-size distribution of ZVI were 2.43 g cm-3, 7.15 g cm-3, 66.0%, 0.055 m2 g-1, and 195.73 lm, respectively (Yang et al. 2005).SoilsSurface 15 cm of two different soils, Chonbuk clay loam (CCL) and Chonbuk loamy sand (CLS) soils, were used in this study. The soils were collected from experimental eld at Chonbuk National University, Jeonju, Korea. The soil samples were air-dried and crushed to pass a 2-mm sieve. Selected physical and chemical properties of the soils are shown in Table 1. Particle-size distribution was determined by a modied procedure based on the methods developed by the USDA-SCS and Tanner and Jackson (Malo 1993). Free (dithionite-citrate extractable) Fe was determined by the method described by Olson and Ellis (1982). Soil pH was measured using soil-to-water ratio of 1:5 with a pH meter (Orion 3 Star, Thermo Scientic). Other soil properties were determined using the methods recommended by Rural Development Administration, Korea (2000). Exchangeable cations were determined by use of 1.0 M ammonium acetate (CH3 COONH4, pH 7.0). Soil organic matter content was determined by Tyurin titrimetric method.Procedures for determining alachlor and metalaxyl content changesA set of samples was prepared to determine the daily changes in alachlor or metalaxyl content in water and soilsolution systems. Exactly 20 mL of 10 mg L-1 alachlor or metalaxyl solution was placed into 50 mL centrifuge tubes with or without 0.5 g of ZVI (Fe0). Also, 10 g of CCL soil (oven-dry basis) with or without 0.5 g of ZVI was weighed into 50 mL centrifuge tubes and treated with 20 mL of 10 mg L-1 alachlor or metalaxyl solution. The mixtures were agitated on a reciprocal shaker for 2 h every day at a speed of 120 rpm, and samples were taken in 0, 1, 3, were centrifuged at 45,0009g for 10 min to separate the iron/soil-iron sediments and supernatant (clear pesticide solution). The other set of samples was also prepared to examine the changes in alachlor and metalaxyl contents in the both systems as affected by different amounts of ZVI application. Exactly 20 mL of 10 mg L-1 alachlor or metalaxyl solution was placed into 50 mL centrifuge tubes with or without 0, 0.1, 0.25, 0.5, and 1.0 g of ZVI. Also, 10 g of CCL soil samples (oven-dry basis) was weighed into 50 mL centrifuge tubes and treated with 20 mL of 10 mg L-1 alachlor or metalaxyl solution with or without adding 0, 0.1, 0.25, 0.5, and 1.0 g of ZVI. The mixtures were placed horizontally on a reciprocal shaker and shaken for 24 h at a speed of 120 rpm. The suspensions were centrifuged at 45,0009g for 10 min to separate between iron/soil-iron and supernatant. All samples were prepared in triplicate. Procedures for determining alachlor and metalaxyl contents in the separated subsamples, iron/soil-iron and supernatant, were modied from the methods proposed by Research Institute for Pesticides (Rural Development Administration, Korea 1992). To determine the pesticide concentrations, gas chromatographic analysis was conducted using Hewlett Packard 4890 and 5890 model gas chromatographs (GCs) with electron capture detector (ECD) for alachlor and with nitrogen-phosphorus detector (NPD) for metalaxyl, respectively. For Hewlett Packard 4890 model GC with ECD, the column was a high-performance (HP-1) capillary column (0.32 mm in diameter 9 25 m length, 0.52 lm thickness). For Hewlett Packard 5890 model GC with NPD, the column was a highperformance (HP-1) capillary column (0.32 mm in diameter 9 25 m length, 0.25 lm thickness). Also, pH and chloride ion concentrations in the water systems containing alachlor and ZVI were measured using a pH meter (Orion, Thermo Scientic) and ion chromatography (Dionox, ICS 1000) to verify the dechlorination of alachlor by ZVI.Adsorption curves for alachlor and metalaxyl in soilsTen grams of soils, CCL and CLS, were weighed into 50 mL polypropylene centrifuge tubes with 20 mL of the alachlor or metalaxyl solution (0, 0.5, 1.0, 2.5, 5.0, 10, 20, 50, and 100 mg L-1) and ZVI (0, 0.5, 1.0, and 2.0 g). The mixture was placed on a reciprocal shaker to equilibrate for 24 h at a speed of 120 rpm. After equilibration, the mixture was separated between supernatant and sediment (soil-iron) by the centrifugation described above. The concentrations of alachlor or metalaxyl in the supernatant (soil solution) and in the sediment were applied as intensity (I) and quantity (Q) factors, respectively. The buffer capacity (BC) of the pesticides in the soil-solution systems was evaluatedfrom the slope of the pesticide sorption curves with selected physical properties of the soils as follows: BC DQ=DI hv qKd 1 where BC is the pesticide buffering capacity, hv is the measured volumetric moisture content(m3 m-3), q is the bulk density (kg L-1, the difference caused by adding ZVI was ignored), and Kd is the distribution coefcient (L kg-1) that was obtained from the following equation: Q KdIb 2 where Q is the quantity factor of pesticide (mg kg-1), I is the intensity factor of pesticide (mg L-1), and b is a constant (Anderson and Christensen 1988; Van Rees et al. 1990; Dang et al. 1994; Lee and Doolittle 2004, 2006; Lee and Ahn 2010).Results and discussionEffects of ZVI on alachlor and metalaxyl concentrations in water and soil systemsDaily changes of alachlor and metalaxyl concentrations in aqueous system with or without ZVI application are presented in Fig. 1. The concentrations of both pesticides were gradually reduced by approximately 1520% of the initial concentrations during the test days (from 0 to 28 days) without ZVI treatment. However, with ZVI application (0.5 g, 1:20 w/v ratio), both pesticide concentrations signicantly declined. Alachlor decreased approximately 40% of total concentration within the rst day of ZVI application, kept dramatically decreasing, and nally was not detected at about 5 days after ZVI treatment. On the other hand, metalaxyl was reduced about 25% within the rst day of ZVI treatment and then slightly declined till the last test day. In soil-solution system (Fig. 2) without ZVI application, the solution alachlor and metalaxyl concentrations were reduced about 45% and 2530%, respectively, within the rst 7 days and then negligibly decreased during the rest of experimental period. In addition, the reductions in alachlor and metalaxyl in the soil-solution systems with ZVI treatment (0.5 g, 1:10