昆承湖沉积物重金属的环境地球化学特征

对昆承湖9个采样点柱状沉积物中主要重金属元素(Pb,Cu,Zn,Cd,Cr)的垂向分布进行了测定,结果表明,5种重金属元素具有非常相似的垂向变化特征,表现为随沉积深度增加含量降低的态势;横向上表现为靠近污染源的含量高,远离污染源的含量低。各重金属元素均与TOC之间呈显著正相关关系,表明沉积物中重金属污染受人类活动作用较为明显。地积累指数评价结果显示,Zn污染最重,且污染主要集中在表层;潜在生态风险性指数反映出全湖沉积物中的重金属污染属于中等生态危害程度,Cd是最主要的生态危害元素;生物毒性效应评价则表明目前昆承湖沉积物的金属毒性效应不高,但各样点的ΣTUs都表现为由底层向表层逐渐增大的态势,必须予以相当的重视,避免加重该湖的生物毒性。     

鄱阳湖沉积物重金属生态风险评价：SQGs和AVS-SEM模型法

鄱阳湖是我国最大的淡水湖,对我国长江中下游平原的水体环境有着重大影响。2018年测定了鄱阳湖表层沉积物中Cd、Zn、Cu、Pb的含量,并采用沉积物质量基准法(SQGs)和酸可挥发性硫化物(AVS)-同步可提取态金属(SEM)模型法评价了其生态风险。研究发现:鄱阳湖沉积物中4种重金属Cu、Pb、Zn、Cd的平均值分别是其背景值的1.58、1.18、1.30、8.87倍;AVS浓度范围为0.101～0.887μmol g-1,平均值为0.278μmol g-1;而SEM浓度范围为0.281～2.170μmol g-1,平均值为0.803μmol g-1。依据沉积物基准法计算,重金属风险值为0.15～0.23,表明具有一定的风险毒性;[SEM-AVS]模型法评价结果表明也具有一定的潜在生态风险,但若用考虑有机碳的修正模型[SEM-AVS]/foc评价结果则其无生态风险;相对而言,整个湖区风险较高的地点为三江口(S11、S12)和饶河口(S16、S17)。     

昆承湖沉积物重金属的环境地球化学特征

对昆承湖9个采样点柱状沉积物中主要重金属元素（Pb,Cu,Zn,Cd,Cr）的垂向分布进行了测定,结果表明,5种重金属元素具有非常相似的垂向变化特征,表现为随沉积深度增加含量降低的态势;横向上表现为靠近污染源的含量高,远离污染源的含量低。各重金属元素均与TOC之间呈显著正相关关系,表明沉积物中重金属污染受人类活动作用较为明显。地积累指数评价结果显示,Zn污染最重,且污染主要集中在表层;潜在生态风险性指数反映出全湖沉积物中的重金属污染属于中等生态危害程度,Cd是最主要的生态危害元素;生物毒性效应评价则表明目前昆承湖沉积物的金属毒性效应不高,但各样点的∑TUs都表现为由底层向表层逐渐增大的态势,必须予以相当的重视,避免加重该湖的生物毒性。     

乐清湾养殖区表层沉积物重金属含量分布及污染评价

以乐清湾养殖区表层沉积物中Cu等7种重金属为研究对象,在野外实地调查取样及重金属含量测定基础上,以中国海洋沉积物质量(GB18668-2002)一类标准值为评价标准,利用单因子指数评价法、内梅罗综合污染指数评价法和沉积物质量基准(sediment quality guideline,SQG),对单项重金属污染程度、多种重金属综合污染效应及重金属潜在生物毒性风险进行了评价。结果表明,乐清湾养殖区表层沉积物重金属含量分布差别明显,所有采样点表层沉积物均受到Cu污染,局部受到严重Hg污染;大部分养殖区表层沉积物重金属污染达到轻度等级;所有养殖区均可发生由Cu偶尔引起的不利生物毒性效应,个别养殖区可发生由Hg频繁引发的不利生物毒性效应。乐清湾养殖区表层沉积物重金属主要来源于沿岸电镀企业废水排放及农药化肥造成的农业面源污染。开展Cu、Hg污染治理修复是实现乐清湾养殖环境安全的迫切需求。     

东平湖表层沉积物中多氯联苯的污染特征

[目的]查明东平湖表层沉积物多氯联苯(PCBs)的污染特征,为东平湖沉积物的污染控制及风险评价提供科学依据。[方法]于2015年7月对东平湖16个不同点位的表层沉积物进行采样,使用GC-ECD检测了PCBs(PCB28,PCB52,PCB101,PCB118,PCB153,PCB138,PCB180)的含量,对东平湖PCBs的空间分布进行分析。运用EPA法对东平湖表层沉积物中多氯联苯进行生态风险评价。[结果]东平湖表层沉积PCBs总的含量范围为nd～605.9ng/kg,均值为126ng/kg,标准差为153。在空间分布上,湖区中部(184.5ng/kg)入湖口(149.9ng/kg)湖区西南部(101.4ng/kg)湖区北部(46.7ng/kg)。研究区PCBs同系物组成以七氯联苯为主,占总量的66.72%。与其他地区的沉积物相比较,东平湖表层沉积物中PCBs处于较低水平,风险评价表明该研究区域生物毒性效应概率远远小于10%。[结论]由于水文因素的影响,东平湖表层沉积物中多氯联苯(PCBs)呈现出由大汶河入湖口向西北方向递减的空间分布趋势;东平湖表层沉积物中的多氯联苯属于轻微污染水平,未对水体环境安全造成严重影响,沉积物中PCBs的浓度水平对大多数底栖生物无毒性影响。     

北京市五环内绿地土壤4种重金属的形态特征及其生物有效性

[目的]了解北京市五环内绿地表层(0—20cm)土壤重金属(Cu,Cd,Pb和Zn)的形态特征及其生物有效性,为北京市绿地土壤重金属污染防治提供比较可靠的参考依据。[方法]在建成时间为2~400a的绿化区内共采集表层土壤样品151个,运用改进BCR提取法分析样品中重金属的赋存形态,而后通过风险评价编码法(RAC)和次生相与原生相分布比值法(RSP)对重金属生物有效性进行评估。[结果]样品中重金属Cu,Cd,Pb和Zn的含量分别为31.42,0.29,29.89,76.78 mg/kg,Cu,Zn在中部和东北部含量较高,Pb在中部地区含量较高,Cd在西北部、东北部和南部存在少量高值区。Cu,Cd,Pb和Zn形态分布的总体规律均为:残渣态可氧化态弱酸溶态可还原态,稳定态含量均远高于有效态,有效态含量比例表明重金属生物有效性大小顺序为:CdZnCuPb风险评价编码法(RAC)表明,Cd和Zn环境风险程度为低风险,Cu和Pb无环境风险。次生相与原生相分布比值法(RSP)显示,Cu,Cd,Pb和Zn元素RSP值分别为0.06,0.49,0.18,0.13,土壤整体上未受到重金属污染,但是有少部分地区存在被污染现象。[结论]北京市五环内绿地土壤总体上不存在重金属Cu,Cd,Pb和Zn污染,环境风险较低,但应对重金属赋存形态保持关注。     

巢湖表层沉积物中重金属污染的时空变化特征及潜在生态风险评价

2008年3月至7月连续对巢湖8个采样点的表层沉积物中Zn、Hg、Cr、Pb、Ni和Cu6种重金属含量进行分析,据此探讨巢湖表层沉积物中重金属污染程度及时空分布特征,评价巢湖重金属污染的潜在生态风险并筛选出主要生态风险因子。结果表明：3月至7月期间,全湖范围内表层沉积物中重金属含量逐渐降低,河流入湖区的污染程度高于其他区域,Zn、Cu、Pb的污染程度高于其他重金属,表层12cm沉积物中的重金属含量随深度增加污染情况呈加重趋势;从潜在生态风险角度分析,巢湖表层沉积物总体只具有轻微潜在生态风险,生态风险指数排名前两位的区域是南淝河入湖区和十五里河入湖区,3月至7月期间重金属潜在生态风险级别逐渐降低,巢湖生态安全主要风险因子为Hg,其次是Pb和Cu。     

水源涵养和生态保育清洁小流域河流沉积物重金属的特征及潜在风险——以董铺—大房郢水库为例

[目的]为了解安徽省合肥市饮用水源地水源涵养和生态保育清洁小流域(董铺水库和大房郢水库)汇水河流表层沉积物中重金属对下游水库的影响。[方法]在该区域3条主要汇水河流采集了23个沉积物样品,分别测定了沉积物中7种重金属(Zn,Cu,Cr,As,Cd,Pb和Hg)的含量,并采用潜在生态风险指数法(I_R)和地累积指数法(I_(geo))评估其潜在生态风险,主成分分析法解析其可能来源。[结果]研究区域重金属分布存在差异,As和Cd在泗水河上的C_1和C2两点含量超过了维护人体健康的土壤环境质量二级标准限值,且Cd在此两点的易利用态占比为34.97%和37.67%,具有较强的生物有效性;Cd生态风险指数普遍偏高,达强度等级,其中泗水河上的C_1和C2两点达极强等级;同时S_8点Hg生态风险达到强度等级,其余6种重金属生态风险水平较低。该区域重金属主要来自于人与自然混合源和人为源,贡献率分别为51.11%和27.70%。[结论]在泗水河下游流域Cd污染较为突出,为减小其对下游水库的影响,应加强Cd的污染治理。     

武汉市中小河流沉积物重金属污染特征及其生态风险

调查了武汉市9条中小河流表层沉积物中7种重金属的含量及其不同形态组成,并探讨了沉积物重金属污染的来源.研究结果表明,沉积物中7种重金属含量均超过武汉土壤背景值,污染程度中等,其中Cd,Zn和Hg富集严重;基于沉积物质量基准值.Cr,Ni和Zn是沉积物重金属污染生物毒性的主要贡献者;流经武汉市区的罗家渠、府河和巡司河重金属污染急性生物毒性较强.沉积物中不同重金属形态分布迥异,Cd的生物可利用态含量最高,其次为Zn,Ni和Cr,沉积物重金属来源复杂,相关分析和主成分分析表明,Pb和Cd可能主要来源于大气沉降和城市污水,Cr,Zn和Hg来源于金属加工冶炼.而As来源于岩石风化等地球化学过程.     

河口湿地沉积物中腐殖酸含量对外源重金属分布的影响研究

通过向不同腐殖酸含量的河口湿地沉积物添加人工配制的重金属污染海水,测定污染后沉积物的重金属总量与形态分布,以研究不同腐殖酸含量条件下外源重金属在水-沉积物系统中的转化。结果表明,腐殖酸含量对重金属在沉积物中的吸收量和形态组成有较大的影响,尤其对酸可提取态与可还原态。但是不同重金属之间有一定差别,腐殖酸含量对Cu,Pb的作用较明显,而对Zn,Cd的影响较小。此外,由于河口湿地沉积物处于较高盐度的环境,海水中的离子浓度影响有机质与金属的络合反应,因此与土壤相比,河口湿地沉积物中腐殖酸含量对重金属的生物有效性的影响有所不同。     

Effects of iron-ore mining and processing on metal bioavailability in a tropical coastal lagoon

Background, aim, and scope

In water systems, water quality and geochemical properties of sediments determine the speciation of trace metals, metal transport, and sediment–water exchange, influencing metal availability and its potential effects on biota. Studies from temperate climates have shown that iron-ore mining and tailing wastewaters, besides being a source of trace metals, usually show high levels of dissolved ions and particulate suspended matter, thus having the potential of indirectly changing metal bioavailability. For the first time in the tropics, we identified the effects of iron-ore mining and processing on metal bioavailability in a coastal lagoon. With an extensive sampling scheme, we investigated the potential sources of metals; the links among metal levels in water, sediments, and invertebrates; and the contrasting effects on metal speciation and bioavailability.

Methodology

The metals Fe, Mn, Al, Cr, Zn, Cu, Ni, Pb, Cd, Hg, and As were measured in water, sediments (surface and profiles), and invertebrates from Mãe-Bá Lagoon and in the sites directly influenced by the mining operations (tailing dams and nearby rivers). In addition, samples from two other lagoons, considered pristine, were analyzed. The study area is located in the southeast of Brazil (Iron Quadrangle Region and a coastal area of Espírito Santo State). General water characteristics included pH, dissolved organic carbon, alkalinity, and anion composition. Water metal speciation was assessed by a speciation model (Chemical Equilibria in Aquatic Systems). Grain-size distribution, organic carbon, carbonate, and acid volatile sulfide (AVS) were determined in sediments. Statistical methods included comparison of means by Mann–Whitney test, ordination and correlation analyses, and analysis of regression for geochemical normalization of metals with grain size.

Results and discussion

The dissolved metal concentrations, the total metal levels in sediments, and the normalization based on the fine sediment fraction showed that the mining operations constitute potential sources of Fe, Mn, Cr, Cu, Ni, Pb, As, and Hg to Mãe-Bá Lagoon. However, trace metal availability was reduced because of increased pH, hardness, and sulfide content (356 μmol/g) in the sites influenced by the mining. The lagoon showed similar water chemistry as in the mining sites, with metal bioavailability further decreased by the presence of dissolved organic carbon and chloride. Although AVS levels in the lagoon were low (0.48–56 μmol/g), metal bioavailability was reduced because of the presence of organic matter. Metal levels in invertebrates confirmed the predicted low metal bioavailability in Mãe-Bá Lagoon. The lagoon was considered moderately contaminated only by Hg and As.

Conclusions

The iron-ore mining and processing studied here constitute potential sources of metal pollution into the tropical lagoon. Contrary to expectations, however, it also contributes to reducing the overall metal bioavailability in the lagoon.

Recommendations and perspectives

These findings are believed to be useful for evaluating metal exposure in a more integrated way, identifying not only the sources of pollution but also how they can affect the components involved in metal speciation and bioavailability in water systems, leading to new insights.     

Mobilization Potential of Heavy Metals: A Comparison Between River and Lake Sediments

Toxic metals introduced into aquatic environments by human activities accumulation in sediments. A common notion is that the association of metals with acid volatile sulfides (AVS) affords a mechanism for partitioning metals from water to solid phase, thereby reducing biological availability. However, variation in environmental conditions can mobilize the sediment-bound metal and result in adverse environmental impacts. The AVS levels and the effect of AVS on the fate of Cu, Cd, Zn, Ni in sediments in the the Changjiang River, a suboxic river with sandy bottom sediment and the Donghu Lake, a anoxic lake with muddy sediment in China, were compared through aeration, static adsorption and release experiments in laboratory. Sips isotherm equation, kinetic equation and grade ion exchange theory were used to describe the heavy metal adsorb and release process. The results showed that AVS level in the lake sediment are higher than that of the river. Heavy metals in the overlying water can transfer to sediments incessantly as long as the sediment remains undisturbed. The metal release process is mainly related to AVS oxidation in lake sediment while also related to Org-C and Fe–Mn oxyhydroxide oxidation in river sediment. The effect of sulfides on Zn and Ni is high, followed by Cd, and Cu is easy bound to Org-C. AVS plays a major role in controlling metals activity in lake sediment and its presence increase the adsorption capacity both of the lake and river sediments.     

The Impact of Biochar Addition on Nutrient Leaching and Soil Properties from Tillage Soil Amended with Pig Manure

Poses dam in the Seine River estuary acts as receptacle of water drain-offs from highly urbanized and industrialized catchment area; therefore, this water is highly contaminated by trace metals. Most trace elements are mainly bound to particulate matter and are incorporated rapidly into the sediments. Scavenging of these metals in the sediments can be reversible due to several perturbations so as sediments also act as a source of pollutants for the overlying water. For instance, natural events (tide, flood, storm) and anthropogenic processes (water management actions) can cause disturbance of sediments and subsequent remobilization of pollutants to the water column, thereby posing a potential threat for aquatic organisms. The purpose of this study was to evaluate the mobility of trace metals by different methods in the Seine estuary sediments. The surface sediment sampled at Poses dam was characterized by high pollution level of Cd, Cu, Zn, and Pb. The estimation of metal bioavailability through ratio ΣSEM/AVS (simultaneously extracted metals/acid volatile sulfides) indicates a potential bioavailability of trace metals. The chemical partitioning using the European Community of Bureau of Reference sequential extraction method revealed that over 85, 82, and 80 % of the total Cd, Zn, and Pb, respectively, were found to be associated with the exchangeable and reducible fractions of the sediment. Another approach used consists in the quantification of dissolved metals released by sediment resuspension experiments in laboratory under controlled conditions. The results indicated that metals are released rapidly from sediment with a sharp peak at the beginning of the experiment, followed by a fast coprecipitation and/or adsorption processes on the suspended particles. Also, the Cd, Pb, and Ni mobility is higher compared to that of the other metals.     

应用相平衡分配法建立滇池沉积物金属环境质量基准

For the past 20 years, numerous studies have been carried out on the application of equilibrium partitioning approach （EqPA） for the derivation of sediment quality guidelines （SQGs）. However, for metals, few Equilibrium-partitioning- based numerical SQGs have been developed or are currently available because of the confounding factors mediating the bioavailability of metals. A study was conducted at Dianchi Lake, which is a heavily eutrophicated lake on the Yunnan- Guizhou Plateau, China with the focus on the measurement of partitioning coefficient （Kp） and SQGs derivation and normalization to acid volatile sulfide （AVS）, fine material, and organic carbon. Using new normalization methods, SQGs were formulated for seven metals including copper, zinc, lead, cadmium, chromium, mercury, and arsenic in Dianchi Lake. In Dianchi Lake sediments, the fine material contributed 25.4%-36.0% to the SQG values, with the largest contribution to the SQG value of mercury; AVS contributed 2.9%-75.0% to the SQG values, with the largest contribution to the SQG value of cadmium. This indicated that the fine material and the AVS were the most important controlling factors to the bioavailability of mercury and caximium, respectively. The contribution of total organic carbon （TOC） to the SQG values of copper and leaxi was 3.8% and 7.1%, respectively, indicating that at relatively lower concentrations, the contribution of TOC was not significant. In addition to normalization methods, appropriate procedures for the application of EqPA including sample collection, storage, and analysis are also essential to improve the reliability of SQGs. The normalized Dianchi Lake SQGs were higher than most of the empirically based SQGs developed in North America, but lower than Hong Kong interim SQGs except for cadmium and arsenic. The differences could be attributed to the approaches used for derivation of SQGs and the water quality criteria adopted and the differences in the physical and chemical characteristics of the sediments.     

Relation of acid-volatile sulfides (AVS) with metals in sediments from eutrophicated estuaries: Is it limited by metal-to-AVS ratios?

Purpose

The role of acid-volatile sulfide (AVS) as a factor affecting (or reflecting the environmental conditions influencing) the behavior of metals has been evidenced in anoxic sediments. However, sediment quality studies tend not to consider any potential AVS role when sum of simultaneously extracted metal (ΣSEM) concentrations exceed AVS concentrations, restricting the application of the AVS model to predict toxicity, rather than coupling this model (when applicable) with other possible interpretations of metal–AVS relations.

Materials and methods

The relations between total organic carbon (TOC), AVS, and simultaneously extracted Fe, Cd, Cu, Ni, Pb, and Zn were investigated in sediment cores from two eutrophicated estuaries in Guanabara Bay (SE Brazil) in order to contribute to our understanding about metal–AVS relations in conditions of variable ΣSEM and AVS levels, due to gradients of eutrophication and metal contamination.

Results and discussion

Correlation analyses indicated a more important role of TOC, AVS, and Fe in the mechanisms affecting trace metal distribution in the less eutrophicated estuary. This suggests that AVS was a more important binding phase, or at least a better proxy for biogeochemical conditions affecting metal distribution, when it exceeds the sum of simultaneously extracted Cd, Cu, Ni, Pb, and Zn concentrations (ΣSEM). However, this potential role of AVS in anoxic estuarine sediments should not be discarded before evaluating individual metals–AVS relations even when ΣSEM levels exceed AVS levels, since the biogeochemical controls on the behavior of individual metals may be also related to metal–AVS associations in this situation (as indicated for Cu and Ni in the more eutrophicated estuary). The same is suggested for all AVS-based approaches, such as the (ΣSEM???AVS)/f _OC (organic carbon normalization of excess ΣSEM), since (ΣSEM???AVS)/f _OC values were mostly positive and significantly higher in the more eutrophicated estuary.

Conclusions

Although the importance of metal relations to AVS in evaluating individual metal behavior in anoxic estuarine sediments may not be restricted to situations in which AVS levels exceed ΣSEM levels (as observed for Ni and Cu in the present study), metal–AVS relations were apparently favored in this situation. Approaches in this way are recommended for future research, coupling the possibilities of metal behavior interpretations (and often predictions) allowed by AVS models.     

巢湖表层沉积物中重金属的分布及污染评价

对巢湖湖区不同位点的表层沉积物中的Fe、Cr、Pb、Cu、Co、Zn、Ni7种重金属含量进行的分析表明,湖泊沉积物中重金属含量分布呈现一定的区域特征,由于巢湖西半湖靠近合肥市区,大量的工业废水和生活污水通过河道排入巢湖,引起西半湖区中重金属含量高于东半湖区。采用富集因子法和地积累指数法对巢湖沉积物重金属污染现状进行了评价,结果表明,巢湖沉积物中存在Pb、Cu污染,个别地区已相当严重,并呈现沿湖心区至东半湖区逐渐降低趋势。研究表明,两种方法均能对人为污染行为做出较为科学的评价,且两种方法得到的评价结果基本一致。由于重金属元素有很强的毒性,并且能够在食物链中传递,有关部门应及早从流域环境综合规划入手,对重金属污染问题采取有力的控制对策,保护沿湖地区居民免受危害。此外,对巢湖表层沉积物中重金属污染物来源进行了初步分析,据分析结果判断,巢湖沉积物中重金属总量Co、Fe、Cr的来源相似,Zn和Cu的来源相似。     

Modeling the Effect of pH and Salinity on Biogeochemical Reactions and Metal Behavior in Sediment

A mathematical model is developed to investigate the effect of pH and salinity fluctuation on biogeochemical reactions and metals' behavior in sediments. The model includes one-dimensional vertical advective and diffusive transport of species, serial reductions of electron acceptors, and precipitation/dissolution of species, acid–base chemistry, and metal sorption to sediments. The model was tested using data obtained from laboratory microcosm experiments which exposed metal (Cd, Zn) contaminated sediment to alternating fresh and salty overlying water. The model successfully reproduces the contrasting metal's release behavior and the vertical profiles of pH, Cl^?, SO₄ ^2?, Mn and Fe in porewater and the acid volatile sulfides (AVS) and simultaneously extracted metals (SEM) in sediments. The model showed that FeOOH_(s) was the dominant sorption phase controlling the solubility of the metals at the surficial sediments while AVS controlled the solubility of the metals in anoxic sediments. The model also showed that the release of the metals to overlying water was controlled by the oxidation of metal sulfides in a very thin layer of oxic sediments (2–3 mm). The proposed model can be useful in managing metal contaminated sediments where pH and salinity are fluctuating by assessing the underlying biogeochemical processes and metals' behavior.     

Heavy-Metal Concentrations in Sediments Collected from ICRISAT Lake,Patancheru, India

To determine and characterize the initial background concentrations of heavy metals, a total of 50 sediment samples were collected from the largest lake at the International Crops Research Institute for the Semi-arid Tropics (ICRISAT) in Patancheru, India. The finely ground sediment samples were digested using a microwave-assisted digestion method and analyzed for 15 heavy metals using inductively coupled plasma–optical emission spectrometry (ICP-OES). The results showed that the concentrations of the heavy metals varied greatly with metal and sediment sample, but in general the concentrations were low. Our results suggest that the sediments from this lake (15 ha in area) at the ICRISAT center do not appear contaminated with the heavy metals evaluated, and they indeed reflect normal background concentrations of these metals released through the natural process of weathering.     

Tin concentrations in river / bay sediments of Tokyo in 1984 and 2000

Abstract

To analyze in greater detail the fate and behavior of toxic organotin compounds in the environment, total tin (Sn) concentrations were determined for sediments of the Arakawa River, the Sumida River, and Tokyo Bay by using a graphite furnace atomic absorption spectrophotometer (GFAAS). Sn concentrations in 2000 were compared with those of 1984 (8 years before the regulation on tributyltin-based antifouling paint) as well as with other heavy metals (Cu, Ni, Pb, and Zn). The Sn concentrations ranged from 1.04 to 4.43 mg kg^?1 for sediments sampled in 2000. Although the average concentration of Sn in the sediments was low compared with that of 1984, the concentration tended to increase at several sites in 2000. Moreover, the Sn concentration showed significant correlations with the Cu, Ni, Pb, and Zn concentrations. These results suggest that a significant proportion of the overall Sn content in these sediments was probably introduced from the sources other than antifouling paint. The metals extracted from air-dried sediments with 0.1 m HCl showed that the mobility and bioavailability of Sn was low compared with those of other heavy metals.     

Heavy‐metal displacement in chelate‐treated soil with sludge during phytoremediation

Heavy metals (HMs) in domestic sewage sludge, applied to land, contaminate soils. Phytoremediation is the use of plants to clean‐up toxic HMs from soil. Chelating agents are added to soil to solubilize the metals for enhanced uptake. Yet no studies report the displacement of HMs in soil with sludge following solubilization with chelates. The objective of this work was to determine the uptake or leaching of HMs due to a chelate added to a soil from a sludge farm that had received sludge for 25 y. The soil was placed in long columns (105 cm long; ?? 39 cm) in a greenhouse. Columns either had a plant (hybrid poplar; Populus deltoides Marsh. × P. nigra L.) or no plant. After the poplar seedlings had grown for 144 d, the tetrasodium salt of the chelating agent EDTA was irrigated onto the surface of the soil at a rate of 1 g per kg of soil. Drainage water, soil, and plants were analyzed for three toxic HMs (Cd, Ni, Pb) and four essential HMs (Cu, Fe, Mn, Zn). At harvest, extractable and total concentrations of each HM in the soil with EDTA were similar to those in soil without EDTA. The chelate did not affect the concentrations of HMs in the roots or leaves. With or without plants, EDTA mobilized all seven HMs and increased their concentrations in drainage water. Lower concentrations of Cd, Cu, Fe, Ni, and Zn in leachate from columns with EDTA and plants compared to columns with EDTA and no plants showed that poplars can reduce groundwater contamination by intercepting these HMs in the soil. But the poplar plants did not reduce Pb and Mn in the leachate from columns with EDTA. Concentrations of Cd and Pb in the leachate mobilized by EDTA remained above drinking‐water standards with or without plants. The results showed that a chelate (EDTA) should not be added to a soil at a sludge farm to enhance phytoremediation. The chelate mobilized HMs that leached to drainage water and contaminated it.