Arsenic toxicity in crop plants: physiological effects and tolerance mechanisms

Heavy metals are toxic substances released into the environment, contributing to a variety of toxic effects on living organisms in food chain by accumulation and biomagnifications. Certain pollutants such as arsenic (As) remain in the environment for an extensive period. They eventually accumulate to levels that could harm physiochemical properties of soils and lead to loss of soil fertility and crop yield. Arsenic, when not detoxified, may trigger a sequence of reactions leading to growth inhibition, disruption of photosynthetic and respiratory systems, and stimulation of secondary metabolism. Plants respond to As toxicity by a variety of mechanisms including hyperaccumulation, antioxidant defense system, and phytochelation. Arbuscular mycorrhizae symbiosis occurs in almost all habitats and climates, including disturbed soils. There is growing evidence that arbuscular mycorrhizae fungi may alleviate metal/metalloid toxicity to host plant. Here, we review (1) arsenic speciation in the environment and how As is taken up by the roots and metabolised within plants, and (2) the role of arbuscular mycorrhizae in alleviating arsenic toxicity in crop plants.     

Heavy metals,occurrence and toxicity for plants: a review

Metal contamination issues are becoming increasingly common in India and elsewhere, with many documented cases of metal toxicity in mining industries, foundries, smelters, coal-burning power plants and agriculture. Heavy metals, such as cadmium, copper, lead, chromium and mercury are major environmental pollutants, particularly in areas with high anthropogenic pressure. Heavy metal accumulation in soils is of concern in agricultural production due to the adverse effects on food safety and marketability, crop growth due to phytotoxicity, and environmental health of soil organisms. The influence of plants and their metabolic activities affects the geological and biological redistribution of heavy metals through pollution of the air, water and soil. This article details the range of heavy metals, their occurrence and toxicity for plants. Metal toxicity has high impact and relevance to plants and consequently it affects the ecosystem, where the plants form an integral component. Plants growing in metal-polluted sites exhibit altered metabolism, growth reduction, lower biomass production and metal accumulation. Various physiological and biochemical processes in plants are affected by metals. The contemporary investigations into toxicity and tolerance in metal-stressed plants are prompted by the growing metal pollution in the environment. A few metals, including copper, manganese, cobalt, zinc and chromium are, however, essential to plant metabolism in trace amounts. It is only when metals are present in bioavailable forms and at excessive levels, they have the potential to become toxic to plants. This review focuses mainly on zinc, cadmium, copper, mercury, chromium, lead, arsenic, cobalt, nickel, manganese and iron.     

Measuring heavy metal migration rates in a low-permeability soil

Heavy metals at high concentrations are often toxic to living organisms, and their environmental toxicity depends on soil properties. It has long been thought that in clay-rich, low-permeability soils, heavy metals are bound to soil particles, and thus there are only few toxicity risks. This study questioned this perception and tested heavy metal mobility in such a soil, of the London Clay series, using a benchtop centrifuge. Soil columns were placed in the centrifuge and were infiltrated with solutions of Cu, Ni and Zn ions, while the centrifuge was running at three different gravity levels, at 5,280, 2,600 and 1,300 gravities. The measured rates of migration of Cu, Ni and Zn ions were extrapolated down to 1 gravity, which represents field conditions, the conditions for which an assessment of risk due to metal toxicity would be needed. It was found that heavy metal movement was significant in London Clay, Ni being the most mobile metal in the study, followed by Zn and then Cu ions. Centrifuge infiltration tests were proven to be a valuable tool in the study and quantification of metal mobility in low-permeability soil, because they were easy to run and precise in predicting metal movement in London Clay. Electronic Publication     

邻苯二甲酸二乙基己酯(DEHP)污染及其毒性研究进展

邻苯二甲酸二乙基己酯(DEHP)作为重要的增塑剂被广泛应用于涂料、食品包装、医疗器材、儿童玩具等产品中。研究表明DEHP在水、土壤、空气等各个环境要素以及食物、饮用水中已被普遍检出,并对环境产生潜在的危害。本文通过分析国内外DEHP的环境暴露和毒性效应的研究成果,总结了DEHP在室外大气、室内空气、土壤、地表水、地下水、食品和饮用水中的污染现状,并对DEHP的替代产品进行总结;此外,本文深入探讨了DEHP对水生生物和陆生生物的生态毒性效应,以及对生殖发育、肝脏、呼吸系统和神经系统等的健康毒性效应。最后,结合DEHP在环境暴露调查和毒性效应研究方面的不足,指出需要进一步加强我国DEHP的环境暴露调查,制定相关环境基准值与标准限值,开展慢性生态毒性效应和人体健康毒性效应等方面的研究。     

中国电子废物处理处置典型地区污染调查及环境、生态和健康风险研究进展

电子废物含有大量的金属、塑料和阻燃剂等物质,如果处理不当,电子废物将向环境排放种类繁多的有毒有害物质,从而产生严重的环境污染问题。近年来,国内外学者对电子废物处理所致的生态环境问题给予了相当的关注,已经开展了不少相关研究,这些研究主要集中在我国的几个电子废物处理处置典型地区。本文对近5年来的相关研究成果进行了系统综述,内容涉及电子废物处理处置过程中产生的主要环境污染物,电子废物处理处置活动所致的土壤、水体和大气的重金属和持久性有机污染物污染以及电子废物处理处置活动对动植物和人体的污染风险等,并提出将来关于电子废物研究中需要关注的问题。     

Regional ecotoxicological hazards associated with anthropogenic enrichment of heavy metals

Regional geochemical data of heavy metals are commonly used for environmental risk assessment and management. Often these data are based on so-called total concentrations, whereas the exposure to the mobile or reactive fraction of these elements finally determines whether the exposed ecosystem is at risk and to which extent. The objective of our research was to develop a wider applicable method for quantitative hazard assessment of soil metal contamination attributable to the activity of man, based on and illustrated with data from the Netherlands. Since chemical availability (0.43 M HNO3 extractable concentrations) of Cd, Cu, Pb and Zn appeared strongly related to the estimated anthropogenic enrichment, we used these concentrations to assess the hazard of human-induced enrichment of these metals. We expressed the enrichment hazard using the toxic pressure concept, which estimates the fraction of biological species (varying between 0 and 1) potentially affected due to the level of exposure to single metals or their local mixtures. This is done using logistic (enrichment) concentration/response models parameterized with ecotoxicological effect data from toxicity tests and mixture models. Hazards varied from very low toxic pressures (lower than 0.01) to (most often) toxic pressure less than 0.05, whereby the latter relates to the so-called 95%-protection criterion used in some soil protection legislations. In rare cases, the toxic pressure exceeded the value of 0.05, to an upper limit of 0.054 for Cd. The rank order of metal enrichment hazards suggests that Cd enrichment induces the largest hazard increase. There are limited (rank order) differences in enrichment hazards between soil types. Comparing the judgement of soils based on soil screening levels and based on toxic pressure of anthropogenic Cd, Cu, Pb and Zn enrichments, the soil screening values appear to more conservative. This exemplifies the use of soil screening values as a method to note regulatory concern, but not always indicating an actual hazard or risk. When screening values are exceeded, refined hazard insights can be obtained, as illustrated in this paper. This provides a more refined insight in the ecotoxic implications of human-induced metal enrichments in soils, as refined basis for risk management decisions.     

环境中丙烯酰胺检测方法和健康危害的研究进展

丙烯酰胺广泛应用于工业生产,是一种潜在的环境污染物。本文从丙烯酰胺的检测方法和健康危害2个方面总结了目前的研究进展。检测方法上,以高效液相色谱-质谱串联法(HPLC-MS/MS)最为常用,一些新技术也逐渐应用到分析中。健康危害方面,丙烯酰胺可引起实验生物的神经、生殖、遗传和发育等毒性和潜在致癌性。其毒性机理为:直接损坏神经元;使活性氧(ROS)积累导致氧化损伤;诱发基因位点突变,或与DNA形成加合物而致其损伤等。鉴于目前研究存在的问题,对以后的工作进行了展望:加强监管与治理工作,保护生态环境和人类健康;深入开展丙烯酰胺对生物体的毒性效应研究;加强我国环境中丙烯酰胺的跟踪监测工作;建立一种快捷的生物测试系统来评估水体(尤其是海洋环境)中丙烯酰胺的毒性风险。     

重金属对水生生物的生态毒理效应及生物耐受机制研究进展

近年来,随着国民经济的快速发展,重金属以其特有的性质而被大量的应用于生产生活当中,同时也由于各种原因造成了水体重金属污染现象。水体重金属污染不仅对水生生物的生长和繁殖造成了严重的威胁,同时也威胁到人类的健康。因此,重金属污染具有潜在的生态与健康风险。本文主要概括介绍了重金属对水生植物、动物、微生物的生态毒理效应以及水生生物对重金属的各种耐受机制,展望了重金属对水生生物生态毒理效应的未来研究重点和方向。     

根际环境的调节与重金属污染土壤的修复

根际环境的pH和Eh会产生影响土壤中重金属的化学过程。pH的变化影响到重金属的固定和活化，根际的酸化能够活化大多数重金属，使其毒性增强；反之，则固定大多数重金属，减轻其毒性。Eh的变化可改变重金属的价态和存在形态，使其毒性减弱或增强。根分泌物可从多方面影响金属的毒性和有效性，如改变根际环境的pH值和Eh来改变金属的存在形态和活度；与金属络合或者吸附、包埋金属污染物；通过影响根际微生物特征来改变金属的毒性。根际环境中微生物能改变金属离子存在形态，其代谢产物能对金属离子产生沉淀、螯合等作用。土壤脲酶对重金属污染最敏感，可以用于监测土壤重金属污染。调控根际环境，可以有效地调节土壤中重金属污染物的活度、毒性及其转移，对重金属污染土壤起到修复作用。     

陆地生物配体模型（t-BLM）初探：镁离子降低铜离子对小麦根的毒性

生物配体模型(BLM)同时考虑了水中金属离子的化学形态以及阳离子与金属离子在生物配体(BL)上的竞争对其毒性的影响,能成功预测水体金属的生物毒性/有效性.最近,BLM呈现出向土壤环境中拓展的趋势,发展能预测重金属对土壤生物毒性的陆地生物配体模型(t-BLM)正成为最新的国际研究热点.论文模拟土壤溶液,以土壤溶液中的主要阳离子Mg2+为例,通过单因素浓度控制-恒pH营养液培养-陆生植物根伸长抑制试验,定量探讨了不同浓度Mg2+存在下,铜离子(Cu2+)对小麦(Triticum aestivum)根的毒性.结果表明,Mg2+浓度升高显著减弱了Cu2+对小麦根的毒性,即呈现出保护效应.证实陆地生态系统中也存在阳离子对重金属植物毒性的保护效应,支持了BLM中阳离子和重金属离子在生物配体上存在竞争结合的假设,即BLM概念适用于陆生植物.定量分析表明,小麦根生长抑制的毒性效应指标EC50(以自由铜离子活度表示)与自由镁离子活度间存在良好的相关性,线性回归方程为:pEC50(Cu2+)=-0.36(Mg2+)+6.47(r2=0.9976),Mg2+对Cu2+毒性的影响强度可以通过该方程进行预测.论文积累了重金属铜对典型陆生受试植物小麦的毒性数据,探讨了t-BLM的构建方法学,并为其发展提供了思路.联合了土壤理化性质、金属形态及生物积累和毒性效应的t-BLM,将提供一个环境风险评价和制定土壤质量标准的新工具.     

农田土壤镉生物有效性及暴露评估研究进展

随着工业化和城市化进程的发展,我国在农田土壤污染领域面临较大挑战,其中镉(Cd)为最优先控制元素之一。农田土壤Cd污染风险类型为健康风险,其主要暴露途径为经土壤-植物系统,并经膳食进入人体。在当前的土壤Cd风险评估中,一般不考虑生物有效性问题,这使得风险评价中实际暴露评估的不确定性普遍偏高。所以,近年来欧洲国家有许多研究者提出将生物有效性因素放在土壤污染物风险评价框架内。基于此,本文立足于农田系统,并从土壤、植物、污染物及环境因素等4个方面详细综述了农田土壤Cd生物有效性的影响因素及其作用机理。其次,分别综述了近年来土壤Cd生物有效性预测模型和土壤Cd膳食暴露评估模型研究进展。最后,分析了我国土壤重金属风险评价中存在的不足,并对农田土壤Cd暴露评估发展态势和研究方向进行了初步预测,以期为农田土壤Cd健康风险评估及安全基准研究提供一定参考。     

涕灭威农药的残留、毒性及其对生态环境的影响

本文描述了涕灭威农药在土壤、水体和生物中的残留、降解和归趋以及对生物的毒性。涕灭威是一种剧毒农药、在环境中虽能很快降解成亚砜,并能进一步降解成毒性更低的化合物,但它仍有可能造成对地下水的污染和对生物与人体的潜在危害。     

植物修复土壤重金属污染中外源物质的影响机制和应用研究进展

重金属进入土壤后难以被降解,并通过食物链在生物体内富集,长此以往会导致中毒、癌症、畸形、突变,严重影响了人类生产活动及地球生态系统的稳定。植物修复技术是一种经济有效的重金属污染修复技术,其依靠超富集植物强大的自身抗性机制,从土壤中提取或稳定重金属,达到污染治理的目的。然而修复土壤重金属污染的超富集植物通常生长缓慢、生物量低,其抗性机制也会受到植物本身对重金属胁迫的阈值限制,当胁迫超过这个阈值,植物修复的效率就会大大降低甚至失去修复功能。文章在解析植物重金属相互作用机制的基础上,综述了添加外源物质对重金属毒害植物的缓解效应以及其在强化植物修复土壤重金属污染中的应用研究进展;介绍了应用外源物质调控植物吸收转运重金属的3种途径,分别为提高土壤重金属生物利用度、促进植物生长以及增强植物耐性。提出了应用外源物质作为强化植物修复措施的潜力及今后的研究方向,其未来的研究应着重于以下方面:明确外源物质的应用浓度、时期、方式与植物吸收转运重金属之间的关系;从植物内源激素及信号分子间的互作、抗逆基因表达、内生及根际微生物等不同层面上揭示外源物质对植物积累重金属的调控机理;开展外源物质与其他植物修复强化技术的联合应用研究。这些研究可为土壤重金属污染的植物修复技术及其强化措施研究提供科学依据,同时也对植物修复工程技术的发展实践具有一定的指导意义。     

Heavy metals and soil microbes

Heavy metal pollution is a global issue due to health risks associated with metal contamination. Although many metals are essential for life, they can be harmful to man, animal, plant and microorganisms at toxic levels. Occurrence of heavy metals in soil is mainly attributed to natural weathering of metal-rich parent material and anthropogenic activities such as industrial, mining, agricultural activities. Here we review the effect of soil microbes on the biosorption and bioavailability of heavy metals; the mechanisms of heavy metals sequestration by plant and microbes; and the effects of pollution on soil microbial diversity and activities. The major points are: anthropogenic activities constitute the major source of heavy metals in the environment. Soil chemistry is the major determinant of metal solubility, movement and availability in the soil. High levels of heavy metals in living tissues cause severe organ impairment, neurological disorders and eventual death. Elevated levels of heavy metals in soils decrease microbial population, diversity and activities. Nonetheless, certain soil microbes tolerate and use heavy metals in their systems; as such they are used for bioremediation of polluted soils. Soil microbes can be used for remediation of contaminated soils either directly or by making heavy metals bioavailable in the rhizosphere of plants. Such plants can accumulate 100 mg g^?1 Cd and As; 1000 mg g^?1 Co, Cu, Cr, Ni and 10,000 mg g^?1 Pb, Mn and Ni; and translocate metals to harvestable parts. Microbial activity changes soil physical properties such as soil structure and biochemical properties such as pH, soil redox state, soil enzymes that influence the solubility and bioavailability of heavy metals. The concept of ecological dose (ED₅₀) and lethal concentration (LC₅₀) was developed in response to the need to easily quantify the influence of pollutants on microbial-mediated ecological processes in various ecosystems.     

铊的环境地球化学研究进展

铊（Tl）作为一种高毒害性的元素越来越受到人们的关注。大量含Tl矿物的开采和冶炼、化石燃料的燃烧等人类活动,导致Tl及其化合物进入环境,进而通过食物链进入生物体,从而对动植物特别是人类健康造成严重的危害。文章对铊在各环境介质中的存在、迁移、转化,以及Tl的生物效应研究进展进行了概述。Tl在岩石中的平均质量分数为0.5~10 mg.kg-1,在大气中的平均质量浓度为0.22~1.0 ng.m-3,在天然水体中的平均质量浓度为0.001~1.264μg.L-1,在土壤中的平均质量分数为0.01~3.0 mg.kg-1,在植物中的平均质量分数为0.02~0.25 mg.kg-1。大气中的铊可随大气迁移,导致全球Tl污染;土壤中Tl的迁移主要受pH影响,pH越小其迁移能力越强,而水中溶解态的铊迁移能力最强。植物对Tl具有较强的富集能力,而动物实验则表明Tl具有一定的致畸性,可能存在一定的致癌性,并且职业暴露是人体Tl中毒的主要原因。尽管有关有Tl的地球化学以及生态毒理学方面的研究取得了一定的进展,但有关Tl在环境介质之间的界面化学机理、Tl在分子水平上吸附机理、不同形态的Tl在生物体中的致毒代谢机理以及铊的同位素在环境介质中的变化等方面仍有待于进一步的研究。     

页岩气压裂返排液的水生生态毒性效应研究

页岩气压裂作业过程产生大量压裂返排液,这类废液富含有毒且致癌的芳香烃、有毒金属和铀、钍、镭等放射性物质、石油类添加剂等,具有可生化性差和难处理的特点。这类废液若不经任何处理就进行排放,将给环境和人群健康带来潜在的危害和风险。目前尚不清楚它们的生态毒性效应。论文从涪陵页岩气开采基地采集了4口开采井(2号井、6号井-1、6号井-2和9号井)的压裂返排液,采用国家废水测试标准分析4种压裂返排液的水质理化指标,采用斜生栅藻(Scenedesmus obliquus)、大型溞(Daphnia magna)等标准毒性试验生物探究压裂返排液污染物体系的水生生态毒性效应,并研究水质理化指标与压裂返排液综合毒性的关系。结果表明,采集的所有压裂返排液样品均具备较大的水生生态毒性效应。以斜生栅藻的96 h的半数效应浓度(96 h-EC_(50))或大型溞的96 h的半数致死浓度(96 h-LC_(50))和毒性单位(TUa)为评价指标进行生态毒性分级,4个位点压裂返排液的生态毒性均为中毒及以上。压裂返排液的重金属、阴阳离子及有机物含量与其综合毒性的相关性结果表明,这些污染物成分与其藻类综合毒性无显著相关性。但Li、V、Cu、Ga、Rb、Ba等6种重金属及Na+、Cl-等2种阴阳离子对压裂返排液的溞类综合毒性有显著影响,影响程度依次为LiGaBaCl-VNa+RbCu。因此,在对压裂返排液进行处理时,这些与毒性相关的污染物是需要重点考虑的化学成分。     

Effective remediation of organic-metal co-contaminated soil by enhanced electrokinetic-bioremediation process

• A new EK-BIO technology was developed to decontaminate e-waste contaminated soil. • Adding sodium citrate in electrolyte was a good choice for decontaminating the soil. • The system has good performance with low cost. This work investigates the influence of electrokinetic-bioremediation (EK-BIO) on remediating soil polluted by persistent organic pollutants (POPs) and heavy metals (mainly Cu, Pb and Ni), originated from electronic waste recycling activity. The results demonstrate that most of POPs and metals were removed from the soil. More than 60% of metals and 90% of POPs in the soil were removed after a 30-day EK-BIO remediation assisted by citrate. A citrate sodium concentration of 0.02 g/L was deemed to be suitable because higher citrate did not significantly improve treatment performance whereas increasing dosage consumption. Citrate increased soil electrical current and electroosmotic flow. After remediation, metal residues mainly existed in stable and low-toxic states, which could effectively lower the potential hazard of toxic metals to the surrounding environment and organisms. EK-BIO treatment influenced soil microbial counts, dehydrogenase activity and community structure.     

Schwermetalle in Regenwürmern Baden-Württembergs

Goal and Scope

The heavy metal burden of the soil and of earthworms from representative long-term forest observation plots has been measured since 1984 as one component of the media-embracing environmental monitoring network of the State of Baden-Wuerttemberg. These investigations are aimed at elucidating and assessing adverse effects of pollutants on the soil biocenosis

Methods

So-called characteristic curves for the metals Cd, Cu, Ni, Pb, and Zn were developed for the assessment. Earthworm toxicity data and background values in soil served as criteria. This procedure facilitates a comparative assessment of different pollutants. The mobility of the metals, which greatly influences their bioavailability and toxicity, was taken into account for the effects assessment.

Results and Conclusion

Besides inventorying the heavy metals (Part 1), the question of threshold values for toxic reactions as well as for accumulation was raised. The metal concentrations were assessed in the soil with regard to its habitat function. The ecotoxicological assessment revealed that the heavy metal burden of the investigated plots lies within the background- or precautionary range, well below the screening value established here to indicate the effect threshold in earthworms. This result means that a pollution of the forest observation plots with the metals cadmium, copper, lead, nickel, and zinc is low or absent. Only the distribution of the lead content is centered slightly above background (but clearly below the toxicity threshold). This slight lead burden of the soil of the observation plots can be explained by emissions from motor vehicles. Investigations at sites that are contaminated with either chromium or copper or cadmium showed that an accumulation of these metals in the body of the worms can be observed only above a threshold concentration of several hundred micrograms of mobile metal per kilogram in the upper layer of the soil.

Recommendations and Perspectives

The hitherto unknown threshold values for the accumulation in the body of the earthworm should be statistically validated and extended to other elements. Further research is needed in order to build a well founded basis for the ecotoxicological assessment of soil pollution. Acute and chronic earthworm effect thresholds are neither available yet for arsenic, cobalt, and mercury nor for some other elements occurring less frequently as soil pollutants. Background values depending on the kind of rock have been measured so far for total chromium only. They are lacking for the more toxic chromium (VI) which is a frequent soil pollutant but naturally occurs in traces only.     

基于植物重金属毒性的陆地生物配体模型(t-BLM)研究进展

陆地生物配体模型(t-BLM)是生物配体模型(BLM)理论在陆地生态系统中的应用,目的是通过量化土壤重金属形态、土壤基本性质以及生态毒理剂量-效应三者之间的关系,评价重金属对陆生生物的毒性。BLM已经成功地预测重金属对水生生物的毒性,但t-BLM的发展相对较为缓慢。基于植物重金属毒性综述了t-BLM近年来国内外的研究进展,介绍了t-BLM的原理、基于t-BLM的重金属(Cu、Ni、Zn、Cd等)的植物毒性及其影响因素,并且提出基于植物重金属毒性的t-BLM研究面临的主要挑战。     

Role of plant growth promoting rhizobacteria in the remediation of metal contaminated soils

Pollution of the biosphere by the toxic metals is a global threat that has accelerated dramatically since the beginning of industrial revolution. The primary source of this pollution includes the industrial operations such as mining, smelting, metal forging, combustion of fossil fuels and sewage sludge application in agronomic practices. The metals released from these sources accumulate in soil and in turn, adversely affect the microbial population density and physico-chemical properties of soils, leading to the loss of soil fertility and yield of crops. The heavy metals in general cannot be biologically degraded to more or less toxic products and hence, persist in the environment. Conventional methods used for metal detoxification produce large quantities of toxic products and are cost-effective. The advent of bioremediation technology has provided an alternative to conventional methods for remediating the metal-poisoned soils. In metal-contaminated soils, the natural role of metal-tolerant plant growth promoting rhizobacteria in maintaining soil fertility is more important than in conventional agriculture, where greater use of agrochemicals minimize their significance. Besides their role in metal detoxification/removal, rhizobacteria also promote the growth of plants by other mechanisms such as production of growth promoting substances and siderophores. Phytoremediation is another emerging low-cost in situ technology employed to remove pollutants from the contaminated soils. The efficiency of phytoremediation can be enhanced by the judicious and careful application of appropriate heavy-metal tolerant, plant growth promoting rhizobacteria including symbiotic nitrogen-fixing organisms. This review presents the results of studies on the recent developments in the utilization of plant growth promoting rhizobacteria for direct application in soils contaminated with heavy metals under a wide range of agro-ecological conditions with a view to restore contaminated soils and consequently, promote crop productivity in metal-polluted soils across the globe and their significance in phytoremediation.