Chromium toxicity and tolerance in plants

Chromium (Cr) is the second most common metal contaminant in ground water, soil, and sediments due to its wide industrial application, hence posing a serious environmental concern. Among various valence states, Cr(III) and Cr(VI) are the most stable forms. Cr(VI) is the most persistent in the soil and is highly toxic for biota. Since Cr is a non-essential element for plants, there is no uptake mechanism; Cr is taken up along essential elements such as sulfate through sulfate transporters. Cr accumulation in plants causes high toxicity in terms of reduction in growth and biomass accumulation, and Cr induces structural alterations. Cr interferes with photosynthetic and respiration processes, and water and minerals uptake mechanism. Various enzymatic activities related to starch and nitrogen metabolism are decreased by Cr toxicity either by direct interference with the enzymes or through the production of reactive oxygen species. Cr causes oxidative damage by destruction of membrane lipids and DNA damage. Cr may even cause the death of plant species. Few plant species are able to accumulate high amount of Cr without being damaged. Such Cr-tolerant, hyperaccumulator plants are exploited for their bioremediation property. The present review discusses Cr availability in the environment, Cr transfer to biota, toxicity issues, effect on germination and plant growth, morphological and ultrastructural aberrations, biochemical and physiological alterations, effect on metabolic processes, Cr-induced alterations at the molecular level, Cr hyperaccumulation and Cr detoxification mechanism, and the role of arbuscular mycorrhizae in Cr toxicity, in 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.     

Arsenic bioaccumulation in rice and edible plants and subsequent transmission through food chain in Bengal basin: a review of the perspectives for environmental health

Arsenic (As) is a metalloid that poses serious environmental threats due to its behemoth toxicity and wide abundance. The use of arsenic-contaminated groundwater for irrigation purpose in crop fields elevates arsenic concentration in surface soil and in the plants. In many arsenic-affected countries, including Bangladesh and India, rice is reported to be one of the major sources of arsenic contamination. Rice is much more efficient at accumulating arsenic into the grains than other staple cereal crops. Rice is generally grown in submerged flooded condition, where arsenic bioavailability is high in soil. As arsenic species are phytotoxic, they can also affect the overall production of rice, and can reduce the economic growth of a country. Once the foodstuffs are contaminated with arsenic, this local problem can gain further significance and may become a global problem, as many food products are exported to other countries. Large-scale use of rainwater in irrigation systems, bioremediation by arsenic-resistant organisms and hyperaccumulating plants, and the aerobic cultivation of rice are some possible ways to reduce the extent of bioaccumulation in rice. Investigation on a complete food chain is urgently needed in the arsenic-contaminated zones, which should be our priority in future researches.     

Arsenic uptake by plants and possible phytoremediation applications: a brief overview

This review focuses the behaviour of arsenic in plant?Csoil and plant?Cwater systems, arsenic?Cplant cell interactions, phytoremediation, and biosorption. Arsenate and arsenite uptake by plants varies in different environment conditions. An eco-friendly and low-cost method for arsenic removal from soil?Cwater system is phytoremediation, in which living plants are used to remove arsenic from the environment or to render it less toxic. Several factors such as soil redox conditions, arsenic speciation in soils, and the presence of phosphates play a major role. Translocation factor is the important feature for categorising plants for their remediation ability. Phytoremediation techniques often do not take into account the biosorption processes of living plants and plant litter. In biosorption techniques, contaminants can be removed by a biological substrate, as a sorbent, bacteria, fungi, algae, or vascular plants surfaces based on passive binding of arsenic or other contaminants on cell wall surfaces containing special active functional groups. Evaluation of the current literature suggests that understanding molecular level processes, and kinetic aspects in phytoremediation using advanced analytical techniques are essential for designing phytoremediation technologies with improved, predictable remedial success. Hence, more efforts are needed on addressing the molecular level behaviour of arsenic in plants, kinetics of uptake, and transfer of arsenic in plants with flowing waters, remobilisation through decay, possible methylation, and volatilisation.     

锑和砷对固氮菌的毒性效应及其机制研究

锑作为一种具有毒性和致癌性的类金属,其不合理的开发造成了严重的生态环境污染,尤其是土壤中高浓度锑和砷污染导致了环境中多种营养元素的缺乏。其中,氮素的缺乏严重阻碍了环境的恢复。然而,固氮微生物不仅能为氮素匮乏环境提供稳定的氮素来源,而且其固氮潜能可以作为监测土壤金属污染的敏感指标。为此,该文通过乙炔还原法(ARA)微宇宙培养试验手段,研究了不同价态锑和砷(三价及五价)在不同质量浓度(100、200、500、1 000、2 500、5 000 mg·L^-1)水平下对棕色固氮菌固氮潜能的影响,同时进一步探究了土壤固氮菌群落固氮潜能对土壤中主要锑和砷价态[Sb(Ⅴ)和As(Ⅴ)]的响应机制。结果表明,锑和砷浓度与棕色固氮菌和土壤固氮微生物的固氮潜能均呈显著负相关,验证了以固氮微生物固氮潜能作为生物指示物的可行性。此外,Sb(Ⅴ)对土壤固氮微生物的毒性显著小于As(Ⅴ)。三价锑和砷污染对固氮菌固氮潜能的毒性高于五价[As(Ⅲ)>Sb(Ⅲ)>As(Ⅴ)>Sb(Ⅴ)],这可能是由于Sb(Ⅲ)和As(Ⅲ)对细胞的致裂性强于Sb(Ⅴ)和As(Ⅴ)。相较于Sb(Ⅴ)和As(Ⅴ)对于棕色固氮菌固氮潜能的抑制作用,其对土壤固氮菌群落的固氮潜能的影响相对较弱。这一差异可能是由于土壤复杂的理化性质以及微生物群落和功能多样性而导致的。     

碳纳米管影响无机砷(As(III)和As(V))对大型蚤毒性的研究：特定砷形态的作用

作为一种新兴的纳米材料,羟基多壁碳纳米管(OH-MWCNTs)可能与其他污染物在水环境中共存,并进一步影响它们的毒性、输移和归趋。因此,评价碳纳米管存在下砷的毒性变化需要得到更多的关注。该试验探索了在不同pH值条件下,OH-MWCNTs诱导砷(As(III)和As(V))对水生生物大型蚤的毒性变化的潜在机制。发现了H₂AsO₃^-和H₂AsO₄^-是对大型蚤毒性最大的As(III)和As(V)。比较As(III)和As(V)的结果,发现pH值是影响砷毒性最重要的因素。此外,OH-MWCNTs影响砷对大型蚤毒性的结果表明,OH-MWCNTs的存在可以提高砷的毒性。通过吸附实验进一步研究了砷与OH-MWCNTs的相互作用。OH-MWCNTs 对As(V)吸附容量高于As(III)。总而言之, OH-MWCNTs对某些形态砷的吸附是解释砷毒性增强的可靠证据。
精选自Xinghao Wang, Ruijuan Qu, Ahmed A. Allam, Jamaan Ajarem, Zhongbo Wei, Zuoyao Wang. Impact of carbon nanotubes on the toxicity of inorganic arsenic [As(III) and As(V)] to Daphnia magna: the role of the certain arsenic species. Environmental Toxicology and Chemistry: Volume 35, Issue 7, pages 1852–1859, July 2016. DOI: 10.1002/etc.3340
详情请见http://onlinelibrary.wiley.com/doi/10.1002/etc.3340/full
     

A review of arsenicals in biology

The most toxic form of arsenic is arsine gas. Arsenite is also highly toxic and arsenate is moderately toxic. Arsine gas will lyse red blood cells, arsenite inactivates particular enzymes and arsenate uncouples oxidative phosphorylation. Arsenic does not appear to be a significant mutagen. Epidemiological studies have implicated arsenic as a cause of lung cancer and skin cancer, but arsenic generally does not induce cancer in laboratory animals. Arsenic may bioaccumulate in some plants and marine organisms. Bacteria can be resistant to arsenic by preventing arsenate from entering the cell (chromosomal resistance) or pumping arsenic out of the cell (plasmid resistance). Many different organisms, including mammals, have the ability to methylate inorganic arsenic. Biomethylation seems to be a mechanism of arsenic detoxification.     

内蒙古自治区河套平原砷中毒高发区作物中砷的检测及健康风险评价

为了研究地方性砷中毒高发区作物中砷含量及其对人体健康的威胁,在内蒙古自治区河套平原4个自然村采集了72个谷物蔬菜水果、81份人体尿样和8个自来水样品。用高效液相色谱-电感耦合等离子体质谱(HPLC-ICP-MS)分析测定采集的样品中各形态砷及其含量;用ICP-MS分析测定消解后的作物样品中砷总量。结果表明,自来水中总砷含量均小于1.0μg·L-1。尿液样品中总砷含量为4.50～319μg·L-1(平均值为56.9μg·L-1),二甲基砷(DMA)是尿砷的主要形态(>70%)。作物中砷的主要形态有无机三价砷As(III)、无机五价砷As(V)和DMA。谷物和蔬菜水果中总砷含量的最大值分别为102和335μg·kg-1。成人和儿童最大日摄入砷量分别为232和205μg。通过分析采样地人体尿砷、作物砷和地方性砷中毒发病率的相关性得出,作物中砷的含量虽未明显超过国家标准,但对人体健康有明显的潜在威胁。政府改水后(饮用水由井水变为达标的自来水),人体的健康风险主要来自作物中的砷,而不是饮用水中的砷。     

Effect of natural organic matter on arsenic release from soils and sediments into groundwater

Arsenic (As) contamination in groundwater has received significant attention recently. Natural and anthropogenic sources contribute to the worldwide occurrence of As contamination. As speciation is an important factor related to its toxic and mobile behavior. The release of As from soils and sediments into groundwater is governed by several geophysicochemical processes, of which, As sorption behavior is of principle significance. This review paper summarizes existing information regarding the effects of natural organic matter (NOM) on the fate and mobility of As species in the environment. NOM may enhance the release of As from soils and sediments into the soil solution, thereby facilitating As leaching into the groundwater. The main influencing mechanisms include competition for available adsorption sites, formation of aqueous complexes, and/or changes in the redox potential of site surfaces and As redox speciation. NOM may also serve as binding agents, thereby reducing As mobility. However, comparably little research has been performed on this aspect. Since most investigations have been done on purified minerals under laboratory conditions, further research involving various geological materials under natural environmental conditions is required. Development of proper geochemical conceptual models may provide means of predicting the role of NOM in arsenic leaching and/or immobilization.     

Red mud-modified biochar reduces soil arsenic availability and changes bacterial composition

Environmental Chemistry Letters - Worldwide arsenic (As) contamination in soils induces pollution of surface and ground waters, reduces crop quality and yield, and threatens human health....     

不同分子量的腐殖酸存在下2种无机砷的生物毒性效应研究

水环境中天然有机质会与砷形成络合物,进而影响砷的迁移、转化和生物毒性。研究利用超滤方法将腐殖酸(humic acid, HA)分为5个不同分子量的组分,以大型溞为受试生物,探究了不同分子量HA存在下砷对大型溞的毒性效应。结果表明,不同分子量的HA均缓解了As(Ⅲ)和As(Ⅴ)对大型溞的氧化应激损伤和细胞膜损伤,并降低了砷对MT的诱导量。其中1～30 k Da的HA对砷的缓解效果最好,1 k Da的HA毒性缓解效果最差,可能的原因是HA与砷的络合增加溶液中络合态砷的含量,而络合态砷难以进入细胞并被生物利用。不同分子量的HA对砷毒性的缓解差异与其跟砷的络合比例不同有关。     

外源洛克沙胂对水生态系统砷蓄积及底泥微生物生长的影响

为探明洛克沙胂(ROX)对水生态系统的毒性效应,采用模拟水生态系统,研究了外源添加不同浓度洛克沙胂(0、10、20、40、80和160 mg·L-1)对水生态系统砷含量及底泥微生物生长的影响。结果表明,水体及底泥砷含量随外源ROX用量增加而增加,但随暴露时间延长水体砷含量降低的同时底泥砷含量逐渐增加。金鱼藻和鲫鱼体内均出现明显砷蓄积现象,且160 mg·L-1ROX处理的水生态系统鲫鱼毒害效应明显,暴露1 d的死亡率为100%。金鱼藻对砷具有较强的富集能力,暴露32 d后砷富集量达398.1~1 538.91 mg·kg-1。不同浓度ROX对底泥真菌、细菌和反硝化细菌生长均具有不同程度的抑制效应,而对放线菌和氨化细菌生长具有一定的促进作用,且低浓度ROX(10 mg·L-1)对放线菌生长的促进作用明显。总体上,外源ROX进入水生态系统导致水体砷污染的同时在生物及非生物媒介中再次迁移、分配和蓄积,进而对鲫鱼及部分底泥微生物生长产生毒害。     

Arsenite oxidation by <Emphasis Type="Italic">Alcaligenes</Emphasis> sp. strain RS-19 isolated from arsenic-contaminated mines in the Republic of Korea

Arsenite [As(III)]-oxidizing bacteria play important roles in reducing arsenic [As] toxicity and mobility in As-contaminated areas. As-resistant bacteria were isolated from the soils of two abandoned mines in the Republic of Korea. The isolated bacteria showed relatively high resistances to As(III) up to 26 mM. The PCR-based 16S rRNA analysis revealed that the isolated As-resistant bacteria were close relatives to Serratia marcescensa, Pseudomonas putida, Pantoea agglomerans, and Alcaligenes sp. Among the five As-resistant bacterial isolates, Alcaligenes sp. strain RS-19 showed the highest As(III)-oxidizing activity in batch tests, completely oxidizing 1 mM of As(III) to As(V) within 40 h during heterotrophic growth. This study suggests that the indigenous bacteria have evolved to retain the ability to resist toxic As in the As-contaminated environments and moreover to convert the species to a less toxic form [e.g., from As(III) to As(V)] and also contribute the biogeochemical cycling of As by being involved in speciation of As.     

Uptake and accumulation of potentially toxic elements in colonized plant species around the world’s largest antimony mine area,China

To provide information on reclamation of multi-heavy metal polluted soils with conception of phytostabilization, a field survey on the uptake and accumulation of potentially toxic elements such as antimony (Sb), arsenic (As), lead (Pb), cadmium (Cd), copper (Cu), and zinc (Zn) in colonized plant species around the world’s largest antimony mine area, China, was conducted. Samples including leaves and shoots (including roots and stems) of colonized plants as well as rhizospheric soils were collected from eight sampling zones in the studied area. The results showed that the contents of Cu, Zn, and Pb in rhizospheric soils below plants were comparable to the corresponding background values of Hunan province, otherwise Sb, Cd, and As contents were extremely high (17–106, 17–87, and 3–7 times of the corresponding background values). The highest concentration of Sb was found in Aster subulatus (410 mg kg^?1); Cd, As, and Zn were in Herba bidentis bipinnatae (10.9, 264, and 265 mg kg^?1, respectively); and Cu was in Artemisia lavandulaefolia (27.1 mg kg^?1). It also exhibited that all the contents of As in leaves were several times of those in shoots of plants, Cd and other heavy metals showed in a similar pattern in several studied species, implying that the uptake route of these heavy metals via foliar might contribute to the accumulation. With high bioconcentration factors of heavy metals (more than 1, except for Zn), together with the growth abundance, Herba bidentis bipinnatae was considered as the most suitable colonized species for phytostabilization of the multi-heavy metal pollution in soils on this antimony mine area.     

Trace element uptake in plants grown on fly ash amended soils

Four crop plants were grown in a greenhouse in soils amended with 0, 5, 10, and 20% by weight of coal combustion fly ash to evaluate potential trace element uptake by the vegetation. The leaves and stems from each plant were harvested and analyzed for As, Cd, Co, Cu, Mn, Mo, Pb, Se, Tl, and Zn content during early, middle, and late growth. The trace element data were statistically analyzed using Analysis of Variance (ANOVA) to determine whether the trace element uptake in the four crop plants differed significantly between the soil treatments, and to identify significant differences in trace element uptake through time. The results show that the amount of amended fly ash does not significantly influence the concentration of most trace elements in plant tissue, and that some concentrations actually decrease with time. Although this study did not find a significant increase in trace element uptake, care must be taken in a natural environment where plants may behave differently.     

Toxicity of tri- and penta-valent arsenic, alone and in combination, to the cladoceran Daphnia carinata: the influence of microbial transformation in natural waters

The acute toxicity of arsenic(III) and arsenic(V) alone and in combination to a cladoceran, Daphnia carinata, was studied in both cladoceran culture medium and natural water collected from a local suburban stream. As(III) was found to be more toxic than As(V) to Daphnia survival. The LC₅₀ values for As(III), As(V), and As(III) + As(V) were 0.554, 1.499, and 0.692 mg l⁻¹, respectively. Although various species of As, particularly As(III) and As(V) co-exist together in natural waters, the existing guidelines for water quality are based on individual As species. The results of this investigation suggest that As(III) and As(V) can interact either synergistically or additively resulting in an increase in the overall toxicity of the mixture compared to individual As species. Also, indigenous microorganisms in natural water may play a significant role in the transformation of As, thereby influencing the toxicity of As in receiving waters. This study clearly suggests that the joint action of As species should be considered in the development of water quality guidelines. To our knowledge this is the first study on the interactive effect of As(III) and As(V) to a cladoceran. Thus, this study suggests that these two species of As, when present together above 0.1 mg l⁻¹ concentration, are toxic to fresh water invertebrates; therefore, pollution with these compounds may adversely affect natural ecosystems.     

Sequestration of As by iron plaque on the roots of three rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) cultivars in a low-P soil with or without P fertilizer

A pot experiment was carried out in a greenhouse to investigate the sequestration of As in iron plaques on root surface of three rice (Oryza sativa L.) cultivars. Phosphate (P) fertilization increased both plant biomass and tissue P concentrations significantly, indicating that the soils used in this study was highly P-deficient. Results from this study confirmed that low P supply improved the formation of iron plaque on rice roots. As a consequence, arsenic (As) concentrations in DCB-extracts with no P addition were significantly higher than those with P fertilization. Arsenic was highly sequestrated in iron plaque; arsenic concentration in iron was up to nearly 120 mg kg⁻¹, while arsenic concentrations in roots were just several mg kg⁻¹. Both arsenic and phosphate concentrations in iron plaque were highly positively correlated with the amounts of iron plaque (DCB-extractable Fe). Contrary to normal understanding that increasing P supply could reduced As accumulation in plants, results from the present study showed that P fertilization did not inhibit the As uptake by plants (As accumulation in aboveground), which was probably due to the fact that iron plaque formation was improved under low P conditions, thus leading to more As sequestration in the iron plaque. Thus results obtained in this study indicated that the iron plaque may inhibit the transfer of As from roots to shoots, and thus alter the P–As interaction in plant As uptake processes.     

不同价态无机砷对罗非鱼肝脏砷积累及GSH/GST解毒代谢的影响

低剂量中长期暴露下的氧化胁迫是砷对水生生物致毒的重要机制之一。本文通过对罗非鱼进行32 d的食物相砷暴露,测定不同时间点罗非鱼肝脏中谷胱甘肽(glutathione,GSH)含量和谷胱甘肽巯基转移酶(glutathione S-transferase,GST)活性,揭示不同价态无机砷对罗非鱼肝脏中GSH/GST的影响机制。经三价砷(As(III))暴露后,砷含量在2 d内显著增加而在随后的30 d内无显著性差异; 0～2 d内GSH含量显著增加,后降低,13 d后GSH含量均低于空白组; 0～6 d GST活性均大于空白组,6～8 d GST活性降低,8 d后活性高于空白组,且32 d达到最大值。经五价砷(As(V))暴露后,罗非鱼肝脏中砷含量逐渐增加,在20 d时达到最大值而后无显著性差异; 0～2 d时GSH含量降低,随后逐渐增加,在16 d达到最大值,16 d后GSH含量均低于空白组; 0～8 d时GST被大量诱导合成,8～20 d时GST合成被抑制,20 d后活性增加,在32 d达到最大值。As(III)和As(V)对罗非鱼GSH/GST的不同影响与其在罗非鱼体内的积累量有关。As(III)暴露后各时间点罗非鱼肝脏中的砷含量与GSH含量呈统计学正相关,而As(V)暴露无明显相关性。这是因为As(V)进入罗非鱼肝脏后会还原为As(III),进而GSH作为可提供巯基的还原剂而被大量消耗。另外,As(III)暴露后各时间点罗非鱼肝脏中的砷含量与GST活性呈显著负相关,而As(V)暴露却呈现出很强的滞后性,这是由于进入生物体内的As(V)需转化为As(III)后,才可直接作用于酶系统。可见,不同形态砷对水生生物的致毒机制需进一步深入研究。     

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.     

链霉菌的抗砷特性及其对蜈蚣草富集砷的作用

本文研究了链霉菌Streptomyces sp.的耐砷特性及其对蜈蚣草富集砷的影响。结果表明,Streptomyces sp.可在100mmo·lL-1的砷酸盐溶液中生长,具有较强的抗砷毒害能力,且在48h内对As(Ⅴ)的还原率达96.5%。施用Streptomyces sp.能促进植物对砷的吸收,蜈蚣草地上部砷浓度为930mg·kg-1,地上部砷累积量达到对照组的2.09倍。加入Streptomyces sp.后,能促进根际土壤中As(Ⅴ)还原成As(Ⅲ),大幅度降低根际土壤残渣态砷含量,从48.15mg·kg-1下降至28.75mg·kg-1。Streptomyces sp.通过影响蜈蚣草根际环境,提高根际土壤pH,增加DOC含量,促使砷形态变化,从而增加砷生物可利用性。该菌可作为强化蜈蚣草修复砷污染土壤的材料。