Insights into the Roles of Melatonin in Alleviating Heavy Metal Toxicity in Crop Plants

Alleviating heavy metal pollution in farmland soil, and heavy metal toxicity in plants is the focus of global agricultural environmental research. Melatonin is a kind of indoleamine compound that wide exists in organisms; it is currently known as an endogenous free radical scavenger with the strongest antioxidant effect. As a new plant growth regulator and signaling molecule, melatonin plays an important role in plant resistance to biotic or abiotic stress. Recent studies indicate that melatonin can effectively alleviate heavy metal toxicity in crop plants, which provides a new strategy to minimize heavy metal pollution in crop plants. This study summarizes the research progress on the role of melatonin in alleviating heavy metal toxicity in crop plants and the related physiological and ecological mechanisms such as reducing the concentration of heavy metals in the rhizosphere, fixing and regionally isolating of heavy metals, maintaining the mineral element balance, enhancing the antioxidant defense system and interacting with hormonal signaling. Furthermore, future prospects for the mechanism of melatonin in regulating heavy metal toxicity, the pathway regulating synthesis and catabolism, and the interaction mechanism of melatonin signaling and other phytohormones are presented in this paper, with the goal of providing a theoretical basis for controlling heavy metal ion accumulation in crop plants grown in contaminated soil.     

杨桃对土壤重金属元素的吸收与富集

通过对廉江市杨桃（Averrhoa carambola）绿色食品基地不同土质、不同树龄的土壤样品及果实样品重金属元素Cd、Hg、Cu、Pb、As、Cr含量的检测,分析杨桃果实对土壤重金属元素的吸收与富集作用。结果表明：①果园土壤pH≤5．50,为酸性土壤,杨桃果园土壤和鲜果中的重金属含量均符合我国水果绿色食品生产的质量要求;②杨桃对土壤重金属的吸收因土壤质地和重金属元素的种类不同而异;③杨桃对重金属元素的富集,以Cd元素为最强,富集系数高达0．947,各种重金属的富集系数按大小排序为：Cd（0．947）〉Hg（0．098）〉Cu（0．023）〉Pb（0．003）〉As（0．001）：Cr（0．001）。     

Impact of Soil Heavy Metal Pollution on Food Safety in China

Food safety is a major concern for the Chinese public. This study collected 465 published papers on heavy metal pollution rates (the ratio of the samples exceeding the Grade II limits for Chinese soils, the Soil Environmental Quality Standard-1995) in farmland soil throughout China. The results showed that Cd had the highest pollution rate of 7.75%, followed by Hg, Cu, Ni and Zn, Pb and Cr had the lowest pollution rates at lower than 1%. The total pollution rate in Chinese farmland soil was 10.18%, mainly from Cd, Hg, Cu, and Ni. The human activities of mining and smelting, industry, irrigation by sewage, urban development, and fertilizer application released certain amounts of heavy metals into soil, which resulted in the farmland soil being polluted. Considering the spatial variations of grain production, about 13.86% of grain production was affected due to the heavy metal pollution in farmland soil. These results many provide valuable information for agricultural soil management and protection in China.     

Heavy metal absorption status of five plant species in monoculture and intercropping

Absorption ability for heavy metals varies among plant species. This study is to evaluate the absorption characteristics of different plant species and planting patterns for heavy metals. Five plant species (tomato, maize, greengrocery, cabbage, and Japan clover herb) were cultivated in monoculture and in intercropping in soil contaminated with heavy metals (Cd, Pb, Cr, Cu, and Fe), to determine the absorption status. Tomato absorbs greater amounts of heavy metals (especially Cd). Furthermore, accumulation of heavy metals increased when tomato was intercropped with other plant species. Maize accumulates greater amounts of Cr, Cu, and Fe. The heavy metal concentrations were reduced when maize was intercropped. Cd and Pb accumulated more in roots of Japan Clover Herb, and the levels of all five heavy metals decreased when intercropped. Tomato intercropping is a feasible method for phytoremediation of heavy metal-contaminated soil, and maize intercropping is feasible for obtaining safe harvest which can be eaten securely.     

江苏省典型区农田土壤及小麦中重金属含量与评价

为了研究江苏省典型区地震带农田土壤和小麦中重金属的污染,在具有代表性的农田采集收获期小麦及耕层土壤,分析和评价了土壤和小麦中重金属Cu、Pb、Cd、Ni、Cr、Hg、As和Zn的含量及污染程度。结果表明,土壤样品中Cd、Zn、Pb的含量均超过江苏省土壤背景值,Cr、Cu、Ni和As分别有25.64%、97.44%、92.31%和92.31%的土壤样品中超过江苏省土壤背景值,Hg的含量均在背景值以下;与国家土壤环境质量标准(GB15618—1995)中Ⅱ级标准相比,Cd的含量均超出标准限值,其它7种重金属元素含量均在标准限值以下。土壤中重金属相关分析表明,Cd、Cu、Cr、Ni、Pb、Zn、As具有相同的来源的可能性较大,而Hg与Cd、Cu、Cr、Ni、Pb、Zn、As的来源均不相同。以NY 861—2004为评价标准,小麦籽粒Pb、Cr、Hg、Ni、As样品超标率分别为100%、58.97%、33.33%、10.26%、2.56%,Cu、Zn和Cd没有样品超标,由此可见小麦籽粒中Pb的污染最为严重。采用单因子污染指数法、综合污染指数法和Hakanson潜在生态评价指数法以国家土壤环境质量标准(GB15618—1995)和江苏省土壤背景值为参比值,对农田土壤重金属污染进行评价,结果显示,从单项污染指数来看只有Cd达到重度污染水平,其它元素均在安全范围以内,从综合污染指数来看土壤重金属污染达到中度污染水平,从潜在生态评价指数法来看,研究区域表现为很强的生态危害,并以Cd为主要污染因子。     

利用生物固定土壤重金属的机理及在农产品安全中的应用

生物固定技术是土壤重金属污染防治和保障农产品安全的有效手段。目前利用生物固定土壤中的重金属主要有三种途径：①利用土壤微生物固定重金属;②利用植物根分泌物固定重金属;③利用植物一微生物联合固定重金属。本文阐述了生物固定技术在解决土壤重金属危害中的重要意义及利用土壤微生物和植物根分泌物固定重金属的机理,提出了农作物选育及改良、高效微生物菌剂的选育及应用等具体措施以保障农产品安全。     

Heavy metal pollution assessment in a mangrove ecosystem scheduled as a community reserve

Heavy metal pollution is one of most toxic pollutions and cause serious threat to organisms as well as the environment. The tremendous increase in industrialization and other anthropogenic activities magnify the rate of heavy metal pollution. The present study reveals the heavy metal pollution assessment in Kadalundi Vallikunnu Community Reserve (KVCR), a scheduled community reserve of Kerala, India. The results from the study indicate that the heavy metal pollution index of KVCR was less because of the mangrove cover in this region. KVCR is endowed with different mangroves and it plays a significant role in controlling the heavy metal pollution and water quality. The higher Importance Value Index and Relative Importance Value Index was shown in the case of Avicennia officinalis, followed by Acanthus ilicifolius and the lowest values of these indices were observed in the case of Sonneratia alba. The less accumulation of heavy metals in the soil sediments was due to the potential of mangrove species for effective absorption of toxic metals from the soil sediments. Mangrove vegetation in the wetlands is potent phytoremediators and can play a significant role in phytoremediation of wetlands. The high BCF value of A. ilicifolius indicates its suitability for heavy metal remediation in wetlands. Eco restoration of heavy metal polluted wetlands using mangroves is a promising and sustainable solution for heavy metal pollution in such ecologically fragile areas.

     

Native Australian Species are Effective in Extracting Multiple Heavy Metals from Biosolids

Selecting native plant species with characteristics suitable for extraction of heavy metals may have multiple advantages over non-native plants. Six Australian perennial woody plant species and one willow were grown in a pot trial in heavy metal-contaminated biosolids and a potting mix. The plants were harvested after fourteen months and above-ground parts were analysed for heavy metal concentrations and total metal contents. All native species were capable of growing in biosolids and extracted heavy metals to varying degrees. No single species was able to accumulate heavy metals at particularly high levels and metal extraction depended upon the bioavailability of the metal in the substrate. Metal extraction efficiency was driven by biomass accumulation, with the species extracting the most metals also having the greatest biomass yield. The study demonstrated that Grevillea robusta, Acacia mearnsii, Eucalyptus polybractea, and E. cladocalyx have the greatest potential as phytoextractor species in the remediation of heavy metal-contaminated biosolids. Species survival and growth were the main determinants of metal extraction efficiency and these traits will be important for future screening of native species.     

阜新市农田土壤重金属含量及其分布特征

通过对辽宁省阜新市城郊区县180处农田土壤的取样调查分析,初步了解了农田土壤重金属As、Cu、Zn、Ni的含量特征及其空间分布,并探讨了当地矿业开采活动对农田土壤重金属积累及空间分布的影响.结果表明,研究区域内农田土壤Cu、Zn和Ni的几何平均含量均高于背景值,且这3种重金属存在普遍累积的现象;不同种植类型土壤中,菜地土壤Cu、Zn、As含量显著高于粮田,且重金属积累更为明显;4种重金属的空间分布均呈城区高于郊县的趋势;重金属含量较高的区域与矿山开采区域基本重叠.研究区域内采矿活动是农田重金属的重要来源,同时畜禽养殖业所产生的畜禽粪便可能对农田土壤中Cu、Zn和As的增加有一定作用.当地农牧业生产和布局应适当考虑土壤污染的风险.     

Geochemical baseline determination and pollution assessment of heavy metals in urban soils of Karachi,Pakistan

Karachi is one of the most populated urban agglomerations in the world. No categorical study has yet discussed the geochemical baseline concentrations of metals in the urban soil of Karachi. The main objectives of this study were to establish geochemical baseline values and to assess the pollution status of different heavy metals. Geochemical baseline concentrations of heavy metals were estimated using the cumulative frequency distribution (CDF) curves. The estimated baseline concentrations of Pb, Cr, Cu, Zn and Fe were 56.23, 12.9, 36.31, 123.03 and 11,776 mg kg⁻¹, respectively. The pollution status of heavy metals in urban soils was evaluated using different quantitative indices (enrichment factor–EF, Geo-accumulation Index–I_geo, and pollution index–PI). Enrichments factors of the selected heavy metals determined by using Fe as a normalizer showed that metal contamination was the product of anthropogenic activities. The urban soils of Karachi were found to have a moderate to moderately severe enrichment with Pb, whereas Cr and Cu has moderate and Zn has minor enrichment. I_geo results indicated moderate soil contamination by Pb at some of the sampling locations. PI for Pb, Cr, Cu and Zn was found in the range of 0.04–3.42, 0.19–1.55, 0.27–2.45 and 0.32–1.57, respectively. Large variations in PI values of Pb revealed that soil in those areas of the city which are influenced by intensive anthropogenic activities have exceptionally high concentrations of Pb. The findings of this study would contribute to the environmental database of the soil of the region and would also facilitate both at the local and the international scales, in a more accurate global environmental monitoring, which will eventually facilitate the development of management and remediation strategies for heavy metal contaminated urban soil.     

分级分筛式异位重金属污染土壤淋洗技术

本研究采用去离子水作淋洗剂,开发一种分级分筛式异位重金属污染土壤淋洗技术,研究显示,土壤中粒径大于25μm颗粒占比接近80%,重金属Pb、Cu、Ni、Cd和Cr含量分别为125.85 mg/kg、85.93 mg/kg、63.29 mg/kg、1.31 mg/kg和108.39 mg/kg,基本符合土壤环境质量二级标准,可用于农田回用土;土壤中粒径小于25μm颗粒占比低于20%,其对应重金属含量超出土壤环境质量三级标准,可用作制砖原料。     

Potential of Siderophore Production by Bacteria Isolated from Heavy Metal: Polluted and Rhizosphere Soils

Recently, heavy metals have been shown to have a stimulating effect on siderophore biosynthesis in various bacteria. In addition, several studies have found that siderophore production is greater in bacteria isolated from soil near plant roots. The aim of this study was to compare the production of siderophores by bacterial strains isolated from heavy metal-contaminated and uncontaminated soils. Chrome azurol sulphonate was used to detect siderophore secretion by several bacterial strains isolated from heavy metal-contaminated and rhizosphere-uncontaminated soils with both a qualitative disc diffusion method and a quantitative ultraviolet spectrophotometric method. Siderophore production by rhizosphere bacteria was significantly greater than by bacteria isolated from contaminated soil. The Pearson’s correlation test indicated a positive correlation between the amount of siderophore produced by bacteria isolated from the rhizosphere using the quantitative and qualitative detection methods and the amount of heavy metal in the soil. However, a significant negative correlation was observed between the amount of siderophore produced by bacteria isolated from heavy metal-contaminated soil and the amount of heavy metal (r value of ?0.775, P < 0.001).     

基于序贯指示模拟的农田土壤重金属风险区域识别

农田土壤重金属的日益累积已对农作物安全、生态环境和人类健康造成严重威胁,高效、精确地识别农田土壤重金属风险区对农田的环境保护、污染预警和风险管控等有重要意义.以广州市增城区为研究对象,共采集204个农田土壤样点,测定了铜(Cu)、锌(Zn)、铅(Pb)、镉(Cd)、铬(Cr)、砷(As)和汞(Hg)7种重金属含量.针对实际采样数据中存在异常值与偏态分布,以及传统克里格法存在的平滑效应等问题,将序贯指示模拟引入农田土壤重金属的风险识别中,与常用识别方法进行比较,并根据Hakanson风险指数评价进行风险区划.结果表明:(1)对比普通克里格法,在精度相似情况下,序贯指示模拟法较为精细地模拟了重金属的空间分布,平滑效应低,预测的细节表现好;对比指示克里格法,其在划分风险区域时的不确定评估中准确度较高,其误判率仅为4.9%~17.1%,表明其能更好地适用于模拟农田土壤重金属的空间分布和风险识别;(2)增城区的农田土壤重金属均未超标,但在南部的极少数区域存在潜在中等风险,主要成因是包括企业生产、人类活动和河流沉积物等.本研究以序贯指示模拟为基础,有效克服了传统克里格法存在的异常值信息丢失和平滑效应问题,结合Hakanson风险指数法,为非均匀采样的土壤重金属空间风险的识别提供一种新的尝试.     

Siderophores,NTA, and Citrate: Potential Soil Amendments to Enhance Heavy Metal Mobility in Phytoremediation

Phytoremediation of heavy metal-contaminated sites is often limited by the low bioavailability of the contaminants. Complexing agents can help to improve this technique by enhancing heavy metal solubility. We investigated the effect of three organic chelating agents, that is, the siderophore desferrioxamine B (DFOB), nitrilotriacetate (NTA), and citrate on binding of Cu, Zn, and Cd by either Namontmorillonite, kaolinite, or goethite. The different effects of the complexing agents on metal sorption can mainly be explained by the differences in stability constants and surface charge characteristics. In the presence of clay minerals, NTA was the most efficient ligand with respect to mobilization of heavy metals. In goethite suspensions, the effect of DFOB was more pronounced. In all systems, Cu proved to be the most affected element by the presence of the ligands. In batch experiments with heavy metal-contaminated soils from field sites, NTA was the most efficient metal mobilizer.     

工矿区不同类型生物结皮对大气降尘重金属的富集规律及其影响因子

大气降尘是矿区土壤重金属的主要来源,而生物结皮对大气降尘重金属有显著的富集作用。为探究不同类型生物结皮对大气降尘重金属的富集规律及其影响因子,选取宁东典型火电厂周边生物结皮广布区作为试验样地,3类生物结皮作为研究对象,并以临近裸土作为对照,对比分析了生物结皮富集大气降尘过程中土壤理化性质、酶活性及重金属含量的变化,采用相关分析、冗余分析和方差分解方法探讨了不同类型生物结皮的结皮层(A层)和层下土壤(B层)重金属含量与其土壤物理、化学性质及酶活性之间的关系。结果表明：燃煤烟尘是矿区大气降尘重金属污染的主要来源,涉及重金属元素包括Cd、Cr、Hg、Pb、Zn、As。生物结皮对源自大气降尘的重金属元素均具有显著的富集作用,且在不同演替阶段生物结皮间的富集规律完全一致：藓结皮>混生结皮>藻结皮;重金属综合污染指数评价结果显示：生物结皮对重金属具有表层富集效应,表现为A层污染程度高于B层。不同类型生物结皮A、B层综合污染指数存在显著差异,排序为：藓结皮>混生结皮>藻结皮;和对照相比,三类生物结皮均能通过富集大气降尘增加其A、B层养分和细颗粒物含量并改善土壤质地。方差分解结...     

Heavy Metal Pollution Characteristics of Surface Sediments in Different Aquatic Ecosystems in Eastern China: A Comprehensive Understanding

Aquatic ecosystems in eastern China are suffering threats from heavy metal pollution because of rapid economic development and urbanization. Heavy metals in surface sediments were determined in five different aquatic ecosystems (river, reservoir, estuary, lake, and wetland ecosystems). The average Cd, Cr, Cu, Ni, Pb, and Zn concentrations were 0.716, 118, 37.3, 32.7, 56.6, and 204 mg/kg, respectively, and the higher concentrations were mainly found in sediment samples from river ecosystems. Cd was the most anthropogenically enriched pollutant, followed by Zn and Pb, indicated by enrichment factors >1.5. According to consensus-based sediment quality guidelines, potential ecological risk indices, and risk assessment codes, all five types of aquatic ecosystems were found to be polluted with heavy metals, and the most polluted ecosystems were mainly rivers. Cd was the most serious pollutant in all five aquatic ecosystems, and it was mainly found in the exchangeable fraction (about 30% of the total Cd concentration, on average). The results indicate that heavy metal contamination, especially of Cd, in aquatic ecosystems in eastern China should be taken into account in the development of management strategies for protecting the aquatic environment.     

南京市14种绿化树种对空气中重金属的累积能力

分析了南京化工厂（污染区）和江苏省林科院（对照区）不同绿化树种叶片重金属元素（Pb、Cd和Cu）的含量,揭示了14种绿化树种对3种重金属污染物的累积能力。结果表明,城市绿化树种对大气重金属污染物具有一定的吸收净化能力,并依重金属和树种的不同具有明显差异;同种植物对不同重金属的累积量也有很大差别,其中对Cu的累积量最高;采样区植物叶片重金属含量明显高于对照区;对Pb累积量高的树种有：杨树、广玉兰、女贞和紫叶李; Cd累积量高的树种为杨树;Cu累积量高的树种为构树;累积3种重金属综合能力最强的树种有杨树、构树、雪松、广玉兰、悬铃木、栾树。     

湖南石门、冷水江、浏阳3个矿区的苎麻重金属含量及累积特征

对湖南省石门、冷水江、浏阳3个矿区土壤和苎麻体内重金属进行测定和分析。结果表明,石门雄黄矿区As污染严重,伴随Cd、Sb污染和轻微的Pb污染;冷水江锑矿区Sb为主要污染物,伴随Cd、As、Pb污染;浏阳七宝山矿区Cd污染严重,伴随Pb、Zn、Cu污染。15个采样点的苎麻群落生长繁茂,Sb和As在苎麻不同部位间的分布次序为叶片中含量最高,根茎中次之,其余重金属在部位间分布没有规律。所有采样点苎麻地上部的Cd含量比一般植物的Cd含量大2-10倍,As含量大9.9-147.5倍,Sb含量大1.2-338.4倍;Cd富集系数和转移系数最高值为2.07和3;As富集系数和转移系数最高值为1.04和12.42,Sb富集系数和转移系数最高值为1.91和9.04。3个矿区苎麻地上部生物量分别为3.47,14.3,15.7 t/hm²,地上部Cd、Pb、As、Sb、Zn和Cu的累积量分别高达0.11、1.17、0.72、7.97、6.71,1.69 kg/hm²,兼具一定的经济价值和观赏性,适合用作矿区重金属污染土壤的环境治理和修复。     

Field accumulation risks of heavy metals in soil and vegetable crop irrigated with sewage water in western region of Saudi Arabia

Wastewater irrigated fields can cause potential contamination with heavy metals to soil and groundwater, thus pose a threat to human beings . The current study was designed to investigate the potential human health risks associated with the consumption of okra vegetable crop contaminated with toxic heavy metals. The crop was grown on a soil irrigated with treated wastewater in the western region of Saudi Arabia during 2010 and 2011. The monitored heavy metals included Cd, Cr, Cu, Pb and Zn for their bioaccumulation factors to provide baseline data regarding environmental safety and the suitability of sewage irrigation in the future. The pollution load index (PLI), enrichment factor (EF) and contamination factor (CF) of these metals were calculated. The pollution load index of the studied soils indicated their level of metal contamination. The concentrations of Ni, Pb, Cd and Cr in the edible portions were above the safe limit in 90%, 28%, 83% and 63% of the samples, respectively. The heavy metals in the edible portions were as follows: Cr > Zn > Ni > Cd > Mn > Pb > Cu > Fe. The Health Risk Index (HRI) was >1 indicating a potential health risk. The EF values designated an enhanced bio-contamination compared to other reports from Saudi Arabia and other countries around the world. The results indicated a potential pathway of human exposure to slow poisoning by heavy metals due to the indirect utilization of vegetables grown on heavy metal-contaminated soil that was irrigated by contaminated water sources. The okra tested was not safe for human use, especially for direct consumption by human beings. The irrigation source was identified as the source of the soil pollution in this study.     

Analysis of Spatial Variations and Sources of Heavy Metals in Farmland Soils of Beijing Suburbs

To understand the effect of intense human activities in suburbs on environmental quality, we obtained 758 measurements of the heavy metals in certain farmland soils of the Beijing suburbs. Multivariate statistical analysis and geostatistical analysis were used to conduct a basic analysis of the heavy metal concentrations, the distribution characteristics and the sources of pollution of the farmland soils in these suburbs. The results showed the presence of eight heavy metals in the agricultural soils at levels exceeding the background values for As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn. In particular, all the measured Cr concentrations exceeded the background value, while As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were present at 1.13, 1.68, 1.95, 1.43, 1.63, 0.79, 0.92 and 1.36 times their background values, respectively. The results of correlation, factor and spatial structure analyses showed that Cd, Cu, Pb and Zn were strongly homologous, whereas Cr and Hg showed a degree of heterogeneity. The analysis further indicated that in addition to natural factors, Cd, Cu, Pb and Zn in the soil were mainly associated with distribution from road traffic and land use status. Different agricultural production measures in the various areas were also important factors that affected the spatial distribution of the soil Cr concentration. The major sources of Hg pollution were landfills for industrial waste and urban domestic garbage, while the spatial distribution of As was more likely to be a result of composite pollution. The regional distribution of the heavy metals indicated that except for Cr and Hg, the high heavy metal levels occurred in districts and counties with higher organic matter concentrations, such as the northwestern and southeastern suburbs of Beijing. There was no significant Ni pollution in the agricultural soils of the Beijing suburbs.