Small Heat Shock Proteins Protect Electron Transport in Chloroplasts and Mitochondria During Stress

Evidence indicates that small heat-shock proteins (Hsps) areinvolved in stress tolerance, but the specific cell componentsor functions that small Hsps protect or repair are mostly unidentified.We recently showed that the chloroplast small Hsps of higherplants (1) are produced in response to many environmental stresses(e.g., heat, oxidative, and high-light stress); and (2) protect(but do not repair) photosynthetic electron transport in vitroduring stress, specifically by interacting with the oxygen-evolving-complexproteins of Photosystem II (PSII) within the thylakoid lumen.However, in vivo evidence of the importance of these Hsps tophotosynthetic stress tolerance is lacking. Here we report positiverelationships between chloroplast small Hsp production and PSIIthermotolerance in (1) a heattolerant genotype of Agrostis palustris(bentgrass) and a heat sensitive genotype which lacks one ormore chloroplast small Hsps produced by the tolerant genotype;(2) ecotypes of Chenopodium album (lambs quarters) from thenorthern vs. southern U.S. (New York vs. Georgia); and (3) nineLycopersicon (tomato) cultivars/species differing in heat tolerance.These in vivo results are consistent with our previous in vitroobservations and indicate that genetic variation in productionof the chloroplast small Hsp is an important determinant ofphotosynthetic and, thereby, whole-plant thermotolerance. Recently,we showed that the mitochondrial small Hsp of plants protectsrespiratory (specifically Complex I) electron transport in vitroduring heat stress, and here we present evidence for previouslyunidentified small Hsps in mitochondria of mammal (rat) cellswhich also protect Complex I during heat stress. These resultssuggest that the mitochondrial small Hsps, like the small chloroplastHsps, are general stress proteins that contribute significantlyto cell and organismal stress tolerance.     

城市绿化树种香樟不同器官对土壤重金属的富集特征

为了了解不同土壤重金属浓度梯度及污染梯度下香樟不同器官的富集特征,测定了香樟树叶、树枝、树干和根际土壤中6种重金属元素(Cu、Zn、Pb、Cr、Mn、Ni)的含量.结果表明: 香樟地上部分重金属含量因器官、元素种类、根际土壤重金属浓度的不同而存在差异.香樟树叶和树枝重金属含量的大小顺序均为:Mn＞Zn＞Cu＞Cr＞Pb＞Ni,树干重金属含量为:Mn＞Zn＞Cr＞Pb＞Ni＞Cu.树叶对Mn的富集系数较高,为2.409;树干对Ni的富集系数较高,分别为树叶、树枝的8.6和17倍,且在不同土壤重金属浓度梯度下,香樟树干对Cu、Zn、Pb、Cr、Ni的富集系数均明显高于其他器官.香樟地上部分器官对Cu、Zn、Pb、Cr、Mn、Ni 6种重金属元素的综合富集能力大小顺序为:树叶＞树干＞树枝.随着土壤重金属污染等级的增加,香樟地上部分各器官的富集系数均逐渐降低.研究区域平均胸径为22 cm的单株香樟对重金属元素富集效能的大小顺序为:树叶＞树干＞树枝,其中树干对Cu、Zn、Pb、Cr、Ni的积累量均显著高于树叶和树枝.表明香樟对6种重金属元素均有一定的富集能力,并且树干对Pb和Ni的富集效能明显,分别占地上部分总积累量的82.7%和91.9%,能很好地富集并稳固土壤中的Pb和Ni,可作为修复治理土壤重金属污染的备选树种.     

Response of ectomycorrhizalPinus banksiana andPicea glauca to heavy metals in soil

Pinus banksiana andPicea glauca inoculated or not with the ectomycorrhizal fungusSuillus luteus were grown in a sandy loam soil containing a range of Cd, Cu, Ni, Pb and Zn concentrations. Ectomycorrhizal colonization rates were significantly reduced on Pinus and Picea seedlings by the heavy metals, particularly Cd and Ni. Needle tissue metal concentrations were lower in ectomycorrhizal seedlings at low soil metal concentrations. However, at higher soil concentrations, heavy metal concentrations of needle tissue were similar in ectomycorrhizal and nonmycorrhizal plants. The growth of nonmycorrhizal seedlings exposed to heavy metals was reduced compared to those inoculated withSuillus luteus. Apparently ectomycorrhizal colonization can protect Pinus and Picea seedlings from heavy metal toxicity at low or intermediate soil concentrations of Cd, Cu, Ni, Pb and Zn.     

Physiological Effects of Heavy Metals on the Moss Rhytidiadelphus squarrosus

Experiments on the effect of Cd, Cu, Ni, Pb and Zn, suppliedas single salt solutions between 10 µM and 0·1M, on the moss Rhytidiadelphus squarrosus showed little alterationto respiratory rates but reduced photosynthetic rates, and somemembrane damage as assessed by K leakage. Two distinct morphologicalforms of the moss showed different responses to supplied heavymetal. Storage of material, after 30 mins exposure to heavymetals, resulted in a further decrease in the photosyntheticrate. Expressing the photosynthetic decline relative to thetotal heavy metal recovered from the moss showed a similar pattern.Transfer of metal from extracellular exchange sites into theprotoplast was also demonstrated with storage after exposure.An approximately linear relationship was demonstrated betweenphotosynthetic decline and intracellular heavy-metal concentration,irrespective of the duration of exposure or morphological natureof the material used. Photosynthetic decline on storage is concludedto be a response to additional metal stress rather than a progressivedeterioration of the physiological process. Cadmium, copper, lead, nickel, zinc, photosynthesis, respiration, membrane damage, intracellular metals, Rhytidiadelphus squarrosus (Hedw.) Warnst     

Accumulation of Heavy Metals in Water,Sediments and Wetland Plants of Kizilirmak Delta (Samsun,Turkey)

In this study, concentrations of heavy metals (Fe, Mn, Ni, Co, Zn, Cu, and Pb) were measured in water bodies including streams, bottom sediments and various wetland plants of K?z?l?rmak Delta. K?z?l?rmak Delta is one of the largest and the most important natural wetlands in Turkey and has been protected by Ramsar convention since 1993. The heavy metal concentrations in water were found lower than that of national standards for protected lakes and reserves. In bottom sediments and wetland plants, however, the accumulated amounts of different heavy metals varied in the following order: Fe>Mn>Zn>Ni>Co>Cu>Pb, and Fe>Mn>Zn>Ni>Co respectively. Heavy metal uptake of Hydrocharis morsus-ranae and Myriophyllum verticillatum plants among others were found far above the toxic levels and they might be used as bio-indicators and heavy metal accumulators in polluted natural areas.     

Source identification and availability of heavy metals in peri-urban vegetable soils: A case study from China

The purpose of this study was to investigate the total and available concentrations of Pb, Cr, Cu, Ni, and Zn in the vegetable soils from the outskirts of a heavy industry city, Northeast China, and to assess the sources of heavy metals and their availability. The average concentrations of Pb, Cu, and Zn were significantly higher than their background values of Changchun topsoil. Principal component analysis, cluster analysis, and geostatistical analysis results suggested that Pb, Cu, and Zn were consistently from anthropogenic sources, while Cr and Ni were from natural sources with low concentrations. Kriging results showed that several hotspots of high metal concentration were identified by the geochemical maps and caused by different environmental factors. Although the available (ethylene-diamine-tetraacetic acid-extractable) fractions showed much lower values than total concentrations of metals, Pb and Cu had relatively high AR^a (average availability ratio of metals) values. Our findings show that most of the studied metals had accumulated to some extent in vegetable soils and several hotspots of high metal concentration appeared at the peri-urban of Changchun. The concentrations of some metals in peri-urban vegetable soils have been largely affected by anthropogenic activities. Appropriate measures should be taken to effectively control heavy metal levels in vegetable soils and thus protect human health.     

Bioremediation of Heavy Metals in Liquid Media Through Fungi Isolated from Contaminated Sources

Wastewater particularly from electroplating, paint, leather, metal and tanning industries contain enormous amount of heavy metals. Microorganisms including fungi have been reported to exclude heavy metals from wastewater through bioaccumulation and biosorption at low cost and in eco-friendly way. An attempt was, therefore, made to isolate fungi from sites contaminated with heavy metals for higher tolerance and removal of heavy metals from wastewater. Seventy-six fungal isolates tolerant to heavy metals like Pb, Cd, Cr and Ni were isolated from sewage, sludge and industrial effluents containing heavy metals. Four fungi (Phanerochaete chrysosporium, Aspegillus awamori, Aspergillus flavus, Trichoderma viride) also were included in this study. The majority of the fungal isolates were able to tolerate up to 400 ppm concentration of Pb, Cd, Cr and Ni. The most heavy metal tolerant fungi were studied for removal of heavy metals from liquid media at 50 ppm concentration. Results indicated removal of substantial amount of heavy metals by some of the fungi. With respect to Pb, Cd, Cr and Ni, maximum uptake of 59.67, 16.25, 0.55, and 0.55 mg/g was observed by fungi Pb3 (Aspergillus terreus), Trichoderma viride, Cr8 (Trichoderma longibrachiatum), and isolate Ni27 (A. niger) respectively. This indicated the potential of these fungi as biosorbent for removal of heavy metals from wastewater and industrial effluents containing higher concentration of heavy metals.     

Lead,cadmium and nickel removal efficiency of white-rot fungus Phlebia brevispora

Widespread of heavy metals contamination has led to several environmental problems. Some biological methods to remove heavy metals from contaminated wastewater are being widely explored. In the present study, the efficiency of a white-rot fungus, Phlebia brevispora to remove different metals (Pb, Cd and Ni) has been evaluated. Atomic absorption spectroscopy of treated and untreated metal containing water revealed that all the metals were efficiently removed by the fungus. Among all the used metals, cadmium was the most toxic metal for fungal growth. Phlebia brevispora removed maximum Pb (97·5%) from 100 mmol l⁻¹ Pb solution, which was closely followed by Cd (91·6%) and Ni (72·7%). Scanning electron microscopic images revealed that the presence of metal altered the morphology and fine texture of fungal hyphae. However, the attachment of metal on mycelia surface was not observed during energy-dispersive X-ray analysis, which points towards the intracellular compartmentation of metals in vacuoles. Thus, the study demonstrated an application of P. brevispora for efficient removal of Pb, Cd and Ni from the metal contaminated water, which can further be applied for bioremediation of heavy metals present in the industrial effluent.     

Ethylene reverses photosynthetic inhibition by nickel and zinc in mustard through changes in PS II activity,photosynthetic nitrogen use efficiency,and antioxidant metabolism

We investigated the influence of exogenously sourced ethylene (200 μL L^?1 ethephon) in the protection of photosynthesis against 200 mg kg^?1 soil each of nickel (Ni)- and zinc (Zn)-accrued stress in mustard (Brassica juncea L.). Plants grown with Ni or Zn but without ethephon exhibited increased activity of 1-aminocyclopropane carboxylic acid synthase, and ethylene with increased oxidative stress measured as H₂O₂ content and lipid peroxidation compared with control plants. The oxidative stress in Ni-grown plants was higher than Zn-grown plants. Under metal stress, ethylene protected photosynthetic potential by efficient PS II activity and through increased activity of ribulose-1,5-bisphosphate carboxylase and photosynthetic nitrogen use efficiency (P-NUE). Application of 200 μL L^?1 ethephon to Ni- or Zn-grown plants significantly alleviated toxicity and reduced the oxidative stress to a greater extent together with the improved net photosynthesis due to induced activity of ascorbate peroxidase and glutathione (GSH) reductase, resulting in increased production of reduced GSH. Ethylene formation resulting from ethephon application alleviated Ni and Zn stress by reducing oxidative stress caused by stress ethylene production and maintained increased GSH pool. The involvement of ethylene in reversal of photosynthetic inhibition by Ni and Zn stress was related to the changes in PS II activity, P-NUE, and antioxidant capacity was confirmed using ethylene action inhibitor, norbornadiene.     

Pb、Ni胁迫对大羽藓抗氧化酶系统的影响

研究了Pb、Ni单一及复合胁迫下大羽藓细胞活性氧自由基的累积与清除、光合系统和膜系统的受损情况及其抗氧化酶系统的变化.结果表明：在较低胁迫浓度(Pb<0.1 mmol·L^-1,Ni<0.01 mmol·L^-1)下,大羽藓叶绿素含量具有应激效应,在较高胁迫浓度(Pb>0.1 mmol·L^-1,Ni>0.01 mmol·L^-1)下则具有抑制效应;随Pb-Ni复合胁迫浓度的增加,苔藓活性氧自由基和丙二醛的累积量逐渐增大;大羽藓超氧化物歧化酶和过氧化氢酶活性降低,过氧化物酶活性增加,过氧化物酶在清除Pb、Ni胁迫产生的活性氧自由基的过程中起着重要作用.大羽藓丙二醛含量和过氧化氢酶活性对Pb、Ni胁迫具有浓度依赖性,可以将其作为监测该类重金属污染的生物标志物.     

Phytoextraction of zinc, copper, nickel and lead from a contaminated soil by different species of Brassica

In a pot culture experiment, five different species of Brassica (Brassica juncea, Brassica campestris, Brassica carinata, Brassica napus, and Brassica nigra) were grown for screening possible accumulators of heavy metals, viz. Zn, Cu, Ni, and Pb. The plants were grown to maturity in a soil irrigated with sewage effluents for more than two decades in West Delhi, India. The soil analysis showed enhanced accumulation of Zn, Cu, Ni, and Pb in this sewage-irrigated soil. Among all species, B. carinata showed the highest concentration (mg kg(-1)) as well as uptake (microg pot(-1)) of Ni and Pb at maturity. Although B. campestris showed a higher concentration of Zn in its shoots (stem plus leaf), B. carinata extracted the largest amount of this metal due to greater biomass production. However, B. juncea phytoextracted the largest amount of Cu from the soil. In general, the highest concentration and uptake of metal was observed in shoots compared to roots or seeds of the different species. Among the Brassica spp., B. carinata cv. DLSC1 emerged as the most promising, showing greater uptake of Zn, Ni, and Pb, while B. juncea cv. Pusa Bold showed the highest uptake of Cu. The B. napus also showed promise, as it ranked second with respect to total uptake of Pb, Zn, and Ni, and third for Cu. Total uptake of metals by Brassica spp. correlated negatively with available as well as the total soil metal concentrations. Among the root parameters, root length emerged as the powerful parameter to dictate the uptake of metals by Brassica spp. Probably for the first time, B. carinata was reported as a promising phytoextractor for Zn, Ni, and Pb, which performed better than B. juncea.     

豚草叶片和果实气体交换特性与11种土壤重金属相关性

对10个样地中Cu、Pb、Zn、Mn、Cr、Co、Ni、Cd、As、Sb和Hg11种土壤重金属含量及样地内豚草叶片和果实气体交换特性进行测定.结果表明,样地内豚草叶片的净光合速率在1·88~9·41μmol·m-2·s-1,而果实的净光合速率最高可达2·81μmol·m-2·s-1.叶片的呼吸速率、气孔导度、光合速率和水分利用效率的平均值分别为1·81μmol·m-2·s-1、75·7mmol·m-2·s-1、6·05μmol·m-2·s-1和4·72μmol·mmol-1,分别是果实的5·26、0·64、1·31和1·69倍,说明非同化器官幼嫩果实具有与叶片相当,甚至更强的呼吸、光合能力和水分利用效率;研究地点重金属Ni达到轻微污染水平,其它重金属含量都接近或者显著低于重金属污染的阈值.相关分析和多元回归分析显示,大部分土壤重金属(如Cu、Pb、Zn、Cd、As、Sb和Hg)含量的高低对豚草气体交换特性没有显著影响,仅部分重金属含量与豚草的叶片、果实气体交换特性密切相关,如Ni和Cr对豚草叶片、果实的气孔导度及水分利用效率显著相关;Cr与豚草叶片饱和光合速率显著相关;而As与豚草果实的气孔导度显著相关.表明大部分土壤重金属对叶片和球果的气体交换没有直接影响,而Ni、Cr和As可以在轻微污染甚至没有达到污染水平时影响豚草的气体交换特性.     

深圳市不同功能区土壤表层重金属污染及其综合生态风险评价

在综合考虑深圳市城市功能区分异特征的基础上,进行全市表层土壤系统采样,全面监测土壤表层8种重金属元素污染状况,分析不同重金属元素含量的统计学特征,探讨不同城市功能区对土壤表层重金属污染的影响,采用内梅罗指数和潜在生态危害指数评估不同重金属元素和不同城市功能区的生态风险水平,分别进行基于两种方法的全市重金属污染生态风险分区。结果表明: 1)深圳市土壤表层的Mn、Ni、Cr和Pb 4种元素受人为活动的影响程度较低,Cd、Zn、Cu和As 4类元素受人为活动影响较大。地表环境约束因素背景下的高强度城市化和工业化过程,是各种重金属污染区域分异和功能区分异的决定性因素。2)深圳市土壤重金属污染风险较高的重金属元素为Cd、Zn、Cu和Pb,特别是Pb污染问题尤为突出,必须加强管控工作。深圳市总体土壤表层重金属污染风险水平高于国内相关城市,需要引起足够重视。3)内梅罗指数法和潜在生态危害指数法的侧重点不同,在单一重金属元素风险判断、不同城市功能区生态风险的总体评价,以及市域土壤重金属污染生态风险分级评价方面结果差异较大,组合使用效果更好。     

Heavy Metal Phytotoxicity to Radish (Raphanus sativus L.) in a Digested Sludge-amended Gangetic Alluvium

A limiting factor in land application of sewage sludge is the resultant heavy metal accumulation in soils followed by biomagnification in the food chain, posing a potential hazard to animal and human health. In view of this fact, pot experiments were conducted to evaluate the effect of digested sludge application to soil on phytotoxicity of heavy metals such as Cd, Cr, Ni, and Pb to radish (Raphanus sativus L.) plants. Increasing sludge levels resulted in increased levels of DTPA-extractable heavy metals in the soil. Cadmium was the dominant metal extracted by DTPA followed by Ni, Pb, and Cr. The extractability of metals by DTPA tended to decrease from the first to the second crop. Dry matter yield of radish increased significantly as a function of increasing sludge treatments. Soil application of sludge raised the concentration of one or more heavy metals in plants. Shoots contained higher concentrations of Cd, Cr, and Ni than the roots of radish plants. Shoot concentrations of Cd, Cr, Ni, and Pb were within the tolerance levels of this crop at all rates of sludge application. Shoot as well as root concentration of Cd was above 0.5 mg kg^?1, considered toxic for human and animal consumption. The levels of DTPA-extractable Cd and Ni were less correlated while those of Cr and Pb were more correlated with their respective shoot and root contents. The results emphasize that accumulation of potentially toxic heavy metals in soil and their build-up in vegetable crops should not be ignored when sludge is applied as an amendment to land.     

Sources and Contamination of Heavy Metals in Sediments of Kabul River: The Role of Organic Matter in Metals Retention and Accumulation

In this study, sediment samples were collected from Kabul River (Pakistan) and analyzed for heavy metals including zinc (Zn), cadmium (Cd), chromium (Cr), nickel (Ni) and lead (Pb). The physico-chemical characteristics were also determined which are known to influence the metal accumulation within the sediment matrix. Heavy metal concentrations (mg kg^?1, dry weight basis) in the sediment were in the order of Zn > Cr > Ni > Pb > Cd. Heavy metal concentrations were found in moderately polluted category set by U. S. Environmental Protection Agency (USEPA). However, Cr and Ni concentrations exceeded the screening levels at the sites where a larger volume of industrial effluents enter into Kabul River. Higher concentrations of almost all the tested metals were detected at locations of greater industrial and sewage entry points. Sediment organic matter (OM) exhibited strong correlation with Pb (R² = 0.80), Ni (R² = 0.67) and Zn (R² = 0.46), indicating that OM plays a significant role in metal retention and accumulation. The findings of this study showed that Kabul River is reasonably contaminated with selected heavy metals released from anthropogenic sources. In the study area, sewage discharge was the major source of heavy metals including Zn and Pb, which were observed at locations where sewage effluents enter into the river.     

Field studies on the relation between the accumulation of heavy metals and metabolic and HSR in the bearded horse mussel Modiolus barbatus

The present study aims to examine whether the seasonal changes in the levels of heavy metals Cd and Pb in the gills of sublittoral mussel Modiolus barbatus from populations distributed in Thermaikos Gulf are correlated to seasonal molecular (Heat Shock Response) and metabolic stress responses of this species. Our results indicate a season effect in the accumulation of heavy metals in the gills of bivalves in the area of Thermaikos Gulf, possibly implicating biological (reproductive cycle), natural (rivers' flow) and anthropogenic factors. Among the members of heat shock proteins (Hsps) examined, inducible Hsp70 seemed to play a major cytoprotective role against toxicity of metals. However, bivalves' tolerance against heavy metals may decrease during warming, arising further questions for their survival in context of global warming.     

Mitigation of Heavy Metal Contamination in Soil via Successive Pig Slurry Application

This study evaluates heavy metal removal associated with phytomass management in a Typic Hapludox after three applications of pig slurry. Like humic acids in pig slurry were characterized through physics and chemical spectroscopy technics. Heavy metal levels were determined in ration that was offered to pigs, anaerobically digested pig slurry, and plant tissues from pig slurry-fertilized black oat (Avena strigosa Schreb.) and ryegrass (Lolium multiflorum Lam.) intercrop. Soil contamination was evaluated by the pseudo-total heavy metal levels in six soil layers and the bioavailable levels in the top soil layer. Results indicate that the ration is the origin of heavy metals in the pig slurry. The approximate levels in the ration were as follows (mg kg^?1): Cu 23.9, Zn 92.02, 153.15, Mn 30.98, Ni 0.23, Pb 10.75, Cr 0.34, Co 0.08, and Cd 0.05. The approximate levels of these metals in the pig slurry were as follows (mg kg^?1): Cu 71.08, Zn 345.67, Fe 83.02, Mn 81.71, Ni 1.13, Pb 4.35, Co 0.28, and Cd 0.16. Like humic acids contained 55% aliphatic chains, 14% oxygenated aliphatic chains, and 15% carboxyls, demonstrating their high capacity for interaction with heavy metals by forming soluble complexes. Soil contamination was indicated by the accumulation of heavy metals in the six soil layers in relation to the applied pig slurry dose (ranged as follows (mg kg^?1): Cu 110 to 150, Zn 50 to 120, Ni 20 to 40, and Pb 12 to 16) and as bioavailable forms (levels ranged as follows (mg kg^?1): Cu < 1, Zn 1.0–1.5, Ni 0.1–1.5, and Pb 1.9–6.3). The positive correlation between heavy metal accumulation in the plants and soil bioavailable heavy metal levels and the lowest heavy metal levels under higher intensity of phytomass removal demonstrate the ability of phytomass management to reduce soil contamination.     

Lead induced changes in phosphorylation of PSII proteins in low light grown pea plants

Light-intensity and redox-state induced thylakoid proteins phosphorylation involved in structural changes and in regulation of protein turnover. The presence of heavy metal ions triggers a wide range of cellular responses including changes in plant growth and photosynthesis. Plants have evolved a number of mechanisms to protect photosynthetic apparatus. We have characterized the effect of lead on PSII protein phosphorylation in pea (Pisum sativum L.) plants grown in low light conditions. Pb ions affected only slightly photochemical efficiency of PSII and had no effect on organization of thylakoid complexes. Lead activated strongly phosphorylation of PSII core D1 protein and dephosphorylation of this protein did not proceed in far red light. D1 protein was also not degraded in this conditions. However, phosphorylation of LHCII proteins was not affected by lead. These results indicate that Pb²⁺ stimulate the phosphorylation of PSII core proteins and by disturbing the disassembly of supercomplexes play a role in PSII repair mechanism. LHCII phosphorylation could control the distribution of energy between the photosystems in low light conditions. This demonstrates that plants may respond to heavy metals by induction different pathways responsible for protein protection under stress conditions.     

Evaluation of Heavy Metals and Associated Health Risks in a Metropolitan Wastewater Treatment Plant's Sludge for Its Land Application

The objectives of this study are to monitor the heavy metal concentrations in sludge samples collected from the Ankara Central Wastewater Treatment Plant (ACWWTP) in Turkey, check if these concentrations comply with the Turkish Regulation (Regulation Regarding the Use of Domestic and Urban Sludges on Soil), and evaluate possible health risks of heavy metals in sludge due to ingestion of sludge by a child. Monthly sludge samples were collected from the ACWWTP during 2012 and analyzed for seven heavy metals (Cd, Cr, Cu, Hg, Ni, Pb, and Zn). According to the results from the study, heavy metal concentrations showed no common seasonal trend. All heavy metal concentrations, except for one sample in which Zn was found to be at the limit value, are below the Turkish Regulation limits. In addition, health risks calculations for the “child ingesting biosolids” pathway, which is one of the most critical pathways identified by the U.S. Environmental Protection Agency (USEPA) for land application, were carried out. Among the seven heavy metals, Pb contributed the most to the cumulative non-cancer health risks throughout 2012. Nevertheless, the results showed that cumulative non-cancer health risks associated with this pathway are within the acceptable non-cancer health risk level suggested by USEPA.     

行道树毛白杨树干中重金属元素分布

采用电感耦合等离子体发射光谱法(ICP),测定分析首都机场高速公路旁毛白杨(Populus tomentosa Carr.)树干中Pb、Cd、Cr、Cu、Zn、Ni和Mn 7种重金属元素的含量及积累量,比较分析树干不同组织、不同方位、不同龄级年轮重金属含量差异及与交通量、关键气候因子的相关性。结果表明:树干木质部中各重金属平均含量由大到小依次为Zn、Cu、Cr、Mn、Ni、Pb、Cd,树皮中依次为Zn、Mn、Cr、Pb、Cu、Cd、Ni,树皮中各重金属元素的含量明显高于木质部;同一树干木质部中,各重金属元素在不同方位的分布有所差异,其中,靠近车道一侧的各重金属元素含量均高于背离车道一侧,南北向比较中,Ni、Zn为南侧含量高于北侧,其他5种重金属元素均为北侧高于南侧;以5a为一个龄级将年轮划分为5个龄组,各龄级年轮中重金属含量随时间的变化趋势各异,其中Pb、Cd、Cu、Zn总体呈递减趋势,且与年降水量、最低气温、日照时数、雨天日数和大风日数呈正相关趋势,与年平均气温和最高气温呈负相关趋势;各元素在毛白杨树干木质部中的积累量表现为ZnCrCuMnPbNiCd。