Heavy metals in white lupin: uptake, root-to-shoot transfer and redistribution within the plant

The translocation of manganese (Mn), nickel (Ni), cobalt (Co), zinc (Zn) and cadmium (Cd) in white lupin (Lupinus albus cv. Amiga) was compared considering root-to-shoot transport, and redistribution in the root system and in the shoot, as well as the content at different stages of cluster roots and in other roots. To investigate the redistribution of these heavy metals, lupin plants were labelled via the root for 24 h with radionuclides and subsequently grown hydroponically for several weeks. 54Mn, 63Ni and 65Zn were transported via the xylem to the shoot. 63Ni and 65Zn were redistributed afterwards via the phloem from older to younger leaves, while 54Mn remained in the oldest leaves. A strong retention in the root was observed for 57Co and 109Cd. Cluster roots contained higher concentrations of all heavy metals than noncluster roots. Concentrations were generally higher at the beginning of cluster root development (juvenile and immature stages). Mature cluster roots also contained high levels of 54Mn and 57Co, but only reduced concentrations of 63Ni, 65Zn and 109Cd.     

Copper uptake and translocation in chicory (Cichorium intybus L. cv Grasslands Puna) and tomato (Lycopersicon esculentum Mill. cv Rondy) plants grown in NFT system. II. The role of nicotianamine and histidine in xylem sap copper transport

The effect of rooting media Cu concentration (0.05–20 mg Cu L^-1) on amino acid concentrations and copper speciation in the xylem sap of chicory and tomato plants was measured using 6 week old plants grown in a nutrient film technique system (NFT). Irrespective of the Cu concentration in the nutrient solutions, more than 99.68% and 99.74% of total Cu in tomato and chicory xylem sap was in a bound form. When exposed to high Cu concentrations in the rooting media, amino acid concentrations in the sap increased. Relative to other amino acids, the concentrations of glutamine (Gln), histidine (His), asparagine (Asn), valine (Val), nicotianamine (NA) and proline (Pro) in tomato xylem saps, and His, γ-aminobutyric acid (Gaba), glutamic acid (Glu), leucine (Leu), NA and phenylalanine (Phe) in chicory xylem saps showed the greatest increases. The data indicate that induced synthesis of some free amino acids as a specific and proportional response to Cu treatment. For a single complexation amino acid, the solution Cu²⁺concentration vs pH titration curve for NA at 0.06–0.07 mM was most similar, closely followed by His at 0.5–0.6 mM, to the solution Cu²⁺concentration behaviour in both tomato and chicory xylem sap. It is concluded that increased Cu concentrations in the rooting media induced selective synthesis of certain amino acid which include NA, His, Asn and Gln which have high stability constants with Cu. NA and His have the highest binding constants for Cu and the concentrations of NA and His in chicory and tomato xylem saps can account for all the bound Cu carried in the sap. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ecological and human health risk assessment of agricultural soils based on heavy metals in mining areas of Singhbhum copper belt,India

Risk characterization of agricultural soils in the mining areas of Singhbhum copper belt was done by determining the total concentrations of metals using inductively coupled plasma-mass spectrometry and assessing the potential ecological and human health risks. The concentrations were above the average shale values for most of the metals. Principal component analysis showed anthropogenic contributions of Cu, Ni, Co, Mn, Pb, and Cr in the soils. Ecological risk assessment revealed that 50% of the soil samples were at moderate to very high ecological risk. Health risks for adults and children were calculated using hazard quotients (HQs), hazard index (HI), and Cancer risks for the oral, dermal, and inhalation pathways. The HQs for all the metals except As and Co were below 1, which suggested that non-carcinogenic risks due to metal exposure through soils were within the safe limit. However, considering all the metals and pathways, the HI for adults and children was 0.71 and 5.61, respectively, suggesting appreciable risk to local residents. The carcinogenic risks due to As and Cr in the soils were within the acceptable value of 1E–04. For both carcinogenic and non-carcinogenic risks, oral ingestion appeared to be the primary pathway followed by dermal and inhalation pathways.     

植物抗旱和耐重金属基因工程研究进展

干旱和重金属污染严重影响植物的生长发育.植物耐逆相关基因的克隆和功能鉴定研究,为通过基因工程途径提高植物的抗逆性奠定了理论基础.水分亏缺、高盐、低温和重金属胁迫都能诱导LEA(late embryogenesis abundant protein)基因的表达.转基因研究表明,LEA蛋白具有抗旱保护作用、离子结合特性以及抗氧化活性;水孔蛋白存在于细胞膜和液泡膜上,在细胞乃至整个植物体水分吸收和运输过程中发挥重要作用.干旱和盐胁迫促进水孔蛋白基因转录物的积累.过量表达水孔蛋白可增强水分吸收和运输,提高植物的抗旱能力.金属转运蛋白参与重金属离子的吸收、运输和累积等过程.这些蛋白基因在改良草坪草植物的抗旱节水和耐重金属能力等方面具有潜在的应用价值.     

乐安河—鄱阳湖湿地植物群落特征及其优势植物对重金属Cu、Pb、Cd的富集

选择乐安河—鄱阳湖湿地典型植物群落,采用重要值方法评价各样点植物群落特征并筛选出典型优势植物,通过室内理化测试分析不同生境中优势植物植株及其根区土壤中重金属Cu、Pb、Cd的含量;采用生物富集系数(BCF)方法评价不同优势植物对重金属Cu、Pb、Cd的富集特性。结果表明:研究区湿地植物以草本为主,在各样点共发现124种物种,包括蕨类植物2科2属2种,种子植物40科97属122种,并从中筛选出羊蹄、红蓼、鼠曲草、紫云英、苎麻等5种富集能力较强的优势植物;植物根区土壤中的Cu、Cd含量均超过土壤环境质量三级标准,而且Cu、Cd的最高含量分别为824.03、5.03 mg·kg-1;不同优势植物对Cu、Pb、Cd等3种重金属元素中的1种或2种表现出较强的富集能力,其中优势物种红蓼对Cu具有较强的富集能力,含Cu量最高为148.80 mg·kg-1,另一种优势物种鼠曲草对三种元素的生物富集系数均较高,且对Cd的最高富集含量为15.17 mg·kg-1,对Cd的生物富集系数最高值为19.14,高于其他植物10倍以上,鼠曲草对重金属Cd具有富集植物的基本特征,且对Cu和Cd具有共富集特征并具有较高的耐性,紫云英、羊蹄等对Cd的富集能力也较强。上述5种优势植物种群对鄱阳湖湿地Cu、Pb、Cd等重金属污染物的生态修复具有一定参考价值,可作为鄱阳湖湿地重金属污染修复植物的选择对象。     

鄱阳湖地区多尺度流域水体重金属输送特征及其污染风险评价

鄱阳湖流域的生态健康是维系长江下游区域生态安全的重要保障,而流域内丰富的重金属矿排放的工业废水会对流域生态健康产生巨大威胁。通过对不同级别河流水体中8种重金属（As、Cr、Fe、Mn、Mo、Pb、Se和V）的浓度进行监测,分析和探讨鄱阳湖流域河流重金属污染状况、来源及迁移输出特征,评估通江河流重金属迁移运输对鄱阳湖流域生态健康的影响。研究结果表明：鄱阳湖流域内梅罗综合污染指数平均值为2.67,属于中度污染,丰水期污染情况较为严重,污染指数在4.14-4.74之间,处于重度污染水平,水体主要污染元素是V和Se,V的最大浓度达331.90 μg/L,超过国家水质标准（50 μg/L）6.64倍。重金属浓度和由季节差异造成的水文特征变化是控制流域重金属输出通量的主要原因,而小流域的重金属输出通量对丰枯水期的响应更为敏感。香溪对架竹河、架竹河对赣江以及赣江对鄱阳湖的重金属输出通量分别为7.30 kg/km²、4.06 kg/km²和28.10 kg/km²。不同尺度流域对下游的重金属输出贡献率与径流量相关,丰水期,香溪流域对下游架竹河流域重金属输出的贡献率为1.10%,架竹河对赣江的贡献率为0.02%,而在枯水期,上述贡献率分别为1.61%和0.02%。主成分分析表明鄱阳湖流域水体溶解态重金属的主要污染来源为工业采矿,因此,在预防和治理鄱阳湖流域水体重金属污染问题时,应重点控制工业污染来源。     

Heavy metals in the Rosetta estuary of the Nile and the adjoining Mediterranean waters: evidence of removal of dissolved heavy metals from waters as a result of possible binding to suspended matter

The Rosetta estuary was partially separated from the Rosetta branch of the Nile by Edfina Barrage, which controls the Nile discharge into the Mediterranean Sea. The study area covers the Rosetta estuary (lotic environment) and the adjoining seawaters (lentic environment) to investigate the local and seasonal distribution of dissolved and particulate copper and zinc, as well as dissolved cadmium in this estuary and to illustrate its influence on the distribution of these metal forms in the inshore seawaters. Besides, emphasis on the removal of dissolved heavy metals from waters by their adsorption onto suspended matter (SM) was also considered. Contrary to particulate copper (PCu), the vertical values of dissolved copper (DCu) decreased generally with depth. Planktonic scavenging and regeneration processes might determine the vertical profiles of the copper forms. The copper data suggest that the surface sources of DCu exceeded the bottom sources, contrary to the sources of PCu. The markedly high and maximum seasonal averages of DCu in the estuary and inshore seawater in July inspite of the high uptake in summer possibly reflect higher amounts of humic materials. The lowest seasonal average value of DCu in the inshore seawater in January suggests removal of copper in presence of maximum value of SM during highest discharge. The highest regional average of DCu at the estuarine mouth coincided with desorption process during mixing of the fresh and salt waters. The vertical values of dissolved zinc (DZn) and particulate zinc (PZn) showed irregular variations and their high concentrations in the surface of the estuarine and inshore seawater indicate possible land-based sources. The high bottom DZn values, however, resulted from its contribution from the interstitial water of the sediments. The data suggest that the surface sources of DZn exceeded the bottom sources and PZn showed the opposite trend in the open sea area. In the estuary, the maximum seasonal average value of DZn accompanied by the lowest seasonal average of PZn in April inspite of the high uptake in spring suggest that desorption was the dominant process. The minimum regional averages of both zinc forms at the estuarine opening and the highest average of PZn near Edfina Barage are correlated with the amounts of SM, which decreased toward the estuarine mouth. The vertical values of dissolved cadmium (DCd) were much lower in the estuary than the other metals. They showed in both environments irregular variations with depth. The bottom maximum value of DCd can be attributed mainly to contamination from the sediments. There was a distinct seasonal variation of DCd. The minimum seasonal average value of DCd in the estuary in April seems to be caused by its specific binding to living plankton found in abundance. The minimum regional average of DCd value was found at the estuarine mouth. The decrease in Cd concentration due to removal from dissolved state is most pronounced in the early stage of mixing. The correlation coefficients of DCd were positive with salinity and negative with SM, indicating that Cd increased seaward. Statistical correlation between Cd and Zn concludes that the factors affecting their distribution are generally the same.     

Phloem translocation of Fe,Cu, Mn,and Zn in Ricinus seedlings in relation to the concentrations of nicotianamine,an endogenous chelator of divalent metal ions,in different seedling parts

During the first 8 days of germination the Ricinus seedling is supplied with all nutrients by the endosperm via phloem transport. In 4- to 8-days-old seedlings the concentrations and contents of Fe, Cu, Mn and Zn, and nicotianamine (NA) in the endosperm, cotyledons, hypocotyl and roots were estimated. From the data obtained translocation rates and flow profiles for the metals were established. The main sink for Fe, Mn and Zn were the cotyledons whereas Cu was mainly imported into the hypocotyl. Maximum flow rates occurred between days 5 and 7, for Zn between days 6 and 8.The time kinetics of NA and divalent metal ion concentrations and contents are interpreted as co-transport. The role of NA as transport vehicle of micronutrients in the sieve tubes is discussed.     

Distribution and bioavailability of heavy metals in different particle-size fractions of sediments in Taihu Lake,China

Abstract

Taihu Lake is one of the most important water sources in the economically developed central-eastern part of China, and metal pollution is a major concern for the lake. The distribution and bioavailability of Cd, Cr, Cu, Pb, Sb and Zn were analysed in undifferentiated bottom sediments and in various particle-size fractions of the sediment from different parts of the lake. The average concentration of total metals in undifferentiated sediments ranged from 0.86 mg kg^-1 (Cd) to 95.45 mg kg^-1 (Zn) for the entire lake, with the highest concentrations in Zhushan Bay. The concentration of heavy metals was higher in extremely fine sands (0.064–0.125 mm) and fine sands (0.125–0.25 mm) than in other fractions. Sequential extractions showed that Cu, Zn and Cd were the most bioavailable accounting for 55.6%, 38.7% and 30.0% of their total concentration, respectively. However, the bioavailable proportion of many metals was not significantly different between grain grades except for Cu and Zn, which were higher in silts (<0.064 mm) than in other grades. Compared with the background values of local soils, the concentration of Zn, Cd, Cu, Pb and Sb was higher, indicating enrichment in the sediment. From ecological safety concerns, Zn, Cd and Cu should be examined closely because of their higher bioavailabilty in the sediment.     

Modeling of phytoextraction efficiency of microbially stimulated Salix dasyclados L. in the soils with different speciation of heavy metals

Bioaugmentation of soils with selected microorganisms during phytoextraction can be the key solution for successful bioremediation and should be accurately calculated for different physicochemical soil properties and heavy metal availability to guarantee the universality of this method. Equally important is the development of an accurate prediction tool to manage phytoremediation process. The main objective of this study was to evaluate the role of three metallotolerant siderophore-producing Streptomyces sp. B1–B3 strains in the phytoremediation of heavy metals with the use of S. dasyclados L. growing in four metalliferrous soils as well as modeling the efficiency of this process based on physicochemical and microbiological properties of the soils using artificial neural network (ANN) analysis. The bacterial inoculation of plants significantly stimulated plant biomass and reduced oxidative stress. Moreover, the bacteria affected the speciation of heavy metals and finally their mobility, thereby enhancing the uptake and bioaccumulation of Zn, Cd, and Pb in the biomass. The best capacity for phytoextraction was noted for strain B1, which had the highest siderophore secretion ability. Finally, ANN model permitted to predict efficiency of phytoextraction based on both the physicochemical properties of the soils and the activity of the soil microbiota with high precision.     

Comparative strategies of heavy metal accumulation by crustaceans: zinc,copper and cadmium in a decapod,an amphipod and a barnacle

This study investigates the comparative strategies of accumulation under standardised laboratory conditions of the essential metals zinc and copper, and the non-essential metal cadmium by three crustaceans of different taxa; vizPalaemon elegans Rathke (Malacostraca: Eucarida: Decapoda),Echinogammarus pirloti (Sexton & Spooner) (Malacostraca: Peracarida: Amphipoda) and the barnacleElminius modestus Darwin (Cirripedia: Thoracica).The decapodP. elegans regulates body zinc concentrations to a constant level (ca. 79 µg Zn g^–1) over a wide range of dissolved metal availabilities until regulation breaks down at high Zn availabilities and net accumulation begins. The amphipodE. pirloti accumulates zinc at all dissolved zinc concentrations but at a low net rate such that the accumulation strategy approaches that of regulation. The barnacleE. modestus accumulates zinc to high body concentrations with no significant excretion of accumulated zinc. In the case of copper,P. elegans similarly regulates body copper concentrations to a constant level (ca. 129 µg Cu g^–1) over a range of dissolved copper availabilities until regulation breaks down at high copper concentrations. Both the amphipodE. pirloti and the barnacleE. modestus on the other hand accumulate copper at all dissolved copper exposures with no evidence of regulation. All three crustaceans accumulate the non-essential metal cadmium at all dissolved cadmium concentrations without regulation.Heavy metal accumulation strategies therefore vary between crustacean taxa and between metals. Uptake rates for zinc and cadmium have been estimated for the three crustaceans and can be interpreted in terms of cuticle permeability and way of life of each crustacean. Examination of these uptake rates provides an insight into possible reasons behind the adoption of particular metal accumulation strategies.     

Assessment of potentially toxic heavy metals and health risk in water,sediments, and different fish species of River Kabul,Pakistan

Contamination of freshwater bodies and consequently freshwater fish with toxic heavy metals is a serious environmental issue. The trophic transfer of potentially toxic heavy metals in the human food chains, especially in fish has important implications for human health. The present research study was designed to assess the concentrations of the heavy metals Cr, Ni, Cd, and Pb in the water, sediments, and different freshwater fish species of River Kabul, Pakistan. The heavy metals were quantified in the samples with Atomic Absorption Spectrophotometer. Heavy metal contamination in fish muscles was characterized in terms of metal pollution index and biota-sediments accumulation factor, while human health risk was assessed through calculation of estimated weekly intake. The average concentrations of Cr, Ni, Cd, and Pb in muscle samples of the analyzed fish species at different sampling sites of the river ranged from 12.3 to 33.0, 33.2 to 109.2, 0.98 to 1.5, and 13.9 to 29.6 mg kg^?1 wet weight, respectively. Based on the current study data, consumption of the analyzed freshwater fish species from River Kabul was generally safe in terms of potential risk from Cd and Pb but the observed Ni accumulation may pose a potential health risk to regular/excessive fish consumers.     

Identification of high levels of phytochelatins, glutathione and cadmium in the phloem sap of Brassica napus. A role for thiol-peptides in the long-distance transport of cadmium and the effect of cadmium on iron translocation

Phytochelatins (PCs) are glutathione-derived peptides that function in heavy metal detoxification in plants and certain fungi. Recent research in Arabidopsis has shown that PCs undergo long-distance transport between roots and shoots. However, it remains unknown which tissues or vascular systems, xylem or phloem, mediate PC translocation and whether PC transport contributes to physiologically relevant long-distance transport of cadmium (Cd) between shoots and roots. To address these questions, xylem and phloem sap were obtained from Brassica napus to quantitatively analyze which thiol species are present in response to Cd exposure. High levels of PCs were identified in the phloem sap within 24 h of Cd exposure using combined mass spectrometry and fluorescence HPLC analyses. Unexpectedly, the concentration of Cd was more than four-fold higher in phloem sap compared to xylem sap. Cadmium exposure dramatically decreased iron levels in xylem and phloem sap whereas other essential heavy metals such as zinc and manganese remained unchanged. Data suggest that Cd inhibits vascular loading of iron but not nicotianamine. The high ratios [PCs]/[Cd] and [glutathione]/[Cd] in the phloem sap suggest that PCs and glutathione (GSH) can function as long-distance carriers of Cd. In contrast, only traces of PCs were detected in xylem sap. Our results suggest that, in addition to directional xylem Cd transport, the phloem is a major vascular system for long-distance source to sink transport of Cd as PC–Cd and glutathione–Cd complexes.     

Evaluation of three different types of nitrogen,heavy metals,and endocrine disruptors in water and sediments of Wenyu River

Concentrations of NO₃^?(nitrate), NO₂^?(nitrite), NH₄⁺(ammonia nitrogen), Mn, Fe, Ba, As, Se, Cd, Pb, Cr⁶⁺, estrone (E1), estradiol (E2), ethinylestradiol (EE2), estriol (E3), bisphenol A (BPA), nonylphenol (NP) and 4-tert-octylphenol (OP) had been estimated in water and sediments of Wenyu River. Using single factor, ecological risk assessment, geoaccumulation index, human health risk assessment and multivariate statistical analysis, we described the current situation of river contamination, human health risks of different age groups and possible sources of pollutants as well as their transformation characteristics. The results showed that main contaminants were NH₄⁺, NO₃^?, NO₂^?, EE2 and E3, E1 in water, while sediments have been slightly polluted by heavy metals, whose order of polluting degree is Zn>Cr⁶⁺>Cd>Cu. Residents in the study area are exposed to the risk, and EE2 made the greatest contribution to it. E1, As, and NO_3^- also affect negatively on the health of the residents, and NO_2^- only do harm to juveniles. Human activities and industrial production are main sources of contaminants, also they can transform into each other between water and sediments. Heavy metal ions can be easily precipitated by Ferric oxide or hydroxide, E2 and EE2 are also transformed into E3 in natural environment.     

Mitotic chromosomal abnormalities and DNA polymorphism in the Nile tilapia (Oreochromis niloticus,Linnaeus, 1758) as a biomarker for water pollution by heavy metals

Mitotic chromosomal aberrations and DNA polymorphism (RAPD marker) were carried out on the Nile tilapia Oreochromis niloticus collected from five sites in Minia governorate, Egypt to test their applicability as biomonitors for heavy metal contaminants of water. The diploid chromosome number of O. niloticus population was 2 n = 44. Different types of chromosomal aberrations were recorded (e.g., deletion, ring, centromeric attenuation, end-to-end association, dicentric chromosome, stickiness chromosomes, endomitosis, fragments and chromatid gap). The chromosomal aberrations varied between O. niloticus population collected from five sites, and the most common type was ring (R) chromosomes. Samples obtained from Bahr Yousef and Irrigation drain exhibited the highest aberration frequency. The frequency of chromosomal aberration was positively correlated with the concentration of heavy metals where their concentration in the surface water of Irrigation drain and Bahr Yousef exceeded the limits defined by WHO as well as the concentration of Pb in muscles. The RAPD marker was also used to identify genetic variation among Nile tilapia samples collected from five different water sources. It created polymorphic and unique bands that can be used as genetic markers to track DNA variations. The dendrogram also revealed that exposure to heavy metal pollution causes gradual accumulation of variance, whereas areas subjected to environmental stress showed higher genetic variation and clustered together.     

Effectiveness of naturally occurring Aphis gossypii on tomato plants as a bio-indicator for heavy metals in Riyadh and Hafar Al-Batin,Saudi Arabia

Although certain pollutants can be biologically degraded by microorganisms, rendering their impact short-term, others can not be impaired, such that their effect persists. The present study evaluates the effectiveness of using a field-collected aphid, Aphis gossypii, as a bio-indicator for heavy metals in tomato farms in Riyadh and Hafar Al-Batin, Saudi Arabia. Heavy metals were selected (Cd, Cu, Zn, and Pb) and measured for comparative screening in field-collected plants, soil, and aphids using inductively coupled plasma-mass spectrometry (ICP-MS). Field-collected aphids from both studied regions were identified as Aphis gossypii. In Riyadh, there was no significant difference observed for Cd, Cu, and Zn for all experimental samples, while, Pb was showed differences among samples especially tomato leaves None of the studied samples in Hafar Al-Batin were showed statistically significant differences in Cd, in reverse to significant differences in the other heavy metals. Comparing concentrations of selected heavy metals between the two studied regions was showed that neither region showed a significant difference in heavy metals except for Cu. This study demonstrates that tomato leaf samples showed the highest concentrations of most studied heavy metals, followed by soil, then aphids. Aphids were utilized as a bio-indicator of heavy metals in the studied regions.     

Alleviation of heavy metals toxicity by the application of plant growth promoting rhizobacteria and effects on wheat grown in saline sodic field

The aim of the study was to determine tolerance of plant growth promoting rhizobacteria (PGPR) in different concentrations of Cu, Cr, Co, Cd, Ni, Mn, and Pb and to evaluate the PGPR-modulated bioavailability of different heavy metals in the rhizosphere soil and wheat tissues, grown in saline sodic soil. Bacillus cereus and Pseudomonas moraviensis were isolated from Cenchrus ciliaris L. growing in the Khewra salt range. Seven-day-old cultures of PGPR were applied on wheat as single inoculum, co-inoculation and carrier-based biofertilizer (using maize straw and sugarcane husk as carrier). At 100 ppm of Cr and Cu, the survival rates of rhizobacteria were decreased by 40%. Single inoculation of PGPR decreased 50% of Co, Ni, Cr and Mn concentrations in the rhizosphere soil. Co-inoculation of PGPR and biofertilizer treatment further augmented the decreases by 15% in Co, Ni, Cr and Mn over single inoculation except Pb and Co where decreases were 40% and 77%, respectively. The maximum decrease in biological concentration factor (BCF) was observed for Cd, Co, Cr, and Mn. P. moraviensis inoculation decreases the biological accumulation coefficient (BAC) as well as translocation factor (TF) for Cd, Cr, Cu Mn, and Ni. The PGPR inoculation minimized the deleterious effects of heavy metals, and the addition of carriers further assisted the PGPR.     

Root development and heavy metal phytoextraction efficiency: comparison of different plant species in the field

Heavy metal phytoextraction is a soil remediation technique which implies the optimal use of plants to remove contamination from soil. Plants must thus be tolerant to heavy metals, adapted to soil and climate characteristics and able to take up large amounts of heavy metals. Their roots must also fit the spatial distribution of pollution. Their different root systems allow plants to adapt to their environment and be more or less efficient in element uptake. To assess the impact of the root system on phytoextraction efficiency in the field, we have studied the uptake and root systems (root length and root size) of various high biomass plants (Brassica juncea, Nicotiana tabacum, Zea mays and Salix viminalis) and one hyperaccumulator (Thlaspi caerulescens) grown in a Zn, Cu and Cd contaminated soil and compared them with total heavy metal distribution in the soil. Changes from year to year have been studied for an annual (Zea mays) and a perennial plant (Salix viminalis) to assess the impact of the climate on root systems and the evolution of efficiency with time and growth. In spite of a small biomass, T. caerulescens was the most efficient plant for Cd and Zn removal because of very high concentrations in the shoots. The second most efficient were plants combining high metal concentrations and high biomass (willows for Cd and Zn and tobacco for Cu and Cd). A large cumulative root density/aboveground biomass ratio (L_A/B), together with a relative larger proportion of fine roots compared to other plants seemed to be additional favourable characteristics for increased heavy metal uptake by T. caerulescens. In general, for all plants correlations were found between L _A/B and heavy metal concentrations in shoots (r=0.758^***, r=0.594^***, r=0.798^*** (P<0.001) for Cd, Cu and Zn concentrations resp.). Differences between years were significant because of variations in climatic conditions for annual plants or because of growth for perennial plants. The plants exhibited also different root distributions along the soil profile: T. caerulescens had a shallow root system and was thus best suited for shallow contamination (0.2 m) whereas maize and willows were the most efficient in colonising the soil at depth and thus more applicable for deep contamination (0.7 m). In the field situation, no plant was able to fit the contamination properly due to heterogeneity in soil contamination. This points out to the importance and the difficulty of choosing plant species according to depth and heterogeneity of localisation of the pollution.     

Spatial and seasonal characteristics of dissolved heavy metals in the aquaculture areas of Beibu Gulf,South China

Abstract

To study the contamination of heavy metals in the aquaculture area of Beibu Gulf, the concentrations of seven metals in seawater were investigated. The results showed that significant seasonal and spatial distributions of heavy metals were observed in the four aquaculture areas. Generally, the heavy-metal concentrations in the Maowei Sea were higher than the other three aquaculture areas, which may be related to local industrialization and urbanization development. The concentrations of some metals were obviously higher in wet seasons than in dry seasons, which may be attributed to the seasonal river discharge, rainfall and seawater intrusion. Compared to other regions, some metal levels revealed relatively high contamination. Remarkably, the concentrations of Hg, Cu and Cd were much higher than concentrations found in the past 20?years in the seawater of the Guangxi Beibu Gulf, suggesting that there were increasing anthropogenic inputs of those metals in the aquaculture areas. The assessment of ecological risk index (ERI) indicated that the highest ERI value was found in the Maowei Sea, followed by Pearl Bay, Lianzhou Bay and Hongsha. Hg is the main ecological risk factor, and the heavy-metal contamination in the aquaculture areas must not be ignored.     

天山土壤微量(类)重金属的来源解析及潜在生态危害评估

从天山山地3个区段(巴里坤-伊吾、乌鲁木齐-阿克苏、昭苏-特克斯)采集土壤样品,测定了其中(类)重金属Pb、Ni、Cd、Co、Hg、Cu、Mn、Zn、Cr和As的含量.运用经典统计学与多元统计方法分析了这些(类)重金属的来源;同时采用污染指数法与潜在生态风险指数法,并结合天山及新疆土壤背景值、国家土壤质量标准开展了区域土壤微量(类)重金属生态风险的评价.结果表明： 所测10种(类)重金属的平均含量均高于天山或新疆土壤背景值.从变异系数来看,均为中等变异.总体上看,天山山地土壤中10种(类)重金属的含量均较低;主成分分析显示,10种元素可以辨识出 2 个主成分,主成分1(PC1,包括Cd、Pb、Hg、Mn和Zn)为人为源因子,主成分2(PC2,包括Cu、Ni、Cr、Co和As)为自然源因子.Mn 和As在PC1和PC2上均有较大载荷,主要受人为源和自然地质背景的共同控制;污染评价表明, 重金属Hg、Cd在天山中部的乌鲁木齐-阿克苏区段、As在天山西部的昭苏-特克斯区段的单因子污染指数(P_i)属于警戒等级,其他均属于安全等级和清洁水平.从综合污染(P_z)指数来看,天山中部乌鲁木齐 阿克苏区段土壤中10种(类)重金属元素的综合污染程度均属于轻度污染,其他两个区段均属于清洁水平;生态风险评估表明,重金属Hg、Cd在天山中部乌鲁木齐 阿克苏区段,As在天山西部昭苏 特克斯区段的潜在生态风险系数(E_i^r)和生态危害指数(RI)相对较高.